A Space & astronomy forum. SpaceBanter.com

Go Back   Home » SpaceBanter.com forum » Astronomy and Astrophysics » CCD Imaging
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

CCD Camera design



 
 
Thread Tools Display Modes
  #11  
Old February 13th 04, 01:49 AM
Alan Chen
external usenet poster
 
Posts: n/a
Default CCD Camera design

Hi Leonard, Stu,

With all due respect, narrow band imaging can be done with color detectors.
There is an interpolative process to yield the final image, but the results
are not as bad as one might think, especially for imagers with small pixels.

If you get a chance, here are links to my only 2 H-alpha images with a
one-shot.

http://www.heavenlyview.com/b33halphasxvh9c.htm

http://www.heavenlyview.com/ic405sxvh9c.htm

I don't have an OIII filter, but there's no reason to suspect this would be
much different. Depending on the filter cross-over, this could generate
signal in the blue or green filtered pixels, or both.

Maybe these are "less than desired" to some, but I'm quite happy with the
outcome. Judge for yourself.

Best regards,

Alan
http://www.heavenlyview.com/

"Leonard" wrote in message
...
There is another big drawback to using a "color" detector.
You are stuck with the filters the manufacturer placed on the front of
the chip. While fine for the daytime snapshot they do not have the
high efficiency of or color balance available in astronomical filters.
You could not do a Ha or OIII shot very well (yes you could put one of
those filters in front of a color detector but I believe the results
would be less than desired.

Of course if you have already selected a specific chip there may not
be a color filter option for it. You can only buy / get what they
make.

In general CMOS sensors do not offer as low as noise as CCDs.
Howerver the new Canon digital SLR cameras have CMOS sensors and dark
noise far below what my CCD based camera would produce (at the same
sensor temperature).

I wish you the best of luck on your endeavors.
Please publish the design if you get it to go.

Leonard

On Fri, 06 Feb 2004 09:09:18 GMT, "David Nakamoto"
wrote:

Color CCDs achieve their results by placing a matrix of color filters ove

r
the sensor array. This cuts down on the sensitivity of the array,
increasing exposure times 2 to 3 times or more. It also reduces the
resolution, since every three to four pixels are used to recreate a

single
color one.

CMOS does have higher noise, and less low light sensitivity.

The best color results are still from using a black and white CCD with a
color filters, taking one exposure per filter.


"Alain J" wrote in message
...
Hi

I want to build my own astronomical camera. I don't have decided which
I'll use. I want to put a color CMOS sensor but many web sites relates
that CMOS sensors are not very good (high dark level)
I've seen a color CMOS sensor with 1,3 Mpixel (1280x1024) at a very low
price (about $140).

For best performance, do I use a color sensor or B&W sensor ? In term
of sensitivy, dark noise which is the best (colour or B&W)?

Cordially

Alain






  #12  
Old February 14th 04, 10:13 PM
Leonard
external usenet poster
 
Posts: n/a
Default CCD Camera design

They are nice shots.
I didn't say you could not.

But assuming a RGBG Bayer color filter on the front of the chip,
it throws away 3/4 of the light / signal.
Same depth in 1/4 the time or 4x the resolution sounds really good in
comparison.

I notice you mention Sigma reject.
I know Russell Crowman. He really is a nice guy.
Here is his shot.
It is less than 10% longer in exposure time on a 4" f5 scope.
Granted it is a different camera (Kodak CCD) but it is deeper and
higher resolution (click on image to see the full resolution details).
http://www.rc-astro.com/nebulae/ic434_region_ha.htm

It is quite a bit better than my shot.
Mine was shot unfiltered line of site to 3 streetlights.
CB245, 27 x 15s (6.75 minutes), cooling off, ambient ~ +35 deg F, with
darks, no flats, no defect map, 8" f5.3 Newtonian
http://photos.yahoo.com/z_leonardh

Leonard

On Fri, 13 Feb 2004 00:49:48 GMT, "Alan Chen"
wrote:

Hi Leonard, Stu,

With all due respect, narrow band imaging can be done with color detectors.
There is an interpolative process to yield the final image, but the results
are not as bad as one might think, especially for imagers with small pixels.

If you get a chance, here are links to my only 2 H-alpha images with a
one-shot.

http://www.heavenlyview.com/b33halphasxvh9c.htm

http://www.heavenlyview.com/ic405sxvh9c.htm

I don't have an OIII filter, but there's no reason to suspect this would be
much different. Depending on the filter cross-over, this could generate
signal in the blue or green filtered pixels, or both.

Maybe these are "less than desired" to some, but I'm quite happy with the
outcome. Judge for yourself.

Best regards,

Alan
http://www.heavenlyview.com/

"Leonard" wrote in message
.. .
There is another big drawback to using a "color" detector.
You are stuck with the filters the manufacturer placed on the front of
the chip. While fine for the daytime snapshot they do not have the
high efficiency of or color balance available in astronomical filters.
You could not do a Ha or OIII shot very well (yes you could put one of
those filters in front of a color detector but I believe the results
would be less than desired.

Of course if you have already selected a specific chip there may not
be a color filter option for it. You can only buy / get what they
make.

In general CMOS sensors do not offer as low as noise as CCDs.
Howerver the new Canon digital SLR cameras have CMOS sensors and dark
noise far below what my CCD based camera would produce (at the same
sensor temperature).

I wish you the best of luck on your endeavors.
Please publish the design if you get it to go.

Leonard

On Fri, 06 Feb 2004 09:09:18 GMT, "David Nakamoto"
wrote:

Color CCDs achieve their results by placing a matrix of color filters ove

r
the sensor array. This cuts down on the sensitivity of the array,
increasing exposure times 2 to 3 times or more. It also reduces the
resolution, since every three to four pixels are used to recreate a

single
color one.

CMOS does have higher noise, and less low light sensitivity.

The best color results are still from using a black and white CCD with a
color filters, taking one exposure per filter.


"Alain J" wrote in message
...
Hi

I want to build my own astronomical camera. I don't have decided which
I'll use. I want to put a color CMOS sensor but many web sites relates
that CMOS sensors are not very good (high dark level)
I've seen a color CMOS sensor with 1,3 Mpixel (1280x1024) at a very low
price (about $140).

For best performance, do I use a color sensor or B&W sensor ? In term
of sensitivy, dark noise which is the best (colour or B&W)?

Cordially

Alain






  #13  
Old February 15th 04, 01:27 AM
Alan Chen
external usenet poster
 
Posts: n/a
Default CCD Camera design

Thanks Leonard,

I was just questioning the phrase "less than desired", since I'm quite happy
with this result. As it turns out, when I increased the contrast and
resampled down to match sizes, the 2 images are not all that dissimilar. If
you are interested, I can send my resampled shot for you to compare. It
really doesn't give much away at all at such a small scale. In fact, mine
is deeper in stars (due to use of a wider 13nm H-a bandwidth), but Russell's
has better contrasts of detail, due to the small 3nm bandwidth. The
passband has much to do with the outcome of H-alpha images. I do agree that
the resolution cannot be equal all else constant, due to the interpolative
routines required to fill in the data, but the depth is similar for the
given times.

Russell's SigmaReject is a great tool. I only recently started to use that.
I've also enjoyed his work over the past year and he is one of the premier
imagers. Your shot only needs more time, but it's tough to overcome light
pollution unfiltered. I'm thinking of going to a 10" f/4.5 Newt, since the
optics on my SCT really aren't all that good along with the mirror shift. I
think you have the right idea with the 8" Newt!

Take care,

Alan
http://www.heavenlyview.com/

"Leonard" wrote in message
...
They are nice shots.
I didn't say you could not.

But assuming a RGBG Bayer color filter on the front of the chip,
it throws away 3/4 of the light / signal.
Same depth in 1/4 the time or 4x the resolution sounds really good in
comparison.

I notice you mention Sigma reject.
I know Russell Crowman. He really is a nice guy.
Here is his shot.
It is less than 10% longer in exposure time on a 4" f5 scope.
Granted it is a different camera (Kodak CCD) but it is deeper and
higher resolution (click on image to see the full resolution details).
http://www.rc-astro.com/nebulae/ic434_region_ha.htm

It is quite a bit better than my shot.
Mine was shot unfiltered line of site to 3 streetlights.
CB245, 27 x 15s (6.75 minutes), cooling off, ambient ~ +35 deg F, with
darks, no flats, no defect map, 8" f5.3 Newtonian
http://photos.yahoo.com/z_leonardh

Leonard

On Fri, 13 Feb 2004 00:49:48 GMT, "Alan Chen"
wrote:

Hi Leonard, Stu,

With all due respect, narrow band imaging can be done with color

detectors.
There is an interpolative process to yield the final image, but the

results
are not as bad as one might think, especially for imagers with small

pixels.

If you get a chance, here are links to my only 2 H-alpha images with a
one-shot.

http://www.heavenlyview.com/b33halphasxvh9c.htm

http://www.heavenlyview.com/ic405sxvh9c.htm

I don't have an OIII filter, but there's no reason to suspect this would

be
much different. Depending on the filter cross-over, this could generate
signal in the blue or green filtered pixels, or both.

Maybe these are "less than desired" to some, but I'm quite happy with the
outcome. Judge for yourself.

Best regards,

Alan
http://www.heavenlyview.com/

"Leonard" wrote in message
.. .
There is another big drawback to using a "color" detector.
You are stuck with the filters the manufacturer placed on the front of
the chip. While fine for the daytime snapshot they do not have the
high efficiency of or color balance available in astronomical filters.
You could not do a Ha or OIII shot very well (yes you could put one of
those filters in front of a color detector but I believe the results
would be less than desired.

Of course if you have already selected a specific chip there may not
be a color filter option for it. You can only buy / get what they
make.

In general CMOS sensors do not offer as low as noise as CCDs.
Howerver the new Canon digital SLR cameras have CMOS sensors and dark
noise far below what my CCD based camera would produce (at the same
sensor temperature).

I wish you the best of luck on your endeavors.
Please publish the design if you get it to go.

Leonard

On Fri, 06 Feb 2004 09:09:18 GMT, "David Nakamoto"
wrote:

Color CCDs achieve their results by placing a matrix of color filters

ove
r
the sensor array. This cuts down on the sensitivity of the array,
increasing exposure times 2 to 3 times or more. It also reduces the
resolution, since every three to four pixels are used to recreate a

single
color one.

CMOS does have higher noise, and less low light sensitivity.

The best color results are still from using a black and white CCD with

a
color filters, taking one exposure per filter.


"Alain J" wrote in message
...
Hi

I want to build my own astronomical camera. I don't have decided

which
I'll use. I want to put a color CMOS sensor but many web sites

relates
that CMOS sensors are not very good (high dark level)
I've seen a color CMOS sensor with 1,3 Mpixel (1280x1024) at a very

low
price (about $140).

For best performance, do I use a color sensor or B&W sensor ? In

term
of sensitivy, dark noise which is the best (colour or B&W)?

Cordially

Alain









 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Novel Camera Set to Produce the First Direct Images of Exoplanets Ron Astronomy Misc 2 June 23rd 04 03:41 PM
CCD camera design problems Doug Hanz CCD Imaging 2 December 24th 03 05:56 AM
Digital Camera as Light-Pollution Meter: Initial Results Tony Flanders Amateur Astronomy 4 September 17th 03 12:11 PM
World's Largest Astronomical CCD Camera Installed On Palomar Observatory Telescope Ron Baalke Science 0 July 29th 03 08:54 PM
Asteroid Hunters Discover Near-Earth Object with New Camera Ron Baalke Science 0 July 16th 03 01:03 AM


All times are GMT +1. The time now is 08:09 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 SpaceBanter.com.
The comments are property of their posters.