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Archive 2015 · My 50g and 35d expose differently

  
 
trevanian
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p.1 #1 · p.1 #1 · My 50g and 35d expose differently


Anyone know why my 35d exposes darker than my 50g?


Jul 26, 2015 at 04:10 PM
lexdiamonnyc
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p.1 #2 · p.1 #2 · My 50g and 35d expose differently


which one? the 35 f2 af-d? some had issues with oil on the aperture blades, which caused them to underexpose at lower apertures. I've had 3 copies of this lens and one had the oil problem, it would underexpose from f8-f22...had no issues wide open to f8.


Jul 26, 2015 at 07:00 PM
M635_Guy
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p.1 #3 · p.1 #3 · My 50g and 35d expose differently


Pix and details would be useful


Jul 26, 2015 at 09:17 PM
EB-1
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p.1 #4 · p.1 #4 · My 50g and 35d expose differently


At which apertures? Wide open most lenses have some vignetting and the T stops are also slower (higher numerically) than the f stops anyway. Are you using manual exposure at least to keep the exposures consistent?

EBH



Jul 26, 2015 at 10:13 PM
CanadaMark
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p.1 #5 · p.1 #5 · My 50g and 35d expose differently


How extreme is the difference? Probably the T stop. Despite the aperture rating, every lens also has a T stop, which is how much light it actually transmits. For example's sake, the Canon 24-105/4 comes to mind because it is particularly bad, having a T stop of over F5 which is on the high end. Primes lose some light too, usually just not as bad. The other thing it could be is sticky aperture blades. You haven't given us much to go on...


Jul 27, 2015 at 01:07 AM
trevanian
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p.1 #6 · p.1 #6 · My 50g and 35d expose differently


Like a whole stop at f8 and versus my light meter 478d. Yes everything manual, strobe ab1600.


Jul 27, 2015 at 11:45 AM
eSchwab
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p.1 #7 · p.1 #7 · My 50g and 35d expose differently


It's important to know if it exposes darker using the same settings (aperture, shutter, iso), or if it is metering the scene darker.


Jul 27, 2015 at 11:48 AM
trevanian
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p.1 #8 · p.1 #8 · My 50g and 35d expose differently


yes it exposes darker using the same settings as my meter, compared to my 50g and my 85.


Jul 27, 2015 at 03:38 PM
Lance B
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p.1 #9 · p.1 #9 · My 50g and 35d expose differently


How are you testing the exposure? Is it outside shooting a landscape or the like? Or is it inside in a controlled lighting environment? The reason I ask is that if you are shooting outside you may be getting say more sky in the photo due to the wider angle of the 35mm and the sky is generally brighter and therefore causing the meter to think it is brighter than it actually is and thus underexposing when compared to the 50mm.


Jul 27, 2015 at 11:17 PM
johnctharp
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p.1 #10 · p.1 #10 · My 50g and 35d expose differently


CanadaMark wrote:
How extreme is the difference? Probably the T stop. Despite the aperture rating, every lens also has a T stop, which is how much light it actually transmits. For example's sake, the Canon 24-105/4 comes to mind because it is particularly bad, having a T stop of over F5 which is on the high end. Primes lose some light too, usually just not as bad. The other thing it could be is sticky aperture blades. You haven't given us much to go on...


I'm thinking sticky blades, given that he's claiming a whole stop for a prime.



Jul 28, 2015 at 12:39 AM
CanadaMark
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p.1 #11 · p.1 #11 · My 50g and 35d expose differently


johnctharp wrote:
I'm thinking sticky blades, given that he's claiming a whole stop for a prime.


Yeah a stop is quite a bit, if his description is accurate. I doubt there is a full stop difference between those two lenses' T values if operating properly all else being equal. There might be though if he is shooting them both wide open, then one is starting at F1.8 and the other at F2 before transmission losses, but he says F8.



Jul 28, 2015 at 12:42 AM
snapsy
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p.1 #12 · p.1 #12 · My 50g and 35d expose differently


johnctharp wrote:
I'm thinking sticky blades, given that he's claiming a whole stop for a prime.


I'm thinking it's the aperture coupling on the lens being out of calibration - it's not uncommon for those to be off by up to 1EV.



Jul 28, 2015 at 12:43 AM
theSuede
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p.1 #13 · p.1 #13 · My 50g and 35d expose differently


Actually really easy to test. If you shoot in raw...

Just do a controlled test in constant light (no flickering fluorescents, not incandescent) from tripod against a large flat surface. The surface has to be in the center of the image to circumvent falloff issues (vignetting). In full manual mode off course, and no auto ISO.
Start at wide open, chose a shutter speed to get normal exposure. Grab a frame.
Stop down 1 full stop, double the shutter time. Grab a frame.
Stop down 1 full stop, double the shutter time. Grab a frame.
Stop down 1 full stop, double the shutter time. Grab a frame.
Stop down 1 full stop, double the shutter time. Grab a frame.

All images should be equally bright in the center, on the flat surface. Easy to check in your raw converter, or in PS. If they're not, your aperture mechanism isn't working as it should.

This has a very small error margin, and only with f/1.4 or faster lenses (due to pixel vignetting). On a typical f/1.2 you loose about 1/4-1/3 Ev WO with modern sensors (up to 1/2Ev with Canon sensors)



Jul 28, 2015 at 01:05 AM
trevanian
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p.1 #14 · p.1 #14 · My 50g and 35d expose differently


Thanks guys, I never noticed because I never used a light meter and don't use my 35 f/2 often. I'm shooting indoor portrait with alien bee and a sb800. I usually use my 85 or 58 but I needed wider so I had to use my 35 f/2 d. So when I switched from a whole body shot to head shot, I realized my light meter wasn't off it was the 35 lens.


Jul 31, 2015 at 12:57 PM





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