Quote:
Originally Posted by Rich Hibner
judging from the size of your camera, a 72mm achromat is overkill. your lens diameter is like 40something mm's. so no, you'd waste your money on a 72mm achromat.
are you positive the fl is 77mm? that's a high powered achromat.
thats' called barrel distortion when the outer edges are all blury. that's just the type of achromat being used. you can have cheaply made glass as well making it difficult to focus.
i wouldn't use an achromat bigger than 50mm for you camera. stick with something around that size. to determine the best distance from you achromat to your GG is some math. for instance.
some of your problems sound like it could boil down to a bad lens. lens can create trouble as well.
An achromat at 77mm focal length would be 1000/77 equals power. Divide your Fl by 25.4. Having a 77fl achromat would equal to you having it at or around 3inches away.
1000/Focal length=Power
Focal length/25.4=equals distance.
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Hi Rich,
The lens diameter on my cams is 37mm, so you were just about spot on.
Am I positive about the FL of the achromat? That's the number quoted from the surplushsed website for this particular lens. I can't guarantee that's what the FL is, but that's what they claim.
The achromat setup I am currently using is a single 45mm with a 77mm FL, and it had been 2 inches from the GG. Since reading your reply I moved it out to as close to 3 inches as I have tubing for. I am anxious to see what difference that might make.
And the 45mm achromats are in relatively poor condition - very different from the smaller lenses I received in the same shipment. Oh well...
Paul