FD 85L f/1.2: a real gem

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

ronchappel
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p.3 #1 · FD 85L f/1.2: a real gem

Here is the almost finished mount.
About all there is to do now is properly black out the element surround to match the already blacked mount.For now it just has a permanent marker 'black' (looks black/red in this pic)
For this conversion i found a much better way of attaching the mount.The screws actually come from the inside so it's all quite neat and strong.

This image is copyrighted by the owner

One other interesting thing i have to mention! I had been putting off this whole project because i had doubts my local machinist would be interested in such tiny fiddly stuff,but the other day i finally asked him and was amazed just how much he was willing do on his huge machines

The mount for this lens is a standard chinese M42 to EOS adapter with stop down flange.What he managed to do was cut a 0.5mm pitch thread through the 1mm thick flange part!But what REALLY stunned me was that in the process of cutting the thread the lathe is backed off and restarted,cutting deeper each time.It was incredible to think that it was so accurate it could be catch the exact same thread start each time!!
(half mm thread remember,on a lathe with a 12 inch chuck!)

It's got me thinking of what other projects i can throw at him

Edited on May 19, 2009 at 04:17 PM · View previous versions

May 19, 2009 at 03:23 PM

ronchappel
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p.3 #2 · FD 85L f/1.2: a real gem

wjlapier wrote:
Give me some specifics on how you'd like the measurement taken and I'll do it. I have a D700 and a F3HP--no cropped body. I don't have tools to take precise measurements, but I can get close if I know what you're looking for.

Thanks !

I'll work out a quick and easy way to do it and get back to you

May 19, 2009 at 04:05 PM

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

JimBuchanan wrote:
Welcome, Ron.

I am in the middle of a FD85L conversion to EOS, myself.

I did a brief study during a FD50L to EOS conversion concerning moving the rear element for more mirror clearance, and decided there is just one correct position for the rear element, in order to retain optimum image quality. Since both the FD50L and FD85L have identical rear lens positions relative to the film/sensor, I'm assuming that is the same case with the FD85L.

Although these 2 lenses, when accurately converted to EOS, are 50-70% of the cost of the EF L lenses, and while the 85mm lenses are equal in image quality, a case could be made for the FD 50L version being better than the EF version, due to the floating element. Why would you want to compromise lens quality for the sake of mirror clearance, by moving the rear element away from its designed placement?

The image quality of either of these 2 FD lenses are reason enough to reduce the profile of the 5D mirror, in my opinion.

Thanks Jim

Yes i have to do testing to see how the optical qualities of the lens are affected.
In theory its a definite no-no.In practice it might be fine.Basic testing so far shows image quality is still very good.Enough to make it worth trying anyway

May 19, 2009 at 04:09 PM

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

Here is a pic of the f-mount FD85L and the one of the mount itself. Not sure you can see it, but there is a shiny arc on the ring around the last element. That is the part that is hitting the inside of the Nikon body.

2012 © wjlapier

May 19, 2009 at 05:43 PM

AlexTokyo
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p.3 #5 · FD 85L f/1.2: a real gem

m-a-x wrote:
Is there anybody who has an explosion drawing,
a repair manual,
a good cross section
or any other valuable information on the FD 85 L ?

Here is a set of measurements (in mm) that I posted a while ago at Cogitech's forum. All measurements are taken from the lens' "frame" base screw holes. Hope that helps.

This image is copyrighted by the owner

May 19, 2009 at 10:19 PM

ronchappel
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p.3 #6 · FD 85L f/1.2: a real gem

wjlapier wrote:
Here is a pic of the f-mount FD85L and the one of the mount itself. Not sure you can see it, but there is a shiny arc on the ring around the last element. That is the part that is hitting the inside of the Nikon body.

Thanks,thats interesting.I can see what you mean- there is very little room to cut things back any more!
Nice detailed job they did.I wonder why there is a little window?

May 20, 2009 at 03:45 AM

m-a-x
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p.3 #7 · FD 85L f/1.2: a real gem

Alex, thank you! I found that drawing already.
What I am looking for is something as a basis to guess how the lens placement could be modified (both rear lens and the lens group). I would like to show such a quality drawing to a friend who is a studied optician.

JimBuchanan wrote:
I did a brief study <...> and decided there is just one correct position for the rear element, in order to retain optimum image quality.

Jim, on what basis do you come that conclusion? What was wrong with the rear element in different positions? Sharpness? Flare? CA?
I found other statements in the internet, saying that you would not see any difference.
I would not go so far but somebody even said that he left the rear lens completely out, and the "only" negative result was visible CA.

This picture below is from an ebay auction some months ago. Unfortunately, I could not afford that lens

but I kept the description.
It said that this lens can focus to infinity and that there are no mirror issues on full frame. You can see that the rear element is inside the M42(?) thread.

This image is copyrighted by the owner

JimBuchanan wrote:
The image quality of either of these 2 FD lenses are reason enough to reduce the profile of the 5D mirror, in my opinion.

My FD85L (untouched) was not half as expensive as my 5D which I bought used.
For that reason I am reluctant to shave the mirror.
Second, the resale value of the lens is much higher if it does not require mirror shaving.

May 20, 2009 at 08:11 AM

m-a-x
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p.3 #8 · FD 85L f/1.2: a real gem

This is also interesting - it's from the Mamiya 645 AFD thread:
Dim.ka_ wrote:
There is one trick - it is possible to use this combo if you remove the last lens element - which is the element of floating design <...>

May 20, 2009 at 04:00 PM

JimBuchanan
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p.3 #9 · FD 85L f/1.2: a real gem

m-a-x wrote:
My FD85L (untouched) was not half as expensive as my 5D which I bought used.
For that reason I am reluctant to shave the mirror.
Second, the resale value of the lens is much higher if it does not require mirror shaving.

3 amigos, caught with there parts down, or at least their backsides removed, awaiting identical machining for all 3:

This image is copyrighted by the owner

There are many common parts to the back construction of these lenses, save for the rear element of the left 2. Other common measurements are the outmost distance of the rear element, as detailed in AlexTokyo's drawing to be 10.4mm above the lens body base.

I am no lens designer, and have no interest in redesigning an otherwise excellent lens, or playing what-if concerning lens spacings. I can't help you with that. I can suggest that removal of the rear element will ruin the image qualities of the lens and the lens will be worthless.

In the process of determining accurate placement of the rear element, I moved the rear element further away from the sensor, and then, the main group had to be moved toward the sensor to get back infinity focus wide open. This brought the 2 groups too close together compared to the original lens spacings. As a lens technician, my only concern is to retain the original lens orientation and lens group placement relative to each other.

My replacement back, will place the rear element of the L lenses at exactly the original position, and AlexTokyo's 10.4mm position of the rear element on all 3 of the above lenses will be a tad under 2mm protrusion from the EOS adapter backs I use. There is a slight chance the FD50/1.2 will provide slightly more mirror clearance as it has no mounting frame like the L elements.

Stay tuned for the mirror shave episode.

Edited on May 21, 2009 at 12:23 AM · View previous versions

May 20, 2009 at 04:57 PM

wjlapier
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p.3 #10 · FD 85L f/1.2: a real gem

A couple of shots I wished I could make with my D700.

2012 © wjlapier

May 20, 2009 at 07:08 PM

ronchappel
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p.3 #11 · FD 85L f/1.2: a real gem

m-a-x wrote:
.....There is one trick - it is possible to use this combo if you remove the last lens element - which is the element of floating design ....

... on what basis do you come that conclusion? What was wrong with the rear element in different positions? Sharpness? Flare? CA?
I found other statements in the internet, saying that you would not see any difference.
I would not go so far but somebody even said that he left the rear lens completely out, and the "only" negative result was visible CA.

I tried removing the rear element also.The image quality issues were so obvious i didnt bother going any further.
Moving the rear element forward on the other hand seems to still give good image quality so i will test that further

Just waiting until i can borrow a 5D for a proper -provable- test,which may take several weeks

May 20, 2009 at 09:41 PM

AlexTokyo
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p.3 #12 · FD 85L f/1.2: a real gem

ronchappel wrote:
Moving the rear element forward on the other hand seems to still give good image quality so i will test that further

Be careful here. The rear element is really near the next element, which happen to also have a convex shape. If they touch each other, you will likely end up w/ damage.

May 20, 2009 at 10:00 PM

ronchappel
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p.3 #13 · 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 21, 2009 at 12:08 AM

ronchappel
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p.3 #14 · 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 21, 2009 at 12:10 AM

ronchappel
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p.3 #15 · 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 11:14 AM

Dim.ka_
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p.3 #16 · FD 85L f/1.2: a real gem

m-a-x wrote:
This is also interesting - it's from the Mamiya 645 AFD thread:
Dim.ka_ wrote:
There is one trick - it is possible to use this combo if you remove the last lens element - which is the element of floating design <...>

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 12:08 PM

ronchappel
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p.3 #17 · 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 12:05 PM

pengland
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p.3 #18 · 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 05:44 PM · View previous versions

Sep 11, 2009 at 05:06 PM

cogitech
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p.3 #19 · 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 05:43 PM

pengland
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p.3 #20 · 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 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.

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 06:21 PM

cogitech
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p.3 #21 · 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 06:27 PM

pengland
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p.3 #22 · 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 10:10 PM

JimBuchanan
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p.3 #23 · 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 10:44 PM

cogitech
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p.3 #24 · FD 85L f/1.2: a real gem

Nick,

Understood.

I think "envy" is the right word!

(shame on me)

Sep 11, 2009 at 10:51 PM

cogitech
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p.3 #25 · 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 10:55 PM


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