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simon gale

2"eyepieces on back of SCT

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What diameter is the thread on the rear cell? On my Celestron 9.25" I use a Baader Clicklock, 2" diagonal and then the 2" EP in that order.

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28 minutes ago, Owmuchonomy said:

What diameter is the thread on the rear cell? On my Celestron 9.25" I use a Baader Clicklock, 2" diagonal and then the 2" EP in that order.

Me too. :)

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Simon,

you need to replace the 1.25 inch visual back (supplied with the scope - the bit that screws onto the back of the scope) with a 2 inch visual back.

i do not know if the visual back is removable on your scope, it can be unscrewed on the 8" version, you will have to give it a try.

If it does unscrew then you also need to buy a 2" star diagonal to fit into the 2" visual back.

you then need to buy some 2" eyepieces to put into the 2" diagonal.

https://www.firstlightoptics.com/adapters/baader-click-lock-2-for-celestron-meade-sct.html

https://www.firstlightoptics.com/diagonals/skywatcher-di-electric-star-diagonal.html

 

You can get these items second hand to save some dough.

Alan

 

 

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Before you do this get some measurements of your replacement parts to check once connected up you have enough clearance from the EP end to top of mount as you raise the altitude. Should be OK with a 6, but the 8 and 9 are very tight and might need a slew limit added. You can and should front load an Evo to maintain accurate tracking.

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8 minutes ago, Itabot said:

Will this diagonal SCT fit, take 2" EP's without the requiring a seperate 2" visual back?  on a Celestron Nexstar SE8 or have I got it wrong?

http://www.rothervalleyoptics.co.uk/altair-astro-lightwave-2-dielectric-diagonal-sct-fit.htm

 

Yes, you screw the diagonal onto the rear port of the scope in place of the visual back.

You just need to make sure that the larger diagonal will clear the mount when the scope is pointing upwards.

Edited by John

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Yes it will fit.

Just means you have to leave the diagonal permanently mounted to the scope. You could always get the visual back later if you find it a pain. For example, if you want to put a filter onto the diagonal then you need to remove it from the scope to add the filter.

 

 

Edited by alanjgreen

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Thanks John & Allan, I'll wait and see how get on with my 1.25" EP's before spending any more money, as I only have one 2" Skywatcher Panaview 32mm EP, I may decide to sell?

Edited by Itabot

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There's no rush, the stars come around every year!

Switching up to 2" is worth it as you get a wider view which is great to frame objects most notably large open clusters and large nebulas (Veil Nebula is a good example where it is simply too big to frame in a smaller EP and the extra light from the 2" can reveal more detail).

But it can be expensive by the time you add in all the bits you need. You may also want to add 2" UHC filter to the list of "potential" bits & bobs.

Edited by alanjgreen

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I don't think 2" eyepieces let in any more light and reveal any more detail. The additional field width can be useful / nice for framing larger DSO's though.

 

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The 1.25 inch visual back blocks several mm (.75 inch) of the (hole diameter) light path from the SCT tube to the eye, this must have some sort of "light reduction" effect

 

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1 minute ago, alanjgreen said:

The 1.25 inch visual back blocks several mm (.75 inch) of the (hole diameter) light path from the SCT tube to the eye, this must have some sort of "light reduction" effect

 

I don't think it does otherwise no SCT would be able to perform to the resolution limits of their aperture when using with 1.25" accessories, which they clearly do, or at least all the ones that I've owned have.

 

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The Celestron 6" has a rear baffle tube size of 27mm and this will restrict the field of view. Any eyepiece with a field lens of 27mm or greater will vignette on this scope. You may find the 2" diagonal and eyepieces disappointing.

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Thank you for raising the size of the rear baffle tube, Michael. I suppose that means I should buy a 1 1/4 inch 24mm e/p.  Or use a focal reducer.

Simon Gale

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You can get longer 1.25 inch focal lengths.

celestron xcel 25mm are pretty reasonable. See FLO website.

televue do a 32mm and 40mm plossl in 1.25 inch format. See widescreen centre website.

i believe there are longer ones too.

Edited by alanjgreen

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