Do you know this zoom??

[Raph-in-the-sky]

Hello,

I was wondering if anyone knew this zoom and if it was any good? It's a 7,14,21mm 

Cheers,

 

 

[Raph-in-the-sky]

[johninderby]

All I can see are blank images.

[xtreemchaos]

na ive never seen that one before 😀. try uploading as a png.

[Rob Sellent]

[johninderby]

[MarsG76]

Can't see the pic but a zoom eyepiece will always be of lesser quality than fixed focal length optics.....

 

[John]

10 minutes ago, MarsG76 said:

Can't see the pic but a zoom eyepiece will always be of lesser quality than fixed focal length optics.....

 

Depends on the zoom.

[MarsG76]

25 minutes ago, John said:

Depends on the zoom.

Of course.. but ultimately the best zoom will not be as good as the best fixed fl ep... just like with camera lenses.. a prime lens will be better than a zoom lens of the same class.

 

[John]

7 minutes ago, MarsG76 said:

Of course.. but ultimately the best zoom will not be as good as the best fixed fl ep... just like with camera lenses.. a prime lens will be better than a zoom lens of the same class.

 

Which zooms have you compared to which fixed fl eyepieces ?

 

[MarsG76]

11 minutes ago, John said:

Which zooms have you compared to which fixed fl eyepieces ?

 

Comparing a Celestron 8-24 mm zoom and Televue 11mm, LV 7mm, Televue Ethos 17mm eps. on Jupiter and Saturn.

The fixed EPs were noticeably crisper and showing more detail.

 

 

Edited December 11, 2019 by MarsG76

[John]

Well I'm not surprised at that

 

 

[Stu]

The high end zooms can be as good or better on axis, but it would be interesting to see which one the OP is referring to. The very entry level Sebens are pretty rubbish, but above that they are generally not bad. I have the Opticstar 7.2 to 21.5mm and whilst not as sharp as an ortho, gives a creditable performance and is very convenient.

[bingevader]

One of the Seben zoom EPs is supposed to be good.

The one not made of plastic.

I'm tempted to have a punt at one of these for £14!

[Stu]

19 minutes ago, bingevader said:

One of the Seben zoom EPs is supposed to be good.

The one not made of plastic.

I'm tempted to have a punt at one of these for £14!

The cheap 7.5 to 22.5mm Seben is bad, lots of internal reflection. I think it's the more expensive 8 to 24mm which is better, I've had both at one point.

The description for the £14 one implies metal and glass construction but I fear it would be disappointing.

[bingevader]

14 minutes ago, Stu said:

I fear it would be disappointing.

Me too!

We're looking for one for school.

Your Opticstar looks like it might fit the bill, very similar to the OVL and TS and wouldn't break the school budget!

Apologies for the thread hijack!

[Stu]

28 minutes ago, bingevader said:

Me too!

We're looking for one for school.

Your Opticstar looks like it might fit the bill, very similar to the OVL and TS and wouldn't break the school budget!

Apologies for the thread hijack!

Yes, I'm pretty sure all these 7.2 to 21.5mm zooms are clones so pick the best deal. The Lunt is very expensive but I don't think it is any better although it is possible it has better coatings. I've been pleased with the OpticStar.

Hopefully this is all relevant for the OP 👍👍

[Raph-in-the-sky]

Let's try this again... Can you guys see it now?

[Raph-in-the-sky]

[Rob Sellent]

This is just a guess, Raph. No doubt I'm going to be wrong but bear with me. 

• unbranded 7-21mm
• probably has four elements
• 7-21mm zooms tend to be (not always) inferior in reviews
• my guess its apparent field of view will range from around 43º degrees at high power to 30º degrees at low power
• edge perfomance won't be perfect
• might introduce chromatic aberration
• won't be as sharp or as contrasty as a fixed focal length eyepiece
• probably retails new at less than €50
• mechanically it should be okay, useful in your BVs, at star parties or when bound by laziness

[Raph-in-the-sky]

16 minutes ago, Rob Sellent said:

This is just a guess, Raph. No doubt I'm going to be wrong but bear with me. 

• unbranded 7-21mm
• probably has four elements
• 7-21mm zooms tend to be (not always) inferior in reviews
• my guess its apparent field of view will range from around 43º degrees at high power to 30º degrees at low power
• edge perfomance won't be perfect
• might introduce chromatic aberration
• won't be as sharp or as contrasty as a fixed focal length eyepiece
• probably retails new at less than €50
• mechanically it should be okay, useful in your BVs, at star parties or when bound by laziness

The idea was buying 2 of them second hand (only £20/p) to use with a cheap BV... I think it will fit the bill.

This will come much cheaper then 2 or 3 pairs of plossl which I might get later on if I like the BV experience. Worse case I'll resell everything at the same price.

[Rob Sellent]

2 hours ago, Raph-in-the-sky said:

The idea was buying 2 of them second hand (only £20/p) to use with a cheap BV

Your reasoning is sound. I bought a second Mark IV zoom here on SGL for the same reasons you're contemplating the zoom pair.

As you are aware, binoviewing eyepieces do not have to be premium. Edge correction also becomes more tolerable when using a barlow or barlow lens element. My only concern with these particular zooms would be whether on-axis performance was good. If that were not the case, there's little room for improvement.

What will make these good binoviewing eyepieces is how you answer some of these questions:

• is there easy eye placement?
• can they be merged easily to fit both your eyes? (Does your nose fit between them?)
• are they light in weight?
• do they have safety grooves or undercuts? (making them harder to use in BVs)
• do they produce sharp images across the field of view?
• do they have reasonable - 50º or  so - apparent field of view?

Another interesting option (but no cheaper) is to use two longer fixed focal length eyepieces - 20-24mm, for example - and 'zoom' through them with the use of short Barlows, glass path correctors (GPS) or extension tubes. A x1.6, x2, & x2.6 GPS would give a 20mm eyepiece focal lengths of 12.5mm, 10mm and 7.5mm, suffice for most observations I would think.