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kirkster501

Flats at 49000 ADU with shortest possible exposure

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Hi all,

Tryign to get flats with my G2-8300 and luminance and the shortest possible shutter speed is 100ms according to the Moravian web site.  That said, I can set it to 0.01 (10 msecs) on flats wizard in SGP.

Anyway, when I have the fastest possible exposure the camera is capabale of the flats are at 49000 ADU.  There is no way to have a shorter expsoure so the flats with that filter can't be any less than the 49000 ADU.  I normally aim for 23000 for flats.

Any thoughts please guys?

flats.thumb.PNG.1d428b0d46d7a1d50cd3785fdecf7b14.PNG

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.... thought occured to me, use a dimmer panel????

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What are you illuminating with ?

Dave

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Crossed posts, some 8300 cameras have a shutter that interferes with "fast" flats, I've got a dimmable light box and aim for at least 1 second.

Dave

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I just use a few sheets of typing paper as diffusers, Steve. I need a different number depending on the filters. Any irregularities will be too far out of focus to matter. (Think of secondary mirrors in the same position at the front of the tube.) It's probably best not to use flats which are too short because you'll be out of the camera's window of best linearity.

Edit: Ah yes, I'd forgotten the shutter issue. I've never owned an 8300 camera but I've heard people talk of two or three seconds to avoid a gradient introduced by shutter wipe. Good point from Dave.

Olly

Edited by ollypenrice
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Thanks guys! 

So because of the mechanical shutter I need the exposure to be of a much longer exposure than on the Atik (that has no mechnical shiotter) but of the same ADU......?  So the light box needs to be dimmer accordingly (or obstrictions placed in front of it to dim it down??)  Hmmm, always something isn't there!!!!??

What about BIAS with a cameras with a shutter?  Still set the camera to its fastest possible exposure?

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Apart from shutter issue, I think that 49000 ADU is quite OK for 8300 judging from linearity graph for that sensor.

ATIK383L+-Exposure-Duration.jpg

2 minutes ago, kirkster501 said:

What about BIAS with a cameras with a shutter?  Still set the camera to its fastest possible exposure?

Bias actually don't depend on light, and you should have scope covered when taking them, or software should keep mechanical shutter closed for both bias and dark files.

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3 minutes ago, kirkster501 said:

Thanks guys! 

So because of the mechanical shutter I need the exposure to be of a much longer exposure than on the Atik (that has no mechnical shiotter) but of the same ADU......?  So the light box needs to be dimmer accordingly (or obstrictions placed in front of it to dim it down??)  Hmmm, always something isn't there!!!!??

What about BIAS with a cameras with a shutter?  Still set the camera to its fastest possible exposure?

Yes, bias is unaffected. It's a lightless capture so it needs to be the shortest possible.

There IS always something, of course, but a few sheets of typing paper offer a remarkably low-cost solution in a game in which solutions frequently cost as much as a small villa on the Riviera!

Olly

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Thanks Vlaiv.  However, the shutter time is so small to get 49000 ADU that the mechanical shutter will impart a gradient......  So I am looking at a solution to get the 23000 ADU with an expsure time of a second or so to elimnate that issue.  Even four pieces of white paper is 65535 ADU because my panel is too bright....  Will need to think about this.  Don't want to disturb the scope since I got 8 hours in on M81/M82 lasty night with lumninance filter.

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...going to look at my iPad pro and dim it right down....

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Can you fit a dimmer switch to the panel ?

Dave

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5 minutes ago, Davey-T said:

Can you fit a dimmer switch to the panel ?

Dave

That'll be the solution longer term.  It's an electro-lunminance one so not sure you can do that though...

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What you want is this https://www.sblite.co.uk/neutral-density/265-rosco-299-12-neutral-density.html and this one https://www.sblite.co.uk/neutral-density/264-rosco-211-9-neutral-density.html

I have sandwich one sheet of 299 between the frosted screen and backing for my NB Flat panel and 1 x 299 & 1 x 211 for my LRGB it sandwiches flat and is protected, I now use thanks to someone on here flat panels from Beam LED http://www.beamled.com/biard-10w-panel-light-300-x-300mm-led.html

I am getting the fastest my 8300 chip can take at 0.22sec for my lum and between 3-9 secs for my NB

All I did was remove the frame, cut a perfect fit of the Gel and then put the front screen in and then reassembled, it works absolutely perfectly and I am using an ADU of 25,000

Hope that helps?

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Thanks guys.  For now eight sheets of A4 paper....

IMG_4003.thumb.jpg.76f40533e0544c3d0436387f7bb0c164.jpg

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QSI used to have a page dedicated to the Full Frame Kodak chips ( Not full frame as in DSLRs )

The figure they used was 35000 ADU for the KAF 8300.

I would use at least 2 to 3 seconds for shutter shadow.

As a quick rule of thumb, taken from another site years ago, the minimum number of flats is 500000 divided by the ADU. In this case that's 14 / 15. This figure derived from work by Richard Crisp.

Dave

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To get my 24000 ADU on above rig with the "eight sheets of white A4 paper" method, the expsoures had to be 6.37s on the flats on the luminance (astrodon filter).

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Well the flat seems ok and has eliminated the huge vignetting on the raw subs

flat.thumb.PNG.7282250957138023e7b7fe658091a562.PNG

6.25 hours of 1x1 lum.  I love these particular galaxcies in a wide field.  Delicate processing (that I am not completely sure of) not to kill the intergalactic gas that such a long exposure has captured.

 

light-FILTER_Lum-BINNING_1.thumb.jpg.174dd69070e82421fe0a18c55f0de67b.jpg

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Dimmed down my lightbox with ND film to get 25k, but the acrylic route looks more durable.

Last night did a session binned and in the wee small hours discovered tbat soo much more sensitive had to add another layer of  ND tbat luckily I had left over.

Michael 

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I decided to automate my flats procedure by using the panel and electronics from this project:-

https://www.cloudynights.com/topic/536533-diy-alnitak-flat-panel/

I now have an A2 panel I can use as part of my SGPro imaging "events sequence" Each filter has it's own lightness valve set from within a range of 0 - 255 levels. 

Steve

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Ingenious idea Steve and i have been theorising something similar..... I shall investigate that link.  I'm an old BSc in electrical engineering - 1992 - so I'm sure I can work it out !:confused1:

Where did you get your A2 panel from please?

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19 hours ago, kirkster501 said:

Well the flat seems ok and has eliminated the huge vignetting on the raw subs

flat.thumb.PNG.7282250957138023e7b7fe658091a562.PNG

6.25 hours of 1x1 lum.  I love these particular galaxcies in a wide field.  Delicate processing (that I am not completely sure of) not to kill the intergalactic gas that such a long exposure has captured.

 

light-FILTER_Lum-BINNING_1.thumb.jpg.174dd69070e82421fe0a18c55f0de67b.jpg

Good result and this target is a terror to flatten because of the IFN confusing matters.

Olly

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7 hours ago, kirkster501 said:

Ingenious idea Steve and i have been theorising something similar..... I shall investigate that link.  I'm an old BSc in electrical engineering - 1992 - so I'm sure I can work it out !:confused1:

Where did you get your A2 panel from please?

Hi Steve,

5a808f22a01f4_A2Panel.thumb.jpg.97acd590f3771d8c0de66bc900739085.jpg

Steve

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