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7D High ISO Noise & Auto ISO Questions...

Dan Bloch , Sep 05, 2010; 02:05 p.m.

I took some pictures at my friends wedding a couple weeks ago. There was no professional photographer and I wanted to help them document the event.

I was shooting a Canon 7D with an EF-S 18-55, (my Xsi kit lens), in AV mode with the aperture set to F/8 and the ISO set to AUTO.
I attached an example picture that has been converted from the RAW file with no adjustments being made, other than the exposure was raised +1.0 because it was underexposed.

My first question is why my camera would have picked such a high ISO, (3200), as the room was well lit with a huge window and lots of sun coming through a thin, white curtain. I didn't even think to check the ISO, (which is a lesson I wont ever forget), because I assumed in such a bright room it would be fine. I suppose it is possible that I had the ISO set at 3200 by accident, but I really remember setting it to AUTO and just leaving it there, (which is what I usually do). Any other reasons the ISO might have been so high? As another point of reference, I was also using a Lumix LX-3, and in the same room with the ISO set at 400 and the aperture F/4, it produced a great exposure, (although somewhat noisy which I would expect from that camera).

My second question has to do with the noise in the picture I attached from the 7D. The picture seems REALLY noisy to me, as do all the others taken in this room at 3200 ISO, (AUTO). These pictures are REALLY noisy, especially if you zoom in or crop them at all. One of the reasons I upgraded from my Xsi was for the ability to shoot at higher ISO. I am just wondering if there is something going on with my camera or if this is the kind of noise you would expect from a 7D at 3200 ISO?

Thanks from a noob.

Dan


Noisy image

Responses


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Mars C , Sep 05, 2010; 02:16 p.m.

First, The picture would be under exposed due to the white background.

Second, The picture is noisy because you raised the exposure artificially by 1 stop.

Solution ,You should have increased the exposure compensation in the camera during shooting. Then use bigger lens opening .

Btw, what is the shutter speed in this exposure?

Steve Wagner , Sep 05, 2010; 02:29 p.m.

Hi Dan, auto ISO can be extremely useful, but you do need to keep an eye on the shutter that you're achieving (if in aperture priority). If auto ISO is picking a setting that affords you a faster shutter than you really need, then you can manually set the ISO lower to gain an edge on noise.

For example you're in AV, auto ISO, and you're shooting a more or less static subject at 100mm focal length. If auto ISO is picking say, 1600 ISO, and the resulting shutter is 1/250th, you can likely manually set the ISO to 800 and still have a fast enough shutter.

As far as noise in this photo, doesn't look too bad, but I believe you that it probably looks worse at full size. Beyond the fact that bumping the exposure in post will make already noisy images much noisier, your goal of lower noise by switching from Rebel XSI to 7D is perhaps going to disappoint you, as they have basically the same SNR across the ISO range that they share.

(link)

Granted the 7D has a higher top end, but sites like Photozone that do stringent testing of sensors are not too positive about 7d high ISO performance. Photozone says 1600 ISO "may still be useable at times." That's not a glowing endorsement.

Personally my advice is that for a shot like this you should have been using a flash, bouncing it off the walls and/or ceiling. Not only would you have much lower noise, but likely better color and tone.

Dan Bloch , Sep 05, 2010; 02:29 p.m.

Shutter speed is 1/40th of a second, lens is zoomed all the way to 55mm.

I didnt know that raising the exposure in post processing results in higher noise. I thought it was considered a good, (conservative?), thing to slightly underexpose, then fix in camera RAW...?
I am a little confused about your solution... I understand I could have increased exposure compensation, EV value), to brighten up the picture. I also could have metered it differently to get the same result, correct? But chossing a bigger lens opening in AV mode would have just resulted in a faster shutter speed and had no effect other than DOF, ... or am I missing something?

Mars C , Sep 05, 2010; 02:35 p.m.

Oh I see it now, The exif file says that you have f8, 1/40 speed and -0.7 in camera compensation at 55mm of the kitlens and AV mode.

The biggest mistake here is the -0.7 exposure compensation.

If it were me I'd just use P mode and auto iso, With 0 compensation, An under exposed iso 3200 image would look alot noisier than a properly exposed one. But that's just me, I hope more people that are more experienced that I am, Would chime in their thoughts and settings for this matter.

Steve Wagner , Sep 05, 2010; 02:36 p.m.

I thought it was considered a good, (conservative?), thing to slightly underexpose, then fix in camera RAW...?

No, other way around. The higher the exposure the better the signal to noise ratio

I understand I could have increased exposure compensation, EV value), to brighten up the picture. I also could have metered it differently to get the same result, correct? But chossing a bigger lens opening in AV mode would have just resulted in a faster shutter speed and had no effect other than DOF, ...

or am I missing something?

Yes, it would have also given you a lower ISO, if you'd dialed the shutter back down, or opened the lens up. Again though, this should have been flashed. The light was too funky in any case. Flash, done right, would have given you much better color, and negated the noise/ISO issue.

Dan Bloch , Sep 05, 2010; 02:36 p.m.

Brett: What you said in your first paragraph makes alot of sense, and I will be sure to keep an eye on my shutter speed and ISO in the future!
But why would my camera have picked 3200 ISO in the first place?
And your info about the relation to high ISO noise between the Rebel and 7D surprises me. I read the 7D review on photo.net and it said that, "At ISO 1600 and 3200 noise is still quite low but at 6400 it starts to become objectionable," and, "Overall, I’d say that the 7D has the best noise performance of any Canon APS-C sensor camera to date."
Thank you for your advise on a flash. I NEVER even think of my flash, mostly because I have no real idea on how to use it. And I thought I would get better color and tone with natural light as opposed to flash...
I obviously have alot of learning to do.

Steve Wagner , Sep 05, 2010; 02:49 p.m.

But why would my camera have picked 3200 ISO in the first place?

Auto ISO is generally smart but isn't perfect. In your case it was actually generous in only picking 3200 given that your shutter speed was slower than your focal length.

Thank you for your advise on a flash. I NEVER even think of my flash, mostly because I have no real idea on how to use it. And I thought I would get better color and tone with natural light as opposed to flash...
I obviously have alot of learning to do.

Bounced flash can work very well for images like this. The walls and ceiling provide a huge surface to scatter and diffuse the light of the flash, so you get all the benefits of full illumination, accurate color, low noise, etc. without the harsh shadows or flat, washed out look that aiming the flash right at their faces would produce.

Conceivably you could have gotten good color with this natural light, but it looks like funky mixed light. To me it has the typical pinkish. washed out look of a shot that probably should have been flashed. The choice of flash vs. not is a personal one, but in the heat of the moment you need to take some shots in the available light, using the best settings and technique you can, and see if the results are attractive. Then do the same with flash and decide which route to go. Otherwise you can spend a lot of time at your even getting subpar shots when a change in technique would produce much better results.

Dan Bloch , Sep 05, 2010; 02:57 p.m.

Thanks Brett. And off-topic, your photo's are inspiring and amazing. I just spent a few minutes perusing your website. What I wouldn't do for your eye!

Puppy Face , Sep 05, 2010; 03:39 p.m.

I tried auto ISO for a short while and, while it was okay 2/3 of the time, about 1/3 of the time it picked a crazy high ISO. You can't really trust it if you're picky about IQ. So I turned it off and dial it in myself. With that said, 7D auto ISO is much better than 40D auto ISO, so it's slowly improving.

And, like others have said, large areas of white or light colors will fool any meter as it expects an average distribution of tones. And weddings, snow and white sand beaches are typical places you need to override the meter by adding +.5 to 2.0 EV depending on the situation. And I agree a burst of fill flash would have helped the couple "pop" and controlled the contrast.


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