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Old 18-11-2013, 07:40 PM
raymo
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Sensitivity DLSR versus CCCD camera

I have been astroimaging for over 50yrs; have made the switch to a
DSLR, but I think that it is a little late to go the next step to a CCCD
camera; however, I have a question that I haven't seen raised anywhere,
but that I would like an answer to.
I have bought " Imaging the Southern Sky' which gives all the
exposures that were used, using CCCD cameras that used the popular
KAF-8300 sensor. I understand that CCCDs are much more sensitive than
DSLRs. Can the ISO of a CCCD camera be changed, or are they fixed?
If they are fixed, does anyone know what the ISO is, so that I can
find out what ISO I would have to use with my DSLR to get
equivalent exposures[ always assuming that my DSLR can reach the
necessary ISO, that is]. Thanks in advance.
raymo
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Old 18-11-2013, 08:49 PM
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Quote:
Originally Posted by raymo View Post
I have been astroimaging for over 50yrs; have made the switch to a
DSLR, but I think that it is a little late to go the next step to a CCCD
camera; however, I have a question that I haven't seen raised anywhere,
but that I would like an answer to.
I have bought " Imaging the Southern Sky' which gives all the
exposures that were used, using CCCD cameras that used the popular
KAF-8300 sensor. I understand that CCCDs are much more sensitive than
DSLRs. Can the ISO of a CCCD camera be changed, or are they fixed?
If they are fixed, does anyone know what the ISO is, so that I can
find out what ISO I would have to use with my DSLR to get
equivalent exposures[ always assuming that my DSLR can reach the
necessary ISO, that is]. Thanks in advance.
raymo

The ISO is just a digital gain.
You could never expose a DSLR for as long as a CCD camera because
thermal noise will make the picture turn red.

On a Canon EOS 1000d I used an ISO of 800 normally.
ISO 1600 was no advantage because it amplified the noise.
You need to find out the "natural" unamplified ISO for your camera.
I think that was ISO 800 or maybe ISO 400 for the Canon EOS 1000d.
You'll find that in summer any longer than 2 to 3 minute exposures will have too much noise.
In winter you can go to 5 to 10 minute exposures at the most.
( if the air temperature is below 4 degrees C.)

Hope that helps?

cheers
Allan
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Old 18-11-2013, 10:24 PM
raymo
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Thanks Allan, information appreciated, but I would still like to know
how much more sensitive a CCCD camera is than a DSLR-3x-10x-20x?
I understand that I can't take very long exposures, but some of the exposures listed in the book are quite short, only a minute or two, so maybe I could have a try at some of those targets with my DSLR. I am
finding that I can use ISO 3200; Neatimage is miraculous at removing
noise.
raymo
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Old 18-11-2013, 11:05 PM
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Quote:
Originally Posted by raymo View Post
Thanks Allan, information appreciated, but I would still like to know
how much more sensitive a CCCD camera is than a DSLR-3x-10x-20x?
I understand that I can't take very long exposures, but some of the exposures listed in the book are quite short, only a minute or two, so maybe I could have a try at some of those targets with my DSLR. I am
finding that I can use ISO 3200; Neatimage is miraculous at removing
noise.
raymo

CCD is about 3 times more sensitive - from memory.
I wouldn't use ISO 3200 unless that's the native gain of your camera.
A lower ISO means less noise & you won't reach the well depth as quickly.
Removing noise creates artifacts - the idea is to get a good signal to noise ratio to start with.

I would say - just get out there & try it.
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Old 19-11-2013, 12:59 AM
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Thanks again Allan. At my age I am finding digital imaging/processing
a steep learning curve, and as I am producing what I consider very promising single exposure results, I'm thinking of sticking with that.
I'm pushing 80 and don't want to spend large chunks of my remaining
years sitting at a computer.
raymo
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Old 19-11-2013, 01:21 AM
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Quote:
Originally Posted by raymo View Post
Thanks again Allan. At my age I am finding digital imaging/processing
a steep learning curve, and as I am producing what I consider very promising single exposure results, I'm thinking of sticking with that.
I'm pushing 80 and don't want to spend large chunks of my remaining
years sitting at a computer.
raymo

80? - you're still a spring chicken!
But you need to process & Louie has made it easy for you if you have Photoshop.
see link:

http://www.youtube.com/channel/UCJ5b6pFHBGe66vsuSaXb-0A


You won't see much at all unless the image is stretched with curves.
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Old 19-11-2013, 04:07 PM
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Quote:
Originally Posted by alpal View Post
CCD is about 3 times more sensitive - from memory.
I wouldn't use ISO 3200 unless that's the native gain of your camera.
A lower ISO means less noise & you won't reach the well depth as quickly.
Removing noise creates artifacts - the idea is to get a good signal to noise ratio to start with.

I would say - just get out there & try it.
I don't think its 3-4 times but it might be 2 to 3 times depending on the CCD of course.

Depending on the DSLR. I have a link somewhere to the various sensitivities of various brands and models but they typically are between 30 and 60% QE. QE is quantum efficiency which is what percentage of photons that hit the sensor get converted to electrons (signal).

Your average CCD is about 45-55% or less. But because they are monochrome every pixel counts whereas DSLRs take 4 pixels to make one colour dot in an image so that reduces the sensitivity a lot.

CCDs usually have minimal gain applied to the signal. So say for example the Nikon D800, ISO 1600 is close to minimal gain like a CCD. That ISO level would vary also with brands and models of cameras.

My Nikon D800E has 59% QE and my astro CCD cameras are mostly 60%. The difference is mainly the mono of the CCD versus the colour filters
on the DSLR. A closer approximation of sensitivity is a one shot colour CCD camera and a DSLR. There is still usually a greater sensitivity with the one shot colour but the difference is less. Mostly due to the cooling reducing the noise. Sometimes the sensors are the same for example the Starlight Express M25 one shot colour uses the same CCD sensor as the old Nikon D70.

Greg.
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Old 19-11-2013, 05:42 PM
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Quote:
Originally Posted by gregbradley View Post
I don't think its 3-4 times but it might be 2 to 3 times depending on the CCD of course.

Depending on the DSLR. I have a link somewhere to the various sensitivities of various brands and models but they typically are between 30 and 60% QE. QE is quantum efficiency which is what percentage of photons that hit the sensor get converted to electrons (signal).

Your average CCD is about 45-55% or less. But because they are monochrome every pixel counts whereas DSLRs take 4 pixels to make one colour dot in an image so that reduces the sensitivity a lot.

CCDs usually have minimal gain applied to the signal. So say for example the Nikon D800, ISO 1600 is close to minimal gain like a CCD. That ISO level would vary also with brands and models of cameras.

My Nikon D800E has 59% QE and my astro CCD cameras are mostly 60%. The difference is mainly the mono of the CCD versus the colour filters
on the DSLR. A closer approximation of sensitivity is a one shot colour CCD camera and a DSLR. There is still usually a greater sensitivity with the one shot colour but the difference is less. Mostly due to the cooling reducing the noise. Sometimes the sensors are the same for example the Starlight Express M25 one shot colour uses the same CCD sensor as the old Nikon D70.

Greg.

Thanks Greg,
the fact is that CCD out performs Bayer matrix CMOS every time.
I was amazed at the difference it made when I switched to CCD.

I went from this:
http://www.flickr.com/photos/2471943...in/photostream

to this - using the same telescope:

http://www.flickr.com/photos/2471943...in/photostream

cheers
Allan
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Old 19-11-2013, 06:55 PM
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Quote:
Originally Posted by gregbradley View Post

My Nikon D800E has 59% QE and my astro CCD cameras are mostly 60%.
Carl Sagan was fond of saying :" extraordinary claims require extraordinary evidence"

59% QE for a bayer-martix covered CMOS chip? Really?

60% for a mono CCD?

At what wavelength?

The very best CCD's are pushing 95% QE

see
http://www.e2v.com/products-and-serv...ccd/qe-curves/

Most (unmodded) DSLR's are useless at H-alpha wavelengths. Plus most CCD's have very low noise amps and are chilled from 30-60 degrees below ambient....and that is the elephant in the room

Just my 2 cents worth
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Old 19-11-2013, 07:18 PM
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Im not 100% sure on the "sensitivity" difference of a CCD and a DSLR, but in the real world the cooling on most astronomical CCDs is what sets the two apart as Peter is alluding too. Sensitivity to me is how many electrons the sensor creates from a signal, and this may well be very similar between the two. The fact is that the noise level of DSLRs is far higher than CCDs, and thats before you take into account the bayer matrix and the ability to do narrowband imaging.
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Old 19-11-2013, 07:35 PM
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Quote:
Originally Posted by alpal View Post
Thanks Greg,
the fact is that CCD out performs Bayer matrix CMOS every time.
I was amazed at the difference it made when I switched to CCD.

I went from this:
http://www.flickr.com/photos/2471943...in/photostream

to this - using the same telescope:

http://www.flickr.com/photos/2471943...in/photostream

cheers
Allan
A picture is worth a thousand words! A very striking example.

Greg.
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Old 19-11-2013, 07:54 PM
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Quote:
Originally Posted by raymo View Post
Thanks again Allan. At my age I am finding digital imaging/processing
a steep learning curve, and as I am producing what I consider very promising single exposure results, I'm thinking of sticking with that.
I'm pushing 80 and don't want to spend large chunks of my remaining
years sitting at a computer.
raymo
That's funny. If you main concern is learning curve you are in for a shocker using a DSLR. sure you can produce good images with a DSLR, but you are going to spend FAR more time at the PC learning PS to extract good images than with say a colour astro CCD. If you can't afford an astro CCD, then fine, if learning curves are a worry, your kidding yourself with a DSLR
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Old 19-11-2013, 08:02 PM
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Over at Cloudynights the same very faint target (Sh2-129 and OU-4) have been imaged very recently by Nicola (who also posts here) with a QSI583 CCD and by Scott Rosenfraz with a modded Canon 450D DSLR.

Nicola's CCD image: http://www.cloudynights.com/ubbthrea...l/fpart/1/vc/1

Scott's DSLR image: http://www.cloudynights.com/ubbthrea.../o/all/fpart/1

The scope that Nicola uses - Tak FSQ85ED - is nominally F/5.3, not sure if he used a focal reducer.
Scott used a 200mm F/2.8 lens - 2.5(?) F-stops faster, yet total exposure time is much, much great than Nicola's image.

Hard to make too many judgements. There should be more signal-to-noise in Scott's H-a data, Sqrt(99 subs)=10 x 10-minute subs. Nicola used sqrt(8 subs)=3 x 20-minute subs. I think they look almost identical. That ratio of normalised exposure would give the difference at 656nm in sensitivity. So by my very rough calculation we'd be seeing 1.67 (normalised exposure difference) x 2.5 (F-stop difference) = 4x difference at H-alpha.

Lots of caveats of course,
Cam
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Old 19-11-2013, 08:22 PM
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Since the OP is concerned about time on the PC (inc imaging time perhaps?) thats 12 vs 44 hrs just on imaging time!.

Also, the caveat elephant in the room of course is, how much time and expertise did Scott spend in PS reducing horrendous noise etc!. No mention of that.
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Old 19-11-2013, 08:34 PM
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Quote:
Originally Posted by alpal View Post
Thanks Greg,
the fact is that CCD out performs Bayer matrix CMOS every time.
I was amazed at the difference it made when I switched to CCD.

I went from this:
http://www.flickr.com/photos/2471943...in/photostream

to this - using the same telescope:

http://www.flickr.com/photos/2471943...in/photostream

cheers
Allan
wow, thats amazing. I dont think ive seen such a stark improvement presented like this. Well done Allan...............what the hell is the next quantum leap going to be like
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Old 19-11-2013, 08:46 PM
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wow, thats amazing. I dont think ive seen such a stark improvement presented like this. Well done Allan...............what the hell is the next quantum leap going to be like

Believe it or not - the images were taken from the same
light polluted location with the same ALP filter &
the same integration time - only about 2 hours.

I couldn't be bothered with DSLR after getting such improvements with mono CCD.
All I need now is decent weather.
I hope to make my next improvement with more integration time -
to be a quantum leap too - especially if I have a dark site.

The full frames are here:

DSLR:
http://www.flickr.com/photos/2471943...in/photostream

CCD
http://www.flickr.com/photos/24719437@N03/8804611627/
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Old 19-11-2013, 09:09 PM
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That large CCD pic is very, very good indeed Alan, just sublime.
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Old 19-11-2013, 09:16 PM
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That large CCD pic is very, very good indeed Alan, just sublime.
Thanks - much appreciated.
I was going to delete all those DSLR pics but it's a reminder of
what it used to be like struggling with a DSLR.

It's also a lesson for others.
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Old 19-11-2013, 09:24 PM
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This is fun .

M8 and Helix. DSLR vs CCD. WHY would you BOTHER .

Im cheating a bit, some minor differences in gear and exposure time.
Attached Thumbnails
Click for full-size image (fxv-helix.jpg)
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Click for full-size image (NGC7293 Ha Ha Ha OII sml.jpg)
134.5 KB44 views
Click for full-size image (fxv-m8.jpg)
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Click for full-size image (m8_vanderhaven_big.jpg)
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Old 19-11-2013, 09:31 PM
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This is fun .

M8 and Helix. DSLR vs CCD. WHY would you BOTHER .

Im cheating a bit, some minor differences in gear and exposure time.
Good examples - why would you bother?

I didn't want to get a CCD until I could prove that I could guide properly
for as long as I wanted - 20 minute even 30 minute subframes with a DSLR.
I had to get new tube rings and an OAG before it would work properly
but even then I needed a special corrector with enough back focus &
a Varilock adjuster to get the distances right for CCD.
This is not an easy or inexpensive hobby.
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