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Cheap but good Zoom Eyepiece


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So my partner asked me what I would like for Christmas. I told her I would like some BST's to which she swore at me when she saw the price, I tried to explain that they were good quality and reasonabl

Managed to get some time with it today - used Seben eyepiece to have a look at Venus using Skywatcher 150p. Could focus OK throughout the zoom range. At the longest focal length of 22.5mm it was compa

sounds like a bargain. most eyepieces, zooms included, will provide pretty reasonable views in most scopes. I like Televue but there's truly not a massive difference between them and cheaper options.

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The £76 version from the same supplier states:

http://www.ebay.co.uk/itm/Orbinar-HQ-FMC-Zoom-7-2-21-5mm-Eyepiece-1-25-31-7mm-OZ2-/380750174838?pt=UK_Photography_Telescopes&hash=item58a67a9a76#ht_2730wt_1400

  • Field of vision: 53-40°
  • Interpupillary distance: 15mm
  • 7 lenses / 4 groups
  • Fully-multi-coated (FMC)
  • Blackened lens edges

The £20 version doesn't.

http://www.ebay.co.uk/itm/380697725280?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649#ht_3318wt_943

So we can safely assume that none of the above is applicable to the cheapy.

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Speak of the devil - it has arrived.

My standard eyepiece test is to focus in on the football ground floodlight tower which is over 1/4 of a mile away.

I can see the halogen light bulbs and 240v cables on a good day.

Minimum zoom = better than the skywatcher 25mm.

Better clarity, focus, with a nice wide view which is pin sharp.

Maximum zoom = this is where the limits of the scope come into play, it was very hard to focus.

I even tried it with a Barlow to try and fool some better results out of the eyepiece - it made it worse. 

At 7.5mm the quality was not quite as good as the barlowed skywatcher 10mm eyepiece (10mm with the 1.5x magnifier = 6.5mm equivalent)

Once I knocked the zoom back to 2/3 full power it was OK.

Conclusion

The results were variable due to the heat haze and daytime viewing conditions.

Low mag settings were noticibly better than standard SW gear, and on par with the Revelation Plossls.

Once you dial in some magnification, the field of view pleasantly widens as it zooms in, but the finer detail is lost.

For my set-up on the 700/76 reflector, it did what I expected, and reached the limits of the scope.

I need to try it in the 8" dob to find out what the limits of the eypiece are.

And try it out on the moon with the 3".

For £20 it does what it says on the tin, and matches the performance of similar priced EP's.

Advantages: Price / wide views / one size fits all / good construction  - with black coated metal threads for the filter (not cheap painted threads)

Disadvantages; You need to use the rubber eye cup for internal reflections / usable range is only 2/3 of maximum for pin sharp performance.

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An update to the spec of the £20 verison.

  • Field of vision: 53-40° = The cheapy is much better, mine was about 50-degrees to 60-degree plus = super wide
  • Interpupillary distance: 15mm = Yes - about the same
  • 7 lenses / 4 groups = don't know
  • Fully-multi-coated (FMC) = definitely not, eyeball reflections were significant
  • Blackened lens edges = don't know
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Ordered one for my son, thought it would make a good xmas gift. Bought direct from Seben on Amazon. Delivery says upto 4 weeks.....crikey that is going to be cutting it real fine.....gulp!

He'll be so chuffed, He only has the standard 10 and 25 at the moment. I'm now dying to know what its like myself. I've owned the Seben 8-24 in the past and that was one of the true astro bargains. Not expecting this one to be anywhere near as good but hoping it will be still be okay. Better than the £20 would suggest.

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I would love to hear your opinions on first light with the zooms when they arrive Fredster and Stargazer2013

Will do, but i'll have to do it on the sly. Get caught using it and my wife will not be best chuffed :)

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Managed to get some time with it today - used Seben eyepiece to have a look at Venus using Skywatcher 150p.

Could focus OK throughout the zoom range.

At the longest focal length of 22.5mm it was comparable to standard SW 25mm eyepiece with about 50% in the centre OK and getting progressively worse as I got towards the edge.

Taking zoom down towards minimum focal length started showing some colours at around 10mm and going totally "rainbow" at 7.5mm.

So clearly not very suited for relatively fast (f/5) reflector.

I wanted to use it in my TAL-1 (which at f/7,3 should be a lot more tolerant), but it is out of commission while I am working on it's focuser, so instead I have stopped down my Skywatcher and did some observing of Venus through the small front hole (which converts the fast reflector to very slow off-axis Herschelian like scope).

This made the Seben zoom piece much more usable with only a hint of rainbow at 7.5mm and altogether much more positive experience.

I am glad that I have bought it.

I will not be using it in my Skywatcher 150p.

Hopefully it will be fine with my TAL-1 used as a grab and go scope with just one zoom piece for quick ad hock viewing sessions.

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I'm still playing about with mine.

The field of view is very narrow at minimum magnification.

So the Skywatcher 25mm eyepiece is better for the wider angle views.

The 12mm and 9mm Revelation Plossls are pin sharp compared to the slightly blurred Zoom.

So the Plossls will stay, to be used with the 1.5x magnifier (8mm and 6mm equivalent)

They are much better optical quality than the Zoom.

Lunar observing would have been good if it could be Barlowed easily above 93x magnification (it can't at the moment)

That is my next challenge.

Make it work at 93x maximum magnification on the moon.

With the option to use the 1.5x magnifier to get it up to a 140x maximum.

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Yes - on the 3" travel scope, and the 8" 200P dobsonian.

The results were the same on both scopes 93x max and 160x.

The eyepiece works well up to a 10mm equivalent Zoom on the 3" .

Then once the red dot marker reaches the "P" text on eyepiece the optical quality drops away,

The top 1/3rd of the Zoom is poor, that's when I start reaching for another eyepiece.

I used it on Jupiter in the 8" (with and without the 2x Barlow).

The Barlow makes the image bigger - but it still stops working at 10mm equivalent.

The Zoom will replace the 10mm Skywatcher tat which came free with the scope.

But the superior 9mm / 12mm Revelation Plossls would have done that anyway.

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Just to clarify - the full zoom is usable, but not optically perfect at full magnification.

And using the barlow / or 1.5 magnifier is hitting the magnification limits of both scopes (3.6mm / or 5mm equivalent)

I needed to strip my zoom assembly down and rebuild it to get it to work properly.

http://stargazerslounge.com/topic/200672-%C2%A320-seben-zoom-75mm-225mm-first-light/

Now that it is working better, I am still finding the slight imperfections at full Zoom which aren't there with other eyepieces.

I know the moon is more tolerant of collimation and focus issues.

So I am hoping it will come into focus better at full zoom during Lunar observing.

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Now thats what I would call a "bolt tube". I was thinking of this (see below) that many zooms seem to come in. Not that the shape of the plastic container matters that much !:

Hi John, now that's the one on the Celestron and Sky Watcher versions, and if I am not mistaken, was also used with the Seben version 8-24mm.  Got to be the same factory.

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Just a coment.

I sent a mail to Seben the other day, asked for more details about this zoom, such as FOV for the focal range, eye reliefs, weight, etc. A quick reply from Seben says that this is a beginner's zoom eyepiece, these technical details are not available. They recommend the 8-24mm zoom and provided som details.

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Just a coment.

I sent a mail to Seben the other day, asked for more details about this zoom, such as FOV for the focal range, eye reliefs, weight, etc. A quick reply from Seben says that this is a beginner's zoom eyepiece, these technical details are not available. They recommend the 8-24mm zoom and provided som details.

Thats a slightly disappointing response I feel. Why should beginners have to put up with stuff of indeterminate quality ?  If anything they need something that is going to impress them and draw them into the hobby.

I don't mean that it should cost a lot but just that it should be decent in quality and have some information to help assess it's suitability.

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