Anyone with QSI683 - What Flat ADU value do you use?

[NickMorris]

Hi,

As the title says - Which ADU value do you use for flats with your QSI683?  I have been trying to calculate the correct value relating to full well depth and gain but was wondering what others use?

Cheers

Nick

[perfrej]

Currently, I am using 22000 as a target with a +/- 1000 tolerance. I have tried 30000 as well and cannot really see a difference. Always do sky flats - definitely easier that fiddling with a panel or the obligatory stack of A4 papers and t-shirts

/per

[kirkster501]

I too use 22-23000.  Not that I know why, its more of a question of monkey see, monkey do.  But they work.  You adjust exposure to get the ADU in that range.  Sometimes only a 0.01 seconds increment/decrement is needed to get into that range.  And in mono the exposure is different for each filter.  So create a flats plan in your imaging capture software.

[davew]

You could read this information here - http://www.narrowbandimaging.com/images/ML8300_Flat_Fielding_Experimental_Data.pdf

He's only using an FLI mind you

Short answer is, the lower the ADU, the more flats required. I also gather different cameras require different ADU values. FYI I tend to use around 20000 x 20 with an 8300 chip.

Dave.

Per. A write up of your methods may go down rather well. With me at least !

[NickMorris]

Thanks for the replies,

I have subsequently found a page on QSI website which indicates 35,000 ADU, way higher than I have been trying.  What do you guys think?

http://store.qsimaging.com/kb_results.asp?ID=28

cheers

Nick

[perfrej]

There are two ways to look at it. One is to target a linear range of the sensor, i.e. not too high nor too low. Another is to go as low as possible in order to have them end up in the most used part of the dynamic range.

A write-up of my method? How's this?

/per

[davew]

Thanks for the replies,

I have subsequently found a page on QSI website which indicates 35,000 ADU, way higher than I have been trying.  What do you guys think?

http://store.qsimaging.com/kb_results.asp?ID=28

cheers

Nick

To use the figures QSI give is a no brainer in many ways. Why buy from a particular manufacturer and then ignore the work they've done on your behalf ?

The small print at the bottom would indicate they use 70% for that chip unlike the article I linked to which stated 80%. QSI seem to like 80% on the NABG chips.

QSI don't give a number of flats to use so I'd use the linked article for pointers.

I've tended to use lower figures as an attempt to stabilise on one level. That's because I used to take flats using either a white board, laptop or ceiling. I now use a flats panel, which after this thread, I may well increase the ADU value ! Just to let you know, the best flats I've used were from the ceiling ! It's just a bit awkward to work that way so gave up on it. I really should take more but didn't find 30 flats made any difference to my perception. I have proved that laptops don't always work so never use that method any more ( Two Samsung screens ) no matter what people say. I have the proof somewhere on a hard drive.

Dave.

Note this quote on the QSI site -  You should always experiment with your particular sensor and camera to achieve the best results.

[davew]

Thanks Per. I've used the flats plug-in with Maxim before now but found it a struggle getting organised sometimes. I take it you set up the scope well before it's needed.

On the other hand, using the scope on the balcony is rather like having an Obsy. I set up every night !

Dave.

[perfrej]

Well, set up in the late afternoon and tell CCD Autopilot (which is great for one night stands) to do flats before the night's imaging run. Go to sleep, wake up, pick up gear. Any questions?

/per

[perfrej]

Perhaps you should consider setting up in a permanent way and using a cover for the stuff. Like this:

[davew]

 Any questions?

/per

Not really It's as important to know what you don't want to do as well as what you do.

I should get my head in gear before night fall. Leaving my stuff outside unattended isn't an option for me.

I notice no footprints out to the scope. Softy !

Dave.

[perfrej]

Given the situation at the door, I resorted to climbing out from the bedroom window in order to be able to clear the snow out. Took a while

[NickMorris]

Thanks for all the input, much appreciated.

As suggested, will use the figures from QSI but experiment a bit too and find out if there is much of a difference.

Per, Wow that is some snow on your balcony!  do you leave your 10 Micron out there all the time in these temperatures?  With scope and camera, or just the mount?

Makes me feel cold just looking at that picture - no wonder you run ACP.....

cheers

Nick

[perfrej]

Full kit out there. GM2000HPS, camera, wheel and the Takahashi FSQ-106. The bag is a garden grill cover altered to fit and has a ventilation opening. No frost, no moisture, all clear. It wasn't that cold, though, just a mere -22°C.

/per

[ollypenrice]

As all you QSI buffs are on here can I ask your opinion on this? http://stargazerslounge.com/topic/197827-ccd-camera-design-an-idea/ Since integrated cameras/wheels are coming in it might be a time to rethink an old assumption.

Olly

[NickMorris]

Hi Olly,

My preference would be on the side for cable entry to camera.  If the bend radius of the cable causes a problem with fouling anything, right angled connectors (USB/DC power)  could be the answer......

Cheers

Nick