Canon XI 50mm f0.75 Mount Help

stephenmcleod · Joined: 05 Jan 2018 Posts: 15

Hello!

I've been lurking here for a while, but this is my first post, so hello.

I've picked up a Canon 50mm f0.75 XI lens, which I believe was originally used in X-Ray applications. So far I've been using it on a Sony A7 body, with a DIY mount I've hammed together using some macro rings and rubber bands. It works fairly well, but I'd like to get something a bit more secure.

There are two different thread mounts on the back of the lens. It's difficult to get exact measurements as the rear element protrudes so much, but one is about 55mm, and one is about 76mm. The barrel of the lens itself also has marks that look like a clamp with screws could be used, and it's about 82mm across.

I was looking at getting a clamp similar to https://www.ebay.co.uk/itm/78mm-to-M65x1-thread-adapter-for-Super-Cinephor-2-152mm-lens/252927243601?hash=item3ae3a37551:g:xKgAAOSwC6dZrEVO

but wondered whether anybody had any more information on the XI lenses before I go down that road. It's proved almost impossible to find anything useful so far.

Thank you for any help!

cooltouch · Joined: 15 Jan 2009 Posts: 9096 Location: Houston, Texas

At another forum, our member Woodrim posted a note about an M42 to Sony E-mount adapter he found on eBay that has a helical. So, I'm thinking that you might be able to McGuyver something together, especially if your lens's 55mm threads are the same as a lens or filter's 55mm threads. There might be a way to get from 55mm to 42mm (I'm thinking adapters used to reverse mount lenses). The helical might be handy because we don't know what the registration distance is for that lens. If it's less than M42, then, well, never mind. But if it's the same or greater, then an M42 adapter with helical might be just what you need.

To get an accurate measurement of the diameter of the threads on the rear of your lens, you really need a set of calipers. Even a compass will work. The type with the two pins work best. Come to think of it, the thing that looks like a compass you find in drafting kits but has two pins instead of one pin and a lead is called a caliper, isn't it? Anyway, you just transfer the measured diameter over to a ruler and there you go.

iangreenhalgh1 · Expire: 2014-01-07

You can buy helicoids with various thread sizes:

Here's an example:

https://www.ebay.co.uk/itm/M58-to-M58-Lens-Adjustable-Focusing-Helicoid-Macro-Tube-Adapter-25mm-to-55mm/122212675511?epid=22008775080&hash=item1c74716fb7:g:5vcAAOSwA3dYHUhY

stephenmcleod · Joined: 05 Jan 2018 Posts: 15

So... the problem with the Helicoids is that most of them start out with the lens too far away from the sensor for it to be useful for anything but macro shots. I can get it to a decent fixed focus length by using a combination of macro rings to gradually get to the right place, but fixing the lens to that length is the tricky part.

It's also tough to get affordable filter adaptors in the less common thread sizes without getting them from China. I don't mind doing that, but I've no way of being sure what the pitch size etc is, and don't want to buy things that take a month or two to arrive only to discover they don't work.

Getting M42 to Sony etc isn't a big deal obviously - just getting the lens itself into a usable mount.

I did some measurements by getting the circumference of the threads, then doing the math to find the diameter:

First thread:

Circumference: 180mm
Diameter: 57.3mm
Length (width): 5mm

Second thread:

Circumference: 200mm
Diameter: 63.6mm
Length (width): 4mm

Lens Barrel:

Circumference: 234mm
Diameter: 74.5mm
Length (width): 8mm
Screw bevel length from the front of the lens: 5mm
Screw bevel length from the rear of the lens: 8mm

Though using a compass is a great idea. I'll try that out.

I'm in talks with RAFcamera to get a mount that would work. Will report back if I have any success.

visualopsins · Expire: 2025-04-11

What's the camera register distance for the lens?

stephenmcleod · Joined: 05 Jan 2018 Posts: 15

visualopsins · Expire: 2025-04-11

http://forum.mflenses.com/canon-xi-lenses-t62899.html

and

http://forum.mflenses.com/canon-xi-100mm-f1-5-lens-t78438.html

kymarto · Posted: Thu Jan 25, 2018 2:49 am Post subject:

I wrote to you on my thread about the 100mm XI. Iâ€™ve read your dimensions. Here is what I suggest: Your second thread is ~63mm. That will snug right into a M65 helicoid with a few wraps of PVC tape. There are two convenient sizes: 17-31mm and 22-55mm. It looks like your length from the top of the second thread to the end of the rear element is ~20mm, so I recommend the 17-31. It doesnâ€™t matter if the rear element goes deeper than the mount flange as long as it canâ€™t hit the sensor. To the 17mm of the helicoid you will add a few mm anyway with the M65 to camera mount adapter.

Since 4mm is not very deep for the tape to hold the lens securely, I then suggest for security a wrap of tape on the barrel of the lens than continues down to wrap around the top part of the helicoid. The tape is quite stretchy and that should be possible, even with the disparity in diameters. It wonâ€™t be beautiful but it should be secure. You could glue the into the helicoid too but I would avoid anything permanent. You might well regret that later.

https://m.ebay.com/itm/M65-to-M65-Mount-Lens-Adjustable-Focusing-Helicoid-Macro-Tube-Adapter-25-to-55mm/272620235901?epid=22008775219

kds315* · Expire: 2021-03-09

Good idea about using a 65mm helicoid, I would have proposed the very same.

Btw. I think your lens is incomplete, there are elements missing on its rear, as I
have the very same lens in my collection and its rear looks different, which may
has quite some impact on the results and its rear back focal length.

I don't have pictures of that very lens at hands, but the lens back should look like this:

[This is the Canon XI 0.75/65mm]

kds315* · Expire: 2021-03-09

1) I found pics of that Canon XI 0.75/50mm lens you have and indeed, the rear part seems to be missing on yours:

(C) thephoblographer.com

I quote some of the text from there as it contains useful info:

This is an unusual lens. Itâ€™s incredibly fast â€“ and heavy. The front element is about 70mm diameter and the rear element is about 17mm diameter. Its original purpose was to focus an image onto the face of a 1â€³ video camera tube. It is designed to perform best at infinity. There is a focus adjustment built into the lens barrel, but it is a very limited range. The back focus (Distance from the surface of the rear lens element to the plane of focus) is very short â€“ perhaps 1/4 inch. The lens has a standard Leica 39mm mount, so mounting it is relatively simple.

2) Here on another find is a guy who (also) has your very lens and has adapted it to his camera (without focusing it seems), also shows a complete lens:

http://www.pbase.com/pganzel/superfast_x_ray_lenses_adapted_to_dslrs

There are also images taken with that lens, so this may help you to decide if you would like to continue to invest into such an adaptation...

3) Here another link which hows a complete such lens, rear focusing has been removed though:
https://plaza.rakuten.co.jp/utsurundesu/diary/201012280000/

4) And here on a Chinese site also about that lens, including its cross section with lens images and sample images:
https://www.photoworld.com.cn/post/53006

[Strange you could not find anything about that lens, it took me just a few minutes to find quite a bit....]

kds315* · Expire: 2021-03-09

Digging through my image database found those I took

f0.75/50mm ultra high speed lens

kymarto · Posted: Thu Jan 25, 2018 9:30 am Post subject:

Yes, thatâ€™s rightâ€”the rear element group is missing. You would not have a concave rear element normally. What that means is that what you have will most probably about double in focal length and have quite intense haloing, rendering it pretty useless, sorry to say.

stephenmcleod · Joined: 05 Jan 2018 Posts: 15

Thanks for the replies! It's interesting that all of the lenses look quite different at the rear.

kds315* · Expire: 2021-03-09

Well, some people have deliberately removed the rear group, at this achieves a greater distance between lens end and focus plane. Maybe you're was such an attempt. It is just not a Canon XI 50mm f0.75 anymore, but with altered focal length and especially speed.

Rafael and I work together since many years, I will inform him that what you have is no standard Canon XI 50mm f0.75 but a heavily modified lens version without its rear lens group, as it might harm his business if he continues to sell it as "Canon XI 50mm f0.75 adapter", which it isn't.

Glad you got some useful results.

stephenmcleod · Joined: 05 Jan 2018 Posts: 15

stephenmcleod · Joined: 05 Jan 2018 Posts: 15

To square the circle, I put together a blog with my experience and samples:

https://allmyfriendsarejpegs.com/2018/02/14/canon-50mm-f0-75-xi-lens-review/

cooltouch · Joined: 15 Jan 2009 Posts: 9096 Location: Houston, Texas

Your blog article made for an interesting read and I enjoyed viewing the photos at the end. The specular highlights it exhibits remind me a lot of those produced by my Canon FD 85mm f/1.2 SSC Aspherical -- the granddaddy of Canon's 85/1.2 lens family.

To me, the sharpness it produces is more than adequate, considering what it is and all. I guess if it were my lens, I would continue to look for a way to find a narrower set of adapters, so I could chip away at achieving infinity focus with a helical, and then it would be a supremely practical lens.

Good luck with it and congrats on your success so far.

stephenmcleod · Joined: 05 Jan 2018 Posts: 15

kds315* · Expire: 2021-03-09

kds315* · Expire: 2021-03-09