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dawziecat
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Re: A used STL-11000? Still on the fence. new [Re: Jared]
      #5993492 - 07/27/13 07:23 PM

Thanks all. Especially to Mike for bringing up the relatively poor QE. It was something else I needed to investigate before commiting to the camera.

Floyd:
It this camera has more than a mere handful of hours on it, I'd be surprised!

It's decided. I'm going to buy it!

I have more gear about than any guy without a mount I know!

Edited by dawziecat (07/27/13 07:34 PM)


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blueman
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Re: A used STL-11000? Still on the fence. new [Re: dawziecat]
      #5993779 - 07/27/13 10:33 PM

Quote:

Thanks all. Especially to Mike for bringing up the relatively poor QE. It was something else I needed to investigate before commiting to the camera.

Floyd:
It this camera has more than a mere handful of hours on it, I'd be surprised!

It's decided. I'm going to buy it!


Like I said, a barely used camera that is well discounted can be a good deal.
Blueman

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Rick J
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Re: A used STL-11000? Still on the fence. new [Re: blueman]
      #5993940 - 07/28/13 12:08 AM

My 11K has been used every clear night all night for 7 years now. Yes there's a few changes, especially with more hot partial columns. But all vanish with proper calibration, even without dither which would (if I took enough frames) help even more. At least with my camera I don't see those many thousands of hours hurting the final image at all. I keep expecting the cooling fan to die. I've gone through three of them on the imaging computer. Apparently SBIG uses a really high quality bearing. Unfortunately its been getting a lot of rest this past year with the rotten weather

Rick


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Alph
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Re: A used STL-11000? Still on the fence. [Re: blueman]
      #5994007 - 07/28/13 01:24 AM

Quote:

Like I said, a barely used camera that is well discounted can be a good deal.
Blueman




Every CCD ages regardless of whether it used or not. After all the dark current always accumulates unless you store the CCD at -100C.


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blueman
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Re: A used STL-11000? Still on the fence. new [Re: Alph]
      #5994086 - 07/28/13 02:45 AM

Quote:

Quote:

Like I said, a barely used camera that is well discounted can be a good deal.
Blueman




Every CCD ages regardless of whether it used or not. After all the dark current always accumulates unless you store the CCD at -100C.



That is true too. What I was mentioning was how most all chips get more hot pixels and column defects may also increase with hours of use.
Not to mention of course, wear and tear on the plugs, fan and TEC cooler system.
Blueman


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freestar8n
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Re: A used STL-11000? Still on the fence. new [Re: dawziecat]
      #5994373 - 07/28/13 09:30 AM

If you have two identically sized sensors at the same price and one has higher QE than the other - the higher QE is obviously the one to pick. But if you are comparing different sized sensors at different prices with different QE's and different pixel sizes - there are many trade-offs involved and it sounds like you made a sensible choice since you want a big detector at low price.

There is nothing inherently low QE about interline or CMOS because the Sony 694 is interline and it has high QE, and the Aptina CMOS sensors also have high QE - but they both have small pixels and only come in small sizes. Although a small sensor with high QE will capture more photons per unit area than a bigger one with lower QE, if you find yourself imaging an object that requires a 4x mosaic with the small, high QE sensor vs. a single image with the big, low QE sensor, your actual time to image will be less with the low QE sensor. So a lot depends on your imaging system and what objects you intend to capture.

As for ageing - the dark current and number of hot pixels does tend to increase over time - but that is more dependent on terrestrial cosmic rays than usage or what temperature it is stored at. Although an unused sensor will "accumulate dark current" over time - it will just saturate and have no impact on performance the next time it is used. But there will be accumulated damage from terrestrial radiation. So you might want to avoid buying from someone who lives at the top of a mountain. Also, I have seen studies showing that the defect rate increases with smaller pixels - so your relatively large pixels help there also.

Anyway - have fun with it - and when you image a big object just think how much time you are saving by not doing a 4x mosaic.

Frank


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dawziecat
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Re: A used STL-11000? Still on the fence. new [Re: freestar8n]
      #5994525 - 07/28/13 11:06 AM

Quote:

So you might want to avoid buying from someone who lives at the top of a mountain.
Frank




The camera has spent its life at sea level.

Seller is vacationing and I will not get my hands on the camera for a week or so. But the deal is done.

Now, if only A-P would get to work and start shipping the 1100 mounts, I could make some progress!


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Alph
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Re: A used STL-11000? Still on the fence. new [Re: freestar8n]
      #5994985 - 07/28/13 03:43 PM

Quote:

that is more dependent on terrestrial cosmic rays



There is more at play than just cosmic rays. Storing a CCD at low temperatures (and protecting it from cosmic rays) will definitely help to slow down aging.


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Alph
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Re: A used STL-11000? Still on the fence. new [Re: dawziecat]
      #5994994 - 07/28/13 03:48 PM

Quote:

But the deal is done.



Did you request dark and bias frames from the seller? I would not buy an old camera (used or not) without evaluating it first.

I would also request the S/N and would check with SBIG if they have original dark and bias frames. QSI does it.

Edited by Alph (07/28/13 03:59 PM)


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freestar8n
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Re: A used STL-11000? Still on the fence. new [Re: Alph]
      #5995001 - 07/28/13 03:54 PM

Reference? Preferably journal paper?

It's not like a pixel just keeps on accumulating dark current electrons and then they start zapping the thing. I have never seen an explanation for the increase of dark current being caused by accumulated charge - but a good reference would change my view.

There are many references that tie it to cosmic rays - and an increased impact caused by usage in aircraft and spacecraft - with more cosmic ray exposure.

I was mainly joking about buying from someone on top of a mountain - but presumably it would have some impact.

Frank


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dawziecat
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Re: A used STL-11000? Still on the fence. new [Re: freestar8n]
      #6085626 - 09/17/13 10:04 AM Attachment (13 downloads)

I'm back!

The camera has been acquired and given a very brief workout when a friend visited and we were able to use his mount. I am still mountless and A-P is now saying my AP1100 will ship in November.

I quiried SBIG and they confirm the camera has an X class chip and was manufactured by SBIG in Feb. of 2010. So, I guess that makes it an STL-11000XM.

A trial exposure of NGC7000, with the AD Ha 5nm filter looked promising although it was ruined by guiding issues. We were not able to avail ourselves of the self-guiding feature in the time we had but I have already started looking for a MMOAG as I want to do lots of Ha and the behind-the-filter guiding chip is unlikely to be satisfactory.

As I say, the trial Ha subs looked very good, other than for poor guiding. However, the single L sub we took looked terrible! It was a 300sec L sub of M31 through the TAK FSQ106EDXIII. Most unfortunately, I did not have the presence of mind to keep it.

Attached is a dark, 300secs, -20C. It is given an auto STF stretch in PI. The gradient troubles me. It seems to be the same horrendous gradient we saw in the L sub. Is it normal for the STL?

Edited by dawziecat (09/17/13 10:10 AM)


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elbee
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Reged: 05/02/09

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Re: A used STL-11000? Still on the fence. new [Re: dawziecat]
      #6085696 - 09/17/13 10:38 AM

looks "perfect" (nice X chip). the gradient is "normal" for the STL-11k. your screen stretch makes it look like "more" than it is (what are the actual ADU values in each area -- probably not very different). also, when you calibrate your light frames there will be no gradient.

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Peter in Reno
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Re: A used STL-11000? Still on the fence. new [Re: elbee]
      #6085712 - 09/17/13 10:48 AM

Looks like a great dark image to me. I don't see any hot pixels. Like Lee said, it's heavily stretched. Did you measure the range of ADU of this dark frame? You can have extremely low ADU which is what you want and heavily stretch the image to make it look bad.

Peter


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dawziecat
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Re: A used STL-11000? Still on the fence. new [Re: Peter in Reno]
      #6085774 - 09/17/13 11:30 AM

If I am not making some error, the min/max ADU values, as measured in PI, are 849/1060.

Thanks Peter and Lee for the reassuring replies.


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Peter in Reno
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Re: A used STL-11000? Still on the fence. new [Re: vpcirc]
      #6085781 - 09/17/13 11:34 AM

Quote:

I'll never buy another interline chip




Interline has little to do with QE. It's the way Kodak makes them and I don't know why their interline chips have low QE. Look at Sony's CCDs, their interline chips have the highest QE in the astronomy market.

Yes, it's true that interline chips by design may naturally have a little less QE than full-frame chips but it does not mean Kodak can't make high QE interline chips. If Sony can make high QE interline chips, why can't Kodak do it?

Bottom line, it's an over generalization to say that all interline chips have too low QE.

Peter


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