Over correcting flats, out of ideas.

[narrowbandpaul]

and for RBI info, as Olly points out Richard Crisp is the guy for it.

[steppenwolf]

Hi Olly, I have been working on resolving this over-correction problem on my QSI camera. I have resolved it completely and I am hoping that the cause of my issue may have some bearing on yours.

Having tried increasing the flush intensity to no avail (the camera disengages if a flush higher than 'Normal' is used), I re-evaluated some images that I took some time ago and confirmed that the Flats worked perfectly in the past so I started looking for anything that had changed.

Full automation is the biggest change I have made which means, amongst other things, that MaxIm DL is now controlled by CCD Commander and therein lay the issue. Not a problem with CCD Commander as such but a simple case of CCD Commander taking its lead from a preset within MaxIm DL.

I have set the exposure presets in MaxIm DL's Readout Mode to download images in 'fast mode' when manually locating stars, manually focusing or when checking the framing of deep sky objects. Unbeknown to me, CCD Commander was taking the readout mode from the first preset in the list and applying it to Light, Bias, Dark and Flat frames so all the frames were suboptimal. The solution was simple - make a new preset called 'Imaging Session' with the readout mode set to 'Image Quality' and place it at the top of the list!

If your camera control software allows for more than one download rate, try setting yours to the slowest rate available - perhaps you will share some of my joy!

[ollypenrice]

 

Thanks Steve. It's not impossible that Nebulosity is doing something similar, though I never ask it to change its download speed. However, it may be doing so of its own accord. It has a preview mode which may well instigate fast download and I've noticed that, although it works unbinned, Preview gives a different ADU value to Capture Series. For this reason I always set my flat exposures using Capture Series and then delete the test shots. It might even be that Nebulosity sees fast exp. times and defaults to fast downoad for them. It loves to try and second guess your every move. I'll look into this possibility.

One curiosity: I tried lowering the contrast in my over correcting flats in Photoshop just to see if anything happened and it did. The over-correcting was worse. I found this too odd to disturb my poor brain with it any further!

Olly

[steppenwolf]

Quote

One curiosity: I tried lowering the contrast in my over correcting flats in Photoshop just to see if anything happened and it did. The over-correcting was worse. I found this too odd to disturb my poor brain with it any further!

Tee hee, I tried that last night as well - the results were horrendous and inverse to expectation!

[opticalpath]

2 hours ago, steppenwolf said:

Hi Olly, I have been working on resolving this over-correction problem on my QSI camera. I have resolved it completely and I am hoping that the cause of my issue may have some bearing on yours.

Having tried increasing the flush intensity to no avail (the camera disengages if a flush higher than 'Normal' is used), I re-evaluated some images that I took some time ago and confirmed that the Flats worked perfectly in the past so I started looking for anything that had changed.

Full automation is the biggest change I have made which means, amongst other things, that MaxIm DL is now controlled by CCD Commander and therein lay the issue. Not a problem with CCD Commander as such but a simple case of CCD Commander taking its lead from a preset within MaxIm DL.

I have set the exposure presets in MaxIm DL's Readout Mode to download images in 'fast mode' when manually locating stars, manually focusing or when checking the framing of deep sky objects. Unbeknown to me, CCD Commander was taking the readout mode from the first preset in the list and applying it to Light, Bias, Dark and Flat frames so all the frames were suboptimal. The solution was simple - make a new preset called 'Imaging Session' with the readout mode set to 'Image Quality' and place it at the top of the list!

If your camera control software allows for more than one download rate, try setting yours to the slowest rate available - perhaps you will share some of my joy!

 

Very tricky ..... great detective work there, Steve!

Adrian

[cgarry]

On 31/01/2016 at 18:20, opticalpath said:

I've hit the same problem.  It happens if you start a reply to a post using Quote, but then abort before submitting the reply. Even if you have entered no text it appears impossible to escape and you can't delete the '3 hours ago so and so  said:' bit of header text; the system retains your unsent skeleton reply and presents it every time you try to reply to something else!  Once you start a reply-quote, you have to either submit the reply, or actively delete it entirely; otherwise it will come back and haunt you forever!  I got the answer from Grant.  If you want to abort a reply-quote, you must actively delete ALL the text by hovering over the top left corner of the text box and click on the 'move' icon that appears. This highlights an outer box that includes ALL the text, which can then be deleted.

If you hold down the CTRL key and right-click on the quote box you are given the option to remove the quote in a pop-up dialogue.  Pretty simple when you know how but not obvious when you don't.

Cheers,
Chris

[opticalpath]

On ‎08‎/‎02‎/‎2016 at 15:21, cgarry said:

If you hold down the CTRL key and right-click on the quote box you are given the option to remove the quote in a pop-up dialogue.  Pretty simple when you know how but not obvious when you don't.

Cheers,
Chris

Ah, useful to know.  Thanks.

Adrian

[tony210]

Great thread- I have the same problem with my QSI 683 flats and hope Steve's download speed option solves it-never had an issue with my old Atik interestingly - best wishes Tony

[steppenwolf]

@tony210 I hope that I have good news to bring you! I have some empirical testing under my belt now and as the three deliberately hideously stretched single exposure images below show, I have resolved the issue and can repeat the experiment with the same result(s) each time. All three images have been Bias, Dark and Flat calibrated with calibration frames captured in 'Image Quality' readout mode (apart from the Flat frame in the third image) but the image with the bright corners at the right was captured in 'Fast' readout whereas the images with a flat background were captured in 'Image Quality' readout mode.

The problem is not so much to do with capturing the Flats in 'Fast' readout but capturing the Lights in the wrong mode!

Image Quality Lights + Image Quality Flats

Fast Lights + Image Quality Flats

Image Quality Lights + Fast Readout Flats

And just for the fun of it as it seems a shame to waste the test data, here's a cropped stack of 5 test frames:-

[opticalpath]

Good work, Steve.  Nice to get a clear cut answer.  Hope it points the way to solving Olly's problem too!

I never saw the issue on my 583wsg but, as I discovered last night, that's probably because I don't have the 'fast download' option available.  Even after updating to the latest driver, I only have 'Image quality' available: I think the extra options are in firmware not supported on the 500 series.

Adrian

 

[steppenwolf]

Quote

I think the extra options are in firmware not supported on the 500 series.

@opticalpath I can confirm that Fast readout is not supported at all in the 500 series - it was a much requested feature for use when focusing or plate solving where there is a quality v speed tradeoff. Using MaxIm DL on its own is fine but for some reason, CCD Commander seems to read the last used mode rather than defaulting to 'Image Quality' mode. 

I too hope that this helps to sort out Olly's issue - it is strange though the it is the Light data that takes the hit, the actual Flats don't appear to suffer when using Fast readout as my test above shows.  

[tony210]

Thanks Steve - seems the message is be careful how you readout/download subs with the 683-Tony

[opticalpath]

A little off topic, but may be of interest to anyone with a QSI 500/ 600 series camera, wondering about the mechanical shutter and how it works for short exposures (a potential issue for flats?), I got this info from Kevin Nelson in response to a question about shutter latency:

http://universalconstant.com/QSI_500-600_Shutter_Timing.pdf

The shutter has a slit and a wider 'gate' aperture in a rotating disk.  For exposures 0.03-0.10 sec. the narrow moving slit passes across the sensor to provide the exposure.  For 0.11-0.29 sec. it's done using the (moving) wider gate aperture on the rotating disk. For 0.3 sec and above, the wider gate is also used, but does a start-stop rotation rather than a continuously moving sweep.  All modes apparently are designed to illuminate the sensor evenly.  The different modes are relevant if you want to record accurate timings, because the latencies are different.

Adrian

[steppenwolf]

That's very interesting data, Adrian, thanks for posting.

[martin_h]

Ollie you say in an earlier post that Nebulosity gives you a Min and Max ADU reading.........If you go to View - Pixel Stats it well give a pop up box with min,max and average for the whole screen or where the cursor is positioned.... Just for future refrence

[ollypenrice]

An old thread but I now have the answer to my problem so I'll post it for anyone searching this issue.

The problem was Nebulosity. When I made a set of flats in AstroArt and applied them to my Nebulosity-captured lights the flats worked perfectly. I suspect that Nebulosity was not adequately flushing the chip between read outs. Harry Page said he'd encouraged the AA authors to build in more thorough flushing. This explanation may or may not be correct but there is no doubt that AA flats work when Neb ones didn't. One catch, though: the AA flats are vertically flipped relative to the Neb lights, but that's easy to fix by simply vertical-flipping the master flats.

Olly

[Astroscot2]

Olly is flushing automatic in AA ? Ive never seen an option unless I need to update to AA6?

[ollypenrice]

44 minutes ago, Astroscot2 said:

Olly is flushing automatic in AA ? Ive never seen an option unless I need to update to AA6?

I think it's automatic in all capture software but some may have different options for its extent outside any default setting.

Olly

[harry page]

Hi

I asked for 2 flushes to be installed in AA and this  sorted out my problems  , as you say it is not user alterable .

The ASCOM driver for sx cameras does have a setting for adjusting the amouts of flushes ( Many thanks to the mighty bret writter of the driver)  this is now what I use

with SGP

Regards

 

Harry

[sharkmelley]

I've never heard of this flushing.  I'm intrigued.  Can you explain what it is all about?

Mark

[harry page]

Hi

Here is the tech bit http://web.pdx.edu/~d4eb/ccd/RevScInstr_73_2002_2028.pdf

but effectivley flushing removes the previous image from the ccd chip , but if this is not done well some of the previous image ( charge ) remains and this affects the next image

you take and because flats have a lot of signal it very important to flush the camera well ( and or repeated times ).

Regards

 

Harry

[sharkmelley]

1 hour ago, harry page said:

Here is the tech bit http://web.pdx.edu/~d4eb/ccd/RevScInstr_73_2002_2028.pdf

but effectivley flushing removes the previous image from the ccd chip , but if this is not done well some of the previous image ( charge ) remains and this affects the next image

you take and because flats have a lot of signal it very important to flush the camera well ( and or repeated times ).

 

Interesting - thanks!

Mark