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Meade f3.3 reducer with sct

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#1 Bowlerhat

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Posted 04 November 2019 - 06:05 AM

Is there any real benefit for getting one, mainly for visual use? 

 

Is it effective for photography?



#2 kjacek

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Posted 04 November 2019 - 07:16 AM

Hi. Yes it is benefit when using reducer f6.3, both in astrophotography and in visual.
It reduces F10 to F6.3 -> shorter exposure time.
In visual you can easier obtain greater exit pupil -> this is important to simpler discover faint objects.

#3 Tapio

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Posted 04 November 2019 - 07:33 AM

A f/6.3 reducer would be more useful.

F/3.3 reducer has so much reduction that edge of field has bad stars and it's use of photography use is limited to small chip size cameras (like Lodestar).


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#4 JoeR

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Posted 04 November 2019 - 08:01 AM

It works for imaging but you need a camera with a small sensor, like the 1/1.8”. It was designed around the time when the Meade Deep Sky Imager II was the norm for amateurs.



#5 Bowlerhat

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Posted 04 November 2019 - 09:08 AM

I'm planning to use it visually, I know that it is optimized for chip imaging but not so much for dslr. I've been using the f6.3 reducer with C5 for visual and it's pretty nice, but not sure about f3.3

#6 Jon Isaacs

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Posted 04 November 2019 - 09:24 AM

I'm planning to use it visually, I know that it is optimized for chip imaging but not so much for dslr. I've been using the f6.3 reducer with C5 for visual and it's pretty nice, but not sure about f3.3

 

Why?

 

Few eyepiece's work well at F/3.3, there's no gain in maximum TFoV over F/6.3.

 

Jon



#7 mclewis1

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Posted 04 November 2019 - 09:31 AM

The f3.3 reducer was designed for very small sensors ... in the type 1/3" range. It will not work well with anything much above type 1/2" and certainly not with a type 1.1".

 

The aggressive nature of the .33x reduction requires a lot of in focus travel so the placement of the reducer is very important. It usually will not come to focus unless it's place directly on the rear cell of the SCT. So external focusers and things like that won't work out.

 

The focal length is short so the spacing requirement is very limited ... it's in the 57-63mm range (dependent on where it's measured from) so it's just about impossible to setup for visual work with a diagonal. Some folks have tried it with a straight through mounting and it's very tough to use and very limited in optical quality (very constricted in terms of optical quality in the field of view)

 

I would strongly suggest not bothering with this reducer for visual work. The f6.3 SCT reducer is a much more "visual friendly" setup, and even it imposes some rather severe restrictions. A 2" .5x reducer can also be used but again the amount of in focus required is pretty dramatic and for many examples the optical quality across a low power field of view isn't great.


Edited by mclewis1, 04 November 2019 - 09:32 AM.

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#8 eros312

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Posted 04 November 2019 - 12:02 PM

I'm planning to use it visually, I know that it is optimized for chip imaging but not so much for dslr. I've been using the f6.3 reducer with C5 for visual and it's pretty nice, but not sure about f3.3

I've read somewhere on these forums that it won't work for visual. Doesn't reach focus. 



#9 Jeff Lee

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Posted 04 November 2019 - 12:38 PM

Yep, I have one for my ZWO 224 and I have to use it directly on the SCT with the T-Adapter only. However, for the 224 is makes the camera a lot more usable.  No go for visual.


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#10 Mitrovarr

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Posted 04 November 2019 - 12:58 PM

Yep, I have one for my ZWO 224 and I have to use it directly on the SCT with the T-Adapter only. However, for the 224 is makes the camera a lot more usable. No go for visual.


I've had good luck stacking a f/6.3 reducer and a standard 0.5x reducer with the 224 for EAA. Might be a cheaper option since I think the f/3.3 reducer is getting hard to find.

#11 Dwight J

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Posted 04 November 2019 - 01:22 PM

Visually you will have an obvious secondary shadow.  I used one extensively for EAA observing and used an eyepiece to sync on a star at the start of the night.  I used a 26 mm FL eyepiece giving about 35X on a C11 with the reducer in place.  The secondary shadow was immediately obvious.  I used a 60 mm extension to achieve even more reduction but this only worked with a Mallincam astrovideo camera with a 6.7 mm diagonal chip.  Additionally, the earlier “ Made in Japan” versions are optically superior to later Chinese made versions.  Coma was terrible even with the tiny chip.  If you want a wider low power field get a faster FL scope like a 80 mm F4 finder and mount it on your SCT. 



#12 Eddgie

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Posted 04 November 2019 - 04:55 PM

I'm planning to use it visually, I know that it is optimized for chip imaging but not so much for dslr. I've been using the f6.3 reducer with C5 for visual and it's pretty nice, but not sure about f3.3

 

The problem is that to use a diagonal, the scope is going to go into aperture reduction. 

 

Imagers can get away with using f/3.3 because they do not have the long light path a diagonal has and when you use a diagonal, to reach focus, the primary mirror has to be moved very far forward, and when you do this, the light cone entering the primary baffle gets shaved down in size, and this essentially reduces the aperture, and because the aperture is reduced, the scope is no longer working at f/3.3, and the obstruction is a longer percentage of remaining aperture. 

 

Next is strong vignetting.  I mean pretty serious with anything but fairly short focal length eyepieces.

 

Then there is the inability of most eyepieces to handle a light cone this fast. Only highly corrected eyepieces like Ethos or Nagler would work.

 

If the goal is a wider field, consider a small Newtonian or larger refractor.  Geometry is pretty rigid stuff, and the tiny baffle in the C5 is going to cause aperture loss, vignetting, and off axis aberrations. 

 

f/6.3 Is the practical limit for the C5 (and C6 and C8) unless you are imaging and don't have a lot of light path behind the rear port.   


Edited by Eddgie, 04 November 2019 - 04:56 PM.

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#13 Bowlerhat

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Posted 04 November 2019 - 07:50 PM

Why?

 

Few eyepiece's work well at F/3.3, there's no gain in maximum TFoV over F/6.3.

 

Jon

I see, someone mentioned wider fov. Maybe it was for something else.

 

 

The problem is that to use a diagonal, the scope is going to go into aperture reduction. 

 

Imagers can get away with using f/3.3 because they do not have the long light path a diagonal has and when you use a diagonal, to reach focus, the primary mirror has to be moved very far forward, and when you do this, the light cone entering the primary baffle gets shaved down in size, and this essentially reduces the aperture, and because the aperture is reduced, the scope is no longer working at f/3.3, and the obstruction is a longer percentage of remaining aperture. 

 

Next is strong vignetting.  I mean pretty serious with anything but fairly short focal length eyepieces.

 

Then there is the inability of most eyepieces to handle a light cone this fast. Only highly corrected eyepieces like Ethos or Nagler would work.

 

If the goal is a wider field, consider a small Newtonian or larger refractor.  Geometry is pretty rigid stuff, and the tiny baffle in the C5 is going to cause aperture loss, vignetting, and off axis aberrations. 

 

f/6.3 Is the practical limit for the C5 (and C6 and C8) unless you are imaging and don't have a lot of light path behind the rear port.   

Hmm, that's why they made it for CCD. Makes sense, I thought it could work. Thanks!




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