budget zoom eyepiece

[iantobach]

Don`t know about the rest of you, but getting anyone intrested in astronomy can be a challenge. Getting the wife to come and have a quick look at saturn/m32 can be hard enough- but then when they knock the scope, and then having to go down on magnification with changes eyepieces usually had her back inside in the warm. So I saw the SEBEN eypiece on Ebay- quite cheap- could be a turkey I thought but what the hell- Turns out to be not too bad - The specs are

Seben Super-Zoom Plössl Eyepiece 8-24mm:

steplessly adjustable focal length 8mm – 24mm

outfitted with up-to-date 1.25” thread

field of view: 60° (8mm) – 40° (24mm)

increases the image quality of your telescope or scope

high light transmission

high resolution

multi-coated lenses

outfitted with a thread for screw on filters

receptacle, which protects against dust and moisture during transit, is included

steplessly adjustable eyeguards for spectacle wearers

It gave a good view of saturn ( with meade 2 x barlow)- with a hint of cassini division in poor seeing, reasonable contrast. Not as good as my meade plossls at 8mm on my 102 refractor- but meant the wife could zoom in and out and spent more time looking than usual!!

There`s plenty of more expensive zoom`s out there- and I know It`s cheating- but for a cheap zoom i`d recommend it.

[GordonCopestake]

I've used the Vixen 8-24 zoom before now and liked it. The only thing that put me off was the fact it's not parfocal along it's range. Refocusing after zooming is a real pain. If someone could make a 6mm-32mm 50 degree parfocal zoom that cost £100 i'd buy it!

[flapjackboy]

I ordered a Seben zoom as well, thanks for the info iantobach. I had my doubts about it...

[paulestar]

>field of view: 60° (8mm) – 40° (24mm)

Not specifically related to this zoom EP as I've seen it on many other adverts too...why does the field of view decrease with increasing focal length? I thought increasing the EP focal length reduced the magnification, hence increasing the FOV?

Where have I gone wrong? Is it something to do with apparent FOV versus true FOV?

Paul

[GordonCopestake]

Yes Paul, it's the AFOV, eg, all plossls are around 50 degrees regardless of there focal length.

As an aside, the baader hyperion zoom looks much more interesting being parfocal and having a 50-68 degree FOV

[GazOC]

Where have I gone wrong? Is it something to do with apparent FOV versus true FOV?

Thats exactly right, the true field of view (ie what you see through the eyepiece) doesn't decrease when you increase the EP focal length, it increases as you'd expect.

The apparent FOV decreases as you increase the focal length due to restrictions imposed by the lens configuration.

[Cloudwatcher]

I have a Sky-Watcher 7-21 Zoom which does not need to be refocused in use except at

extreme ends of the range. With a lens detatched from a 2x barlow and screwed into

the end of the zoom the views of the Luna surface are great as you zoom in. A bit like

a dive bomber's view homing in on target.

Not that I've done any dive bombing of course!

[paulestar]

Thanks guys - I knew there had to be an explanation!

[GazOC]

I case anyone is wondering why increasing the focal length on an eyepiece decreases the magnification (the opposite froma telescope) it because an eyepiece is actually -f optically.

[proflight2000]

I have one of the seben 8-24mm zooms which i got when i ordered a small spotting scope 2 years ago, its got a nice feel to it, quite chunky but for a reasonable view its ok. If anyone wants one cheap give me a shout.

[Stormwatch]

I have the Seben zoom EP too, got it for £30 inc. P+P and it was well worth that. It's a great fun EP. On my little 102mm refractor it performs as well as any of my EP's.