Hi all. I have completed the design and measurement stage for a
focusable wide-angle lens set. Before I get into it I must say that I
agree with Sam about the quality of the Mamiya lenses and the degree
of quality that the company achieved. I bought three lens sets and
initial trial matching photo shoots with the taking lenses still in
their mounts showed 2 of the 3 possible combinations were a match,
with one being very slightly better than the other. Further tests
with the viewing lens put into a taking lens body gave equally superb
results. One only has to note the use of shims as thin as 0.05mm
under either of the lenses to realize the degree of perfection they
were after. They would hardly bother shimming to that tolerance if
the focal length wasn't VERY close, as the shimming would only bring
alignment at one point! Moving along...............

Here is my KISS proposal. (Keep It Simple Stupid)
I am machining mounting blocks from the same material I used for the
trial shooting sessions, ie, a black industrial Nylon. It is called
Cast Nylon 6 MoS2, which has Molybdenum Disulphide added to give
excellent low friction/self lubricating properties. It is easily
machined (including without coolant) and is very tough. It is also
quite cheap. My supplier has it for $45 Aus (500mm x 65mm) See it
here http://www.rsaustralia.com/cgibin/bv/rswww/searchBrowseAction.do?
D=nylon%206%20stock%20&Nr=AND%28avl%3aau%2csearchDiscon_au%3aN%
29&Ntk=I18NAll&Nty=1&Ntt=nylon%206%
20stock%20&Dx=mode%20matchpartial&Ntx=mode%
20matchpartial&N=0&name=SiteStandard&forwardingPage=line&R=1935294&cal
lingPage=/jsp/search/search.jsp&BV_SessionID=@@@@0742364922.1204243187
@@@@&BV_EngineID=ccdfadedgkdkdfkcefeceeldgondhgm.0&cacheID=auie

I realised that the simplest answer was to utilize the lens's own
mounting thread (0.5mm pitch) as the focus adjustment means.
Normally, with such a fine thread this would be a no-no, but with the
Nylon MoS2 as the mating part, no worries mate! This makes the blocks
quite simple to machine, with the possible exception for some (me,
I'm only ), the thread, which will need precise machining.
An alternative to machining a thread is to have the barrel 0.1 -
0.15mm smaller than the thread diameter, and then let the lens thread
cut a thread when it is screwed in!
See them here..... http://www.flickr.com/photos/14946872@N04/

Screws can be put in to mount the blocks on the lens plate by just
drilling a pilot hole and screwing it in. No need to tap them!
As seen in the first image, the shutter back has to be machined to
take the rear of the lens barrel, 33mm dia x 1.5mm deep. This is
easily done with a Dremel High Speed Cutter. Naturally, the rest of
the camera has to be covered with plastic and taped up with duct tape
to 100% protect it from shavings, and have someone hold a vacuum
nozzle close to suck it all away. The machined area has to be black
matt painted of course.

The lens bodies have to have the protuberances cut back to allow
rotation. The shutter cock and trip can be cut back to 2-2.5mm. The
shutter trip has to have a small hole drilled to take a locking pin
bent from a paper clip to permanently hold the lever in the trip
position. The shutter is of course left on B, and is quite difficult
to move out of B when the shutter trip is held on.
The lenses are screwed fully into their blocks, and the blocks then
mounted onto the lens plate with the aperture mark at the top for
ease of use. With the block thickness of 9.7mm, this gives focus at
approx. 30 meters. Screw the lenses out 1/2 turn gives 10 meters, one
full turn gives 8 meters, 1 1/2 turns gives 5 meters and 1 3/4 turns
gives 3 meters. (All approx.)

The rear part of the block which takes the rear lens barrel has to be
a close fit as this supports the lens and keeps it aligned taking the
burden off the lens thread. Making the blocks out of anything but the
recommended material would require grease lubrication on the thread
and rear barrel. You could of course screw the lenses out and add a
shim if you wanted to fix the focus at a particular setting, but I
don't really think this is necessary.

Any comments or questions?

Happy 3Ding, Peter

Peter Thomson wrote:

> Here is my KISS proposal. (Keep It Simple Stupid) I am
> machining mounting blocks from the same material I used
> for the trial shooting sessions, ie, a black industrial
> Nylon.

This looks good, Peter.
Do you have any plans to make some of these for sale?
I was about to finalize my monolithic-board tonight and get
moving on the manufacture. I'm going to put the brakes on
while I look over what you have here.

> This makes the blocks quite simple to machine, with the
> possible exception for some (me, I'm only ), the thread,

This is where I got stumped when I was doing measurements and
layout. As far as I can tell, the thread is a non-standard
metric thread. Are you able to precisely identify it?

As for letting the shutters cut their own threads in the
nylon, have you tried it? The aluminum threads on those
shutters are pretty soft. You may have success using the
taking-lens's fixed-block as the tap, but I'd be afraid to
try cutting threads with the shutter.

> As seen in the first image, the shutter back has to be
> machined to take the rear of the lens barrel, 33mm dia x
> 1.5mm deep.

This is the part which really scares me :( How are you going
to keep the shavings out of the shutters?

> With the block thickness of 9.7mm, this gives focus at
> approx. 30 meters. Screw the lenses out 1/2 turn gives 10
> meters, one full turn gives 8 meters, 1 1/2 turns gives 5
> meters and 1 3/4 turns gives 3 meters. (All approx.)

What f/stops do you expect use? I wonder why you would want
to focus any farther out than 8 meters.

I'm not trying to pick a fight here. I'm trying to picture a
case where I will want to focus my wide angle lenses at 10m
when I wouldn't also have sufficient light to focus nearer
and use a smaller stop to cover the distance.

>
> The rear part of the block which takes the rear lens
> barrel has to be a close fit as this supports the lens and
> keeps it aligned taking the burden off the lens thread.

Trying to make this close enough to support your lens, I
fear, will also make it close enough that you will be
unscrewing the rear element from the shutters each time you
try to focus it. If you are going to go down this route, I
suggest that the threads on the shutters are good enough to
hold the relatively light weight of the mamiya lenses and to
relieve the inner sections sufficiently to let the rear
elements move freely.
________________________________________
John Thurston
Juneau, Alaska
http://stereo.thurstons.us

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

>
> > This makes the blocks quite simple to machine, with the
> > possible exception for some (me, I'm only an amateur machinist),

the thread,

>
> This is where I got stumped when I was doing measurements and
> layout. As far as I can tell, the thread is a non-standard
> metric thread. Are you able to precisely identify it?

The thread is a standard Metric form with 0.5mm pitch. It is not any
specific diameter size like you would be trying to describe for a tap
or die, it is a thread which is only cut on a lathe.

>
> As for letting the shutters cut their own threads in the
> nylon, have you tried it?

I'm saying that only the tip of the thread would be involved in this
process, and would press into the nylon OK, it's not rock hard.
I will try it on a spare piece of material and let you all know.

Another idea I forgot to mention (which I used on my trial blocks) is
to mount the retaining ring into a recess in the block. This however
is little too loose a fit for my liking.

> > As seen in the first image, the shutter back has to be
> > machined to take the rear of the lens barrel, 33mm dia x
> > 1.5mm deep.

> This is the part which really scares me :( How are you going
> to keep the shavings out of the shutters?

By keeping the shutter open with a lockable cable release on B
setting and taping up with 50mm duct tape and plastic sheet, there is
nowhere for the shavings to go.

> What f/stops do you expect use? I wonder why you would want
> to focus any farther out than 8 meters.
>

I just don't like being restricted by some barrier which need not be
there! You wouldn't be happy not being able to focus further out than
8 meters on another camera would you? I like to have a full deck of
cards to play with, especially as you would know, a lens's best
sharpness is NOT at its smallest aperture, and on this lens is around
f8-f11.

> > The rear part of the block which takes the rear lens
> > barrel has to be a close fit as this supports the lens and
> > keeps it aligned taking the burden off the lens thread.
>
> Trying to make this close enough to support your lens, I
> fear, will also make it close enough that you will be
> unscrewing the rear element from the shutters each time you
> try to focus it. If you are going to go down this route, I
> suggest that the threads on the shutters are good enough to
> hold the relatively light weight of the mamiya lenses and to
> relieve the inner sections sufficiently to let the rear
> elements move freely.

Not THAT close John that it touches or applies any tension, just that
it doesn't let the lens droop in any degree, which would most likely
happen as you rotate it. About 0.06mm or slightly more (or about
0.001-0.0015" all around) clearance. This also, most importantly I
should have mentioned before, aligns the lens barrel when it is
inserted, so that the chance of cross-threading is minimised. By
design, it must be engaged here before the thread engages.

>Do you have any plans to make some of these for sale?

John, could you email me off list please at
peter.3dtreasures@bigpond.com

Happy 3Ding, Peter