Long Exposure Noise

[mitch_mick]

Hello I am completely new to this and therefore this is my first post so I sincerely apologise if there is an older post devoted to this issue. Please point me in the right direction if there is and if I'm mucking up the posting in anyway. So here is my situation:

I really like long exposure photography and have been trying to improve my technique lately. I use a Canon Rebel XTi (400D). I shoot in RAW in shutter priority mode (TV). I use the Noise reduction function. I use a tripod for all my shots and self timer to reduce vibration (as I haven't purchased a wired remote as yet). I tend to shoot with a low ISO. I have an ND filter. However, some of my images still have this kind of grainy, fuzz or haze almost. Any advice on this issue would be greatly appreciated.

Thanks.

[Trainboy]

http://img171.imageshack.us/img171/3313/worthless20thread20withqz6.gif

[mitch_mick]

Yeah I should have thought of that Trainboy sorry. I don't upload any of my pics to flickr.com or anything so here is a public facebook link to a pic if you would like to see an example of what I'm talking about. This particular exposure was for 30 seconds and was taken well after the sun had gone down. Prior warning it is a very poorly taken picture.

http://www.new.facebook.com/photo.php?pid=1227712&l=de68e&id=616266531

[Mike-DT6]

Welcome to the forum Mitch_Mick :-)

Keeping the ISO low is the right thing to do. I would keep it to 100 to minimize any potential noise problems. You won't need to go higher as you are using a tripod and are not in need of shutter speeds necessary for hand-holding.

Make sure you aren't underexposing your photographs as you can create noise during post processing if trying to lighten underexposed areas too much.

If you post a few examples it would be helpful as there may be other factors contributing to the problem that might be apparent.

Mike

:-)

[Mike-DT6]

Sorry, you posted just before I posted my reply.

Is that photograph processed at all to brighten it, or is it as taken? What ISO setting did you use?

Mike

[mitch_mick]

It has been processed to brighten it up. I used ISO 100. I suppose it is the underexposure that is giving me the noise problems. Do you agree? Thanks for the welcome also.

Mitch

[Trainboy]

It could be if it's more than a stop underexposed. Here (http://www.railpictures.net/viewphoto.php?id=24111) is a good example of what night shot noise should look like. (with minor noise reduction) my pic was slightly underexposed too, not more than a stop, how underexposed was yours? (Also, mine was at 200 ISO, fyi)

[mitch_mick]

Thank you for the example. Sorry to sound naive but how do i determine how many stops an image is underexposed? I used auto settings when I processed it through Adobe RAW and it corrected it to the exposure to +0.95...is this what you mean?

[Mike-DT6]

That sounds as if it might be your problem - underexposing then causing noise by adjusting the exposure upwards in post processing. If you had to adjust it up +0.95, then it was virtually 1 stop underexposed.

Your lighting for that photograph was a bit on the difficult side too. Even with the low light level the sky was much brighter than the land and rocks. That, combined with the direction of the light source has given you quite a bit of shadow with no detail. The best way round this would be to bracket your exposures, taking one exposure for the shadow areas and one for the sky and water. Then you would combine them in Photoshop to create an image exposed correctly throughout.

Another suggestion in these types of circumstance would be to use a gradient ND filter, but in this case you haven't got a reasonably straight horizon on which to place the edge of the gradient.

Sometimes it's just a matter of choosing a scene where the light is coming from the right direction. It's not always possible to get a good photo out of any particular setting, even with the help of Photoshop.

Mike

:-)

[mitch_mick]

Thanks very much for your advice Mike. I have a rough idea of what bracketing exposures is but I'm going to read up on it to. I agree the light wasn't particularly good in this case also. The main thing that I needed to know was whether I was getting noise from errors I was making or if it was the environment. It appears to be a combination of both. Thanks again. I'll definitely have to work on the underexposure.

Mitch

[Mike-DT6]

You're welcome. :-)

Regarding bracketing, it is simply taking additional photographs that underexpose and overexpose, in addition to the main exposure. I usually bracket two stops either side of what I judge (or meter) to be the 'correct' exposure. A bit of trial and error will tell you what extent you will need to go with the bracketing.

For example, if I can still meter on the camera and it is telling me that 20 seconds is the correct exposure, I would take additional frames at 5 seconds (2 stops underexposed) and 80 seconds (2 stops overexposed). Once you need to go over 30 seconds you simply set the shutter speed to Bulb, lock it open with your remote shutter release and read the exposure time from the digital display on top of the camera.

For longer exposures (over 30 seconds) I usually guess, then inspect the test shot. After that I'll take a suitably longer exposure if I need to bring out any shadow detail and maybe a shorter one if there is any bright light in the frame (street lights, the moon etc), so I can use that exposure to avoid burnt-out highlights when I put the image together in Photoshop.

Mike

:-)

[mitch_mick]

You do this in Aperture priority mode is that correct? The reason I ask is because that is the only mode that will meter your exposure automatically isn't it? Otherwise you use your own judgement is that correct? I like the sound of bracketing. I just purchased a remote shutter release so I look forward to testing it out.

Mitch

[Mike-DT6]

You should use Manual mode. You simply adjust your settings manually, until the meter indicator is where you want it. Keep the same aperture (for example, f/8 ), then adjust the shutter speed for the correct exposure. Then when you come to bracketing simply adjust the shutter speed again until the indicator is where you want it (-2 or +2, or whatever you wanted).

In Aperture Priority it will be trying to meter the correct exposure all the time (keeping the indicator in the centre), so that's not much help when bracketing.

Mike

[mitch_mick]

Oh okay I see. Thanks very much for that. Much appreciated

[Ockie]

there's also the option of shooting a "burst" with different EV values, which can be set in the menu on the XTi / 400D.

*gets camera, looks for the option in the menu*
follow these steps to get there:

With the camera on Tv / Av / M mode:
Go to Menu>2nd List
Select AEB and put it on -1, 0, +1 or whatever different exposures you want.

Go out of the menu, put the camera on continuous shooting and take 3 shots, one should be underexposed (good for the sky in this case), one should be correctly exposed (good for the area where the camera has metered the exposure) and one should be over-exposed (good for the rocks and other dark areas).


As replied before, you could also do this manually by simply using the manual mode, however, this might be easier ;)

[PhotosGuy]

In Aperture Priority it will be trying to meter the correct exposure all the time (keeping the indicator in the centre), so that's not much help when bracketing. This shows how the subject can affect the exposure & why manual keeps me worry free:
Post #47 (http://photography-on-the.net/forum/showpost.php?p=5191658&postcount=47)

For a good starting point, first set the f-stop & shutter speed you need. Then adjust the ISO.
Need an exposure crutch? (http://photography-on-the.net/forum/showthread.php?t=89123) Then when you come to bracketing simply adjust the shutter speed again until the indicator is where you want it (-2 or +2, or whatever you wanted). That would be the easiest solution. Then you could blend the parts of each image that you like in PS.
Image blending (http://photography-on-the.net/forum/showthread.php?t=189518)

Blending Modes in Photoshop and Elements (http://www.northlite.net/ps/blend.htm)

Photoshop's Five Essential Layer Blend Modes For Photo Editing (http://www.photoshopessentials.com/photo-editing/layer-blend-modes/)

[Mike-DT6]

Frank, are we on the same subject here? :lol:

I was talking specifically about using the meter reading to indicate the bracketed exposure as a plus or minus value during low light photography. The point being that it's not much help trying to adjust the shutter speed to show a plus or minus value (in stops) if it's being held in the centre by Aperture Priority. :-)

Again, I was talking specifically about low light photography, so the ISO isn't the final variable that gets altered. For low light photography (landscapes and seascapes) I always use ISO100 and f/8, the shutter speed being the only variable. Even if altering the aperture the ISO is only ever going to be 100.

That's also why I don't use automatic exposure bracketing because I'll often alter the bracketing at the last moment, or add extra bracketed shots, so I want total flexibility. This is most useful when the sun is setting and the light is changing considerably by the second.

I already said, as part of my suggestions, that image blending is part of the whole process.

Mike

:-)

[mitch_mick]

Thanks very much Ockie that sounds great also. I just tried it out and it does it all automatically which is very handy. Thanks again.

[mitch_mick]

Thank you for your links PhotosGuy very helpful and much appreciated. To Mike, I see what you mean about AV mode also so I don't think I'll be shooting much long exposure in the mode anymore I like the freedom you were describing in Manual. Funny thing is the book "Digital Photography" by Scott Kelby was recommending this mode hence why I was using it. Thanks again for everyone's input to this. I am definitely learning from all this information. Much appreciated.

Mitch

[PhotosGuy]

The point being that it's not much help trying to adjust the shutter speed to show a plus or minus value (in stops) if it's being held in the centre by Aperture Priority. My point was that that you should get off Av. Not stated is that noise can be reduced by proper exposure which I think was your primary question. Maybe I should have said that. ;)

[Mike-DT6]

Ahh okay, I see your point now! :-D

Mike