Long shutter speeds on 300D - Really Low Noise!

[dtrayers]

It's about 10PM and there's a nice full moon out. While I wait for the laundry to dry I thought I'd experiment with some long shutter speeds. Here's the longest I tried tonight, 16 minutes at f/11 and 200 ISO. A shot of my backyard. Shot in RAW mode, converted with PS-CS. I just adjusted white balance off of the paint on the playhouse (I know it's white). No exposure adjustment or sharpening:

http://home.comcast.net/~dtrayers/photos/backyard.jpg

Here's a 200% crop:

http://home.comcast.net/~dtrayers/photos/backyard_200_percent.jpg

I was really surprised by the low noise. When there isn't any moon out and we have clear skies I'm going to put the camera on my telescope's equatorial mount with a clock drive and try to get some wide field star pictures.

[Jim_T]

That's pretty good...

You'll have to try a shot where there is more black.. That's where the noise shows up.

I've done exposures up to 20 minutes with my 10D.. (Star trails etc).. The sensor does create quite a bit of noise in black areas that I have to clean up.

This shot was a 10 minute exposure and was taken well after dark. The sky isn't black due to the fact it was taken in the city and the sky was washed out by all the bright city lights. The streak is an airplane going by. (It's a direct crop from a full size image. It's not resized or edited in any way).

http://members.shaw.ca/jamestownsend/10-min.jpg

Note the sky has lots of little 'stars'.. This is noise. It can't be seen in the bright areas.. (Like the building).. I'd be interested in how the DRebel makes out against a perfect black sky... Youre shot is pretty clean.. It could be they improved the sensor somewhat..

[nomel]

Jim_T, does that noise show up in print?

[Tom W]

Nice shot, Dave!

Jim, I see the noise, but do keep in mind that there are a lot of stars out there - many of those dots really are stars. I'm not sure how one might differentiate between the real and the noise though.

[Guillermo Freige]

Tom:
It's noise. A 10min exposure doesn't show stars as dots but as lines (the earth rotates, remember?? :)

Jim:
PS CS uses a more aggresive noise reduction algorythm than Canon in-camera JPEGS or Canon FVU RAW converter. I've processed a 30min ISO 100 exposure (forced to 6400 during conversion) with Canon libraries used by BreezeBrowser, C1Rebel and PS CS, and the results were VERY different!!!. Take a look here:

http://gfreige.homelinux.org/faq/dr_raw_noise.html

[Tom W]

Tom:
It's noise. A 10min exposure doesn't show stars as point but as lines (the earth rotates, remember?? :)

Duh! (slapping self on forehead). I've taken a few such photos, so I should know better. Hey, even 15 seconds will show movement.

Jim:
PS CS uses a more aggresive noise reduction algorythm than Canon in-camera JPEGS or Canon FVU RAW converter. I've processed a 30min exposure with Canon libraries used by BreezeBrowser, C1Rebel and PS CS, and the results were VERY different!!!. Take a look here:

http://gfreige.homelinux.org/faq/dr_raw_noise.html

I think I'll check that out myself.

[larsesp]

Hi Dave,

I have a 10D myself.. How do you set exposuretimes greater than 30 seconds?? Do you use "bulb"?

Lars

[dtrayers]

Lars,

Yes, the camera was set to bulb. I used an RS60-E3 remote release. You can slide the shutter release on the remote so it stays pressed.

I used a Whirlpool RBD305PD double oven for a timer. :lol: :wink:

[Jim_T]

Jim_T, does that noise show up in print?

Yes.. what you see is what you get :) But it isn't as bad as it appears on the screen.

Fortunatley this stuff can be cleaned up.. I use Linux and my photoeditor is GIMP... I'm using a 'despeckle' plug-in that allows me to remove these dots. It works really well.

[Johnnynf]

Let me post a really stupid question if I may. If you can't tell, I have never done anything like this before, but it looks very interesting. Work with me here...I am learning. What is the point of leaving your shutter open for minutes at a time in shots like this? What advantage do you gain from leaving a shutter open for 10 minutes as opposed to one minute. It seems to me that after a certain point (which will obviously change from shot to shot), all of the available light will be "let in" to the camera, and anything more than that is just overkill. If you had some sort of action in the shot (people, cars moving, fireworks, etc.), I could see the very long shutter speeds more, but for these motionless shots, what do you gain?

Also, why the huge difference between the pictures of dtrayers and Jim_T? The first picture looks like it is almost day time out (definately not 10pm in MN during the spring), while Jim's picture is obviously taken at night. Not to say that one picture is any better than another...just wondering what the technical differences are between the two?

Thanks a lot for any information!

[Jim_T]

Not a stupid question :)

If you look at dtrayers original image, you'll see his neighbourhood looks almost like it's a sunny day, yet it was no doubt quite dark to the unaided eye.. (late dusk). My shot was taken near midnight in the winter.. There was no moon.. it was totally dark (Hence the black sky and the extra noise)..

With long exposures, you can get some very bright landscapes with nothing more than starlight..

What I really like is the fact you can do star trails.. Film is still the best for this, because you can leave the shutter open for hours and get stuff like this: (10 hr shot) http://www.ast.cam.ac.uk/AAO/images/captions/aat006.html

[karusel]

Holy guacamoly, how impressive!

[theoldmoose]

If you want to see how noisy the sensor is, just put the lens cap on (and the cover on the viewfinder) and set the thing for manual exposure and manual focus, and try various shots.

You will find that ISO 100 will be the least noisy, even for long duration shots, compared to say, a shorter exposure at ISO 1600.

Also, you may notice 'hot pixels' that show up fairly early, even as short as 30 seconds or so into the exposure. It's a good idea to take a number of shots like this when you first get the camera, and save them for future reference, so you can tell if the sensor starts to degrade.

You can also use such 'dark shots' to subtract out noise from long exposures, although it is usually more useful to take such shots with the sensor at the same temperature as the remaining exposures on that shoot. The colder the sensor, the less noise you will see.

[tony873004]

How can you use dark shot to subtract the noise? Can I do that with Photoshop Elements, or do I need Photoshop or some other software? I know software that is designed for processing astrophotos from telescope ccds does this this, but can I do it too from my Rebel?

[theoldmoose]

You can't do it in the camera. It seems that in-camera dark-frame noise-reduction subtraction is a feature found mostly on Nikons and digicams. If you take a 'reference' dark frame, though, before starting a series of long-exposure shots, you usually can use it with various image editing programs to do the same thing after the fact.

Someone has posted some good digital camera astrophotography links here before -- do a forum search and/or a Google search. You should turn up some good techniques. One I recall is to take something like 8 shots of the same thing, and then sum and average over all the frames. This tends to blur out noise artifacts, since they generally won't show up in all the frames at the same intensity or location. Kind of a poor man's self-correlation filter, if you will.