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SX 35/SGP "Double Exposures"

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#1 Alex McConahay

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Posted 14 February 2018 - 01:04 PM

I recently took delivery of an SX35. This is my first camera without a shutter. And it is doing some things I consider weird.

 

When I am taking framing pictures in SGP, I am getting what look like trailed/double images. I have never had this before. Specifically, say I am using the "Centering" function in SGP. It takes a picture, figures where it is, and how far it has to move, moves, and takes another picture. That second picture almost always is a double exposure (with streaks connecting the two "stars" which are really one). It kinda works (does the plate solving somehow), and gets me to where I need to go. But it is disturbing to see. What is happening here?

 

I have theorized that for some reason, since there is no shutter, the camera is actually picking up photons as it slews. Seems to me that at the beginning of each exposure, it should somehow flush the system (zero it out). But maybe it is not doing so.

 

Alternatively, SGP is starting the exposure before the slew is finished. Of course this is possible, but I have never had the problem before with my QSI.

 

I also get really ugly "Flats." Maybe this is related somehow.

 

Anybody have ideas?

 

Alex

 



#2 buckeyestargazer

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Posted 14 February 2018 - 01:19 PM

For the sake of elimination increase your mount settle time and see if that solves the problem.

#3 Goofi

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Posted 14 February 2018 - 01:35 PM

Alex, I was going to suggest what Joel did ... check your mount settling time. It sounds like your mount is still slewing while the 2nd image is started.

 

As for the flats ... what do you mean by ugly?



#4 buckeyestargazer

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Posted 14 February 2018 - 01:47 PM

Yeah, can you post a flat for us to see?



#5 Alex McConahay

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Posted 14 February 2018 - 02:17 PM

Thanks for the suggestion, but "Settle Time" does not seem to have anything to do with it. My QSI had two second settle time and never had such a "double" exposure. I've increased it all the way to 10 seconds, and the SX35 has it. 

 

Here is a flat. Superstretched in PI. And, no, it does not adequately flat out in calibration. 

 

(Note, I have two problems.....the double exposures, and the flats. I have no pics of the double exposures.)

 

Alex

 

 

 

Attached Thumbnails

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#6 Alex McConahay

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Posted 14 February 2018 - 06:13 PM

So, I'm poking around trying to find something to explain both my phenomena.......

 

Could this be some form of RBI?  Residual Bulk IMage. I've never really dealt with it before. But I have heard of it.

 

What does a "CCD Flush" do? Seems I have it set to "0" in the ASCOM driver. Maybe I need to flush something before I take a picture.....

 

Alex



#7 Goofi

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Posted 14 February 2018 - 06:20 PM

Alex, RBI might make sense ... basically it's a ghost of the previous image impacting the next.  I'd thought cameras susceptible to it included RBI preflash to clear the problem automatically. You might have to set it in software.  That would be your CCD flush option.

 

There's a chance this is also the problem with your flats - residual data from the previous flat impacting the next one. I'd think you can check this easily by looking at the first flat taken ... .there shouldn't be an RBI problem with it. So compare the 1st flat to the master ... if there's a large difference it could be RBI.



#8 Alex McConahay

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Posted 14 February 2018 - 08:04 PM

I just tried updating the ASCOM driver. And I messed with the "additional CCD flush" setting. No difference. 

 

I guess I shall see what I see. 

 

Alex



#9 Goofi

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Posted 15 February 2018 - 11:37 AM

Have you contacted Starlight Express about this?



#10 Alex McConahay

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Posted 15 February 2018 - 12:52 PM

I've contacted them about the ugly flats. They say it is normal, and have told me that it calibrates out. That has not been my experience.

 

I have not contacted them about the "Double exposure" issue, thinking it was somehow SGP triggering an exposure before the scope had come to rest. However, as I continued to have the problem, even after setting the settling parameter at ten seconds, and watching that it really was waiting appropriately, I started to pursue some other possible causes, including not having a proper flush of the chip before starting the real exposure. I'm pretty much at a loss to explain the problem.

 

The camera is being shipped back to the vendor today. I certainly understand learning curve with new equipment,  but I have spent enough time on this (Including comparing my camera's performance to my buddy's identical camera). Time to let it go and let my vendor make me happy. 

​Alex



#11 jhayes_tucson

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Posted 15 February 2018 - 01:18 PM

Alex,

What temperature are you running the sensor?  You probably won't see strong RBI effects much above about -20C.  You can tell if the "double image" is due to RBI by blinking through your stack of subs in the same order that you took them.  If the "double" image is in the same place as it was from the previous exposure, then it's due to RBI.  Your flat pattern slightly resembles an RBI pattern--but not quite.  Take some darks and look at them.  If that same pattern exists, then it's due to RBI; otherwise, you've got something else going on.

 

If you see RBI effects, you've got to either raise the temperature of the sensor or use RBI pre-flash to fill the traps in the bulk material.  In that case, you'll have to create a new dark and bias library as well.  You can create a new flat library too but that isn't strictly required.

 

John


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#12 Alex McConahay

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Posted 15 February 2018 - 03:31 PM

I generally run at -20. From what I have looked up about RBI, it is a "ghost" image. What I am getting are genuine double exposures with some trailing in between, connecting one version of the star to another. Not a ghost image.  I have no idea how PlateSolve2 figures which stars are which......I cannot really see it in my regular light frames. It was only happening during successive plate solve exposures as the solver and SGP were centering. 

 

I have not noticed the pattern in the darks. 

 

By the way that pattern in the flat I posted persisted regardless of filter (tried five filters--LRGBHa AND NO filter.....all showed the pattern) , power sources (four different power sources, including the supplied one), light sources (Sky flats, LED Panel, Sky flats with milk-Lucite panel in front of scope). So, it has to be somewhere in the chip/camera or how the software is handling the chip/camera.

 

At any rate, the camera has been shipped. We'll see what happens with the exchange, or whatever. Meanwhile, it is time for the QSI to step back into the job.

 

Alex



#13 Goofi

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Posted 15 February 2018 - 04:37 PM

Good luck with this, Alex ...and please, keep us informed!



#14 R Botero

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Posted 16 February 2018 - 02:42 AM

Have you tried taking a picture with SX’s native software? Try and do that if not; of a bright object - several are well placed right now - and calibrate it with your current flats. That will tell you if the problem is your camera’s or software related, ie SGP. 

Good luck!

Roberto



#15 Alex McConahay

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Posted 16 February 2018 - 11:14 AM

Where did you fine the software. I went looking, and could not find the software they said they shipped with it. 

 

The software shipped with the system was two to three years old. (It had no Windows 10 software on it, for instance.)  I went to the web and found more recent stuff. I never did find a "native program."

 

Alex


Edited by Alex McConahay, 16 February 2018 - 11:18 AM.



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