383L+OSC - Ha Flats

[ktaylor807]

I was using an Ha Filter on my 383L+OSC. After my session I took flats with the filter still in-place.

I had to take exposures of 90s to get a value of over 30,000 in Astroart.
Is this seem normal?
Ken

[chrisjbaileyuk]

Depends on the brightness of your light source. With twilight flats I am not too surprised.

With 90second exposures, you are starting to get to the point where dark current builds up so you may need to take flat darks to calibrate them with.

I use an EL panel and typically have Ha flat exposures of 6 seconds to get to and ADU value of ~20,000.

[Chris]

A Ha filter only lets about 3% of the light through so you can expect that the exposure required will be 30 times as long, so if your exposure without the filter is 3 to 5 seconds (and it should be because of the shutter) then 90 seconds seems about right.

I'm building a light box with a variable brightness so I can turn it down for no filters and up when using narrow band filters.

AIUI you should keep the filter in place because your flats are compensating for any dust or vignetting by that filter.

Chris

[ktaylor807]

I do use an EL Panel.

What should be the value when taking flats?
I was told around 35,000-40,000.
Is this correct?

About 35,000 was the value when I took my Ha Flats.

[chrisjbaileyuk]

I have found my 383L flats overcompensate at an average ADU of around 35,000 and have found better results in the 15-20,000 range.

[MikeM]

I use a Gerd Neumann EL panel and find that I get good results in the 24-29,000 range.

[ktaylor807]

Thanks
I will try ranges between 15,000 and 25,000.
You all are a Great Help.
Thanks Again

[Lex]

Hi,

I do use an Neumann EL Panel to and my ADU is at 25,000
This is widely the best range I think...

Best