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John Quinn
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, March 02, 2004 - 05:31 pm: | 
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I've owned this camera since new around 1980 and I've allways questioned the split screen focus. I can't say I've had any focus problems, error is mostly within depth of field, but the split screen focus point is off compared to the lens markings. The error is quite marked with the screen focussing say at 4' when the subject is actually nearer to 3'. Even at infinity, it's as though the lens needs to go past infinity to align the split screen. Any info on adjusting the screen is welcome. Thanks in advance, John. |
Jan Dvorak
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, March 02, 2004 - 06:18 pm: |
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John,
Is this happening with other lenses if you have more than one? The problem could be the lens and not the screen.
You should also check when is the actual focus accurate - when the image in the finder is in focus, or when the lens is set to what you consider as the correct distance.
I don't recall if the A-1 has interchangeable screens, if yes, check if the screen is propeerly inserted.
Jan |
John Quinn
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, March 02, 2004 - 06:34 pm: |
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Jan, Thanks for the fast response. It happens with both canon lenses that I bought with the camera, a std. 50mm and a 24mm. I did once try to verify where the error is but depth of field makes it very difficult. I tried putting a piece of ground glass at the film plane but it's nearly impossible to see the focus clearly so I gave up. From memory, the A1 does have interchangeable screens, but it's not easy to see how it comes out. It looks in place, but who knows. Just looking at the construction it's hard to imagine that the lens/body combination can be off, but I'm guessing that the focus screen mounting is somehow adjustable. I've never seen the problem in actual photographs, but it's niggled me for years and I really don't have a good feeling about sending it to a lab to be serviced, it works fine otherwise.
John |
Jan Dvorak
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, March 02, 2004 - 06:51 pm: |
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John,
The only way to do a good test without using a collimator is to shoot a few pictures at very close distances and the lenses wide open, when the depth of field would be very narrow - even with the 24mm.
A check with a piece of ground glass at the film plane would work under those circumstances as well, just use a good loupe.
To sum it up:
1) If your pictures are sharp when your ground glass image is in focus, than the focusing rings on the lenses need adjusting.
2) If the pictures are not sharp when the ground glass indicates proper focus, than the culprit is probably the screen or the mirror, as I cannot imagine the lens flange to film plane distance to be out of alignment.
Good luck,
Jan |
Manuel
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, March 02, 2004 - 07:13 pm: |
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The A-1 does not have user changeable screens. |
Jan Dvorak
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, March 02, 2004 - 08:22 pm: |
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There - the screen is most probably not the culprit, unless the camera was tampered with or dropped. I would go through with the focus check as described above and focus your attention (pardon the pun) on the mirror.
Jan |
john quinn
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, March 02, 2004 - 10:52 pm: |
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You've been a great help, thank you both. I'll try as you suggest and check with the ground glass screen again. After speaking with you today I had the bright idea (no pun) of using a clear light bulb as the suject. At least I think I'll be able to get a clear image of the filament at the film plane.
Also, I'd no idea that the focus rings on the lens are adjustable. Think I might leave that to a professional.
Thanks again. John |
Howard
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, March 03, 2004 - 05:23 am: |
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Hi all. Actually the A1 had 6 optional focussing screens available, but they had to be fitted by a "technician". It is possible that yours is not perfectly positioned. |
David Ritchie
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, March 03, 2004 - 09:05 am: |
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Do not forget the mirror. I bought a new Nikon and found that the mirror was not seating properly which caused a problem such as you described. Of course I sent it back to Nikon for repair. |
John Quinn
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, March 03, 2004 - 05:25 pm: |
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Well, I've found the culprit(s) and it's not the body. I compared the split screen focus point to the visual focus on a piece of matt mylar at the film plane, using a loupe and a light bulb as the subject. With all four of my lenses, the agreement was exact. However, the calibration numbers on a 24mm and a 50mm Canon lenses were way off while those on a Sigma 80-200 and a Vivitar 28-105 were almost spot on. It would be just an irritation, but both Canon lenses don't quite come into focus on distant objects so it looks as though both need to be adjusted. Does anyone out there know how this is done or do I just live with it. I love this camera and I'm not likely to part with it soon if ever. John |
Jan Dvorak
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, March 03, 2004 - 06:04 pm: |
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Hi John,
I would live with it. I had an FD f:4/200 lens that exhibited a similar problem, but pictures were fine. I don't recall how to disassemble the 24mm and the 50mm both should be the same, however the 24 uses a floating element costruction and might be a little tricky.
Glad the problem was solved!
Jan |
John Quinn
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, March 03, 2004 - 07:46 pm: |
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Thanks Jan. I stumbled on this board just the other day and I have to say that the response was much better than I expected. Thanks to everyone for the comments and suggestions.
As I mentioned at first, this problem has never manifested itself in photographs and I feel much better that I have proved to myself that the body is good. I really like the feel of the A1 and personally, I hate the plastic look and feel modern Canon products. I suppose if I spent the equivalent today of what the A1 cost me way back when I might be able to equal it, but then maybe not.
Thanks again to everyone for the help. John |
