Strange Speckles on long exposure shots

10/25/2004 09:47:14 PM · #1

When I take a long exposure shots with my DRebel and then upload to my computer they appear to have blue and red dots all over them in various places. You can only see them when the image is at high resolution. Im not sure if this is a problem with my monitor, my camera sensor or something I am doing wrong while taking the picture. I have posted the picture here (warning the file is large I tried saving at lower resolution but you cant see it). My questions are as follows:

1.) Can you see the red and blue dots on your monitor?
2.) If you can see it does anyone know whats causing it?

Thank you for any help in advance

Sample Pic Here

Message edited by author 2004-10-25 22:21:19.

mrorange002

Canon EF 16-35mm f/2.8L USM

10/25/2004 09:50:34 PM · #2

thats noise.
it happens at longer exposures
quick read about noise

google it for more info

Message edited by author 2004-10-25 21:51:58.

10/25/2004 10:03:11 PM · #3

Thanks for the link.
In that article it says that the noise should be much lower in new cameras. Is noise of this magnitude common even in DSLR's or is there something wrong with my camera. Also has anyone with a DRebel also seen noise of this magnitude. For the photo posted I had the shutter open for about 15 sec and got that much noise. I was hoping to get a remote for my camera to do longer shots to capture the star rotation effect. If noise like this is common how do people take photos like that with digital cameras. Am I doing something wrong or do I need a better camera for that?

mrorange002

Canon EF 16-35mm f/2.8L USM

10/25/2004 10:11:25 PM · #4

I can't open the link you provided to the sample image

moswyn

Canon EOS-7D

Sigma 18-50mm f/2.8 EX DC for Canon

10/25/2004 10:19:34 PM · #5

That doesn't look like noise to me. This might be silly, but is it stars?
And although I don't think this is it: My fuji finepix has a pixel screwed up so every picture has a little white dot in the same place. However, it looks nothing like your red and blue dots.

Canon RF 24-70mm f/2.8 L IS

10/25/2004 10:25:08 PM · #6

Originally posted by moswyn:

I thought stars at first glance too but it happens when I do long exposure indoors and in the day time too.

Also I posted The image in the forum incase others have trouble with the link. I hope its not to big.

kirbic

Canon EOS R5

10/25/2004 10:27:56 PM · #7

What it is is "hot pixels." All cameras will show these, and the longer the exposure, the more severe they will be. They can be just about perfectly cancelled out by subtracting a "dark frame". Some cams can do this automatically (e.g. my ol' trusty Nikon 995) but, strangely, most if not all DSLRs seem to lack this feature.
If you Google "dark frame subtraction" you'll find some interesting reading.

Edit for typos

Message edited by author 2004-10-25 22:42:54.

cloudsme

Canon EOS R5

Canon RF 100-500mm f/4.5-7.1 L IS USM

10/25/2004 10:32:12 PM · #8

It doesn't look like noise to me either. What iso are you using? Are the speckles on the same site in different shots? I mean, if you overlap different pictures, do the speckles overlap? By the way, I am a neighbor. We don't have many clear nights in Binghamton for astrophotography. I've found film to be better than digital for long exposure astrophotos. Digital is ok for lunar or planetary.

mrorange002

Canon EF 16-35mm f/2.8L USM

10/25/2004 10:42:17 PM · #9

that is long exposure noise. Look in your manual and see if there is a custom setting that says something like "Long exposure NR
set your Long Exposure NR to "on"

Google this term "long exposure digital noise"

night spots

Message edited by author 2004-10-25 22:44:17.

Canon EF-S 18-55mm f/3.5-5.6

10/25/2004 10:43:13 PM · #10

Originally posted by cloudsme:

I shot these using ISO100 and after looking through some other images the dots do seems to follow some what of a pattern. Also its good to see there are other people from the Binghamton area on this site.

Thank you everyone for your input this has been something that has been bothering me for a while.

bledford

Canon EOS-300D Rebel

10/25/2004 11:26:03 PM · #11

I have the same situation with Digital Rebel on shots over 2 secs long. I was going to send it in but it's such an easy fix in Photoshop I thought, what the heck, I'll clone em out.

Natator

Canon EF 24-105mm f/4.0L IS

10/26/2004 06:59:29 AM · #12

Originally posted by kirbic:

Some cams can do this automatically (e.g. my ol' trusty Nikon 995) but, strangely, most if not all DSLRs seem to lack this feature.

That feature is on the 20D, but was not found on the 10D. I haven't used it yet so have no idea how effective it is.

dacrazyrn

Nikon D300

Nikon AF-S DX NIKKOR 18-200mm f/3.5-5.6G ED VR II

10/26/2004 07:25:16 AM · #13

kirbic is on it. Hot pixels...and it is basically noise. My Nikon 5700 loved to do this, even with noise reduction. Found a program that remapped the sensor and it all went away (a do it at your own risk thing).
I have read that the camera companies will do this for you also (Nikon will anyway)

PhilipDyer

Canon EOS-5D Mark II

Canon EF 24-105mm f/4.0L IS

10/26/2004 08:02:00 AM · #14

I have the same camera and I don't have any spots like that on long exposures. Those are definitely hot pixels and they should be repaired either by Canon or with a program like the one dacrazyrn mentions.