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Old Tuesday 21st March 2017, 23:18   #1
henry link
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Zeiss Gavia 85 Review

I borrowed a Zeiss Gavia 85 for a couple of days last week with the idea of writing a review. Two days turned out to be too little time to get around to checking out everything, so here are the results of the tests I had time to do.

The Gavia is one of several recently introduced iterations of a Kamakura design that has been around for at least six years. I have one of the earlier versions (the discontinued Brunton ICON), so I was particularly interested to see how the Gavia might differ from the ICON. My original review of the ICON can be found here:

http://www.birdforum.net/showthread.php?t=297258

One positive change in the Gavia is a new zoom eyepiece with improved performance. I don’t know whether this eyepiece is a unique Zeiss design or is also available on the current Kamakura siblings of the Gavia, like the Vortex Razor or Maven spotting scopes. Looking at reflections returning from the lens surfaces of the old and new eyepieces shows very little in common. No visible mechanical parts look interchangeable. Bayonet mounts are not compatible.

The basic specs of the new and old eyepieces are not very different. Eye relief and AFOV are about the same for both over the zoom range, but it was quickly obvious that the new one has lower field curvature and off-axis astigmatism and a worthwhile reduction in lateral color. Distortion has changed from mustache (which I initially mistook for barrel) in the old eyepiece to fairly strong barrel at 30x in the new one that gradually weakens to approximately zero rectilinear distortion at 60x. The barrel distortion is necessarily accompanied by very strong angular magnification distortion at 30x. AMD is weaker but still strong at 60x. The distortion pattern over the zoom range resembles the distortion of the Kowa 25-60x zoom.

Moving on to the scope body, I found only one significant difference in the basic optics between the ICON and the Gavia and that, I’m sorry to say, was inferior color correction in the Gavia.

The star test photos below show a focused artificial star in the center, flanked by defocused diffraction patterns, inside-focus on the left and outside-focus on the right. The Gavia is the top row. At best focus the Gavia isn’t nearly as color free as the ICON. The outside-focus diffraction pattern shows a very vivid red fringe surrounding it in contrast to a milder green fringe surrounding the inside-focus pattern. At high magnification the red fringe on a high contrast focused object is quite obvious. The red fringe becomes wider and more vivid on objects that are slightly closer to the viewer than a perfectly focused object. The misty green fringe is less obvious, but still visible on objects that are slightly farther away than best focus.

I think the most likely explanation for the Gavia’s poorer color correction is that the ICON probably used a Fluorite equivalent ED glass (like Ohara FPL53) with an Abbe value around 95. That gave it truly apochromatic correction and establishes that this Kamakura objective design can be essentially color free with the right glass. For the Gavia Zeiss presumably specified one of the ED glass types with an Abbe value around 80-85 (like Schott FK51). Those have a lower potential for color correction, but they may be seen as good enough for a scope where very high magnification isn’t likely to be used. It would be very interesting to see the level of color correction for the Vortex and Maven siblings of the Gavia.

One other unpleasant surprise was an undersized internal stop in the Gavia that reduces the scope’s effective aperture to about 80mm. I almost didn’t bother checking this, because I just assumed Zeiss would get it right.

I used two methods to determine the effective aperture and repeated the measurements several times. One test is the “flashlight” method, proposed by Glenn LeDrew at “Cloudy Nights”. It involves shining a collimated flashlight beam through the eyepiece end of the scope and measuring the diameter of the light cylinder that emerges from the objective lens. The other method is to examine a transparent ruler stretched across the front of the objective lens by looking through the eyepiece with a magnifying loupe. Both methods were in good agreement and showed effective apertures of 80mm for both the ICON and the Gavia.

I’ve used both methods many times and have always found high end optics to have clear apertures as specified or very close. Inexpensive binoculars, on the other hand, are notorious for undersized prisms or other internal stops that reduce the axial clear aperture. Also scopes that use moving prisms for focusing typically loose effective aperture as the prism moves out of its optimum position at close focus. The Gavia has quite effective internal baffling, usually a good thing, but I think it’s likely that at least one of those baffles is a bit too small.

Just like the ICON, the Gavia suffers from serious spherical aberration at all distances, but SA strongly increases in both scopes at close focus. The image quality of the Gavia at the closest focus is very poor, though a bit better than the truly terrible ICON. That might be attributable to the Gavia’s slightly higher focal ratio. Both scopes are effectively 80mm, but the ICON has a focal length of around 450mm (f/5.6) and the Gavia around 495mm (f/6.2).

Using my indoor set-up I measured the Gavia’s resolution on a USAF 1951 glass slide as 2.17” at 13’ and 1.9” at 30’, poor results for an 80mm scope. I couldn’t conduct a reliable resolution test using my outdoor set-up because the air was too turbulent during the time I had the scope. My estimate is that this particular Gavia’s resolution at long distance is about the same or slightly better than my ICON, which would make it about 1.6”- 1.65”. That might rise to the level of mediocre resolution by spotting scope standards, but it's pretty far from 1.36”, which is what a diffraction limited scope with a clear aperture of 85mm should do.

One other similarity between the Gavia and ICON is Kamakura’s excellent variable speed focuser. I didn’t have time to determine if the focusing speeds are identical, but they seemed so in normal use. As I said in the original ICON review this feature is something that would benefit every scope.

In summary I have to say that I found the Gavia to be a somewhat disappointing mixture of a very nice eyepiece mounted on a not so nice scope body. A street price of $2000 places it $400 above two of its closest competitors, the 85mm Vortex Razor (which could be exactly the same scope) and the 82mm Nikon Monarch HG (which looks like it could be the old 82mm Fieldscope resurrected with a new wide angle zoom). Then there is the Kowa 883, a much better scope for about $600 more. I think if I were shopping for a $2000 telescope I would be inclined to just skip the current $1600-$2000 offerings and save up for the Kowa, which is looking like the biggest bargain in scopes right now.

Henry Link
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Old Tuesday 21st March 2017, 23:37   #2
etudiant
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Thank you, Henri, for another superb product evaluation.
It is factual and informative, reflecting deep experience and sound judgment.
Would that more reviews were up to your standard.
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Old Wednesday 22nd March 2017, 11:40   #3
jring
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Hi,

thanks a lot Henry, the review is good, unlike the scope. An FK51 doublet at f5.8 (or rather f6.2) seems not such a good idea.

Joachim
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Old Wednesday 22nd March 2017, 22:49   #4
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Thanks, etudiant and Joachim.

Joachim,

I'm only offering a downgrade of the ED glass as a plausible explanation for the color in Gavia since Kamakura demonstrated with the ICON that this objective design can do better, but it's purely conjecture on my part. I don't know what glass is in any of these Kamakura scopes. It's possible the ICON might have been the only one with really good color correction.

FWIW, the Gavia and ICON objectives are fixed triplets followed by doublet focusing lenses.
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Old Thursday 23rd March 2017, 10:16   #5
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Quote:
Originally Posted by henry link View Post
A street price of $2000 places it $400 above two of its closest competitors, the 85mm Vortex Razor (which could be exactly the same scope) and the 82mm Nikon Monarch HG (which looks like it could be the old 82mm Fieldscope resurrected with a new wide angle zoom).
That remark about the Nikon Monarch HG caught my eye. What I'd quite like to know whether the Monarch also has an oversized Schmidt prims, like the old fieldscopes. That prism was one of the reasons why the Fieldscopes were so good, simply because far fewer things can go wrong with it than with any other roof prism design.

Hermann
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Old Thursday 23rd March 2017, 10:19   #6
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Moving on to the scope body, I found only one significant difference in the basic optics between the ICON and the Gavia and that, Im sorry to say, was inferior color correction in the Gavia.
I've heard rumours there will be a new range of Zeiss scopes some time. Maybe Zeiss intentionally limited the Gavia's performance to make sure there's a clear gap to a new top of the range scope.

Hermann
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Old Thursday 23rd March 2017, 11:19   #7
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Thanks Henry for the excellent review. On another note I am keeping the slightly used Nikon 82ED Fieldscope! I have not done a test of it , but what I see makes me very happy.
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Old Thursday 23rd March 2017, 11:23   #8
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Henry,

Thanks for the detailed report and the photos. The one positive I see in the Gavia star-test photos is the absence of obvious prism-related defects. I have also seen those in at least one Gavia specimen.

Hermann,

I have seen one Monarch HG 82. It certainly does have the oversized offset Schmidt prism. The optics of that one specimen were very good, with CA levels reminding me more of the Fieldscope ED 82 A than scopes like the Gavia. Without a side-by-side, I cannot say whether it is on the same level as the Fieldscope or not, but the impression was similar. That specimen had a bit of miscollimation, meaning slightly eccentric diffraction rings, but the image held up just fine to the 60x maximum, and the eyepiece was easy to view with and sharp to the edge.

The scope is very heavy for its size, though.

Kimmo
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Old Thursday 23rd March 2017, 13:02   #9
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Interesting review, thanks.
The Gavia looks rather expensive in the US and Kowa 883 seems to be quite cheap.

The price difference in Europe is much bigger. A Gavia (inc. 30-60x EP) can be found (online) here for 1730 € and a 883 (inc. 25-60x) for about 2700 € so the diff is about 1000 € (aprox. $1100).

But still the Gavia seems a bit overpriced to me. For example a Meopta S2 HD + 20-70x can be found here for around 1975 €.
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Old Thursday 23rd March 2017, 13:38   #10
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I've heard rumours there will be a new range of Zeiss scopes some time. Maybe Zeiss intentionally limited the Gavia's performance to make sure there's a clear gap to a new top of the range scope.

Hermann
I heard two rumors about new Diascopes. One was that they won't be available until sometime in 2018 and the other very juicy rumor was that a prototype of a 110mm scope with Diffractive Optics had been developed, but then rejected. Here's some stuff about Canon's DO camera lenses:

http://cpn.canon-europe.com/content/...cal_element.do

I don't know how good those lenses are, but if DO objective lenses are ever successfully brought to scopes it could give us a new generation of small light scopes with very large apertures.

Henry
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Old Thursday 23rd March 2017, 13:51   #11
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The one positive I see in the Gavia star-test photos is the absence of obvious prism-related defects. I have also seen those in at least one Gavia specimen.
Hi Kimmo,

I didn't detect any serious problems that seemed likely to be sample defects, so I think the specimen I tested is probably about as good as a Gavia gets.

Henry
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Old Thursday 23rd March 2017, 14:16   #12
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Interesting review, thanks.
The Gavia looks rather expensive in the US and Kowa 883 seems to be quite cheap.

The price difference in Europe is much bigger. A Gavia (inc. 30-60x EP) can be found (online) here for 1730 and a 883 (inc. 25-60x) for about 2700 so the diff is about 1000 (aprox. $1100).

But still the Gavia seems a bit overpriced to me. For example a Meopta S2 HD + 20-70x can be found here for around 1975 .
Just checked the B&H Photo prices, lower prices might be available.

Zeiss Gavia 30-60X - $2000

Meopta S2 HD 20-70x or 30-60x - $2400

Kowa TSN-883 25-60x - $2560
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Old Thursday 23rd March 2017, 19:58   #13
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Originally Posted by henry link View Post
Just checked the B&H Photo prices, lower prices might be available.

Zeiss Gavia 30-60X - $2000

Meopta S2 HD 20-70x or 30-60x - $2400

Kowa TSN-883 25-60x - $2560
Netto (ex VAT) USA prices would be in Euro's:
Zeiss 1.499,00;
Meopta 1.749,00;
Kowa 2.199,00.

BTW Henry, excellent review

Jan
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Old Monday 21st August 2017, 21:39   #14
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man what a through review! i have played with this scope and really like it, much better than a razor. but cant argue with saving for a kowa.
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Old Thursday 31st August 2017, 17:55   #15
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cost of Kowa "scope"

Very nice review and informative about scopes I am considering, the Gavia and Razor.

One question though...you mention that the Kowa is only about $600 more than a $2000 scope (such as the Gavia). I'm seeing it for around $2900 as the best price for scope and eyepiece set (comparing w/ Zeiss and Vortex setup prices).

If you were going to stay in the $2000 and under range, would you purchase the Razor over the Gavia, a savings of $400 and a better warranty?

Edit- Sorry, didn't read responses until after I posted this.

Last edited by Mick50 : Thursday 31st August 2017 at 18:29.
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Old Thursday 31st August 2017, 18:24   #16
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Edit- sorry...read the responses after my initial post.
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Old Thursday 31st August 2017, 23:03   #17
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One question though...you mention that the Kowa is only about $600 more than a $2000 scope (such as the Gavia). I'm seeing it for around $2900 as the best price for scope and eyepiece set (comparing w/ Zeiss and Vortex setup prices).

If you were going to stay in the $2000 and under range, would you purchase the Razor over the Gavia, a savings of $400 and a better warranty?
The price of the 883 with the 25-60x has increased since that review. I see the B&H price is $3150 today.

I'd check out the Nikon 82mm Monarch at about $1600. I still don't know for sure whether it's a re-issue of the old 82ED Fieldscope. If it is, a good sample should be superior to the Gavia. I haven't seen the Vortex, but it appears to be a close sibling, if not a twin, of the Gavia.

Henry
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