Phillip Reeve Offline • • • • Upload & Sell: Off

Fred Miranda wrote:
Phillip Reeve wrote:
Fred Miranda wrote:
@BastianK@@@, @sebboh@@@ and @Phillip Reeve@@@,
Have any of you tested the CV 28/2 Ultron with a PCX lens (2m or 2.5m)?
If so, would a short adapter make it reach infinity?
Let me know if someone has this lens. I need some pictures to calculate the perfect PCX for it.
Thanks!
Fred
Bastian sold his copy before this thread was started. But some days ago he thought about giving it a second chance.
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Based on the lens likely need of a 2m or 2.5m PCX, do you think that infinity could be reached even with our short adapters? There is absolutely no way to adjust this lens....Show more →
I have no idea. But assuming that the formula posted by artur5 is correct:
artur5 wrote:
Fred, if by longer you mean that the focal length increases then no, it’s actually the opposite. When you add a positive diopter element to any lens, the focal of the combo becomes shorter. It’s a basic law of optics. The simplified formula is : F3 = F1*F2/(F1+F2). Where F3 is the final length, F1 is the focal of the original lens and F2 is the focal of the PCX filter.
In this case : F3 = 35*5000/(35+5000) = 34.76
That’s why you’re able to focus nearer when you use this PCX on your CV 35/1.7. The focal goes from the original 35mm to 34.76mm. To practical effects, it’s like adding a 0.24mm. tiny extension tube. Therefore you can focus nearer than with the ‘naked’ lens. Of course that means also that, in order to reach infinity, you need to shorten 0.24mm. the length of the adapter or remove internal shims from the lens.
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A 28 mm lens with a 2500 mm PCX would need a 0.310 mm shorter adapter which is 0.066 mm more than the CV35 needs (0.143 mm for the 2 m). I am traveling right now so I can't measure my adapter which still has some more room. Will be a close call. And I don't know how good the CV28 performs on a thin filter camera. So I look forward to your results
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