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08/06/2005 12:14:20 AM · #1 |
I have several SMC Takumar (Pentax) M42 mount lens that I like to use, and one thing about them is bugging me. Take a look at the lens. There is a 'feature' of these lenses that allows you to line up the red markings, and you will know that pretty much everything will be focus. (specifically this 35mm SMC)
BUT, if you move the focuser to infinity, infinity will be out of focus! I tried infinity at different f's (but not all of them), but infinity is not in focus. But I can back off of infinity and it will be in focus. What gives?
-Chad |
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08/06/2005 12:20:34 AM · #2 |
I think you can go a little past infinity on most MF lenses. The reason for that is expansion and contraction in varying enviroments. At 98F the lens charecteristics will be different then they would be at 20F. This allows you to compensate.
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08/06/2005 12:41:14 AM · #3 |
You can definitely focus past infinity on those lenses, as nsbca says. Still, in normal conditions infinity centered over the central line should provide infinity focus, assuming the lens is not knocked off its designed specs.
Another factor to consider is that you're mating this pentax mount lens to a 300D Rebel with an adaptor, and it may not be precisely as far from the image plane as it would have been on the old pentax bodies. Just a tiny difference will throw infinity focus off enough to notice.
Robt.
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08/06/2005 08:21:05 AM · #4 |
Thanks guys for the help. I did think about the adapter changing things. I will try it on my old Pentax to see what happens.
-Chad |
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