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jonnydreads

Zoom eyepieces

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Hi.

I have recently purchased a nexstar se8" 

I am wondering if anyone could recommend a good zoom eyepiece. I do have a few eyepieces that I use for my skywatcher but I've never purchased a zoom eyepiece before as I was put off them once when I first bought my telescope. 

The convenience of it strikes me mostly, I'm a complete novice in comparison to others on this forum and would like some advice.

Thanks in advance jon 

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Hi Jon and welcome to the forum.

The Baader 8-24mm zoom is a good quality zoom eyepiece. It's not exactly low cost but it does replace, say, 4 eyepieces so the cost should be viewed in that light. The optical quality rivals decent quality fixed focal length eyepieces.

Like most zooms the field of view at the longest focal length is a little restricted but it widens out nicely as the focal length is shortened. The Baader zoom plus a fixed focal length eyepiece of, say, 32mm for low power views could be all the eyepieces that an 8 inch SCT owner needs.

 

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I've had a 8se for a few years now, the F10 works well with zoom eyepieces. A binoviewer is fantastic with this telescope on the Moon and planets.  

Welcome to SGL.    😀

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wow, I've never even heard of a binoviewer, I always wondered why that hadn't been invented yet haha.

does that limit the view at all? detail wise? 

I've never had a goto telescope and always thought that it was quite lazy to have one without knowing the sky well, almost like having an automatic car and having never used a manual one....... I've got to that point in life where I just want to see things and this is my best shot I think..... I've given up being proud 😂

apparently I need a power pack too!

Edited by jonnydreads

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+1 on the baader zoom. It's in my scope 90% of the time- with the Barlow it effectively gives me 3.5-24mm. 

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1 hour ago, jonnydreads said:

wow, I've never even heard of a binoviewer, I always wondered why that hadn't been invented yet haha.

does that limit the view at all? detail wise? 

Binoviewers are a whole 'nother topic.  Basically, the traditional binoviewer adds about 100mm to the optical path.  As a result, many scopes won't come to focus with them.  SCTs and Maks are the exception because they move the primary to focus and the secondary magnifies how far the focus plane is moved.  As a result, they have tremendous potential backfocus.  The downside is increased focal length and slightly increased spherical aberration.  For other scope types, an OCA/GPC/barlow element needs added to the nose of the binoviewer to reach focus.  This generally results in an increase in focal length from 1.25x to 3x thus decreasing the lowest power possible.

Maximum field of view is also limited by the clear aperture (CA) of the binoviewer.  Entry level ones have about 22mm of CA while high end ones are 27mm or more.  Eyepieces with a field stop larger than the CA will vignette somewhat when used in a binoviewer.  Larger CA is achieved using larger prisms which increases the path length beyond 100mm and increases the size, weight, and cost of the entire unit.  Almost all binoviewers are 1.25"-only.  2" binoviewing is best done with a binoscope (two scopes side-by-side and aligned with eyepieces mounted right across from each other via a series of star diagonals).

The amount of light reaching each eye is split in half.  This is actually good on solar system objects which tend to be overly bright but bad for faint fuzzies like nebula and galaxies.  With two eyes working on the same subject, more detail is generally seen than with one eye.  When looking at the full moon, eye strain is basically eliminated because you don't have the dramatic mismatch in brightness between eyes as in mono-viewing.

Eyepiece selection is complicated by the fact you have to be able to get them at least as close together as your IPD.  This rules out using really fat eyepieces.  They also have to allow your nose to fit between them.  If you have deep set eyes, this can be a problem.

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Never tried a Zoom, but did some research a few months ago about them. There seems to be a trade-off between performance (they tend to have a worse FoV, exit pupil output, and image quality) and convenience (may be very useful for Moon, Planets, and the Sun, because a smooth change in their focal length allows the observer to quickly find the optimal useful magnification in a changing atmosphere, without taking the eye from the EP).

2 models seem to come up the most:

- Baader Hyperion Zoom 8-24mm
- Tele Vue Zoom 3-6mm

I also found a post from someone using 2 Zooms with a binoviewer, but BVs are a different topic - I suggest opening a different thread if you're interested.

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The exit pupil for a zoom works on the same basis as a fixed focal length eyepiece, except that the zoom enables the observer to vary it as the effective focal length is varied. With the Baader and Tele Vue zooms, the optical quality is as good as a decent plossl eyepiece or the fixed focal length Baader Hyperions (actually the zoom seems better corrected at the field edges in faster scopes than the Hyperions). The AFoV of the 8-24 zooms (of all brands) ranges from 40 degrees at 24mm to 60 degrees at 8mm.

One of the combinations that I use often is a relatively low cost 7.2mm - 21.5mm zoom and the Baader 2.25x barlow lens. This gives a very useful high power range of 9.55mm to 3.2mm and the optical quality is really rather good - it compares well with much more expensive high power eyepieces that I also own. The ability to instantly "fine tune" the magnification to get the best from the conditions and target is something that I've come to value highly.

There are lower cost 8-24 zooms available branded, Skywatcher, Seben, Celestron etc, etc which are not quite as good as the Baader and Tele Vue zooms but still do a useful job especially for outreach.

 

 

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Get anything but the £21 Seben 7.5-22.5mm Zoom eyepiece.

They are made with plastic internal parts, including the bottom two lenses in the Zoom mechanism.

Seben1.JPG Seben2.JPG

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Not everyone likes zoom eyepieces. I suggest to have a look through one at a star party or something. If you don't have the option I would start with Celestron zoom. It's not as good as the Baader but it will allow you to get the idea of what to expect from zoom eyepiece. If you see that it is what you were looking for you can upgrade to Baader, or you may find out that it's good enough but you want to add some single FL eyepieces to complement it, or maybe you don't like it at all, then going straight to Baader would be a pricey mistake to make.

16 hours ago, John said:

The AFoV of the 8-24 zooms (of all brands) ranges from 40 degrees at 24mm to 60 degrees at 8mm.

The Baader goes to about 70° AFoV at 8mm

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Hello @jonnydreads and welcome to SGL

The Baader 8-24 zoom is as others have said a good zoom and suits the C8 well giving magnificatons from x 85 to x 254.

As John said earlier if you add a 32mm eyepiece for low power/wide field you will have the full range covered for DSO's, Lunar and planets.

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12 hours ago, pregulla said:

...The Baader goes to about 70° AFoV at 8mm

It's been independantly tested at 48 degrees to 68 degrees.

Close to 70 though :)

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