question about adapting projector lens

chris_zeel

I just picked up a Leitz Wetzlar projector with a Dimaron 100mm f/2.8 objective for 5 euros and have some questions about adapting the lens.

I cannot easily find the information in a search on the forum so I thought I would start a new topic.

What is the register distance of a projection lens like this Dimaron?

So what is the distance (from either the rear element or rear of the housing) to the sensor when focused at infinity?

And how big is the image circle?
Can it fill a full frame camera? Or only 1.5x crop sensor? Or smaller?

So far, I understand that adapting can be done in several ways.

Does anyone have experience with generic focusing helicoids?

Thanks for the replies!

calvin83 · Joined: 12 Apr 2009 Posts: 7576 Location: Hong Kong

You can answer some of the questions yourself - just held the lens in front of your camera.

There are some information here in Germany:
http://www.digicamclub.de/showthread.php?t=17041&p=184784&viewfull=1#post184784\

IAZA · Joined: 16 Apr 2010 Posts: 2587 Location: Indonesia

Pete · Joined: 01 Feb 2011 Posts: 240 Location: Denver, San Jose

Although I have not used projection lenses, I have used press camera and enlarging lenses on my Nikon Bellows. Nikon has the least distance available so I need to stay over 100mm for infinity focus. I think a Helicoid adapter would give a bit more. Anyway, you can easily test the lens for yourself. Use a cardboard tube from paper towels between the lens and your camera body and just move it into focus so you can take measurements. If the tube is too small, just slit it and tape it. It may be worthwhile to put the camera on a tripod so you can use both hands to hold the lens. I do this myself and sometimes just let the lens focus on a ground glass or paper.
Pete

chris_zeel · Posted: Thu Jan 07, 2016 11:44 pm Post subject:

I did some tests with extension tubes on my 6D and found out that it cover the full sensor.

It turned out that the tube in was housed in and extents from is a M39 tread, which I then mounted in my M39 adapter (1.3mm shortened for my Industar-69) on my NEX-3.

It looks like this:

In this setup I have to screw the lens 4mm out from the maximum inward position to get infinity focus.
That means with this "mount" with M39 tread, the register distance is roughly 33,5mm.

To mount in on my 6D, I would need a M39 adapter (without glass).
Assuming that this adapter gives a register distance of 45,4mm I would need to get the lens 11,9mm closer to the sensor.

When the lens in fully screwed in the green tube, the lens housing itself it about 30mm from the M39 mount.
This means that I can shorten this tube to get it at infinity when the lens in screwed fully in the tube.

I just ordered a $1.65 adapter with free shipping and see if I can get this tube shortened in the machine shop at work.
Of course I would need to do some more measurements and calculations to be sure of the exact number.

I did a quick test shots on the NEX and noticed low contrast and a very strong proneness to flare.
These things might all be related to the lack of coating.

Pete · Joined: 01 Feb 2011 Posts: 240 Location: Denver, San Jose

There you go!
Show some pics of what it can do...
Pete

chris_zeel · Posted: Fri Jan 08, 2016 10:43 am Post subject:

I'll go out today with lunch and shoot some.

It's sunny here so it will be likely to suffer from reflection.