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10-31-2019, 01:04 AM   #1
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will a lens hood really decrease value of lights?

On some camera hands book that tell me a hood will decrease light value about 0.3 aperture , somebody says there is no effect at all.
Which one is real?
And, could somebody tell me why rangefinder usually use green light?
I see some camera use dark orange light, but that is a compact entry level..

10-31-2019, 01:19 AM - 1 Like   #2
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Using a hood might decrease EV if it's blocking some light that would otherwise appear as flare but I haven't seen a "normal" situation where having a hood reduced exposure.
For the green light, if you mean the AF-assist pointer, I think it's because it's an easier colour for the PDAF module to "see" in.
10-31-2019, 01:23 AM   #3
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QuoteOriginally posted by Serkevan Quote
Using a hood might decrease EV if it's blocking some light that would otherwise appear as flare but I haven't seen a "normal" situation where having a hood reduced exposure.
For the green light, if you mean the AF-assist pointer, I think it's because it's an easier colour for the PDAF module to "see" in.
I see, Thank you.
10-31-2019, 01:48 AM - 1 Like   #4
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A hood doesn't affect exposure. After all, when you use a handheld incident light meter, it doesn't have two different settings for with a hood and without one.

10-31-2019, 02:32 AM   #5
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QuoteOriginally posted by Dartmoor Dave Quote
A hood doesn't affect exposure. After all, when you use a handheld incident light meter, it doesn't have two different settings for with a hood and without one.
A hood could affect exposure if for instance the sun was striking the front element. But all that light would be just white noise killing your contrast. And that is why we put a hood on of course!
10-31-2019, 03:11 AM - 1 Like   #6
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Yes, but the OP asked a really straightforward question, and is it fair for us to overcomplicate the answer in a way that might cause confusion? I'd rather stick to the simple answer that adding a lens hood doesn't change exposure. Lens flare of different types can happen with or without a hood, depending on the particular shooting circumstances, but that's not a factor that changes the underlying general principle. After all, shielding the lens from oblique light with your hand can prevent flare too, but nobody in their right mind would suggest that having your hand somewhere near the lens but out of the frame affects exposure in general use.

So to make things clear for the OP: Adding a lens hood doesn't change exposure in the way mentioned in your original post.
10-31-2019, 03:20 AM   #7
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Yeah I know - over thinking things again !
10-31-2019, 05:11 AM   #8
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I would try to explain it this way.

Using a lens hood will more likely give a correct exposure. While the reading the in camera meter may well represent a lower EV than without the hood, it will be more likely to be correct. It will achieve this by eliminating or at least reducing flare and stray light from reaching the metering circuits..

10-31-2019, 05:23 AM - 1 Like   #9
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If the hood increases vignetting it may decrease the light. This shouldn't happen with a properly designed hood.

But to put this in perspective, 0.3 stops would barely impact the image.
10-31-2019, 05:43 AM   #10
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QuoteOriginally posted by UncleVanya Quote
If the hood increases vignetting it may decrease the light. This shouldn't happen with a properly designed hood.
I would have guessed that any hood, no matter how well designed, will cause some vignetting, at least when a lens is most susceptible to vignetting in the first case, e.g. at wide open aperture and/or at the widest focal length (in case of a zoom lens). It may not matter that much or any at all when the lens is stopped down or in the middle or at the long end of its zoom range

Last edited by ehrwien; 10-31-2019 at 05:49 AM.
10-31-2019, 05:52 AM   #11
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QuoteOriginally posted by ehrwien Quote
I would have guessed that any hood, no matter how well designed, will cause some vignetting, at least when a lens is most susceptible for vignetting in the first case, e.g. at wide open aperture and/or at the widest focal length (in case of a zoom lens). It may not matter that much or any at all when the lens is stopped down or in the middle or at the long end of its zoom range
As far as I know a well designed hood is completely outside the boundaries of the angle of view. But I haven't done extensive testing.
10-31-2019, 07:22 AM - 1 Like   #12
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I have done testing. A properly designed lens hood is outside the angle of view. Properly designed rectangular hoods are outside the picture area even at close focus at minimum aperture.
11-01-2019, 06:30 AM - 1 Like   #13
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QuoteOriginally posted by ehrwien Quote
I would have guessed that any hood, no matter how well designed, will cause some vignetting, at least when a lens is most susceptible to vignetting in the first case, e.g. at wide open aperture and/or at the widest focal length (in case of a zoom lens). It may not matter that much or any at all when the lens is stopped down or in the middle or at the long end of its zoom range
It is possible to make a bit of a trade off and accept some subtle vignetting at the extreme ends for more flare protection, but there's no reason this needs to be the case. I'll also add that if a hood causes a hard mechanical vignette, it sucks (or is misaligned or designed for another lens/camera).

This website is no longer live, but there's a nice bit on lens hood design stored in the internet archive: Lens hoods
11-01-2019, 06:59 AM   #14
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QuoteOriginally posted by UncleVanya Quote
As far as I know a well designed hood is completely outside the boundaries of the angle of view. But I haven't done extensive testing.
Correct.
11-26-2019, 09:01 PM   #15
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QuoteOriginally posted by Karen the Star Quote
On some camera hands book that tell me a hood will decrease light value about 0.3 aperture , somebody says there is no effect at all.Which one is real?
Both are correct, however there is some crucial context missing in that statement. An imperfectly designed lens hood can restrict the amount of light passing through the lens. A perfectly designed lens hood will not affect the path of light excepting that of non image forming light [Flare].
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