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Old 14-02-2010, 08:53 PM
TrevorW
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OSC v DSLR

I've not the time to go into mono/filter imaging nor for that matter the patience

is there any significant gain buying a OSC CCD over a modified DSLR



if answered before please direct me
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Old 14-02-2010, 09:00 PM
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Quote:
Originally Posted by TrevorW View Post
I've not the time to go into mono/filter imaging nor for that matter the patience

is there any significant gain buying a OSC CCD over a modified DSLR



if answered before please direct me
It has been asked before:
http://www.iceinspace.com.au/forum/s...ad.php?t=35971
http://www.iceinspace.com.au/forum/s...ad.php?t=49803
http://www.iceinspace.com.au/forum/s...ad.php?t=47309

It's the cooling and much simpler long exposure that make the difference.
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Old 14-02-2010, 09:04 PM
Hagar (Doug)
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The biggest gains in buying a dedicated cCD is The removal of the filter in front of the CCD allowing higher sensitivity and easier use of other filters.
The second is cooling, this is a big one in a relatively hot climate.
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Old 14-02-2010, 10:13 PM
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Dont forget 16bt colour, as opposed to 12bt from DSLR (maybe 14bt in better cameras?)

make such a difference.


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Old 14-02-2010, 10:41 PM
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Duncan - Its not so much 16bit colour, but 16bit depth. Its a measurement of dynamic range, indicating that the sensor is capable of discerning 65536 individual, discrete shades of grey. Whether its an OSC camera or a monochrome camera, this measurement indicates how many shades of grey the camera can capture.. The difference is that an OSC CCD splits the pixels into groupings of 4, each pixel in the grouping has a tiny little filter over it that cuts out all light except the relevant information. in the QHY8 it is R G G B, pixel 1 accepts only red light, pixels 2 and 3 accept green light, pixel 4 accepts blue light. again, the pixels are only seeing 65535 shades of grey, but the filter in front of the pixels allows the camera to capture RGB data in one shot. Hence, OSC. Software is then used to debayer the grey information to create a colour image from a sensor that only detects shades of grey..

Although its already summed up,

Cooling and inherent noise levels as a result of cooling
Dramatically improved dynamic range
Increased sensitivity to all the important spectra of light.

There is no ifs, whats or buts about it... An OSC CCD imaging camera will produce better images of the night sky than even a cooled, UV/IR modified DSLR.. Not to mention that something like the QHY8 is not much more expensive than the standard consumer level DSLR like the 50D, once you pay to have the DSLR UV/IR modified, the price difference is all but gone... Then weigh up the differences between a modded DSLR and an OSC CCD..

Without a doubt, the thing that speaks the loudest (pardon the pun..) is noise... A QHY8 or any other astro camera with the Sony ICX-453 sensor has such a low dark current that dark frames are completely unnecessary even when taking 20 to 30 minute frames.. Lets see you get noise free 30 minute subs from ANY DSLR, even the most expensive DSLR's like the Canon 1D mk III / 1D mk IV and the Nikon D3Xs / D700...
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Old 15-02-2010, 12:48 PM
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Thanks guys for the feedback and Alex for the detailed summary
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Old 15-02-2010, 06:10 PM
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Quote:
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Without a doubt, the thing that speaks the loudest (pardon the pun..) is noise... A QHY8 or any other astro camera with the Sony ICX-453 sensor has such a low dark current that dark frames are completely unnecessary even when taking 20 to 30 minute frames.. Lets see you get noise free 30 minute subs from ANY DSLR, even the most expensive DSLR's like the Canon 1D mk III / 1D mk IV and the Nikon D3Xs / D700...
Maybe the Sony based CCDs don't need dark frames for the current. You still need them for any hot pixels. My QHY8 has some.
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Old 15-02-2010, 06:51 PM
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A bad pixel map solves it, or a single dark frame will show up any hot cold pixels...

I ran a QHY8 for about 8 months and NEVER used a dark frame.. Not once.
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Old 15-02-2010, 07:06 PM
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Maybe the Sony based CCDs don't need dark frames for the current. You still need them for any hot pixels. My QHY8 has some.
You may find that a bias frame is enough to remove the hot pixels
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Old 15-02-2010, 07:12 PM
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Originally Posted by toryglen-boy View Post
Dont forget 16bt colour, as opposed to 12bt from DSLR (maybe 14bt in better cameras?)

make such a difference.



16 Bit is not so much of an advantage. Most OSC cameras don't have the well depth to take advantage of it. Full well depths of OSC cameras are typically around 25000 e's, and your signal is typically much less, so a lot of the AD converter range is wasted. 14 bit of the more expensive DSLR's is probably enough.

Cheers
Stuart
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