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question about a focal reducer

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5 replies to this topic

#1 donald41

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Posted 23 October 2021 - 10:55 AM

i have a celestron 8" sct and was wondering what the purpose is for using a focal reducer. is it just for doing AP. would there be any advantage to use one for viewing. what does it reduce to ( 2000 f/l for a 8" sct) and does it give a wider field of view. thanks, don 



#2 maheitka

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Posted 23 October 2021 - 11:01 AM

Hi Don

 

Checkout https://www.youtube....h?v=sFYD4aR8WQs

That's quite a good theoretical (and practical) video explanation

 

CS

Martin



#3 jmillsbss

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Posted 23 October 2021 - 12:09 PM

My reducer LIVES on the back of my C8.

 

Takes the focal length down to F/6.3 from F/10.  A 13mm Nagler has a native field of 0.52 degrees but add the reducer and you have a fov of 0.83 degrees.  Doesn't sound significant?  But, the native focal length 13 Nagler means the moon just baaarrrrely fits in the FOV but the .63x reducer gives you about a 20% diameter of the the moon space around the full moon to the field stop.   Granted, it reduces the power/magnification, but the context makes the views much more comfortable.

 

In addition to having the faster focal length and wider fields, the Celestron reducer is also a flattener, which is a tremendous help on stars in the outer 25% of the field, even with wide field EPs.  My 100 degree 9mm Stellarvue has pinpoint stars and perfectly flat and round planetary discs.

 

Of all the money I've ever spent in this hobby, the reducer/flattener is certainly near the top of the heap when it comes to $100 purchases.  They come up every now and then used on the classifieds and if, for some unknown possible reason, you can resale it and be out nothing if you don't like it.  You'll like it, though!


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#4 MarMax

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Posted 23 October 2021 - 12:13 PM

If you are referring to the Celestron f/6.3 reducer for a regular 8" SCT (not Edge) you can use it visually to increase your field of view. You just need to observe the back spacing (typically 105mm) for the reducer.

 

The above post explains what is does nicely.

 

I use the f/6.3 reducer with my 11" SCT all the time visually.



#5 donald41

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Posted 23 October 2021 - 01:04 PM

first of all thanks for all the replies, very helpful!! so, as far as purchasing one, I've had the reducer for a number of years and never used it because i was going into ap but changed my mind because it takes a lot of time and i just dont observe for long periods of time and even less now being a lot older so i divided to stick with observing only. i put it on my celestron 8" and will try it out the next clear day. ive purchased a number of altazimuth mounts and very unhappy with them. a couple months ago i took a chance and bought another one and struck gold!!!! a stellarvue MC2 mount with the 11" extinction. love this mount, its a gem. i will come back and give a report on my thoughts after using it on my scope. thanks again for the replies, don  



#6 bytesbull

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Posted 23 October 2021 - 02:05 PM

I don't have a large telescope like a 8" with 2000 focal length but my focal reducer is the most valuable eyepiece I own. I have the Celestron 114 which is 114mm aperture and 900mm focal length. So using my SVBONY x0.5 focal reducer it makes viewing many deep sky and a few galaxies possible that otherwise I would never fit into the FOV.

 

Below is an example using Stellerium and my telescope info with and without the reducer.

 

 

 

First this is my FOV of Andromeda Galaxy with no reducer using a 25mm Kellner eyepiece at the full 900mm focal length.

 

 

gallery_375067_18045_76003.jpg

 

 

 

 

 

Now this is with the x0.5 focal reducer and a 25mm Kellner eyepiece and as you can see I now have a FULL view of the Andromeda Galaxy using the reducer.

 

 

 

gallery_375067_18045_149087.jpg


Edited by bytesbull, 23 October 2021 - 03:02 PM.



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