Future Swarovski spotting scope (3 Viewers)

[Mike Crawley]

I wonder whether Swarovski think that they have an interim solution to this question with the BTX eyepiece module ?
Maybe they’ll never produce the 'scope you crave because they have created the BTX ?

I haven’t looked through one but a mate I rarely see who lives in Norfolk uses one (especially for sea watching) and enjoys the view provided by the eyepiece.

 

[Tringa45]

Very interesting. Wonder what the military prefers?

I believe the US military use or used a Leupold 12-40x60 spotting scope. Another possibility is the Swarovski STR 80 and the old Meopta S1 scope was available with a 30x reticle eyepiece.
Most biathlon coaches today seem to use either the Swarovski STX or the Meopta Meostar S2.

John

 

[andylast]

The fundamental difference is that Swarovski uses a zooming eyepiece and the Zeiss Harpia uses a zooming objective. The latter comes with the disadvantage of a comparatively small exit pupil at the lower magnifications and impaired low light capability.
An AFoV of 57° at the lowest magnification of a zoom eyepiece is pretty good and was not to be had 15-20 years ago.
One cannot expect a quantum leap in development every decade and there are many old designs that still have some relevance today.
The Abbe orthoscopic eyepiece was invented in 1880 and is still appreciated by some amateur astronomers.

John

This means that the aperture is stopped down at lower magnifications than 70x? So the only time the scope has a 95mm entrance pupil is at 70x?

 

[Tringa45]

This means that the aperture is stopped down at lower magnifications than 70x? So the only time the scope has a 95mm entrance pupil is at 70x?

IIRC, Henry Link estimated that the Harpia was at full aperture from about 40x upwards.

John

 

[andylast]

OK so I am guessing that Zeiss are perhaps trying to give the user the impression that with this scope, as you go up in magnification, the image doesn't drop in brightness much? The marketing guys have obviously had the last say on the design of this scope. On an evening with poor light, I would want a decent size exit pupil, say 4mm. Never going to get that with this scope. Seems very odd to me. Give me a scope with a fixed aperture/entrance pupil, and I will stop the aperture down at the front if I want it stopped down.

 

[Hermann]

OK so I am guessing that Zeiss are perhaps trying to give the user the impression that with this scope, as you go up in magnification, the image doesn't drop in brightness much? The marketing guys have obviously had the last say on the design of this scope.

Your assumption is wrong. The Harpias are the only scopes I know of were the AFOV doesn't change at all when you zoom from the lowest to the highest magnification. The AFOV is 72 degrees throughout the range. That's a huge advantage in the field.

Hermann

 

[pppppvvvv]

OK so I am guessing that Zeiss are perhaps trying to give the user the impression that with this scope, as you go up in magnification, the image doesn't drop in brightness much? The marketing guys have obviously had the last say on the design of this scope. On an evening with poor light, I would want a decent size exit pupil, say 4mm. Never going to get that with this scope. Seems very odd to me. Give me a scope with a fixed aperture/entrance pupil, and I will stop the aperture down at the front if I want it stopped down.

Harpia is very well designed for birdwatching. FOV at lowest magnification is so big, you are immediately on your subject.
Then zoom in to ~40x or above for optimum views/detail.

I would say it's the "fastest" scope for getting high magnification views on a bird.
Something that is important but rarely discussed.

 

[andylast]

Your assumption is wrong. The Harpias are the only scopes I know of were the AFOV doesn't change at all when you zoom from the lowest to the highest magnification. The AFOV is 72 degrees throughout the range. That's a hugeAt advantage in the field.

Hermann

Harpia is very well designed for birdwatching. FOV at lowest magnification is so big, you are immediately on your subject.
Then zoom in to ~40x or above for optimum views/detail.

I would say it's the "fastest" scope for getting high magnification views on a bird.
Something that is important but rarely discussed.

I don't think either of you have understood what I said. The apparent field of view is not relevant to this discussion. It plays no part in this image brightness issue. The issue with the Harpia 95 is its aperture at different magnifications.

This is a copy and paste from Zeiss website on the Harpia 95 eyepiece.

Eyepiece​

Magnification	23 – 70 ×
Focal length	7.48 mm
Field of view at 1,000 m (yds)	58.8 – 19.5 m (176 – 59 ft)
Zoom factor	3 ×
Exit pupil diameter	2.50 – 1.34 mm

The eyepiece has a fixed focal length of 7.48mm. If we accept that 70x is correct and the corresponding 1.34mm exit pupil is correct, then the effective focal length of the scope at max zoom is 523.6mm. At 23x the effective focal length of the scope is only 172mm. If we look at it from stated magnification and exit pupil diameter at extremes of zoom range, then at 70x the full aperture is around 95mm. If the stated aperture of 95mm is correct then the max mag is just shy of 71x. If the max magnification is exactly 70x than the max aperture is 93.8mm. Some said previously that from 40x to 70x, the exit pupil diameter corresponds to the aperture being about 95mm. Below this magnification, it appears not to. At the low end of the mag range, if the stated 23x is correct then the scope only has an effective aperture of 57.5mm. This will likely be due to an internal iris in the zoom that maybe moves longitudinally.
Wherever the iris is, it is acting as an aperture stop forming the new entrance pupil. The exit pupil is an image of the entrance pupil. An exit pupil of 2.5mm at 23x is hardly a low light scope. An 80mm scope with an eyepiece of 20x will have an exit pupil of 4mm. On a dull very poor light day, that is fine. An effective aperture of 57.5mm at 23x is not what I would call a low light optic. On a bright sunny day there is no problem, but seeing as Zeiss themselves state the max exit pupil size is 2.5mm, it doesn't fill me with any confidence. I think the marketing team won their battle in the boardroom about the design of the scope, rather than the optical designers.

 

[pppppvvvv]

I'm just saying that to use the scope, as a birdwatcher, it is very well designed and ticks the right boxes in terms of practicality, usability.
Whatever flaws you have calculated, I just don't notice. Now if you look at it from equations, and numbers it might look terrible. As a birdwatcher, it is fine.

 

[andylast]

I'm just saying that to use the scope, as a birdwatcher, it is very well designed and ticks the right boxes in terms of practicality, usability.
Whatever flaws you have calculated, I just don't notice. Now if you look at it from equations, and numbers it might look terrible. As a birdwatcher, it is fine.

I am glad you enjoy using it. If people get what they want from their instruments then all is well. My comments about the design of the scope remain. As a low light scope, its not good. The numbers and equations don't lie. Optics IS maths. What the numbers suggest will happen, will happen. Its not subjective. If the pupils of your eyes are 4 or 5 mill in low light, you receive a brighter image if the exit pupil in the eyepiece is of a similar diameter. I make these comments because low light performance is a very important feature of a birding optic. You can't read a review anywhere of a birding optic without the reviewer remarking on its performance in poor light. In normal daylight conditions, I suspect the Zeiss scopes perform very well. Given that the eye pupil (depending on the individual) in bright daylight will be between 2mm and 3mm, then an exit pupil at 2.5mm is fine. At powers of 40x to 70x the corresponding exit pupils will deliver bright detailed images with the Zeiss scope. In low light conditions where your eyes pupils are about 4mm, you will see a brightness difference between a 57.5mm scope at 23x and an 80mm scope at 23x. The low light performance that a larger exit pupil can deliver is not realised with this scope. This is not a matter of opinion, it is fact from Zeiss own stated figures.

 

[pppppvvvv]

Out of interest, how many minutes would I lose? At the end of a day. Southern UK.

 

[andylast]

Out of interest, how many minutes would I lose? At the end of a day. Southern UK.

Don't know the answer to that. I suppose you could work out the time it takes for image brightness to drop below an acceptable level if its a clear day and the sun has set. If its cloudy and the level of cloud is changing it would be more difficult to work out. The way to do it is to have two identical 95mm scopes side by side. One having the internal zoom system that the Harpia has and the other a zoom eyepiece, so that both zoom from 23x to 70x. You design the zoom eyepiece to have a moving internal lens group so that the field stop has an acceptable large AFOV at all mags. Those zoom eyepieces already exist. The difference would be that on one scope at 23x the exit pupil is only 2.5mm in low light, the other scope would have an exit pupil of 4.13mm. You would see a clear difference in low light.

 

[henry link]

There is a simple way to test the visible effect of this loss of aperture at low magnification by using a normal scope with a stop down mask. When I first realized that the Harpia's exit pupil shrinks to 2.5mm at its lowest magnification I set up a simulation of that with a 90mm refractor. I used an eyepiece that produced 20x (4.5mm exit pupil) and made a 50mm stop down mask (2.5mm exit pupil) that could be positioned just in front of the objective lens and flipped in and out of the light path.

With my eye closed to 2-2.5mm in very bright sunlight there was essentially no difference in the image with the mask flipped in or out of the light path, However, as you would expect there was an obvious loss of brightness and contrast under twilight conditions with the mask in place and there were also obvious, but less serious, visible losses under dimmer daylight conditions like cloudy days or looking into dark shadow areas.

Try that test if you want to see what's actually happening to the image quality of the Harpia at low magnification compared to what it would be without the aperture loss.

 

[andylast]

There is a simple way to test the visible effect of this loss of aperture at low magnification by using a normal scope with a stop down mask. When I first realized that the Harpia's exit pupil shrinks to 2.5mm at its lowest magnification I set up a simulation of that with a 90mm refractor. I used an eyepiece that produced 20x (4.5mm exit pupil) and made a 50mm stop down mask (2.5mm exit pupil) that could be positioned just in front of the objective lens and flipped in and out of the light path.

With my eye closed to 2-2.5mm in very bright sunlight there was essentially no difference in the image with the mask flipped in or out of the light path, However, as you would expect there was an obvious loss of brightness and contrast under twilight conditions with the mask in place and there were also obvious, but less serious, visible losses under dimmer daylight conditions like cloudy days or looking into dark shadow areas.

Try that test if you want to see what's actually happening to the image quality at low magnification compared to what it would be without the aperture loss.

Yes I have done similar experiments before with all sorts of different instruments in the past, just messing around at a loose end. Its pretty obvious what differences there are in low light conditions. This surprised me when I saw what Zeiss had done. There are existing zoom eyepieces around (Meopta for one) that state a decent size constant AFOV at all mags, so Zeiss designing one for their scope would not have been difficult for them to achieve. They could then boast a top quality low light scope as well as a convenient wide range zoom scope.

 

[pppppvvvv]

But have you been out after dusk with your scope? What were you seeing that I'm missing?
(And I'm usually the last birder to arrive back at the car park)
Because I'd go so far as to say in 30 years, I can't recall a scope's low light capabilities ever being the limiting factor.
This is what I'm saying, there are lots of experiments and equations, but they don't mean anything in reality, or we'd all have the best low light scope.

 

[andylast]

Of course I have been out after dusk, countless times. I have used hundreds of scopes in all conditions. There are lots of things maths tell us about optics, and yes they DO mean everything in reality, its just that you have yet to experience them so you don't understand. If low light performance was unimportant as you suggest, we would all have 50mm scopes. Just enjoy your scope and don't worry about it.

 

[Hermann]

If low light performance was unimportant as you suggest, we would all have 50mm scopes.

I don't quite agree with you here. Most people want to use high magnifications as well, at least occasionally, and with a 50mm scope you're essentially limited to ~50x at best as any exit pupil below ~1mm is pretty difficult to use when it comes to terrestrial applications. In windy conditions it can also be quite difficult to align the exit pupil of the scope with the entrance pupil of the eye.

BTW, I looked at the Harpia when it came out, and while I really liked the field of view a lot, I definitely wanted a larger exit pupil at low magnifications. Not so much because of the limitations of the 2.5mm exit pupil in poor light, but simply because larger exit pupils are so much more comfortable to use even in bright light. So I stuck to my old Nikon fieldscopes. Sure, they've got old-fashioned (and narrow) zooms, but if I want (or need!) a wide field of view, I can always switch to one of the wideangle eyepieces. Not quite as convenient and fast as a zoom, but that's a price I'm prepared to pay.

Hermann

 

[pppppvvvv]

Of course I have been out after dusk, countless times. I have used hundreds of scopes in all conditions. There are lots of things maths tell us about optics, and yes they DO mean everything in reality, its just that you have yet to experience them so you don't understand. If low light performance was unimportant as you suggest, we would all have 50mm scopes. Just enjoy your scope and don't worry about it.

But I have experienced it. I had an ATX95 for many years, and on one occasion I was blown away by how bright a Green Sandpiper was in near darkness.
But it's a feature that very rarely gets used. You don't see birders wandering round with scopes well after sunset, why? Because it's nearly dark, diurnal birds have gone to roost, nocturnal species haven't really got active.
A Low light scope is a very poor choice in fading light compared to binoculars, night vision and torch/spotlight. The wildlife tends to be monochrome, closer, faster moving.

I'd rather have a wider field of view for all times of daylight, either by design or being able to zoom out to lower magnification. 30-70x on the ATX95 wasn't very good in that respect. And the rubber band with a stick coming off it that Swarovski supplied with that scope as a guide was admitting this!
That's where I think Swarovski can make their improvements.

 

[andylast]

But I have experienced it. I had an ATX95 for many years, and on one occasion I was blown away by how bright a Green Sandpiper was in near darkness.
But it's a feature that very rarely gets used. You don't see birders wandering round with scopes well after sunset, why? Because it's nearly dark, diurnal birds have gone to roost, nocturnal species haven't really got active.
A Low light scope is a very poor choice in fading light compared to binoculars, night vision and torch/spotlight. The wildlife tends to be monochrome, closer, faster moving.

I'd rather have a wider field of view for all times of daylight, either by design or being able to zoom out to lower magnification. 30-70x on the ATX95 wasn't very good in that respect. And the rubber band with a stick coming off it that Swarovski supplied with that scope as a guide was admitting this!
That's where I think Swarovski can make their improvements.

You contradict yourself. You say you were blown away with the image in a large aperture scope in very poor light, and then argue against its usefulness. If you don't use this feature of a large aperture scope then that is your choice, but to argue its importance objectively is just, well, plain stupid. In poor light, I can see details on birds with a larger aperture scope that a low power binocular can not show. In the many years of birdwatching, I see many birders observing with scopes after sunset, in fact on reserves, many of them turn up when the light fades at the end of the day. As I said, just enjoy the equipment you have and we will leave the topic there.

 

[andylast]

I don't quite agree with you here. Most people want to use high magnifications as well, at least occasionally, and with a 50mm scope you're essentially limited to ~50x at best as any exit pupil below ~1mm is pretty difficult to use when it comes to terrestrial applications. In windy conditions it can also be quite difficult to align the exit pupil of the scope with the entrance pupil of the eye.

BTW, I looked at the Harpia when it came out, and while I really liked the field of view a lot, I definitely wanted a larger exit pupil at low magnifications. Not so much because of the limitations of the 2.5mm exit pupil in poor light, but simply because larger exit pupils are so much more comfortable to use even in bright light. So I stuck to my old Nikon fieldscopes. Sure, they've got old-fashioned (and narrow) zooms, but if I want (or need!) a wide field of view, I can always switch to one of the wideangle eyepieces. Not quite as convenient and fast as a zoom, but that's a price I'm prepared to pay.

Hermann

Yep, higher powers are something that I use regularly when the air conditions permit.