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12-26-2009, 12:33 PM   #16
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fyi, as I recall the formula for calculating the mag ratio using a reversed lense is:

ratio = 1 + (FL of attached lense)/(FL of reversed lense)

So say you have a 70mm lense on the body and reverse a 50mm lense on the end of it the mag would be:

ratio = Exisiting mag for attached lense + (70/50) = 1 + 1.4 = ~2.4x magnification

Real fun is when using a zoom reversed on the end of another long prime lense. I used a Simga 24-60mm reversed on the end of my sigam 180mm Macro lense...at 24mm on the zoom that gave aa ratio of ~ 8.4x....how cool is that?


Last edited by brecklundin; 12-26-2009 at 12:39 PM. Reason: revised formula for accuracy
12-26-2009, 12:35 PM   #17
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I believe that any lense reversed on the body only will give approx. a 2x ratio...
12-26-2009, 12:39 PM   #18
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QuoteOriginally posted by brecklundin Quote
CR:

I believe that any lense reversed on the body only will give approx. a 2x ratio...
No, that's not true. Visualize the angle of view of the lens and extend it to the film plane. The wider the lens, the smaller the fraction of the image that is registering in the film gate or on the sensor. The lens mount to film/sensor distance allows the image to be enlarged, the wider the lens mounted reversed. What does not change is the lens to subject distance, which is exactly the mount to film plane distance. If you manage to mount a 16mm fisheye on there, you can get really interesting photos.
12-26-2009, 12:44 PM   #19
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yeah, i realized that when i went back to the original formula to verify it....thanks!! And I just bet the results could be FUN witha reversed fisheye...the trick being if figuring the adapters to allow the reversing to even attach.

12-26-2009, 12:54 PM   #20
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QuoteOriginally posted by joodiespost Quote
I know that in my K-x Kit Lens the aperture is set automatically in relation to whatever setting my focal length is. Which is to say I can't set the aperture to 3.5 at 55mm. I can only do that at 18mm. With a manual aperture lens, is there a locking mechanism that will keep me from turning the aperture to a 3.5 while at 55mm focal length?
The raising aperture of a "zoom lens" zooms is not a function of having or not having an aperture ring.

A lens like the DA 18-55mm is not a fixed aperture lens. The aperture changes as the lens zooms, going from a maximum of f3.5 to f5.6. There is no way to lock a variable aperture lens at f3.5 as the lens zooms, even if it had a aperture ring. There are zoom lenses with fixed apertures however, old and new. If you are looking at lenses that are currently in production, fix aperture zoom lenses tend to be more expensive than variable aperture lenses. They usually tend to be overall better optically as well. The DA 16-45mm f4, DA 17-70mm f4, DA 16-50mm f2.8, DA 50-135mm f2.8, and the DA 60-250mm f4 zoom lenses are all fixed aperture lenses. These lenses will stay at their maximum apertures as they zoom.

Thank you
Russell

Last edited by Russell-Evans; 01-25-2010 at 11:52 PM.
12-26-2009, 01:02 PM   #21
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QuoteOriginally posted by brecklundin Quote
yeah, i realized that when i went back to the original formula to verify it....thanks!! And I just bet the results could be FUN witha reversed fisheye...the trick being if figuring the adapters to allow the reversing to even attach.
The real fun is trying to see anything with the fisheye reversed through the viewfinder. I saw one once, and it was DARK IN THERE!
12-26-2009, 01:19 PM   #22
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QuoteOriginally posted by Canada_Rockies Quote
The real fun is trying to see anything with the fisheye reversed through the viewfinder. I saw one once, and it was DARK IN THERE!
hahaha...I think I dated her!!
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