zoom eyepiece

[Chippy3476 (Danial)]

Hi all,
I have seen an advertisement for a zoom eyepiece and was wandering if these are any good?? It states that it is a 7.5mm-25mm. It sounds good in theory but I wander if they are any use or whether its best to just buy a range of set size eyepieces??
Just wanted to get some other peoples thoughts on this.
Thanks
Dan

[raymo]

Hi Dan, There several parts to this question. Firstly, how good are your
optics? no point in buying expensive eyepieces if the scope is only of
moderate quality. How deep are your pockets? EPs can go up to over a grand each. Are you looking for a premium viewing experience, or will
you be happy with a very good one? If you can afford a range of high
quality EPs, by all means go that way. Even the best zooms cannot quite match single EPs. The same goes for camera lenses. Having said that, a
zoom can be great value for money. The best budget level zoom I have come across is the Seben 8-24mm. I have one, it's very good indeed for the price. I really enjoy using it on the moon. You can get it on ebay for around $70. Used with and without a 2x barlow, you have a range all the way from 4-24mm. I would also suggest that you need one decent quality
high power EP, and ditto low power one in the 30-36mm range.
raymo

[julianh72 (Julian)]

I have the Seben 7.5 mm - 22.5 mm zoom eyepiece, which only cost me about $35 on eBay from memory. I suspect this is the same eyepiece that you can get from a lot of sources, under a lot of brand names. (The Seben 8 mm - 24 mm is reputed to be even better, but costs about twice as much.)

The image quality is much better than the price would suggest, but not as good as a fixed focal length Plossl, for example. For me, it's really convenient for scanning the sky at long focal length, and then zooming in to a convenient focal length on whatever target you select.

Negatives:

Apparent Field of View is about 50 degrees when zoomed in from 7.5 to 15 mm, but winds back to about 40 degrees for focal lengths from about 15 to 22.5 mm, so it's a bit "tunnel vision" at low magnification.

I think it's a really handy eyepiece for general purpose star-gazing, but you'll want to swap in a better eyepiece for detailed observing once you've picked your target.

[raymo]

You're quite right Julian, the 8-24 doesn't suffer as badly with
tunnel vision.
raymo

[Renato1 (Renato)]

I have the Seben 8-24mm eyepiece and it is very good, having a good 60degree field of view at 8mm and not so good 40 degree FOV at 24mm. On the other hand I have an older 7-22mm no-name zoom that I wouldn't recommend, as it's fairly average.

By all means get something like the Seben one to muck around with (though you'll probably just be using highest and lowest power most of the time).

But for the same money at the Seben Ebay store you can get nearly four Orbinar Plossls or nearly three Orbinar Super Wideangle eyepieces or combination there of, which will give you better views than the zoom at lowish powers, and lower power than 24mm if you want it.
Regards,
Renato

[Chippy3476 (Danial)]

Are seben eyepieces good? Becouse they seem so cheap thats all,

[Chippy3476 (Danial)]

Would a zoom eyepiece be of any use on my 114 newt? At Christmas im thinking of getting a 8" dob too so I would be using it for that too, but for now just on my 114??
Thanks all
Dan

[julianh72 (Julian)]

Dan,

As the several respondents here have suggested, something like an 8 - 24 mm zoom eyepiece is a really handy all-purpose eyepiece in most telescopes, providing a reasonably wide-angle view for scanning, and moderate magnification for basic lunar observing, brighter nebulae, etc. (It's also really handy if you have a refractor or Mak with an erect-image diagonal, for use as a zoom terrestrial telescope.)

My 7.5 - 22.5 mm "lives" in my 130 mm Newtonian (650 mm focal length) as my "starter" eyepiece, but I tend to swap it out for one of my Plossl eyepieces with optimum focal length once I have found a target. In my 650 mm focal length telescope, it gives me a magnification range of 29x to 87x, and a Field of View of about 1.4 degrees at 29x (about three times the disc of the full Moon), down to about 1/2 degree at 87x (just big enough for the whole disc of the Moon). Longer focal length telescopes will have higher magnification and narrower field of view, and vice versa.

The Seben zooms (and I imagine many of the "clones" which are the same eyepieces under different brands - but I don't know how you would tell without trying it out) are exceptionally good value for money, especially for beginners. No, they are not as good as a premium zoom, but they are a fraction of the price, and provide a reasonable view. The view isn't as sharp or bright at any focal length as a reasonable Plossl or similar, but the convenience of being able to zoom in and out, with minimal refocussing, makes it a worthwhile trade-off for me.

Note that an 8 - 24 mm zoom pretty much spans the range of the standard two eyepieces that many basic telescope kits come with (10 mm and 25 mm or similar being a common pair of starter Plossls), so it doesn't really add anything to your viewing range, but it's the convenience of being able to view at any magnification in that range that is handy.

In all probability, you will still want to add at least one higher power eyepiece for planetary work (6 mm or so - or maybe a 2x Barlow with a 10 mm), and one lower power / wide-angle eyepiece (say 32 mm - 40 mm), but a basic zoom is a good buy as one of your first upgrades.

[sil (Steve)]

I love my Baader Hyperion 8-24 zoom. To my eyes its as good as my Baader Hyperion eyepieces for viewing quality and the convenience of the range is so great. Its good to be able to see where my local sky conditions start to fail badly at highest zoom, saves me wasting money on an expensive 6mm eyepiece that might only work for me once or twice a year when conditions are perfect, instead I have my heart set on saving for a high quality 10mm for showing off. My only disappointment is it doesn't work at all on my 100mm desktop dob, which is my quick grab scope for a 5min look at something, but my regular Hyperions work just fine on it.

Another plus I find with the zoom is it makes star hopping easier. to be able to quickly just back out the zoom if i lose where I am. Likewise on a goto mount thats drifting, we've all had the experience of lining up somthing cool like saturn in the eyepiece, then draggin someone over to look only to find its drifted out of viw in the meantime. being able to quickly zoom out so you can see which direction it drifted and re-center makes it much easier to get back to the business of showing off to your mates.