11 replies to this topic

[Ahilevs]

Hello everyone,

 

I am not sure if this is the right place to start this topic but my friend has been experiencing some calibration problems recently. He has Asi294 mc cooled camera and shooting from Bortle 6 zone with Optolong L-Extreme and L-Pro. Recently he started having some reddish, pinkish type of circle at the center of images after stacking. We tried to figure out what was the problem so I wanted to his flats. You can see his flats down below that they don't look wrong. The problem is that what we see in those flats, they show themselves exactly in the stack image. Can someone tell what is the problem with this issue:

Attached Thumbnails

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Edited by Ahilevs, 09 February 2022 - 05:15 AM.

[Chrisofweden]

Hi,

I have the 294mc pro myself and it is a little “tricky” to get the flats correct.
It’s important to take flats that are a minimum of 2 seconds exposure and match that with dark flats of the same exposure, temperature etc. Use the master dark flat instead of any bias frames. You might struggle to get the correct ADU level (roughly 1/3 from the left on the histogram) with 2s exposure, I use a flats panel, but I’ve read from others that it’s possible to achieve it using other light sources that are dimmable. 
I haven’t used the optolong filters yet, so can’t comment on that, but would certainly advise using the “long” flats and dark flats.
Good luck and hope you get it worked out!
/Chris

Edited by Chrisofweden, 09 February 2022 - 05:34 AM.

[ex-Bubblehead]

There was actually quite a lot of conversation here a while ago regarding the phenomenon you are seeing with that camera. I'd help with a link, but I need to scramble to get some young kids out the door and don't have time to search!

[Ahilevs]

Hi,

I have the 294mc pro myself and it is a little “tricky” to get the flats correct.
It’s important to take flats that are a minimum of 2 seconds exposure and match that with dark flats of the same exposure, temperature etc. Use the master dark flat instead of any bias frames. You might struggle to get the correct ADU level (roughly 1/3 from the left on the histogram) with 2s exposure, I use a flats panel, but I’ve read from others that it’s possible to achieve it using other light sources that are dimmable. 
I haven’t used the optolong filters yet, so can’t comment on that, but would certainly advise using the “long” flats and dark flats.
Good luck and hope you get it worked out!
/Chris

Thanks for the reply Chrisofweden. It was what I thought in the beginning and asked how long the exposure of the flats but they were 4 seconds and also he uses asiair flat autorun so the device makes some test and figures out the right ADU level. Bias issue can be tried because I also read the same type of suggestions on different issues about Asi294 mc but I couldn't understand how correct dark flats can reduce this problem. Still we need to try before deciding whether it is a calibration or sensor problem.

[Ahilevs]

There was actually quite a lot of conversation here a while ago regarding the phenomenon you are seeing with that camera. I'd help with a link, but I need to scramble to get some young kids out the door and don't have time to search!

I have almost read everything on this subject and most of them address the sensor problems. Like I said above, I am planning to calibrate with dark flats to see if anything will be different tonight.

[KTAZ]

Yes, there is a very long thread on this issue, and it is a known issue when using the Optolong L filters in conjunction with the 294. I'll try to find it. Try a few searches on both the filter and the camera.

 

BTW, it seems to be specific to individual cams, not all of them.

Edited by KTAZ, 09 February 2022 - 08:53 AM.

[larryjh]

Even if you are not using Siril, this tutorial is very illuminating:

https://siril.org/tu...nthetic-biases/

One very important takeaway from it is that problems with flats are often actually due to a problem with your master dark.  You may want to confirm that you are using the correct dark for your exposure/temp/etc.

[Ahilevs]

It is a very good source to find out what is his problem. Thank you larryjh, I will read it directly. By the way, we made that stack above I shared by using SIRIL but we used the standard script to see the result.

Even if you are not using Siril, this tutorial is very illuminating:

https://siril.org/tu...nthetic-biases/

One very important takeaway from it is that problems with flats are often actually due to a problem with your master dark.  You may want to confirm that you are using the correct dark for your exposure/temp/etc.

[thenightinthesky]

Hello guys, when I take small galaxies I have these results from Pixinsight; generally I use 120 as gain and 30 as offset, and my flats has the histogram at 30-40% but we can see from the photo calibrated the green gradient that not have when I not put the flats (but the image is more opaque).

I have asi 294 mc pro with Idas P2 filter.

 

LINK TO CALIBRATED IMAGE BY BATCH PREPROCESSING https://i.postimg.cc...integration.jpg

Edited by thenightinthesky, 20 February 2022 - 03:09 AM.

[audioengr]

If you use a good flat light panel, not too blue, and set the exposure based on the SharpCap histogram, and make sure you have the same configuration in the OTA (not turned camera etc.), then you should get an accurate flat frame.   I do this and never have any artifacts.  If you stretch to the limit, then you might see some red bands however.  Probably a function of the spectra of your light panel.

[reifheck]

If you use a good flat light panel, not too blue, and set the exposure based on the SharpCap histogram, and make sure you have the same configuration in the OTA (not turned camera etc.), then you should get an accurate flat frame.   I do this and never have any artifacts.  If you stretch to the limit, then you might see some red bands however.  Probably a function of the spectra of your light panel.

hi audioengr,

 

Can you take flats with just the camera and a light source (I have a Canon EOS 7D used with BYE and ASTAP) or do you have to use the entire optical path (Scope to Camera)?

 

Thanks,

Reif
 

[thenightinthesky]

If you use a good flat light panel, not too blue, and set the exposure based on the SharpCap histogram, and make sure you have the same configuration in the OTA (not turned camera etc.), then you should get an accurate flat frame.   I do this and never have any artifacts.  If you stretch to the limit, then you might see some red bands however.  Probably a function of the spectra of your light panel.

Hello, always at 30% of histogram?