sharkmelley

9 minutes ago, lalou said:

I don't raw convert my images before stacking and I just put the raw files directly into DSS. Should I raw convert them first?

No, don't raw convert them first.  But white balancing should be one of the first operations you do after stacking - while the data are still linear.

Those histograms do not look like the histograms of linear data.  White balancing cannot be performed on non-linear data.  It raises the question about what kind of workflow you are following.  For instance, are you raw-converting your images before stacking or do you put your raw files directly into DSS?

Very nicely done!

If you choose ISO 1600 then shorter exposures will be sufficient to achieve your chosen 5*read_noise criterion.  

On 22/02/2024 at 18:12, MalcolmP said:

Questions :-
(1) How can I measure my read noise? *
(2) Given a lp level **(of eg. 20mag/sqarcsec) how long does my sub exposure need to be for my rn to be 5x *** lower than the lp

 

Your Canon 60D read noise at ISO 800 is approx 3e:

https://www.photonstophotos.net/Charts/RN_e.htm#Canon%20EOS%2060D_14

If you want the light pollution noise to be 5x higher then you want it to be 15e.  That means you need to collect 225 (i.e. 15^2) electrons.

http://tools.sharpcap.co.uk/ will allow you to approximate your sky background rate (e/sec) which will depend on the f-ratio of your lens/scope.  You can then work out how long your exposures need to be to achieve 225e.

That's a stunning result that puts those popular Winter targets in their context.

You will capture the same amount of light with both approaches.  But the stack of 1000 subs will have 1000 contributions of read noise whereas the stack of 80 subs will have only 80 contributions of read noise.  Almost certainly the stack of 1000 subs will be noisier therefore making it a bit more difficult to detect fainter objects.

8 hours ago, Bugdozer said:

My main suspect here would be light entering the viewfinder window. 

Why would light leaking through the viewfinder be purple?

What happens if you take a long-exposure dark frame - first with the lens on and secondly with the lens removed.

To help diagnosis, you need to calculate the additional length to the light path caused by the reflected rays.  The CCDWare dust donut calculator will do this for you:

http://76.12.87.114/resources/dust.cfm 

The Nikon D5300 is a special case.  It's best to keep ISO really low e.g. ISO 100 or 200 in order to keep the peak of the back-of-camera histogram well over to the left and avoid those annoying coloured concentric rings in the background, caused by Nikon's badly implemented lossy compression.

Mark

I was a bit confused by your expression:

corrected dark:=dark * factor - mean_dark * (1-factor) 

Now I've worked it out

It looks like the scope is VERY out-of-focus.

I'm a bit confused by the expression:

 corrected dark:=dark * factor -  mean_dark * (1-factor) 

Normally the scaling factor is applied to the (bias-subtracted) master dark before it's used to calibrate the light.

On 11/08/2023 at 20:57, han59 said:

I did an other test with scaling the darks. This only works for dark above 0 degrees Celsius when the dark current is significant.  The factor 4.34 comes from 17.8 e-/4.1 e- (noise 26°C/noise 11°C)

The factor of 4.34 is the wrong factor to use because it is calculated from the ratio of noise.  Generally speaking accumulated dark current in an exposure will double for each 5C-7C increase in temperature, so the thermal noise increases by the square root of this.   The factor used for dark scaling is usually calculated using max entropy or calculated from the relative brightnesses of the "warmer" pixels.  Alternatively use "trial and error" to determine the factor that minimises the noise in the final image.

11 hours ago, 900SL said:

In three years of both wide field and DSO imaging with Nikon D5600 and D610 I've yet to see any of the artifacts or issues you allude to in your webpage.

That's great!  If you're not already seeing those artifacts then definitely don't go looking for them.

1 hour ago, lguise said:

Thank you for your article, exactly the information I need. Is there a favourite from the Canon mirrorless range? Not the R6 it would seem. 

I don't know whether or not there is a favourite Canon mirrorless. Choice depends on your budget and what other features interest you.

Mark

Double-posted

Canon mirrorless cameras are a good choice but avoid the Canon EOS R6 which has amp glow issues and cannot do long exposures with the electronic shutter.

I don't recommend Sony, Nikon and Fujifilm mirrorless cameras because of various artefacts caused by the in-camera raw-data processing which I've summarised here:

https://www.markshelley.co.uk/Astronomy/camera_summary.html

Mark

3 minutes ago, Anthonyexmouth said:

Thanks, Any idea on odd LR vs PS issue? 

Sorry - I don't use LightRoom.

On 14/03/2023 at 11:12, Anthonyexmouth said:

New to the printing of my images and wondering if I should be saving as 16bit or 32bit Tiff. When I save as 32bit the image is super over exposed when I open in lightroom or PS but 16bit looks similar to the image in Pixinsight. Any hints on how I should be doing it?

32-bit data is always treated by Photoshop as linear and will be displayed with a linear profile.  It therefore displays differently to equivalent 16-bit data unless the 16-bit data has an embedded linear ICC profile.  In general, if you want your image to look the same in Photoshop as it does in PixInsight  then do not export it from PixInsight in 32-bit format.

Mark

That all makes complete sense!

3 hours ago, Richard_ said:

I wonder if the Red filter is first in sequence, and perhaps I don't give enough time to settle after a dither, so the camera starts exposing before guiding is restored and settled? This may explain the moving artifacts in mostly Red channel. 

That certainly sounds like a plausible explanation.

The star blips are almost certainly caused by some subs that have "doubled stars" because of wind gusts or periodic error.  Blink through your raw subs and you are likely to find the offending ones.  Remove those faulty subs from your workflow.

Blinking your subs should be a standard part of your processing because it catches a whole range of issues.

Mark

The halos are caused by the filter.  For a small percentage of the light rays, a double internal reflection takes place within the filter glass and then the rays continue onwards to the sensor where they arrive out of focus because of the extra distance travelled.  The diameter of the halo is therefore proportional to the thickness of the glass and the (inverse) focal ratio of the optics.