Zoom eyepieces, What's your take

[great_bear]

my biggest gripes are the lack of fov at 24mm, and the fact it isnt parfocal, no matter what it says on the box!

From CloudyNights:

If a zoom eyepiece is designed to be parfocal through its focal range it can only behave parfocally if the observer is neither short-sighted nor far-sighted. If he is one or the other and does not wear glasses, his eye will need diverging or converging light beams from out of the eyepiece. This will be accomplished by moving the eyepiece out of its nominal position. If he for example is short-sighted by 2 diopter (his eye lens is too powerful by 2 diopter) and the focal length of the zoom is set to 22mm (the equivalent of 45.5 diopters) the resulting focal length of the eyepiece will be 21mm (the equivalent of 47.5 diopters). So in order to focus the eyepiece he will have to move it closer to the objective by 1mm. If the zoom is now set to 7.3mm (the equivalent of 137 diopters) the resulting focal length of the eyepiece will be 7.2mm (the equivalent of 139 diopters) and in order to focus the eyepiece he will have to move it closer to the objective by only 0.1mm from its nominal position. His impression will be that the eyepiece is not parfocal through its range by 0.9mm although the real reason is his eyesight.

- of course such comments also apply to any range of fixed eyepieces too that are claimed to be parfocal.

[step_hen]

Thanks for that great bear- very informative. I am shortsighted, but i do however wear glasses while observing, and the zoom is still not, or at least doesnt 'appear' to be parfocal

[great_bear]

Thanks for that great bear- very informative. I am shortsighted, but i do however wear glasses while observing, and the zoom is still not, or at least doesnt 'appear' to be parfocal

It certainly explains why I've always thought "how can they claim range (x) of eyepieces are parfocal, when I can see they're not!" - still, at least with fixed lenses you can add those little parfocalling rings and set them to match your eyesight...

With regard to the zoom not appearing parfocal, it may well be that even eyesight being *slightly* off causes a problem - but that's a bit beyond my level of expertise, so I don't know for certain.

[cootuk]

There's a Speers-Waler 5-8mm zoom on Ebay atm

SPEERS WALER ZOOM 5-8mm EYEPIECE on eBay (end time 11-May-10 19:39:15 BST)

(auction nothing to do with me)

[johninderby]

I had the 3 to 6 Nagler zoom and found it was just as good as a regular Nagler except for the 50 degree FOV. However it's now been replaced by a set of the 2.5mm, 3.5mm and 5mm Naglers. The 82 degree FOV is useful when used with an undriven mount.

I had the Hyperion 8 to 24 zoom which was a fine eyepiece for a zoom, but a bit on the big and bulky side. The Hyperion has now been replaced by a Pentax XF 6.5 to 19 zoom which was bought primarily for Ha solar use. The range is more useful, and for Ha observing it's just as sharp and contrasty as an ortho. Even for regular nighttime observing it's a very sharp eyepiece. It's also a small and lightweight eyepiece, and not really that much more expensive than a Hyperion zoom.

John

[brantuk]

Yup the Baader zoom's a very nice piece for what it is - you don't expect zooms to be like individual e/p's but they are very useful on occassion. I use mine quite frequently, especially when demo'ing for the public and don't want them to get their grubby little hands on my pristine TV's lol

[Merlin66]

I've tried many before settling on the Pentax!! Double the size of the TV zoom.

TV 21mm compared with the TV zoom and the Pentax

[simon84]

I have also just got myself the Baader Hyperion Zoom, and have let my set if 4 Vixen Lanthanums go to get it.

One of the main reasons to get it was to make use of the M54 thread it has and be able to connect my dslr to it. The other reasons being that my 25mm Vixen had the same FOV as the Baader at 24mm but was better than the Vixens at higher powers going to 68 degrees at 8mm. My 9mm Vixen only had about 45 to 50 degrees if I remember rightly.

Not sure what the view will be like compared to the Vixens but to only have 1 EP to worry about its a winner already in my book.

If I were to get something else I would probably go for the TV 3 - 6mm to cover high power and then get a single 32mm EP for widefield.

Three EP's to cover everything cant be bad.

[Brinders]

I have a Seben 8-24mm zoom, which I suspect is probably the Skywatcher rebranded. Anyway, I'm happy with it although the FOV does narrow as you get to the 8mm highpower end and I do need to refocus slightly.

Brinders

[John]

I had the 3 to 6 Nagler zoom and found it was just as good as a regular Nagler except for the 50 degree FOV. However it's now been replaced by a set of the 2.5mm, 3.5mm and 5mm Naglers. The 82 degree FOV is useful when used with an undriven mount.....

Thats the "journey" I've been on as well - with the same result

The Nagler 3-6mm is superbly flexible though - if it had a 65 degree FoV I'd have probably stayed with it.

[johninderby]

Thats the "journey" I've been on as well - with the same result

The Nagler 3-6mm is superbly flexible though - if it had a 65 degree FoV I'd have probably stayed with it.

Of course that Ethos SX 3.7mm is coming out later this year. Could my 3.5mm and 5mm Naglers be doomed?

John

[A McEwan]

Interesting discussion. I'm tempted by a zoom for h-alpha viewing, so much more convenient. It seems there are two models of Skywatcher Hyperflex out there - the 8E (7.5mm - 22.5mm, 66' - 42', 8 elements in 5 groups) and the 7E (7.2mm - 21.5mm, 60' - 40', 7 elements in 4 groups). The 8E is listed at £199 and the 7E at £119.

So, apart from the slight extra field of view, does anyone know if there are any differences in performance that will validate the £80 price difference?

I could get a Pentax XF for the same price as the 8E, but if the 7E is not a slouch, it would probably suffice perfectly... Opinions?

Ant

[johninderby]

The Hyperflex 7.5 to 22.5 zoom is the same as the William Optics Zoom II. The WO's cheaper as well.

The opinion seems to be the WO Zoom II is very good, but the Hyperion is a bit better. However I found that the Pentax XF is a bit better than the Hyperion so the Pentax would be my first choice.

So

[A McEwan]

Thanks John for valuable input. Making a deal for the XF now...

[johninderby]

Thanks John for valuable input. Making a deal for the XF now...

I'm really pleased with the XF Zoom. It may not have quite as wide a FOV as the Hyperion but it's so much smaller and lighter. I found that for solar Ha observing it was a sharp as a Baader GO. And it's not exactly embarrassed by the Badder GO in regular nighttime observing either.

I think you'll really like it.

John

[Kef9]

There's a Speers-Waler 5-8mm zoom on Ebay atm

SPEERS WALER ZOOM 5-8mm EYEPIECE on eBay (end time 11-May-10 19:39:15 BST)

(auction nothing to do with me)

I just bought this so it will be interesting to see what it is like. It has good reviews.

[AndyH]

I've got the very same eyepiece.

Simply superb

Andy.

[Moonshane]

not in the same class but just to make up the numbers on my order to save postage I bought one of the £7 weird looking zooms off the Astroboot at Scopes N Skies.

I am sure it will be rubbish but it's got nice green coatings, a smooth action and not much internal reflection. I might try and test run it tonight in my dob. it seems to have the usual narrow field at lower and wider field at higher mags so might be OK but might also end up in a skip too.

I'll update when I get a chance to use it.

[Kef9]

I've got the very same eyepiece.

Simply superb

Andy.

Well that sounds good. Another person who has told me that its great. Have you got anything to say about it? I was attracted to the high power, wide FOV, good eye relief with the option to change mag. Unbeatable combo it seems. Do you have the series 1 or the series 2? Which is supposed to be better. I got the series 1.

Im getting quite a nice collection already! Ive only been doing this a month and I've got a 13mm ethos aswell. Just need a low power eyepice now!

[AndyH]

If it's that one that was on ebay, then it's the same as mine, ie series 1.

Which series is the better? Probably not much difference. I like the finish on the series 1's better.

I've used it on Mars this season and was pleasantly surprised at how sharp it was. I've been after one of these series 1's for many years after reading the excellent reviews and have to concur with them. Great, great eyepiece.

Andy.

[Moonshane]

if you are on a low budget check this out http://stargazerslounge.com/heads-up/103989-cheap-zoom.html#post1433594

[Kef9]

If it's that one that was on ebay, then it's the same as mine, ie series 1.

Which series is the better? Probably not much difference. I like the finish on the series 1's better.

I've used it on Mars this season and was pleasantly surprised at how sharp it was. I've been after one of these series 1's for many years after reading the excellent reviews and have to concur with them. Great, great eyepiece.

Andy.

So whats the difference betwen the series 1 and series 2?

Can't wait to get it now. Im hoping for some clear skies!

[AndyH]

There were really 3 series of the whole speers waler range. Series 1(black with red inscribed lettering), series 1.5(same glass as S1, but with a silver finish and screen printed lettering)and series 2(same finish as S2, but I think the eyelenses are slightly larger).

Series 1 and 1.5(don't think the 14, 18 and 24mm was available in S1.5) had a 5-8mm zoom and fixed lengths of 7.5, 10, 14, 18 and 24mm.

Series 2 has zooms in 5-8 and 8.5-12mm. Fixed of 4.9, 7.2, 9.4, 13.4 and 17mm.

Andy:)

ps: To confuse matters further, there was a series 1 range that had 72 degrees fov(with better eye relief) instead of the usual 82 degrees.

[Mogster]

I've had about 4 over the years, I'm seduced by the concept but in the end they just don't cut it when compared to standard fov ep's. zooms tend to have bad internal reflections from the mechanisms, dodgy fov's at higher fl's and not be too sharp at the lower end.

The last one I bought is a badged Vixen LV zoom which cost about £140. Its quite fun to use on the moon as you can zoom in an out on details, I really bought it to use for solar viewing but the internal/external reflections drive me nuts. If you can get one cheap (astroboot...) then give one a go, just don't expect too much.

[Merlin66]

Pentax 8-24mm SMC 1.25” long eye relief astronomical zoom; 21-63x or 26-78x spotting scope zoom 70509

This is the one that I think works!

"Tried the rest...went for the best"

Ken