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09-08-2010, 11:15 AM   #16
Pentaxian
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QuoteOriginally posted by RioRico Quote
Just remember that a Raynox or other +diopter adapter is less effective at longer focal lengths. A Raynox on your kit lens will magnify much more at 55mm than at 200mm.
That is exactly opposite. A diopter increases in magnification with longer focal lengths. As Marc said, I get about 1:4 at 50mm with a 4.8 diopter Raynox 150. I get about 1.4:1 at 300mm.

I mostly use the Raynox 250 on my shorter primes, and the 150 on my long zooms.

PS Your font is small and hard to read.


Last edited by audiobomber; 09-08-2010 at 11:28 AM.
09-08-2010, 11:24 AM   #17
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QuoteOriginally posted by RioRico Quote
Raynox and similar adapters label their glass by focal length: the DCR-150 is 150mm, etc. Diopter is calculate as the 1-meter inverse of the focal length. So a DCR-250 is 1000/250= +4 dpt, and a a DCR-150 is 1000/150= +6.66 dpt. Diopters are additive. A DCR-250 on a 50mm lens gives (1000/250)+(1000/50)= 4+20= +24 dpt. A DCR-250 on a 200mm lens gives (1000/250)+(1000/200)= 4+5= +9 dpt, considerably less.
I don't know where your numbers are coming from, but Raynox spec for the M-150 is 4.8 diopters and 8 diopters for the M-250. The calculation for diopters to focal length is 1000/diopters, so the FL for an M-150 is 1000/4.8 = 208mm. The M-250 is 1000/8 = 125mm. The M-150 will give 1:1 magnification when mounted on a 208mm lens, an M-250 is 1:1 on a 125mm lens, when the lens if focussed at infinity. You can sometimes get closer, depending on the lens. Some lenses vignette badly when close focussed with a diopter, and IF lenses lose magnification and focal length with a diopter mounted as you move away from infinite focus.
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