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  #41  
Old 10-02-2009, 08:15 PM
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Apogee engineers take this line and not so much the sensor but the soldered connections etc - they don't want thermal shock.

But really I have seen no evidence in my camera or others that there is a real problem here. I think its a case of engineers being conservative and protecting against an imaginary problem.

Slow cooling and slow warmup is for the birds for those who use equipment that takes more than 2 seconds to work before they get impatient! - --- uhm thats me.!!

I love my Apogee camera but the slow cooling does annoy me and causes some delays at times. The new firmware has sped it up but still you have to plan if you want to take dusk flats. A warm camera gives useless flats.


Greg.




Quote:
Originally Posted by Gama View Post
Mike, turning the power off at -35 is fine, as it will take time to warm up. But going from 26.5 deg to -35 in a minute or 2, isnt a good idea. Kodak may be basing there response on a warm up temp range, and not out right "Flat out" hot to cold thermal transfer.
Still, gota love them cameras..

Theo
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  #42  
Old 10-02-2009, 08:31 PM
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Quote:
Originally Posted by gregbradley View Post
.............

Of course a dark site is more important again but if you had 2 cameras and all other things were equal then the one with the superior cooling should be your choice................

Greg.
Sorry Greg, (not surprisingly) I don't agree at all. All other things are rarely equal. Steve's analysis is quite thorough...what aspect of the physics would you care to take issue with or debate?

The few S/N percentage points you gain by extra cooling are easily swamped by having the option to use a device...well, like an AO...which can easily add 20% more flux under a stellar Gaussian curve (translation: brighter & tighter stars)...as does self guiding.... as the pick off chip is looking at the same aplanatic field as the imager. *All* other guiding methods are less terse, and to say otherwise is...as I like to say: "bollocks"

Dismissing these benefits I think is a bit like knocking back Cindy Crawford
because she has a mole....
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  #43  
Old 10-02-2009, 08:39 PM
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You missed my point. I was referring to ugly lines warmer temps on chips can leave behind in the KAI series.

Its no good having optional extras (which are often problematic to use and expensive although the benefits are there for long focal length scopes) if you have an ugly line going through your image due to inadequate cooling. Nice tight stars are wonderful but will be spoilt by the line which is hard/next to impossible to Photoshop out without leaving a trace.

Are you telling me you've never seen these ugly KAI lines in images?

Did you know they nearly disappear with stronger cooling?

Also I never mentioned anything about self guiding. But now you bring it up I think it is overplayed as a marketing point for SBIG.

I get far better autoguiding results using a separate guide scope and an ST402ME than I ever did with self gudiing using the tiny and extremely noisy ST237 chip. It picks up the edge of the FOV of the scope where most optics are weakest, is very noisy and has a very small FOV. Also blue filter often requires longer exposure times which for my setup meant less optimum where 1 second guide exposures have almost uniformly given the best result.
Also with Ha, S11 or O111 self guiding is virtually useless as often unless the object is super bright it requires something like 30 second guide exposures to register a guide star.

Also the way the camera ceases to autoguide when it is downloading an image and in the case of the STL that is something like 26 seconds means tracking errors are building up requiring time for the autoguider to catch up. I see this problem is addressed with the latest STX cameras which do not interrupt the guider when downloading. If you don't program in a delay between exposures you will get eggy stars from the initial errors having built up.

So if you are imaging LRG and no blue or Ha O111 or S11 there is no problem! As well as using a scope with lovely pinpoint stars right to the very outermost edge of the FOV where the pickoff prism collects the guide star. Having said that self guiding is still handy, especially with long exposures, but a guide scope and guide camera are really too easy to use to argue against them.

So self guiding is a bit ho hum. QSI with their offaxis guider built in before the filter would be way superior. If you get flexure you'd be way better off to use an off axis guider than self guiding.

Lets face it, if you weren't selling SBIG cameras and protecting your business we wouldn't be having this discussion which is about protecting SBIG's camera sales. The vested interest factor is too strong.

Greg.




Quote:
Originally Posted by Peter Ward View Post
Sorry Greg, (not surprisingly) I don't agree at all. All other things are rarely equal. Steve's analysis is quite thorough...what aspect of the physics would you care to take issue with or debate?

The few S/N percentage points you gain by extra cooling are easily swamped by having the option to use a device...well, like an AO...which can easily add 20% more flux under a stellar Gaussian curve (translation: brighter & tighter stars)...as does self guiding.... as the pick off chip is looking at the same aplanatic field as the imager. *All* other guiding methods are less terse, and to say otherwise is...as I like to say: "bollocks"

Dismissing these benefits I think is a bit like knocking back Cindy Crawford
because she has a mole....

Last edited by gregbradley; 10-02-2009 at 08:53 PM.
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  #44  
Old 10-02-2009, 08:40 PM
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Quote:
Originally Posted by Peter Ward View Post
Dismissing these benefits I think is a bit like knocking back Cindy Crawford
because she has a mole....

Awesome analogy...
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  #45  
Old 10-02-2009, 08:51 PM
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Quote:
Originally Posted by gregbradley View Post
............

Are you telling me you've never seen these ugly KAI lines in images?

Did you know they nearly disappear with stronger cooling?

Greg.
1) On class 2 (or lower) devices you can certainly see these...but that's why I use a class one chip: it dosen't have hot columns.

2) The hot columns I have seen fade with delta T....but...and here's the rub.... if you calibrate the data accurately...hot/dark pixels and columns disappear.....unless you have defect on the chip.
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  #46  
Old 10-02-2009, 08:56 PM
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Quote:
Originally Posted by Peter Ward View Post
1) On class 2 (or lower) devices you can certainly see these...but that's why I use a class one chip: it dosen't have hot columns.

2) The hot columns I have seen fade with delta T....but...and here's the rub.... if you calibrate the data accurately...hot/dark pixels and columns disappear.....unless you have defect on the chip.
I have seen it one a class 1 chip.

Theoretically the line will go and often does but mysteriously I found it also often did not. Its also not a column defect as you know - there is a paper on it on the SBIG site - its caused by a hot pixel and the readout process of KAI family chips.

They can also appear later on as a CCD deteriorates over time.

Greg.
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  #47  
Old 10-02-2009, 09:07 PM
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Quote:
Originally Posted by gregbradley View Post
I have seen it one a class 1 chip.
Not saying you haven't...but if it didn't dark subtract out...it was no longer a class one and good reason for a warranty claim.[/quote]

Quote:
Originally Posted by gregbradley View Post

Theoretically the line will go and often does but mysteriously I found it also often did not. ....
Without exception ( I've tested hundreds of cameras) I have traced this to less than perfect dark frames....sure, lowering the temperature made the effect less obvious, but nailing the dark frames extinguished the problem.

Last edited by Peter Ward; 10-02-2009 at 09:12 PM. Reason: omission
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  #48  
Old 10-02-2009, 09:18 PM
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Quote:
Originally Posted by Peter Ward View Post
Not saying you haven't...but if it didn't dark subtract out...it was not longer a class one and good reason for a warranty claim.
No, it was brought to the attention of SBIG and they said it was normal and not a column defect and merely a hot pixel which does not cause it to not be a Class 1. You'll see these lines also on the 16803 chips as well although these chips are quite noisefree at -10C.

From memory a class 1 has no column defects and hot pixel groups are less than a certain number.



Without exception ( I've tested hundreds of cameras) I have traced this to less than perfect dark frames....sure, lowering the temperature made the effect less obvious, but nailing the dark frames extinguished the problem.[/quote]


Yes you would be right there. I wondered what that difference was sometimes. Perhaps the bias frame reduction on the flats caused it.
It sometimes seemed a bit random. My darks were quite good. Oh well a bit of a mystery, sometimes it went and others it did not. Perhaps using a bias puts it back in there as the dark subtracts it and then it is gone and then if you use a bias in your flats you put it back in the flat and it comes through again? Perhaps better not to use a bias frame in this instance when making your flats.

Greg.
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  #49  
Old 10-02-2009, 09:21 PM
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Quote:
Originally Posted by AlexN View Post
Terry, what secondary cooler are you using? I've devised my own little plan (being quite the ingenious fellow I am ) Rather than just running a bucket of water under the mount with the pump feeding the water jacket of the ST9E, I'll be putting a dual core radiator in line with 2x120mm fans feeding air through the radiator... this will ensure the water is as close to ambient temperature as possible... every little bit counts
When I bought my camera (second hand) it has a secondary cooler and water cooler installed. The secondary cooler didn't work so I removed it and purchased a new peltier device to replace it. It needs a 30mm square peltier and the closest I could find is a called a TES1-12703 from these guys.
I bought 2 for US$19 plus postage. (so now I have a spare).
I run it with 13.8V from a marine battery.
I think it is a bit more hefty than the one that SBIG uses hence the good temp drop.
My water is just a 20L drum that sits in the observatory and is at room temp. I don't change the water much as I'm on tank water. It seems to stay OK.
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  #50  
Old 10-02-2009, 09:27 PM
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Some people use water chillers. I know Fred simply put chunks of ice in a bucket of water.

Greg.



Quote:
Originally Posted by Terry B View Post
When I bought my camera (second hand) it has a secondary cooler and water cooler installed. The secondary cooler didn't work so I removed it and purchased a new peltier device to replace it. It needs a 30mm square peltier and the closest I could find is a called a TES1-12703 from these guys.
I bought 2 for US$19 plus postage. (so now I have a spare).
I run it with 13.8V from a marine battery.
I think it is a bit more hefty than the one that SBIG uses hence the good temp drop.
My water is just a 20L drum that sits in the observatory and is at room temp. I don't change the water much as I'm on tank water. It seems to stay OK.
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  #51  
Old 10-02-2009, 09:29 PM
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Quote:
Originally Posted by gregbradley View Post
Lets face it, if you weren't selling SBIG cameras and protecting your business we wouldn't be having this discussion which is about protecting SBIG's camera sales. The vested interest factor is too strong.

Greg.
This really needed a separate response.

http://www.atscope.com.au/BRO/gallery20.html

AO guided from the urban lights of Sydney.

Vested interest? I disagree as I simply could not have got that resolution (AO guided at 15Hz) with any other system....and invite IIS members to have a look at all other M104 images on the web and decide whether this technology works.
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  #52  
Old 10-02-2009, 09:38 PM
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Quote:
Originally Posted by gregbradley View Post
..... Perhaps better not to use a bias frame in this instance when making your flats.

Greg.

Dark and dark-subtracted flat and frames automatically have bias subtraction ....to repeat the process buggers up the data.
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  #53  
Old 11-02-2009, 12:08 AM
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Indeed a marvellous image.

Don't get me wrong I am not against SBIG and I loved my STL camera.

My point really was that the various manufacturers have their relative strengths and weaknesses. One of FLIs strengths is the best cooling of anyones and it is a valuable feature. SBIG has a large range of accessories.

Its a good time to buy a CCD camera as its never been this competitive before. So many good manufacturers with excellent cameras.

Greg.
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  #54  
Old 11-02-2009, 12:26 AM
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Dismissing these benefits I think is a bit like knocking back Cindy Crawford
because she has a mole....
If Cindy Crawford was an autoguider, every guy on the planet would take up astronomy!!!!
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  #55  
Old 11-02-2009, 09:12 PM
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Well look here for REAL cooling. Down to -100 deg C. I note they don't mention prices anywhere. If you have to ask...etc
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  #56  
Old 11-02-2009, 10:31 PM
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I always liked the stats of the temp used for the receivers on the ATCA dishes. They are cooled to about 18deg K and get oxygen frost in the dewer in front of the receiver.
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  #57  
Old 11-02-2009, 11:14 PM
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I always liked the stats of the temp used for the receivers on the ATCA dishes. They are cooled to about 18deg K and get oxygen frost in the dewer in front of the receiver.
You mean one of these Terry

This LS-band (~2GHz) receivers' cold finger in this unit is immersed in a nice cool 14-18 degK bath. It's all so critical that they hire a bloke just to maintain it and several others. He's our mate John - the cryogenics engineer at ATNF Narrabri. He's the one on the left. The other is Jenny, my wife. Confusing them earns me a slap across the chops.
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  #58  
Old 12-02-2009, 12:47 AM
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....The other is Jenny, my wife. Confusing them earns me a slap across the chops
Now we know why you're wearing sunnies in your avatar....to hide the black eyes!!!!!
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  #59  
Old 13-02-2009, 12:43 AM
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Quote:
Originally Posted by gregbradley View Post

Also I never mentioned anything about self guiding. But now you bring it up I think it is overplayed as a marketing point for SBIG.

I get far better autoguiding results using a separate guide scope and an ST402ME than I ever did with self gudiing using the tiny and extremely noisy ST237 chip. It picks up the edge of the FOV of the scope where most optics are weakest, is very noisy and has a very small FOV. Also blue filter often requires longer exposure times which for my setup meant less optimum where 1 second guide exposures have almost uniformly given the best result.
Also with Ha, S11 or O111 self guiding is virtually useless as often unless the object is super bright it requires something like 30 second guide exposures to register a guide star.

Also the way the camera ceases to autoguide when it is downloading an image and in the case of the STL that is something like 26 seconds means tracking errors are building up requiring time for the autoguider to catch up. I see this problem is addressed with the latest STX cameras which do not interrupt the guider when downloading. If you don't program in a delay between exposures you will get eggy stars from the initial errors having built up.

So if you are imaging LRG and no blue or Ha O111 or S11 there is no problem! As well as using a scope with lovely pinpoint stars right to the very outermost edge of the FOV where the pickoff prism collects the guide star. Having said that self guiding is still handy, especially with long exposures, but a guide scope and guide camera are really too easy to use to argue against them.

So self guiding is a bit ho hum. QSI with their offaxis guider built in before the filter would be way superior. If you get flexure you'd be way better off to use an off axis guider than self guiding.
Well?....hard to argue with all that Peter, isn't it? ... and this is why so many imagers with selfguiding cameras are forced to purchase a guide camera and guide scope anyway.

Mike
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  #60  
Old 13-02-2009, 12:52 AM
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Quote:
Originally Posted by Peter Ward View Post
This really needed a separate response.

http://www.atscope.com.au/BRO/gallery20.html

AO guided from the urban lights of Sydney.

Vested interest? I disagree as I simply could not have got that resolution (AO guided at 15Hz) with any other system....and invite IIS members to have a look at all other M104 images on the web and decide whether this technology works.
Well actually Peter, that image as presented is terribly low res and looks quite pixelated...?

Mike
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