Moved: Flat frames advice please

[Grandad]

I have avoided flat frames up to now but have just ordered a Gerd Neumann flat frame panel as my latest effort on M33 was rightly diagnosed as being lacking in the flat frame department.

I have been using Artemis Capture and Nebulosity2 but neither seem to offer help or provision for taking flats.

Would this idea give a reasonal guide to the correct exposure for my flat frames... In Nebulosity I expose until I have a saturated image and then work backwards until my exposures show a histogram that is roughly in the centre of the range between black and white.

Many Thanks

[ollypenrice]

Artemis capture is perfect. I use it all the time for flats.

Start with a short exposure to try the flat, say 0.1 second.

In the display window you have two bits of info marked Black and White (the lowest and highest values on a scale out of 65,000.

Look at your test exposure's white point. It should be between a third and two thirds of the way up so I aim for about 30,000. Go up or down incrementally

but TURN OFF AUTOSAVE WHILE TESTING!!!!!!!!

And that's it. I take 30 to 50 depending on how tired I am! I also take one set of bias (at least 50) which I will use exclusively as darks for all the flats. This is all you need, a case of one size fits all, and beats doing dedicated darks for flats.

Try to avoid over-saturating in Artemis. The screen will go jet black. Shortening the exposure will usually bring it back to life but on rare and very annoying occasions the only way I could revitalize it was to take out the camera and screw on the metal absolute blackout cover to reset it. That's only happened a couple of times and never recently.

You'll find Ha needs a lot longer than LRGB, more like several seconds rather than sub-second.

Flats will transform your pictures and enhance your enjoyment of processing. They are totally, utterly, essential.

Olly

[Grandad]

Thanks Olly

Seems so obvious now that you've explained it.

When I started imaging last winter I thought a few simple shots and I would be happy but the more you do the higher you raise the bar of expectation.

Many thanks

[AndyUK]

Hi John - Obviously all scopes will be slightly different, but just to give an idea, the exposures for my LRGB and Ha flats for an ATIK 314L+ through an MN190/f5.3 using one of those EL panels are as follows:

L - 0.03s

R - 0.16s

G - 0.09s

B - 0.055s

Ha - 3.5s

These gave me an ADU of about 23,000, but I know there's arguments for going higher (and, looking at Olly's images, I certainly wouldn't argue with him !)

[ollypenrice]

Hi John - Obviously all scopes will be slightly different, but just to give an idea, the exposures for my LRGB and Ha flats for an ATIK 314L+ through an MN190/f5.3 using one of those EL panels are as follows:

L - 0.03s

R - 0.16s

G - 0.09s

B - 0.055s

Ha - 3.5s

These gave me an ADU of about 23,000, but I know there's arguments for going higher (and, looking at Olly's images, I certainly wouldn't argue with him !)

I used to go for 23,000 too, Andy. I just upped it thinking you might get a better SN ratio. It matters not a jot, methinks.

Your figures are certainly faster than mine in the F7 TEC, you lucky boy.

Olly

[Tim]

I'm going to pop this thread into the appropriate section for future reference, thanks.

Tim