| Author |
Message |
    
Harlee
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 03, 2006 - 07:03 pm: | 
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I have a Promaster Spectrum 7 28-210 zoom lens [Canon mt.]which will not coincide the split image at infinity. I've previously reset rangefinder camera lenses [Electro 35] using a second camera focusing through the front of the lens and a scribed ground glass taped to the film plane. Will this method also work on a zoom lens mounted on a slr camera body? Harlee |
Stuart Willis
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 04, 2006 - 12:02 am: |
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First satisfy yourself that the camera body itself is sound. That is to say it will register infinity correctly with other suitable lenses.
In this way you are not chasing lens faults which may not exist.
Your first move ought be to adjust/rotate the front element group.
That is - set the lens focus barrel at infinity and whilst viewing the film-plane image on ground glass, then adjust the front element to produce a coincident infinity split image. (The focusing barrel remains at infinity, of course).
The chances are that this will fix the described error but if it does not, then you have a compound problem in that zoom lenses are factory set up by focusing at both ends.
You will therefore need to startover and first focus the rear element group.
Hope this helps |
Jan Dvorak
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 04, 2006 - 11:03 am: |
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Harlee,
Is the lens focusing 'past' infinity, or does it not reach infinity? If focusing past infinity, it might be that the lens was designed to allow for heat expansion, which might affect focus. I have seen this on many Canon lenses and notice it also on my Leica 280mm Telyt.
Another thing - is the focusing discrepancy the same at all zoom settings? What are you using as your 'infinity' reference? Particularly at the 210mm setting infinity has to be real infinity and not a house across the street. For accurate checking specially with long lenses your subject has to be at leat 500 meters away; I prefer to use the moon if weather permits ;-) .....
Also bear in mind that adjusting the infinity setting on a zoom lens tends to be a little more complicated than on a prime lens. Stuart's last paragraph is an indication of what you might run into.
Good luck,
Jan |
Harlee
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 04, 2006 - 08:30 pm: |
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Well, I paid out a whopping $10 for this lens, so it may end up being a "project" lens for me. I'm supposing the screws holding everything together are under the rubber focusing collar. I don't see any visible screws showing. Thanks for the help guys. Thiswill be helpful. Harlee |
