Re: "That's a REALLY nice 1500mm lens you have there"
- From: "Rich" <rander3127@xxxxxxxxx>
- Date: 12 Apr 2007 16:38:50 -0700
On Apr 12, 7:06 pm, ASAAR <cau...@xxxxxx> wrote:
On 12 Apr 2007 14:53:21 -0700, Rich wrote:
A 500mm f5-6 telescope gives you the option of "prime focus"
(just the front lens and the camera) or you can use an eyepiece
adapter for longer focal length work. Inevitably, the results
are superior to using a spotting scope.
Stating the obvious and missing a significant point. Astronomers
and advanced amateurs use "real" telescopes. Birder usually don't.
How practical do you think it would be to trek through the brush
carrying a huge, heavy telescope? These pictures, after all, were
of birds, which should have provided some clues for you to use.
"Huge" scope like this?
366mm focal length. Apochromatic. (As in "really" and not "camera
lens" apochromatic) f5.9 focal ratio. All metal, anodized and
plated. 2 speed focusing. ZERO plastic. $299.99.
So now you're down to 366mm from 500mm, both of which are
significantly less than Nikon's 1000mm scope which (with its
adapter) is designed to interface with and provide data to a digital
camera. Anodized and plated could indicate a flimsy aluminum tube.
Maybe we could tell more about it, but you weren't proud enough of
your feeble telescope to have mentioned the name of the company that
manufactured it. Was it on sale at Radio Shack? :)
Yeah. Radio Shack:
http://www.williamoptics.com/telescopes/zenithstar66sd_features.htm
For what it's worth, what kind of image quality can we expect from
that 366mm telescope? As good as the images you'd get from one of
Nikon's 300mm lenses?
At least as good as the Nikon. Good telescopes are "diffraction
limited" which basically means they are fabricated to deliver as much
resolution as is possible given the diameter of the front lens. The
average camera lens is nowhere near as accurately made, which is one
HUGE reason why you have to stop down a camera lens to maximize image
quality, residual aberrations make it this way.. However, if you want
the Nikon lens's speed (f4 or so) in a 500mm telescope with that kind
of optical correction, you are looking at around $2300. The William
Optics model I showed you has a smaller front element so it's speed is
f5.9 at 366mm.
The difference in focal length isn't very
significant and you can get an AF 70-300mm f/4-5.6G for as little as
$129.95 & $139.00 from B&H, or $294.95 & $319.95 for the better AF
70-300mmD ED version. You can pay as much as $479.95, but that's a
VR lens. They all have several advantages over your anodized
aluminum scope. All of the normal lens features, AF, metering and
passing lens data to the camera. They may also include the 5 year
extended warranty often included with some of Nikon's lenses. Do
you actually own that $299 lens and know how it performs, or do you
just know of it as a web surfer?
No, I own it. I put it up against an Olympus 300mm F4.5 telephoto on
Dpreview's Olympus forum.
No contest, the apo scope clobbered the camera lens in every
department. I stopped down the camera lens to
f5.6 in order to equalize the "speed" and give the camera lens a bit
of help in the image department. The Olympus 300mm was one of the
first camera lenses from them to use ED glass. The result of the test
was a foregone conclusion because a good telescope uses few optical
elements in the train as possible, something people who use telescopes
know all about. It maximizes contrast and if the scope is designed
correctly, aberrations are kept at a minimum.
In terms of speed of use, compactness, etc, a camera lens will
definitely win. But in order to achieve these attributes, the optical
design of the camera lens suffers. If you can accommodate its design
in the field (unless you have the very best Canon or Nikon telephotos,
the 300-600mm f2.8 and f4 models) a good telescope will provide the
best image quality.
http://forums.dpreview.com/forums/read.asp?forum=1022&message=21875592
But don't take my word for any of this. For $299 buying one is an
afterthought and well worth the experiment.
.
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