Highest ISO during Star Photography?

tyqre · Sep 21, 2011

I've been reading some tutorials on star photography and they all say to use the highest ISO. When i tried to do this all i got was a very, very grainy image with my f4.0 10mm WA lens with my T2i. Any suggestions?

Heitz · Sep 21, 2011

yea, that's understandable. You might consider using a tripod and a slow shutter speed with a less extreme ISO. I'm not quite sure about the t2i specifically, but if you were really using the 'highest' ISO, it's probably much too high. many SLRs perform quite well up to about 1600 (some even higher), but again, using a tripod and slow shutter speed might be best.

analog.universe · Sep 21, 2011

My suggestion is to be careful of what you read. The highest ISO on any camera is pretty much never appropriate (a couple exceptions, but certainly not if quality is your goal). I would say do some test shots to figure out how high your camera can go and still maintain an acceptable noise level, and then use that. My camera maxes out at 12,800, but I shoot stars at 800, anything over that and the noise reduction becomes star reduction as well. f/4.0 is certainly a limiting factor however... the shots I've done were at 1.8, ISO 800, like 20 seconds (with a 28mm lens).

analog.universe · Sep 21, 2011

One more thought.... shooting at 10mm will allow you a longer shutter speed than my shots at 28, so you make up a little bit of the difference in aperture.

tyqre · Sep 21, 2011

I use a tripod by the way. I do have a f1.8 lense but its 50mm. I could try that. I guess it depends if i want a wider image or more light. But for the f4.0 would you say 800 is the max for a 40-60 second exposure or would you go lower (or higher)? Thanks for your help by the way.

analog.universe · Sep 21, 2011

The highest usable ISO is 100% dependant on the camera body, and I've not used yours so I'm not sure. Some cameras will be totally fine at 1600, others will struggle at 400. You can take some shots with the lens cap on to test yours out, see what kind of noise floor you end up with at each level. Also, make sure you've enabled "long exposure noise reduction" in your camera (the manual will tell you where to find that option). This noise reduction algorithm actually measures sensor noise immediately after taking the shot, so it's more effective than the purely mathematical reduction you can do in post.

tyqre · Sep 21, 2011

I turned on "long exposure noise reduction". I also see something called "high iso speed noise reduction" should i turn that on too? by the way i see that you are from Vermont, im form Mass

analog.universe · Sep 21, 2011

There is debate about whether "high iso speed noise reduction" does any better than noise reduction performed in post (assuming you shoot raw). I leave mine off, because I like to be able to control the NR myself. If you enable it, it takes a step out of your post processing, but leaves the NR settings up to the camera to decide. If you shoot jpg, there is a definite advantage to the in camera reduction, but I wouldn't recommend shooting jpg, especially for star shots.

<3 New England

tyqre · Sep 21, 2011

of course i soot RAW

I guess ill turn it off and do some NR in lightroom. or something. And yes <3 NE live here all my life.

dakkon76 · Sep 21, 2011

If you're on a tripod, why would you want to shoot anything but 100 ISO? Did the source you read say why you should be shooting at a higher ISO?

analog.universe · Sep 21, 2011

You're limited on shutter time because of star trails. The earth is constantly turning, so the rule of thumb is you can get away with 600/focal length seconds, before the points start to become lines.

tyqre · Sep 21, 2011

that same source that said that i need to shoot at a higher iso also said that with crop sensors (which that t2i is) you should really go with 400/fl because of the magnification ultimately upping your focal length. So.. im going to try 40 seconds and see what happens. 100 may take too long since my aperture is 4.0 but 400-800 shouldn't do much harm anyway.

Robin Usagani · Sep 21, 2011

who are we shooting? Kim Kardashian? Justin Bieber?

analog.universe · Sep 21, 2011

tyqre said:
that same source that said that i need to shoot at a higher iso also said that with crop sensors (which that t2i is) you should really go with 400/fl because of the magnification ultimately upping your focal length.

Right, I should've said "effective focal length". Pretty much any time those sorts of rules get tossed around it's relative to 35mm format, so you need to adjust by whatever crop factor if you don't have a full frame sensor. So technically that's 400 for Nikon, and 375 for Canon.