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12-26-2011, 07:15 AM   #1
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problem with 50mm f1.7 reversed

This is my first time to shoot macro so bare with me...

here's my current setup:

Pentax k-x w/ 50mm-M f1.7 reversed on some extension tube(cheap)... When i'm taking macro photos, i noticed that there was a white fuzzy circle on my pics =( with flash or w/out..the strange thing is that when i'm using my 50mm f1.7 as a prime, there's no problem at all. Thanks for the help guys!





12-26-2011, 10:10 AM   #2
dms
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Flare from cheap tube(s). They are not properly blackened/baffled.
12-26-2011, 05:53 PM   #3
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what do you mean by baffled? blackened? is that a sort of modification to my extension tubes? thanks
12-26-2011, 06:11 PM   #4
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Does it do that with just the lens reversed? If so then it's probably light on the rear element. You could fix that by removing the center of a rear lens cap and shooting with that in place. If it doesn't do it with just the lens then it's probably the extension tubes.

12-26-2011, 06:31 PM   #5
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Better tubes/optics have the inside of the tube painted mat black and/or have baffles (e.g., pleated bellows). In your case no--it is not really a viable modification--just buy a better tube. (If it was an expensive telescope you could purchase felt or mat black paint and apply it.) If in doubt get the Pentax tubes.

Actually using the 50mm f1.7 lens and a Vivitar macro 2x teleconveter may be a lot more convenient and similar to the magnification you are getting--on a Pentax dslr (likely about 1:1.5 magnification [m=1.5] and auto, diaphragm).

For more information about these matters and macro in general I suggest reading Blaker "Field Photography" or Lefkowitz "The Manual of Close-Up Photography."
12-26-2011, 06:44 PM   #6
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That looks to me like you are leaking light. I think either the tube, or the seal to the lens, or the seal to the body is leaking. You might try wrapping it with some black paper or a thick cloth to prove or disprove.
12-26-2011, 07:11 PM   #7
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IMO it is flare--the only question (again IMO) is it from the cheap tube(s) or the lens--inferior lens/dirty optics, cheap or dirty filter, or lack of lens hood. The look is a "classic" case of internal flare--thus I said it is the (cheap) tube. As you are using M50 f1.7 the lens is likely not an issue.

Certainly, to the extent practical, make sure about the other causes, before spending more money, but again IMO it is most likely the cheap tube.

BTW if you had said you are using high quality tube--then the look would be that of a poor quality lens: a lens that was way out of adjustment and/or shot close to/at wide open. The central flare spot has the look of an internal flare--thus I tend not to suspect lack of lens hood--which likely would be a more even haze.
12-26-2011, 09:52 PM   #8
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Also, try putting a short section of macro tube on the other end of the lens, to act as a hood.

12-27-2011, 03:36 AM   #9
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I live in the Philippines so buying a TC is not an option =( unless i buy it on ebay (which i don't know how). Ill update you guys once i come home and check if there's a light leaking... maybe just like what has been said above, i'll just wrap my ET(China made) and see what happens. Thanks a bunch guys for your fast replies =)
12-27-2011, 06:39 AM   #10
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Silly question here............does this happen with the lens reversed, but without any extension tubes?.......or with the f1.7 mounted to the camera and/or tubes, and the host lens reversed?

.....just curious.
12-28-2011, 04:00 PM   #11
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tried it yesterday... the reverse ring is not the culprit(no flare when just reversed), it's the extension tube =)
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