Problem with Flats

PM Sent

Looking at the software and Maxim DL for the 383L+ I do not see an option for "Overscan" so the correct process from what I have read

1. Flats - BIAS "Master" is subtracted
2. Darks - BIAS "Master" is subtracted

I've already started working on my Darks to get the V and M values by using ImageJ and adding 5000 to the first dark as per the Stark Labs guide

Simon

Dave

When doing the flats, due to the shutter on the 383L+ I need to take an exposure of 2 seconds for the min "Flat", if I add more sheets of paper in between the EL Panel and the scope, this should be fine right? I know I will have to subtract darks from each exposure time pair

Simon

Simon - that sounds about right for the bias frames then.

I've discovered a later version of the DTC/PTC spreadsheet. This was one I had posted over to Richard Crisp who amended and then returned it.

I'm struggling to see where some of the columns came from but I can take a closer look later.

I've sent you only the one spreadsheet (the first set of measurements I took for contrcuting both the DTC and PTC). It looks like I did the PTC a second time because the linearity looked suspect in the first. The light frames were significantly longer (up to 90 secs v 65 sec for the first PTC) so I must have popped on a few more sheets of A4 paper. The linearity looks a whole lot better anyhow - linear from 10K to 58K. But I suspect the darks are more forgiving because I didn't bother doing that a second time. But I do see that I did go all the way up to 7200 second darks the first time round.

Spreadsheet on its way now...

Cheers
Dave

That sounds fine - I seem to have started at 0.5 secs for my own flats. Perhaps the FLI shutter is bit quicker than the 383L. I do know that anything lower than about 0.5 sec is useless for me anyhow - all you see is the shutter pattern.

2 seconds minimum shouldn't have any major impact. When you see the spreadsheet, you'll see that the key data is extrapolated anyhow.

The more paper you use, the longer the exposure you can take before you hit full well. So, for example, if you use one sheet of paper and you max out after 10 seconds, you won't have many measurements. If you use 10 sheets and max out at 60 seconds, you'll have a lot more points so better data.

I seem to have maxed out on my first PTC at about 65 seconds. When I did it a second time (with more paper), I maxed out at 90 seconds - and I got a very much smoother line.

Keep us all posted...

Dave

Gone for

2
4
8
16
32
48
64
80

Would that be enough? Looking at your spreadsheet you went for a lot more

Already have the DTC data...I think

Simon

Simon - just looking at your PTC data.

1, Are your Mean/SD's only for the ROI or for the whole image?
2. Did you do the pixel math piece? (see page 12 of Richard Crisp's document) - if so, is that your column "Combined SD"?
3. You need to plot the data on log-log axes

As mentioned by Crisp on page 9:

The next thing we do is accurately measure and remove the offset from each frame. I use the
overscan region for making the offset measurements. Not all camera vendors support overscanning
for some reason, presumably to protect you from your own ignorance (they say) and perhaps to
make it hard for you to do an accurate characterization if they feel there’s something to hide;
because if you cannot accurately measure the offset you aren’t going to get accurate results in the
PTC….

I'm not sure how to deal with the overall data is there is no overscan data. Is there an overscan region that you can analyse on the 383L?

Dave