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Hi

I was reading another thread about darks and it made me think about this question. I've no idea what is normal or what is acceptable.

Anyway, here are a couple of my master darks - 600s and 900s. I'm not sure if there's anything between them. They were created as tifs by dss and I've save them as jpegs to post:

600s:

post-33532-0-63545500-1407717080_thumb.j

900s:

post-33532-0-04355900-1407717092_thumb.j

I'd be grateful for any feedback/opinions - good or bad!

Thanks!

Louise

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Well, unless there's something wrong with the rendition you've posted you have a near- perfect chip. I don't see any hots. This may be a result of the size of the image presented, though.

If you want a fright, have a look at this dark from my full frame Kodak 11 meg chip. This has been given one good log stretch to show what would find its way into the final image without calibration. In fact I always stretch my images more than this so what you see here is an understatement!

demo%20dark%20stretched-XL.jpg

This is a particularly clean 11 meg chip, by the way. But who cares? It doesn't get into the final image.

Olly

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Here's a stretched master dark frame from my KAF8300 based camera, as you can see it's a touch snowy..  but that's OK,   it doesn't really matter if you have just one hot pixel or hundreds, you should be running some kind of hot pixel mitigation, either a hot pixel repair algorithm on each sub prior to stacking or a statistical stack or both.

snowstorm.jpg

post-8988-0-27047000-1407746322_thumb.jp

Edited by rfdesigner
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If you feel that you are getting too many hot/dead or stuck on pixels with some canon DSLRs you can remap the sensor to improve things.

1) Remove the lens and place the cap on the camera
2) In the menu functions find the Sensor Cleaning menu
3) Select "Clean Manually"
4) Let it sit for 30 seconds and then switch the camera off
5) When you power back on all pixels should be remapped

It works because manual clean "disengages" the sensor to prevent static damage.
 

Alan
 

Edited by Alien 13
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It is very difficult to say from your posted images how 'noisy' your chip is but a quick (and savage!) stretch in PS3 shows some actual hot pixels. No one likes hot pixels but these are not excessive and could be removed using a hot pixel map. I am assuming that these images are from your QHY8L ?

Stretched version of 900secs:-

post-1029-0-23386800-1407748427_thumb.pn

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Hi Guys

Thanks for all your responses! Yes, these are darks from my qhy8l that I'm referring to :). It seems hard to upload an image of a dark that actually shows the hot pixels! I can't really see any too well on the other darks uploaded but thanks Olly and rfdesigner. I've cut a section (about 1200 x 1000) from one slightly stretched 900s dark and put it on Flickr: https://www.flickr.com/photos/108862926@N05/14698800820/in/photostream/lightbox/

It's still not that easy to see them! I'm probably fussing over nothing really but when I don't know for sure, and when I've not properly seen what is 'normal' in another person's camera, I suppose I get a bit insecure!

I've noticed that if I aggressively stretch a dark it can show gradients up - indeed, one particular 900s dark I've been using actually showed a fair bit of light leakage from when I took it  :eek:. I've deleted that one now... I try to cover everything when taking darks to prevent any stray light getting in but I'm fallible!

I sometimes get hot pixels showing through in calibrated images and they play havoc when it comes to gradient removal. DSS is supposed to remove (hide?) hot pixels and it generally seems to do a good job but it seems that sometimes a few can still get through. In that case, are there any utilities out there that might do a better job or will I have to remove them manually?

Alan - thanks for the tip re dslr pixel remapping  :police:  As I plan to still use one that might come in handy and I've added your info to my 'useful' document :grin:.

Cheers

Louise

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If you feel that you are getting too many hot/dead or stuck on pixels with some canon DSLRs you can remap the sensor to improve things.

1) Remove the lens and place the cap on the camera

2) In the menu functions find the Sensor Cleaning menu

3) Select "Clean Manually"

4) Let it sit for 30 seconds and then switch the camera off

5) When you power back on all pixels should be remapped

It works because manual clean "disengages" the sensor to prevent static damage.

Alan

Does this really work? What make and model of DSLR? I tried it with my Canon 450D but I did not have the option of "Clean Manually" My Canon seems to have more hot pixels than not.

Ian

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It does work on my 650D i think the camera needs to have a built in ultrasonic sensor clean, the manual clean option moves the  mirror up then opens the shutter and disables the chip so that it can be cleaned without being effected by static it sits in this mode till the camera is switched off i dont know if there is an alternative method that does the same for other models.

Alan

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