#21  
Old 15-03-2010, 04:01 PM
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wasyoungonce (Brendan)
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Attached is an ISO800 Dark, 300s, 450D done 06 Jan this year by me.

I've posted it as a jpg but the raw was equally noise free.

I suggest those pics you posted are very noisy!

I'll try an ISO1600 tonight...I usually don't to that rating.
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  #22  
Old 15-03-2010, 06:53 PM
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Moon (James)
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Also what setting did you have for High ISO speed noise reduction (item 5)

Mine is set to the default : Standard = 0
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Old 16-03-2010, 12:18 AM
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dhein (David)
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Hi all,

Thanks for the feedback. To answer some of the questions -

  • I started off taking 1600 ISO shots of 30, 60, 120 & 240 secs and placed them in the marked folders. However someone suggested that ISO 1600 wasn't the best setting to test noise, so I then took 800 & 400 ISO equivalents of each. Because the film speed was being 1/2'd in each case, I had to double the exposure times to compensate so that the dark frames had the same overall exposure. These make up the other 2 files in each folder.
  • My high speed noise reduction was set to default. However I've previously tried all the settings including "disabled" , which provided minimal difference.
  • Also for reference I do of course have the camera's in built dark frame subtraction routine disabled as this will be handled by DSS.
  • These examples are straight JPG's from camera in fine quality mode. Not RAW converted to JPG. I know RAW is better, but I've already been emailed some dark frame samples in native JPG format from a Canon 40D that's virtually all black bar a few pixels @ around 2 mins. Look at my ISO 1600 2 min shots (or the 800, 400 ISO equivalents) and you'll see heaps of noise.
  • Shooting temp was around 24 degrees c. I shot these indoors with the Aircon set as this temp, no lens, just a cap over the lens opening, and subdued lighting.
I've heard a few comments that the Canon 40D was the last decent camera, before the pixel density on the newer (same size) chips caused these noise issues. That seems to make sense, and seems to be backed up by dark frame samples I've been emailed. However the one niggle is the article link I orginally posted which specifically tests the 500D's dark frame abilty with long exposures up to 5 mins, and shows very cleans results.

Cheers
David
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  #24  
Old 16-03-2010, 11:02 AM
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wasyoungonce (Brendan)
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Here is an enlarged crop of a 5 min ISO1600 dark frame I took last night indoors, lens off, body cap in place.

Maybe I'm not doing it tight but it appears less noisy than yours.

I can zoom in to pixel level and it shows artifacts (noise) but as I said...a lot less than you are showing.

edit:
I didn't resize the image (just made it a small enough jpg to fit the forum
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Old 16-03-2010, 08:19 PM
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Yes, I can see straight away that it's cleaner. I'll study in more detail against my 4min frame when I get back to my main PC.

What Camera is this taken on?

Cheers
David
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  #26  
Old 17-03-2010, 08:32 AM
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wasyoungonce (Brendan)
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Quote:
Originally Posted by dhein View Post
What Camera is this taken on?

Cheers
David

450D..stock std @ around 25 degrees C.
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Old 18-03-2010, 08:16 PM
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500D vs 450D Noise

Here's a side by side comparison. I resized my orginal down to the same size as yours, and then overlayed my image.

Pretty amazing the difference, particularly in that my exposure is even less than yours - and is quite obviously noisier.

I'd love to know how these guys achieved the noiseless 500D dark frames that they show in their review.
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Last edited by dhein; 19-03-2010 at 12:15 AM.
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Old 18-03-2010, 08:27 PM
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dhein (David)
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500D Noise

And this is a 100% scale crop of my 500D dark frame as per previous comparison.

ISO 1600
4 mins
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  #29  
Old 18-03-2010, 08:36 PM
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500D 1600 ISO Noise 30 sec, 1min, 2min, 4min

.. and while I'm on roll (and in Photoshop mode), here's side by side comparisons

500D 100% Crops
30 sec / 1 min / 2 min / 4min
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Last edited by dhein; 18-03-2010 at 08:58 PM.
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  #30  
Old 18-03-2010, 08:57 PM
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dhein (David)
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Post your 500D shots

If anyone else has a 500D and could post their own ISO1600 shots for comparison, that would be the ultimate apples vs apples test.

Are these results typical for a 500D - or does my camera have a chip from a poor quality batch of CCD chips?
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  #31  
Old 18-03-2010, 10:43 PM
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wasyoungonce (Brendan)
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David...this noise doesn't seem right. Something is not right here wit your noise subs.

The canon have always been touted as lower noise compared to most others and I thought the 500D to be a step better than mine yet they appear a step backwards by a quantum.

Have you contacted Gary Honis to compare or Canon?
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  #32  
Old 19-03-2010, 12:14 AM
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Yes, it certinaly doesn't add up. I may very well contact Gary and see if he has any ideas.

Cheers
David
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  #33  
Old 19-03-2010, 12:22 AM
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Octane (Humayun)
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You shouldn't bother with ISO-1600, anyway. Your images will be far too noisey.

A better approach would be to compare ISO-400 to ISO-800 sub-exposures.

H
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  #34  
Old 19-03-2010, 01:04 AM
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dhein (David)
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Yes I did that.

If you refer the link with samples on my orginal post, I ran tests @ 800 & 400 ISO (doubling the shutter speed in each case to provide the same overall exposure). Same noise.

Cheers
David
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  #35  
Old 19-03-2010, 01:22 AM
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Octane (Humayun)
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OK.

Now try taking 19 or so of those ISO-400 dark frames and median combine them.

Don't stretch them or alter them in any way. Take them straight from the camera (ensure that the viewfinder is covered with the viewfinder cover which is attached to the strap when taking them) and median combine them in the astrophotographic processing software of your choice.

Post your resultant master dark frame -- no processing done on it.

H
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  #36  
Old 19-03-2010, 08:31 AM
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For reference I have been using Darks, Flats & Bias in DSS, however I was starting to get artifacts (blue speckles in final image) on longer exposures over 1 min. I traced this back to the the orginal quality of my darks frames, hence my interest in comparing the initial dark frame output quality between difference DSLR's.

Below is example of post processed image (100% crop) from DSS, before processing in Photoshop.

Cheers
David
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  #37  
Old 19-03-2010, 10:42 AM
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Octane (Humayun)
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David,

1. are you taking your dark frames immediately after shooting your light frames?
2. how many dark frames are you typically stacking?

You simply do not need to shoot bias/offset frames. The bias is included in your dark frame. It is automatically subtracted from your lights via the master dark.

Bias frames should only be used when you're using dark frames which weren't taken at the same temperature/after exposing your light frames. I consider DSLR dark frame libraries to be an astrophotographic sin. The consistency is not there, unlike a dedicated cooled CCD. And, even then, people flush their libraries once a month, or once every couple of months.

H
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  #38  
Old 20-03-2010, 11:57 AM
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500D Noise .. yes it can differ between cameras

Well I can now confirm (thanks to Fiona at our DSS imaging group) that my Canon 500D IS much noisier than typical. Last night we compared 4 min ISO 1600 exposures produced by 2 x 500D's .. and the difference in noise was dramatic. I'll post examples later today.

Cheers
David
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  #39  
Old 20-03-2010, 02:19 PM
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I'm still interested to see your results as per the instructions left above.

H
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Old 20-03-2010, 02:50 PM
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500D vs 500D Noise

Hi Humayn,

Thanks for your suggestions & feedback. I typically take 50 lights & 25 subs, and they are always created fresh in the same session over a few hours. My experience has been that initial results shooting at 30 secs worked well, and it it was possible to see the improvement through Deep Sky Stacker of combining lots of data. It's only since I started trying guiding and longer exposures 2min+ that I've had this noise issue using the same methodology that worked before for shorter exposures.

I'm about to post further results from my 500D vd 500D comparison, and this demonstrates my issue .. eg. that even before manipulation I'm handicapped.

Cheers
David
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