STT-8300 First light report
Posted 27 April 2013 - 05:01 AM
Posted 27 April 2013 - 05:53 AM
Since the topic of RBI of broader interest than purely with the STT-8300 cameras, shouldn't we start a separate topic so that it is easy to find should somebody be searching for RBI related information?
True, and I'm fine with your suggestion. However, I still have a few questions about how SBIG approaches RBI mitigation as it relates to user settable conditions for flood/flush/integrate. This ties in to the technical questions raised by Frank in a previous post. For example, does the predefined 1 second flash and single flush Matt spoke to accomplish the 100X full well level to ensure all traps are filled as Janesick (2001, pg. 664) recommends? If not, then (for me) this will still be a SBIG specific topic related to the implementation of changes that allow client software access to these default settings.
Posted 27 April 2013 - 06:55 AM
First off, I have never personally seen it on the hundreds (thousands?) of subs I've taken with my ST-8300M. Maybe it's there on some and I'm not sophisticated enough to spot it? Could well be.
My camera does not offer pre-flash to mitigate RBI.So, what do I do about it?
1/Run at minus 10C instead of minus 20? Even zero C?
2/Run at minus 20C but turn cooling off for a couple of minutes between subs? Perfectly feasible for long NB subs but not practical for LRGB subs of 5 minutes or so.
3/ Just ignore the whole thing until it actually bites me?
Even if my camera did offer pre-flash, after reading here, I'd be reluctant to use it. Raising the overall noise level, quite irregardless of how "uniformly" you do it, seems counter to what CCD imaging is supposed to be about.
Posted 27 April 2013 - 07:48 AM
I remain puzzled as I read through the thread as to what to do about RBI.<snip>
My questions were posed because the STT cameras implements enhanced cooling and RBI mitigation. Janesick (isbn:0819436984) details the relationship between temperature and RBI as well as the other things we have touched on here. So, I feel the implementation is important when I compare them to the accepted scientific data on the subject.
I hope my inquiries haven't prompted anyone to think they should fix something that isn't broken for them.
Posted 27 April 2013 - 12:10 PM
But if you did have a cold camera, then shorter exposures would reduce the impact of rbi if they kept stars from saturating that otherwise would have. In reality, though, you would probably be better off with longer exposures and a less cold camera.
A key point in all this is - if you don't have problems with rbi - then you don't have problems with rbi - and none of this, including pre-flash, matters. But people running cold cameras should be aware of rbi and know what to look for because it may be happening without them realizing it. And they can try the tests described in this thread.
Oh - and if you are asking simply if the process of reading the camera somehow clears the charge and dumps it - no. That's why you can take repeated darks after taking a single flat - and see the background level slowly going down in each dark - as the person from sbig measured.
Posted 28 April 2013 - 04:55 PM
I do want to post another STT8300M issue here. I also posted this at the Yahoo SBIG Group, so if you look in both places ignore this post [I am not sure how many people overlap].
I am concerned about calculating the right times for "sky limited images" with the STT8300m.
I have gone to the Starzona site:
That descibes the concept of sky limited exposures. Also has a calculator, unfortunate does not cover the STT8300M, though does cover the ST8300M.
In any case, in my light polluted universe for 600s exposures the get the horrible ADU sky readings of approximately 16000-20000 for L using M101 as a target. The readings for RGB are about 6700, 6000 & 5500. The good news is the center of M101 is at least 22000... at least I can see the center of M101...
In any case, It appears the gain of the 8300M is 0.37e/ADU and Read Noise is < 10e- rms. [manual]
Now if I plug my values into the Starzona calculator I get 1.15 for L, 3.46 for R,3.87 for G and 4.22 for B.
If I try to do the calculations manually from the equations I am not sure but I think I get similar results ... 79.3s for L [I believe].
Are these the maximum lengths for sky limited exposures I can expect for each filter? Is the downside that if I expose longer than these the LP will overwhelm the readable signal?
When I look at the 600s images they sure seem to have a lot of noise in the "dark" areas... [yuck].... I guess I better focus on narrow band targets.... I am currently running an experiment using both sets of settings [600s and the shorter ones] on the same nights.
Thanks for any decyphering possible.
Posted 29 April 2013 - 12:31 AM
Posted 29 April 2013 - 04:18 AM
On the other hand, 1 minute sounds about right for an L exposure with light pollution. But just because the "optimal" exposure is 1 minute doesn't mean you can't go longer - to 5 or 10 - as long as the image doesn't saturate features too much. But those longer exposures won't help reduce noise much because your main source of noise is the sky itself - unless you go to a dark site. The only way to improve SNR in light pollution is just to accumulate a long total exposure time.
And if you are sky limited then you don't need to run the camera too cool, and you don't need to worry about rbi - etc.
Posted 29 April 2013 - 04:53 AM
Posted 29 April 2013 - 09:00 AM
I think I am going to check with SBIG to see if my math is correct and about the technical details of the camera.
Finally, I know Hilmi has said he is tired of hearing about complaints about light polution when he has to deal with sand storms, but here is an image of what I am dealing with. There was no moon when this was taken.
Posted 29 April 2013 - 09:07 AM
Posted 29 April 2013 - 10:07 AM
Posted 29 April 2013 - 11:56 AM
i wonder if your reducer spacing is right. is it normal to have such strong vignetting with the C8 and celestron reducer?
I am afraid that is what you get. We also get flares at times from stars in the periphery. I guess eventually a new scope is the solution...
If I take off the reducer the FOV gets small, makes guiding harder and the f goes up to 10.0.....
Any ideas if my calculations above are OK?
I asked the guys at SBIG for a sanity check and they pretty mcuh said I should expose to the max... 600s is fine as long as the center of the object is not blown out.
Posted 29 April 2013 - 12:14 PM
For some reason the subject of how long to shoot each frame seems to come up a lot and cause people a lot of worry.
When I got my ST-2000XM I took some pictures at various exposures varying from about 3min to about 5 or 6min. I found that for what I was shooting going longer than 5 or 6min didn't seem to help much, so I stuck with that. At least that's what I tell myself. Probably what happened was that I found nothing really wrong with going for 5min and it's a convenient amount of time, and I took a lot of 5min darks so I just lazily stuck with it.
Later I found three articles about calculating "optimal" subexposure times.
The first is the one that most of the calculators on the web are based on:
The second is this one by Craig Stark:
The third is this much more complicated one by Charles Anstey:
Note that the last two both point to doing longer exposures to improve the SNR of the object that you are trying to capture.
The general rule is to get some reasonable amount of signal in each frame and then shoot as many frames as you can. Each frame you stack averages out the noise a bit more. This is the real reason to use image stacking, btw. It's not so much to get more signal. It's more to average out the noise so you can see the signal better.
The idea behind the Smith paper is that under the assumption that sky noise and read noise are the dominant contributors to what you are putting on the CCD, taking exposures that are longer than it takes for to capture a lot of sky noise is pointless. The later two papers add more possible tradeoffs.
But, the easiest thing to do is to just try a few different exposures and see where you get to diminishing returns and then just go with that.
Posted 30 April 2013 - 10:07 PM
Posted 02 May 2013 - 02:14 AM
I suspect corrupt firmware, and anything could have caused it, from static electricity to high levels of humidity in the air messing with the electronics. I don't really think this is an indication of any QC issue. But just because it's not a QC issue, doesn't make me a happy man. I now have to ship a very heavy camera at a high cost to the US for repair
I wonder if there is something that can be done at home, such as some software that allows you to flash the new firmware even if the camera is bricked.
Posted 02 May 2013 - 05:40 AM
The instruction from Jan at SBIG was to install the new CCDOPS or installer app too (to make sure all the files make it to your computer).
Posted 02 May 2013 - 07:25 AM
Posted 02 May 2013 - 04:48 PM
Sorry to hear. Mine is finally working up to expectations, so there is hope.
Posted 02 May 2013 - 04:56 PM
Contact us directly. We may be able to give you something that can help resolve this.
Posted 06 May 2013 - 10:53 AM
I was trying to figure this out too, I am going to a dark sky location at high altitude in a few days time. I put the details of the location I was going to in Skytools 3 and it keeps on telling me the optimal exposure is 1 minute long, this doesn't sound right to me. I would barely be able to capture any data with 1 minute exposures even from a dark site.
It is important to make sure you have everything set up properly in SkyTools, particularly your level of light pollution.
Remember that you are supposed to be stacking the images, so it doesn't matter what each individual image looks like. What matters is the end result. That said, the estimated optimum sub exposure time for your optical system + conditions is probably not a critical factor in your particular case. The algorithm finds the mathematical "optimum" time but it doesn't currently say anything about how relevant it is. It may well be that it makes no practical difference if it is one minute, or ten. In that case you should use whatever sub exposure time is most practical. So how do you know if the sub exposure time is relevant? Use the Exposure Calculator! The Exposure Calculator is a very powerful tool for investigating just this sort of thing. It is not designed to give simple one-line answers. It is designed as a tool of exploration. To find out if the sub exposure time matters, select a target and night and then vary the sub exposure time. Compare the estimates of the final SNR of the stacked images. If there is very little difference in SNR, then the the sub exposure isn't critical. So use whatever works best from a practical standpoint. Always remember, if the target or observing conditions change, then the result may change as well. There is no universal answer, which is why the Exposure Calculator is so useful. I suggest using this tool to investigate how your optical system works with different kinds of targets under different amounts of sky brightness. You may be surprised how moonlight does not affect your results, or how important the altitude of the object is, etc.
P.S. People should consider bringing this sort of questions directly to me, or posting them to the SkyTools group. I don't always see the posts here, and it may take me some time to notice.
Posted 19 June 2013 - 01:50 AM
I am looking forward to getting my camera back.
Posted 21 June 2013 - 04:40 PM