Higher ISO vs. fixing the exposure PP?

tmL

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Hey guys, I'm wondering what would be best in a low light situation, raising the ISO to get exposure closer to what it should be or just taking the picture with less than perfect exposure and fixing it PP? I'm talking what would be best in terms of preserving image quality?

For example, I'm shooting a night market and see a great scene. I hop over to take a shot at 1/80 (I prefer not to go below so let's make this a constant) F/4 (lowest the lens will go) and ISO 400. I know from reading my meter that the picture will come out darker than I would like but let's pretend I have to make a quick decision between taking the shot or switching the ISO to 800 and taking it. Should I change the ISO or just just fix the exposure PP? In other words, would the noise that I save from staying at ISO 400 result in a better image (after PP to fix exposure) than if I just took the picture at ISO 800 and did less PP? What if I were in same situation but my original ISO is 800 and I have to move it to 1600 to get the more correct exposure, would that change your answer? Keep in mind I'm on a T2i (and a 17-40L just for pretends).

Am I correct in assuming that PP (increasing exposure, brightness, whatnot) has some negative effect on image quality (sharpness)? I just don't know how to weigh the quality loss with the quality loss of higher ISOs. Thanks for the help, input greatly appreciated!
 
Personally i would raise the iso and overexpose by 1/3 stop. FWIW
 
It's always best to have the correct exposure out of camera.

You can recover a stop or two in RAW but you will more than likely give up highlights if you underexpose too much.
 
Raise the ISO.
 
Adding exposure compensation in post process can also bring out noise in an image. But then about a year ago I was shooting a birthday party for a one year old and with a few images I didn't allow enough time for the flash to recharge and the images came out very dark. My first impulse was to delete them but decided to try to save them as an experiment and was pleasantly surprised at how well they came out. I was just a month or so into my D7000 coming from a D80 and I, at the time, partly attributed the lack of noise from the fact I was using an ISO of 100. I agree it is best to try to get the correct exposure from camera but I have saved a few images that were very underexposed.

Jerry
 
All depends on your preference and camera...
Not sure how much you know, let's equate digital to film. Shooting JPGs is like shoot Polaroid, while shooting raw is like film.
When the polaroid gets printed, assuming you scan it in and edit it you can only do so much. However, when you take the film to the lab (or develop it your self) you have more room to play with.
The same idea is here: when you're shooting raw, based on what you're describing, it is the better way to go. Since you have about 2 stops +/- to work with you can play with the image in PP and add or subtract that light w/o significantly (and at times at all) sacrificing the image quality. Of course you also have to adjust other parameters when processing raw file but that depends on the software you're using and your final vision of the image.
When you're shooting JPG, you can't push certain parameters too far w/o loosing image quality. For example underexposing in camera (1/80, f/4 at iso 400) and later adding 1 EV of light in jpg will not necessarily give you the optimal IQ that you're looking for (unless again you shoot raw and do that).
I'm not very familiar on rebel series cameras but put it this way, if it is a model that was release w/in last 2 years, shooting at iso 800 in terms of noise is similar as 5-6 y/o camera models at iso 400. On Nikon, my D70/D200 at iso 400 is the same as my d90 at iso 1000 and d300s at iso 1250 (in terms of noise only).
Hope that helps.
Good Luck
 
Crank the ISO as high as you need it to get a proper bright exposure.
Noise increases dramatically more if you have to increase the exposure in post, big difference. Also the shutter speed benefit.
 
Shoot an image that's 2 stops under exposed and shoot and image that's properly exposed by adding two stops worth of sensitivity to the ISO
Expose the under exposed image properly in post
See the difference
Shoot properly in camera
????
Profit
 
It's not sharpness you need to worry about, it's noise. Your camera always has noise, just varying levels of it. If you increase the brightness of an image you by effect also increase the noise.

This was discussed here ages ago and at the time I whipped out the camera and did a little test to prove the theroy: http://www.thephotoforum.com/forum/beyond-basics/221509-noise-iso-push-vs-pp-push.html

The answer is it's always best to up the ISO.
 
With my D700, I'd raise the ISO because I know what it does. However this is based on my experience with my camera. I'd suggest you to do a few test shots using the set up that you are going to use to make informed decision.

BTW I typically go with ISO1250 with F2.8 to F4 in night market scenes, with F1.4 50mm or F2.8 20mm.
 
Aperture - Shutter - ISO

These are the holy trinity and your camera is the church.

PP is the devil's work (just kidding!). PP is great to make final adjustments or to make some corrections where things didn't turn out quite as you planned; but to plan shots with PP in mind isn't ideal.
 
Thanks for all the responses I did some tests before posting the thread but didn't notice a significant difference. The thread Garbz linked to was also very interesting. I did some more tests and found that going from ISO400 underexposed 2 stops and +2 exposure in LR3 is way worse than just shooting 1600 to begin with. It was a lot more difficult to make a call going from 400 to 800 or 800 to 1600 though. I did seem to prefer the images shot at higher ISO over the ones that were exposed in lightroom. Consider this case closed I guess.
 
Aperture - Shutter - ISO

These are the holy trinity and your camera is the church.

PP is the devil's work (just kidding!). PP is great to make final adjustments or to make some corrections where things didn't turn out quite as you planned; but to plan shots with PP in mind isn't ideal.

Really? Because sometimes composites are the only way to go about some of those amazing photos out there. Not to mention if you tell that to someone shooting cars with rigs, they're going to laugh in your face.
 
Village Idiot said:
Really? Because sometimes composites are the only way to go about some of those amazing photos out there. Not to mention if you tell that to someone shooting cars with rigs, they're going to laugh in your face.

The topic isn't about recomposing from multiple images or doing HDR and I don't think Fred's comment had that in mind.

Your guy shooting cars will use the parts of each images that where exposed properly to start with and not rely on PP for these base image capture. They aren't shooting at random iso, speed and aperture thinking it'll be fixed later on.
 

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