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

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

I'm going to be doing this conversion to my FD 55 1.2. Any idea where I can find a cheap donor EF lens with a metal mount? Obviously a broken, non-functioning lens would be the cheapest. I'm having a heck of a time finding anything.

Apr 29, 2009 at 01:18 PM

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

Perhaps at ebay. Or a small camera repair shop. In Munich is such a tiny shop with an elderly guy within lots of camera gear. It's actually a real mess. Very sympathic.
I guess if you'd find something similar you'd get cheap broken stuff.

Did you consider using an M42/EOS or any other xy/EOS adaptor? They are pretty cheap online and they have a nice and flat flange.

Apr 29, 2009 at 05:29 PM

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

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 ?

I could not find any more valuable information on the net, that's why I'm so stubbornly asking...
Thanx in advance!

May 05, 2009 at 03:23 AM

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

Hi guys
Im new on this particular forum but have been doing conversions for some time.Maybe i can help with some hard to find info!
Im currently converting an FD85/1.2 to EOS mount.
The basic conversion is now done,i just have to make up a actuating link to work the aperture.No hurry for that though,i'm using it wide open all the time anyway,lol

There is quite alot of talk about the possibility of using this model lens (or the optically identical(?) SSC version) on full frame cameras at infinity.The theory is that it may be possible to move the (fixed) rear element forwards slightly so that the mirror doesn't bump up against it ,while still achieving infinity focus ,AND not affecting the optical
performance .

This particular subject i think i can help with!
Like a few others,i made rear element surround on my converted lens so it could be screwed in or out easily.I've seen others use similar designs for the same reason but
haven't (as yet) seen anyone doing in depth testing with this feature.
Also in this design the surround doubles as a spacer in the forward direction ,meaning it prevents the last two elements actually touching.By careful hand finishing i got the
clearance down to about 0.5mm.Actually its abit less than that but i had trouble measuring the thickness of squashed blu-tak ,

(thats what i used to protect the glass from touching and as a 'measuring gauge')
The design i've used for the rear element holder is as minimal as it can possibly get.In fact the rearmost protruding part is the element itself.The surround/holder doesnt even cover the last 1.5mm of it.

Anyway the upshot of all this is that-
...if there is ANY way for a normal 5D to use one of these conversions,this particular lens is going to be it.There is zero chance of finding any more clearance by reducing the sizes of the parts or decreasing the clearance of the parts/elements involved.
Now having said all that,the bad news...

It is indeed impossible to make this lens focus to infinity on a 5D (and still have normal mirror operation).Even with the last two elements actually touching,the rearmost one still protrudes back too far.
The good news is that moving the rear element doesn't seem to make much difference to the optical qualities of the lens.I have to do more testing in that area but it looks promising

I have yet to fully test the lens on a 5D body but measurements suggest the lens could be focused to about 40m,which might suit the vast majority of users

I'll do more testing when my brother visits again with his 5D
Also i ill try to work out reasonably accurate numbers on how much needs to be shaved off the 5D's mirror so it can used at infinity with either the 'optimum' converted lens and also the version with the moved rear element

May 19, 2009 at 08:49 AM

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

While on the subject - ive noticed that the published diagrams of this model lens show a slightly convex rear lens surface.It's actually slightly concave,meaning there is little chance of damaging the lens surface even if it DID meet up with the flip-up mirror (not that that's something you would allow too often!)

Incidentally i had great plans to convert this particular lens to Nikkor mount instead and use an adapter to fit it to EOS,which would of course make the lens much more versatile.However i'm having great difficulty finding anyone who is willing to measure the mirror clearance of their nikon body for me!So sadly this idea will have to wait abit...

May 19, 2009 at 08:53 AM

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

Had some spare time today so tried it on the puppies

It's really hard getting in focus shots of these guys at f1.2!Managed a couple of decent ones tho.
One thing i've always loved about the FD/EF 85/1.2's is their incredible colour accuracy.It doesnt show so much in these shots

Shot at 2009-05-19

May 19, 2009 at 09:47 AM

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

Shot at 2009-05-19

May 19, 2009 at 09:48 AM

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

Dear Ron, this is very interesting!
40m are a lot. It would now be interesting to determine the hyperfocal aperture setting to achieve DOF until infinity while the lens is focused at 40 m.

Sweet puppies!

Edited on May 19, 2009 at 09:57 AM · View previous versions

May 19, 2009 at 09:56 AM

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

ronchappel wrote:
While on the subject - ive noticed that the published diagrams of this model lens show a slightly convex rear lens surface.It's actually slightly concave,meaning there is little chance of damaging the lens surface even if it DID meet up with the flip-up mirror (not that that's something you would allow too often!)

Incidentally i had great plans to convert this particular lens to Nikkor mount instead and use an adapter to fit it to EOS,which would of course make the lens much more versatile.However i'm having great difficulty finding anyone who is willing to measure the mirror clearance of their...Show more →

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.

May 19, 2009 at 09:57 AM

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

ronchappel wrote:
Hi guys
Im new on this particular forum but have been doing conversions for some time.Maybe i can help with some hard to find info!
Im currently converting an FD85/1.2 to EOS mount.

There is quite alot of talk about the possibility of using this model lens (or the optically identical(?) SSC version) on full frame cameras at infinity.The theory is that it may be possible to move the (fixed) rear element forwards slightly so that the mirror doesn't bump up against it ,while still achieving infinity focus ,AND not affecting the optical performance .

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.

May 19, 2009 at 09:58 AM

ronchappel
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p.3 #11 · p.3 #11 · 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.

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 11:17 AM · View previous versions

May 19, 2009 at 10:23 AM

ronchappel
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p.3 #12 · p.3 #12 · 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 11:05 AM

ronchappel
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p.3 #13 · p.3 #13 · 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...Show more →

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 11:09 AM

AlexTokyo
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p.3 #14 · p.3 #14 · 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.
http://farm4.static.flickr.com/3582/3340595663_11fede2b84_b.jpg

May 19, 2009 at 05:19 PM

ronchappel
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p.3 #15 · p.3 #15 · 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 19, 2009 at 10:45 PM

m-a-x
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p.3 #16 · p.3 #16 · 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.
http://i618.photobucket.com/albums/tt265/tmsidr-max/4a83_1.jpg

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 03:11 AM

m-a-x
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p.3 #17 · p.3 #17 · 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 11:00 AM

JimBuchanan
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p.3 #18 · p.3 #18 · 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:
http://farm4.static.flickr.com/3563/3549263084_8e318e04e0_o.jpg
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 20, 2009 at 07:23 PM · View previous versions

May 20, 2009 at 11:57 AM

ronchappel
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p.3 #19 · p.3 #19 · 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 04:41 PM

AlexTokyo
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p.3 #20 · p.3 #20 · 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 05:00 PM

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