Atik 383L+ How many flats

[rubecula]

I've just run the SGP Flat Calibration Wizard with a Target Mean ADU set at 23,000 and a minimum time of 3 sec (to allow for mechanical shutter).  I needed to cover a light panel with 8 sheets of 80g paper to get an exposure above 3 sec for the Luminance filter but it took 922 sec to get to 23,000 for the HA filter.

I was hoping to go for 40 flats with each filter but as I stand it will take over 15 hours to get 40 Ha flats!!!

What would you advise as the minimum number of flats and would it make sense to take more flats for those filters not requiring such long exposures.

Thanks

[Davey-T]

You can use less sheets of paper for HA to get the same exposure time as RGB, I use 6 sheets for RGB and 2 for HA.

I wouldn't bother taking any more than sixteen calibration frames for a start and see how it goes, they work on a law of diminishing returns which if you plot it on a graph quickly becomes a straight line once you pass 16, this is only theory though so a bit of experimenting is in order.

Dave

 

[spillage]

I think I would do a run with the wizard for my broadband filters first. Then remove some sheets of paper and run another for narrowband to the get the exposure time down.

I normally run about 50 off.

[davew]

A few years ago QSI had a section on their website about ADU values and they promoted somewhere upto 35000 ADU for the KAF 8300 chip. It's still all about SNR even with flats. I think the web pages have now gone.

Re numbers. As Davey-T says, 16 is a good enough number for most people. Doing that square maths wotsit, the next number to aim for would be around 25, then 36, then 49 etc, as Spillage says.

Dave.

[jjosefsen]

I had the same problem, although to a lesser degree..

Turned out I could use my old 2 channel dewheater controller to control the voltage of my flatspanel, so now I just dim it.

Needed a phono to 12v plug cable, those can be bought or made your self.

Edit: If your flats panel is 12v that is..

[carastro]

Gosh I don't remember having to take anything like that when I had an Atik383L.  I am sure I didn't take more than 1 - 1 1/2 mins per flat.  Just wondering if you have actually set minimum of 3mins instead of 3 secs.

Carole 

[rubecula]

I managed to get all the flats (16 x 7 filters) finshed last night. Reducing the sheets of paper worked for Ha, it brought the exposure down to 34 sec.  

I do like the idea of being able to vary the voltage on the flat panel.  I don't have a spare dew heater but I'll look into finding something else.

The minimum was definitely 3 sec Carole.

Thanks for your help everyone.

[carastro]

Lol less paper did the trick

[JOC]

Can I please ask the casual observer question?  What's a flat please?

[Thalestris24]

6 minutes ago, JOC said:

Can I please ask the casual observer question?  What's a flat please?

It's an imaging frame taken through the optical path and used for calibration - negates dust bunnies and  vignetting.  

Louise

[Davey-T]

1 hour ago, JOC said:

Can I please ask the casual observer question?  What's a flat please?

Flat field not to be confused with field flattener 

Dave