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Archive 2009 · FD 85L f/1.2: a real gem

ronchappel
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p.4 #1 · FD 85L f/1.2: a real gem

Yes i've allowed for that possibility.The rear element holder is also a spacer-see my previous post

May 20, 2009 at 07:08 PM

ronchappel
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p.4 #2 · FD 85L f/1.2: a real gem

Yes i've allowed for that possibility.The rear element holder is also a spacer-see my previous post

Oh by the way- thanks for posting the diagram of the mount parts!My measurements match up perfectly with yours which is encouraging

May 20, 2009 at 07:10 PM

ronchappel
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p.4 #3 · FD 85L f/1.2: a real gem

Just tried a quick comparison with the rear element in different positions.
The first below is normal,the second has the rear element moved forward so it could be used on a 5D,and the last shot shows what happens with no rear element at all.

Obviously removing the element is not an option-the results are hopeless!

Moving it forward however may still be worthwhile.i'll do more testing as i find time

May 21, 2009 at 06:14 AM

Dim.ka_
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p.4 #4 · FD 85L f/1.2: a real gem

m-a-x wrote:
This is also interesting - it's from the Mamiya 645 AFD thread:

This applies only for my convertion for 645 format, because the image area is 2.7 times bigger and this floating element straightens light rays and mainly useful for close range photography when the other lens block is farer away from the focal plane then when it is at infinity mark.

May 21, 2009 at 07:08 AM

ronchappel
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p.4 #5 · FD 85L f/1.2: a real gem

Hi Guys
I've finished my lens some time ago but ended up too busy to do much with it.

As i mentioned before,it has a convertible design that can be used both on EF-s mounts (with perfect image quality) or on the 5D (with a *possible* slight reduction in image quality due to the rear element being moved forward 1mm).
I say possible because all the testing i've done so far show no difference

.However i won't be completely convinced until i do some accurate back to back comparisons ,while checking to the extreme edges of the images.

Hopefully i will get time soon!

Sep 11, 2009 at 07:05 AM

pengland
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p.4 #6 · FD 85L f/1.2: a real gem

I recently converted my FD 85 1.2L to EOS mount. It sits resting quietly in its soft protective case waiting to be used. I have adjusted it for infinity focus and done some initial tests on a borrowed crop body but have not found the time to shave the mirror on my 5D so that I can start actually using the lens.

I elected to fix the rear element in position (I confirmed the 10.40 mm positioning) rather than use an adjustable positioning method. Although I think it is a nice idea to be able to adjust the lens for use on an unshaven 5D; I decided not to employ this method as IMHO there are a couple of caveats to this method that I wanted to avoid.

Firstly, by virtue of the design of a thread (play between meshed helical wedges) there is a possibility of the rear element faces sitting somewhere off the ideal (designed) 90 degree axis to the light path. The degree of free play and consequent misalignment is reduced when using a fine pitch thread but the risk increases with threads of greater pitch and shorter length. The original threads on the outside of the rear element are kept "loaded" when the element is threaded all the way to the bottom of the original holder. The element faces are positioned exactly perpendicular to the light path in this position because the flat face of the holder bottom is forced against the flat face of the outer diameter of the element threads. Without a similar axial locking method being employed for an additional set of positioning threads, positioning accuracy could be compromised.

Secondly, there is the question of securing the rear element in the selected position. I have not read any mention here of how the rear element is prevented from "working loose" when an adjustable rear element mount is employed. As there is no room for a thin lock nut or pin I would assume that some type of removable thread lock adhesive is employed. This method would introduce the risk of getting adhesive on the glass and possibly getting the rear element "stuck" in one position or the other.

Finally, as I found in my testing (and as previously mentioned by Jim Buchanan), for each position of the rear element there is a different infinity position for the floating element. This means that even though the rear element can be moved to accommodate an unshaven 5D, the infinity position for the floating element would have to be re-calibrated and the infinity stop adjusted for each position as well.

Something else of note that should be mentioned about this particular conversion is the clearance between the rear element holder and the components within the camera body mirror box. Jim Buchanan gave me a "heads up" on the potential clearance issue but I decided to quantify it before I tackled the conversion.

When the lens is mounted on the camera the outside edge of the rear element extends all the way to the focus screen/superimposing plate retention latch plate (not sure if this is the correct name). By virtue of this the supporting material for the rear element is limited to a depth that does not interfere with this plate. It was difficult to get an exact measurement of this depth but it is VERY close to the 2mm that the rear element must extend into the mirror box. Furthermore the mouth of the mirror box tapers inwards and reduces the available width of any supporting mount for the rear element. The combination of these factors severely limits the width and depth of any fabricated rear element holder. I found that any material extending beyond approximately 1.5mm of the diametrical edge of the rear element interfered with the mirror box on my 5D.

Edited on Sep 11, 2009 at 12:44 PM · View previous versions

Sep 11, 2009 at 12:06 PM

cogitech
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p.4 #7 · FD 85L f/1.2: a real gem

While I fully respect your attention to precision, I just want to mention that in comparison I basically "slapped mine together" and the results are simply superb (as you can see from any of the numerous images I have posted). I suspected that any inaccuracy in the position and axis of the rear element would cause sharpness and/or CA issues, but the lens is sharper than I could have ever dreamed and shows far less CA than the EF versions. One has to zoom to 100% to see it, and even then, it is so subtle that it basically requires no correction. So, did I just get lucky, or is the precision not quite as important as I thought initially?

Rather than fabricate a new rear element holder, I just Dremel'd out the existing one and mounted it inside the new mount. I found that the rear element stays very firmly in place regardless of how far it is threaded in. Maybe that's just my sample.

Sep 11, 2009 at 12:43 PM

pengland
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p.4 #8 · FD 85L f/1.2: a real gem

cogitech wrote:
While I fully respect your attention to precision, I just want to mention that in comparison I basically "slapped mine together" and the results are simply superb (as you can see from any of the numerous images I have posted). I suspected that any inaccuracy in the position and axis of the rear element would cause sharpness and/or CA issues, but the lens is sharper than I could have ever dreamed and shows far less CA than the EF versions. One has to zoom to 100% to see it, and even then, it is so subtle that it basically requires...Show more →

Paul,

Your results speak for themselves. There is no doubt about the performance of your lens and your capabilities.
I am not judging the methods of others in carrying out their respective conversions. I am also not attempting in any way to discourage others from attempting to carry out this type of conversion. I was simply offering an insight into the reasoning behind the approach I took in the hope that it inspires others ingenuity and helps them to carry out their conversions to the highest degree of accuracy and precision within the limits of the tools available to them.

Nick

Sep 11, 2009 at 01:21 PM

cogitech
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p.4 #9 · FD 85L f/1.2: a real gem

Nick,

I think you misunderstood my intentions. I wasn't trying to say right or wrong, or anything of the sort. Just that I didn't aim anywhere close to your level of precision and ended up with truly unbelievable results. If I had the skills, tools and time to achieve that sort of precision, I certainly would. Like I said, I really respect it. Even envy it, to be honest.

Maybe I did just get lucky.

Sep 11, 2009 at 01:27 PM

pengland
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p.4 #10 · FD 85L f/1.2: a real gem

cogitech wrote:
Nick,

I think you misunderstood my intentions. I wasn't trying to say right or wrong, or anything of the sort. Just that I didn't aim anywhere close to your level of precision and ended up with truly unbelievable results. If I had the skills, tools and time to achieve that sort of precision, I certainly would. Like I said, I really respect it. Even envy it, to be honest.

Maybe I did just get lucky.

Paul,

Nothing misunderstood and no offense taken. In light of your comments and considering some other posts I have made regarding conversion methods I thought it might be important to clarify my perspective.

I have been involved in the alt lens scene for less than a year and I have converted a lot of lenses in quite a short time. I have found the challenge of doing so to be almost as enjoyable as actually using the lenses. It was actually a thread here in which you were sharing your enjoyment and appreciation of the Rokkor 58mm f1.2 that got me hooked (my wife may hunt you down and make you pay for that some day...ha ha...). Your enthusiasm and resourcefulness have been an inspiration to me and many others.

I am fortunate at my work to have both the tools and the time to carry out precision work. I work on a ship with a well equipped machine shop. I do all of my work after hours when I am "on shift" on the ship. Other than going to the gym most nights I spend the rest of the evening hours tinkering with lenses. I can't go home anyway. At home I don't do any conversions because I have no time for it at all.

Nick

Sep 11, 2009 at 05:10 PM

JimBuchanan
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p.4 #11 · FD 85L f/1.2: a real gem

pengland wrote:
...The original threads on the outside of the rear element are kept "loaded" when the element is threaded all the way to the bottom of the original holder. ... Without a similar axial locking method being employed for an additional set of positioning threads, positioning accuracy could be compromised. ...

Wow, Nick, very comprehensive description. Those are all of the FD 50/85L issues, as I see it!

To maintain trueness of the secondary threaded frame that I use with the M42 female threads of the EF back, is a method of taking up the slack of the mating threads. I use flat black paint as it sprays on the female M42 threads very uniform. After it dries, I then take a male M42 thread and work down any high spots, so when I thread on the new rear element holding piece, it is true and smooth to thread on. I then lock it into place with a dab of paint on the threads. To test the trueness, I turned the new back at speed, to observe any variance in placement, which there was none.

If there was wobble or offcenteredness in the above scenario, this condition would contribute to degradation of lens IQ. Compromises in conversion of this lens, or any other for that matter, may not be apparent or obvious in snapshot screen jpegs that we are used to seeing here in these forums. Granted, 100% crops could start to show evidence of aberations, especially comparative shots. While I enjoy looking at the shots, for the most part, a conclusion of absolute IQ or compromised IQ can not be determined from these jpegs. I would rather rely on large prints for that.

When I finish a lens conversion, easy or difficult, I don't feel lucky that it focuses to infinity, has full accurate aperture control, fits the camera precisely, and maintains the original image qualities, I plan for it. This outcome would not happen and repeatedly happen, if Nick's example of attention to precision was not adhered to.

Sep 11, 2009 at 05:44 PM

cogitech
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p.4 #12 · FD 85L f/1.2: a real gem

Nick,

Understood.

I think "envy" is the right word!

(shame on me)

Sep 11, 2009 at 05:51 PM

cogitech
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p.4 #13 · FD 85L f/1.2: a real gem

Jim,

If you ever feel the desire to see 100% crops of my snapshots, just say the word.

Sep 11, 2009 at 05:55 PM

ronchappel
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p.4 #14 · FD 85L f/1.2: a real gem

Just a few comments of the issues raised -

Nick,you are right of course about the infinity issue.I have the infinity on mine adjusted so that the scale is accurate when used in the normal position.
However when i adjust the rear element forwards for use on the 5D,the focus scale is way out...but of course it can't reach infinity now anyway....

I too think that shaving the camera mirror is by far the best overall idea

.The lens will reach infinity,there are no potential image quality losses and no focus scale issues.Of course it also has it's risks,and can only be done to one camera at a time so its unfortunately not the perfect solution

With regards to the accuracy of the rear element mounting (the threads)- in my case they are a little too tight so it's not a worry.
To be honest i couldnt imagine a tiny amount of (potential)play in 1/2mm pitch threads would adversely affect the optical qualities ,but your right about the risk of losing the whole element.Thats something one wouldnt want to see!

I did measure and check the mirror box on the 5D before i did the conversion but to be honest i can't remember now what the measurements were.My design is extremely 'slim' in that regard,but other designs may not be so lucky.
I have no idea if my lens will fit the 5DmkII .Maybe i'll get a chance to try one day

Sep 16, 2009 at 07:40 AM

Booone0
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p.4 #15 · FD 85L f/1.2: a real gem

JimBuchanan wrote:
Wow, Nick, very comprehensive description. Those are all of the FD 50/85L issues, as I see it!

To maintain trueness of the secondary threaded frame that I use with the M42 female threads of the EF back, is a method of taking up the slack of the mating threads. I use flat black paint as it sprays on the female M42 threads very uniform. After it dries, I then take a male M42 thread and work down any high spots, so when I thread on the new rear element holding piece, it is true and smooth to thread on. I then...Show more →

Thanks to everyone who has contributed to this thread. I've been kicking around doing a conversion of an 85L. I converted a 58 1.4 MC Rokkor. I ended up enjoying doing the conversion (admittedly rushed and somewhat sloppy, but a first conversion to get my feet wet) more than using the lens.

Jim, I have a question for you as I am trying to piece together all the excellent information in this thread. Does the rear element of the 85L share threads with, and easily thread into, a female M42 mount?

If so, besides aperture linkage and function, are there any other issues to worry about when converting this lens for use on a crop EOS Body?

This is exactly the thread I've been looking for, and I'm considering picking up a 50/1.2 and/or 85/1.8 to practice a conversion (although I realize these may come with different issues.)

Sep 18, 2009 at 04:23 AM

JimBuchanan
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p.4 #16 · FD 85L f/1.2: a real gem

Booone0 wrote:

No, the rear element thread size is smaller than M42 threads. I am currently using the common M39-M42 thread adapter, and fitting the rear element and part of the housing into the M39-M42 thread adapter piece.

Those are the top 2 bugga boo's as I see it. However the aperture linkage is slightly different on all of them, the FD 50/1.2 is just like the FD50L without the rear element part.

Good luck.

Sep 18, 2009 at 06:19 AM

Booone0
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p.4 #17 · FD 85L f/1.2: a real gem

So, you're modifying an m39-m42 adapter to fit the rear element and housing, then you use that whole piece to screw into the m42 mount which is then mounted to the back of the lens?

Sorry if I'm slow to comprehend, but I haven't looked at the back of FD glass in person so it's difficult to imagine.

Sep 18, 2009 at 05:29 PM

cogitech
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p.4 #18 · FD 85L f/1.2: a real gem

Another option is to use a C/Y-EOS adapter as the new mount. All you need to do is use a Dremel to remove the circular piece that holds the rear element in the old mount. The circumference fits perfectly inside the C/Y adapter (once the internal flanges have been Dremeled off the C/Y adapter). With the circular piece from the old mount fastened inside the C/Y adapter, you simply thread the rear element in.

Sep 18, 2009 at 05:43 PM

Booone0
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p.4 #19 · FD 85L f/1.2: a real gem

Hm... I wonder if this would work with the 85 1.8? Might be worth a try.

Sep 18, 2009 at 06:58 PM

cogitech
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p.4 #20 · FD 85L f/1.2: a real gem

Booone0 wrote:
Hm... I wonder if this would work with the 85 1.8? Might be worth a try.

Does the 85/1.8 even have a static rear element?

Sep 18, 2009 at 07:05 PM

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