>Don sent me the formula for estimating the stereo window as:
>
>lens separation x focal length / deviation
>
>This equations on the TL-120 as:
>
>63.5mm times 80mm, divided by (67mm minus 63.5mm) =
>
>5,080mm/ 2.5mm = 2,032mm = 2m = 6.7 feet.

--- In MF3D-group@yahoogroups.com, "Michael K. Davis" wrote:

>
> 67mm - 63.5mm = 3.5mm (not 2.5mm)
>

--- In MF3D-group@yahoogroups.com, "Michael K. Davis" wrote:

> I'm surprised your deviation is so great (at 3.5mm).

I believe that Sam was describing where the "in camera window" was and not the OFD of
any particular slide. Yes, he had a math error.

> 2.5mm would be 100%
> of MAOFD (where MAOFD = Viewer FL / 30).

You still seem to be hung up on the 1:30 rule (your version of it). Best to go by what
actually limits useable OFD than by the old "rule of thumb" for novices.

You're confusing the definition of MAOFD with the Near/30 "rule of thumb" some people use for calculating stereo base.  I don't use the Near/30 rule for calculating stereo base, but I do make use of MAOFD when discussing the limits of on-film deviation - and the very definition of MAOFD is FL/30. 

It's not a coincidence that both formulas use the same constant, but FL/30 and Near/30 serve two entirely different purposes.  So, feel free to say I'm "hung up" on the use of MAOFD when discussing the limits of on-film deviation, but please don't suggest I'm "hung up on the old 'rule of thumb' for novices [to calculate stereo base]."

> 3.5mm is 140% of MAOFD. Anything
> greater than 100% MAOFD would...
>
> A) Place the Near homologs in front of the window (when mounting the Fars
> at Ininfity).
>
> -OR-
>
> B) Force the eyes to diverge considerably to fuse the Fars (when mounting
> the Nears to the window).
>

It really depends on your slide mounts and viewer as to what limits OFD to a confortable
range.

I understand why you're saying that, but I believe that MAOFD should be honored, just the same.

If the far homologs (infinity) are no wider than the interocular spacing of the viewer, you
will not have to diverge your eyes to view them.

Good point.  The SaturnSlide, for example, has an extra 0.9 mm of lens separation (at 65.5mm) as a safety margin for accommodating OFD's that exceed MAOFD.  For a 78 mm focal length, MAOFD would be, by definition, 78 / 30 = 2.6 mm.  For mounts with a window spacing of 62.0mm, MAOFD says that when the Near homologs are mounted at 62.0 mm, the Far homologs must not exceed 64.6 mm.  Thanks to the SaturnSlide's 65.5 mm lens spacing, we can view OFD's as great as 3.5 mm without having to diverge the eyes. 

But...  3.5mm is still 34.6 % greater than Maximum Allowable On-Film Deviation.  I submit that many people will find a scene with this much depth to be uncomfortable - even though it can be mounted in a SaturnSlide without window violations and without forcing the eyes to diverge.

We could design a 78mm viewer that has a 67.2 mm lens separation for use with mounts that have a 62.0 mm window spacing.  Such a viewer would permit us to mount views having an OFD of 5.2 mm (or 200% of MAOFD), with no fear of either window violations or divergence (assuming the user's IPD is compatible with the lens separation).  Are you willing to say that an OFD of 5.2mm in such a viewer would be "comfortable"?

We have to draw the line somewhere.  It's a given that wherever we draw that line, we're going to have to build a viewer that can support it, so let's not put the cart before the horse. 

In addition to John Bercovitz and his "disciples", there are surely many stereographers who would agree that there is a limit to the range of convergence the average Joe will find comfortable when traversing a stereo view from Far to Near and back. 

I've found FL / 30 to be a very reasonable mechanism for determining that limit and I make every effort to shoot scenes such that the OFD's in my views never exceed MAOFD, nor fall short of about 50% of MAOFD.  I have a personal preference for 70% MAOFD views and find anything over 120% of MAOFD to be truly uncomfortable - even in the absence of divergence or window violations.

I believe, with all the MF viewers I have
used, the interoculars were 65mm or greater.

My Uni-Colour STL viewer has a lens separation of 64.5mm, and again, my SaturnSlide is at 65.5, but I would hope that there aren't any viewers out there with separations much greater than that.  Combining such a viewer with mounts that have a 62.0 mm window separation would be more reckless than accommodating.

The closest near homologs, should you wish to have everything behind the window would
equal the spacing of the aperatures in the mounts. That seems to be 62mm in all the
commercial mounts I have used.

With the exception of the original Uni-Colour mounts, which had a 65.0 mm window separation - a full 0.5mm greater than the lens separation - forcing the eyes to diverge even when fusing Near homologs!   Sam's "revised" mounts solved that problem by taking the window spacing down to 62.

So maximum spacing for far of 65mm - minimum spacing for the mounts of 62mm gives
you 3mm MAOFD before you have to diverge your eyes or view anything in front of the
window.

Your use of the acronym MAOFD, above, infers that you're talking about a viewer with a focal length of 100mm ( 100 / 30 = 3 ). 

I think you meant to say:

"So maximum spacing for far of 65mm - minimum spacing for the mounts of 62mm permits you a 3mm OFD before you have to diverge your eyes or view anything in front of the window."

If you're talking about a 78mm viewer (SaturnSlide), a 3mm OFD would exceed MAOFD by 15.4 %, which is very close to what I find uncomfortable, but would Joe Public be able to handle it?   I don't think so.

If you're talking about a 75mm viewer, a 3mm OFD would exceed MAOFD by 20.0 %, which is definitely uncomfortable for me.  Again, would the average user find it tolerable?   I don't think so.

Going back to Sam's example, if we're talking about a 75mm viewer (3D World), Sam's 3.5 mm OFD would exceed MAOFD by 40%, which I would find very unappealing.

Here's something else to consider:  If a viewer is focused at Infinity, a given OFD is not as stressful to the user as that same OFD in a viewer of equal focal length that's focused at an image distance of 20 inches, or worse, 10 inches.   When shooting for variable focus viewers, like Sam Smith's Regal, or the SaturnSlide, OFD's should be held well below MAOFD.  A user looking at a view focused at an image distance of only 10 inches, experiences 25% more deviation than is experienced with that same view focused at Infinity.   OFD's at 75% of MAOFD look great (to me) in a viewer focused at an image distance of 10 inches.  

This begs the question, "Is there really anyone out there consistently producing OFD's that fall at 120% of MAOFD, or 140%, or more?"

Thanks,

Mike Davis

> If all your measurements are correct, just remove 1mm off both sides of the septum.

--- In MF3D-group@yahoogroups.com, "Charles F. Holzner" wrote:
>
> --- In MF3D-group@yahoogroups.com, "Sam Smith" wrote:
>
> > I agree the window is too close, but fortunately it is an easy fix.
> > 2.5 would be ok with me, so theoretically I just have to add 1mm to
> > the left side of the left chamber, and remove 1mm off the left side of
> > the septum, correct?
>
> If all your measurements are correct, just remove 1mm off both sides
of the septum.
>
> Chuck
>

> Removing metal from the sides of the septum (down the middle) will:
>
> Increase the width of the images giving more "wiggle room".
>
> Move the "in camera window" out.
>
> If done carefully, will not hurt the camera or its operation.

> Most stereo cameras seem to have the in-camera-window too far out so none of the above
> will help them.

>Okay Mike. So where did you get " MAOFD = Viewer FL / 30" ?
>Who determined that and how? What is magic about the "30" ?

>Excessive eyeball convergence is defined [snip] as anything more than the
>arctangent of 1/30, or two degrees

> > But... 3.5mm is still 34.6 % greater than Maximum Allowable On-Film
> > Deviation. I submit that many people will find a scene with this much
> > depth to be uncomfortable - even though it can be mounted in a SaturnSlide
> > without window violations and without forcing the eyes to diverge.
>
>Why would they find it uncomfortable? What happens to their eyes that
>makes them
>uncomfortable?

> >
> > We could design a 78mm viewer that has a 67.2 mm lens separation for use
> > with mounts that have a 62.0 mm window spacing. Such a viewer would permit
> > us to mount views having an OFD of 5.2 mm (or 200% of MAOFD), with no fear
> > of either window violations or divergence (assuming the user's IPD is
> > compatible with the lens separation). Are you willing to say that an OFD
> > of 5.2mm in such a viewer would be "comfortable"?
>
>Yes.

>The Holmes viewers push the lens center seperation even farther, somewhere
>around
>85mm.
>
>I have made views with greater than your 5.2mm OFD that view well in a
>un-modified
>Saturn if you can tolerate some soft focus. The problem is DOF, not OFD.

>So you are happy with less depth than you can get. Some of us aren't. I
>want the depth to
>look the same as it did in person to me when I was there. I take some
>pictures with
>shallow depth, some with moderate depth, and some with more depth as I
>desire. Again,
>the limit to depth is DOF, not OFD.

> > and again, my
> > SaturnSlide is at 65.5, but I would hope that there aren't any viewers out
> > there with separations much greater than that. Combining such a viewer
> > with mounts that have a 62.0 mm window separation would be more reckless
> > than accommodating.
>
>Have you tested that theory?

> > This begs the question, "Is there really anyone out there consistently
> > producing OFD's that fall at 120% of MAOFD, or 140%, or more?"
>
>I for one shoot to get the view I want without reguard for "MAOFD". My
>concern is to have
>all the depth in reasonable focus. I know I can mount for any OFD my
>camera will produce
>as long as I have the total depth in focus. I am in 2 folios and try to
>put at least one view
>in each round that has at least 3mm OFD in it just to see if anyone
>complains about the
>depth. If you have seen my slides at one of the conventions, you have
>viewed such slides.
>I have had views in folios exceeded 5mm OFD and not had complaints of to
>much OFD. I
>must have something too far out of focus to get a complaint on the depth.

>Mystery solved?

> I think I would be perfectly comfortable with> window to infinity
> on-film deviation of, say, 3mm,

>>>The dividing of focal length by 30 to obtain the "maximum allowable
>>>OFD" can be found in the writings of Ferwerda, Waack, John Bercovitz,
>>>Bob Mannle, Paul Talbot, Tom Deering, David Lee, and many others.

>>>Six years ago, when I first started researching stereo math, their
>>>consensus made sense to me. I jumped on the bandwagon and have found
>>>it to work well for me ever since.

>So if you are standing looking at a distance building and someone
>walks into your field of vision at a distance less than 5 feet it
>will hurt your eyes to look at them?

>>>.... the longer I look at such views, the harder it
>>>gets to fuse them. In contrast, 70% MAOFD views are a pleasure
>>>2to look at.

>I would like to see one of the slides you have trouble viewing.
>We could design a 78mm viewer that has a 67.2 mm lens separation
>.for use with mounts that have a 62.0 mm window spacing. Such a
> viewer would permit us to mount views having an OFD of 5.2 mm
>(or 200% of MAOFD), with no fear of either window violations or
>divergence (assuming the user's IPD is compatible with the lens
>separation).

> I have noted that those who seem to have problems with OFD greater
> than "MAOFD" seem to all mount "To the Window". Doing so with
> "excess OFD" will cause eye divergance which hurts me too.

>> I do make use of MAOFD when discussing the limits of on-film deviation
>> - and the very definition of MAOFD is FL/30. News to me.

> I have made views with greater than your 5.2mm OFD that view
> well in a un-modified Saturn if you can tolerate some soft focus.
> The problem is DOF, not OFD.

>> My Uni-Colour STL viewer has a lens separation of 64.5mm,

> That was an error that has been corrected, I am told.

>> This begs the question, "Is there really anyone out there consistently
>> producing OFD's that fall at 120% of MAOFD, or 140%, or more?"

> I for one shoot to get the view I want without reguard for "MAOFD".
> My concern is to have all the depth in reasonable focus.
> I know I can mount for any OFD my camera will produce
> as long as I have the total depth in focus. I am in 2 folios
> and try to put at least one view in each round that has at least
> 3mm OFD in it just to see if anyone complains about the
> depth. If you have seen my slides at one of the conventions,
> you have viewed such slides. I have had views in folios exceeded
> 5mm OFD and not had complaints of to much OFD. I
> must have something too far out of focus to get a complaint
> on the depth.

>

>> I have made views with greater than your 5.2mm OFD that view
>> well in a un-modified Saturn if you can tolerate some soft focus.
>> The problem is DOF, not OFD.
>Amazing, as that puts the, (significantly out of focus), near point at
>about 3.2 feet, when using a Sputnik, if infinity is included.

>
>> I for one shoot to get the view I want without reguard for "MAOFD".
>> My concern is to have all the depth in reasonable focus.

>How does one get, "all the depth in reasonable focus",

>It must be difficult to measure the OFD, when the
>near point is so fuzzy.

> I assumed that the person would not be so big as to block your total
> view of the background.

> To each his own. I got into stereo photography to add depth I could
> see to my pictures. 70% 0f 2.5mm is only 1.75mm and has the window
> at 9 feet. That would make indoor photos difficult and not allow
> much detail for the closest objects. I feel no requirement for
> the handicap.

>> How about using a viewer that has an adjustable interocular ?

> I don't have an MF viewer with an adjustable interocular. I therefore
> adjust my slides to the viewer I have.


>>Why should anyone, purposely, produce MF, 3D slides with, "excess OFD"?

> To better do close-up views. I started to use double depth with

>>> I have made views with greater than your 5.2mm OFD that view
>>> well in a un-modified Saturn if you can tolerate some soft focus.
>>> The problem is DOF, no OFD.

>>>Somewhere near f/32 (Something you can't do with that $1400 China
>>>camera.)I bet Sam can do it.

>> It must be difficult to measure the OFD, when the
>> near point is so fuzzy.

>>> I don't shoot 'so fuzzy" shots unless it is a test. I mount with
>>> infinity at 65mm spacing and then check for Window Violations. OFD
>>> will have to exceed 3mm to get any WVs. If there are WVs, I mask
>>> them off at the outside edges of the apperatures (as in Ferwerda's
>>> Chapter 25) except I only mask off enough to delete the WV. After
>>> masking off any WV I can measure the resulting aperature spacing
>>> and get the near point spacing. OFD is = to 65mm-nearpoint spacing
>>> on my slide. How do you measure an OFD of 5.2mm ?

>
>Over the last 5 years, I have not seen very many Sputnik slides, with an
>excessive OFD. Maybe 3, at the most. It is not easy to do with a
>Sputnik, as the closest object must be about 5 feet from the camera with
>infinity in the background.

>>Chuck said: The problem is DOF, not OFD.

>I disagree, as I consider the problem to be both, the OFD, and the DoF,
>when the OFD is 5.2mm +.
>I would prefer a, sharp image, from the near point to the far point.

>>Somewhere near f/32 (Something you can't do with that $1400 China
>>>>camera.)

>I bet Sam can do it.

>An OFD of 5.2mm, begets a depth from about 3 feet to infinity.
>The best range I can find for f/32, is, from 7 feet out to infinity,
>which is a long ways from achieving a reasonably sharp image, from 3
>feet to infinity.

>>Somewhere near f/32 (Something you can't do with that $1400 China
>>>>camera.)

>I bet Sam can do it.

> Over the last 5 years, I have not seen very many Sputnik slides, with an
> excessive OFD.

>>> You are claiming that any OFD over 1.75mm is too much OFD.

>>> I personally like to do about 5 feet to infinity,
>>> with the Sput, resulting in 3mm OFD.
>>> (Don't have to mask the mount)

>>> I know I can mount even more OFD than 3mm and that DOF
>>> is the limiting factor for depth, I have been saying
>>> that all along.

> Chuck said: The problem is DOF, not OFD.

>>> An OFD of 5.2mm, begets a depth from about 3 feet to infinity.
>>> The best range I can find for f/32, is, from 7 feet out to infinity,
>>> which is a long ways from achieving a reasonably sharp image, from 3
>>> feet to infinity.


> I don't know where you got the 3 feet. Sounds like a "goal post move" to me.

> I am saying I can do 3mm OFD with my Sput, my Saturn viewer,
> and standard 80X132 cardboard mounts. (They are easy to view
> without hurting novice's eyes.) That will give me rather sharp
> depth from 5.24 feet to infinity.

> the apperatures in the mount. DOF s the limiting factor, not OFD.
> That is all I have to say and am expecting Someone to chimein
> and say "Take that tech BS off list and get back to the art of
> 3-D" anytime now.

>The deviation should not exceed 1/30 of the entire image width. Thus, with
>the European slide format 24 mm x 36 mm, one obtains for the deviation 36
>mm/30 = 1.2 mm and for the American 24 mm square format, a result of 24
>mm/30 = 0.8 mm. Both are also empirically found and generally accepted values.

>Check this out - the ISU has a "Golden Rule" that calls for even LESS
>deviation than I get at my personal preference for 70% of MAOFD (where
>MAOFD as defined by Bercovitz, is FL/30):
>
>>The deviation should not exceed 1/30 of the entire image width. ........

> Check this out - the ISU has a "Golden Rule" that calls for even LESS
> deviation than I get at my personal preference for 70% of MAOFD (where
> MAOFD as defined by Bercovitz, is FL/30):

>>The deviation should not exceed 1/30 of the entire image width. Thus, with
>>the European slide format 24 mm x 36 mm, one obtains for the deviation 36
>>mm/30 = 1.2 mm and for the American 24 mm square format, a result of 24
>>mm/30 = 0.8 mm. Both are also empirically found and generally accepted values.copy.com/isu/goldenrules.html

> Interesting! So, for a 50x50mm RMM mount, is the ISU saying we should keep
> our deviations at or below 50mm/30 = 1.67mm? Amazing! 1.67mm is only
> 63% of MAOFD (1.67mm is only 63% of 80/30).

> Here is John Bercovitz' explanation of MAOFD...

> http://www.angelfire.com/ca2/tech3d/images/maofdexpl.doc

--- In MF3D-group@yahoogroups.com, "Michael K. Davis" wrote:
>
>
> Here is John Bercovitz' explanation of MAOFD...
>
> http://www.angelfire.com/ca2/tech3d/images/maofdexpl.doc
>
> Mike Davis
>

I wish you wouldn't post URLs that require signing up for something.

Chuck

What did you have to sign up for?

Mike Davis

>
>What did you have to sign up for?

Michael K. Davis wrote:
> Here is John Bercovitz' explanation of MAOFD...

> http://www.angelfire.com/ca2/tech3d/images/maofdexpl.doc

I was not able to access the, above URL,

The link you can't open is a Microsoft Word document.  If you have Adobe's Acrobat Reader, try opening this file instead (from the Files section of this group):

         MAOFD_Explained_-_John_Bercovitz.pdf

I've been waiting for Chuck's response to the last paragraph, which discusses "double depth" in a way he'll find appealing, but take note that this does not change the definition of John's term, "MAOFD". 

but John B. is wrong, if he
believes that the MAOFD is FL/30, as quoted. The MAOFD number depends
on the focal length of the lens being used.

All of John's writings assume that camera lens and viewer lens have the same focal length.  Given a mismatch, the viewer focal length is the obvious choice for any discussion of on-film deviation - analogous to  seating position relative to OFD when projecting stereo views.

Are you able to use the suggested MAOFD number,(1/30th of 43mm= 1.4MM),
and (1/30th of 80mm=2.7MM), with your Mamiya stereo rig ?

No, but I am able to use 1/30th of 78mm (1/30th of my viewer focal length) to know where MAOFD is, no matter what focal length I use on my camera.  When shooting a twin-camera rig you can compensate any mismatch of camera focal length and viewer focal length by multiplying the stereo base given by John Bercovitz' general equation by the ratio VFL / CFL, to shoot with a stereo base that will deliver an OFD equal to MAOFD..  And if you don't want that much depth in your views, you can easily achieve some percentage of MAOFD, 70% for example, to produce OFD's that are consistently 70% of MAOFD, just by reducing the mismatch-compensated stereo base calculation by 30%.

Mike Davis

>> but John B. is wrong, if he believes that the MAOFD is FL/30,
>> as quoted. The MAOFD number depends on the focal length of the
>> lens being used.

> All of John's writings assume that camera lens and viewer lens have the
> same focal length. Given a mismatch, the viewer focal length is the
> obvious choice for any discussion of on-film deviation - analogous to
> seating position relative to OFD when projecting stereo views.

>> Are you able to use the suggested MAOFD number,(1/30th of 43mm= 1.4MM),
>> and (1/30th of 80mm=2.7MM), with your Mamiya stereo rig ?

> No, but I am able to use 1/30th of 78mm (1/30th of my viewer focal
> length) to know where MAOFD is, no matter what focal length I use
> on my camera. When shooting a twin-camera rig you can compensate any
> mismatch of camera focal length and viewer focal length by multiplying
> the stereo base given by John Bercovitz' general equation by the
> ratio VFL / CFL, to shoot with a stereo base that will deliver an OFD
> equal to MAOFD. And if you don't want that much depth in your views,
> you can easily achieve some percentage of MAOFD, 70% for example,
> produce OFD's that are consistently 70% of MAOFD, just by reducing the
> mismatch-compensated stereo base calculation by 30%.

>I am not aware of there being any commercially available stereo viewers
>which offer interchangeable fl. viewer lenses capable of matching the
>commonly available, interchangeable fl. taking lenses.

> MAOFD_Explained_-_John_Bercovitz.pdf
>
>I've been waiting for Chuck's response to the last paragraph, which
>discusses "double depth" in a way he'll find appealing, but take note that
>this does not change the definition of John's term, "MAOFD".

>> I am not aware of there being any commercially available stereo viewers
>> which offer interchangeable fl. viewer lenses capable of matching the
>> commonly available, interchangeable fl. taking lenses.

> What commercially (commonly) available MF stereo camera offers interchangable
> FL lenses? I know Sam made one but only one.! Is it for sale ?

>Did I said anthing about, What commercially (commonly) available MF
>STEREO CAMERA offers interchangeable...?
>
>Talking about being moving the, "goal posts", WOW !
>

> Take a Chill Pill guys. Some on this list are very enthusiastic about
> MF3D and want to stay that way.

>I agree with the suggestion that there is no universal MAOFD.

>
>I consider 70 percent of MAOFD to be a usefull compromise.

>
>My experience indicates, to me, that any MAOFD above 1.0mm can work.

>
>I recall inserting a MF stereo slide into a folio , and it was, later,
>labled, "extreme deviation", even though it contained a deviation of
>only 1.0mm.

>
>I have never wasted much time worrying about OFD,

>I consider composition to be the most important ingredient of a quality
>stereo image.

>> I agree with the suggestion that there is no universal MAOFD.

>> I consider 70 percent of MAOFD to be a usefull compromise.

> I am not sure what you want to compromise. I want an OFD that displays the
> depth as it was seen with the naked eyes, whatever OFD it takes to do so.

>> My experience indicates, to me, that any MAOFD above 1.0mm can work.

> I agree as long as you can keep everything in focus.
> 1.0mm is the proper OFD for 16 feet to infinity; larger OFD for more depth, less
> OFD for less depth.

>> I recall inserting a MF stereo slide into a folio , and it was, later,
>> labled, "extreme deviation", even though it contained a deviation of
>> only 1.0mm.

> As I recall, that slide had a mounting problem. Rotation as I remember, not an
> OFD problem. It was re-mounted and sent around the folio a second time. Is that
> the slide you are recalling?

>>I have never wasted much time worrying about OFD,

> Agreed. Depth of field is what to watch. Keep everything in focus as best you can
> and OFD takes care of itself.

>>I consider composition to be the most important ingredient of a quality
>>stereo image.

> I consider all the ingredients to be important for great stereo images. Anything out
> of wack gets noticed.

> MAOFD_Explained_-_John_Bercovitz.pdf

> I've been waiting for Chuck's response to the last paragraph, > which discusses " double depth" in a way he'll find appealing, > but take note that this does not change > the definition of >John's term, "MAOFD".

>Mike Davis wrote:
>
> > MAOFD_Explained_-_John_Bercovitz.pdf
>
> > I've been waiting for Chuck's response to the last paragraph, > which
> discusses " double depth" in a way he'll find appealing, > but take note
> that this does not change > the definition of >John's term, "MAOFD".
>
>Ok Mike, If John Bercovitz had defined what MAOFD means it is his. I do
>not agree with his reasoning on several points and feel that his
>definition (MAOFD) is misleading. It has the basics of the "1 to 30 rule"
>(of thumb) and no more valid then it.

>That said; I propose another term: Maximum On Film Deviation for Behind
>The Window viewing (MOFD-BTW) and define it to be the difference between
>the inter-ocular of the viewer and the aperture spacing on the slide mount.

>Again, we really don't know what the average person can tolerate, but it's
>completely reasonable for you to consider FL/30 to be unnecessarily
>limiting. You can enjoy more deviation than I can and it's possible you
>are among the majority in that regard. Who knows?

>Seriously, per your previous posts, DoF requirements could limit us to a
>deviation less than MOFD-BTW, especially with MF (as opposed to the smaller
>formats where DoF is more easily attained for double-depth scenes).

>In any case, I acknowledge the usefulness of your suggestion to calculate
>MOFD-BTW for a given viewer's combination of aperture spacing and lens
>spacing. That's a limit we should all be able to agree is the absolute
>highest deviation we should impose on any user, if we want to avoid window
>violations with the Near homologs -and- divergence of the eyes with the Far
>homologs.)

> The average person on this group seems to be able to handle parallax from about
> 18 inches (computer screen) on out to "yonder mountain" with no problem. That
> would give a parallax of no less than 8 degrees. I have to believe that you can do
> the same.

>According to Ferwerda, page 236, a 75mm fl lensed, MF stereo camera,
>provides an on film deviation, (OFD), of about 2.4mm, at a distance of 2
>metres, with a parallax angle of about 0.93 degrees. If one
>multiplies 8 x 0.93, one gets an angle of about 7.4 degrees, (almost the
>same as the suggested 8 degrees of usable parallax), or an excessive
>OFD, of about 19.2mm. Too much OFD for my old eyes !
>

>>Don Lopp wrote
>>According to Ferwerda, page 236, a 75mm fl lensed, MF stereo camera,
>>provides an on film deviation, (OFD), of about 2.4mm, at a distance of 2
>>metres, with a parallax angle of about 0.93 degrees. If one
>>multiplies 8 x 0.93, one gets an angle of about 7.4 degrees, (almost the
>>same as the suggested 8 degrees of usable parallax), or an excessive
>>OFD, of about 19.2mm. Too much OFD for my old eyes

> One major mistake for many stereographers is the assumption >that the stereo camera captures the world the same way the eyes >see it.

> Although stereo photography tries to mimic the world we >perceive it in real life, we only partially succeed through >compromise.

> The eye perceives depth through two factors: accommodation >(focus) and convergence (toeing into the subject).

> Convergence on the other hand does not rest, and is forced to >view the distorted image of a spherical world transformed to a > plane. The combination of these abnormalities severely limits > the range of depth what we can capture on a stereoscopic image > without causing eye strain.

> I trust the experts like by Mike, John B and Abram Klooswyjk >to determine the mathematical limits to MAOFD, but just wanted >to add afew physical considerations as to why you can't capture >the same depth in film as the eyes see in real life.

>Actually, I did post a corrected E-mail, at 10:38 PM, 8 minutes after
>the above E-mail, was posted.

>
>Did you find any math errors in my corrected E-mail ?

>
>My corrected E-mail made a change in the parallax angle, from 0.93
>degrees up to 2 degrees, and changed the OFD , from 19.2mm, down to
>being only 9.6mm, which is still, "too much for my old eyes."

>Chuck, are you able to view, comfortably, a MF stereo slide that
>contains an OFD as large as 9.6mm, which was inferred in your previous
>E-mail ?

> In fact I re-mounted a slide in the IMF folio (with the permission of the owner)
> that had over 1 CM of OFD and sent it around. There was nothing I could
> do about the focus and that and too much grain was all the other viewers complained about.
> None mentioned excess OFD.

> DoF is the limit to depth.

> I put one as a test in the IMF folio with depth from less than 1/2 ameter to infinity.
> I had a Pitcher Plant in sharp focus and the forground and background rather
> fuzzy. It was shot at F/22. Again, no one liked the out of focus near and far
> but there was no complaint about parallax.

> I have one in Folio II (that you are in) that has 4mm OFD and one in the IMF
> folio that exceeds 3mm. So far no complaints.

>According to the the circular, (Sputnik), slide rule, designed by Mike
>Davis...

>One major mistake for many stereographers is the
>assumption that the stereo camera captures the
>world the same way the eyes see it.

>According to the the circular, (Sputnik), slide rule, designed by Mike
>Davis, the DoF at f/32,ranges from about 94 inches, (about 8 feet) out
>to infinity.

>I remember a MF slide titled, "Wheat Girl", which had an OFD of 4mm.
>
>Because it was, 'properly', composed, the slide did provide comfortable
>viewing.
>

>> Davis, the DoF at f/32,ranges from about 94 inches, (about 8 feet), >> (about 2.4 meters), out to infinity.

> Apparently Mike made more than one circular Sputnik slide rule.
> I have the one he posted which doesn't have F/32 on it (until I added it)
> and has the distance in meters. With F/32 you can do infinity to less than
> 5 ft (1.5 meters) if you set the focus to 3 meters.

>>I remember a MF slide titled, "Wheat Girl", which had an OFD of 4mm.
>>Because it was, 'properly', composed, the slide did provide comfortable
>>viewing.

> So you know it can be done.

> Actually, "if you set the focus, (of the circular slide rule), to 3
> meters", at f/32, the DoF will cover from 1.8, meters, (5.9 feet), out
> to 8 meters, (26 feet).
> Not from, "infinity to less than 5 ft", as has been suggested !

> > So you know it ( OFD over 3mm) can be done.

> Yes, it can be done, but only if the photographer has taken the time to
> compose the picture properly. Sam did take the time to compose the
> picture properly !
>

>> Actually, "if you set the focus, (of the circular slide rule), to 3
>> meters", at f/32, the DoF will cover from 1.8, meters, (5.9 feet), out
>> to 8 meters, (26 feet).
>> Not from, "infinity to less than 5 ft", as has been suggested !

> Both are more aggressive than the Sputnik manual. Nether
> have f/32 on them.

>At about f/50, the DoF will cover the range of from 5 feet out to infinity.
>
>

> In my 35mm work I routinely use twice the "maximum" deviation.

> I do not use double depth much with medium format, however,
> due to its limited depth of focus.

> I believe the real culprit when it comes to viewing discomfort is
> distortion in the viewer lenses. As the eyeballs swivel about to take in
> the corners of each view they have take sub-optimum lines of sight through
> the magnifying lenses.

>> At about f/50, the DoF will cover the range of from 5 feet out to infinity.

> So it is now obvious to you that Depth of field will be the limiting factor
> for depth and not On Film Deviation?

>
>Sorry to break your bubble Chuck, but I personally complained about
>this view to you in person at the Irving NSA convention. It was
>completely unviewable to me and my eyes hurt trying to view it. It's
>the ugly baby analogy again I'm afraid. Just because nobody says it's
>bad does not automatically mean it's good. It can just mean they're
>polite!
>
>

>OK, let's back up here a second. Chuck's original post I responded to was:
>
>"The average person on this group seems to be able to handle parallax
>from about 18 inches (computer screen) on out to "yonder mountain"
>with no problem. That would give a parallax of no less than 8 degrees.
>I have to believe that you can do the same."
>
>Are you saying the ONLY reason the large majority of us cannot view
>the stereo image Chuck is suggesting is because of viewer lenses?

> I have yet to see a mathematical derivation of the F/30 definition of MAOFD Ferwerda indicates that the OFD for a 75mm fl. lensed MF stereo camera

> ... our eyes are capable of at least 8 degrees of parallax without pain,

> I have noticed that those who "Mount to the Window" and those who

> "Too much OFD" seem to be the same people. When one mounts high amounts of
> depth (OFD) and "Mounts to the Window" they are pushing the "excess" OFD out
> past the interocular spacing of the viewer.

> If you have more OFD then your mount/viewer combination can handle
> (MOFD-BTW), Mount with infinity spaced at the interocular of the viewer
> (about 65mm) and mask off the window violations at the outer edges of the
> chips. Simple as that

>>In my 35mm work I routinely use twice the
>>"maximum" deviation.
>Does that mean the, on film deviation, (OFD), is 2.4mm ?

>In the latest folio, your 4 MF slides OFD
>was 1mm, 1.5mm, 2mm, and 2mm.

>I am not aware of any, "viewing discomfort", "or distortion
>in the viewer lenses",when I use a MF viewer which has
>decent viewer lenses

> >
> > I personally complained about
> >this view to you in person at the Irving NSA convention. It was
> >completely unviewable to me and my eyes hurt trying to view it.

> Funny how we remember things differently. I remember you saying "It

> In fact, at one point I had a plan to plot the rectilinear
> "distortion" in a normal slide as the eye sees it and use some sort of weak
> fisheye-like lens to present the eyes with the imagery they expect. What was meant by, "the imagery they expect."

> As for focus accommodation, all evidence seems to indicate that there is no
> hard linkage between focus and eyeball convergence.

> I do not use double depth much with medium format, however, due to
> its limited depth of focus.

> I believe the real culprit when it comes to viewing discomfort is
> distortion in the viewer lenses. As the eyeballs swivel about to take in
> the corners of each view they have take sub-optimum lines of sight through
> the magnifying lenses. You might note that you can often get a clearer
> view of the corners by moving your head a bit off center of the eyepieces.

> It seems all the talk about excessive deviation, double depth > mounting,and whatever is just a way to try and salvage a >poorly taken image.

I double checked the "Mono", slide which has an OFD of about 1.0mm.

I find your slides to be extremely well mounted, which does make for
comfortable viewing.

I have taken pictures with a similar composition which had an OFD of
about 3.. with no viewing problems that I am aware of.

Best regards,

DON

> > As for focus accommodation, all evidence seems to indicate that

> > hard linkage between focus and eyeball convergence.

> I am in total agreement.

>>As for focus accommodation, all evidence seems to indicate that
>>there is no hard linkage between focus and eyeball convergence.

> I wrote:
>
>>>As for focus accommodation, all evidence seems to indicate that
>>>there is no hard linkage between focus and eyeball convergence.

On 22 Jan, 2007, at 12:33, Don Lopp wrote:

Oleg Vorobyoff wrote:

As for focus accommodation, all evidence seems to indicate that
there is no hard linkage between focus and eyeball convergence.

Don wrote:

I agree with Oleg regarding his premise that, "there is no hard linkage
between focus and eyeball convergence."

I (Chuck Holzner) also agree that there is no "Hard Linkage" between focus and eyeball convergence. Having old eyes that don't have a large range of focus and being "Far sighted" I generally focus the viewer for somewhere near infinity and view without glasses. I do not have a problem with my eyes changing focus on items that were close in the photograph while toeing in to view them.

Don also wrote:

If the difference in
convergence is large, the probability is high that a photograph of the same scene would present a stereo image that contains an excessive amount of, (OFD).



I really don't know what Don's definition of "excess OFD" is. To me, If the OFD provides the same parallax that would be there viewing the scene direct then it is the right amount of OFD. To me, excess OFD would provide more parallax than seen in the view directly. Two ways to produce more OFD then normal are to use an extended base and/or to use taking lenses with longer FL than the viewer lenses' FL. I believe that Don has a different definition, so we are not in total agreement.


Best,

Chuck






________________________________________________________________
Sent via the WebMail system at mail.firstva.com

>I agree with this, however it has been suggested (by McKay as well as
>others) that this is NOT universal. Some people cannot trick their
>eyes into keeping accomodation at rest when viewing a stereo image.
>Some can relax focus, but not converge on a stereo image. This is why
>the stereoscope was very popular tool for eye training. Obviously
>nobody here on this list has a problem, but keep this in mind if you
>encounter someone who says they only see a double image when they look
>through a stereoscope. While not the only causes, accommodation and
>convergance issues need to be considered.
>

>What is the meaning of, "past the end of the comfortable range of focus"?

>
>IMO, if I am taking a picture of the moon, the parallax should be close
>to ZERO.

> The meaning of, "past the end of the comfortable range of focus"?

> Do you have a slide, shot using a normal base stereo camera, where the DoF
> is just fine but it has too much OFD (Parallax)?

>I trust the experts like, Mike, John B, and Abram Kklooswyjk to
>determine the mathematical limits to MAOFD...

>Why you can't capture the same depth in
>film as the eyes see in real life

>
>> The meaning of, "past the end of the comfortable range of focus"?
>Is DoF.
>
>IMO, the above is a strange definition of DoF. %^)

>
>"DoF", only requires the use of, 3 letters.
>

>> Do you have a slide, shot using a normal base stereo camera, where the DoF
>> is just fine but it has too much OFD (Parallax)?
>You have not defined, "has too much OFD."
>

>>I trust the experts like, Mike, John B, and Abram Kklooswyjk to
>>determine the mathematical limits to MAOFD...
>I consider MAOFD as being a subjective problem, not a mathematical problem.
>

>I believe that Mike has said that 70 percent of MAOFD was OK with him.

>
>I am not aware of the stereo book, by Ferwerda, mentioning MAOFD.

>
>>Why you can't capture the same depth in
>>film as the eyes see in real life
>What is the basis for the, above, categorical statement ?
>
>Are, "in film", the operational words ?

>>"DoF", only requires the use of, 3 letters.

> So what 3 letters will assure you won't have any problems with DoF?

> I trust the experts like, Mike, John B, and Abram Kklooswyjk to
> determine the mathematical limits to MAOFD...


>>I consider MAOFD as being a subjective problem, not a mathematical problem.

> Are you now contradicting yourself?

> I was told that MAOFD was defined as (camera) FL/30. That is mathematical

>>>Why you can't capture the same depth in
>>>film as the eyes see in real life

> I don't understand the above statement either, it doesn't seem to be all there.
> Possibly it refers to the ability of the eye to change focus as it views the
> scene directly; something that doesn't happen in the camera when making a slide
> I do believe it has to do with focus and not parallax.

>>You have not defined, "has too much OFD."

> Leaving it up to you, you use the phrase often. I want to
> see what you are talking about. For DoF, use the Maximum Circle of
> Confusion Diameter of 0.060mm, 0.030mm, or whatever you thing is a
> "comfortable" measure of sharpness. I want to see a slide shot with a

> also think has an "uncomfortable" amount of OFD

> When using a normal stereo camera, DoF is the limiting factor for depth, NOT OFD.

>Confusing. Does not 1/30th of a 75mm lensed Sputnik equal 3mm,
>instead of the suggested 2.5mm ?

>Confusing. Does not 1/30th of a 75mm lensed Sputnik equal 3mm,
>instead of the suggested 2.5mm ?

>Iam not aware of ever suggesting that I could produce a slide that I
>think, is "comfortably sharp that you also think has an 'uncomfortable'
>amount of OFD." It was not I that made the exagerated claim that the
>Sputnik, at f/32, can provide a DoF of from 5 feet to infinity. If
>this were a fact, your Sputnik could, easily, produce the slide. My
>Sputnik will not stop down to an honest, f/32.
>

>I do not believe that the, "DoF is the limiting factor for depth",
>suggestion, is true, as I have seen stereo slides which produced
>uncomfortable viewing because of excessive OFD. The problem
>resulting from the excessive OFD was not eliminated by having either the
>near point or the far point not being in sharp focus. Is not the
>Pitcher Plant slide a good example ?

>> Confusing. Does not 1/30th of a
>> 75mm lensed Sputnik equal 3mm,
>> instead of the suggested 2.5mm ?

> Not when I went to school. When I 75 divide by 30 I get
> 2.5 not 3. 90 divided by 30 would equal 3.

> The dividing of focal length by 30 to obtain the "maximum allowable OFD"
> can be found in the writings of Ferwerda, Waack, John Bercovitz, Bob
> Mannle, Paul Talbot, Tom Deering, David Lee, and many others. Six years
> ago, when I first started researching stereo math, their consensus made
> sense to me. I jumped on the bandwagon and have found it to work well for
> me ever since.

> I try to avoid projecting my personal experience as being equal to that of
> the "average person", but when my own experience validates the writings of
> dozens of people, all of whom have said that FL/30 is the Maximum Allowable
> OFD, it's tough for me to believe that my experience is
> "extra-ordinary".

>Michael K. Davis wrote:
>
> > The dividing of focal length by 30 to obtain the "maximum allowable OFD"
> > can be found in the writings of Ferwerda, Waack, John Bercovitz, Bob
> > Mannle, Paul Talbot, Tom Deering, David Lee, and many others. Six years
> > ago, when I first started researching stereo math, their consensus made
> > sense to me. I jumped on the bandwagon and have found it to work well for
> > me ever since.
>
> > I try to avoid projecting my personal experience as being equal to that of
> > the "average person", but when my own experience validates the writings of
> > dozens of people, all of whom have said that FL/30 is the Maximum
> Allowable
> > OFD, it's tough for me to believe that my experience is
> > "extra-ordinary".
>
>Hi Mike:
>
>Do you still contend the above statement is true ?
>
>I can't find anything in Ferwerda that backs up your contentions.
>
>Best regards,
>
>DON