Upgrade route?

[Andy0306]

Hi,

I currently own a Celestron Onmi XLT 102 F6.5 frac, this one https://www.skyatnightmagazine.com/reviews/mounts/celestron-omni-xlt-az-102/

I've used the scope a few times on the usual suspects, Jupiter, Saturn, Pleiades and Mars with differing results. Pleiades was great with the supplied 25mm eyepiece, Saturn and Jupiter were OK, but lacked any detail, which I wasn't expecting given the scope size and 25mm eyepiece.

My kids bought me a Vixen NPL 8mm, but i'm struggling with focus, especially on Mars. I can get more detail on Saturns rings, but not enough to see the Cassini division.

I fully understand the above may be a limitation of the scope (and my eyes), but I would like to try and improve things. My options are below, but which one would give the best upgrade first?

Replace the erecting mirror diagonal for a dielectric?
Get a different eyepiece, but which.
Add a 2x Barlow?
 

One thing to add is that I have astigmatism, so may need decent eye relief.

Thanks in advance  

Edited November 22, 2020 by Andy0306

[Andy0306]

Just to note, I'm aware of the scopes limitations and I'm not expecting miracles. I had a Skywatcher Skyliner 150P, so know what I'm missing, but I needed a smaller more portable scope and this fits the description.

[KP82]

Vixen NPLs are decent eyepieces although the 8mm has very short eye relief, so might not be comfortable to use.

I'd replace the cheap erecting image diagonal with a proper 1.25" star diagonal.

[Cosmic Geoff]

Replace the mirror diagonal if you like, but I have not found that replacing diagonals made much of an observable difference.  The extra cost tends to get you better build quality rather than a flatter mirror.

Even a 8mm eyepiece will not give you a lot of planetary magnification in that scope.  (x83) You need a lot more magnification than that to see much.

I found that using a x2 Barlow (the one supplied with it) significantly improved the image quality of my 102mm f5 Startravel achromat, asides from the increase in magnification, when looking at planets.   So I suggest your next purchase should be a x2 Barlow lens.

[Andy0306]

17 hours ago, KP82 said:

Vixen NPLs are decent eyepieces although the 8mm has very short eye relief, so might not be comfortable to use.

I'd replace the cheap erecting image diagonal with a proper 1.25" star diagonal.

Your right in that it is uncomfortable to use, I think I definitely need more eye relief.

 

4 hours ago, Cosmic Geoff said:

Replace the mirror diagonal if you like, but I have not found that replacing diagonals made much of an observable difference.  The extra cost tends to get you better build quality rather than a flatter mirror.

Even a 8mm eyepiece will not give you a lot of planetary magnification in that scope.  (x83) You need a lot more magnification than that to see much.

I found that using a x2 Barlow (the one supplied with it) significantly improved the image quality of my 102mm f5 Startravel achromat, asides from the increase in magnification, when looking at planets.   So I suggest your next purchase should be a x2 Barlow lens.

I've read differing views on diagonals, mostly on this site. I will need to change it at some point, as the screw that holds the eyepiece in has stripped the threads of the plastic. 

I'm thinking maybe get a 9mm eyepiece (with decent eye relief) with a 2x barlow, which I believe should get me around 146x mag.

Any more suggestions welcome  

[John]

If your diagonal is made of plastic, an upgrade may be well worth while.

On eypeieces, a BST Starguider 5mm eyepiece is good quality, has longer eye relief than a plossl, a wider field of view and will give you 133x magnification.

Seeing the Cassini Division is quite possible with a 102mm scope but it is not easy and the seeing conditions need to be at least moderately good for it to be seen. The low altitude of Saturn currently does not help matters either.

 

Edited November 23, 2020 by John

[DaveL59]

The spherical body diagonal is in fact prisms as it is an erecting type, at least assuming it is the same as the one that came with the LT70AZ. There's a big difference moving to a proper star diagonal I found when I swapped the TAL one in to compare. I ended up buying the SVbony 1.25 metal body diagonal which they state is dielectric, was a great price off Ali and arrived quite quickly. Also it's threaded to take a filter which was partly why I bought it, since my TAL one doesn't. Plan is to use the variable polariser with one half on the diagonal and the other on the eyepiece. When I tried that with the celestron erecting one you got an off effect of only half of the image polarising - hence saying it's using prisms.

[Andy0306]

The SVbony range seems to get decent reviews, so probably worth a look at their diagonal. 

I am leaning towards the BST 5mm as my next eyepiece, with maybe a 15mm and 2x barlow at some point later.

[DaveL59]

I can vouch for the diagonal, ended up buying two of them 🙂 No idea how you verify if it is dielectric but it works well and is a very solid build.

Also have their zooms SV135 (7-21) and SV171 (8-24) which are both quite good and if still on discounted pricing are a bargain. Note that the SV171 is huge and heavy tho optically is a little better than the SV135. Eye relief is reasonably good too. A good convenience option as it saves swapping eyepieces but there are others like the hyperflex (?) that are also well regarded. Add a decent x2 barlow and you get down to 3.5/4mm. You do get better views with single FL eyepieces but that's true of most zooms.

Edited November 23, 2020 by DaveL59

[DaveL59]

in case someone comes across this one
Dielectric Star Diagonal 1.25" Telescope | eBay

don't, or at least check what the new price from SVbony is as that is what the advertised diagonal could be.

[Andy0306]

I have considered a zoom eyepiece, but thinking this will be one for another day. Just need to use the scope more and build over time