Author Topic: Is this a gradient?  (Read 4468 times)

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RobertM

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Re: Is this a gradient?
« Reply #30 on: Nov 18, 2013, 14:25:39 »
It's already a very useful tool !  The only issue I have is that my copy doesn't release memory so dies after about 40 or so images.  Yes the are things that can be done to make it simpler but it already does a really good job.

Robert

Ivor

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Re: Is this a gradient?
« Reply #31 on: Nov 18, 2013, 22:38:00 »
A weekend away delayed the new flat capture so here it is with the resulted RGB channels merged in PS and slightly darken. A slight gradient remains bottom left to upper right, nothing significant though.






The new flat has clearly has made a big improvement in the resulting data, so I'll do the CCDinspector test tomorrow as the weather is promising.

Is CCDinspector straightforward to use? the free version only has 30 days so I want to know if I need to research its use.

Secondary issue why does the image have no colour, but that's should really be a different thread.


Ivor

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Re: Is this a gradient?
« Reply #32 on: Nov 20, 2013, 12:30:12 »
I ran CCDInspector three times last night setting the FF with a .5mm adjustment either side of the calculated 70.5mm. I think I might of made a mistake in my workflow as I didn't refocus after each adjustment but I'm not sure it's particularly relevant based on the results.

FF set to 70mm



FF set to 70.5mm




FF set to 71mm




So 70.5mm appears to be a good position, but are the stats good and is there anything I can do to improve them?

Rocket Pooch

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Re: Is this a gradient?
« Reply #33 on: Nov 20, 2013, 15:30:19 »
Is the focuser not square to the focal plane?

Ivor

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Re: Is this a gradient?
« Reply #34 on: Nov 20, 2013, 16:51:31 »
It appears to be, there's no flex in the system either. What makes you think there is?

MarkS

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Re: Is this a gradient?
« Reply #35 on: Nov 20, 2013, 17:28:43 »
There's a diagonal gradient in CCDInspector.
If the CCD were orthogonal it should be a circularly symmetric gradient.

RobertM

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Re: Is this a gradient?
« Reply #36 on: Nov 20, 2013, 18:43:57 »
As I mentioned before.  The stars didn't look bad so it was never going to be the reducer spacing causing the vignetting.

If the focuser isn't square then taking flats with it a various positions should show vignetting getting better or worse.  If that isn't the cause then is the corrector/camera fixed in squarely ?  The last thing is lens cell collimation but I hope it doesn't come to that.

Robert

Ivor

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Re: Is this a gradient?
« Reply #37 on: Nov 20, 2013, 21:05:54 »
It's first time I've used CCDInspector so I'm not sure what to expect or deduce. Looking at the 70.5mm curvature map I see a red circle at NNE being bisected by the inner circle, looking at 71mm the red circle is SES and touching the edge of the frame. Based on the help with CCDInspector the colour mapping is as follows:

Black:    lowest FWHM
Blue:     slightly defocused
Green:   more defocused
Red:      highest defocus

As I'd expect the centre of the image to be the most focused I'm now at a loss at what to read into this.

What are acceptable values? Assuming my flats and subs will be better with FF at the correct setting how much will this matter?

MarkS

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Re: Is this a gradient?
« Reply #38 on: Nov 20, 2013, 23:56:18 »
Quote from: Ivor
What are acceptable values?

If you find out then plese let me know, since I've never been able to work what they mean!

Mark