Re: [APML] D60/D100 was (new image: IC1396-Provia and halpha CCD)

[Rob Miracle <rwm@photo-miracles.com>]

At 10:54 AM 10/11/2002 -0400, you wrote:
>In a message dated 10/11/2002 9:38:36 AM Central Daylight Time, 
>rwm@photo-miracles.com writes:
>>However, the new 11 megapixel Canon 1Ds completely
>>resolved the resolution chart,  well past 2000 lines per picture height.
>>(www.dpreview.com).   The D100 and D60 were both up around 1800 lpph.
>
>
>Again, you are confusing resolution with image size.

No I'm no.   Resolution is the ability to image two distinct areas of 
contrast, for instance, take this example:

|||||||||

Its hard to resolve because the is almost no contrast between the vertical 
lines. But this:

| | | | | |

is much easier to resolve.

The greater an imager (be it film, CCD, or CMOS) ability to separate lines 
of contrast.   More photosites per square mm will allow the imager to 
separate those lines better because the resulting output is one pixel on 
your computer.   Fewer but bigger photosites will end up not with black and 
white pixels, but grey pixels as well and the ability to resolve fine 
detail is lost.

>If you had a fixed lens with fixed focal length, then the resolution of 
>any particular target (say the Enke division on Saturn) would not change 
>at all if you had .1 megapixels or 11 megapixels. The ONLY criteria is how 
>many pixels per arc second. Real resolution is strictly a matter of pixel 
>spacing, not how many pixels you have.

I think were we are differing here is primarily an area issue.   CCD's for 
photographic cameras come in fixed sizes.   For instance the D100 uses a 
16x24mm sensor.   The EOS 1Ds is a 24x36mm sensor.    The D1 was also a 
16x24mm sensor, but only had 2.7 million photosites where as the D100 has 
6.1 million.    The D100's photosites are packed much denser allowing for a 
much higher ability to resolve fine detail.   You can almost look at it as 
a measure of pixels per mm.   The D1 and D1H have around 82 pixels per 
mm.   The D100 has 125 pixels per mm, yet the EOS 1Ds has 112 pixels per mm 
because its pixels are spread out over a larger area.

If each pixel row in theory has the ability to resolve a line of 
contrast,  Provia 100 resolves either 60 or 140 lines per mm depending on 
contrast.  You can see that the current crop of 6 megapixel cameras (The 
d60 and d100) are resolving nearly as well as Provia.

Naturally photosite size has something to do with the resolving 
power.  Larger photosites packed more tightly will resolve better than 
smaller, loosely packed photo sites.

>The present 6.8 micron REAL resolution of the monochrome chip used in the 
>ST10E is still the leader. There may be other monochrome chips out there 
>that I don't know about with smaller spacing, but I have not run across 
>them. You will not be able to resolve nearly as well using a tri-color 
>chip versus a monochrome chip. The fact that you can capture color in one 
>shot is a convenience, but I believe at this point you will need to suffer 
>for your art if you wish to achieve truly high resolution in your images.

Yea, but you can't use an ST10E to take landscape photos or pictures of 
your dog either.   Its tuned specifically for photographing the night 
skies.  They are designed for long exposures necessary for serious 
astrophotography.

Cameras like the D60 and D100 are general purpose cameras and their use for 
Astrophotography is still somewhat limited, however, stacking multiple 5 
minute exposures is now practical where it wasn't before these.

Now it seems to me, and I might be wrong, but one of the reasons you use an 
11" scope over a 4" scope isn't to get closer to the subject but to gather 
more light.    Its all about collecting stray photons.   For this you would 
want a digital camera with tightly packed, large photo sites.  You don't 
want any photon's slipping through the cracks between loosely packed 
photosites and the larger the photosite the more light sensitive it is, so 
its more likely to pick up that stray photon which would allow it to SEE 
the sky better.    I would think a 7.5 micron photosite would have a better 
chance of gathering the photons that a 6.8 micron one would, especially if 
the overall sensor size is the same and the number of photosites is the 
same (different density).


Rob
--
Rob Miracle
Photographic Miracles
203 Carpenter Brook Dr.
Cary, NC 27519
http://www.photo-miracles.com


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