Beginner Red dots, Blue dots and white crosses on long exposure images

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307
Name
Simon
Edit My Images
Yes
#1
Good morning,
I'm after some advice please. Two weeks ago I purchased a Canon 70D from a reputable camera shop and have noticed on my long exposure images that I have a number Red and Blue dots and a number of very small white crosses when the image is viewed at 100%. The images are taken at f8, ISO100 and anything from 1 - 5 minutes in RAW. Normal speed images seem not to be affected. When viewed at "normal" magnification only the white crosses are visible, as tiny white spots. Is this normal?, should I be worried?, should I return the camera? I haven't, ever, seen anything like this with my Nikon D5300. I purchased the body Mint in box with just under 3000 actuations and it is a fantastic camera apart from this.

Many thanks in advance
Simon
 
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1,703
Name
David
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Yes
#2
Totally normal! During long exposures all sensors will experience 'hot' pixels - that's what you're seeing. You can probably turn on something like 'long image noise reduction' on your camera, where it will take another identically timed exposure (but with the shutter closed) to identify the same, and then 'subtract' those from the original image, but it does mean your 5 min exposure takes 10 min, so I never bother and just fix in post.
 
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6,504
Name
Ned
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#4
As above, totally normal and Canon sensors are typically much worse for this compared to Nikon which is why you might not have seen it before.
 
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3,122
Name
Jan
Edit My Images
No
#5
If you zoom right in on them they should be little squares (and the crosses made up of little squares). There will also be green ones but they may not be as noticable as the red, blue and white ones. I use an old 350D for astrophotography so I see these a lot. 3 options (that I can think of) -
Use the camera's long exposure noise reduction. As David said, this effectively doubles the length of the exposure as once the shutter closes it'll take another identical exposure to 'map' the sensor then subtract it in camera from the original. The 350D will only do this for exposures of more than 30sec so if you forgot to turn it off and took a 'normal' exposure it wouldn't do it, but your camera may be different.
Do it yourself. It's called a dark frame. You put on the lens or body cap and take an exposure at the same temperature and exposure as the original. This is what you do for astro all the time but I see no reason why you can't use it for anything. The advantage of this is that if you took several images in the same conditions and same settings you'd only need to create one dark frame. Disadvantage is you then have to do the subtraction yourself in post. I know you can do it in PS and the like but I've always used astro integration software that does it at the click of a button.
Depending on how often you're seeing this, just clone them out. The more you zoom in the more you'll see so have a think about how the image is going to be used and set a level accordingly.
 
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