A1 focusing discrepency

Discussion in 'Canon FD' started by Mark Z, Oct 13, 2015.

  1. When I focus on an object at infinity with a 50mm lens and use the A1's focusing screen, the distance scale on the lens falls at 25 feet. With a 24mm lens, again looking through the viewfinder and focusing at infinity, the lens scale says 5 feet. Conversely, setting the lens to infinity results in a blurry image in the viewfinder. When I use the same lenses on my AE-1 there is no problem - when an object at infinity is sharp in the viewfinder, the lens is at infinity - so I'm convinced the lenses are not the problem.

    Inside the A1, everything looks kosher. The mirror and the focusing screen appear to be in the correct location and are not loose. There has been no disassembly or repair of the body, and no damage that I know of. I haven't tested yet to see at what point images are sharp at the film plane, but given that the lenses appear to be good and there is no damage to the mount on the camera, I would be inclined to trust the distance scale on the lenses rather than what I'm seeing in the viewfinder.

    Has anyone had this problem? Any guesses as to what is wrong?

    Many thanks.
  2. SCL


    It is so easy to check sharpness at the film plane with a piece of ground glass or even semi-transparent scotch tape, I'd do that as the next step. If you get a sharp image at the film plane and on the viewfinder, I wouldn't worry about what the lens barrel shows. However if only the lens barrel indication and image plane match (you will need to measure the distance from the film plane mark to the point of focus on the subject) but the viewfinder isn't in focus, there may be an issue with the viewfinder - perhaps there is a diopter correction lens on it, or the mirror may be out of alignment, or the viewfinder lens may have slipped out of its "holder". Butt do the test to eliminate some of the variables.
  3. Well I am certainly not any sort optics expert but I will try a few inputs.
    Lens functions and focuses properly on the AE-1 with appropriate distance values and viewfinder focus = lens and the AE-1 would seem indicate that both of those are good.
    Is the A-1 focusing screen inserted properly, not loose, and completely flat to its mounting area?
    Also- you might examine and compare the positions of the mirrors in both cameras to each other with the mirrors down in the view position. Are the the EXACT same angle up and down AND left to right? If so, that is good.
    If the mirrors both seem correct, I would at this point 'think' that something is out of alignment or damaged up inside the A-1 prism. Is there the slightest dent in the prism? Even if not, the camera may have received a shock somewhere that could have caused unseen damage.
    You did not mention if you have obtained the A-1 secondhand, and the focus issue could be the reason it was sold.
    Hope my input was somewhat helpful.
  4. Thank you, Stephen and Keith. I'll check the image at the film plane once I finish the roll that's in the camera. I'd rather not just use the viewfinder and ignore the lens barrel because sometimes I preset the focus, and also the DOF scale is off.

    There is no diopter lens on either camera's viewfinder. The mirrors in both cameras are absolutely identical in every way. The mirrors contact the small stop in the down position, and they stay there. The focusing screen on the A1 is not loose; it's firmly and flatly seated in its mount. Nothing moves, nothing rattles, and all appears to be flat and square.

    The A1 is second-hand. It was in very good condition when I bought it about five years ago. There are no scratches or dents anywhere. I did not notice this problem until today. Of course, as you said, Keith, that doesn't preclude unseen internal damage.
  5. More ponderings:
    If the mirror, pentaprism or eyepiece were out of alignment then I would think the image would never be in focus.
    Since it is possible to get a sharp image, I think the problem is the focusing screen. Perhaps it is installed upside down?
    If not, then the lens mount is not aligned longitudinally correctly which will show up when you test the focus at the film plane...
  6. I agree with all you guys that a logical place to check for a problem is the focusing screen. I checked the Canon service manual (p. 44, fig. 2-31, http://jameskbeard.com/Photography/Legacy_Canon_Manuals/CANON%20A%20-%20SERIES%20CAMERAS/A-1%20Camera%20Service%20&%20Repair%20Guide_z.pdf), which clearly describes and shows the proper orientation of the screen. Also, there was a discussion of screen orientation a few years ago on PN (http://www.photo.net/canon-fd-camera-forum/00Vx5L). I loosened the screen holder in my A1 and removed the screen. It was in the proper orientation. The screen appears to be held against the pentaprism (or its holder) by some spring clips, which should keep the screen in a precise and proper position. I reassembled the screen in its holder and noted that the screen is aligned and snug. After mounting my 50mm lens on the camera, I saw that the problem had not disappeared, which I guess I expected because I had not made any changes from its original condition.

    My next test was to examine the image at the film plane. I stretched some frosted tape from rail to rail and opened the shutter with the camera aimed at a distant utility pole. With a ten-power loupe it was easy to see that when the lens was set at infinity according to the barrel markings, the image was tack sharp, and the image degraded as soon as I turned the lens's focusing ring. So, the markings on the barrel are accurate, and the problem appears to reside in the optical path between the mirror and the viewfinder. The mirror is in its holder tightly, and it rests properly on the metal stop under the mirror, so I can't see a problem there, and it's hard to imagine that the prism is not where it should be.

    This has been an intractable problem, and I'm still looking for suggestions toward a solution.
  7. The reflector components / optical alignments are out of kilter inside the prism. Time for a Tech's evaluation. Perhaps something simple in there that is easy to repair or replace broke or came loose, or shifted. You just never know.
    Mark, are you U.S. based? Give a phone call to Ken Oikawa in Sun City California. 951-246-9136. Ken is a retired Canon Factory Technical expert who still loves to repair the Canon SLR line. He does not do email. His physical address is: 28288 West Worcester Road, Sun City, California, 92586. Sun City is a northern area of San Diego.
    He may be able to advise you over the phone what the issues are and what the cost would be. I have found his repairs to be extremely reasonable in cost. Ken has likely run across your issue at some point. He would also automatically replace the mirror cushion and the door dust seals as a matter of good quality repair policy and longevity, and properly lubricate the drive shaft for long-term service to eliminate and/or prevent the infamous "Canon Shutter Squeal." (Very annoying.)
    Should you end up sending it to him, use USPS. He does not like to use UPS or FEDEX. After he has personally evaluated your camera, he will contact you for payment and his preferred method is by personal check (no cards, PayPal, etc.)
    IMHO, any repair under $100 or so would be a good deal for the future life you will receive from this very fine camera if that is something in which you are interested. I like the A-1 series so much that I have three, which have all been serviced in the past decade to last for many more years. Long term since 1978 when I got my first one, there have been NO service issues other than those 'standard' ones mentioned above, and all of the LED displays still function just as new. The LED displays are apparently quite durable / reliable.
  8. Keith, thank you for your advice. I agree that the problem must lie in the prism, and in my case, that requires a technician, so I am grateful for your recommendation of Mr. Oikawa. I will definitely give him a call. It's good to know that your A-series cameras have been so durable and reliable. I still use the AE-1 I bought in 1978.
  9. My AE-1 purchased at its introduction in 1978 broke the ASA string about a year later and after replacement it is still going strong today. Talk about durability! And this was never a professional type camera.
    Received my EF back from Ken Oikawa this afternoon. It had a power / meter issue. (I had purchased it cheap that way from a camera store.)
    Not only is it polished to look almost new, the meter is functioning right on and agrees with both my first EF and a professional PENTAX Studio VI Spotmeter.
    Could not be happier with Ken's work, ethics and attitude. All of my Canon work goes to him from now on. I have had issues with two other well-known Canon repair facilities (to remain unnamed here.)
    Ken included a note that he also repairs: The A-1, AE-1, AE-1 PROGRAM, F-1, F-1N, and "most" of the FD and FDn lenses. Clean, Lube, Adjust, whatever services you need. And he obviously does not run up charges for extraneous things that do not actually require service. He also includes a detailed, dated invoice for any future reference.
  10. Ken sounds like a great resource. Again, many thanks for recommending him.
  11. One last thought, you said,
    "...I saw that the problem had not disappeared, which I guess I expected because I had not made any changes from its original condition...."
    Maybe try inserting the screen in its holder upside down (if possible) just to see if it "fixes" your issue before sending the camera out for repair?
  12. Thanks, Steven. I really wanted to get the problem fixed, and I went as far as I could to do that. It was time for a qualified person to work on it.
  13. Just as a follow up, I sent my A1 to Ken Oikawa, and he found and fixed the problem. His note back to me did not say specifically what the issue was. He returned my camera in a short time, nice and clean, well packaged, all for a reasonable price. I will second Keith's recommendation of Ken for servicing older Canon cameras.
  14. Ken is the best. He's done a number of cameras and lenses for me over the years, can't say enough positive about his work.
  15. Hi. Don't know if you got your camera sorted but your problem is definitely the focus screen and it's in upside down. Just had exactly the same problem with mine. Turned the screen the other way and it's now fine.

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