Guiding

[Wasp]

Does anyone here start off doing there dark frames whilst sorting out there guiding?

[vlaiv]

8 minutes ago, Wasp said:

Does anyone here start off doing there dark frames whilst sorting out there guiding?

Provided that you have separate guide scope - I don't see why not, you can take darks and calibrate guiding at the same time.

I use OAG so I can't do that as my guide cam depends on light from main OTA and it needs to be open for that thus preventing acquisition of darks (good thing is that I have cooled imaging camera so I take my darks during daytime off the scope).

[Wasp]

2 minutes ago, vlaiv said:

Provided that you have separate guide scope - I don't see why not, you can take darks and calibrate guiding at the same time.

I use OAG so I can't do that as my guide cam depends on light from main OTA and it needs to be open for that thus preventing acquisition of darks (good thing is that I have cooled imaging camera so I take my darks during daytime off the scope).

I have a TEC camera and thought of doing the same. But dosent the temp have to match the light frames? How much can they differ?

[vlaiv]

5 minutes ago, Wasp said:

I have a TEC camera and thought of doing the same. But dosent the temp have to match the light frames? How much can they differ?

Do you have a set point cooled camera? If you do - you can adjust temperature of sensor, so it will be at the same temperature when doing both darks and lights.

Yes, for proper calibration you need to have a matching temperature - not sure how much difference there is allowed to be, I guess it depends on dark current - stronger dark current requires less temperature difference.

[Wasp]

1 minute ago, vlaiv said:

Do you have a set point cooled camera? If you do - you can adjust temperature of sensor, so it will be at the same temperature when doing both darks and lights.

Yes, for proper calibration you need to have a matching temperature - not sure how much difference there is allowed to be, I guess it depends on dark current - stronger dark current requires less temperature difference.

I have the ASI294MC Pro, you can select how much you want to go below ambient. 

[vlaiv]

33 minutes ago, Wasp said:

I have the ASI294MC Pro, you can select how much you want to go below ambient. 

In that case - just set wanted temperature and take darks. When doing lights, just make sure you select the same temperature. Be careful that you can reach set temperature. I use ASI1600 and it can do about 45C delta. This means that I have trouble using -20C in summer time as ambient temperature sometimes goes above 25C at night. I use two set of darks "winter darks" - at -20C and "summer darks" which are at -15C and apply correct ones depending on lights for the night (either -20C or -15C).

If you shoot darks with camera taken of the scope - be careful of any light leak, both in visible light and IR. Some people use aluminum foil in addition to camera cap for this reason. I have a simpler method - just put plastic cap on and place camera face down on wooden desk - it works.

[Starwiz]

1 hour ago, vlaiv said:

In that case - just set wanted temperature and take darks. When doing lights, just make sure you select the same temperature. Be careful that you can reach set temperature. I use ASI1600 and it can do about 45C delta. This means that I have trouble using -20C in summer time as ambient temperature sometimes goes above 25C at night. I use two set of darks "winter darks" - at -20C and "summer darks" which are at -15C and apply correct ones depending on lights for the night (either -20C or -15C).

I read somewhere recently (can't remember where), that the step increase in benefit becomes less the lower the temperature you go.  So, although going from -10C to -15C gives a reduction in noise, the step improvement isn't as much as you would see going from -5C to -10C, for instance.

I've settled on -10C out here in Malta, at least for the summer. 😎

John

[vlaiv]

24 minutes ago, Starwiz said:

I read somewhere recently (can't remember where), that the step increase in benefit becomes less the lower the temperature you go.  So, although going from -10C to -15C gives a reduction in noise, the step improvement isn't as much as you would see going from -5C to -10C, for instance.

I've settled on -10C out here in Malta, at least for the summer. 😎

John

Yes, that should be correct. I think that dark current dependence on temperature is exponential. Most sensors have something called dark current doubling temperature - which is temperature change for which dark current doubles. It is usually about 6C of difference or there about. That would mean that going from -16C to -10C doubles dark current and going from -10C to -4C doubles it again, so between -16C and -4C it is quadrupled (and progressively higher when going warmer).