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Old 15-11-2020, 10:32 PM
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DavidTrap (David)
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I think I'm going to like this camera

First light with my QHY600M over the weekend.

Just a bit of testing really - much to learn about optimal settings with the camera.

10 x 300 sec subframes of B33

AP130 with Quad TCC reducer

Chroma 3nm Ha filter.

Minimal processing in Pixinsight - haven't had time since coming home from Leyburn.

There's a bit of tilt - haven't worked out how to use the tilt corrector yet

Link to Astrobin

Thanks for looking.

DT
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Old 15-11-2020, 11:08 PM
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That looks terrific especially for only .8 hours.

That looks to me more like a spacing issue with the TCC rather than tilt as all 4 corners seem affected. The TCC is fairly intolerant and needs +/- 1mm correct spacing. There is a note by Roland about how to check the spacing if its under or overcorrecting. Focus in the middle and note the focus position then focus on a corner star and note if you had to rack the focuser in or out.

Greg.
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Old 16-11-2020, 08:40 AM
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multiweb (Marc)
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That's a massive fov with good image scale. Good fun ahead for sure.
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Old 16-11-2020, 08:09 PM
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A great start.

I've found the QHY600 is incredibly terse in highlighting focal plane tilt or off axis aberrations....hence have numerous adapters being made to tie things down a much as possible.

That said, once sorted, I can see this camera being responsible for some benchmark imagery in the future.
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Old 16-11-2020, 09:34 PM
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DavidTrap (David)
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Thanks Gents,

Greg - the back focus specs of the TCC are +/- 2.5mm. I’m within 0.5mm of the recommended figure, depending where the tilt corrector is within its range of movement. Analysis of tilt in ASTAP shows a definite skew towards the top right corner - it’s definitely visible at full resolution. I’ll be disappointed if it doesn’t resolve with adjustment of the tilt corrector.

Mark - I’m loving the massive FOV. I always envied the amazing wide field shots taken with big sensors on modest focal length refractors.

Peter - I’ve made up an alignment collar, on the 3D printer, to try to overcome the lateral movement of the dovetail interface to the QHY filter wheel. I’m hoping that will afford a degree of reproducibility in alignment for this itinerant imager. It’s definitely not going to be a point and shoot camera.

DT
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Old 16-11-2020, 09:51 PM
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Congrats on the new gear! That bodes very, very well.


It'd be interesting to see how close you can get to describing one unit of detail per pixel with your gear under ideal circumstances (seeing etc.).


Clear skies!
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Old 17-11-2020, 09:23 AM
Placidus (Mike and Trish)
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Very fine. Those cometary knots toward the top of the image are excellent. Much promise.
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Old 17-11-2020, 12:26 PM
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Well done. Let the full frame journey begin
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Old 17-11-2020, 06:53 PM
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Greg - the back focus specs of the TCC are +/- 2.5mm. I’m within 0.5mm of the recommended figure, depending where the tilt corrector is within its range of movement. Analysis of tilt in ASTAP shows a definite skew towards the top right corner - it’s definitely visible at full resolution. I’ll be disappointed if it doesn’t resolve with adjustment of the tilt corrector.



DT[/QUOTE]

The +/- 2.5mm is for the flattener. The TCC is +/- 1mm.

https://www.astro-physics.com/quadtcc-ap130

https://www.astro-physics.com/13035ff

You most likely have both issues to some degree. Roland has an article (I'd have to look for it on their site) about spacing for the correctors. But the intro is interesting as basically he says that there can be minor variations between scope's lenses. So with +/- 1mm as a tolerance there is a chance a particular scope may need a slightly different spacing. Something to know if things are not round after correcting for tilt. You could make some spacers with your 3D printer.

Greg.
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Old 17-11-2020, 10:16 PM
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Quote:
Originally Posted by gregbradley View Post
Greg - the back focus specs of the TCC are +/- 2.5mm. I’m within 0.5mm of the recommended figure, depending where the tilt corrector is within its range of movement. Analysis of tilt in ASTAP shows a definite skew towards the top right corner - it’s definitely visible at full resolution. I’ll be disappointed if it doesn’t resolve with adjustment of the tilt corrector.



DT
The +/- 2.5mm is for the flattener. The TCC is +/- 1mm.

https://www.astro-physics.com/quadtcc-ap130

https://www.astro-physics.com/13035ff

You most likely have both issues to some degree. Roland has an article (I'd have to look for it on their site) about spacing for the correctors. But the intro is interesting as basically he says that there can be minor variations between scope's lenses. So with +/- 1mm as a tolerance there is a chance a particular scope may need a slightly different spacing. Something to know if things are not round after correcting for tilt. You could make some spacers with your 3D printer.

Greg.[/QUOTE]

You are correct on the specs - my apologies.

I'll try correcting tilt first, then worry about spacing.

DT
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Old 17-11-2020, 10:36 PM
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Thanks also to Ivo, M&T, and Rodney for your kind words.

DT
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Old 19-11-2020, 08:30 AM
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That's looking really good
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Old 19-11-2020, 02:40 PM
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Thanks Chris,

Just need to find time to process some more images I took last weekend...

DT
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Old 21-11-2020, 12:25 PM
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I am curious as to what readout mode you settled on (plus gain/offset) ?

Secondly, I have to say those Chroma filters are pretty awesome as...minimal halos. makes the Baader H-alpha I am currently using for my QHY600 look sad.

Last edited by Peter Ward; 21-11-2020 at 10:51 PM. Reason: typo
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Old 21-11-2020, 04:35 PM
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Quote:
Originally Posted by Peter Ward View Post
I am curious as to what readout mode you settled on (plus gain/offset) ?

Secondly, I have to say those Choma filters are pretty awesome as...minimal halos. makes the Baader H-alpha I am currently using for my QHY600 look sad.
I’m hoping someone like yourself is able to enlighten me on as to what mode, gain and offset I should be using. This was shot in readout mode 1 (high gain), gain 300 and offset 76. Any guidance would be greatly appreciated.

Very happy with the Chroma filters, except for the price tag - although at least they’re less than the Astrodons...

DT
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Old 21-11-2020, 06:29 PM
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Been watching this thread Dave, a good looking result there mate, sounds like you are moving in the right direction, look forward to the high quality results that seem likely to come your (and our) way

Mike
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Old 21-11-2020, 09:51 PM
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Thanks Mike,

It’s a good beginning, but I realise it’s a long process to really get this thing humming.

DT
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Old 22-11-2020, 05:56 AM
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Hi David,
that's a great start.
I read that the IMX455 sensor has about 72% QE efficiency
at the 656 nm Ha wavelength which is very high.
https://www.qhyccd.com/uploadfile/20...5055202120.png

Why did you chose 5 minute exposures?
I'm not familiar with CMOS cameras.
Is there a problem doing longer exposures with CMOS?
I found with my QHY9m CCD that a 20 minutes exposure
was an ideal amount of time when using Ha.

cheers
Allan
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Old 22-11-2020, 08:37 AM
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DavidTrap (David)
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Quote:
Originally Posted by alpal View Post
Hi David,
that's a great start.
I read that the IMX455 sensor has about 72% QE efficiency
at the 656 nm Ha wavelength which is very high.
https://www.qhyccd.com/uploadfile/20...5055202120.png

Why did you chose 5 minute exposures?
I'm not familiar with CMOS cameras.
Is there a problem doing longer exposures with CMOS?
I found with my QHY9m CCD that a 20 minutes exposure
was an ideal amount of time when using Ha.

cheers
Allan
Thanks Alan,

It was more of a testing weekend. The wells on this camera are relatively deep, so I’ll definitely be trying longer exposure. That said, there is a trade off with CMOS between exposure duration and read noise that means you do well with relatively short exposures compared to CCD - I don’t fully understand that, a bit like my lack of understanding about gain, offset and readout mode. Many “knobs to twiddle” and much to learn!

DT
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Old 22-11-2020, 09:24 AM
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Quote:
Originally Posted by DavidTrap View Post
I’m hoping someone like yourself is able to enlighten me on as to what mode, gain and offset I should be using....
DT
I find it weird that you can even vary these parameters let alone have insight to how they affect data gathering. If I have a Eureka moment I'll let you know

BTW I have found that QHY's stated back focus and thickness dimensions are rubbish. AP's Quad compressor has a +/- 1.00mm tolerance, which I found wasn't being met when I actually measured everything with a micrometer. I expect my AP spacer set is now correct but have yet to test it on the sky.....
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