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Canon Rangefinders - Peter Dechert and Peter Kitchingman Peter Dechert is best known for his Canon Rangefinder, Canon SLR, and Olympus Pen books, the latter two long out-of-print. He was a monthly columnist for many years for SHUTTERBUG magazine, and has contributed to many others. Most recently he has written about the pre-WW2 Zeiss 35mm cameras, but his interests in camera equipment and optics are many and varied. As a pro protographer and honorary life member of ASMP, Peter is also expert in using the gear! Peter Kitchingman - author of Canon Rangefinder Lens book Peter Kitchingman's 'Canon M39 Rangefinder Lenses 1939-71' book is the definitive source on these very interesting optics. His interests also go to the entire Canon Rangefinder system and beyond.

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Canon TV 50mm f/0.95 optical construction
Old 06-05-2019   #1
OlivierAOP
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Canon TV 50mm f/0.95 optical construction

Hi. First post here, in search of advice.

I found a Canon 50mm f/0.95 in my lab, it was used 30+ years ago in medical imaging. It is missing the rearmost optical element. That's based on appearance and from the back-focus distance (too long), FOV (too narrow) and image quality (quite poor at large apertures). It is also missing a mount but I made one for my Sony A7.

My hopes of finding a correct replacement lens element are pretty low but maybe Mr. Kitchingman or others have detailed info on that element?

It looks bi-convex from the diagram, and based on rough measurements and calculations it should have a focal length of approx. 50mm.
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Old 06-05-2019   #2
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With no rear element, no wonder the pictures are blurry.

Here's the optical diagram. No idea what type of glass Canon used, or the curvature of the rear element. Good luck.



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Old 06-10-2019   #3
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Thanks. I did lift the curvatures and thickness from the diagram and scaled the results to what I think is the correct OD of the element. I got sensible results (r=75 & 85mm, t=5mm) which gives focal lengths of ~55-80mm depending on glass type. I doubt the diagram is to scale given that there should be a space between the concave doublets for the aperture.

Last edited by OlivierAOP : 06-10-2019 at 09:31. Reason: redid calculations
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Old 06-10-2019   #4
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You're so close to having a neato lens. I guess I wonder why the rear element is missing. Was it intentionally removed? Or some mishap? I know how labs can get filled with the remnants of so many past activities -- kind of fun to peek in my drawers sometimes. So...perhaps that element is sitting in a drawer? Worth a look?
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Old 06-10-2019   #5
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It's funny. When I was researching the lens after it was found (I had no idea it existed nor that it was missing an element), I was thinking this lens might not be for me. Now that it's out of reach I have a bad case of the blue balls LOL.

Anyway. My colleague who was around back then has no recollection of that lens. Too bad. My best guest a a mishap... the lens it quite bad without the element.

I did find an element in the drawer that sort of fitted. Testing (freelensing) did improve the IQ and restored the FOV. That's why (+ some tests/calculations) I think a 50mm element will help but it'll be bad at f0.95 I think.

Short of finding spare parts or hiring a lab that'll have to do!
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Old 06-10-2019   #6
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The bokeh should improve without the rear element.
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Old 06-11-2019   #7
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If you're so inclined, wouldn't it be possible to buy or borrow another specimen, measure the radii of that element, and together with the focal length that your incomplete lens has, calculate what glass properties are needed?
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Old 06-11-2019   #8
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Well right now the images are a hazy mess with no contrast or detail at f0.95. More 'knocked-out' than 'dreamy'. Once I figure stuff out I'll post pictures to illustrate.

Retinax ideally I'd find a broken one for the parts. Buying or borrowing is an option but measuring curvature accurately requires specialised equipment.

I guess this thread shows my wishful thinking. Even if I knew the exact specs of the element I don't know that it could be sourced unless it's coincidentally off-the-shelf like 50mm FL symmetrical bi-convex in BK-7.
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Old 06-11-2019   #9
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Quote:
Originally Posted by OlivierAOP View Post
Well right now the images are a hazy mess with no contrast or detail at f0.95. More 'knocked-out' than 'dreamy'. Once I figure stuff out I'll post pictures to illustrate.

Retinax ideally I'd find a broken one for the parts. Buying or borrowing is an option but measuring curvature accurately requires specialised equipment.

I guess this thread shows my wishful thinking. Even if I knew the exact specs of the element I don't know that it could be sourced unless it's coincidentally off-the-shelf like 50mm FL symmetrical bi-convex in BK-7.

Yes, it seems more likely that you could find one with a broken front. Fortunately normally the fronts are destroyed in a fall or so.
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Old 06-11-2019   #10
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I would send the lens to DAG.
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Old 06-11-2019   #11
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I corresponded with DAG, Japan Camera Hunter and Kamera Service (Netherlands). Asked an optical physicist as well. No luck. I'm a newcomer in my area regarding photography and I haven't found local people. Happy to receive further suggestions!
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Old 06-11-2019   #12
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I think there is no way to build the rear element in the right spec. If you don't want to waste this lens part, just sell it for parts. I guess some technician may need the rest of the element to fix the other Canon 0.95. Or you bought another lens part with the rear element and resemble together.
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Old 4 Weeks Ago   #13
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Small update. Via Marco Cavina's site I found the patent for the lens. It's by Oude Delft (US 3357776) which Canon may have licensed?

I modeled the specs on WinLens3D and without the last element the focal length matches that of my incomplete Canon (f=115-6mm, measured via FOV crop factor vs. a 90mm lens).

I also modeled the Canon f1.2 lens (US patent 283361102) and it doesn't match. So I can't recycle one of those.

So the rear element should be f=40mm. I can't get one in the same glass (high refraction & low dispersion) but I've ordered some in BK7. I'll update when I've tested them.
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Old 4 Weeks Ago   #14
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Exciting! Hope this works out.
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Old 4 Weeks Ago   #15
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The problem is elementary my dear Olivier.
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Old 3 Weeks Ago   #16
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Quote:
Originally Posted by NY_Dan View Post
The problem is elementary my dear Olivier.
Because I need the right element?

Anyway. I tested some BK7 40mm and 43mm assymetric pieces. Correct FOV is right in between (i.e. close enough) but image is kinda poop. Guess I need high refraction glass as per patent.

A piece from the Canon f/1.2 would likely be decent as well.
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Old 2 Weeks Ago   #17
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Olivier, our pal Peter Kitchingman lists Mukai Jirou as the designer of this lens. Why do you think Canon might have used an Old Delft design?
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Old 2 Weeks Ago   #18
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It's only a theory. So far it *seems* to match the lens and while many Canon patents are out there (from H. Ito and M. Jirou), the Oude Delft one is the only one at 0.95 that I could find. It's my only lead basically.
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Old 2 Weeks Ago   #19
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But the patent was applied for in 1963, after being prepared in Nov 1962. The Canon 0.95 hit the market in June 1961. Again, I'm using Peter K's information.
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Old 2 Weeks Ago   #20
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Quote:
Originally Posted by View Range View Post
..... The Canon 0.95 hit the market in June 1961....
Which means it was designed in 1960. Dechert, in his Canon rangefinder book, says that rumors of the Canon 7 camera and 50/0.95 lens began, "more than a year before production began."

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Old 2 Weeks Ago   #21
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Yes the dates don't match. I find it strange that there doesn't appear to be a patent for the Canon f/0.95. The Delft one references the Canon f/1.2 so you'd think that if the f/0.95 existed it would be referenced as well? And then the Canon goes on to be produced in large numbers for 20 years (including the TV version).

There is a good chance that I'm on a false lead. If I had access to an optical lab or lens designer I could verify. Fascinating stuff really.
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Old 2 Weeks Ago   #22
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Quote:
Originally Posted by OlivierAOP View Post
......There is a good chance that I'm on a false lead. If I had access to an optical lab or lens designer I could verify. Fascinating stuff really.
You should pick up a copy of Arthur Cox's book on optics (mine is 1974). He writes about several of Canons high-speed rangefinder optics in his section on symmetrical lenses.

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Old 2 Weeks Ago   #23
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Olivier, there could be a Japanese patent for the 0.95. It won't appear in the US patent listing and may not have been known to Old Delft / US Patent reviewers.
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Old 2 Weeks Ago   #24
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Thanks for steering me in the right direction. The Oude Delft patent was indeed a false lead. I was able to find the Japanese patent! It's a bit of a miracle as those old patents are not indexed by keyword/author/company and are in Japanese only.

Here is the URL. You can also find it by searching 1960-043650 on the patent site. I can't read Japanese but I was able to match the characters for Canon and Jiro Mukai in the document.

The prescription appears to be a better match to my experiments. Hard to be sure without proper equipment but I hope that's it.
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