What are the downsides of converting FD(n) lenses to EF mount?

Question

Are there any downsides of converting an old FD(n) lens to the EF by means of actually replacing the mount with a EdMika or similar? The lens will become a manual focus and manual aperture control lens, but will be a very affordable one since old lenses are quite cheap.

I've tried to think of possible shortcomings of the result, but I've only come to think of

• Only manual focus and aperture control
• The viewfinders brightness will suffer when using high apertures
• There will probably be more lens flare in older lenses, given the lack of multi-coating
• When focusing at certain distances the back element may protrude so far back into the camera body that it could be hit by the mirror and possibly damage it or get damaged itself

As long as using it for portrait at large apertures that would require manual focus anyway or video recording it seems like an affordable option to consider at least. Is there anything important I've missed that would render it pointless to convert old lenses.

Answer 1

Since you also mention video, I assume you want to mount them on a DSLR.

It's not pointless (especially given the saving), but... the result might not be what you expect. This depends of course on the quality of the lens : an excellent one could still perform quite correctly. And maybe tack sharp is not what you need, depending on your artistic aims.

I'll try to sum up the possible issues with using older lenses on digital cameras.

• The imaging sensor is more reflective than the surface of film used to be, which is compensated in newer lenses by an extra coating on the back, that older lenses don't have. So image contrast can be degraded.
• It was not true some time ago but now 20+ megapixel sensors are much more discriminating than film
• Some optical formulas, as well as glass performance have evolved, so you might find a current lens with equivalent performance... at the same price (or cheaper on second hand)

Answer 2

You don't have to replace the mount and can get away with a simple ring adapter if you adapt the lens to a mount with a shallower registration with mirrorless cameras, such as Sony NEX, Fuji X, Canon EOS M, or micro four-thirds.

For mirror clearance with a Canon prosumer full frame, you can also, if you don't care about resale of the camera, and want to use the full focus range of the lens, "shave" the mirror (i.e., grind it down to make it shorter so it doesn't come into contact with the rear of the lens). Or, of course, only consider using these kits with a 1-series or crop body instead.

But that's not the end to the inconveniences. As you've noted, you will have to focus manually. That can be tough with bad eyesight, or with a dSLR, since the viewfinders in them no longer contain the manual focus aids we used to use in film SLRs. Liveview with an LCD might help with zoom and focus peaking capabilities, but then you're composing at arms' length to see what's on the LCD. And you have no electronic communication between the camaera body and the lens.

This means you won't have any lens EXIF information (focal length, aperture setting used, etc.) You can't shoot in any modes other than full manual and aperture priority, because the camera can't tell the lens to change the aperture setting. You have to have a camera with stop-down metering capabilities, or you won't have accurate metering (most digital cameras are designed to meter while the lens is wide open, and then to compensate the metering reading for the aperture setting--without actually stopping down the lens. This way you have the most light possible to compose and focus by. Without knowing what the lens's aperture is, the camera has to then switch to metering solely by measuring the amount of light coming in, and your view can get darker as you stop the lens down and less light comes in.

Whatever monetary savings you may have had comes back to you in inconvenience. Unless you have a love of vintage glass, a need for the larger manual focus throw, or just a luddite like spirit backed with sheer cussedness to do a thing just because you can, this may not be the path for you.