Best eyepeices for Celestron CPC 925?

[Cronulla_Chris]

Yesterday I picked up my new Celeston CPC 925 from Andrews Communications. By 8pm it was assembled and had first light - which was the first-quarter moon - so far so good. At least the optics are ok. the moon is great for aligning the finderscope for the first time. I then spent the next hour trying to do an alignment. In an ideal world this should be straight forward but I was doing this on the balcony of my unit that only has the north and west sides open to the sky!

In the end I gave up and decided to change tack. I got out my motley collection of eyepieces and put them through their paces and instantly my main problem was clear - when changing eyepieces there is a lot of turning of the focusing knob. Now this wasn't so bad on my dob, but with the SC it is more of an issue.

Doing my research on the web, it became apparent that what I need is a collection of eyepieces that are parfocal. i would like some feedback please from other owners of similar scopes as to their experience and recommendations.

I guess the other issues is whether it is worth investing in a 2" prism diagonal together with a say a good 31mm eyepiece. Your thoughts?

[OneOfOne (Trevor)]

As you can see in my sig file I have a number of Pentax eyepieces, all of which are parfocal. It is definitely worthwhile having most of the eyepieces from the same family as it saves a lot of focusing, although I find with the C11 I use the 24 Pan much more than I used to in the F5 8" Newt. The amount of focus change between the Pan and a Pentax is not a lot, so it is not a huge problem, but going from one Pentax to another is just a small tweak of the focus motor.

I must admit, whilst the Pentax eyepieces were excellent in the Newt, they do not appear to be as good in the SCT. Some of this may be due to the larger F number, so whilst the 7 and 10mm used to be the ones used most at F5, they produce much more magnification and are less "useable" in normal conditions. I find I use the 24 and 30 much more, but I am keeping them for when I get a refractor and should use them a lot more again.

So rather than recomending Pentax I would suggest you try some others as well. Hyperion and Stratus are a good family to try if you have a lower budget, Panoptic are a bit more expensive but also great eyepieces. It depends a lot on your budget. I am sure other owners of a 925 will give you lots of valuable suggestions.

As for a diagonal? I find I almost never use the scope visually without one (2" WO dielectric). The eyepiece can find itself in some annoying places (on an EQ) and the diagonal allows you to bring the light out to the side easily, which is very useful for kids. When viewing near the zenith the eyepiece will be very difficult to use on a fork mount.

[MikeyB (Michael)]

That's a very nice scope that you've got there, Chris - congratulations on making such a good choice and welcome to IceInSpace.

First up, make sure you get the benefit of that big aperture you've paid for, by swapping the standard 1.25" prism diagonal for a modern 2" quartz dielectric type. In my experience with Celestron and Meade SCTs, you will see visible improvements in image brightness, contrast and clarity. Andrews have a GSO one in an SCT fitting for only $129 that will screw straight on to the rear of your scope and replace the 1.25" visual back as well as the puny standard diagonal. I believe it comes with the 2" to 1.25" adaptor that you'll need to fit your existing and perhaps future eyepieces.

As to eyepiece choices, that will depend on your budget and your eyesight (comfortable eye relief distance and/or need for spectacles), and your personal preference for normal, medium or widefield views. I've ended up with a mix of Tele Vues for my SCTs: Panoptics (19 & 24mm), a 13mm Nagler and Plossls (Tele Vue plossls are a revelation after the el cheapo brands). Whether by accident or design, these eyepieces are all very close to parfocal, which as you've found is extremely convenient.

if you can afford them, premium brands such as Tele Vue and Pentax, hold their value well and the IceInSpace buy/sell forums are an excellent place to acquire or dispose of good quality items at fair prices. You'll meet some great people that way, too!

You haven't given us much to go on with your alignment issue, but with big SCT GoTo systems, power supply and scope balance are crucial to success. A high power, regulated 240V adaptor will save a lot of heartache, or use one of those 12V car starter booster packs and a suitable adaptor cord.

[Cronulla_Chris]

Thanks for the comments guys.

Sorry if I wasn't quite clear on the alignment problem - because my apartment balcony is closed in on two sides plus a ceiling, the scope isn't picking up enough satellites to align itself. Looking at Sydney's weather forecast for the next week it will not be worth taking it anywhere to let it "stretch its legs". I was lucky to get it together last night and perform the "first-light ritual" before the clouds rolled in!

As for the 2" diagonal MikeyB hit the nail on the head. the scope comes with a 1.25" diagonal and I was wondering if it was worth upgrading to a 2". Andrews are getting in a piggy-back camera mount for me so I will get the 2" diagonal then.

Chris