Canon 5D vs. Medium Format (Film)

Scott W wrote:

Rich wrote:
amateur astronomers use focal lengths like 50,000-200,000mm when

shooting planets?


Who is going to use a FL of 200m? That is like two football fields in
length.

Scott


Here is a guy who does great planetary imaging with a 250 mm
aperture at f/42, so 6,000 mm.
http://www.sg-planets.org/mars.html

I've done something like f/115 at 203 mm apertu
http://www.clarkvision.com/galleries...piter-8-a.html
so 23,460 mm (this was before digital).

I've also done planetary imaging with the UH 88-inch
on Mauna Kea at f/10, so 88*25.4*10 = 22,350 mm (also with film)

Planetary Patrol imaging done on Mauna Kea used 24-inch
(diameter) Cassegrain telescopes working at f/75, so
24*25.4*75 = 45,720 mm (with film). Those telescopes were
decommissioned in the 1980s if I remember correctly.

I'm not aware of any amateur astronomers working at 200,000mm,
but 50,000 wouldn't surprise me.

Roger

acl wrote:

Actually, you may have made a political mistake by labelling it a myth,
since this seems to stir people into negative reactions wrt it. I
imagine your life would be much easier if you had called the article eg
"Some interesting Observations regarding the Significance of the f/ratio
of Photographic Lenses, With Applications to Modern Digital Cameras"
(plus it sounds like the title of a 19th century treatise, which is
always nice).

Yep, I agree. But the fact that people have such negative reactions
is further indication that it is a myth. ;-)

Roger

On Thu, 5 Oct 2006 09:27:15 +0900, "David J. Littleboy"
wrote:


"RichA" wrote:
On 4 Oct 2006 11:07:26 -0700, "Scott W" wrote:
Paul Rubin wrote:
"Scott W" writes:
Using a telescope that you look through is not a good way to analyze
an image capturing system. It is really pretty simple, this limit of
resolution is the wavelength of light / f-number.

Where do you get that? I always thought the diffraction limit
depended purely on the aperture (diameter) and not the focal length.

It depends on where you are defining resolution. For angular
resolution of the scene you are correct it is a function of the
aperture, but when we are dealing with the resolution on the
film/sensor it is a function of the f/number. This is pretty handy
because for any imaging system there will be an f/number that going
higher then will start to blur the image.

You'd be correct, but only for the same lens.

No. The f number uniquely determines the diffraction limited resolution at
the sensor regardless of focal length. At which point, for the same f
number, the focal length determines the resolution of hte subject.

As the f-number of a
specific lens increases, it's aperture is decreasing. However, a
100mm lens at f10 will resolve detail twice as fine as a 50mm lens
at f5 because f-ratio has nothing to do with the resolution of detail,
aperture determines that.

Hello? The 50/5.0 has exactly the same aperture as the 100/10 and the
angular (or subject) resolution will be exactly the same.

Did you actually have this wrong (which would explain why you object to my
TC arguments) or was it just a goof?

No, resolution, the ability to show detail of a specific size, is
solely determined by the aperture and is proportional. F-ratio has
nothing to do with resolution. I only used the faster f-ratio for the
50mm to illustrate the point that f-ration has no bearing on
resolution. However, because lenses used at prime focus cannot
approach their true resolving ability, proving this with camera lenses
is difficult. It's easy with a telescope.

Assuing you meant that a 100/5.0 will resolve twice the detail of a 50/5.0,
no one was ever arguing that it wouldn't. Since TC's reduce the f number
(i.e. don't increase the aperture), you don't get any additional diffraction
limited resolution.

If that were true, then you'd see diffraction effects the moment you
stopped down a lens by even a small amount because you are saying that
you are operating at the lens's diffraction limit when using a lens in
prime focus (just the lens and camera) mode. The fact you don't see
diffraction degrading the image until you hit around f16 or f22 proves
that no camera lens is operating in prime focus at it's diffraction
limit. To do that, you must interpose a second lens to increase the
overall system focal length.
The only way you'll ever get diffraction limited performance using a
lens on it's own is to have a sensor with pixels so small they could
record detail at the diffraction limit using only the fixed
magnification of the lens at prime focus. They would be very small
pixels. According to Olympus, the standard kit lenses they have are
"good" to 22 megapixels in the 4/3rds format. We will likely never
see that kind of density in a consumer camera.

On Tue, 26 Sep 2006 20:22:03 -0500, ASAAR wrote
(in article ):

At the point that Microsoft feels that there's mucho money to be
made by putting all things photographic into a future version of
Windows, including such things as automatically handling RAW files
for all of the popular cameras it deems worthy of support.

You're talking about Apple's MacOS X, right?

On Tue, 17 Oct 2006 16:18:19 -0500, Verne Arase wrote:

At the point that Microsoft feels that there's mucho money to be
made by putting all things photographic into a future version of
Windows, including such things as automatically handling RAW files
for all of the popular cameras it deems worthy of support.

You're talking about Apple's MacOS X, right?

Hey, Verne, It's Ernest! No, I didn't mean that. KnowWhutImean,
Verne?

"Verne Arase" wrote in message
.com...
On Tue, 26 Sep 2006 20:22:03 -0500, ASAAR wrote
(in article ):

At the point that Microsoft feels that there's mucho money to be
made by putting all things photographic into a future version of
Windows, including such things as automatically handling RAW files
for all of the popular cameras it deems worthy of support.

You're talking about Apple's MacOS X, right?

Of course, there's a huge difference when MS does this, as opposed to Apple.
Apple is trying to gain market share by adding value, MS is trying to steer
standards in their direction to tighten their hold on the OS monopoly.
Remember, MS was ruled to be an abusive monopoly by the courts and gets
treated differently than Apple.