DIY Medium Format camera

[wombat2go]

Dan,
Oh yes, Alpa 12 is my kind of camera !
So the Rogonar 50mm is no good.
I know from using this lens on a digital sensor that it is very sharp in range f/8 to rf/11 , whereas the Omagaron 1:4.5 90mm I have here is not so sharp across the plane and anyway i need a shorter lens.
My next step is to make a lens bench so I can experiment to find a little lens less than 90mm to do what i indicated in post 25, mounted behind the lens board and that Prontor svs shutter.
I am interested in making a Crayford focuser out of billet alloy, to be mounted in a Graflex lens board. I think I can do it, I suppose the trick will be how to keep it light sealed
Thanks for your help.

 

[Dan Fromm]

Wombat, you're on the slippery slope. There;s a law of nature to the effect that there are no inexpensive wide angle lenses for formats larger than 35 mm still.

Suggest you visit www.schneideroptics.com, use the info tab to find their data on older lenses, and look at their short lenses' flange-focal distances. Then redesign y'r box (shorter! That's the Alpa trick) to allow you to use one of them, 47 SA, for example.

You're falling into a trap I'm familiar with. Have a cute idea based on a very inexpensive piece of found equipment, start thinking about what more can be done, and get fixated on using the piece of found equipment instead of thinking about what doing the what more really requires. Been there, done that, don't recommend it. Open your little marsupial mind.

 

[wombat2go]

But... But... But...
I can put that Graflex lens board where ever i want in relation to the film plane.
The Eddystone diecast boxes only cost $15 or so and are available in all sorts of dimensions
What about just using a 75mm achromatic doublet .. behind the Prontor and on a Crayford?
I have been reading up on geometric optics but not up to speed on how to calculate image circle
100% home brew, that is what I am aiming for.

 

[Dan Fromm]

100% home brew, that is what I am aiming for.

And good image quality too?

Teasing aside, what you want to do isn't what I'd do, but if that's what you want, why not? Your objectives, your resources including time.

 

[johnnyh]

... (SNIP)
-I wanted a real simple robust camera, the body is such the back balances the lens and forms a robust base. It can be sat on the ground or in the grass etc with the lens and back clear of the ground.The lens has a permanent metal hood with UV filter, and no lens cap. It is carried either by its handle or in an old video bag and does not have to be babied.

-This camera has no batteries (after my dslr batteries laid down in the Michigan winter) and can be used with gloves on which is not possible for example with a dslr.
-Having the spirit level in the viewfinder is good feature, more accurate than the grid in the slr and dslr. However I need to work on a better VF than the present one.
(ENDofSNIP) ...

For me, these reasons are sufficient justification for the project , even if being additional to your satisfaction in the hardware design and implementation. And the technical discussions and contributions in the thread are interesting and useful. Having just come across the thread, I will follow it with interest .

 

[Steve Smith]

Wombat, you're on the slippery slope. There;s a law of nature to the effect that there are no inexpensive wide angle lenses for formats larger than 35 mm still.

But sometimes they can be acquired cheaply. I paid £20 for the 65mm Super Angulon on my 6x12 camera.

http://stevesmithphoto.webs.com/pano612.html


Steve.

 

[wombat2go]

Steve
Excellent job!
The helicoid solution is a smart one, I am thinking about a Crayford

 

[Dan Fromm]

But sometimes they can be acquired cheaply. I paid £20 for the 65mm Super Angulon on my 6x12 camera.

http://stevesmithphoto.webs.com/pano612.html


Steve.

Steve, you're right, miracles do happen. I've had my share and am happy to have had them.

Relying on the right miracle to happen when needed, though, seems a little risky.

 

[etpm]

Great Work

Greetings,
I was looking for a shutter for a DIY medium format camera and found this forum and your posts. As a machinist I can really appreciate your excellent work. Looking at your posted pictures I saw a Computar lens. I may have this lens. I have an optics bench and fiddle around with optics. I bought two Computar lenses from Surplus Center so I could make a camera. You say that your lens needs to be used with a bellows. Though I want to make a camera with a bellows I would like to know why this lens needs to be used with one. Any advice you can give about where to start looking for info about a DIY camera is greatly appreciated. And once again, great work on your DIY camera.
Eric

 

[wombat2go]

Hi etpm,
The Computar 1:16/105~150 needs a bellows to be fully functional because it is a variable focal length lens, and its internal scroll adjusts that.
So the focus has to be adjusted at each focal length, needing the bellows, or a helicoid behind the lens.

It should also be possible to use the lens as an approximate fixed focal lens (eg 135 mm) and obtain focus ability by just using the internal scroll.
So far I am using the lens on the 4x5 Speed with the rollfilm back and using the focal plane shutter. I leave it at 135mm to match the view finder and rangefinder.

I think the lens is pretty good, although i have not used it much.
Here is a photo with it on the Speed, with a 67mm UV filter and an aluminum hood.
At 135mm, note that the lens image circle does not quite cover the RH/8 frame.
Out of camera image (Fuji 400, home processed C41)
https://app.box.com/s/mdtcfsz8tgo77qqrsniq

Here is a heavy crop of the above which is still reasonably sharp even at 22 inch width on the monitor.
https://app.box.com/s/aqvznhvq37b4pwuyfupv

To help with your camera design, here is some data of the Computar from my day book (measured, not calculated):
The register is the rear surface of the lens cylinder which is bolted directly onto a heavy aluminum lens board for the Speed.

At FL= 105 mm the distance from register to film plane at infinity focus, is approx 135 mm at infinity
The focus throw (front standard extension) to focus from infinity down to 5 metre ( 15 foot) is approx 1.6 mm (0.063 inch)

At FL= 135 mm: focus throw :2.4 mm (0.093 inch)

At FL= 150mm register: approx 150 mm at infinity
The focus throw: 4.75 mm (0.187 inch)

So it should be easy to machine a nice helicoid to mount the lens on.

I had the bright idea to allow wider apertures than the fixed f/16. I made a prototype stop to attach to the front of the lens but even f/4 was useless by vignette.
Changing the fixed aperture requires dis-assembly. Then I realized that even at f/16 the image on the ground glass is bright enough to focus fairly sharply.
Anyway I just scale focus it.

Good Luck with your camera!

 

[Mark Fisher]

Nice....I have a secret desire to make something similar out of a LF lens and a 6x12 back. Nicely done.