I'm busy hacking together a viewer for my TL120-55 images. I
have a pair of 50-something millimeter coated achromats I've
been playing with.

I think these lenses are going to do just fine BUT they've
made me wonder. . . . Just how important is a coated lens in
a viewer? If I used uncoated lenses for my next viewer,
would I notice a difference?
________________________________________
John Thurston
Juneau, Alaska
http://stereo.thurstons.us

--- In MF3D-group@yahoogroups.com, John Thurston
wrote:

>
> I'm busy hacking together a viewer for my TL120-55 images. I
> have a pair of 50-something millimeter coated achromats I've
> been playing with.
>
> I think these lenses are going to do just fine BUT they've
> made me wonder. . . . Just how important is a coated lens in
> a viewer? If I used uncoated lenses for my next viewer,
> would I notice a difference?
> ________________________________________
> John Thurston
> Juneau, Alaska
> http://stereo.thurstons.us
>

That's a good question John. I think it depends a lot on how many
elements there are in the lens. Multiple uncoated lenses might
cause internal reflections.

But my other question is: where did you get 50-something mm lenses
that can cover the entire frame size (52x52mm) without distortion
(or should I say, with not too much distortion...) ???

Francois

depthcam wrote:

> John Thurston wrote:
>> I'm busy hacking together a viewer for my TL120-55
>> images. I have a pair of 50-something millimeter coated
>> achromats I've been playing with.

> But my other question is: where did you get 50-something
> mm lenses that can cover the entire frame size (52x52mm)
> without distortion (or should I say, with not too much
> distortion...) ???

I think I purchased them from Surplus Shed. They are
two-element, cemented, coated achromats. 50mm focal length
and 35mm diameter. They don't seem to have anything like them
right now. I've had them in my box of parts for several years.

I bought them long before the TL120 was released and had
planned on using them in a viewer for images from my Sputnik.
I just wanted to see what the images looked like when viewed
that way. I now have a better excuse to put them in a viewer :)

Regarding their distortion and coverage area, I can't say for
sure they will be ideal. I have _just_ made a lens board with
adjustable lens spacing (I'm still covered in sawdust). Now I
need to make a rail/stage to hold the lens board and slide
parallel so I can see if the lenses will do the job.
________________________________________
John Thurston
Juneau, Alaska
http://stereo.thurstons.us

> > John Thurston wrote:

> > But my other question is: where did you get 50-something
> > mm lenses that can cover the entire frame size (52x52mm)
> > without distortion (or should I say, with not too much
> > distortion...) ???
>
> I think I purchased them from Surplus Shed. They are
> two-element, cemented, coated achromats. 50mm focal length
> and 35mm diameter. They don't seem to have anything like them
> right now...

Why is it that the stuff we need is always "no longer available" ???

On that "other forum", there was some discussion of Alan Lewis's
58mm lens panel. Alan also got that from a surplus place and that
too, is no longer available... :-(

Mind you, I would be quite surprised if they covered an MF-format
slide without more than a wee bit of pincushion distortion.

Francois

depthcam wrote:

>>> John Thurston wrote:
>> depthcam wrote:
>>> But my other question is: where did you get 50-something
>>> mm lenses that can cover the entire frame size (52x52mm)
>>> without distortion (or should I say, with not too much
>>> distortion.. .) ???
>>
>> I think I purchased them from Surplus Shed. They are
>> two-element, cemented, coated achromats. 50mm focal length
>> and 35mm diameter. They don't seem to have anything like
>> them right now...
>
> Why is it that the stuff we need is always "no longer
> available" ???
>
> On that "other forum", there was some discussion of Alan
> Lewis's 58mm lens panel. Alan also got that from a surplus
> place and that too, is no longer available... :-(

The most likely reason is that it is _Surplus_ Shed. They sell
off odds-and-ends and odd-lots. The reason they have it is
because no one else wants to deal with it. If you are looking for
a steady supply of something, you would be dealing with with some
other supplier at much higher prices.

> Mind you, I would be quite surprised if they covered an
> MF-format slide without more than a wee bit of pincushion
> distortion.

So would I, but then I'm not expecting them to be perfect. I'm
expecting them to be functional.
_________________________
John Thurston
Juneau, Alaska

John Thurston wrote:

> depthcam wrote:
>> John Thurston wrote:
>>> I'm busy hacking together a viewer for my TL120-55 images.
>>> I have a pair of 50-something millimeter coated achromats
>>> I've been playing with.
>
>> But my other question is: where did you get 50-something mm
>> lenses that can cover the entire frame size (52x52mm)
>> without distortion (or should I say, with not too much
>> distortion.. .) ???

For the record, a preliminary check shows that my lenses won't
cover a 52mm square image without clipping the corners. They do
an ok job with 50mm square and with my 52x46mm (MFW) images.
_________________________
John Thurston
Juneau, Alaska

--- In MF3D-group@yahoogroups.com, John Thurston wrote:

>

> For the record, a preliminary check shows that my lenses won't
> cover a 52mm square image without clipping the corners. They do
> an ok job with 50mm square and with my 52x46mm (MFW) images.

Well, that's pretty amazing as I have never seen a 50mm FL lens that
could cover such a wide area without marked distortion. I have 65mm
large diameter achromats and they do distort at the edges. You should
have bought a few (hundred) more ! ;-)

Francois

> depthcam wrote:

> > On that "other forum", there was some discussion of Alan
> > Lewis's 58mm lens panel. Alan also got that from a surplus
> > place and that too, is no longer available... :-(
>
> The most likely reason is that it is _Surplus_ Shed. They sell
> off odds-and-ends and odd-lots. The reason they have it is
> because no one else wants to deal with it. If you are looking for
> a steady supply of something, you would be dealing with with some
> other supplier at much higher prices.

Yes, I am aware of that. I have bought several lenses from surplus
places, but sometimes their surplus stock of one type of lens runs
in the hundreds and even the thousands. But usually, the ones we
would like are the ones they only have a dozen of... :-(

Francois