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jerryyyyy
Pooh-Bah


Reged: 10/06/11

Loc: Stanford, California
Re: STT-8300 First light report new [Re: mmalik]
      #5814936 - 04/22/13 10:18 AM

Quote:

Quote:

I have to say that on the processing side now I am in love with PixInsight.




Good to hear. I had put together some PixInsight instructions... for my own learning sake; please review and see what could be improved upon given your new found love. Thx




Wow! Quite and effort! But I know why you do it. I got one image processed correrectly and it took 87 steps... unfortunately not written down.

I searched and could not find that you have looked at using BatchPrepocessing to stack RGBL images... if I could get this to work consistently, I would be golden. I (and others) have had problems moving files over from CCDStacker to PI.

BTW, my complements on using SkyDrive to host the pdf.

Finally, do not want to hyjack this thread on the STT8300, but one tiny STT note. There was a post on Yahoo this AM about frosty sensors at -30DEG. Not hurt me, hope others are OK on this. Definately better images for me at -30 compared to -20.


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jerryyyyy
Pooh-Bah


Reged: 10/06/11

Loc: Stanford, California
Re: STT-8300 First light report new [Re: LoveChina61]
      #5814949 - 04/22/13 10:24 AM

Quote:

NICE image! Which object is that by the way?




The galaxy is NGC2903 in Leo. http://en.wikipedia.org/wiki/NGC_2903 ..... There is more there with Ultraviolet filters. This image is a total of about 3 hours exposure.


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MattThomas
Vendor (SBIG)


Reged: 07/28/06

Re: STT-8300 First light report new [Re: Hilmi]
      #5820292 - 04/24/13 05:20 PM

I just want to clear up some of the concerns posted here regarding RBI on the STT cameras (and STX/STXL as they act the same).

The RBI readout mode is enabled via a non-volatile selection in the camera flash memory. Once enabled, the RBI flashing is done on every exposure.

The RBI mode on these cameras adds only about 1 second to the download process. This does not impact the performance of the cameras significantly. Thus the need to enable and disable this feature for Focus or Plate Solves is significantly reduced. (Especially compared to other manufacturer's cameras I have tested that take up to 120 seconds to download an image when RBI mode is enabled.)

Because of the minimum impact on the image download, it was never a priority to have the option be easy to turn on and off. Enable it if you want to use it and then don't worry about it anymore.

However, just to reiterate as I always do, the RBI Pre-Flash adds noise to your image. This reduces the dynamic range possible out of the sensor - especially if you are imaging very faint targets that are not sky background limited. So use with caution.

Thank you.


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Chuck Faranda
professor emeritus
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Reged: 03/31/07

Loc: Florida
Re: STT-8300 First light report new [Re: MattThomas]
      #5820747 - 04/24/13 08:20 PM

Quote:

<SNIP>
However, just to reiterate as I always do, the RBI Pre-Flash adds noise to your image. This reduces the dynamic range possible out of the sensor - especially if you are imaging very faint targets that are not sky background limited. So use with caution.

Thank you.




Matt,

What type of noise you are talking about? I have been using RBI flood/flush/integrate for several years without seeing increases in 'noise' in subsequent frames. Thanks.


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MattThomas
Vendor (SBIG)


Reged: 07/28/06

Re: STT-8300 First light report new [Re: Chuck Faranda]
      #5821120 - 04/25/13 12:03 AM

Quote:

Quote:

<SNIP>
However, just to reiterate as I always do, the RBI Pre-Flash adds noise to your image. This reduces the dynamic range possible out of the sensor - especially if you are imaging very faint targets that are not sky background limited. So use with caution.

Thank you.




Matt,

What type of noise you are talking about? I have been using RBI flood/flush/integrate for several years without seeing increases in 'noise' in subsequent frames. Thanks.




Chuck,

Measure your dark current with RBI enabled.

Warm up your camera, turn off RBI, then cool it back down again.

Measure dark current again. It is much lower with RBI disabled.

Thank you,


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Chuck Faranda
professor emeritus
****

Reged: 03/31/07

Loc: Florida
Re: STT-8300 First light report new [Re: MattThomas]
      #5821350 - 04/25/13 06:50 AM

Quote:

Quote:

Quote:

<SNIP>
However, just to reiterate as I always do, the RBI Pre-Flash adds noise to your image. This reduces the dynamic range possible out of the sensor - especially if you are imaging very faint targets that are not sky background limited. So use with caution.

Thank you.




Matt,

What type of noise you are talking about? I have been using RBI flood/flush/integrate for several years without seeing increases in 'noise' in subsequent frames. Thanks.




Chuck,

Measure your dark current with RBI enabled.

Warm up your camera, turn off RBI, then cool it back down again.

Measure dark current again. It is much lower with RBI disabled.

Thank you,




I will perform your prescribed test on all my RBI flood capable cameras and report the findings. Regardless of the out come, increased dark current is better than ghosts from RBI in my view.

Thanks Matt


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freestar8n
Post Laureate
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Reged: 10/12/07

Re: STT-8300 First light report new [Re: MattThomas]
      #5821375 - 04/25/13 07:15 AM

Quote:

Measure dark current again. It is much lower with RBI disabled.




Wouldn't this take the form of an effective increase in bias noise rather than dark current? There would be a higher baseline noise from read noise and (uniform) rbi shot noise from the pre-flood - but the dark current would add noise on top of that at the same rate - wouldn't it? Or are you saying the dark current really is higher with rbi enabled?

Frank


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Chuck Faranda
professor emeritus
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Reged: 03/31/07

Loc: Florida
Re: STT-8300 First light report new [Re: freestar8n]
      #5821517 - 04/25/13 09:08 AM

Quote:

Quote:

Measure dark current again. It is much lower with RBI disabled.




Wouldn't this take the form of an effective increase in bias noise rather than dark current? There would be a higher baseline noise from read noise and (uniform) rbi shot noise from the pre-flood - but the dark current would add noise on top of that at the same rate - wouldn't it? Or are you saying the dark current really is higher with rbi enabled?

Frank




Yes, and ample cooling will offset the extra charge from flushing the traps. I have reread the emperical data offered on the NASA site and others. A web search on the subject will reveal significant work in this area.

So, the good news is that the STT has RBI to flood/flush/integrate and enhanced cooling >-50 T to minimize the extra charge from the traps.


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freestar8n
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Reged: 10/12/07

Re: STT-8300 First light report new [Re: Chuck Faranda]
      #5821950 - 04/25/13 12:22 PM

I expect that the charge from rbi is emitted as a current with a changing rate that decays more slowly at cold temperatures. So at higher temperatures it would be mostly drained early in an exposure - and be "bias-like" - while at colder temperatures it might be leaking at a nearly steady but small rate.

The whole point of low temperature is to reduce the noise by lowering the dark current, but if you need to flood to avoid rbi and you get an increased noise as a result - then it may still be beneficial, but it would be good to have specs on all these parameters and how they relate to temperature so you can quantify the noise contributions and assess the tradeoffs.

Frank


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MattThomas
Vendor (SBIG)


Reged: 07/28/06

Re: STT-8300 First light report new [Re: Chuck Faranda]
      #5822033 - 04/25/13 12:55 PM

Quote:

Quote:

Quote:

Measure dark current again. It is much lower with RBI disabled.




Wouldn't this take the form of an effective increase in bias noise rather than dark current? There would be a higher baseline noise from read noise and (uniform) rbi shot noise from the pre-flood - but the dark current would add noise on top of that at the same rate - wouldn't it? Or are you saying the dark current really is higher with rbi enabled?

Frank




Yes, and ample cooling will offset the extra charge from flushing the traps. I have reread the emperical data offered on the NASA site and others. A web search on the subject will reveal significant work in this area.

So, the good news is that the STT has RBI to flood/flush/integrate and enhanced cooling >-50 T to minimize the extra charge from the traps.




Actually, no. A bias is too short to see increased noise from the RBI pre-flash.

Remember that the root problem is that the substrate traps charge and slowly leaks it out into the active pixels. The lower the temperature, the slower the leakage.

So, when you have a bright object in the frame the substrate traps the charge from the object. Over the course of the next long image that charge in the substrate slowly leaks out into the active image area resulting in a ghost image.

With the pre-flash, you are saturating the substrate to mask the presence of any charge from a bright object. So now you essentially have a ghost image that covers the entire CCD. Over the course of the next long exposure that charge in the substrate will leak into the active pixels - resulting in a ghost image over the entire CCD. This appears like increased dark current.

So the only way to measure the increase in noise is to look at a long exposure - as if you were measuring dark current. The bias frame will not have much leakage from the substrate - especially if the CCD is very cold.

When testing dark current in our production cameras, we can easily see this effect by cooling the CCD, exposing the CCD to light, then closing the shutter and measuring dark current. The dark current is much higher (sometimes >10x higher) than normal as a result of the saturated substrate leaking into the image.

The best way to clear RBI without impacting the noise is to warm the CCD after the offending image.

I hope this helps.


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Chuck Faranda
professor emeritus
****

Reged: 03/31/07

Loc: Florida
Re: STT-8300 First light report new [Re: MattThomas]
      #5822162 - 04/25/13 01:26 PM

Quote:

Quote:

Quote:

Quote:

Measure dark current again. It is much lower with RBI disabled.




Wouldn't this take the form of an effective increase in bias noise rather than dark current? There would be a higher baseline noise from read noise and (uniform) rbi shot noise from the pre-flood - but the dark current would add noise on top of that at the same rate - wouldn't it? Or are you saying the dark current really is higher with rbi enabled?

Frank




Yes, and ample cooling will offset the extra charge from flushing the traps. I have reread the emperical data offered on the NASA site and others. A web search on the subject will reveal significant work in this area.

So, the good news is that the STT has RBI to flood/flush/integrate and enhanced cooling >-50 T to minimize the extra charge from the traps.




Actually, no. A bias is too short to see increased noise from the RBI pre-flash.

Remember that the root problem is that the substrate traps charge and slowly leaks it out into the active pixels. The lower the temperature, the slower the leakage.

So, when you have a bright object in the frame the substrate traps the charge from the object. Over the course of the next long image that charge in the substrate slowly leaks out into the active image area resulting in a ghost image.

With the pre-flash, you are saturating the substrate to mask the presence of any charge from a bright object. So now you essentially have a ghost image that covers the entire CCD. Over the course of the next long exposure that charge in the substrate will leak into the active pixels - resulting in a ghost image over the entire CCD. This appears like increased dark current.

So the only way to measure the increase in noise is to look at a long exposure - as if you were measuring dark current. The bias frame will not have much leakage from the substrate - especially if the CCD is very cold.

When testing dark current in our production cameras, we can easily see this effect by cooling the CCD, exposing the CCD to light, then closing the shutter and measuring dark current. The dark current is much higher (sometimes >10x higher) than normal as a result of the saturated substrate leaking into the image.

The best way to clear RBI without impacting the noise is to warm the CCD after the offending image.

I hope this helps.




Matt,

Are you saying the noise does not come from charge being detrapped from the traps after the flooding?

Should the noise from the de-trapping be time dependent since it is a relic passed to the following image? To follow what you stated previously, the noise is increased in subsequent images from the flood/flush. If it is the additional dark shot noise associated with trap leakage then wouldn't it show in bias frames and all others too? In any event, for me this is still far better than dealing with the residual image of the stars and the dark fixed patterns caused by the non-uniform trap distribution if no flood/flush is used.

Edited by Chuck Faranda (04/25/13 02:03 PM)


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freestar8n
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Reged: 10/12/07

Re: STT-8300 First light report new [Re: MattThomas]
      #5822337 - 04/25/13 02:42 PM

My second note describes what I mean by "bias-like." If the temperature is high enough that most of the rbi charge is released in one minute, then for exposures of 5, 10, 20 minutes - that charge would not correspond to a steady dark current, but a burst of current (and noise) that does not increase much after that initial burst - which makes it "bias-like" in that the noise contribution doesn't increase much with exposure time.

If the temperature is low enough then the rbi current would be more steady - but it would still be dropping somewhat over time.

I don't think ccd's with rbi pre-flash and low temperature cooling tend to spec. these things - e.g. the 1/e timescale of the pre-flash current decay. Without specs for these things, it's hard to assess the benefits of pre-flash as a function of temperature and exposure time.

Frank


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Alph
Carpal Tunnel


Reged: 11/23/06

Loc: Melmac
Re: STT-8300 First light report new [Re: Chuck Faranda]
      #5822444 - 04/25/13 03:40 PM

Quote:

In any event, for me this is still far better than dealing with the residual image of the stars and the dark fixed patterns caused by the non-uniform trap distribution if no flood/flush is used.



It has been said multiple times that there is very little benefit to cooling the KAF-8300 below -20C. Perhaps if you kept the KAF-8300 at -20C or -15C then you would not have to deal with RBI and still have very low dark current.


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Chuck Faranda
professor emeritus
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Reged: 03/31/07

Loc: Florida
Re: STT-8300 First light report new [Re: Alph]
      #5822569 - 04/25/13 04:48 PM

Quote:

Quote:

In any event, for me this is still far better than dealing with the residual image of the stars and the dark fixed patterns caused by the non-uniform trap distribution if no flood/flush is used.



It has been said multiple times that there is very little benefit to cooling the KAF-8300 below -20C. Perhaps if you kept the KAF-8300 at -20C or -15C then you would not have to deal with RBI and still have very low dark current.




Cooling most certainly reduces the charge leakage created by RBI management, and subsequent total dark current charge. So, the colder the better regardless of who says otherwise. However, I am open to see the data they used to leap to the conclusion so often repeated.

For me, RBI is a must to avoid ‘ghosting’ artifacts (I know the artists out there can work their Photoshop magic to color them out). Therefore, to not have to worry about dark current + RBI mitigation trap leakage charge overtaking read noise I look for camera like the STT that boast >50+ C DT cooling.

Should anyone be interested, the NASA site, Google, and http://astro.cornell.edu/~mmhedman/papers_published/ISS_calibration_PSS.pdf have a wealth of articles on the subject filled with data most of which are far too complex for me to grasp.

Edited by Chuck Faranda (04/25/13 04:49 PM)


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Alph
Carpal Tunnel


Reged: 11/23/06

Loc: Melmac
Re: STT-8300 First light report new [Re: Chuck Faranda]
      #5822666 - 04/25/13 05:24 PM

Quote:

So, the colder the better regardless of who says otherwise.



Not if you want to avoid RBI. RBI is weaker and dissipates faster at higher temperatures. Normally RBI is not an issue with the KAF-8300 unless you are over-cooling and over-exposing.


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Peter in Reno
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Reged: 07/15/08

Loc: Reno, NV
Re: STT-8300 First light report new [Re: Alph]
      #5822693 - 04/25/13 05:38 PM

You can eliminate RBI by simply inserting at least 5-10 seconds delay in between subs. Many image capture software allows you to insert delay in between subs. It's simple and free. No need to pay extra cost for a camera to remove RBI and add noise.

Peter


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MattThomas
Vendor (SBIG)


Reged: 07/28/06

Re: STT-8300 First light report new [Re: Peter in Reno]
      #5822718 - 04/25/13 05:57 PM

Lots to reply to...

Chuck:
Quote:

Are you saying the noise does not come from charge being detrapped from the traps after the flooding?



No - that isn't what I'm saying. The but the "detrapping" is a function of time. It can take more than 5-10 minutes at cold temperature for the substrate to fully purge itself of the flooding. Even longer for some CCDs. (Note that the KAF-9000 CCD takes minutes to clear the RBI even at room temperature!!!) This "detrapping" will appear as added unwanted signal (a.k.a. "noise") in your image. In fact you may even get a ghost image of some of the surface treatment (e.g. polishing) of the silicon.

Quote:

If it is the additional dark shot noise associated with trap leakage then wouldn't it show in bias frames and all others too?



It is purely time related. At cold temperatures, a short (bias) exposure will not experience much leakage from the substrate because the exposure isn't long enough to accumulate that charge from the substrate. The active pixels are flushed, then the exposure performed, then the active pixels are read out. This period leaves very little time for the substrate to affect the image. Thus there is no real contribution from the RBI problem.

Frank:
Quote:

My second note describes what I mean by "bias-like."



You posted after I started my reply. I understand what you are suggesting - but even at warm temperatures with some CCDs the leakage from the substrate spans many minutes (e.g. KAF-9000), so I think it is a mistake to think of it as a bias like effect.

Quote:

Without specs for these things, it's hard to assess the benefits of pre-flash as a function of temperature and exposure time.



Correct - there is no spec for RBI from the CCD manufacturers, so we really cannot make any spec related to this artifact.

Peter:
Quote:

You can eliminate RBI by simply putting at least 5-10 seconds delay in between subs. Many image capture software allows you to insert delay in between subs. It's simple and free. No need to pay extra cost for a camera to remove RBI and add noise.



5-10 seconds is usually not enough. As I mentioned before, if time is not an issue warming the CCD and cooling it again is the best approach to deal with RBI.

If anyone likes, I can provide some real measurements of dark current before flooding and after flooding. Just let me know.

Thank you.


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Chuck Faranda
professor emeritus
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Reged: 03/31/07

Loc: Florida
Re: STT-8300 First light report new [Re: Peter in Reno]
      #5822725 - 04/25/13 06:06 PM

Quote:

You can eliminate RBI by simply inserting at least 5-10 seconds delay in between subs. Many image capture software allows you to insert delay in between subs. It's simple and free. No need to pay extra cost for a camera to remove RBI and add noise.

Peter




Which sensor, and set temp Peter? The KAF-16803 or KAF-9000 have taken hours to totally dissipate the charge even when kept at a sweltering -10 temp!


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Chuck Faranda
professor emeritus
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Reged: 03/31/07

Loc: Florida
Re: STT-8300 First light report new [Re: MattThomas]
      #5822760 - 04/25/13 06:31 PM

Thanks for the response Matt.

Obviously, for some RBI is not an issue, for others the need for 30 minute NB subs creates totally different rules. I will continue to use the welcomed new RBI mitigation and enhanced cooling of the STT (kudos SBIG!) to my best advantage. Moreover, I continue to glean info you and other reliable sources. Indeed, there are volumes of published, peer reviewed, articles and empirical data that should give me a better understanding.


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pfile
Post Laureate


Reged: 06/14/09

Re: STT-8300 First light report new [Re: Chuck Faranda]
      #5822793 - 04/25/13 06:49 PM

does anyone have any examples of what an RBI-spoiled sub looks like? the other night i did a bunch of 30 minute Ha subs with an STT-8300M @ -30C and there's nothing obvious to me that something could be wrong. maybe the target was not bright enough to cause this problem?

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