Dark flat frames with filter

[Menno555]

I don't know if I'm missing something or if this is a bug?

I normally make flats as normal exposures but with some filters (in this case an SII filter on a color camera), the auto Monochrome Flat Frame with the Flat Frame tool of SharpCap is very useful.
It also has the option to make and subtract Dark Flat frames but I don't understand the "Use xxx filter for darks" option there?
I mean, they are Dark Flats, the telescope is covered to make it dark, so it doesn't matter what filter is used?

I tried it because I thought is was purely a name thing. But after the flats were taken, on top a message appeared saying Changing to SII filter before capturing dark flat frames ..." and the captures continue straight on without any chance to cover the telescope. That makes those Dark Flats frames with filter essentially normal Flat frames.
When that option of use filters for darks is not used, then there is a notice to cover the telescope before capturing Dark Flats

Menno

[oopfan]

Menno,

I agree with you. Dark Flats are designed to measure the amount of Dark Signal, therefore the optical train must be occluded as if you were taking conventional Dark frames. Changing the Filter has no impact and a waste of time.

The only relation to the Filter is the exposure time. Therefore, if you captured SII Flats using a 10-second exposure then you must take SII Dark Flats using a 10-second exposure.

Brian

[admin]

Hi,

some people put a dark (opaque) filter into their filter wheel, so that they can take dark frames without needing to cover the telescope. If you do have a dark filter then you can tell SharpCap to use it when capturing the dark flat frames, so that the whole process is pretty much automatic.

Actually, I've just added further support for a dark filter in SharpCap 4.1 - from the next update you can specify which filter to use for darks in the settings, then that setting will carry over to capture dark, capture flat and the deep sky sequence planner.

cheers,

Robin

[Menno555]

Thanks for the explanation Robin I didn't know about dark dark filters.

Menno