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Recommend a 2" SCT Visual back

Uplooker

By Uplooker
in Discussions - Eyepieces

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Uplooker

Uplooker

Posted
Posted

I may be asking this question because I am getting the terminology wrong.

I have a Celestron C8, I bought a 2" Revelation Quartz Dielectric Diagonal. I attach this to the scope using a Astro Engineering 2" visual back.

I am not happy with the fit between the diagonal and 2" visual back as the visual back is not quite deep enough to allow the diagonal to seat fully home meaning that the thumb screws only just make it onto the undercut of the diagonal and thereby do not secure it as securely as i would like. I suspect this is just a design issue with the the AE visual back.

I have done various searches for alternative 2" visual backs with little luck, however I have found this SCt to 2" Adaptor (see 2nd item from top of page):-

Adaptors from Ian King Imaging

Is an "SCT to 2" Adaptor" another name for a 2" visual back?

If it is, I like the fact this one has a compression ring.

Does anyone have experience of this bit of kit?

Can you recommend others?

Any advice greatfully received.

regards,

Uplooker

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Bender

Bender

Posted
Posted
I have a simpler Baader 2" visual back. Simple and solid, with two thumb screws. No compression ring however.

Mine got a compression ring, probably slightly newer. But my Tak has only set screws everywhere, holds just as good.

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  • 2 weeks later...
Uplooker

Uplooker

Posted
  • Author
Posted

Hi All,

Just to give you an update. In the end i went for this Baader 2" Visual Back from FLO:-

First Light Optics - Baader SCT to 2-inch adapter

I am very pleased. Not had a chance to use in anger yet, but it has the following plus points.

  1. Attaches very smoothly and securely to the back of my Celestron C8
  2. Has plenty of depth to accomodate my Revelation diagonal
  3. Has a compression ring
  4. Compression ring lines up correctly with the undercut on the Revelation diagonal.

Basically addresses all of the poor points I found with the Astro Engineering one that I had been using.

In addition I was able to order it from FLO and knew that it was very likely that ordering it on Thursday it would arrive Saturday - it did:icon_salut:

regards,

Uplooker

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  • 6 months later...
kirkster501

kirkster501

Posted
Posted

Hi stumbled onto this thread... Any further updates please? Has it remianed a robust piece of kit?

I want something to connect a 2" Televue Powermate direct to the back of my CPC1100 so I can image at Prime Focus (with or without the Powermate).

Thanks, Steve

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Adrian

Adrian

Posted
Posted

Hi stumbled onto this thread... Any further updates please? Has it remianed a robust piece of kit?

I want something to connect a 2" Televue Powermate direct to the back of my CPC1100 so I can image at Prime Focus (with or without the Powermate).

Thanks, Steve

For a C11 I would recommend this one:http://www.365astron...pes-p-1910.html

I had one on my 10" Meade SCT - using the 3.25" connector removes the SCT thread 38mm constriction in the light path and allows a maximally illuminated 2" field (minimises vignetting).

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Dunkster

Dunkster

Posted
Posted

I have a click-lock for my C11 and it's great - easy to rotate the diagonal as it's on a GEM. Was considering getting one for the C8 too but worried about clearing the base of the SE mount - it just scrapes through with the gso/revelation sct visual back. It's not the smoothest of operations to adjust it, but to be fair I've only felt the need to move it once since I installed it, to get it in the right position (since the mount is alt/az)

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kirkster501

kirkster501

Posted
Posted

Thanks for the input guys. I am a bit confused thought now. Adrian, following your rationale - that I have also read elsewhere - that would imply that the 3.25-2 inch "step down" adapter supplied with that scope constricts some of the light when a 2' diagonal is used and this "wasting" some of the aperture. The click lock looks good but boy - £72 for an adapter ! I would want to get this right though so would pay it if needs be. The "ordinary" 2' click lock - at £60 - can also be used on the ED80 focuser and that appeals to me.

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Dunkster

Dunkster

Posted
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Correct - the visual back Celestron ships has a 38mm aperture internally - the same diameter as the baffle tube in a C8 incidentally - but this is some way off the clear width of a 2" diagonal. If the widest eyepiece you intend to use has a field stop of 38mm or less, then no problem, otherwise you may see some vignetting.

You need some method of stepping down from the 3.25" thread on the C11 rear cell before you can use any 2" adapters. This is the nature of the beast... the smaller SCTs have a 2" thread, but the C11 and C14 are 3.25" :eek:

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kirkster501

kirkster501

Posted
Posted

Cool, thanks again. I am going to buy one of the 3.25' to 2' clicklocks. This will become my main step down on the CPC and will I use this and remove the SCT adaptor on my WO diagonal that connects to the current Celestron supplied 3.25<>2 adapter.

Only issue is trying to get one in UK or Europe - rarer than rocking horse poo by the looks of it.

Rgds, Steve

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michael.h.f.wilkinson

michael.h.f.wilkinson

Posted
Posted

I used a Paragon 40 mm with 45.6mm field stop. No vignetting was evident visually. You could see some takes place by defocussing stars, and a bit of the typical "donut" shape was truncated at the edge, but not a great deal (perhaps 20% light loss at the extreme edge (less than 0.25 magnitudes). The same vignetting occurs in many commercial Newtonians, because the secondary is chosen a bit smaller than need to fully illuminate the 47mm maximum diameter of a field stop in a 2" EP. This is not really cheating, as there is a trade-off between size of the central obstruction and the degree of vignetting,

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