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Old 25-01-2025, 09:58 AM
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gregbradley
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Originally Posted by alpal View Post
Thanks Greg,
it seems you definitely know what you're doing
and you're getting top results.

cheers
Allan
Thanks Allan.

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Originally Posted by PRejto View Post
Hi Greg,

Not to argue a point too much, but from what (little) I know about CMOS cameras (my Player One Poseidon is quite new) there are more than a few guys over at CloudyNights that say the flat-darks are quite unnecessary with the newer CMOS cameras and that just taking flats in the normal way (just subtracting bias) will work just fine. I've done it both ways with my camera and so far I cannot see any difference.

Peter
It would suit those who use illuminated discs for making flats as then you can control the exposure length to just one length rather than it shifting with dusk flats.

It's a bit of a trial and error approach as to what works and what doesn't.

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Originally Posted by Startrek View Post
Greg,
I forgot to ask before and just out of interest, what camera are you using and what temp and Gain/offset settings ?
Thanks

Martin
Hi Martin, it's a QHY600mm and read mode 0 with gain of 26 and offset of 40. Ideally I would use 56 50 for narrowband but it starts to get too complicated as it requires its own set of darks etc.

Last edited by gregbradley; 25-01-2025 at 06:31 PM.
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  #22  
Old 25-01-2025, 01:21 PM
Startrek (Martin)
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Originally Posted by gregbradley View Post
Thanks Allan.



It would suit those who use illuminated discs for making flats as then you can control the exposure length to just one length rather than it shifting with dusk flats.

It's a bit of a trial and error approach as to what works and what doesn't.



Hi Martin, it's a QHY600mm and read mode 0 with gain of 26 and offset of 40. Ideally I would use 26 50 for narrowband but it starts to get too complicated as it requires its own set of darks etc.
Greg,
Here’s an interesting document I found on the IMX455 sensor , well worth a read , if you have the time.
As with the IMX571 , the IMX455 sensor does exhibit random telegraphic noise RTN or 1/f noise ( salt and pepper noise ) which can be mitigated using Darks correction.

https://research.iac.es/preprints/files/PP23035.pdf

Even though it’s a minor problem and only visible when you zoom in and compare bright and darker areas of your image , I take the hard road and use the full calibration suite for all my images as I’ll do anything to improve an image even if it’s ok.

I also read somewhere that these sensors are prone to slight changes in QE ( negative output response ) after 12 to 18 months of use and that Darks are the only sure way to combat this deterioration which include warm pixels and RTN.

Full calibration suite
Darks from Library matched for Lights
Flat Darks for Flats

Using Flat Darks or Bias do not show much difference but I choose Flat Darks as a safe measure.

I capture my Darks library every 9 to 12 months ( I do it in my study ( darkened ) just with the camera itself and cap on , takes a day )

For Flats I use an LED light panel with dimming control and works a treat . The IMX571 in my 2600MM is very co operative ( I believe the IMX455 is as well ) and flats are quick to capture with during a session or after a session during the afternoon or evening.
I have no patience for Sky flats as your options are limited and variable.

Cheers
Martin
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  #23  
Old 25-01-2025, 06:36 PM
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Thanks Martin.

Good to know your procedure.

I do use flats and darks on some images. If they work then great, if they don't I don't stress about it as there is more than one way to arrive.

I should get one of those panels. Not that expensive for a 110mm but getting up there for a 17 inch!

I do notice some odd effects using bias though. I'll make a fresh lot.
I basically have been only using 2 exposure times - 300 and 600 seconds.

The rain noise I have only seen once. It may have been diminished in the qhy firmware, I know the horizontal lines issue is reduced in QHY's firmware.

I imagine these are only problems if there aren't enough subexposures to get a decent stack and let maths get rid of the random noises by dithering.

I have some colour for this image, not sure if its enough exposure time though.

Greg.
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  #24  
Old 25-01-2025, 09:28 PM
Startrek (Martin)
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I use a Huion A2 LED light pad for my 10” Newt and a Huion A3 LED light pad for my 8” Newt

https://www.huion.com.au/product-pag...-led-light-pad

https://www.huion.com.au/product-pag...-led-light-pad

I just used black cardboard from Officeworks , cut it to the size of the light pad then cut a hole say 10mm wider than the diameter of the OTA. This reduces stray light from hitting the rig. Then slew the mount in Ra and Dec until end of OTA is pointing to Zenith, sit the light pad on top and take your Flats , very easy and convenient. I even taken them in during the day inside the Dome ( shutter down and door shut ) with a black large shower cap fitted over the back end of the primary mirror end to block out stray light.

I’ve had these light panels for about 5 years now and no issues at all , although the costs back in 2019/2020 were half the current prices.

Cheers
Martin

Last edited by Startrek; 26-01-2025 at 07:19 AM.
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