ISO Questions

DavidBeier

DavidBeier

Veteran
Ok, I've been shooting a lot with my Rebel XT as of late. This is the first time I've ever dabble in still photography and if anything I've realized that I have no idea what I'm doing (kind of wanna run back to cinematography with my tail between my legs).

I just shot a round of photos that looked absolutly terrible because I didn't realize that at some point the camera had gotten set to 1600 ISO so, of course, even the most well exposed shots were noisy as hell.

I'm curious though what's a good ISO to aim for when shooting with the Rebel XT. Something that offers a nice compromise between sensativity and noise.

For that matter, how exactly is the camera increasing the ISO? I mean, with film the different stocks have different ISO ratings because the different stocks are more sensative to light. From my experience with digital video, I don't know of any way to change the sensativity of a CCD or CMOS with the settings. Rather you just use ND filters, shutter speed, and of course the apature to control things. Is upping the ISO to something like 1600 just uping the gain? If not what exactly is the camera doing?
 
I was afraid of that. I wish they would have just called it gain so I wouldn't have delluded myself into thinking it was something else and I was ruining my image (never dare touch gain in-camera when I'm shooting with digital video). So I take it that I probably should keep things at ISO 100? Is there any point to doing the gain in camera when I can just raise it in post with photoshop?
 
I'll give you a tip that took me a while to realize when shooting digital or raw specfically. It is better to shoot at iso 400 and over expose a little than to shoot at iso 100 and be under exposed. You can try this test but what ends up happening is that with teh iso 400 picture you can bring down the exposure when working with the raw file and it will visibly reduce the gain where the iso 100 photo will cause a lot of grain by trying to bump it up in post. THe reason for this is that the information of the picture increasingly goes up with the highlights. You can bring a lot more detail out of hihglights than shadows.
 
^
Thanks, I'll give that a try. With video I'm used to overexposing slightly to reduce noise/grain and bringing it down in post. Tell me, do you find that the Rebel XT's auto exposure is accurate or should I compensate. I tend to try to get as low an apeture as possible and then let the camera adjust the shutter speed as needed.
 
Did you shoot RAW or JPG. If you shot RAW you can use BibblePro's Noise Ninja to see how that works for you (works great with Nikon noise).

If you shot JPG check out the photoshop denoiser or various other plugins available.

From my limited use with Canon's you should be able to shoot at 1600 and have it work fine (similar to the Nikon D50, great ISO1600 camera, looks like film grain).

Something else... I don't use my LCD to check focus or whether my image is good... when I shoot I use my LCD for histograms to make sure I haven't blown highlights. Make sure you are exposing correctly and then shoot at whatever ISO you need for the light you are shooting in.

Also invest in a flash.

On average with my D200's I shoot at ISO400 for events, ISO100 studio. I will go as high as ISO1600 for weddings where I can't use flash, but I have a specific post processing workflow for those.

OK... finally, photography isn't video, while the concepts of compsotion, framing, content, angle, depth of field, ect. all translate. You don't want to overexpose (unless you are doing it for artistic reasons). Then again, you don't want to under expose either, shoot for proper exposure to ensure you get the cleanest image possible right out of the camera.

Best of luck and happy shooting.
 
ISO 800 and even 1600 are fine in low light its either that or a blurry picture :(

Pretty much 100 - 400 looks the same on the Canons. Just use what ever you have to in order to freeze the action, hence why you need the higher ISOs when shooting at roughly 150mm or longer...
 
Hey Jeremy, would you be able to tell us about how you use Noise Ninja exactly? Im a little uncertain about the work flow in that program, i have played around with both the settings and the noise brush and cant seem to notice much of a difference?

Cheers
 
Setting ISO rating is adjusting the gain, true. The difference with video is that a still camera has much more time to do the math; to run the noise reduction algorithms before writing the file to memory card. Of course the files are also huge compared to a video frame.

Make a simple test: set the camera on auto exposure where tha camera sets the shutter speed and you set the aperture (pictures will look the same if nothing moves, use tripod). Ideal place would be at home after dark with normal room lights, typical low-light situation. Then take shots at 200, 400, 800 and 1600 ISO settings. Compare in Photoshop. Now you know what to expect and how much quality loss you are ready to accept if you really need to get that shot in the dark.

Shooting underaxposed 100 iso and making it lighter in PS is NOT the same as shooting at 800 iso! The camera does a lot of work to make the picture as good as possible when iso (gain) is up and there is much more information in the shadows in the 800 iso shot. The shadow part of a digital file actually carries very littele information, it is not possible to make it lighter without ripping the lightness values apart*.

*) each lighter f-stop value holds twice as much data as the next darker one. Highlight part holds about 32 to 64 times more finely gradiated data than the darkest part of the photo: big adjustements are possible in highlighs, but only minimal in shadows.
 
Thanks for the info guys. I've been playing with the ISO settings and find myself perfectly happy with 400 in outdoors and 800 for indoors. 1600 still looks too noisy for me unless I go into photoshop and de-noise.

As for auto ISO, I don't really care as I'd never touch it. Frankly, unless it was impossible to turn on by accident, I wouldn't even want it as a feature.
 
DavidBeier said:
As for auto ISO, I don't really care as I'd never touch it. Frankly, unless it was impossible to turn on by accident, I wouldn't even want it as a feature.
Click to expand...

Agreed. I don't like to let the camera have that much control over what I'm shooting. My Pentax K110D has that feature and it was among the first features that was turned off. Permanently.:beer:
 
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