Long exposure - DPChallenge Forums

Canon EF 70-200mm f/2.8L IS USM

11/21/2004 11:34:53 PM · #1

Let's assume for a moment that you set your camera on "bulb" left your shutter open and and took multiple exposures over a 3 hour period by shielding the lens from light between exposures.

After looking at the image you get, you realize that all those lessons about noise really did matter, but it is too late to do anything about the exposure. Is there a way to filter out all of the noise and hot pixels?

Thanks

Plexxoid

Canon EOS-30D

11/21/2004 11:39:13 PM · #2

Neat Image can help. Go to neatimage.com
They offer a free version, I use it all the time. It's like taking a step (or two or three) up in quality. You'll be surprised at the difference...

11/21/2004 11:50:19 PM · #3

Originally posted by Plexxoid:

Neat Image can help. Go to neatimage.com
They offer a free version, I use it all the time. It's like taking a step (or two or three) up in quality. You'll be surprised at the difference...

Thanks Plexxoid. I had tried that. I think this was just too far gone. Too bad, I had a great idea for "Time Passing"

Thanks for the note.

Canon EF 24-70mm f/2.8L USM

11/21/2004 11:56:22 PM · #4

Doens't help now, but the best way to do it is to actually take many exposures and keep stacking them. The random noise will cancel out. You can also take an occasional dark frame and subtract it from each image, cancelling much of the fixed-pattern noise. It's a lot of work, but the results can be stunning.

DefyTime

Canon EOS-7D

11/21/2004 11:57:55 PM · #5

You could get meticulous and use the healing tool in PS, if you have that. Magnify the photo and just heal the big spots out as best as possible then use neat image for the rest.

Canon EF 28-135mm f/3.5-5.6 IS USM

11/21/2004 11:59:24 PM · #6

Thanks. It was for a challenge, so it needed to be a single exposure.

downtherabbithole

Canon EOS-30D

11/22/2004 02:18:02 PM · #7

did you do this with a digital camera?

Gordon

RIM BlackBerry Curve

Canon EF 85mm f/1.8 USM

11/22/2004 03:09:33 PM · #8

Another less fiscially prudent option is to buy a Canon 1DII. You can get an hour or so without much noise out of that...

The more common solution is to at the same time, take a 'dark frame' exposure of the same length of time - but with the lens cap on/ covered.

This dark frame will just be a shot of the noise pattern and can be subtracted from the original exposure. Some cameras do this automatically.

It does need to be at roughly the same temperature for the sensor and for the same length of time/ ISO. Aperture doesn't matter. It is best to do this at the same time but it might work later on (could be worth a try if you can roughly recreate the temp conditions)

Once you've got the two frames, you register them in photoshop and subtract one from the other.

Message edited by author 2004-11-22 15:11:48.

11/22/2004 08:13:51 PM · #9

Thanks Gordon. This might be worth a try. I took teh picture in my basement, and that should be pretty stable temperature wise.

Nikon AF-S Nikkor 28-300mm f3.5-5.6G ED VR

11/22/2004 10:21:12 PM · #10

Remember the dark frame is still another "image", so out-of-camera dark-frame subtraction is not allowed, even in advanced editing, since that would be "combining two images" :-P

For cameras that can do dark frame internally, though, it's legal, even for basic editing ):-P

Message edited by author 2004-11-22 22:22:02.

Arcanist

Nikon D810

11/22/2004 10:26:16 PM · #11

I have no idea about a 3 hour time frame. YIKES I would think you would melt the inside of the camera, but I have found the RAW conversion in PScs has a shadow tweak that really does a great job of melting 30-60 second hot spots down to practically nothing. Then you just layer/layer/layer to bring back the full range of the exposure/or up the sharpen/saturation a bit.

Works for long star shots. Not sure about doing a hat trick tho.
...wonder what the effect of packing the camera in ice would do for a cooling system...nah prolly not a good idea.

Message edited by author 2004-11-22 22:28:01.

Canon EF 70-200mm f/4.0L USM

11/22/2004 10:57:29 PM · #12

Originally posted by kirbic:

Thanks Kirkbic. I'm just playing around now, the challenge deadline was last night. But, a multiple exposure challenge with slightly modified rules might be fun.

Arcanist: I don't know about melting, but, there was a battery warning when I was done. ;)

RHoldenSr

Canon EOS-5D

11/22/2004 11:09:50 PM · #13

Gordon

I guess I'm not a photoshop guru :)
What do you mean by "register"?

Originally posted by Gordon:

Once you've got the two frames, you register them in photoshop and subtract one from the other.

Canon 12x IS USM (S3 IS built-in Lens) -- 36-432mm (35mm EQ)

11/22/2004 11:16:52 PM · #14

Originally posted by RHoldenSr:

Gordon

I guess I'm not a photoshop guru :)
What do you mean by "register"?

Originally posted by Gordon:
Once you've got the two frames, you register them in photoshop and subtract one from the other.

He means overlay the images carefully so they are precisely matched up. In prictice, for uncroppped frames, it's dead easy in PS, line up the edges and you're done.

GeneralE

Canon PowerShot S3 IS

11/23/2004 12:07:28 AM · #15

Originally posted by Arcanist:

I...wonder what the effect of packing the camera in ice would do for a cooling system...

Fortunately, BBspot Research Labs has already looked into a similar problem for you, and their extensive network of tech-savvy readers have even contributed their own refinements and improvements.

Actually, true astronomical cameras have extensive cooling systems.

Message edited by author 2004-11-23 00:08:32.

dwoolridge

11/23/2004 01:34:19 AM · #16

Originally posted by kirbic:

He means overlay the images carefully so they are precisely matched up. In prictice, for uncroppped frames, it's dead easy in PS, line up the edges and you're done.

In fact, it's much easier than that (in PS). Just hold shift while dragging one layer to the other window. I don't recall off-hand, but it's probably sufficient to hold shift while releasing the dragged layer to the new window.

GeneralE

Canon PowerShot S3 IS

Canon 12x IS USM (S3 IS built-in Lens) -- 36-432mm (35mm EQ)

11/23/2004 02:36:23 AM · #17

I've heard that for even more fun you can try Registax. There's also another, similar program, but I can't remember what that one's called.

spiffamafied

Nikon D70

11/24/2004 09:13:33 PM · #18

Originally posted by kirbic:

Do you have any examples of cameras that can do this?