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testing sensor on new DSLR camera

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#1 Nicole Sharp

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Posted 17 August 2019 - 04:52 PM

I have a brand-new DSLR camera (the Canon Rebel SL2/200D) but I have never used a DSLR camera before.  Here is the very first photo I have taken with the new camera:

 

https://www.nicolesh...on/IMG_0001.JPG

 

The photo was taken at ISO 100 in manual bulb mode by holding the shutter button down for 2 minutes.  No lens was attached.  I am indoors with air conditioning running so is a normal room temperature.  If you zoom in to 100% magnification though, you can see a number of hot pixels.

 

What I would like to know is whether this is normal sensor performance for this camera, or should I be worried?  I have 57 days left to return the camera if I need to.

 

I am going to attempt a second identical exposure next to see if the hot pixels are random or in the same spots.  Any other suggestions on how to test the DSLR camera sensor while the return policy is still active would be appreciated.

 

If anyone else has a DSLR camera to make similar images (no lens, 2-minute exposure, ISO 100) so I have something to compare to, that might be helpful.


Edited by Nicole Sharp, 17 August 2019 - 04:57 PM.


#2 Nicole Sharp

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Posted 17 August 2019 - 05:14 PM

Here is the second exposure with the same settings (no lens, 2 minutes manual bulb, ISO 100):

 

https://www.nicolesh...on/IMG_0002.JPG

 

It looks like at least two of the hot pixels are in about the same place.  Does that mean the sensor is defective?  I saved some money by getting the older SL2 instead of the newer SL3, but that could mean it has been sitting in a warehouse for 2 years.  If it's defective though, might be better to send to Canon for repairs under warranty instead of returning or exchanging it?  I could still get a webcam instead, but I think a DSLR camera is going to be a better fit for me, especially since I don't have a laptop.



#3 descott12

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Posted 17 August 2019 - 05:32 PM

Hot pixels are expected in all sensors. A master dark frame is used to calibrate them out. There is no such thing as a perfect sensor so yours is probably fine.


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#4 sg6

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Posted 17 August 2019 - 05:38 PM

Hot pixels and dead pixels are to be expected. They just cannot make a sensor of however many megapixels it has where all of them are perfect.

 

Looking though your image I could really only see about 4, which I suspect is very good. One is more like a very small blue galaxy on my screen. Not sure how that has happened.

 

You take a series of darks and throw those into the mix with DSS and it should take care of them. I have seen instances of a lot worse then you appear to have.

 

Sounds like you need an intervalometer to take a series exposures.



#5 Nicole Sharp

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Posted 17 August 2019 - 05:39 PM

Hot pixels are expected in all sensors. A master dark frame is used to calibrate them out. There is no such thing as a perfect sensor so yours is probably fine.

 

What would cause the hot pixels to be in approximately the same place between two identical exposures without any lens attached?  I thought that hot pixels would be random and proportional to temperature?



#6 descott12

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Posted 17 August 2019 - 05:41 PM

Hot/dead pixels are actually faulty pixels. Therefore they don't move. This is perfectly normal.


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#7 ccs_hello

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Posted 17 August 2019 - 05:52 PM

Hot means thermal, which will be random, most of the time.

Stuck means dead or almost dead, can be stuck open (at a very high value) or stuck close (very low.)

Some stuck will not happen when sensor is fairly cold.  <-- marginally dead

Some stuck are always/permanently stuck.



#8 Nicole Sharp

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Posted 17 August 2019 - 05:58 PM

Third try (2 minutes, ISO 100):

 

https://www.nicolesh...on/IMG_0003.JPG

 

Still looks about the same.  So I am thinking they are dead pixels instead of hot pixels maybe.  But that's still normal?  It's brand-new and very expensive.  I sent an email to Canon about it to see if maybe they can do anything.



#9 descott12

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Posted 17 August 2019 - 05:58 PM

Ah I guess, I was using the wrong terminology for "hot"

But both are to be expected. No??


Edited by descott12, 17 August 2019 - 05:59 PM.

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#10 Nicole Sharp

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Posted 17 August 2019 - 06:01 PM

Yikes!!!  But can anyone please explain this image???

 

https://www.nicolesh...on/IMG_0004.JPG

 

That is a 2-minute exposure at ISO 25600.

 

What is all the red and blue stuff???



#11 Jim Waters

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Posted 17 August 2019 - 06:14 PM

All your images are normal for a DSLR.  Both ISO 100 and 25600.  Your camera is GOOD.



#12 Jim Waters

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Posted 17 August 2019 - 06:15 PM

Yikes!!!  But can anyone please explain this image???

 

https://www.nicolesh...on/IMG_0004.JPG

 

That is a 2-minute exposure at ISO 25600.

 

What is all the red and blue stuff???

Its because you increased the ISO and of the long exposure time.  



#13 Nicole Sharp

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Posted 17 August 2019 - 06:16 PM

It looks like what I am seeing at ISO 100 are actually stuck pixels and not dead pixels.  I wouldn't be able to see dead pixels on a black background.

 

https://www.photogra...-vs-hot-pixels/

 

That article suggests that if there are more than 5 stuck pixels in a brand-new camera, then it should be returned?


Edited by Nicole Sharp, 17 August 2019 - 06:19 PM.


#14 Nicole Sharp

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Posted 17 August 2019 - 06:18 PM

Its because you increased the ISO and of the long exposure time.  

Why is it monochrome red and blue?  I know increasing ISO so high would introduce a lot of noise.  But why the monochrome red and blue pixels like that?  Why not gray or white or just random colors?



#15 Nicole Sharp

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Posted 17 August 2019 - 06:20 PM

What would be a typical maximum acceptable exposure time and/or ISO setting for long-exposure imaging on a Celestron Advanced VX or Orion Sirius (Sky-Watcher HEQ5) mount?


Edited by Nicole Sharp, 17 August 2019 - 06:25 PM.


#16 Jim Waters

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Posted 17 August 2019 - 06:20 PM

Some literature to look into 

 

http://www.astropix....agda/index.html

https://www.amazon.c...y/dp/0972973761

http://dslr-astrophotography.com/



#17 Jim Waters

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Posted 17 August 2019 - 06:27 PM

What would be a maximum acceptable exposure time and/or ISO setting for long-exposure imaging on an Orion Sirius (Sky-Watcher HEQ5) mount?

Start with ISO 400 or 800 first. You want to expose until the histogram is about 20%.  Depending on several factors (ISO, f/Stop, LP...) the exposure time can be a few seconds to many minutes.

 

http://dslr-astropho...-canon-cameras/


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#18 Nicole Sharp

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Posted 17 August 2019 - 06:40 PM

Here is 2 minutes at ISO 400:

 

https://www.nicolesh...on/IMG_0005.JPG

 

It looks like ISO 400 has both stuck pixels and hot pixels.  I know the hot pixels are normal based on the ISO.  The question then I guess is whether I should try to return, exchange, or repair the new camera based on the number of stuck pixels present.  I'll have to wait to hear what Canon has to say probably.  Another forum post I saw mentioned that the warranty may specify a certain number of allowable stuck pixels before the camera sensor is considered defective or not.  Not sure what that number would be for Canon.

 

But you think the ISO 100 photos are good for a brand-new DSLR camera?


Edited by Nicole Sharp, 17 August 2019 - 06:44 PM.


#19 Jim Waters

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Posted 17 August 2019 - 06:57 PM

Any noise in the above image can be mitigated with DARK Frames.  Its necessary to take many DARK Frames to average out the noise. You should see a steady increase in image noise as you increase ISO and/or exposure time.

 

If you can post the Canon CR2 image so I can take a better look at it.



#20 Nicole Sharp

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Posted 17 August 2019 - 07:12 PM

Any noise in the above image can be mitigated with DARK Frames.  Its necessary to take many DARK Frames to average out the noise. You should see a steady increase in image noise as you increase ISO and/or exposure time.

 

If you can post the Canon CR2 image so I can take a better look at it.

 

These are each 2-minute exposures at ISO 100:

 

https://www.nicolesh...on/IMG_0001.JPG

 

https://www.nicolesh...on/IMG_0002.JPG

 

https://www.nicolesh...on/IMG_0003.JPG

 

It is difficult to scan the entire image, so what I did is open in the web browser (on a desktop monitor), then click once to zoom to 100% magnification (centered), then hit the left arrow on my keyboard to go to the center-left part of the image.  In each photo, you will see a blue pixel and an orange/brown pixel.  However, the two pixels seem to move between photos.  They appear to be in the same position for the first and third photos, but offset in the second photo.  This is a brand-new camera, so these are the first three images ever recorded by the sensor.  I have not attached the lens yet, so the sensor has never been exposed to atmosphere except at the factory cleanroom.  The camera does an automatic sensor cleaning every time it is turned off, so there were sensor cleanings between the second and third photos.

 

I actually don't see any other rogue pixels in the first and second photos (I thought there was at least one more in the first), and I only see one other in the third photo (so that third pixel might be a hot pixel and not a stuck pixel).

 

So maybe there are only two stuck pixels then.  Not sure if the Canon warranty would cover two stuck pixels or if that should be "acceptable" performance for a new sensor.  But it's difficult to scan the whole 6000*4000 image on a 1920*1080 screen.  A failure rate of 0.00001% isn't terrible I guess :-P .


Edited by Nicole Sharp, 17 August 2019 - 07:25 PM.


#21 Jim Waters

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Posted 17 August 2019 - 07:37 PM

Why is it monochrome red and blue?  I know increasing ISO so high would introduce a lot of noise.  But why the monochrome red and blue pixels like that?  Why not gray or white or just random colors?

Because DSLR's / OSC's have a Bayer Filter in from of the CMOS sensor - RGGB

https://www.cambridg...era-sensors.htm



#22 Jim Waters

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Posted 17 August 2019 - 07:44 PM

These are each 2-minute exposures at ISO 100:

 

https://www.nicolesh...on/IMG_0001.JPG

 

https://www.nicolesh...on/IMG_0002.JPG

 

https://www.nicolesh...on/IMG_0003.JPG

 

It is difficult to scan the entire image, so what I did is open in the web browser (on a desktop monitor), then click once to zoom to 100% magnification (centered), then hit the left arrow on my keyboard to go to the center-left part of the image.  In each photo, you will see a blue pixel and an orange/brown pixel.  However, the two pixels seem to move between photos.  They appear to be in the same position for the first and third photos, but offset in the second photo.  This is a brand-new camera, so these are the first three images ever recorded by the sensor.  I have not attached the lens yet, so the sensor has never been exposed to atmosphere except at the factory cleanroom.  The camera does an automatic sensor cleaning every time it is turned off, so there were sensor cleanings between the second and third photos.

 

I actually don't see any other rogue pixels in the first and second photos (I thought there was at least one more in the first), and I only see one other in the third photo (so that third pixel might be a hot pixel and not a stuck pixel).

 

So maybe there are only two stuck pixels then.  Not sure if the Canon warranty would cover two stuck pixels or if that should be "acceptable" performance for a new sensor.  But it's difficult to scan the whole 6000*4000 image on a 1920*1080 screen.  A failure rate of 0.00001% isn't terrible I guess :-P .

ALL DSLR and OSC camera's have electronic and heat related noise.  Depending on the electronics / sensor some have much less that others.  These images are good.  Your camera is good.


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#23 RedLionNJ

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Posted 18 August 2019 - 10:46 AM

Am I missing something here?

 

You bought a cheap, consumer DSLR.  Yet you expect a scientific-grade sensor in it?  Sometimes you really do get what you pay for.

 

In case you're under any other misapprehensions - don't expect tack-sharp stars from edge to edge at the fastest f-ratio the kit lens can provide, either.



#24 Jim Waters

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Posted 18 August 2019 - 11:06 AM

In case you're under any other misapprehensions - don't expect tack-sharp stars from edge to edge at the fastest f-ratio the kit lens can provide, eitherYes - the

Yes - the kit lens is poor.  Do not shoot wide open.



#25 Nicole Sharp

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Posted 18 August 2019 - 11:33 AM

Am I missing something here?

 

You bought a cheap, consumer DSLR.  Yet you expect a scientific-grade sensor in it?  Sometimes you really do get what you pay for.

 

In case you're under any other misapprehensions - don't expect tack-sharp stars from edge to edge at the fastest f-ratio the kit lens can provide, either.

 

I have never used a DSLR camera or any other type of interchangeable-lens camera before, so I do not know what is normal performance or abnormal performance for a DSLR camera.  My only concern is whether the camera is performing normally or whether it could be defective.  I understand that it is not the best astrocamera in the world.  But 2 stuck pixels out of 24 million is not terrible.  The feedback so far seems to indicate that the camera is performing normally and is not defective.

 

I heard back from Canon, and they told me for single-shot long exposures in JPG, to use automatic noise correction.  I forgot about that feature, though now I remember reading about it last year.  The reason I did not get a Sony camera is specifically because their entry-level interchangeable-lens cameras do not offer an option to turn off automatic noise correction, so even in RAW shooting, they delete stars (the infamous "star-eating" bug).  But it is better to correct noise afterward in postprocessing instead.  Unlike Sony, Canon cameras have the option to turn automatic noise correction on and off.  So I need to try it again with noise correction turned on, and see if the stuck pixels or hot pixels are still there.

 

I got the kit zoom lens specifically just for Terrestrial videography.  I would want to get a prime lens for astrophotography.  But I do not own a tracking mount, so for the time being I only plan to use the DSLR camera for short-exposure Solar, Lunar, and planetary imaging.


Edited by Nicole Sharp, 18 August 2019 - 11:46 AM.



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