#41  
Old 15-06-2014, 06:55 PM
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Interesting idea but not quite true. It does depend on the well depth and the gain used in the CCD. My ST10XME is 16 bit and I use it to do photometry. If the number of levels of grey was less I would not be able to measure the difference on brightness of 2 stars anywhere near as accurately. It is not just stretched data. Big CCD pixels have greater well depth so can be broken into many more individual levels.
I don't know about the noise level at very low signal but this is not where I measure the stars.
your ST10 has one of the expensive chips that does provide a bit better than 12 bits of real data (but still not 16 bits). The read noise level at high levels is exactly the same as that at low levels and you cannot measure to better accuracy than the noise will allow. Your chip has a gain of about 1 electron per ADU (from memory), but a noise level of about 8 electrons RMS, so you cannot make use of the lower 3 bits - your measurements will have an error of about 8ADU RMS because of the noise. ie, you have about 13 bits of usable data.

However, I agree that my earlier statement could have been better worded and it now is.

Last edited by Shiraz; 17-06-2014 at 02:52 PM.
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  #42  
Old 15-06-2014, 07:12 PM
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Originally Posted by MrB View Post
Perhaps if I quote myself....

And change 14bit to 12bit?

So ...every shade of grey that a 12 bit system can resolve, a 16 bit system can break that down further into 16 more shades.
Ok agreed, and see the point you were making now.
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  #43  
Old 15-06-2014, 07:58 PM
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There is a lot of R and D in CMOS and it will show at some point. Perhaps not yet though.

Fuji have an organic sensor which is supposed to have greater dynamic range (15EV compared to about 12 on some of the better DSLRs).
Sony have a curved sensor which makes corners 2X more sensitive and the centre area 1.4 X more sensitive. Expect to see that in a camera this year.

Sony also have a Foveon style sensor where the pixels are at different depths to get the colour rather than a colour filter array.

Sony already are using back illuminated sensors that are 40% more sensitive (largest being a 1 inch diagonal sensor).

There are other developments happening as well. So it all adds up to a dynamic area that could filter down into astroimaging if any of these improvements actually challenge CCDs (it would have to be a big leap).

I can't see that happening anytime soon but perhaps another few years maybe. CCDs seem to be stagnating at the moment and Kodak sold their sensor division to True Sense imaging who didn't really bring anything new and have since sold it to someone else. So a very stagnant scene.

Perhaps CCDs are being passed by for the more favoured CMOS in most applications, no doubt driven by cost.

What is the market for CCDs anyway? Xray machines?

Even Leica who used to use CCDs in their cameras have switched to CMOS.

Greg.
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  #44  
Old 15-06-2014, 08:10 PM
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Originally Posted by gregbradley View Post
Sony have a curved sensor which makes corners 2X more sensitive and the centre area 1.4 X more sensitive. Expect to see that in a camera this year.
Interesting, depending on the curve, what effect will this have on field flattness?
If it's spherical, perhaps coma correctors won't be necessary.
Quote:
Kodak sold their sensor division to True Sense imaging who didn't really bring anything new and have since sold it to someone else.
On-Semi, a very very large semiconductor manufacturer, used to be Motorola.
Hopefully they do something with their newly acquired division.

The future of imaging certainly looks like it will be very interesting.
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  #45  
Old 15-06-2014, 08:19 PM
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I had a bit of fish through Sonys sensor web site, it seems all the premium "industrial" sensors they make are CCDs. Cant imagine Sony would bother with CCDs at all if CMOS was superior generally.
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  #46  
Old 15-06-2014, 08:29 PM
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I had a bit of fish through Sonys sensor web site, it seems all the premium "industrial" sensors they make are CCDs. Cant imagine Sony would bother with CCDs at all if CMOS was superior generally.
That's interesting. I suppose machine vision must be another market. Plus that growth area - speed cameras. I wonder what they use.

Greg.
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  #47  
Old 15-06-2014, 10:12 PM
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Scientific CMOS (sCMOS) style circuitry will likely make its way beyond its existing patent holders and go "mainstream" in the next few years.

http://www.photonicsonline.com/doc/s...-overview-0001

sCMOS has a dynamic range of up to 1:27,000 in existing devices. Only EM-CCDs have lower effective read-noise - sCMOS devices have around 1-1.5 electrons read noise.

CCDs soak a huge amount of electricity compared to CMOS devices and I suspect between that and their serial nature will result in them being reduced to smaller and smaller markets. Outside of astronomy there are few niches where traditional CCDs are not outperformed by an alternative.
-Cam
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  #48  
Old 16-06-2014, 12:39 AM
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I had a bit of fish through Sonys sensor web site, it seems all the premium "industrial" sensors they make are CCDs. Cant imagine Sony would bother with CCDs at all if CMOS was superior generally.
I think that CCDs are still favoured for industrial uses, because precise measurement of moving objects is required - that is not possible with rolling shutter CMOS. However, new CMOS designs with global shutters are coming onto the market and this last refuge of the CCD could be under threat. In other respects, CMOS is up there in quantum efficiency, read noise, etc. A good example of the way things are changing is found in the planetary imaging field, where the premium CCD cameras have now been joined by CMOS ones with at least equivalent sensitivity and noise performance, higher speed readout, more pixels and lower cost.

In terms of Lee's original question, expect a wider variety of choices in dedicated astro cameras in future, with high performance at lower cost as CMOS and it's derivatives makes inroads.

Last edited by Shiraz; 16-06-2014 at 12:52 AM.
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  #49  
Old 16-06-2014, 06:22 PM
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This might sound daft, but search as I may, I cant find a single mainstream CMOS cooled long exposure non-planetary (as in fast exposure), non modded DSLR astrocam. Many have Sony sensors, but they are all CCD.

Can anyone please point me to a superior CMOS-over-CCD cooled astrocam model. Or even any?.
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Old 17-06-2014, 10:00 AM
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This might sound daft, but search as I may, I cant find a single mainstream CMOS cooled long exposure non-planetary (as in fast exposure), non modded DSLR astrocam. Many have Sony sensors, but they are all CCD.

Can anyone please point me to a superior CMOS-over-CCD cooled astrocam model. Or even any?.
You have a point...nothing at all.

I guess that we are still willing to fork out big bucks for 15 year old CCD designs, so why should the astro camera makers change anything? It was only by accident that the new Sony CCDs turned out to be somewhat suitable for astronomy - even though they were designed for a different purpose.

OK, you win, maybe CMOS will not be appearing in cooled astro cams in the near future - not because of the technology, but because of the inertia of a tiny market.

Last edited by Shiraz; 17-06-2014 at 10:18 AM.
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  #51  
Old 17-06-2014, 11:57 AM
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I totally agree with the comments being made on this thread and have been following the thread closely.

One of the major issues facing a lot of us as well is portable vs permanent setup in my mind and if we live in a dark sky site.

For a portable set up where you have to drive several hours and set up and pack up for several hours at a time and be at the mercy of variable weather, nothing can beat the time vs returns vs cost of a DSLR. Sure, not as good as monochrome CCD, but you sure will get lots of images coming close (maybe) to the quality of a CCD.

If you have an observatory at a dark sky site, and even better, if you can operate this remotely, then monochrome CCD is the way to go - even if you live at a dark sky site and can set up quickly every night with a semi-permanent set up this works.

BUT, if you have to pack the car, drive to your dark sky site, set up and then polar align every time, you may only be able to get images of a handful of objects per year with a monochrome CCD.

I am still in awe at what my 9 y.o. Canon 400D can produce after 2 hours under a dark sky. I can shoot at least 2-3 objects per night and walk away with images whilst my monochrome friends are still "gathering data" with CCD cameras worth more than my entire set up.

BUT, if I had a permanent observatory set up at a dark sky site, sure, monochrome CCD is the way to go and mono DSLR is a great low cost evolution especially if it can be cooled.

Also, as has been said, the cost of CCD monochrome cameras can be astronomical - way too expensive and do not appear to have come down at the same rate as the cost of DSLR's.

Always an issues the old time vs cost vs return I guess.

Just my 2 cents worth.

Clear skies.
John K.
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  #52  
Old 17-06-2014, 05:47 PM
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...nothing at all.
Its a shame really, would have been interesting comparing actual results on purpose built CMOS and CCD astro cams. They will come to be sure. Central DS rebuild DSLRs into cooled cases, JJ has one, results look impressive.
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  #53  
Old 17-06-2014, 10:14 PM
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John,

Yes the cost of cameras is falling and with the rise of mirrorless they are getting lighter and more compact as well.

Rumour is Sony is soon to release a compact full frame camera for under $1000.

At the moment a Canon 6D is about $1600, A Nikon D610 is similar and Sony A7 is $1500 or so. These are all full frame.

Greg.
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