Re: CCD misunderstanding/ confusion

On Thu, 21 Apr 2005 17:03:46 GMT, "John Edmund" <12345@xxxxxxx> wrote:

>
>"Chris L Peterson" <clp@xxxxxxxxxxxxxxxxxx> wrote in message
>news:3tce619a7rgisktjq403r6vpp9f13fgtoh@xxxxxxxxxx
>> On Thu, 21 Apr 2005 04:59:11 GMT, "John Edmund" <12345@xxxxxxx> wrote:
>>
>> >There's something I think I have wrong concerning CCDs and I wanted to
>find
>> >out the correct answers. Say I have a webcam, which has an ICX098 CCD
>and
>> >another camera with an ICX424 CCD. I want to image Jupiter with a C8
>and
>> >3x barlow ahead of the webcam and other camera. When the webcam/ barlow/
>C8
>> >combo are used, let's say that the diameter of Jupiter on the laptop
>screen
>> >is 3" across. Now, I remove the webcam and replace with the camera with
>the
>> >ICX424 CCD, making sure the CCD is the same distance as the webcam's.
>What
>> >will the image size be on the screen now?
>> >
>> >The part I'm finding confusing is this: since the ICX424 covers a larger
>> >pixel area than the 098 and also has a larger pixel size(?), I am
>assuming
>> >the amplified Jupiter will not be the same size on the screen that the
>> >webcam produces, and in fact the image will be smaller. Am I wrong? Or
>is
>> >it that the 424 just covers a wider
>> >area and the image size of Jupiter is still the same?
>>
>> Right the first time- the size of Jupiter on the screen will be smaller
>> when using the camera with the larger pixels.
>>
>>
>> >Finally, what benefit, if any, would there be with this combo system if
>> >using just the 424? Would there be better resolution than the 098 offers
>or
>> >worse?
>>
>> Just because the pixel size of one of the cameras is smaller, that
>> doesn't necessarily mean the resolution will be better. That is because
>> something else may be what actually limits resolution- the optics,
>> seeing, etc. If the pixel scale is much smaller than the scale of the
>> seeing, the extra resolution is empty, and the small pixels will be
>> collecting fewer photons and may deliver poorer S/N.
>>
>> Ultimately, what is important isn't the absolute size of the pixels, but
>> the pixel scale, which is determined by the pixel size and the telescope
>> focal length. Once the pixel scale is optimized (usually to a few tenths
>> of an arcsecond for planetary imaging), the size of the sensor simply
>> determines the field of view.
>
>
>Hi Chris,
>
>The reason I brought up the questions was because I've seen a growing trend
>away from webcams and more towards industrial CCD cameras for planetary
>imaging. However, I looked into many of these industrial camera specs and
>most are using an ICX414/424. They claim the faster, uncompressed speeds of
>these cameras is their advantage, but if they're losing both gain and image
>scale due to larger pixel size and area (over 098 ccd), then I can't see the
>advantage is more frames still have to be stacked anyway. In other words,
>if I switched from a webcam to a 414 based camera, I'd have to increase my
>system amplification to get the same image scale with the 414. That makes
>me question the advantage, if any.
>
>John
>
>> _________________________________________________
>>
>> Chris L Peterson
>> Cloudbait Observatory
>> http://www.cloudbait.com


Hi John,

I had the same concerns you have about the image scale differences
but after using my Lumenera with the 424 CCD for two months I have no
doubt that the Lumenera LU075C (yes it is a color camera) has a fair
amount more sensitivity than my Toucam that I have been using for two
years (allowing for equal focal lengths) and that it also has a great
deal less noise.
I have seen the on paper comparisons of the CCD's but after using one
in the real world I am convinced, I am definitely not an electronics
expert but my guess is the Lumenera has higher quality components and
circuitry than the Toucam.
When comparing the gain settings (equal focal lengths using different
barlow powers) at 30FPS I was surprised to see that the gain setting
on the Lumenera was at 25% to get a bright image and the Toucam was
at 80% (Telescope an 18" Newt.).
This is just my experience (certainly not scientific) and I realize
that real testing could come to a different conclusion but anyway for
what it is worth I thought I would tell you my experience with the
Lumenera LU075C, I have a nice Jupiter image taken with the
Lumenera at 60FPS during at best average seeing and I can provide a
link to it you like.
One thing I almost forgot is the Lumenera has an option for 10 bit
precision of which I can only use at 30FPS because the file sizes
are so large

Thanks,

Wes Higgins
.

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