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Equipment Discussions >> Cats & Casses

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rmollise
Postmaster
*****

Reged: 07/06/07

Re: Celestron F6.3 Reducer for visual with C8? [Re: Joe Cepleur]
      #5614992 - 01/10/13 07:51 AM

Quote:



From a marketing point of view, it would be advantageous for Celestron to let people believe that the better solution to Meade's native f/6.3 had been available from the beginning. It sounds as though the truth was that it became truly viable only with the introduction of Celestron's f/6.3 reducer/corrector, but what a great marketing blitz it must have been! Smothered Meade's native f/6.3 in its infancy, with a seemingly objective argument about the size of the central obstruction. The competition between these companies must have been savage.





Celestron never suggested that they had an "answer" to the LX-6 Meade from the beginning. If you go back to the advertisements of the day, you will find ads announcing the new 6.3 reducer (desgined by Jim Riffle), and explaining that it gave you TWO TELESCOPES IN ONE.


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careysub
Carpal Tunnel
*****

Reged: 02/18/11

Loc: Rancho Cucamonga, CA
Re: Celestron F6.3 Reducer for visual with C8? new [Re: Eddgie]
      #5713152 - 03/04/13 07:16 PM

Quote:


...
You get a alightly wider field of view, but the brightness will only be that of a 6.5" telescope, and the contrast for things like planets will be reduced somewhat.

The apture is reduced because to get the focal plane to go far enough to the back to reach the field stop of the eyepiece, the mirror must be moved very far forward using the focuser. When you do this, the outside of the light cone converging on the focal plane is cut off by the baffles in the telescope. And because the outside of the light cone is cut off, rather than being a 34% obstruction, the seconary acts as a 37% obstruction...




I'm not sure how you are arriving at the figure of 6.5", given the CO figures you provide.

If the calculation addresses contrast through the (aperture-CO) rule-of-thumb, then:
(1-0.37)*8 = 5.04
but
(1-0.34)*8 = 5.28

If the calculation is about light grasp then:
((1- 0.37^2)*8^2)^0.5 = 7.43
and
((1- 0.34^2)*8^2)^0.5 = 7.52

In neither case is there a large difference (4.5% and 1.2%), in fact neither is detectable to the eye.


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rflinn68
Carpal Tunnel


Reged: 03/09/12

Loc: Arkansas
Re: Celestron F6.3 Reducer for visual with C8? new [Re: careysub]
      #5714593 - 03/05/13 02:31 PM

I cant reach focus with my C8 using the Celestron f/6.3 reducer/corrector using my 2" diagonal. I have to use my 1.25" diagonal, however, I assume the reason is I have a refractor style 2" diagonal and use an adapter. I just use mine for imaging until I buy a dedicated 2" SCT style diagonal.

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Geo31
Carpal Tunnel
*****

Reged: 01/28/13

Loc: Kingwood, TX
Re: Celestron F6.3 Reducer for visual with C8? new [Re: rmollise]
      #5789389 - 04/09/13 11:52 PM

Quote:

Quote:

This still does not prove or disprove that the focal reducer was intended to be part of the C8 kit from the beginning




Well, what disproves that is that the reducer/corrector did not appear till nearly 20 years after the C8 was first introduced...

There had been reducers (not reducer/correctors) available before then, most of them at f/5, from Celestron and other sources.

Once again, the impetus for the r/c was Meade's release of the LX-6 in the late 80s.






I'm just getting back into this after 35 years away, but, while the current style R/C may have been designed 20 years after the C8, I know for certain that "tele-compressors" have been with us since at least 1975. I know that date as that is the first year I went to Stellafane and it was there that I first encountered (or even heard of) one. And while it's possible that it was homemade (hey, it WAS Stellafane), nothing in this guy's gear appeared to be anything but store bought.

I cannot contribute to any idea that the C8 was designed with a reducer/compressor in mind. I devoured Sky & Telescope (and about any other books/magazines I could get my hands on) from 72-77 and never heard of this.

Now, that said, I would personally like to thank you Uncle Rod for your SCT buyer's guide. It was invaluable for me as I sifted through the SCTs available for sale. It became my buyer's bible and I'm happy to say I have a nice Super C8 with Starbright coatings and Byers drive on its way to me as I write this. I'm totally certain you kept me from making some foolish mistakes. Big thanks! Now if I could just figure out which eyepieces to start with (value minded, but not beginner). Things have changed a LOT since I've been gone. Orthos ruled the day, but Plossls just started becoming popular (and were twice the price of Orthos - go figure).

George Roffe
Kingwood, TX


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jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: Celestron F6.3 Reducer for visual with C8? new [Re: Eddgie]
      #5789398 - 04/10/13 12:01 AM

"Just be aware that when you use a 2" diagonal in a C8 behind the 6.3 focal reducer, it will have the effect of turning your telescope into a much smaller telescope."

What if you use a 1.25" diagonal behind the FF/FR?

Regards,

Jim


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rmollise
Postmaster
*****

Reged: 07/06/07

Re: Celestron F6.3 Reducer for visual with C8? new [Re: jrbarnett]
      #5789819 - 04/10/13 09:09 AM

Quote:

"Just be aware that when you use a 2" diagonal in a C8 behind the 6.3 focal reducer, it will have the effect of turning your telescope into a much smaller telescope."

What if you use a 1.25" diagonal behind the FF/FR?

Regards,

Jim




Jim...don't worry about it. I guarantee that the 6.3 works well, even with a 2-inch diagonal, and most assuredly does NOT turn your telescope into a much smaller one.


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Eddgie
Postmaster
*****

Reged: 02/01/06

Re: Celestron F6.3 Reducer for visual with C8? new [Re: jrbarnett]
      #5790158 - 04/10/13 12:07 PM

I will give you the answer, but I agree with everyone else. Don't worry about it.

With the standard focal reducer in place, just about all of the Celetron SCTs will start loosing aperture once you go past about 100mm of back focus, and most 2" diagonal configurations will be longer than this.

A 1.25" configuration will usually be less than 100mm and the system should still work at full aperture.

But don't worry about it. If you can't tell any difference, then it doesn't matter.

If you would like Ken Hutchinson's SCT vitnetting analysis though, I am happy to send it to you. Just PM me your email address. It has all of the information regarding things like focal ratio change, aperture change, spot size change at the edge of the field, and other such data.


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cn register 5
scholastic sledgehammer


Reged: 12/26/12

Re: Celestron F6.3 Reducer for visual with C8? new [Re: Eddgie]
      #5791089 - 04/10/13 07:12 PM

AIUI it isn't the size of the diagonal that matters. How can the light cone care about what's around it? What matters is the separation between the FR and the EP. The optimum is 105mm and this is achieved with the visual back and 1.25" diagonal.

A 2" diagonal is bigger and so give more separation, especially the refractor style that needs a 2" visual back to connect it to the FR but the type of 2" diagonal that screws directly to the FR may have a short enough light path that the FR to EP separation may be what's required. In this case I can't see a reason why an aperture reduction would be seen.

Hope this makes sense,

Chris


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orion61

*****

Reged: 10/20/07

Loc: Birthplace James T Kirk
Re: Celestron F6.3 Reducer for visual with C8? new [Re: cn register 5]
      #5791253 - 04/10/13 08:30 PM

Well the F6.3 FR/FF is still around and the F6.3 optical system isn't...
I have mine on my C14 and it pretty much never comes off unless I am using my binoviewer.
for any std SCT they are a must have! I may be biased but the origonal (Celestron Japanese units) are the best. I have owned 2 other brands, and can tell the difference in truer Star colors and sharper stars. I think of it as my Edge with the correcting lens on the outside LOL...


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