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03-14-2014, 10:10 AM   #1
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Adapted Lenses - use long hood to encourage Vignetting?

Perhaps a simple-minded question - but it seems that it would make sense perhaps to use a hood that actually would cause a lot of vignetting with a M42 FF manual Tak for example, even on APS-C, when its adapted to the Q.

On the Q, we are only using the centermost portion of the resolved image. What happens to the light entering the camera that does not hit the sensor directly? 'Bounce around' perhaps destroying contrast?

Anyone experimented with this? If so, what hoods to use with what lens? Say the 49mm 135/3.5 - 200/5.6 hood with a 50/F1.4 - or even a 35/3.5?

Or am I all wet - no effect, not needed??

03-14-2014, 10:20 AM   #2
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This effect even happens with 135 format lenses on APS-C. Cheapest thing to use is a cardborad tube (like from the paper towels). If using other materials, make sure the inner side is opaque and does not bounce light.
Other way is to restrict the exit pupil of the lens to the format and size of the sensor so that light won´t bounce in the mirror box. There are some pentax lenses like the SMC 300mm f/4 that had such a thing built
03-14-2014, 11:06 AM   #3
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QuoteOriginally posted by cahudson42 Quote
Perhaps a simple-minded question - but it seems that it would make sense perhaps to use a hood that actually would cause a lot of vignetting with a M42 FF manual Tak for example, even on APS-C, when its adapted to the Q.
If the "shadow" does not impinge on the image circle it is not vignette, though I get what you mean. You are absolutely correct that a deeper hood may offer additional benefit when a lens is adapted to a smaller format.


Steve
03-14-2014, 11:26 AM   #4
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Which hood?

QuoteOriginally posted by stevebrot Quote
If the "shadow" does not impinge on the image circle it is not vignette, though I get what you mean. You are absolutely correct that a deeper hood may offer additional benefit when a lens is adapted to a smaller format.Steve
Thanks Steve. Taking this a bit further, the 49mm M42 Tak Hood 'D' was sold with the Tak 135/3.5, 150/4, and 200/5.6. I would 'assume' it was made so that the length would not cause a problem with the lens with the widest field-of-view - the 135.

Therefore, if we consider the Q/Q10 5.6x crop factor, even the Q adapted Tak 35/3.5 has an 'effective' length equivalent (FOV?) of a FF 196mm... So the 'D' hood - designed for 135 - should be fine to use with the 35/3.5 on the Q.

If fact, an even longer hood should not cause any problems.

Is this thinking (about how to estimate if a hood will cause a problem) correct? If not, please correct me.

Thanks!

03-14-2014, 12:09 PM   #5
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QuoteOriginally posted by cahudson42 Quote
Thanks Steve. Taking this a bit further, the 49mm M42 Tak Hood 'D' was sold with the Tak 135/3.5, 150/4, and 200/5.6. I would 'assume' it was made so that the length would not cause a problem with the lens with the widest field-of-view - the 135.

Therefore, if we consider the Q/Q10 5.6x crop factor, even the Q adapted Tak 35/3.5 has an 'effective' length equivalent (FOV?) of a FF 196mm... So the 'D' hood - designed for 135 - should be fine to use with the 35/3.5 on the Q.

If fact, an even longer hood should not cause any problems.

Is this thinking (about how to estimate if a hood will cause a problem) correct? If not, please correct me.

Thanks!
I think that is a safe approach. My rule of thumb is to take a quick look-see of the lens with hood attached to see if the front element is shaded from oblique light at something close to the expected angle of view. If you get vignette, then a shallower hood is in order.

I don't own a Q, but on APS-C, I routinely shoot "tele" depth hoods originally intended for lenses in the 100mm-200mm range on my 50mm lenses. Likewise, I shoot a "normal" hood with my 28mm lenses. So far, no problems.


Steve
03-16-2014, 02:34 PM   #6
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The extra light bouncing back was a problem on a Fotodiox adapter when used with a Sigma 70-200 lens that had an element near the rear mount.
I solved it by painting the adapter with flat black paint but I can see how a longer hood could help as well
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