What's The Scoop on This Telescope? (Meade Infinity 102)

In looking at the kinds of telescopes sold these days, as a result of the 60mm
for $60 thread, I found this:

http://www.meade.com/infinity-102mm-...refractor.html

With a 102mm aperture, although it won't provide the same planetary views as a 6"
or 8" telescope, still, one can see the bands in the atmosphere of Jupiter. It's
enough to be fascinating for some time.

And the price doesn't sound too outrageous for the aperture either.

But wait a minute...

Obviously, this is an achromat, not an apo, to be at that price.

And that tube looks *awfully short*.

I could also criticize the fact that it comes on an altazimuth mount, since these
days computerized go-to mounts are found on relatively economical telescopes, but
perhaps that's available for another $100 or so on the price tag.

I'm just wondering how on Earth a telescope like this could have acceptable
optical quality. An achromat should have a relatively long tube - one-and-a-half
to twice the length of that of this telescope, I think.

John Savard

A generally positive review of the telescope gives its focal length as 600mm, so that makes it f/6.

That review is available he

http://www.cloudynights.com/page/art...y-102-az-r2915

Another Meade refractor with 102mm aperture has a longer tube and a computerized mount, and is the space.com number one recommendation for beginners:

http://www.space.com/15655-meade-sta...pe-review.html

Ah, yes, its focal length is 800mm. That's f/8, still cutting it rather short for an achromat, but I can believe that *it* can yield decent, if not spectacular, images.

But maybe so can an f/6, and it's just the finicky purists who would expect an
achromat to be f/16 or at least f/12.

John Savard

On Thursday, 19 May 2016 04:18:37 UTC+2, Quadibloc wrote:

But maybe so can an f/6, and it's just the finicky purists who would expect an
achromat to be f/16 or at least f/12.

John Savard

Where an achromat is concerned CA is a function of aperture as well as focal length.

A 100mm [4"] f/6 with a CA ratio of 1.53 is a fair equivalent to a 150mm"[6"] f/9.

The 100mm [4"] is thus slightly better than the typical 6" f/8 at CA 1.3.

But falls [according to Sidgwick's standards] within the filter-friendly camp of psychedelic impressionism. ;-)

On Wednesday, May 18, 2016 at 10:05:29 PM UTC-4, Quadibloc wrote:

I'm just wondering how on Earth a telescope like this could have acceptable
optical quality.

Define "acceptable."

An achromat should have a relatively long tube - one-and-
a-half to twice the length of that of this telescope, I think.

I have an 80mm f/5 that can show polar caps/hood on Mars at about 18x, so go figure.

On Thursday, May 19, 2016 at 8:57:57 AM UTC-4, wrote:
On Wednesday, May 18, 2016 at 10:05:29 PM UTC-4, Quadibloc wrote:

I'm just wondering how on Earth a telescope like this could have acceptable
optical quality.

Define "acceptable."

An achromat should have a relatively long tube - one-and-
a-half to twice the length of that of this telescope, I think.

I have an 80mm f/5 that can show polar caps/hood on Mars at about 18x, so go figure.

You will never see the kind of planetary detail in a fast 4 as an f/15, but you can see basic details. Also, these Chinese achromats tend to be pretty accurate these days owing to being made on fully-automated machines where human hand work can't screw them up.