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bobafett

Does anyone use a 2" diagonal with a Celestron Nexstar ?

15 posts in this topic

I'm all spent out at the moment after my new purchase but I was thinking that my first "upgrade" to my 6SE sometime in the future could possibly be a 2" SCT diagonal ? Mainly so I can use a long FL 2" eyepiece so I can see a nice chunk of sky.

I was thinking along the lines of the Meade 4000 56mm 2" plossl.

Any thoughts ?

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Thought about it.....The problem is the room behind the scope when pointing high. It is easy to catch the mount with the diagonal/ep and loose your alignment.

I have gone the other way for wide views which is to fit an Antares Focal Reducer f6.3. This JUST fits and I can use all my EP/s. Like having a second scope. You may have more room behind the 6SE (mines an 8SE).

I think LULU has gone the 2" Ethos 13mm rout

Best of Luck

Mike

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The 13mm Ethos is a hybrid, it haves both 1.25" and 2" barrels. In fact it's really a 1.25" EP in disguise so you don't need a 2" diagonal.

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With a 56mm eyepiece you may well have problems with the secondary shadow becoming visable. I reckon 40mm is a more viable max focal length eyepiece.

Also a 2" diagonal and a 2" eyepiece adds a lot of weight to the back of the OTA - it could affect the accuracy of the drive system.

....it's really a 1.25" EP in disguise so you don't need a 2" diagonal.

True ....... but it does look a bit precarious hanging out of a 1.25" diagonal ;) - I'd want to be sure that it was a really solidly made diagonal before trusting it with a 600 gram eyepiece worth £400+ !.

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How about a focal reducer?

EDIT: I noticed now big wings had already mention it... sorry... that's what I get for speed reading through the threads. ;)

Edited by pvaz

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How about a focal reducer?

Great idea Paulo ;)

One of the best accessories for a SCT IMHO.

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With a 56mm eyepiece you may well have problems with the secondary shadow becoming visable. I reckon 40mm is a more viable max focal length eyepiece.

Hmmmmm - thing with most standard 40mm is that once you do the calcs with AFOV/mag there's little difference between a 40mm and a 32mm as far as true FOV and I already own a 32mm. The thing that attracted me to the 56mm was the increase in actual sky that i'd be seeing.

Do you think the secondary shadow is likely to be an issue then ? Anyone else had this experience with this or similar setups ?

Also a 2" diagonal and a 2" eyepiece adds a lot of weight to the back of the OTA - it could affect the accuracy of the drive system.

Surely I could just slide the OTA further forward ? Looks like there's an extra 1/2" left to play with on the dovetail maybe even squeeze a full inch out of it. Although as mentioned further up clearance could be an issue.

I guess the Antares f6.3 focal reducer could be the way then......

Cheaper too ! At around £70 it's a lot cheaper than a new 2" diagonal + new 56mm eyepiece.

;)

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Well the focal reducer, as well as being cheaper, will show more sky without adding a lot of weight. The one I used with my Celestron C8 SCT was the Japanese made Celestron F/6.3 reducer which seemed really good optical quality - I often forgot I had it in the scope !.

Apart from the secondary shadow issue, the Meade 56mm plossl has other issues such as kidney beaning because of the excessive eye relief. It's also worth noting that a 40mm SWA eyepiece with a 70 degree AFoV will show you very nearly as much sky as a 56mm plossl with a 50 degree AFoV.

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a 40mm SWA eyepiece with a 70 degree AFoV will show you very nearly as much sky as a 56mm plossl with a 50 degree AFoV.

Can you recommend a 1.25" 40mm with decent FOV ? Most with decent FOV are 2" which brings me back to the same issue.... kind of.

Edited by bobafett

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I use a 2" WO diagonal with my 6SE. Clears the mount until vertical. However, it does add a lot of weight to the rear of the scope, especially with large EPs. A dew shield balances it out. The mount on the 6SE is the same as on the 8SE, whilst the latter is a larger, heavier scope, so it can cope.

Largest EP I use is a 38mm Panaview, which gives nice views in a slow scope like the C6. Hope this helps.

Richard

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I use an ATIK 0.5x reducer. 32mm with 52 degree field with 0.5x reducer gives over 2 degrees of view.

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I use an ATIK 0.5x reducer. 32mm with 52 degree field with 0.5x reducer gives over 2 degrees of view.

I take it this is a 1.25" threaded "filter-fit" style reducer ?

I noticed those but was unsure of the quality/results due to the price compared to the SCT reducers. But if it works and works well then count me in ! The price of a larger chunk of sky keeps coming down with each post in this thread ! ;)

I found these available i the 1.25" threaded style..........

Antares 0.5x - £25

Astro Engineering 0.6x £30

TS 0.5x - £45

Anyone own / have any experience of these ? Any preferences between the 3 ?

Can these be threaded into the front of the diagonal rather than having to put it in each eyepiece one after the other ? Would make life a hell of a lot easier if you could.

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Can you recommend a 1.25" 40mm with decent FOV ? Most with decent FOV are 2" which brings me back to the same issue.... kind of.

No - 1.25" 40mm's are limited to 43 degrees AFoV because of the barrel diameter. I was referring to something like a William Opics SWAN where the 2" 40mm claims an AFoV of 72 degrees.

The lightest long FL 2" eyepiece I've used was probably the Skywatcher Aero ED - they do a 40mm in that range.

My guesstimate is that a 32mm 1.25" eyepiece with a 52 degree AFoV used with a F/6.3 converter will show about as much true field of view as a 2" 40mm 70 degree eyepiece used in the scope without the converter will. You might want to do the maths to be sure on that though ;)

I guess it's a case of "swings & roundabouts" :)

Edited by John

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Boba:

Yes, it screws into the eyepiece, just like a filter.

As to screwing it directly into the diagonal:

(a) I suppose it would be possible if there is a screw thread there

(;) BUT I don't have the math to know if you would be able to bring the scope into focus. They work by halving the cone of light that follows them, so I suspect that you would not be able to.

© I only ever use it with my 32mm anyway. If I want a wider field on anything else, I just change to a longer focal length eyepiece. After all, if you had gone with your original idea, it would have only been one 56mm eyepiece.

Any piece of glass (eg reducers) that are put in the optical train are going to have an effect on quality. I guess like eyepieces it is a question of how much you are willing to pay to get that extra bit of quality. This solution is probably at the 'bottom end of the market'. A 2" diagonal/eyepiece would probably give you better quality results, but at considerably greater expense.

IMO (and I know it is very easy to spend other people's money) you are not risking a lot by trying this approach first. If you buy one, and find you want to upgrade to your original idea later on, for quality or any other reason, I guess you could recoup 50% of your purchase price in the second hand market? In terms of what we all spend on astro-gear ...

HTH

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Another thing I wonder about is whether a focal reducer can recover from the inherent limitations of the diameter of the optical path (the "exit hole", whatever!). I did hear tell that Celestron scopes had "better internal baffling" than e.g. Skywatcher MAKs - And so prevented such (visual!) tweakings? As with most of these things, experimentation (internet search?) is key - But can be a tad expensive... ;)

Edited by Macavity

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