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Equipment Discussions >> Cats & Casses

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Michael2
member


Reged: 06/01/11

Loc: Australia
Celestron F6.3 Reducer for visual with C8?
      #5602067 - 01/02/13 10:28 PM

I am considering purchasing a Celestron F 6.3 reducer for use with my 1977 vintage Orange Tube C8 from OPT .
This will be for visual use only. I am working with Stephen James OMeara’s series of books where he used a Televue Genesis Refractor and the eyepieces gave powers of 23x, 72x, 105x plus the addition of a 1.8x Barlow and a 3x Barlow.
The eyepieces I will be using are GSO 50mm =40x, Celestron Silver Top Plossols 36mm=55x, 26mm=77x, 17mm=117x, and 10mm=200x.
Can anyone see a problem with trying to gain some lower power views by using the reducer in this set up?
I have a 2 inch GSO SCT Diagonal that I will be using. Where exactly is the Reducer placed?
Any advice or comments would be welcome.

Michael

Australia.


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Patrick
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Reged: 05/16/03

Loc: Franklin, Ohio
Re: Celestron F6.3 Reducer for visual with C8? new [Re: Michael2]
      #5602096 - 01/02/13 10:49 PM

Hi Michael!

The reducer is screwed onto the back of the scope where you'd normally put the visual back. The visual back is then screwed onto the reducer.

Adding a reducer is a fine solution to get you to a little more field of view.

Patrick


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Jim-M
super member


Reged: 10/09/09

Loc: Southern Calif.
Re: Celestron F6.3 Reducer for visual with C8? new [Re: Patrick]
      #5602248 - 01/03/13 12:55 AM

Michael,
The 6.3 FR works well with the C8 to give wider and flatter field views. Consider though that the C8 field is limited to about 1.3 deg. FOV by the baffle tube. Believe the 50 mm you have will be close to that without the FR.
Also consider the spacing. The FR needs to be spaced close to 105 mm from eyepiece front element. That might be difficult with the 2" diagonal. The 1.25" diagonal that I use gives near correct spacing.


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Eddgie
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Reged: 02/01/06

Re: Celestron F6.3 Reducer for visual with C8? new [Re: Michael2]
      #5602426 - 01/03/13 06:58 AM

Hello Michael,
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.

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.

The net result is that the field is a little wider, but dimmer, and the view will be vignetted to some degree.

Please keep this in mind and consider removing the reducer when you don't need the entire aperture, or your scope will bascially be working as a 6.5" and performance on most deep sky and solar system targets will be reduced.

So, when you don't need it, it is best to take it off.

And the problem with this is that you will get tired of doing it.

My own recommendation would be to get a 55mm or 56mm Plossl and leave the focal reducer out. You get a slingly narrower field of view, but the quality of the view is far better.

If you choose to leave it in all the time, the next best thing to do is when you don't need 2" eyepieces, remove your 2" diagonal and put your 2" to 1.25" adapter into the visual back and put in the 1.25" diaognal. This will put you back to almost your full apeture, and it is easier than removing the focal reducer every time you want to go to hgher powers.

Also, I think your powers are too compacted into the low power end of the spectrum. The step between 40x and 55x is so small that you will amost always skip int, and the step between 117x and 200x is to big because for deep sky work, you will want some powers intermediate to this.

The reducer goes on to the port at the rear of the SCT.

Your 2" visual back screws on to this. Or if you are using an SCT dedicated diagonal, that would screw on to the focal reducer.

Don't forget though, that when the focal redcuer is used in front of the 2" diagonal, you loose quite a bit of brightness.

Good luck.


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yonkrz
scholastic sledgehammer


Reged: 11/16/06

Loc: SW Minnesota
Re: Celestron F6.3 Reducer for visual with C8? new [Re: Eddgie]
      #5602466 - 01/03/13 07:44 AM

Not trying to hyjack the thread,but i am having the same dilema.So lets say you leave out the FR and keep the 2" diagonal,what EPs would work best for low power,not necessarily wide field.

On the other hand i dont yet have a 2" diagonal but do have the FR,is a person better off getting a good quality 1-1/4" diagonal? Rod helped a while back with pms about a FR,but this just keeps getting more confusing, all i want is the best possible visual views i can get from my c-8.

As i stated above im not trting to hyjack the thread,i just didnt realize all the options and dont know what i need.


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bouffetout
scholastic sledgehammer


Reged: 11/21/12

Loc: Canada
Re: Celestron F6.3 Reducer for visual with C8? new [Re: yonkrz]
      #5602486 - 01/03/13 08:18 AM

Putting a focal reducer Will bring Yuor C8 from f/10 to f/6.3 and 2032mm focal length to 1280mm.
Personally I have one on !


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Eddgie
Postmaster
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Reged: 02/01/06

Re: Celestron F6.3 Reducer for visual with C8? new [Re: yonkrz]
      #5602494 - 01/03/13 08:22 AM

Form an absolute best performance across the field standpoint, the 35mm Panoptic is a perfect perfect perfect match for the C8. The field stop of the 35mm Pan is almost the exact same size as the rear baffle, so the edge of the field is as bright as the design allows.

But you can go wider, and in fact, much wider, if the lowest power and biggest exit pupil is your goal.

For the best brigtness, I advise a 56mm Meade Superplossl. This will give a very nice, bright, wide field with a 5.2mm exit pupil.

Remember, you can get lower magnification with the focal reducer, but because the aperture is reduced when you use a 2" eyepeice, you get a esentailly the same size exit pupil because you are using a 6.5" scope. In other words, you won't get any added brightnss using the focal reducer that you would get just using the 56mm Plossl!!!

And there are two functions of a telescope... Expand the angular size of the target by magnification, or make the target brighter by making the exit pupil larger, but at the expense of angular magnification.

This is why it doesn't make sense to use a focal reducer. You get a smaller image scale, but you loose the exit pupil that the lower magnification would give because the aperture is reduced. My personal belief is that the wider view is no advantage if you can't get a brighter image from it for DSOs. And if you want to get the Pliedes into the field, get a 4" achromat. It is a much better way to get there.

The field of the 56mm plossl will be vignetted near the edge. If you drift a faint star to the field scope, it will wink out just before it gets to the very edge, but it is hard to notice the loss of the faintest stars.

But there is this. The bigger exit pupil often comes at a price. If your sky conditions are not very dark, the bigger exit pupil will cause the sky to look brighter and brighter as it gets bigger and bigger. The sky can appear a bit washed out, and even though deep sky objects will keep the same amount of brightness against the background, to the eye, the view seems less contrasty. It really isn't but it could appear that way.

I had a 56mm Plossl and a 35mm Panoptic in my C8 and did side by side comparisons many times from my central Austin back yard. I felt that while the field was very slightly smaller in the Panoptic, the view seemed more pleasing because of the darker background.

Under darker skies though, and for large objects like Lagoon, Orion, Rosette, and many other very large Nebula, the 56mm Plossl was clearly better because of the very large exit pupil that it offers vs the 35mm Pan.

It is like turning your 8" SCT into an 8" dob.


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rmollise
Postmaster
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Reged: 07/06/07

Re: Celestron F6.3 Reducer for visual with C8? new [Re: Eddgie]
      #5602614 - 01/03/13 09:45 AM

Quote:

Hello Michael,
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.




We've been down this road before.

As a regular user of this combination, I will again say that you will never notice the difference. The only real difficulty you will experience is that longer focal length eyepieces, above about 25mm will vignette. But with this combination, you shouldn't have to use longer focal length eyepieces.

This is personal preference, mind you, but I have a hard time imagining a less comfortable eyepiece to use than a pea-picking 50mm range Plossl.

Edited by rmollise (01/03/13 09:47 AM)


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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: Celestron F6.3 Reducer for visual with C8? new [Re: Eddgie]
      #5602683 - 01/03/13 10:25 AM

This is a popular and complex topic. You may want to read the responses I got in a similar thread.

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Patrick
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Reged: 05/16/03

Loc: Franklin, Ohio
Re: Celestron F6.3 Reducer for visual with C8? new [Re: rmollise]
      #5602829 - 01/03/13 11:52 AM

Quote:

We've been down this road before.




Yep...a well traveled road, too.

I personally don't like long focal length plossl's even if they do give a wider field of view. The view may be wide, but the mags are low as well. Plus a long plossl still feels like I'm looking through a straw.

I think there is a trade off between slight light drop off with a reducer and higher mags, versus no light drop off and low mags. I prefer the higher mags myself. Quite frankly I don't see any light drop off when I use my Denk Power X Switch single eyepiece diagonal in 0.66x reduction mode and a Panoptic 27mm eyepiece. I'm not saying it isn't there, but I just don't see it.

Patrick


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yonkrz
scholastic sledgehammer


Reged: 11/16/06

Loc: SW Minnesota
Re: Celestron F6.3 Reducer for visual with C8? new [Re: rmollise]
      #5603015 - 01/03/13 01:33 PM

Thanks again for the input Rod,so with all the repeatedness put aside. Lets say i want to use a 2" diagonal and was starting fresh with no eps,and wanted two eps for the time being, a low power and mid/high power,what would be the suggestion,i realize eps are a complete other area of discussion but am looking to see what is prefered for this particular setup if i can only have two eps,i wont ask any more questions,i will get what is suggested and just observe.

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rmollise
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Reged: 07/06/07

Re: Celestron F6.3 Reducer for visual with C8? new [Re: yonkrz]
      #5603173 - 01/03/13 02:59 PM

Quote:

Thanks again for the input Rod,so with all the repeatedness put aside. Lets say i want to use a 2" diagonal and was starting fresh with no eps,and wanted two eps for the time being, a low power and mid/high power,what would be the suggestion,i realize eps are a complete other area of discussion but am looking to see what is prefered for this particular setup if i can only have two eps,i wont ask any more questions,i will get what is suggested and just observe.




How much moola...dineros...money are we talking? If on the reasonably modest side, you could do worse than the 82-degree jobs from Explore Scientific.


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Patrick
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Reged: 05/16/03

Loc: Franklin, Ohio
Re: Celestron F6.3 Reducer for visual with C8? new [Re: yonkrz]
      #5603180 - 01/03/13 03:02 PM

I know what I'd suggest because what I have is just about perfect. But no one generally listens to me so spend your money on eyepieces instead.

1) Denkmeier S1 Power X Switch Diagonal for SCT (Scroll down to the S1 for SCT).

The S1 will give you 0.66x focal reduction, 1.0x (straight thru), and a 2x barlow. With one eyepiece you will get three magnifications.

2) 24mm Televue Panoptic eyepiece (or 27 Pan?).

With the S1 and 24 Pan you will get a 36mm eyepiece, a 24mm eyepiece, and a 12mm eyepiece. In your C8 that will give you approximately 55x, 83x. and 166x

Then get an inexpensive plossl or two for your high power planetary observing using the built in barlow.

Patrick


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Michael2
member


Reged: 06/01/11

Loc: Australia
Re: Celestron F6.3 Reducer for visual with C8? new [Re: Patrick]
      #5603255 - 01/03/13 03:41 PM

Thanks very much for the effort everyone has gone to in these replies.
I am thinking that this may come down to a "Suck it and See" scenario for me.
Now I am aware of possible limitations when used with different Eyepiece/Diagonal combinations there will not be any nasty surprises.
Another option is to go back to using the Celestron Multi ocular Holder with the four Plossols. This may put the eyepieces a bit closer to the Reducer and eliminate some of the vignetting (if I understand correctly). The only 2 inch eyepiece I have is the GSO 50mm which might not be needed often if the Reducer works with the Plossols.
How do I work out the magnifications I will have with my current eyepieces when using the Reducer?
Thanks again for all the help and patience.

Michael


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Steve Cobb
member


Reged: 04/26/10

Re: Celestron F6.3 Reducer for visual with C8? new [Re: Eddgie]
      #5604685 - 01/04/13 12:26 PM

A year or so ago you tried to fill me in on this point. I appreciated your patience and have kept copies of your e-mail posts. This brief message does a superb job of explaining what I initially found to be a rather mysterious loss of aperture when using a two inch diagonal and a focal reducer/flattener. Hang on to it for future use. Those of us pretty new to the field will always need it.

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JamesL
member


Reged: 10/19/12

Loc: Pacific,MO
Re: Celestron F6.3 Reducer for visual with C8? new [Re: Steve Cobb]
      #5607432 - 01/05/13 10:38 PM

After reading this I might sell my focal reducer after it comes in the mail, unless someone can come up with a reason to keep it for a c8. I allready have the 56mm meade super plossl!

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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: Celestron F6.3 Reducer for visual with C8? new [Re: JamesL]
      #5607506 - 01/05/13 11:19 PM

Quote:

After reading this I might sell my focal reducer after it comes in the mail, unless someone can come up with a reason to keep it for a c8. I allready have the 56mm meade super plossl!




Try it before you sell it. It's probably fair to say that using both a focal reducer and a two-inch diagonal puts each at cross purposes, but there are folks who leave focal reducers on always, and Celestron designed the scope with the focal refucer in mind. Although Meade's new LX600 breaks the trend, it was thought that SCTs natively faster than f/10 had harmfully large obstructions. I just bought a focal reducer and would like to hear what you think of yours.


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Rick Woods
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Reged: 01/27/05

Loc: Inner Solar System
Re: Celestron F6.3 Reducer for visual with C8? new [Re: Joe Cepleur]
      #5607565 - 01/05/13 11:46 PM

Quote:

...Celestron designed the scope with the focal refucer in mind.




Where on Earth did you hear that?? The C8 came out in the early 70's; a good two decades before anyone thought of an f/6.3 focal reducer.


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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: Celestron F6.3 Reducer for visual with C8? new [Re: Rick Woods]
      #5607628 - 01/06/13 12:36 AM

Fair question. The early focal reducers were 0.50, not 0.63. I'll have to research my source, but it's true. The thought upon design was that the central obstruction became too large below f/10, so for wider fields or faster exposures, the f/10 native optical tube would be modified with a focal refucer.

I'll try to find and post the source.


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rmollise
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Reged: 07/06/07

Re: Celestron F6.3 Reducer for visual with C8? new [Re: JamesL]
      #5608058 - 01/06/13 10:53 AM

Quote:

After reading this I might sell my focal reducer after it comes in the mail, unless someone can come up with a reason to keep it for a c8. I allready have the 56mm meade super plossl!




That would be silly. It works great, and it works great with a 2-inch diagonal. It was designed for 35mm full frame imaging after all. Yes, if you use eyepieces, 2-inch eyepieces longer than 25mm, it will vignette, but so what? You don't have to use eyepieces that long at f/6.3, and, most importantly, the field edge WITH the corrector is better than it is WITHOUT.


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rmollise
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Reged: 07/06/07

Re: Celestron F6.3 Reducer for visual with C8? new [Re: Joe Cepleur]
      #5608067 - 01/06/13 10:56 AM

Quote:



Try it before you sell it. It's probably fair to say that using both a focal reducer and a two-inch diagonal puts each at cross purposes, but there are folks who leave focal reducers on always, and Celestron designed the scope with the focal refucer in mind. Although Meade's new LX600 breaks the trend, it was thought that SCTs natively faster than f/10 had harmfully large obstructions. I just bought a focal reducer and would like to hear what you think of yours.




The reducer/corrector in no way is at "cross purposes" with a 2-inch diagonal, and works just fine with one.

The C8 was not designed with the r/c in mind; it was designed by Jim Riffle about twenty years after the C8.

Not sure how the LX600 breaks the trend. It has a larger central obstruction, just like the LX-6 and the f/6.3 LX200s had a larger central obstruction...



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yonkrz
scholastic sledgehammer


Reged: 11/16/06

Loc: SW Minnesota
Re: Celestron F6.3 Reducer for visual with C8? new [Re: rmollise]
      #5608083 - 01/06/13 11:05 AM



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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: Celestron F6.3 Reducer for visual with C8? new [Re: Joe Cepleur]
      #5608275 - 01/06/13 12:40 PM

Quote:

Fair question. The early focal reducers were 0.50, not 0.63. I'll have to research my source, but it's true. The thought upon design was that the central obstruction became too large below f/10, so for wider fields or faster exposures, the f/10 native optical tube would be modified with a focal refucer.

I'll try to find and post the source.




I have in my hands an original instruction manual for the C5 and C8. (Copies are easily downloaded.) There is no date of publication, but the cover shows a C8 with a sand cast fork, suggesting the material inside predates my particular scope. The "Recommended Reading" on Page 29 further shows my copy to have been printed no earlier than 1973. Page 22 describes an optional telecompressor that brings the optical system to f/5. The f/6.3 Field Flattener/Focal Reducer would appear to be an improvement on this earlier f/5 variant.

This does not wholly answer the question, so I'll keep looking for my source on the notion that Celestron always intended the C8 to be dual focal length with a telecompressor. If I find my source, we'll be able to ponder whether it distorts the actual history, or reveals something not widely known.


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magnus
professor emeritus


Reged: 03/17/04

Loc: Visby, Sweden
Re: Celestron F6.3 Reducer for visual with C8? new [Re: Joe Cepleur]
      #5609108 - 01/06/13 07:36 PM

With my Orange C8 Pacific -73 (deforked, on my CG-5 with vixen rail) and f/6.3 reducer I do not reach focus with my 2" WO diagonal. Instead I bought a 1.25" WO diagonal and with that I have no problems. Very happy with it! The f/6.3 is permanetly mounted on my C8. When I want high mag. I use my 2.4X Intes barlow, rather than threading the f/6.3 off. Simple and convinient at least in my opinion.
/Magnus 57N.


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ensign
scholastic sledgehammer


Reged: 12/16/08

Loc: Southwestern Ontario
Re: Celestron F6.3 Reducer for visual with C8? new [Re: magnus]
      #5609137 - 01/06/13 07:56 PM

Quote:

With my Orange C8 Pacific -73 (deforked, on my CG-5 with vixen rail) and f/6.3 reducer I do not reach focus with my 2" WO diagonal. Instead I bought a 1.25" WO diagonal and with that I have no problems. Very happy with it! The f/6.3 is permanetly mounted on my C8. When I want high mag. I use my 2.4X Intes barlow, rather than threading the f/6.3 off. Simple and convinient at least in my opinion.
/Magnus 57N.




I had the same problem. A simple, inexpensive solution is to get an SCT nosepiece for the WO diagonal (approx $40 shipped). I did this and had no problems reaching focus with any of my eyepieces.

Of late I abandoned my trusty C8 with a .63 reducer for a 9.25 Edge HD. I find the views through the Edge somewhat better.


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orion61

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Reged: 10/20/07

Loc: Birthplace James T Kirk
Re: Celestron F6.3 Reducer for visual with C8? new [Re: magnus]
      #5609144 - 01/06/13 07:59 PM

I use my MIJ R/C all the time, It makes a great dust seal and gets rid of quite a bit of coma!
My opinion is it is a must have for any Standard Schmidt.
I have noticed it does induce a small bit of Spherical Aberration to my C8. I did have a C8 a few years ago that had a bit of SA and it cancelled most if it out!
I'd like to see someone build a corrector into a 2" Diagonal barrel, Inserted inside not screwed on sticking out.
That could eliminate 2 problems!!


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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: Celestron F6.3 Reducer for visual with C8? new [Re: orion61]
      #5609161 - 01/06/13 08:12 PM

Quote:

I'd like to see someone build a corrector into a 2" Diagonal barrel, Inserted inside not screwed on sticking out.




That strikes me as a truly great idea. Would the right design allow a standard SCT with an inexpensive accessory to pretty well mimic the performance of the fancy new EdgeHDs and LXs? Optically, anyway. I know there is a lot about their focusers and mounts contributing to their overall performance.


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orion61

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Reged: 10/20/07

Loc: Birthplace James T Kirk
Re: Celestron F6.3 Reducer for visual with C8? new [Re: Joe Cepleur]
      #5609179 - 01/06/13 08:26 PM

Quote:

Quote:

I'd like to see someone build a corrector into a 2" Diagonal barrel, Inserted inside not screwed on sticking out.




That strikes me as a truly great idea. Would the right design allow a standard SCT with an inexpensive accessory to pretty well mimic the performance of the fancy new EdgeHDs and LXs? Optically, anyway. I know there is a lot about their focusers and mounts contributing to their overall performance.



Thats what gave me the idea, the corrector lens in the focuser baffle,
But then they couldnt sell those 2K tubes SHHH...LOL


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mclewis1
Thread Killer
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Reged: 02/25/06

Loc: New Brunswick, Canada
Re: Celestron F6.3 Reducer for visual with C8? new [Re: orion61]
      #5609751 - 01/07/13 08:34 AM

Moonlite sells an external focuser that has the option of placing a modified SCT focal reducer into the barrel. There are also other sources on the web of repackaged focal reducers and kits that fit inside many 2" barrels.

http://www.optecinc.com/astronomy/catalog/17408.htm

http://www.observatory.org/vpacs.htm (low profile adapters ... no focal reducers)


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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: Celestron F6.3 Reducer for visual with C8? new [Re: mclewis1]
      #5613493 - 01/09/13 10:55 AM

In the last sentence of the Overview, B&H continues the notion that Celestron sells an f/6.3 focal reducer because, "a f/6.3 Schmidt-Cassegrain telescope... is impractical with a large central obstruction and a resulting loss in contrast." That is not the source I intended to quote, so I'll keep looking for a better source, yet it is interesting to see this notion out there, especially in light of Meade's new LX600. Maybe fast focus Schmidt-Cassegrains require fancy, modern optics, or is this entire notion really just a myth?

I'll continue searching for a primary source stating that Celestron originally intended its f/10 SCT as the fastest natively practical, with a reducer intended to reach faster speeds with a reasonable obstruction.


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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: Celestron F6.3 Reducer for visual with C8? new [Re: Joe Cepleur]
      #5613512 - 01/09/13 11:11 AM

Is this notion beginning to sound familiar? Same exact wording! This still does not prove or disprove that the focal reducer was intended to be part of the C8 kit from the beginning, but it suggests that recycled advertising copy could distort the actual history. This site is British, so the notion is spreading world-wide:

"Celestron doesn’t offer a f/6.3 Schmidt-Cassegrain telescope, because the design is impractical, with a large central obstruction, and resulting loss in contrast. This, added to the inability to utilize longer focal ratios for certain objects, led Celestron to design the four-element, fully multicoated f/6.3 Reducer/Corrector."


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rmollise
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Re: Celestron F6.3 Reducer for visual with C8? new [Re: Joe Cepleur]
      #5613534 - 01/09/13 11:31 AM

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.



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Joe Cepleur
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Re: Celestron F6.3 Reducer for visual with C8? new [Re: rmollise]
      #5613573 - 01/09/13 11:49 AM

Okay, thanks, Uncle Rod; time for me to quit hunting for history I can not find because it does not exist, except maybe in some convincing sounding error I read someplace.

After reading an earlier post about the Meade LX-6, I get it... maybe. Meade introduced a natively f/6.3 SCT, with all the attendant advantages of faster exposures for photographers, but with iffy optics, at least in the early models. To compete with the faster exposures while beating the coma-shaped stars at the edge of the Meade's field of view, Celestron introduced the f/6.3 focal reducer for its f/10 scopes. Along with offering better contrast than the competing Meade, due to the smaller central obstruction, this would have made an arguably better f/6.3 system, at least one well tuned to Celestron's advertising copy.

What's the deal with Celestron's eariler f/5 reducer? Presumably it was great for reducing exposure times, but wreaked havoc on the sharpness of stars toward the edge of the wider field of view? That would explain why Celestron needed to introduce a reducer/CORRECTOR.


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rmollise
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Re: Celestron F6.3 Reducer for visual with C8? new [Re: Joe Cepleur]
      #5613797 - 01/09/13 02:14 PM

It was like any other reducer then or now. Yeah, shorter exposure times, but edge of field performance no bettter than--and usually worse than at f/10.

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JamesL
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Re: Celestron F6.3 Reducer for visual with C8? new [Re: rmollise]
      #5614125 - 01/09/13 05:24 PM

My focal reducer came today. I would like to try it out but clouds and rain will prevent me for the next several days.
In the mean time I,ll install this sliding counter weight system and just admire my cat untill the weather clears!


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Eddgie
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Re: Celestron F6.3 Reducer for visual with C8? new [Re: Joe Cepleur]
      #5614153 - 01/09/13 05:45 PM

Hello Joe,

There may be some confusion and some of it may be mine.

At one point, you could buy a "Rich Field Adapter" for SCTs and this was indeed f/5.

It was in essence a special 1.25" diagonal with a reducer built right in.

Horrible to use in my opinion. I used to own one maybe 25 years ago. And that would in iteself explain why it is no longer sold. Really terrible. Loaded with astigmatism as I recall, though to be fair, it could have been the eyepeices made at the time were just not working well with the f/5 light cone.

But the coma from the scope and the astigmatism where so severe that I used it once and threw it in my junk drawer.

So, maybe this is what the f/5 was in reference to...


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Eddgie
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Re: Celestron F6.3 Reducer for visual with C8? new [Re: Eddgie]
      #5614156 - 01/09/13 05:46 PM

Speak of the devil... Regarding my previous post, here is an example:

Celestron f/5 Rich Field Adapter

And by the way... The focal reducer does not make the obstruction any larger unless it is used in a configuration with a lot of back focus so that the scope is loosing aperture.

The Celestron marketing positioned the Celestron focal reducer as a better alternative to an Native f/6.3 SCT, which was made by Meade for a while. The Meade f/6.3 SCT had a 40% obstruction, and Celetron's position was that it was better to use the reducer and keep the smaller CO than go to the Meade f/6.3 with the bigger obstruction.

So, it was a marketing thing.

And it must have worked. The Meade f/6.3 SCT bombed in the marketplace. But this was well before digital imageing came into the picture. Hypered film was the leading edge technology, and because of the expense (processing the film was the big cost) the hobby was not as popular as today, and I doubt that they sold enough scopes to make it worth the production time.

But if you can do it wite a telecompressor, then why bother with a native f/6.3 SCT which had wicked field curvature.

Edited by Eddgie (01/09/13 05:56 PM)


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rmollise
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Re: Celestron F6.3 Reducer for visual with C8? new [Re: Eddgie]
      #5614195 - 01/09/13 06:13 PM

Quote:

Hello Joe,

There may be some confusion and some of it may be mine.

At one point, you could buy a "Rich Field Adapter" for SCTs and this was indeed f/5.

It was in essence a special 1.25" diagonal with a reducer built right in.

Horrible to use in my opinion. I used to own one maybe 25 years ago. And that would in iteself explain why it is no longer sold. Really terrible. Loaded with astigmatism as I recall, though to be fair, it could have been the eyepeices made at the time were just not working well with the f/5 light cone.

But the coma from the scope and the astigmatism where so severe that I used it once and threw it in my junk drawer.

So, maybe this is what the f/5 was in reference to...




There were numerous reducers at f/5 available, including from Lumicon, Orion, etc., etc. The non-correcting reducer was around since the beginning and even Celestron produced a couple of different iterations.

Many were quite useable for imaging, and that was all we had unless you wanted to shoot the deep sky at f/10.

Edited by rmollise (01/09/13 06:14 PM)


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Joe Cepleur
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Re: Celestron F6.3 Reducer for visual with C8? new [Re: Eddgie]
      #5614253 - 01/09/13 06:38 PM

Quote:

Celestron marketing positioned the Celestron focal reducer as a better alternative to an Native f/6.3 SCT, which was made by Meade for a while. The Meade f/6.3 SCT had a 40% obstruction, and Celetron's position was that it was better to use the reducer and keep the smaller CO than go to the Meade f/6.3 with the bigger obstruction.




Thanks, all -- Now the story makes perfect sense. Kinda like the game of "telephone." By the time it got to me thirty years later, either it had morphed or I had morphed it. While a C8 with a focal reducer is not the ultimate rich-field scope, being able to swap between f/10 and f/6.3 is an excellent perk in a flexible system, whatever its origins. Carrying a reducer/corrector beats carrying and setting up a second optical tube!

Celestron's marketing must have been effective. I'm sure I would have bought the pitch. Sounds as though it was true, anyway.

Thanks for the tip on the old f/5 diagonals. I'm a trinkets guy, and love collecting old accessories. I like the feeling of tangible history. I'm happy with my recently purchased, Japanese-made Meade f/6.3 refucer/corrector, happier than with a new Synta! I was the only bidder on eBay, and almost felt sorry for the seller, but fair was fair, he did okay. But -- I've seen these curious f/5 diagonals for sale, and have erased them from my wish list!


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Re: Celestron F6.3 Reducer for visual with C8? new [Re: rmollise]
      #5614280 - 01/09/13 06:53 PM

Quote:

There were numerous reducers at f/5 available, including from Lumicon, Orion, etc., etc. The non-correcting reducer was around since the beginning and even Celestron produced a couple of different iterations.




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.


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rmollise
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Re: Celestron F6.3 Reducer for visual with C8? new [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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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
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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
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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
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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
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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
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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
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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

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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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