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02-23-2014, 08:02 PM   #1
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High ISO, noise and better lenses

Ok, it might be a noob question but I'm curious.

Since forever I have been shooting with bargain bin lenses. Recently I got to the point where I had the chance to get some more expensive ones. Normally I leave the ISO to the camera's judgment (80 to 800 auto) but as I was testing my DA* I ended up pushing the ISO as far as 12 800 for testing various aperture in low light.

As I was browsing my shots, I started noticing many photos at ISO 1100 and 1600 (and even some at 2200) that were showing very little noise or noise much more pleasing (for lack of a better word) than what I was accustomed to. So I did a bunch of ISO tests with my fancier glass and with some of my lower end lenses. To me, noise seems lower at the same ISO (and same shutter and aperture) when I'm using the better lenses. Previously, ISO 800 was pretty much the highest I was willing to go but now I can get similar noise results at ISO 1100 or 1600.

My tests were not very scientific but my environment was pretty well controlled and it's not my first ball game either.

So my question is, can we actually gain almost a full stop of light simply by using better lenses or am I missing something stupid?

02-23-2014, 08:30 PM   #2
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Some lens have better transmittance than others because they use higher quality glass (this is half the reason why some lens are sharper than others, the other being dispersion), but it would be pretty remarkable to gain a full stop.

ISO is basically a measure of how much signal amplification is to be performed. All signals have a nonzero level of noise. The more amplification, the more noise will become noticeable. If a lens transmits a better, clearer image with less light noise, then the image will look better when amplified. The main source of light noise are ambient light (leak in through gaps in the lens, viewfinder, etc.) and internal reflected light (from all the mirrors inside--not everything reflects perfectly!). A lens that directs light with less dispersion should result in less noise reflection light.

HOWEVER, you may be seeing the differences in RESOLUTION from the better lenses. A lens with higher resolution will provide a better signal and thus higher SNR. This means at high ISO, the signal will still overpower the noise and you'll see a better, less noisy image. How much? Well, the differences in resolution between professional and budget lenses can be pretty significant. I'd say that is what you are observing.
02-23-2014, 08:35 PM   #3
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QuoteOriginally posted by fgaudet Quote
So my question is, can we actually gain almost a full stop of light simply by using better lenses or am I missing something stupid?
Oh yea, you can definitely gain more than a stop. For example, if you're shooting with a typical kit lens lens at the long end, wide open is f5.6. Then say you shoot with a fast 50mm f1.4 wide open, that is about 4 stops more light.

Edit: I think I may have misread your post. So the 2 different lenses, are at the same aperture setting? If so, disregard what I said above.
02-23-2014, 09:29 PM   #4
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QuoteOriginally posted by cali92rs Quote
So the 2 different lenses, are at the same aperture setting? If so, disregard what I said above
Yes at the same settings. The most significant test was at ISO 1600 // f/8 // 1/60 at 60mm. I was using a DA* 50-135 vs a Sigma 17-70 (which is not a bad lens).

In other words, the Pentax at ISO 1600 // f/8 // 1/60 would generate just about the same noise as the Sigma set at ISO 800 // f/8 // 1/30

QuoteOriginally posted by MadMathMind Quote
Well, the differences in resolution between professional and budget lenses can be pretty significant.
You're probably right, I checked my best lens against my shittiest lens and the difference is almost 2 stops (2200 vs 800).

I thought that the softness of the budget lens would kind of mask or disguise the effect but I guess I was wrong.

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