New user with a Seben ED Ocular 2.3 8-24 zoom eyepiece

[The Serpent]

Hello All

I'm a new astronomer based in Norfolk. I've always been interested in astronomy but only casually used binoculars up to some weeks ago when I took the plunge and bought a scope. Having a young family though means I have to practice a style of austerity astronomy!

The scope is a bit of a 'classic' - a Prinz Optics 660, had off ebay for £30 from some folks who had inherited it and had no interest in it. It's a 3 inch (76.2mm) refractor with a 1250mm focal length which gives over f/16. It's fine as I'm starting out with the moon and planets, it's able to split double stars easily, however nebulae are almost invisible although I did manage to get a decent look at PANSTAARS a few weeks back.

The problem with it is the original eyepieces - an H20mm and an H6mm (Huygens??). The 20 is fine but the 6 is pretty poor. I'm not any kind of expert but I'd have thought most eyepieces today expect much faster optics so I'm not sure what would work well. Crucially I've also got next to no budget!

I wanted to find out which eyepiece sizes I preferred before worrying about suitable types, so it seemed logical to get a low end zoom eyepiece and see which settings I spent more time with. Don't laugh but I got a Seben ED Ocular 2.3 8-24mm off ebay as it seems to have surprised some folks and met the cash aspect.

What suprised me though is that I can't see how you are supposed to operate the thing! I thought it would be much like a manual camera zoom, but it has no moving parts! I've even (carefully) had it apart where I found four lenses, various spacers and the retaining ring, but no means of varying the mechanism. Apparently they are very similar to the Celestron 93230 and Orion Epic ED-2 zoom. It is utterly identical to the one pictured here: http://www.astromart.com/classifieds/details.asp?classified_id=435210

So hi to all again, and could anyone be good enough to give me a clue about the eyepiece?

[RichieP]

Are you sure you actually have a zoom eyepiece? The link you provided shows a fixed eyepiece which seems to have a focal length of 2.3mm

Your description of the disassembled parts sounds like a fixed eyepiece as well.

[Peter Drew]

Also looks to me that it is a fixed focus very short focal length eyepiece. I have a Seben zoom which is quite different to look at, it certainly works very well at F10.

[The Serpent]

You must be right fellas, I was hoping there was a bit missing. Still, it seems to work better than my ancient H 6mm. 2.3mm, eh? Well at least I know I can work my way up..! Thanks for the info

[ronin]

Yes H20mm and H6mm are a Huygens eyepiece in design, they are not that good.

If you can get hold of a couple of inexpensive plossl's and give them a try you should be better

The eyepiece linked certainly does not look like a zoom, must have been amusing trying to twist some bit of it to get it to move - always best to avoid mole grips on eyepieces. The one shown looks like a copy of what started out I think as an Orion eyepiece and is now sold by a few retailers under names. Nice eyepieces I believe so you haven't lost out. TS sell them and I think that Rother Valley have a line.

Back to plossl's, fairly simple eyepiece and probably the mainstay of many peoples eyepiece collection. For your I would look at ones not much less then 12mm and start with a 15mm and 30mm. If buying new then the Vixen NPL's from FLO are good. The 30mm may be usable on some of the DSO's up there. At f/16 plossl's should work fine.

I have assumed that 1.25" eyepieces will fit the focuser. ?

Scope is 76mm and if reasonable will be fine for quite a lot of things, sounds as if you have already made good use of it already.

[E621Keith]

A few days ago, I saw someone advertised a 2.3mm Seben eyepiece on fleabay as a zoom. He seems to have no idea what he was selling.

I hope you weren't unfortunate enough to have bought it. If you did, I suggest you use Ebay's buyer protection to return it. A 2.3mm eyepiece isn't very useful and gives an unusable 500x on your scope. It was definitely not a zoom.

[spaceboy]

Looks similar to the old Celestron X-Cel fixed fl ep's to me http://www.astrochat.co.uk/forum/viewtopic.php?t=15748&sid=4f45b246154bb5a6ef9f30c192608d87 but I believe Orion USA also used a similar looking design which actually was a zoom http://www.telescopehouse.com/acatalog/info_08631.html

[Steep]

I think Keith has got it right, unless you bought it very cheaply I'd try contacting the seller for a refund.

[The Serpent]

The 2.3 eyepiece was a tenner so I don't really feel ripped off and I genuinely think the seller was simply out of their depth when looking into what it was - the buyer certainly was! It produces a better quality image than the H6mm and I expect it would come into its own when I eventually acquire something with more aperture. Perhaps I should keep it as a reminder to ward off further rookie mistakes!

As the scope is not constructed along modern trends I suspect I'd be better off taking that fact as a main consideration as to what to do next. It has what I believe are termed 'Circle K' optics (the logo is present on the name plate) - from what I read these were excellent in their day and still respectable now. The focusser is original so it takes .965 EPs but I bought a decent aluminium 1.25 adaptor which seems to work fine on this Seben item.

It seems to be a great piece of beginners gear though. With the .965 H20mm it shows a bright, sharp view of Jupiter (and moons) and also the two main equatorial bands. There are craters galore on our own moon. Haven't tried Saturn yet as it is still hiding behind some trees on my easterly view but I'm very much looking forward to it! I had a go at splitting Mizar but I'll have another go at next opportunity before I declare success! As I mentioned, I found PANSTAARS which was unmistakably a comet with a brighter section and cone shaped tail smudge (stop me if I'm getting too technical..)

So the question is where to go next? I agree that something on the order of 12mm/15mm would be a good next step. Plossls are probably the best choice but when we're into names like Vixen and so on, I believe we're getting into the realms of money I can't lay hands to at the moment.

Eventually this situation will ease but as I'm unlikely to buy a new scope any time soon, is it a good idea to buy cheap plossls which would become a hinderance again in a better scope? Don't throw your hands up in horror, but would a set of Kellners be a good idea for this particular scope? Sets of five are available for the price of one decent plossl (probably for a reason!) but from my reading I gather that Kellners are mistrusted because they work poorly with today's fast scopes, whereas mine is about as slow as they get.

I guess I'm just finding by place on the eternal astronomy balancing act!

[Steep]

Others on the forum have recommended BST eyepieces, from eBay seller Skys_unlimited which come in around the £45 mark.

[haitch]

I know your current scope is very slow and not demanding on EPs but I would think about getting some keepers that'll stay with when you eventually move on to another scope. I've spent my time moving from plossls through various other line ups until I ended up with Naglers. I could've saved a load of time and probably some money by going for them in the first place. Just a personal view to throw in the cooking pot of ideas. Of course different scopes give different magnifications with the same EP so don't get carried away buying EPs that'll be unsuitable later on but you'll always probably want a nice widefield EP.

[The Serpent]

Hi Steep - I've seen the discussions around BST eyepieces and they are tempting. But then, so are a lot of things!

All opinions welcome, Haitch! The ultimately cheapest and best way is of course to get stonking eyepieces straight away. I see every bit of sense in that except that I can't stretch to those right now. Therefore all I can do is introduce as few hops on the way as possible. That's the plan anyway.

If I were to plan further, once the eyepiece bother is sorted out to some kind of satisfaction, I'd be tempted to make the purchase of an EQ5 mount a priority rather than a new scope. It'd hold the Prinz just fine if required and it would mean the next scope need only be the tube itself (and thus cheaper). Or perhaps make some cash back by buying tube + mount and then selling off the unwanted, inferior mount.

[Peter Drew]

The genuine Seben 8-24 zoom eyepiece would work very well with your telescope and give you all the magnification range you would need for less than £50. .