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F6.3 Reducer/corrector lens and 9.25 Celestron Evolution.


Greymouser

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https://www.firstlightoptics.com/reducersflatteners/celestron-f63-focal-reducer.html

Well I have now used the scope with the focal reducer in place. ?

Whilst it is billed as mainly to improve imaging, it certainly seems to improve visually too. I will have to experiment further, because I first used the scope on a moonless night at F10, last night with the focal reducer in place, F6.3, there was a full moon, which made things a littler more interesting!  Certainly the view of M31 was wider and seemed sharper, but that may have been my imagination. I am sure I saw more detail, which is surprising considering the full moon, I suppose it may have been just me, if I am being negative, but it did seem better.

It really does make a two scopes for one in my opinion alone, not least because it makes it easier for lower magnifications. The 40mm eyepiece at F10 gives a Magnification of 58.75, at F6.3 it is 37, I think, even though they advise not to use an eyepiece longer than 35mm at 6.3! Never mind, with several eyepieces it seems to have improved things.

Considering the thing cost £99, it seems to be a good buy, especially when you consider that I spent £2349 on my scope. Even more so considering the future benefits when I dip my toes into imaging... As well as it also gives a flatter field.

I can heartily recommend it for those with a similar scope, even if like me it is only for visual versatility. ?

My first impressions of the Nexstar 9.25 Evolution can be found here: 

 

Edited by Greymouser
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Interesting read!  I too experimented with a reducer (a low cost one) in my 8SE, and found that for long FL EPs, the FOV was considerably reduced.  It was increased with shorter FLs, but I might as well just have used longer FLs without the reducer!  But of course, whatever works for any of us is fine.

I was tempted to go for a larger aperture SCT, since I like the 8SE so much, but decided to go for a 10" Dob to broaden my experience as well as the FOV!  (Not to mention saving a few quid!)  But the 9.25 is a fine instrument - enjoy!

Doug.

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Unless the design of the scope has been altered I think you can acheive the same FOV without the reducer as with it if you have a 2 inch visual back. The field is limited by the baffle tube in both cases so it can be reached with a widefield 2 inch EP at F10.

Olly

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9 minutes ago, ollypenrice said:

Unless the design of the scope has been altered I think you can acheive the same FOV without the reducer as with it if you have a 2 inch visual back. The field is limited by the baffle tube in both cases so it can be reached with a widefield 2 inch EP at F10.

Olly

You are not the first to suggest this and I had in fact been considering that, but for two reasons, it could be a possibility. The cost would be considerable, to put it mildly and any field flattening correction would then be lost, unless you can then buy another correcter for the two inch visual back? I wish I could afford it though, especially the top of the range eyepieces! ??

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3 hours ago, Greymouser said:

You are not the first to suggest this and I had in fact been considering that, but for two reasons, it could be a possibility. The cost would be considerable, to put it mildly and any field flattening correction would then be lost, unless you can then buy another correcter for the two inch visual back? I wish I could afford it though, especially the top of the range eyepieces! ??

Yes, 1.25 is cheaper. In our 14 inch SCT we use a 26mm Nagler which gives clean stars to the edge to my eye. Probably the widest format you could obtain would be with a 32mm TV Plossl though there will be comparable modern EPs these days.

Olly

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I went down the f/6.3 reducer and 1.25 inch eyepiece route with my C9.25. I’m now using 2-inch eyepieces, which is giving me better results. This is for wide field views. I still use 1.25-inch eyepieces for planetary observation with shorter FL, though.  

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13 hours ago, Greymouser said:

I was under the impression that they were only a 50 degree FOV, is my assumption wrong?

No, you're correct but I believe that this EP is gives the widest FOV possible in 1.25 format.

There's a discussion here. It seems to me that the conclusion (you'll never find a consensus on CN!) is that the 32 TV Plossl will go as wide as is possible at modest cost, especially second hand. https://www.cloudynights.com/topic/510769-which-eyepiece-is-best-for-the-widest-possible-view-in-125-inch-size/page-2

The best bet, though, apart from cost, is to go for a 2 inch back and a long FL ultra widefield EP. 

Olly

Edit: keep exit pupil in mind. Divide the EP's focal length in mm by the telescope's F ratio.

Edited by ollypenrice
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12 hours ago, Owmuchonomy said:

I went to a Baader Click-Lock and 2” EPS for my 9.25” SCT which gave better results. Using a .63 reducer you just end up with terrible vignetting. I now have a 2” Moonlite in orange anodised finish ???.

Could you tell me which click lock you went to exactly. In fact could you break down to a real easy level, ( for someone quite stupid, like myself, ) exactly what you did please. 

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21 hours ago, Greymouser said:

Could you tell me which click lock you went to exactly. In fact could you break down to a real easy level, ( for someone quite stupid, like myself, ) exactly what you did please. 

Sure. I used one of these https://www.firstlightoptics.com/adapters/baader-click-lock-2-for-celestron-meade-sct.html and a 2” diagonal. The diagonal should come with an additional 1.25” adapter so you can then use 2” or 1.25” fittings such as EPs and cameras as necessary.

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  • 2 years later...
On 26/09/2018 at 12:22, ollypenrice said:

Unless the design of the scope has been altered I think you can acheive the same FOV without the reducer as with it if you have a 2 inch visual back. The field is limited by the baffle tube in both cases so it can be reached with a widefield 2 inch EP at F10.

Olly

If you’re still here, could you use the 0.63 reducer AND 2” EP (eg Baader Hyperion 36mm 72 degree AFOV)?  Per my calculations, this would give a 1.75 degree TFOV for my Evo 9.25” (2350mm focal length, 46mm baffle width), where the theoretical max TFOV for the scope would be 1.78 degrees with the reducer.

(I’m awaiting delivery of the scope so all my workings are theoretical, just using optics maths not practical knowledge)

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11 minutes ago, James1967 said:

If you’re still here, could you use the 0.63 reducer AND 2” EP (eg Baader Hyperion 36mm 72 degree AFOV)?  Per my calculations, this would give a 1.75 degree TFOV for my Evo 9.25” (2350mm focal length, 46mm baffle width), where the theoretical max TFOV for the scope would be 1.78 degrees with the reducer.

(I’m awaiting delivery of the scope so all my workings are theoretical, just using optics maths not practical knowledge)

Yes, still here. I did once try both a 35mm Panoptic and a 31 Nagler in a 10 inch Meade with the 6.3 reducer. I don't remember whether they actually increased the FOV, though I think they didn't. What I do remember was that the view was not very nice and I didn't use that combination.  Sorry but I can't remember what I found stressful about the view. I certainly didn't like it, though. I only used those EPs at native FL.

Olly

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39 minutes ago, James1967 said:

If you’re still here, could you use the 0.63 reducer AND 2” EP (eg Baader Hyperion 36mm 72 degree AFOV)?  Per my calculations, this would give a 1.75 degree TFOV for my Evo 9.25” (2350mm focal length, 46mm baffle width), where the theoretical max TFOV for the scope would be 1.78 degrees with the reducer.

(I’m awaiting delivery of the scope so all my workings are theoretical, just using optics maths not practical knowledge)

I think the F/6.3 reducers are designed for use with 1.25 inch format eyepieces. With 2 inch eyepieces and large field stops they vignette the field of view I believe.

 

 

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1 hour ago, John said:

I think the F/6.3 reducers are designed for use with 1.25 inch format eyepieces. With 2 inch eyepieces and large field stops they vignette the field of view I believe.

 

 

Thanks.  I guess the issue is whether the 0.63x reducer, by reducing the focal length, increases the max true field of view (baffle width/field stop x 57.3/ focal length) or not.  Because the light path passes through the limited baffle width before passing through the reducer, I’m not sure the formula is valid for such a set up - but I really don’t know enough either way!  
If the formula is valid in this case, then a 2” 36mm 72 degree AFOV EP *should* work to give 1.75 degree TFOV and it may be worth me experimenting.  I know I can always return the EP’s etc to FLO if it doesn’t work, but it would be easier all round if I could establish how it works in advance. The Celestron website is particularly unhelpful in this regard.  Thanks again

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1 hour ago, ollypenrice said:

Yes, still here. I did once try both a 35mm Panoptic and a 31 Nagler in a 10 inch Meade with the 6.3 reducer. I don't remember whether they actually increased the FOV, though I think they didn't. What I do remember was that the view was not very nice and I didn't use that combination.  Sorry but I can't remember what I found stressful about the view. I certainly didn't like it, though. I only used those EPs at native FL.

Olly

Thanks Olly.  Your set up sounds very similar/relevant.  It also makes sense to me (as a novice) that the light path is limited to the 46 (48?) mm baffle width BEFORE it passes through the reducer, so the FOV would not be increased by adding the reducer.  I guess I’ll just have to try the supplied EPs with/without the reducer first and see if the FOV is changed or just the magnification, before splashing out on 2” diagonals, EP’s etc.

Maybe it’s just me but I find it bizarre that field of view impact on various set ups is not a standard piece of information provided, like magnification, focal length.  Guess I’m asking too much. Ho hum.

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25 minutes ago, Laurin Dave said:

I believe that your fov will be limited by the telescope field stop to 46/2350 x57.3deg ie to 1.12deg and that no eyepiece/reducer combo will exceed this ..   It can be quite an expensive lesson to learn as I found out !

Dave

Thanks Dave.  Would you recommend not buying the Evo 9.25” then?  I can cancel it and get something else.  Or did you mean that you spent a lot on EP’s, reducers etc trying and failing to get a wider FOV?

Most DSO’s seem to be much much smaller than 1.12 deg and it’s only a few eg M31, M42 that are much bigger - or am I missing something?

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Personally I think going down the 2 inch visual back / 2 inch diagonal / 2 inch eyepiece route is the best way to get the wider views from an SCT. The slight snag is that for the price of the diagonal and 2 inch eyepieces (and 2 inch filters) you could probably buy a nice rich field 200mm F/5 newtonian optical tube :rolleyes2:

 

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Thanks for all the responses.  I’m expecting to eventually progress to astrophotography and will therefore likely also get a refractor with much smaller focal length, so I’ll bear that in mind too.  I’ve understood much more now (basically you can’t increase max FOV with the reducer so no point using a reducer AND 2” diagonal/EP.  Need to decide on one or the other).

Probably best for all that I get the scope with provided accessories and play with it before deciding on anything else.  It’s not as if the stars and planets are going anywhere.  Thanks again 😄

Edited by James1967
Omitted “also”
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