Author Topic: Sky Watcher EQ6 vs. Celestron CGEM  (Read 1066 times)

tricacotin

  • Active Astronomer
  • ***
  • Posts: 115
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Sky Watcher EQ6 vs. Celestron CGEM
« Reply #30 on: February 09, 2018, 04:14:16 AM »
Quote
The Meade's are also very nice scopes. Though with one detail that puts the Edge's above them. The edges have the TEMPest fan retrofit. I cannot stress enough how valuable this is. Also the Meade's tend to be heavier. I like the color better on it though.  Optically they both do well though the Edge series is actually better because of the correction but on the flip side the Meade can get down to f/6.3 and even f/3.3 with the right focal reducer (with vignetting though) whereas the Edge only goes down to f/7


I was under the impression that the Edge can go to f/2 in the Fastar mode. Is that incorrect? I realize you are referring to using a focal reducer, but for AP use the Edge would seem to have the, um, excuse me . . . edge.    However you raise an interesting point--why will the Celestron not reduce to an f-stop as low as the Meade with a FR?

Jeremiah Greer

  • Active Astronomer
  • ***
  • Posts: 134
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Sky Watcher EQ6 vs. Celestron CGEM
« Reply #31 on: February 09, 2018, 09:43:45 AM »
Quote
Quote

The Meade's are also very nice scopes. Though with one detail that puts the Edge's above them. The edges have the TEMPest fan retrofit. I cannot stress enough how valuable this is. Also the Meade's tend to be heavier. I like the color better on it though.  Optically they both do well though the Edge series is actually better because of the correction but on the flip side the Meade can get down to f/6.3 and even f/3.3 with the right focal reducer (with vignetting though) whereas the Edge only goes down to f/7


I was under the impression that the Edge can go to f/2 in the Fastar mode. Is that incorrect? I realize you are referring to using a focal reducer, but for AP use the Edge would seem to have the, um, excuse me . . . edge.    However you raise an interesting point--why will the Celestron not reduce to an f-stop as low as the Meade with a FR?

As I understand it, yes, the EdgeHD telescopes do Fastar at f/2 although I've never done it with mine.

As for focal reducers, we're comparing apples to kumquats. Traditional focal reducers are relatively unsophisticated optical devices that can produce any f-ratio if you use a strong enough lens and put it close enough to the sensor. (You can't do f/3.3 with a DSLR because the reducer lens can't get close enough to the sensor.) However, the image quality is not tip-top. For the EdgeHD series, Celestron makes an f/7 reducer that is optimized to correct aberrations and give as much of a wide, flat, sharp field as possible. That's a quite different animal (to change metaphors).
The EdgeHD is a higher-performing optical design in the first place than Meade's ACF, though the difference is not large. Both of these are much better than conventional Schmidt-Cassegrain telescopes.
You can put the old-style focal reducers on an EdgeHD telescope; I've done so; they work about as well as with a conventional Schmidt-Cassegrain, sharp at the center, not sharp at the corners. The EdgeHD with its custom-designed f/7 reducer is sharp from edge to edge.

More highly corrected reducers for conventional Schmidt-Cassegrains are made by Starizona in Tucson.