Lens adapter

[Nathan Martin]

Hey all,

 

I just got my new canon 40D and i am trying to find a lens adapter that i dont think exhists so if anyone has any ideas of where to find it or who might machine it for me let me know.

 

What i want is a PL adapter to plug into the canon ef mount so i can use most standard PL lenses.

I have checked the specs on the lens widths and Flange focal depths and it all looks very feasible.

The only thing im not sure about yet is the back element clearance from the shutter. From rough looks it should be fine but i may have troubles with some lenses.

 

cheers

[Saul Rodgar]

Les Bosher may be the person to talk to. He is the only tech I know who makes rare and exotic adapters of excellent quality for reasonable amounts -since I very much doubt the adapter you are looking for is available commercially.

 

http://www.lesbosher.co.uk/

Edited August 15, 2008 by Saul Rodgar

[Chris Keth]

I really doubt that it is possible in an SLR due to the design of the viewing mirror.

 

Look at how close the rear element of most PL lenses is from the image plane. They're quite close. In an SLR design, the mirror has to have room to swing up so the cavity of an SLR is mostly unuseable space. In a film camera, the shutter is very space efficient, it only takes up a circular place of space. The SLR's shutter takes up space in the shape of a pie-slice of a cylinder.

 

If I were you, I would get a few lenses and a ruler. Lock the mirror up and just handhold the lenses the correct FFL from the image plane and see if the mirror would hit. My bet is that most will hit the mirror.

 

If you pass that test, then Les Bosher could take care of you.

Edited August 15, 2008 by Chris Keth

[Saul Rodgar]

Guys:

 

I have a variety of excellent mechanical adapters for my ACL, including PL mount.

 

The way a properly designed and built adapter work is: the adapter sticks out of the body far enough for the new lens to be mounted allowing its rear element to clear the shutter properly. See, the end of the PL mount lens has to be roughly where the end of the original (EOS lens in this case) was. Assuming that original lens clears the shutter.

 

The distance from the rear element to the film plane has to stay pretty consistent in both lenses, in other words. So the adapter only modifies the distance where the new lens is mounted to the camera.

 

If the new lens is now mounted an inch or so away from the original camera mount, the rear element of the PL lens will be roughly where the original EOS lens rear element would be in relationship to the film plane, and the shutter- thus maintaining focus, focal lenght and field of view, etc.

 

However, the 40D isn't a full sized 35mm sensor, so you will have a 1.6x magnification with your full sized EOS and PL mount 35 mm lenses

 

S

Edited August 15, 2008 by Saul Rodgar

[Patrick Neary]

Hi-

 

To be clear, the critical number here would be the flange focal distance. Where the rear (glass) element of the lens sits isn't an issue other than whether it hits the mirror or not. Canon EF FFD is 44mm, PL is 52mm, and the diameters of each are about the same so it seems an adapter would be possible. Probably a very tiny market for that sort of thing though!

 

The 40d (and many other DSLRs) have a sensor size around 22mm × 15mm, just a bit smaller than the S-35 frame of 24.89 mm × 18.66 mm, and very close to academy's 21.95mm × 16.00mm, so mounting a PL lens (if it can be done) would give you a good estimation of the field of view of your 35mm MP camera.

 

I used my 10D (with EF primes) shooting "Calvin Marshall" (Academy 1.85) as a director's finder/light meter/pre-vis tool/snapshot-cam/etc. and it was indispensable.

 

Finally, there is no such thing as 1.6 "conversion" Honestly, how many times does someone have to say "a 50mm lens is a 50mm lens is a 50mm lens" before that sinks in around here! :blink:

[Chris Keth]

I still say you need to look at everything very closely with a ruler. Many PL mount lenses do have the rear element much closer to the image plane than SLR lenses do.

 

You can't just take a bunch of lenses and assume they are designed with the rear element the same distance from the image plane.

[Patrick Neary]

You can't just take a bunch of lenses and assume they are designed with the rear element the same distance from the image plane.

 

Exactly, because they're not.

 

They vary quite widely especially if you look at different makes and focal lengths.

[Chris Keth]

Exactly, because they're not.

 

They vary quite widely especially if you look at different makes and focal lengths.

 

Which is why I don't understand why nobody else thinks he should look at the situation long and hard before he has a (probably) 500+ dollar mount adapter custom made.

[Saul Rodgar]

Finally, there is no such thing as 1.6 "conversion" Honestly, how many times does someone have to say "a 50mm lens is a 50mm lens is a 50mm lens" before that sinks in around here! :blink:

 

Um, just slow down there, genius. There is something called angle of view, which is what will change when using the same lens with different size sensors, therefore the image will be magnified when smaller sensors are used. I never said it would change the focal length of the lens. The focal length will remain the same, but the angle of view will change.

 

http://en.wikipedia.org/wiki/35_mm_equivalent_focal_length

 

[Saul Rodgar]

Which is why I don't understand why nobody else thinks he should look at the situation long and hard before he has a (probably) 500+ dollar mount adapter custom made.

 

 

What I am saying is that a tech such as Les Bosher can determine what the distance between the back element of a standard PL mount lens and the film plane of this EOS camera is and make an adapter. But this adapter would be (very likely) away from the original camera mount a good inch or so.

 

I am not a lens tech, but that is how my PL mount adapter works. And I can use ANY PL mount lens on it and have stellar results every time, regardless of the individual lenses back elements lenghts.

[Chris Keth]

I am not a lens tech, but that is how my PL mount adapter works. And I can use ANY PL mount lens on it and have stellar results every time, regardless of the individual lenses back elements lenghts.

 

What I keep saying, though, is that the viewing mirror on an SLR will very likely create a problem. The mirror shutter in your ACL doesn't need room to swing toward the lens like a door.

 

In the end, I just want Nathan to look at everything very closely before he spends the money, which will probably be considerable for a custom precision adapter.

[Saul Rodgar]

In the end, I just want Nathan to look at everything very closely before he spends the money, which will probably be considerable for a custom precision adapter.

 

I agree.

[Nathan Martin]

Chris,

 

The mirror clearance was my main concern and i was planning on testing this before i make a purchase. The only specs ive run through so far are the mount widths, the flange focal distances and the censor size.

All of the variables i have looked into so far point towards it being very possible, however i know i will have trouble with some lenses at least.

 

Patrick, your right on the money. My reason for buying the 40d was largely because the sensor size was very similar to academy. My plan was to use this as a finder for reckies and on set, this way i could have high res stills that should emulate the same DOF and rough field of view as 35mm.

This in line with something like Kodak image look manager could give fairly accurate portrayals of what a motion camera may see.

 

The 8mm ffd difference should roughly take care of the depth of the pl mount give or take a couple of mm. Then the only concern is how much the rear element protrudes from the mount.

 

Not having the specs in my hands i would assume that most zeiss, arri, and cooke primes should be very close to clearing the mirror, but i will test this soon. I was thinking i might cut a piece of 50mm PVC pipe to 8mm deep, and hand hold some lenses against this bracket to check the clearance.

 

If this doesnt work the only other option i would assume would be a P+S styled adapter where the prime will project onto a groundglass and another lense would magnify this to fit the censor.

 

thanks for your help all,

If anyone has any more details to take into account please share them

 

 

cheers

[Patrick Neary]

Hey Nathan-

 

If you find out anything cost/availability wise I hope you post back here- seems like something cool to have and probably could make back $$ easily with kit rentals.

 

Saul, apologies, but what you said was:

 

"...the 40D isn't a full sized 35mm sensor, so you will have a 1.6x magnification with your full sized EOS and PL mount 35 mm lenses"

 

Which not only is wrong, but makes less sense every time I re-read it. 1.6 magnification of what? A DLSR sensor like the 40D gives you essentially the same FOV as Academy 35.

 

And sorry to hammer at this stuff, but this idea of measuring from the rear element of the lens is also wrong. PL FFD is 52mm, Canon is 44mm, there's your measurement. The adapter wouldn't stick out "a good inch or so" from the eos mount, it would be 8mm as discussed in the thread.

[Saul Rodgar]

Saul, apologies, but what you said was:

 

"...the 40D isn't a full sized 35mm sensor, so you will have a 1.6x magnification with your full sized EOS and PL mount 35 mm lenses"

 

Which not only is wrong, but makes less sense every time I re-read it. 1.6 magnification of what? A DLSR sensor like the 40D gives you essentially the same FOV as Academy 35.

 

If you chose to be in denial, that is your problem, amigo.

[Saul Rodgar]

Saul, apologies, but what you said was:

 

"...the 40D isn't a full sized 35mm sensor, so you will have a 1.6x magnification with your full sized EOS and PL mount 35 mm lenses"

 

Which not only is wrong, but makes less sense every time I re-read it. 1.6 magnification of what? A DLSR sensor like the 40D gives you essentially the same FOV as Academy 35.

 

Perhaps I didn't say it the best way I could have, as English is my second language and I may have wrote in haste as well. Perhaps this is what I should have said:

 

"That's important because that sensor is smaller than a 35mm film slide (which is the size of a full-frame sensor). In the camera body, that smaller sensor format effectively "crops" the image produced by the lens. To you, the effect is to magnify the image or increase the telephoto capability of your lens.

 

So, on the 40D, which has an APS-like sensor and a lens magnification factor of 1.6x, a 100mm lens becomes equivalent to a 160mm lens."

 

http://blogs.consumerreports.org/electroni...-impressio.html

 

and here:

 

http://www.canon.com/camera-museum/tech/re...709/table1.html

 

As far as I can tell it is you who has very poor analytical skills. "1.6 magnification of what?" Um, the image? By virtue of the smaller sensor crop factor? But, like I said, if you chose to be in absolute denial and make a fuss about this in your compulsive desire to prove your superior understanding of cinematography, go right ahead.

 

Good day, sir.

Edited August 16, 2008 by Saul Rodgar

[Saul Rodgar]

Anyway, here are some pictures of the PL mount adapter for my ACL. As you can see, the PL mount end is a good inch away from where the adapter mounts to the camera body. This may or may not be the case in a 40D, but this design allows for a side to side or back to front swinging the back of a PL lens, while projecting the image to the film plane in focus, but with nearly a 2X crop factor for lenses designed for 35mm cinematography, as the 16mm gate is much smaller than the 35mm gate. Keep in mind this adapter is made for a 16mm camera, but maybe some of its charachteristics would carry over for a 35mm adapter?

 

 

Edited August 16, 2008 by Saul Rodgar

[Saul Rodgar]

Correction, it should read:

 

this design allows for a side to side or back to front swinging SHUTTER TO CLEAR the back of a PL lens.

 

My apologies

[Patrick Neary]

"That's important because that sensor is smaller than a 35mm film slide (which is the size of a full-frame sensor). In the camera body, that smaller sensor format effectively "crops" the image produced by the lens. To you, the effect is to magnify the image or increase the telephoto capability of your lens.

 

So, on the 40D, which has an APS-like sensor and a lens magnification factor of 1.6x, a 100mm lens becomes equivalent to a 160mm lens."

 

Hi Saul-

 

The confusion here is that you're relating back to an 8-perf, 35mm still frame and we're all talking about a 4-perf 35mm motion picture frame.

 

One of the cool things about the DSLRs like the 40D is that the sensor size is almost exactly the same size as the 35mm motion picture frame, so mounting a 32mm Cooke S4 on a 40D (if you could) gives you basically the same FOV as it does when mounted on a 435 or Moviecam or whatever. I thought that was clear from several of the previous posts, but apparently not.

 

Finally, don't take this all so personally, I know my posts tend to be kind of abrupt, but they're never meant to be unfriendly.

 

This is a forum, after all, there's supposed to be some back-and-forth, right?