[gregbradley]

Originally Posted by allan gould

Use SGPro to calculate an average ADU value of 35,000 for each filter and telescope for flats. completely reproducable and no problems encountered even in light polluted Brisvegas.
Allan

How many flats do you take? Do you subtract flat darks or use a bias?

Originally Posted by RickS

I do dusk and dawn flats with ACP automation by preference. If that's not an option I use a Gerd Neumann EL panel. I like to get a minimum of around 500K e- total for each filter (about 12 flats at 30K ADU with my U16M camera but it would be a lot more for a camera with shallower wells). The 500K e- number is based on the work by Richard Crisp. Not sure if this the paper you were looking for, Greg?

http://www.narrowbandimaging.com/inc...3_expanded.pdf

Cheers,
Rick.

500ke is the midpoint he recommends for the 16803 and it varies with model of camera. Richard uses FLI cameras but having had a U16M myself they seem similar to the FLI in many ways. I don't understand the Ke value. The camera softwares do not report Ke. So how do you translate 500ke into an ADU? As I recall from various posts after this paper by Richard he recommend around 40K ADU. In the paper I notice he also states a bighter image needs a brighter flat. That is interesting. I have noticed sometimes I need a brighter flat to correct better.

Why do you say smaller well cameras need more subs for a master flat? I must have missed that implication in the paper. In reality if you take dusk/dawn flats the failing or brightening light puts a practical limit on how many subs you can take. That varies with camera performance (download times). I know Richard uses the video output of KAI sensors to get millisecond download times and gets many flats quickly.

Originally Posted by SpaceNoob

Never really done them but with the cdk I've found I now need to. I have a flatman XL on the way that should have been here before the scope but there were delays due to shortages from their inverter supplier.

Will be interesting to see how this thread goes as I have no real idea about this flat stuff. Anyone else using a flatman?

If your CDK is similar to my CDK17 you will need flats big time or your images will suffer. Less so for a smaller chip. On the 16803 its vital hence the thread so we can get access to latest data about flats.

Originally Posted by Lee

I made a simple cardboard frame for an EL panel, and use SG Pro to sort out exposure times for each filter/binning.... I have 10 sheets of tracing paper in front of the panel to dim it enough....

These panels are popular.My concern about panels (perhaps groundless) would be there spectrum bias. For example an LED torch looks very white at night. Take a long exposure photo of one and you'll see its quite purple in colour. That may impact on the accuracy of your flats??

Originally Posted by DJT

Hi Greg
For DSLR, I originally used a light box from Icer EXFSO and used BYE to get the histogram to around 70% from the left hand side. Worked very well.

Am now using Gerd Neumann light panels, one for the frac and one for the RC8, (I may have over capitalised...) and find I need longer subs but aiming for the mid point on the histogram, again through BYE. Still playing but seems to work ok.
When I grow up and get a ccd then will have to change again. Great fun

I checked in Nebulosity and the flats that work for me give around 20,000 to 25,00 adu
Good thread..

Have you tried brighter flats like 40,000 ADU?

Originally Posted by DavidTrap

A3 EL panel mounted between 2 sheets of MDF. OZStockman supplied the MDF - one sheet is complete, the other has a hole to sit around the front aperture of the scope and holds the panel in place. It was actually the offcut from around a Bahtinov mask that he cut for me. I just asked him to cut it from an appropriately sized piece of MDF to fit over the A3 EL panel. I had already bought the EL panel so needed something to mount it in. In retrospect, I should have just bought a Gerd Neumann panel from the start. My overall cost was probably about half vs a GN panel, but a lot more fiddling to get into a usable state. The A3 panel is just large enough for a 10 or 11 inch scope.

Seems to work OK. I tell CCD Commander to acquire automatic flats, but not to move the mount or wait until dawn - it works out the exposures. Usually collect 10-20 flats per filter.

DT

Does CCD Commander reduce the exposure times of the flats at dawn as they progress?

If you sit and watch you flat downloads (as I do) you'll see the ADU change between flats at dawn and dusk. I manually compensate by decreasing/increasing the exposure time to try to reach a target ADU reasonably closely. For example a 10 second flat that gives say 25,000ADU will gie 24,750 next sub then 24,500 next one etc. I am surprised often at how quickly the light fades at dusk. Its faster than we think I suppose because our eyes adjust to the failing light levels masking how quickly it is fading.

Martin Pugh mentioned at AAIC when I asked him about ADU flat levels he averages several sets of flats taken at different ADU. I have not done this but it sounded like a good idea so you are evening out the various reponses.

I knew about this 40K ADU by Richard yet I have encountered times when a bright flat damaged the image. So that confused me on this point. It may have been some other error that confused the result. As his paper says a more intense image requries brighter flats. This may have been a not very bright image. He seems to not mention a specific adu in his paper yet in posts he did. I will send him an email to clarify on this.

Greg.