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CCDInspector Image Interpretation

Freff

By Freff
in Imaging - Discussion

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Freff

Freff

Posted
Posted

I have recently collimated my MN190 and have since taken a CCDInspector image to help.

Unfortunately, I am unable to interpret the results.

Could someone have a look please and perhaps tell me if I have all in order. Many thanks

post-19789-133877538987_thumb.jpg

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swag72

swag72

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Posted

I watch this thread with interest, as I would love someone to be able to point to a link where the figures and images are explained in nice simple terms. Without that I found using it to be a little hit and miss. Anyone able to explain what figures you want to achieve for a good CCD image?

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dlp

dlp

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I'm no expert, but on the CCD Inspector help file, '3D curvature plot viewer' subject shows the meanings of the colours. In the OP's example it would appear that the central green area is more defocused than the outer blue area. Not sure about the curvature as that's not shown on the image, but it looks pretty flat.

David

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MartinB

MartinB

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There isn't a magical set of figures! Aspect ratio gives you a figure for the roundness of the stars and suggests less than 30% as being reasonable. Occassionally I get a perfect collimation but it is normally a few arc seconds off and is affected by issues such as camera tilt. Usually I am under 10 arc seconds. If I am getting subs with worse results have a good close look at my stars to see if I need to be concerned.

FWHM varies a lot depending on scope and seeing conditions.

The field flatness 3d pics give a very good visual impression. You have good field flatness. There is a gradation from dark blue to red. You are all in the blue and I think you can relax!

One of the most useful features of CCD inspector is the FWHM monitor. This will graphically present FWHM data on the individual subs and they come rolling in (although this may be dependent on your capture software). If your FWHM numbers are getting higher it can indicate a need to refocus. Another handy feature is that it will measure all your subs and rate them using whichever indicator you choose, FWHM normally. This can point you to the subs you might want to think about rejecting.

Over time you will start to learn the figures which indicate good performance from your set up. With my FSQ I expect a completely flat field - all dark blue and flat as a pancake on the 3D view. When I use a reducer with the scope I expect the same and if it isn't I know I probably have a problem with the spacing. With my LX200ACF I know I will get a bit of field curvature when using a 0.63 reducer but experience has told me it just isn't an issue using my QSI 532 camera because the chip isn't that big. However, I know it might be a problem with an APS sized chip. Also with this scope when using a very heavy imaging train (using an active optics system) CCD Inspector shows that I'm getting some sag which varies as the scope tracks and changes from vertical to horizontal. By having a careful look at the images I know when I should be concerned about this.

CCD Inspector is a very powerful tool. You need to keep using it to analyse real imaging runs and learn over time how best to use the information it is giving you.

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Freff

Freff

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Thanks for the replies. This is the original image taken just for collimation. It's a 30sec exposure, nothing special. Unfortunately, my 2" adapter has been sent back to supplier for change so I had to use a 1-1/4 T-adapter. This may account for the centre gradation, vignetting.

post-19789-133877539079_thumb.jpg

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x6gas

x6gas

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Posted
ouch not cheap is it ??

Crikey - no, in fact you could even say it's pricey.

Surely they'd do better with a lower price point. There must be loads of imagers who'd go for this if it was a tad more reasonable but there's just no way I can justify that...

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steppenwolf

steppenwolf

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Surely they'd do better with a lower price point. There must be loads of imagers who'd go for this if it was a tad more reasonable but there's just no way I can justify that...

I felt I couldn't justify it either and then along came my mother-in-law and a generous Christmas present cheque!

The thing is, there is nothing else on the market like it and it is very, very good - why should they 'give away' such a cool product?

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