FD:EOS conversion problem

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Frank Kolwicz

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I've had my old FD500L professionally converted to mount to EOS bodies (especially my 5dII), but I now have serious flare in the images. Flare was not present when I used the lens with a glassless Canon adaptor, nor is it visible in the viewfinder, it only shows up in an image, most of the time. The flare occurs with or without an extension tube.

The new internal parts of the adaptor are blackened, but not completely, like the black velvet-like cloth used in some Canon lens parts, my EF25mm Extension Tube, for example.

I know that some of my FD lenses have a film-shaped baffle to reduce flare, but I don't remember if this one did. It doesn't now and I've querried the machinist about that. Does anyone who has or had an FD500L know if it had a rear baffle?

Thanks in advance for any help,

Frank
Monmouth, Oregon, USA
 
If you can't see it in the viewfinder, it might be a reflection off the sensor bouncing back off the rear element. It was never a problem with film, so not much was done about it in those days.
 
Thanks, HoppyUK, that makes sense, but I wonder what I can do about it.

The FD lenses and the Canon FD extension tubes I have all have at least a single light baffle with a cut out the shape of the film gate. It's located at the rear of the lens, so I'm looking into putting that back into the modified 500L (it was removed by the machinist). I did make a baffle out of black paper and put it in the drop-in slot to see if it had any effect and it did cut down the flare noticeably.

The machinist said that he has made many such conversions the same way without problems. Maybe he made them to film cameras over the years and film is not so sensitive or so reflective, but the baffles are there for a reason.

Frank
 
It sounds the combination of the super-shiny digital sensor and removal of the baffle might be the problem, as you say.

It's most usually visible with a filter, when light bounces off the back of that and returns to form a ghost image. With a long lens especially, since all the light is coming directly straight down the lens, and not from an angle as it does with wider lenses, it's hard to avoid. With wider lenses, most of the image is projected on to the sensor from an angle, and it bounces off at the same angle where is it absorbed harmlessly by the sides of the mirrorbox and the baffling. Has your machinist converted many longer lenses in this way?

When you see a lens that has been 'optimised for digital' what that means is they have modified the rear and added extra coatings.
 
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HoppyUK said:
It sounds the combination of the super-shiny digital sensor and removal of the baffle might be the problem, as you say.

It's most usually visible with a filter, when light bounces off the back of that and returns to form a ghost image. With a long lens especially, since all the light is coming directly straight down the lens, and not from an angle as it does with wider lenses, it's hard to avoid. Has your machinist converted many longer lenses in this way.

When you see a lens that has been 'optimised for digital' what that means is they have modified the rear and added extra coatings.
Click to expand...
I think that's it exactly, and I don't think there's going to be a solution. (Sorry!)

Some people make disparaging comments about lenses which are "designed for digital", but I think your issue is showing that the lens coatings can be critical.
 
One thing that puzzles me is that I have been using this lens on my 5dII for a year with a Canon glassless converter (essentially an extension tube with a quick aperture ring) without any sign of this issue, so the baffle may do everything that the latest coatings, etc. that have been mentioned, achieve.

The only thing I hope to accomplish with the conversion is to regain infinity focus for those birds, especially, that seem to know just how far I can focus with the adapter.

Just for anyone who is reading this and contemplating something similar, I wish that I had the conversion made in such a way that the adapter was retained - it did a good job of allowing a fast change between wide-open for focussing and stopping down to the shooting aperture. The way this modification was made requires stopping down with the lens's aperture ring, which isn't quite so well placed for making the change quickly.

Thanks much for your thoughtful replies,

Frank
 
Strange! This sounds similar to a problem experienced when adapting the Tamron SP 90/2.5 manual focus macro lens to a digital body...in that case the rear element is too flat, producing a refelection which shows itself as pink flare on the final image. This gets worse as the aperture gets smaller.
 
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