seben zoom eyepiece

[johnnyp]

Hi all. I've just ordered a seben zoom eyepiece for my virtuoso 90 mak. Its the priced at £20 from ebay. Its just to use until i decide on what focal length eyepieces i require. But im interested in peoples experiences with it. Your thoughts please.

Cheers

[Ags]

I've never used it, but i have heard several times that it is not all that bad. It's pretty rare to hear a good word about Seben, so the zoom must be something special (by Seben standards).

[ronin]

Strange but the Seben zoom seems to get good reports.

Usually anything marked Seben and you are told to avoid, somehow this seems to break the rule.

Now having said that you could get a real bummer. :grin: :grin:

[michael.h.f.wilkinson]

The zoom does get good reports. Given that your mak has a large focal ratio, it is not too picky about EP quality, so it may well prove a great investment (it is certainly not much of a risk)

[rowan46]

As far as I remember there are 2 seben zooms. one was quite good the other wasn't. I believe it was the more expensive one that was quite good.

[coulthamst]

I have used the Skywatcher 8-24mm zoom, which is another rebranding of the identical Seben version, for some years for solar viewing, and find it very successful except for the 20-24mm range which has a noticeably restricted field of view. I understand that there is also a 7.5-22.5mm zoom available from both brands, at a cheaper price, which has much less satisfactory reviews. As I have not possessed an example of this model I am unable to speak from personal experience of it,

EDIT - Having checked the ebay seben zoom ads I fear that you may have bought the less satisfactory version. Best of luck.

[johnnyp]

Some good feedback. Cheers lads. I figure its worth a punt at £20 good or bad.

They also do another zoom . the orbinar 7.2 - 22....or thereabouts . priced at £82. Any knowledge of this one?

Thank you for the responses so far.

[johnnyp]

@coulthamst. Yeah I am aware that its the inferior one. Toyed with the idea of the more expensive one but wanted to try this one as its so cheap.

[Stu]

The £20 one is not that great, some internal reflections because the lens edges are not blackened.

There is another version for around £50 which is significantly better and works well in longer focal ratio scopes.

http://pages.ebay.com/link/?nav=item.view&alt=web&id=380307924519

[Reeny]

The £20 is pretty awful optically.

Some people can tolerate the view for £20 and get away with it - I can't.

Others posting the good review have bought the £50/£60 version, which is a different animal altogether.

For £20 you get a 3-element Zoom with 2x plastic lenses, with a glass lens on top.

So there is no edge blackening, and no multi coating - just good old plastic tat.

You can take it to bits, and buy glass elements for it

That's what I did.

The choice for me was to bin it, or make it work.

It is quite well made if you can source some glass lenses to use as replacement parts.

[johnnyp]

Interesting. Where did you source the glass lenses? . could be a little project for the cloudy evenings.

[Reeny]

http://www.stockoptics.com/

19.38mm F/L x 17mm Diameter Plano Concave Spherical

The 17mm diameter glass was ground down to 16mm for the bottom element - £9.50p.

The price is £10.50p now

http://www.ebay.co.uk/itm/19-38mm-F-L-x-17mm-Diameter-Plano-Concave-Spherical-Optica-Lens-PCL-19-38-17-CQ-/110915520768?ssPageName=ADME:L:OC:GB:3160

I used the glass from a cheap 99p jewellers loupe for the 21mm second element.

A better quality equivalent should make a big improvement - but it works OK for me as it is.

http://www.ebay.co.uk/itm/30x21mm-Triplet-Eye-Loupe-Magnifier-Magnifying-Glass-Jewelers-Jewelry-Diamond-HC-/261582015651?pt=LH_DefaultDomain_3&hash=item3ce780cca3#ht_3191wt_1422

It's not par-focal - but neither was the first effort from Seben.

And the eye relief is massive - about 20-30mm, so you will need to screw the eye cup out, and leave it there

The internal travel was stopped down with a rubber spacer to stop the glass touching, and prevent over egging the magnification.

It works well with the 8-inch dob up to about 150x mag (8-mm)

Crystal clear on the moon, and good for hunting down nebula - find it, then zoom in.

But it still fails in the 3-inch.

I put the purchase down to experience - you may need to do the same.

[johnnyp]

Thanks for that reeny. Definitely something I'll have a go at. And its no great loss if I make a pigs ear of it

[glennbech]

I got here when I googled for the seben 7.5-22.5 and just want to add a down vote for it. 

The fov at 22.5 is like looking through a keyhole. When looking at bright objects like the moon - there is a a very visible blue color on edges.

Mechanically its also bad. The zoom is a bit hard to operate so you shake your view while zooming. Waste of 20.

[rwilkey]

Hi there, the 8-24 Seben zoom is not a Seben product, it is made by GSO, and is very good for an interim ep as you suggest.  It is exactly the same product as the Sky Watcher and Celestron versions, only at a better price.  In my opinion it is good value for the views it produces, and a good ep to cut your teeth on.

[rwilkey]

The earlier claims that the Seben Zoom has plastic elements is simply NOT true, this is a GSO rebadged (product code MZT8-24) though Seben typically and falsely claim that it is a Seben original.  Personally I would not deal with this dubious company, their telescope products and 'deals' are rubbish.  The GSO zoom is the exception. 

[Dave In Vermont]

The poster was NOT talking about the Seben 8 - 24mm zoom. He refered to the 7.5 - 22.5mm variety. These are usually getting poor reviews due to factors he cited above. The 8 - 24mm is actually quite good by the majority of people.

Dave

[rwilkey]

Hi Dave, my mistake, I was reading the posts rather quickly.  Greetings from the UK!

[Reeny]

The top lens is glass - but the 2x movable lenses are definitely plastic, held in by a cheap plastic collet - as above.

The zoom assembly has a little bit of backlash - but is well made otherwise.

It is a shame that they used plastic for the most important components - one wipe with a lens cloth and they are scratched beyond repair.

This is £20 I could have spent elsewhere with better results.

 

[triton1]

Oh dear that looks absolutely grim it makes me laugh when you read their advertising spiel saying about how good quality their products are should be ashamed of themselves.

[Cosmic Geoff]

I was mainly interested in a zoom eyepiece for looking at double stars and similar objects, where it is a fag to use a low power eyepiece to find the object and then swap to a high power eyepiece to examine it.  However, on reading the above discussion it becomes clear that zoom eyepieces have a smaller field of view at long focal length than at shortest focal length - the opposite of what one would like.

Worse, on looking at the specs it becomes clear why some posters favour the reassuringly expensive Baader zoom, as it has a decent field of view of 50 deg (minimum).  The Seben has a FOV of 30deg at 22mm, which is a joke.

I have a, antique naval gunsight whose FOV does not change as the magnification is changed from 7 to 18. It has a zoom/erecting eyepiece which is made of brass and is very heavy.

[John]

Actually the Baader zoom has been tested as having a 42 degree field at 24mm widening to 68 degrees at 8mm. The 8-24mm Seben / Skywatcher / Celestron zooms (they are all the same) are quite decent performers for their price but the 7-21mm zooms, while a little less expensive, seem to loose a lot in performance and are hard to recommend.