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Kowa 66A Performance Observations & Questions (1 Viewer)

D Lloyd

Active member
Canada
After much deliberation, I recently purchased a new Kowa Prominar 66A scope with the TE-11WZ II zoom eyepiece. Although I am inexperienced with scopes, in my evaluation it is a well-built scope that manages to be both sturdy and lightweight. At lower magnification, colours appear vividly and images are crisp. I viewed a bald eagle about 400-500 m away and could see the wind ruffling its feathers and how pale its eyes were (paler than I expected!).

However, I've noticed that when I nudge the zoom past 35x or 40x brightness noticeably diminishes and fine details are harder to make out. I assume this is due to the decreasing size of the exit pupil relative to the higher magnification. Is this to be expected with the smaller objective lens? I imagine the 88A would outperform the 66A at this level of magnification, but at what magnification would I expect the brightness to drop off on the 88?

I know many birders choose to use fixed wide angle eyepieces, and these are often in the range of 35x, so perhaps I shouldn't complain that there is a loss of brightness/resolution when I push my zoom eyepiece beyond that number if the view at 35x is crisp and clear and beautiful. It does kind of go against the natural expectation that when one gets closer to something, one sees it better. I would be curious to hear why some prefer the fixed magnification eyepieces?

I chose the 66A for its versatility. With its smaller size, I can take it more readily on longer bird walks. With its premium glass, reviewers say it performs quite well despite its small size. However, I am fortunate enough to live on the coast, with a stellar view of the water. I can do a lot of birding just from my backyard. Would the 88 perform better in this context? With the warm weather recently, I've noticed a fair amount of atmospheric distortion when glassing over the water. Would this distortion be amplified by the bigger objective lens?

Many thanks,

DL
 
After much deliberation, I recently purchased a new Kowa Prominar 66A scope with the TE-11WZ II zoom eyepiece. Although I am inexperienced with scopes, in my evaluation it is a well-built scope that manages to be both sturdy and lightweight. At lower magnification, colours appear vividly and images are crisp. I viewed a bald eagle about 400-500 m away and could see the wind ruffling its feathers and how pale its eyes were (paler than I expected!).

However, I've noticed that when I nudge the zoom past 35x or 40x brightness noticeably diminishes and fine details are harder to make out. I assume this is due to the decreasing size of the exit pupil relative to the higher magnification. Is this to be expected with the smaller objective lens? I imagine the 88A would outperform the 66A at this level of magnification, but at what magnification would I expect the brightness to drop off on the 88?
Some drop in brightness is to be expected. After all, the exit pupil of the scope is well below 2mm at 40x. However, the image should really still be sharp and contrasty. If the atmospheric conditions are good or at least reasonable, there's no reason at all why "fine details should be harder to make out". If they really are, you might have a scope that isn't as good as it should be.
I know many birders choose to use fixed wide angle eyepieces, and these are often in the range of 35x, so perhaps I shouldn't complain that there is a loss of brightness/resolution when I push my zoom eyepiece beyond that number if the view at 35x is crisp and clear and beautiful. It does kind of go against the natural expectation that when one gets closer to something, one sees it better. I would be curious to hear why some prefer the fixed magnification eyepieces?
In the old days: Better field of view and more eyerelief. Nowadays good zooms are just about as good as wideangles. Or almost as good. But they sure are a lot more convenient. BTW, over here most birders who (still) use fixed wideangles, would normally use a magnification between ~25x and 30x. I personally like 24x/25x most.
I chose the 66A for its versatility. With its smaller size, I can take it more readily on longer bird walks. With its premium glass, reviewers say it performs quite well despite its small size. However, I am fortunate enough to live on the coast, with a stellar view of the water. I can do a lot of birding just from my backyard. Would the 88 perform better in this context? With the warm weather recently, I've noticed a fair amount of atmospheric distortion when glassing over the water. Would this distortion be amplified by the bigger objective lens?
Size matters, especially in scopes. That's the general rule. However, atmospheric distortions ("heat haze") are a fact of life, and there's nothing much you can go about them. Except to dial down the magnification. And wait for better conditions. Often the first two hours after sunrise and the last two hours before sunset offer decent conditions.

Hermann
 
Some drop in brightness is to be expected. After all, the exit pupil of the scope is well below 2mm at 40x. However, the image should really still be sharp and contrasty. If the atmospheric conditions are good or at least reasonable, there's no reason at all why "fine details should be harder to make out". If they really are, you might have a scope that isn't as good as it should be.

In the old days: Better field of view and more eyerelief. Nowadays good zooms are just about as good as wideangles. Or almost as good. But they sure are a lot more convenient. BTW, over here most birders who (still) use fixed wideangles, would normally use a magnification between ~25x and 30x. I personally like 24x/25x most.

Size matters, especially in scopes. That's the general rule. However, atmospheric distortions ("heat haze") are a fact of life, and there's nothing much you can go about them. Except to dial down the magnification. And wait for better conditions. Often the first two hours after sunrise and the last two hours before sunset offer decent conditions.

Hermann
Thank you for your reply.

As for loss of detail / contrast at higher magnification, to me it's like being in a dimly lit room - I can still see the books on the shelf, but I have a harder time reading the titles on the spines. I'm not sure if this is due to a loss of contrast in the scope or simply a function of losing brightness.

That said, the images I'm thinking of that seemed to lose sharpness were of birds on the water, so atmospheric distortion may have contributed to that. I will test it again and compare images of water birds to forest birds.

As for scope quality... I've been trying to star test it according to suggestions offered elsewhere in these forums. I've been doing this in daytime using sunlight bouncing off a fixed point like a car's side mirror, positioned about 30 m away. I read that it is best to have between 2-5 rings for the purposes of assessing for flaws. But I find that at what I think is about 2-5 rings the "star" is still quite small in the field of view, making it hard to assess its qualities (at least, hard for my eyes. I do wear glasses). Is the star supposed to fill the field of view in a star test? I find when I increase magnification to this point, it's all a very blurry blob.

I'm also not clear on the distinction between "inside focus" and "outside focus" in star testing. Does "inside focus" mean just slightly off-focus, while "outside focus" means drastically off-focus? Or does it relate to which direction I turn the focus knob (ie, inside focus might be clockwise, while outside focus might be counterclockwise)?

I should have ordered both the 88 and the 66 so as to make a proper comparison!
 
Sounds like the 66A isn’t quite right for you. I’ve never grown to like an optic I wasn’t totally happy with initially. Since you like the view at lower mag the 88 should be a good choice, maintaining that brightness to higher mags. I really like my 883 that replaced my 773 and don’t mind the extra weight for the better performance. I also use the 1.6x multiplier, when more reach is needed and that’s something I imagine the 66 would struggle with.
 
If you mean you are looking at the reflection of the sun in the car mirror itself, STOP doing that immediately! That could damage your eyesight in a fraction of a second! You should only use a tiny glitter point of the sun returning from a small shiny spherical object. The focused glitter point should be small enough to look like a star point in the scope at low magnification or a tiny disc, perhaps surrounded by one or two dim rings at the highest magnification, which is the only magnification you should bother using for a star test.

"Inside focus" means focusing toward infinity. "Outside Focus" means focusing away from infinity. Each way will show a gradual increase in the number rings as you focus further away from best focus, but often you see very strong rings only in one direction and very weak or no rings in the other direction, an indication of spherical aberration. The star at five rings of defocus will still not be very large at 60x, but the rings should quite distinct, at least on one side of focus.

Going straight to another scope may not accomplish anything . A different scope, even if it is larger and more expensive, may be no better and could be worse than what you have now. The first step is to determine if something is wrong with your current scope. A properly done star test is the way to do that.
 
If you mean you are looking at the reflection of the sun in the car mirror itself, STOP doing that immediately! That could damage your eyesight in a fraction of a second! You should only use a tiny glitter point of the sun returning from a small shiny spherical object. The focused glitter point should be small enough to look like a star point in the scope at low magnification or a tiny disc, perhaps surrounded by one or two dim rings at the highest magnification, which is the only magnification you should bother using for a star test.

"Inside focus" means focusing toward infinity. "Outside Focus" means focusing away from infinity. Each way will show a gradual increase in the number rings as you focus further away from best focus, but often you see very strong rings only in one direction and very weak or no rings in the other direction, an indication of spherical aberration. The star at five rings of defocus will still not be very large at 60x, but the rings should quite distinct, at least on one side of focus.

Going straight to another scope may not accomplish anything . A different scope, even if it is larger and more expensive, may be no better and could be worse than what you have now. The first step is to determine if something is wrong with your current scope. A properly done star test is the way to do that.
Thank-you for your reply!

Rest assured, I was not looking at a reflection of the sun in the mirror - I was focusing on the curvature of the metal housing or casing surrounding the mirror, at a point which was glittering in the sun. I should have stated that more specifically. Should I be focusing on something more precisely spherical?

I think I understand what you're saying about focus. "Infinity" means the farthest away point? Just so I'm clear, this is my understanding of the process:

  • Find the star in the field of view.
  • Set the zoom to its highest magnification.
  • Use the focus knobs to bring the star into precise focus.
  • Inside focus: turn the knob as if to bring an object farther away than the star into focus, defocusing the star.
  • Outside focus: turn the knob as if to bring a closer object into focus, defocusing the star.

Is this correct?
 
A 883 which had been in use for 16 years was replaced by 66a recently. Mine was already sold but the new 66a was compared with 2 different 883's in the evening towards dusk.
I am most okay with 66a.
What I sacrificed is long-distance seawatching with the 1,6 extender. I am probably selling it.
 
Hi,

as has been mentioned, the minimum requirement for an ok example of an ED (or in your case fluorite crystal) scope is to deliver a crisp image at 60x or whatever is the max magnification of the zoom EP. Also there should be an easy to find point of best focus. All that in good seeing aka no heat haze and with the scope at outside temperature. Early mornings on an overcast day are good unless its foggy... Or late night, if you opt for real stars.

As for star testing, a tiny reflection of the sun in a convex spherical surface can be used if the distance is sufficient. Or make a very small pinhole in some aluminum foil and mount it in front of a led flashlight.
For small fast refractors, 30m or 100ft are a safe guess, or do the maths and use some lower distance.
Also star tests are usually done at quite high magnifications of 1,6 to 2 times the aperture in mm, which are not available for most spotters unless special EPs or an extender is used. So use the zoom at max magnification. 2-3 rings are fine. More don't give good results.

See Star testing telescope optical quality for some images of what the different aberrations look like (and lots of theory). You want use the upper one for each image pair for the unobstructed case for refractors.

Also please note that perfect examples with identical diffraction patterns inside and outside of focus are exceedingly rare (as in people have star tested a few thousand scopes in their live and do remember the one or two examples that came close) and for the relatively low magnifications that spotters are normally used at, a good example as in better than diffraction limited will work just fine. If you intend to adapt astro EPs or use an extender or two, you want it to be considerably better than diffraction limited...

Joachim
 
Sounds like the 66A isn’t quite right for you. I’ve never grown to like an optic I wasn’t totally happy with initially. Since you like the view at lower mag the 88 should be a good choice, maintaining that brightness to higher mags. I really like my 883 that replaced my 773 and don’t mind the extra weight for the better performance. I also use the 1.6x multiplier, when more reach is needed and that’s something I imagine the 66 would struggle with.
Good point.

I seem to remember a review on Rockslide saying that the extender doesn't work as well on the 66 as it does other models.
 
A 883 which had been in use for 16 years was replaced by 66a recently. Mine was already sold but the new 66a was compared with 2 different 883's in the evening towards dusk.
I am most okay with 66a.
What I sacrificed is long-distance seawatching with the 1,6 extender. I am probably selling it.
Thank you for sharing your experience. I may be ordering a bigger one.
 
Hi,

as has been mentioned, the minimum requirement for an ok example of an ED (or in your case fluorite crystal) scope is to deliver a crisp image at 60x or whatever is the max magnification of the zoom EP. Also there should be an easy to find point of best focus. All that in good seeing aka no heat haze and with the scope at outside temperature. Early mornings on an overcast day are good unless its foggy... Or late night, if you opt for real stars.

As for star testing, a tiny reflection of the sun in a convex spherical surface can be used if the distance is sufficient. Or make a very small pinhole in some aluminum foil and mount it in front of a led flashlight.
For small fast refractors, 30m or 100ft are a safe guess, or do the maths and use some lower distance.
Also star tests are usually done at quite high magnifications of 1,6 to 2 times the aperture in mm, which are not available for most spotters unless special EPs or an extender is used. So use the zoom at max magnification. 2-3 rings are fine. More don't give good results.

See Star testing telescope optical quality for some images of what the different aberrations look like (and lots of theory). You want use the upper one for each image pair for the unobstructed case for refractors.

Also please note that perfect examples with identical diffraction patterns inside and outside of focus are exceedingly rare (as in people have star tested a few thousand scopes in their live and do remember the one or two examples that came close) and for the relatively low magnifications that spotters are normally used at, a good example as in better than diffraction limited will work just fine. If you intend to adapt astro EPs or use an extender or two, you want it to be considerably better than diffraction limited...

Joachim
Thank you. I will run this again using a different object. I think another part of what complicated the tests I did is there was often more than one point of light in the FOV, so the rings would overlap.

As for crispness, can something still be crisp but dim?
 
As for crispness, can something still be crisp but dim?

Hi,

yes, you might not be able to see whether it's crisp if the image is too dark, but observe the same object at the same range in better lighting conditions and it will look quite different.

Joachim
 
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I posted an update in a similar thread I initiated but want to close the loop here as well.

After trying both the Kowa Prominar TSN 66A and 88A, I decided to keep the 88A, mainly due to its greater brightness. I also got a Sirui ST-224 tripod and a VA-5 video head.

7 months on, I’m happy to report I’m very pleased with my purchase. The Kowa is a pleasure to look through. Colours are vivid, images are crisp and clear. It can frequently pick out details on sea birds at long distances that other birders’ scopes cannot. I have not found the whole kit to be too onerous or heavy a carry on longer bird walks, something I was worried about.

I have not used it in very high winds so can’t speak to the stability if the tripod in adverse conditions, but I’ve not noticed any problems on somewhat windy days.

My only issue, which is not specific to the brand of scope, is my fumbling to put the kit down from my shoulder so I can grab my binoculars to see a bird that has just flown by whilst walking between destinations. I often miss the bird. Hopefully this will become easier with practice. Or I’ll invest in one of those backpacks.

I posted several times in these forums requesting assistance with my decision and evaluation of these scopes. Thank you everyone, you were very helpful.

Shout-out also to staff at PeleeWings in Leamington, ON for their excellent customer service, deep knowledge of a range of products, and generous return policy.
 
Sounds like the 66A isn’t quite right for you. I’ve never grown to like an optic I wasn’t totally happy with initially. Since you like the view at lower mag the 88 should be a good choice, maintaining that brightness to higher mags. I really like my 883 that replaced my 773 and don’t mind the extra weight for the better performance. I also use the 1.6x multiplier, when more reach is needed and that’s something I imagine the 66 would struggle with.
I received lots of good advice from forum members in my deliberations, but your comment “I’ve never grown to like an optic I wasn’t totally happy with initially” really resonated. As I note downthread, I ended up going with the 88. The 66 may well have been “good enough” for my needs, but I doubt I would have been able to completely banish my initial misgivings. Thankfully I decided to be brave and cough up the extra cash for the 88. I love it.
 
I'd definitely recommend buying a Scopac-style backpack, which will free up your hands when walking so you don't miss anything through your bins. It'll spread the weight better too and be much easier than carrying your scope over one shoulder.
 
I'd definitely recommend buying a Scopac-style backpack, which will free up your hands when walking so you don't miss anything through your bins. It'll spread the weight better too and be much easier than carrying your scope over one shoulder.
Thanks! I’ll take a look at them.
 
Thanks for saying! And letting us know the outcome. Cudos for seeing it through and finding the scope that works best for you and what a scope the 88 is! Enjoy!
 

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