Which eyepieces for Omni XLT 127/ C5

[robhatherton]

Following a lot of debating and thinking about maybe a goto scope - but moving away from that idea- I have settled on (I think a Celestron Omni XLT 127 or second hand C5 on a CG4 mount which I would be looking to buy in a couple of months (big birthday coming up!). Presently I've just got a Travelscope 70 on an old camera tripod. I still want something portable so I can walk over the fields behind me. We don't have too much LP but living on a main road the car lights every now and then do affect night vision.

So if I choose the SLT what eyepieces would you recommend to get the most range out of the instrument and should I consider a f6.3 reducer? It's general purpose I want at this stage and know I am going to be limited on DSO's.

Any advice appreciated.

[ronin]

As it is 127mm and f/10 means a focal length of 1270mm, you are going to need to consider a few at the longer focal lengths, especially if DSO'a are the intended targets.

At least at f/10 it will be easy on eyepieces which brings reasonable plossl's to mind, so the Vixen plossls from FLO if you like.

I tend to look at an eyepiece the same as the f number, so a 10mm, then say a 12mm for when the 10mm doesn't quite work. After that really 15mm, 20mm, 30mm.

Eyepieces like the BST have a wider view so a 25mm will deliver much the same field as the 30mm plossl.

If the scope has a 10mm and it is OK then perhaps a 12mm, 20mm and 30mm, for now.

If you wear glasses then eye relief may be a factor and the BST are fair for this, they do a 12mm, 18mm and 25mm.

[robhatherton]

Ok thanks for that. The scope just comes with a 2mm.

[ronin]

Guess you meant 25mm ??

2mm is a bit much :eek:

SCT's and Maks mean you need the longer focal lengths just to have a half decent field of view. Now an f/8 SCT would be a good scope

The standard problem I find is that an eyepiece at the f number (10mm here) is a good selection and start point, however then you need one a bit longer for when conditions are not good, and one a little shorter for when they are very good. Thats 3 just to start with.

If you then get a medium and a long that brings the count up to 5.

That oddly is why I like the BST's, the whole set is just 6 so I take the set and simply pick one that gives the view/magnification I want or that works best. Less decision making to be attempted.

Picking eyepieces from a set that means (to my thinking)

BST = 8mm 12mm, 18mm, 25mm.

X-Cels = 9mm, 12mm, 18mm, 25mm.

Vixen Pl's = 8mm, 10mm, 20mm, 30mm.

I tend to go for a single range as in cases like the BST's and Celestrons they are fairly par-focal so less refocusing between changes of eyepiece. In general plossls are not always made par-focal.

[robhatherton]

yes 25 mm! 2mm would be a pinprick not an eyepiece! Thanks for the advice. I fancied some BST's as they seem to get good reviews and are claimed to be parfocal but I don'tbelieve they go beyond 25mm. Would anything give me a wider view?

[rwilkey]

No, the BST's don't go beyond 25mm. A 32mm Plossl would probably do you to start with, and if you can afford a good one, the TeleVue 32 Plossl is great.

[robhatherton]

Yes I thought I would go for a 32mm. Would a focal reducer help too or is there nothing much more to be gained there?

[John]

The F/6.3 focal reducer does get you a wider field of view although it introduces some more pieces of glass of course. It's quite fiddly to use (in my view) as it screws onto the port on the rear of the scope and then the diagonal screws into it. If you are interested in wide fields of view an SCT is not the best scope perhaps ?.

I've deleted your duplicate post above by the way

[Ohmless]

I second the 32mm televue plossl. It is fantastic! It will give 46.9x and about a degree field of view. This isn't quite wide enough to get the biggest open clusters and the andromeda galaxy(if in a dark site), but will get you almost there. If there is a focal reducer for your scope(not familiar with one unless you mean the kind that screws onto the eyepiece) I would recommend only for these objects. You might just be happy with the view you already have. Now if you were to barlow this eyepiece later, due to the wide field stop, you should look at a premium barlow most likely, but ask around for experiences with barlowing this eyepiece.

I like to look at deep sky objects first at about 2mm exit pupil and then magnify until I frame the subject well(often 1mm exit pupil.) This is figured out with a bit of basic math. It is objective diameter divided by the magnification.

I look forward to hearing your progress as you learn the new hobby and scope.

[robhatherton]

Thanks for all the advice. No I'm not after a very wide field of view, just getting the most out of the scope. I do have some nice Steiner 7x50s and the 70mm travel scope will give just 20x magnification with a 20mm eye piece. So maybe I'll leave the focal reducer and see how I get on with what's been recommended first!

[Dunkster]

If you're interested in a bit of everything, then you could eek the aperture out a little more to a C6... that extra inch of aperture collects about 40% more light than the 5, but remains really light and portable.

Any of those 3 scopes however will still bag you a little over a a degree FOV, which will swallow up the majority of objects, excepting some of the real biggies that are probably best viewed with binoculars (if you have a pair) or a shorter focal length scope. Sadly, one scope does not fit all

A 130p heritage Dob is another popular scope of similar aperture and portability.