Appropriate Zoom eyepieces (2 Viewers)

[Humboldt Jim]

What a good cache of information here. This and other sources indicate that zoom eyepieces generally are not at their best at either extreme. So why don't manufacturers work within the range that works best and give us other advantages like eye relief and a wider field of view. 20-45x or 15-40 for a small scope and 25-60 or 20-50 for a large scope would still be great with other advantages like brightness, wider FOV, long eye relief, and less CA were provided. More is not always better.

Wish there was a "general" area for scopes and tripods. some things are universal. :h?

 

[Edward woodwood]

Hi Jim

high magnification is alluring and it sells

atb
Tim

 

[iporali]

Jim and Tim,
You are both so right!

Ilkka

 

[AlanFrench]

I am quite happy with the 20-60x range on my scope, and don't find any reason to settle for a less versatile eyepiece. My only complaint is the narrower apparent field at the low end.

Clear skies, Alan

 

[Bill Atwood]

What Alan said. High magnification may not be perfect but is very useful. And todays zooms are much better at the high end than they used to be.

 

[Keith Reeder]

What Alan and Bill said...

The lower range of the Zeiss zoom is wonderful - wide, bright, and with fantastic resolution - and being able to instantly select the ideal level of magnification for the task at hand is a Godsend.

Bear in mind that if a zoom isn't at its best at (say) 45x on a given scope (usually a light-gathering issue), it's entirely likely that a fixed EP of the same magnification will be just as "flawed"... but that's just physics, not an inherent failing in zoom lenses per se.

It seems that Zeiss have more or less followed Jim's argument anyway - the zoom on the 65mm Zeiss gives 15-45x - and that spread seems to be optimal for the overall package.

And - as Zeiss enthusiasts are always banging on about - the FOV at lower magnification on the Zeiss zoom is as wide as a very wide thing.

 

[henry link]

I have adapted the Swarovski, Zeiss and Nikon zooms for use on astronomical scopes, which has made it possibleto evaluate their performance as eyepieces alone, seperate from the rest of their scope optics. IMO they are all capable of delivering higher quality images than their scopes will allow, and are really fully competitive wth the best single magnification eyepieces in terms of sharpness and light transmission. The Swaro and Zeiss are particularly good at the highest magnification where they have an excellent combination of wide field and reasonably long eye relief.

 

[Bill Atwood]

Wow Henry, I wouldn't have expected that.

On a side note, for those folks who have the previous model Swaro scope, but don't want to spend the big $ for the new model, try the new zoom on your older scope. As far as brightness and sharpness are concerned, its like getting a brand new scope. I put my zoom on a friends old beat up Swaro, now he's thinking of just buying the zoom instead a whole new kit.

I did not play with this setup enough to evaluate other attributes, but from 5 minutes of use there was a definite improvement over the old zoom.

 

[AlanFrench]

To me, it seems the limiting factor on magnification is image brightness. On a sunny day, 60x on a 65mm aperture scope is fine, but on a dreary day it gets a bit dark. For higher powers, added aperture is a blessing. I do a fair amount of scope birding from a fixed location, and use a 90mm aperture scope, at powers of 64x and 94x.

Clear skies, Alan

 

[kabsetz]

As usual, Henry is correct. Present zooms, at least those from Leica, Nikon, Swarovski and Zeiss are so good that any problems with resolution at high magnification or brightness at any magnification are due to the quality of the individual scope, and not to the quality of the eyepiece. You would not gain anything else than field of view and eye-relief from going for a fixed eyepiece of a corresponding magnification.

As far as using the new Swaro zoom on the older scope, it provides slightly truer colours and slightly better light throughput than the old version. More significant is its wider field of view, especially at high magnifications. I once tested both the old and the new zoom in the AT 80 HD, and got the following fields of view at various magnification settings (old/new): 20x: 32/34.3; 30x: 24/28.3; 40x: 19.9/23.8; 50x: 17.8/21.4 and 60x: 15.8/19.1. Figures mean field cross section in centimeters at 10 meters, which equals meters at one kilometer. Additionally, the new zoom gives a slightly higher magnification on the AT than does the older zoom. This difference has not been taken into account in the above figures, which were based on the markings on the eyepieces. I lack the means to accurately measure the true magnification of either, but if we assume the old AT/zoom combo to be true 20x, the AT/new zoom combo gives 21.3x and, at 60x they give 63.8x. Not a huge difference, but all of the above considered, if I owned the AT 80 and it were a sharp specimen, I would definitely buy the new zoom.

Kimmo

 

[Hermann]

As usual, Henry is correct. Present zooms, at least those from Leica, Nikon, Swarovski and Zeiss are so good that any problems with resolution at high magnification or brightness at any magnification are due to the quality of the individual scope, and not to the quality of the eyepiece. You would not gain anything else than field of view and eye-relief from going for a fixed eyepiece of a corresponding magnification.

One interesting point is that with the Nikon scopes the old version of the wideangles (without multicoating) have in fact visibly less contrast than the Nikon zoom. The difference between for instance the Nikon 30WA (old version), an excellent eyepiece, and the zoom at 30x is really quite pronounced. Multicoating really does make a difference with these complex eyepieces.

A question for Kimmo: Did you ever make a comparison between the "old" Nikon zoom (20x-45x with the 60mm scopes) and the new one (20x-60x with the 60mm scopes)? I recently had a chance to look through one of those, the new version with multicoating, and it seemed pretty good even by today's standards. With that eyepiece multicoating also seem to make quite a difference, because the old version without multicoating was good, but not *that* good.

Hermann

 

[kabsetz]

I have never done a head-to-head comparison between the non-MC and MC-versions of the 20-45x zoom. When the 20-60/25-75x zoom came out, I compared it to the old 20-45 and found it much better than the old, especially with regard to contrast.

I made the same conclusion as you did about the new zoom versus the older wide-angles (which, I'm pretty sure, have some multicoated surfaces although the coatings in the "MC" range are clearly much superior). The primary reason why I bought the 25-75x zoom (20-60x) when it came out was that it had visibly superior contrast and brightness and even slightly better resolution than my set of 38x, 50x and 75x Wides with the older coatings.

My guess would be that the MC-version of the 20-45x would be just as sharp and high-contrast than the other MC's. However, why settle for the smaller range of magnifications if you do not get wider fields, better eye-relief or optical improvements to the image? Of course, the 20-45 might now be marginally brighter if it has the same coatings but less glass in it. However, as and if the 20-60 has a roughly 95% transmission, a noticeable difference in brightness or contrast is highly unlikely.

Kimmo

 

[Humboldt Jim]

Objective evaluation

I have adapted the Swarovski, Zeiss and Nikon zooms for use on astronomical scopes, which has made it possibleto evaluate their performance as eyepieces alone, seperate from the rest of their scope optics. IMO they are all capable of delivering higher quality images than their scopes will allow, and are really fully competitive wth the best single magnification eyepieces in terms of sharpness and light transmission. The Swaro and Zeiss are particularly good at the highest magnification where they have an excellent combination of wide field and reasonably long eye relief.

Thanks Henri for that objective (pun intended) eyepiee evaluation.

Interesting how the FOV narrows at low magnification, or is that mearly the apparent FOV?

 

[iporali]

My guess would be that the MC-version of the 20-45x would be just as sharp and high-contrast than the other MC's. However, why settle for the smaller range of magnifications if you do not get wider fields, better eye-relief or optical improvements to the image?

A fair point, but IF I could get a zoom with a wide field (at 20x) and a 20mm eye relief by sacrificing something - that would be the powers 45-60x (I could keep a 2-3x booster in my pocket). If that is not possible I'll continue with my otherwise excellent Swaro 20-60x .

Ilkka

 

[iporali]

Interesting how the FOV narrows at low magnification, or is that mearly the apparent FOV?

Yes - that is the apparent FOV, which decreases at low powers. The true FOV goes from about 2° (at 20x) to 1° (at 60x).

Ilkka

 

[Hermann]

A fair point, but IF I could get a zoom with a wide field (at 20x) and a 20mm eye relief by sacrificing something - that would be the powers 45-60x (I could keep a 2-3x booster in my pocket). If that is not possible I'll continue with my otherwise excellent Swaro 20-60x

A couple of important points here, I think. I'd add to the points you mention the size and weight of a zoom and how easy it is to use in the field at different magnifications. Take for instance the two Nikon zooms mentioned: I personally prefer the size and shape of older 20-45x zoom over the 20-60x. It's smaller, lighter and I also find it slightly easier to use, despite (or maybe because of) it's old-fashioned rubber eyecup.

On boosters: I've been fooling around with the Zeiss 3x12 Mono for some time now, and the more I get used to it the more I like the idea of carrying a small booster for those rare occasions when high magnifications matter *and* the light and atmospheric conditions are good. I don't think I'll ever use a booster all that much with my bins because I nearly always carry a scope anyway, but I can well see myself using one with my scope.

Hermann

 

[kabsetz]

I have used the same 3x12 Zeiss booster with my scope occasionally, especially for nighttime views of the planets. With the 20x45, it probably makes a lot of sense, especially once you have a solid enough attachment figured so you don't need to hold it. With the 20-60 Nikon zoom, it can be simply held in place by the rubber eyecup's edge. To assist in this, I have a piece of rubber bike innertube (racing tyre) streched around the booster's objective. This provides better friction and fit.

Imagewise, though, you lose some brightness and contrast due to the booster not being fully multicoated. We can hope that Zeiss would come out with a T* version of the 3x12 to solve this issue. With the larger mag zoom I have, there are very few daylight situations where the extra magnification helps, as the 75x (on the bigger Nikon scope) I get with the zoom is so close to the performance limit of the scope given what my eye can resolve from the image. If I had the smaller zoom, there would be many more instances where the booster would be beneficial. If I used a wide-angle, the booster would be even more handy, since there you could have almost instant swithcability between say, 30x and 90x.

Kimmo

 

[Hermann]

I have used the same 3x12 Zeiss booster with my scope occasionally, especially for nighttime views of the planets. With the 20x45, it probably makes a lot of sense, especially once you have a solid enough attachment figured so you don't need to hold it. <snip>
If I had the smaller zoom, there would be many more instances where the booster would be beneficial. If I used a wide-angle, the booster would be even more handy, since there you could have almost instant swithcability between say, 30x and 90x.

I usually use the booster when I switch to one of my wideangle eyepieces, for instance for raptor watching or at migrations hotspots where the large field of view of a wideangle eyepiece is really important to me. Even with a cable-tie sighting device the Nikon zoom doesn't really work all that well in such situations, and then the booster provides quick access to high magnifications when I need them. I also made up my own set of attachments for use with my different eyepieces so I don't need to hold the booster.

BTW, I'll never understand why the Zeiss doesn't advertise this use of it's excellent 3x12 Mono. I think it's a great accessory for anyone who often uses fixed low magnification eyepieces.

Hermann

 

[kabsetz]

I agree with all you say, Hermann, except for the zoom/cable tie sight compatibility opinion. I suspect yours might be slightly less than optimally aligned, since with my setup I can locate distant flying raptors quickly even at 75x (0.7 degrees field).

It would be very good, though, to have the 3x12 with better coatings, since the loss of brightness and contrast which are of no consequence at 3x become rather more detrimental at 80-160 (-225)x. In most other respects, I would rate the 3x12 Classic easily good enough for the purpose, since at these magnifications resolution, for instance, is not determined by the booster to any significant degree, but almost solely by the main telescope optics (the objective/focusing achromat/prism system chain). The other slight shortcoming, but one which is more pronounced in other boosters I have checked, is that the roof prism's roof angle creates a diagonal line accross the middle of the view, and right on this line the resolution is slightly compromised. The line can also be seen at high magnifications against a gray surface such as a uniformly cloudy sky. Once you know this, you can position a critical object slightly off-center to avoid the prism effect, but perhaps the prism could be manufactured to somewhat higher tolerances.

Kimmo