B & W Flats

[2Dragons8Buddhas]

Hi there every body, a while back my best mate said my flats were not working properly, so a couple of nights ago I went out and did a short imaging run and watched the flats download individually and they were near all perfectly white, but when I came to run them through Astroart tonight they were all perfectly black ! any suggestions ?

Cheers

Carl.

[Dr_Ju_ju]

Hi Carl,

Need a bit more info, e.g. what camera ?, what software ?  or saved locally to camera (DSLR) ?

[2Dragons8Buddhas]

Hi there Julian,

I am using a QSI 683 WSG-8 and was using Sequence Generator Pro (just out of trial period) to control with and were being saved straight to the laptop as downloaded.

Carl.

[ollypenrice]

Don't worry about what they look like on the screen. You probably have an automatic screen stretch in operation. (A screen stretch changes the way the image looks to you in that window but does not change the underlying data.)

In Astro Art just mouse over the flat and look at the ADU values given in the very bottom of the window. (It gives you Dim x and Dim y which are the x-y co-ordinates of the chosen pixel and then it gives you 'Value = '  This value is the brightness in ADU of your chosen point. Near the middle of a flat I like to be somewhere near 23000. The amount of vignetting depends on the setup but for me it means a corner value might be about 19000 in our most most vignetted setup.

When you stack your flats be sure to stack them while using a master bias as a 'dark for flats' or 'flat dark.' Without this they will be likely to over correct and add noise.

Olly

[2Dragons8Buddhas]

Hi there Olly,

Just checked all the flats and every single pixel in every single flat is reading ADU=64000

Cheers

Carl

[ollypenrice]

3 hours ago, 2Dragons8Buddhas said:

Hi there Olly,

Just checked all the flats and every single pixel in every single flat is reading ADU=64000

Cheers

Carl

OK so they were over exposed and can't be used. How did you decide on the exposure time for your flats?

Olly

[johnrt]

3 hours ago, 2Dragons8Buddhas said:

Hi there Olly,

Just checked all the flats and every single pixel in every single flat is reading ADU=64000

Cheers

Carl

SGPro has an excellent flats wizard to help you achieve the correct exposure time, you simply need to input the desired ADU count and give it a min and max exposure time to start the test run and it will find the perfect exposure for your flats.

[swag72]

IN SGP there's a flats calibration wizard. Select the flats you want to do (ie: Lum bin1) and you need to say the ADU figure you want to get close to.... with a QSI683 it's 35000 ADU. You run the wizard and it will tell you the exposure time needed to get the flats to within 500ADU of 35000. 

Then put that into a sequence and off you go