When Zeiss announced the forthcoming Harpia spotting scope last year and published the specifications, it triggered much speculation and discussion on Bird Forum about the design of the scope and how it functions. I decided to try to cut through the speculation and find out the facts from the leader of the Harpia project. Gerold Dobler has left an indelible mark on the history of sports optics having led the team that created the original Swarovski EL and, much more recently, the Zeiss Victory SF binoculars and now the Harpia spotting scope. He is presently Zeiss Sports Optics Manager of Product Strategy.
Deciding to do this was easy: accomplishing it, less so. It has taken months to arrange, but I was at last able to meet with Gerold Dobler and conduct an interview with him and this is presented below. Please note that the lines commencing with T: indicate me speaking, and the lines commencing with D: are the responses from Herr Dobler. The interview isn’t quite verbatim as our conversation wandered in many directions and I have had to eliminate these diversions and stitch back together the relevant material.
At this point I would like to thank the staff of The Three Horseshoes Inn, in Warham near Wells-next-the Sea, Norfolk, UK, for their hospitality, for allowing us to commandeer a room and for great food and accommodation. I highly recommend The Three Horseshoes and you can find out more by visiting: http://warhamhorseshoes.co.uk/ .
One final point before we begin, to avoid having to quote multiple specifications we only discussed the 95mm version of the scope and not the 85mm.
T: Herr Dobler, thanks for taking the time from your schedule to meet with me to discuss the Harpia scope. My first question is whether the Harpia is based on the Zeiss Photoscope.
D: Actually no. It does borrow the concept of the zoom being made in the objective lens group instead of the eyepiece, but otherwise there is no relationship, and Photoscope was only 15-45x magnification while Harpia is 23-70x.
T: Is the 2.5mm maximum exit pupil due to vignetting of the objective lens during zooming?
D: Yes, that is correct. Of course this was not an accident or some kind of mistake, instead it was a decision from the beginning. But before we talk about exit pupils it is important to understand that we are not discussing binoculars which are subject to handshake, we are discussing spotting scopes mounted on a suitable steady tripod, which is a completely different game. This still leaves the question of brightness of image which I can demonstrate hardly affects the viewer at all in any practical way.
Our goal was to give birders a scope with both a super-large zoom range and a super wide field of view, for all of the practical advantages that come from these, and also a constant angle of view for maximum viewing comfort and pleasure. This could only be done by zooming with the objective lens group, resulting in some (for a telescope) insubstantial vignetting of the objective for just about 40% of the zoom range at the lower end. For sure we knew exactly what we would get and we made the design having in mind some inspiration from the old well-respected Zeiss-Jena Asiola scope, fitted with the 16mm eyepiece. This gave a magnification of 26x and an exit pupil of 2.4mm which was found to be very effective because the human eye is best able to perceive details when the pupil is between 2 and 2.5mm. By the way, Holger Merlitz mentions this fact several times in his recent book although the principal was mentioned by e.g. König and Köhler in 1959. We made sure that the modestly reduced exit pupil at the lower magnifications is within this bracket, and it is actually between 2.5 and 2.2 mm, in the band from 23x to 40x magnification, above which the full objective size is used by the system
Look, the reason for doing this was to achieve a super-wide zoom range with a super wide field. In fact the 3x zoom range is the biggest wide angle zoom range on the market today. As a birder myself this gives me a big choice in magnification and a really tremendous field of view, especially in the low magnifications sector which I use intensively to constantly find birds, or follow flying birds, during the whole observation day.
At the lowest magnification the field of view is wider than any other wide-angle zoom scope today. If you compare with other zoom-scopes at 30x, the Harpia at 23x gives you a 2.8 times bigger area of field of view, that’s almost 3x bigger, which is an enormous help to find birds, and with the bigger depth of field this really helps with identifying flying birds big time.
I can’t think of any habitats where these two things don’t give me positive advantages, and the fact that the angle of view doesn’t change is a nice bonus and makes it so pleasant it encourages you to all the time use the full range of magnifications without any hesitation or reluctance. Once you have experienced this it is disappointing to go back to conventional scopes.
By designing the system to give an EP of 2.5mm at the lowest magnification we made sure that the system would deliver the best image for the human eye and brain to process at this point in the zoom range.
T: OK, but before we examine this question further, when you zoom up from 23x at what magnification do you begin looking through the full objective diameter?
D: From about 40x upwards to the highest magnification the system uses the full objective diameter. This is about 60 Percent of the zoom range.
T: OK, back to the exit pupil at lower magnifications, doesn’t this put Harpia at a disadvantage compared with competitor scopes?
D: The disadvantage is more theoretical than practical, but I am happy to deal with this question full in the face. Only at low magnification there is a minor reduction in brightness restricted to a few minutes at dusk and dawn without practical significance. However the wide field of view (and also the bigger depth of field compared with scopes with a lowest magnification of only 30x) are of much bigger advantage in low light conditions anyway. You can find your subject in the super wide field much quicker, then zoom to about 40x magnification and you get the full objective size with a bigger field of view so you can see the detail you expect from the rules of twilight observation, when high magnification is very well important. If you need the full objective diameter it is there waiting for you to select by zooming to a higher magnification within a second of time.
I have used the scope a lot and from a birder’s point of view the 2.5mm maximum exit pupil at low magnification is of no practical significance because it may appear a little less bright for maybe 10 minutes of the day, compared with the other 710 minutes in a 12 hour day, during which you constantly benefit from the luxury of a 3x super wide-angle zoom range and the bonus of a constant angle of view. And as I said you can get the full objective any time you like by increasing the magnification.
Anyway, most people prefer binoculars for twilight observation and spotting scopes are hardly ever used for night observation, except for some expeditions using spotlights, where you see no difference in brightness anyhow but again benefit from the big field of view.
Second I explained already that there are also compensations coming with the 2.2 - 2.5mm EP in that this is the pupil diameter at which humans can see most detail and at 23x magnification the resolution delivered by Harpia is absolutely better than the human eye can resolve. From 23x to 40x the exit pupil is quite enough and you can see this is correct from your experience of the many variations of well-respected 65mm scopes at around 30x magnification. These 65mm scopes are very popular because they perform nicely even down to an exit pupil of less than 2.0mm for good reasons, but from 40x upwards a larger objective becomes necessary for performance and comfort. At high magnification level the Harpia performs extremely well and gives you much more power than a 65 mm Scope when you need it.
Third, another thing to consider, as I mentioned right at the beginning, is that although small exit pupils can cause difficulties with binos, this is hardly true at all with scopes which are mounted on suitable tripods and not subject to hand shake.
T: OK but as you are mentioning ‘real life’ and ‘practical benefits’ can you give me some examples from real life?
D: Yes and since we are talking about performance at the bottom end of the zoom range I give you two short stories about this. I live in the south of Germany and within reach of the big lakes like the Federsee and the Lake of Constance. So down I went there with some image-stabilised binos and the Harpia, and I wanted to see which was best for viewing the Hen Harriers that roost there, about 50 of them, in the winter time. It is easy to know the males of course but if you want to try to tell the adult females from the young females and young males you need a lot of experience and good optics. A few of the harriers perched on the bushes about 150 to 300 m away, where the high magnification performance of Harpia allowed me to see the face pattern well enough. In between studying these birds I was able to quickly zoom to low magnification and use the big field of view to catch the incoming flying birds before they dropped down into their roosting place among the reeds and to study them while they were still flying. With the binos I couldn’t see enough details on distant birds, but it was very effective to stop panning the Harpia, back off the magnification slightly to 23x to get the full field of view, and take my hand off the scope, and just watch the harriers fly gently across the field of view which was super. In these circumstances and with this technique the Harpia simply out-performed the stabilized binos. With the 23x magnification and 2.5mm EP and the wide field I could see what I needed. I used this technique in summer when I saw a large grey tern at another lake. The question from its size was: is it Gull-billed or Sandwich? It wasn’t behaving like a Gull-billed, it was dipping down to the water then up again and then down.
T: So it was not flying low but rather high?
D: Yes, exactly, and if it would be Sandwich this would be really exciting so far inland. I couldn’t see the bill detail at first and then used the same technique of lowest magnification and maximum field and depth of view and then just watching it fly across. A long black beak with yellow tip made it into a Sandwich Tern and I was really pleased to make this identification making full use of Harpia’s dynamics and agility. By this I mean the ability to go from 23x to 70x magnification and back again, with just a twist of the zoom ring, and no need to swap eyepieces. More birds till the end of the day – this is what counts.
This kind of technique is possible because if you compare it with other zoom-scopes at 30x, the Harpia at 23x, gives you a field of view of 2.8 times bigger area, that’s almost 3x the area of view, which is an enormous help to find birds, and with the bigger depth of field this really helps with flying birds. One more thing. In the south of Germany near these lakes, we often have rain, maybe not so often as in UK but it can be even heavier. A bonus of the 3-times zoom ratio from 23 to 70x is that you have a big choice of magnification without needing to change eyepieces or add a converter which is very convenient when it rains.
T: Tell us more about the big zoom range and how it is achieved.
D: (Sighs) This is not cheap or easy. Moving the objectives to achieve a high quality wide-zoom range is harder than making an eyepiece zoom, but we have a lot of experience with the Photoscope and we have been able to make the system better. To answer your question in detail about how this is done, you would need to be very familiar with the mechanics of how lenses are moved inside optical tubes. The main thing is that over a full day using the scope you appreciate the big choice of magnifications and the comfort from the constant wide angle of view makes you want to stay out longer. Nothing beats the Harpia in dynamics and versatility and this is what makes the whole birding day most successful.
T: What is Harpia 95’s eye relief and does it change with magnification?
D: Good question to ask! It is 18 mm and it does change, but so little it is hardly measureable.
T: Normally low focal ratios can result in serious chromatic and spherical aberration. How well are they controlled? And what can you tell us about perceived sharpness?
This is correct but we have bench-marked opposition scopes and we have worked very hard to achieve a good control of these aberrations and our control of chromatic aberration is absolutely best in class and spherical aberration is at least as good as the best in class, as is the sharpness and contrast. We don’t give these figures out to make it easy for the competition but I am more than satisfied by the results and the market will soon be able to check this.
T: Why no straight eyepiece version?
D: It is governed by demand. About 90% of scopes bought are angled, and some of this is driven by social birding where a group of people is using the same scope. Even tall people can bend down to view through an angled scope but people who are not as tall cannot suddenly grow upwards to look through a straight scope, so the height of the tripod has to be adjusted all the time and this is not popular.
T: Would Harpia eyepiece work on other scopes?
D: We haven’t tried this and it probably works but how well it would work I can’t say because the eyepiece was designed to work with the whole Harpia optical system. The eyepiece isn’t for sale separately.
T: Would astro eyepieces work on Harpia (with suitable adapter) and what magnifications could you expect?
D: Yes, and to achieve something like 105x you would need a 5mm eyepiece.
T: Can you tell us the light transmission achieved by Harpia?
D: Yes, daylight transmission is 88%, helped by our use of High Transmission glass.
T: The Zeiss website said more accessories are coming. What are these?
D: A smart phone adaptor, and adaptor for camera lenses which will allow the fitting of lenses with threads of 49, 52, and 58mm. With standard step rings you can fit other lenses but you need to check if they would work optically
T: Finally, when will the Harpia arrive at the dealers?
D: My latest information is that Harpia will begin arriving in stores starting in September.
T: Herr Dobler, thank you taking time out from your schedule for this interview.
D: You are welcome and I should say Birdforum is welcome. It is the top birding forum in the world and I am happy to make this contribution. As usual I will be at the British Bird Fair in August with the whole Zeiss team and Birdforum members are welcome to visit our stand. Will you be coming to Bird Fair?
T: Definitely, I booked my hotel room last year, for this year’s Bird Fair. So I will see you there and hopefully meet other Bird Forum members.
Lee
I am grateful to the Copyright holder of the photo below, Melissa Penta, for her permission to use it here. She tells me the photo of the Barred-Puffbird was taken at maximum magnification and has not been cropped, using an old iPhone 6.
Deciding to do this was easy: accomplishing it, less so. It has taken months to arrange, but I was at last able to meet with Gerold Dobler and conduct an interview with him and this is presented below. Please note that the lines commencing with T: indicate me speaking, and the lines commencing with D: are the responses from Herr Dobler. The interview isn’t quite verbatim as our conversation wandered in many directions and I have had to eliminate these diversions and stitch back together the relevant material.
At this point I would like to thank the staff of The Three Horseshoes Inn, in Warham near Wells-next-the Sea, Norfolk, UK, for their hospitality, for allowing us to commandeer a room and for great food and accommodation. I highly recommend The Three Horseshoes and you can find out more by visiting: http://warhamhorseshoes.co.uk/ .
One final point before we begin, to avoid having to quote multiple specifications we only discussed the 95mm version of the scope and not the 85mm.
T: Herr Dobler, thanks for taking the time from your schedule to meet with me to discuss the Harpia scope. My first question is whether the Harpia is based on the Zeiss Photoscope.
D: Actually no. It does borrow the concept of the zoom being made in the objective lens group instead of the eyepiece, but otherwise there is no relationship, and Photoscope was only 15-45x magnification while Harpia is 23-70x.
T: Is the 2.5mm maximum exit pupil due to vignetting of the objective lens during zooming?
D: Yes, that is correct. Of course this was not an accident or some kind of mistake, instead it was a decision from the beginning. But before we talk about exit pupils it is important to understand that we are not discussing binoculars which are subject to handshake, we are discussing spotting scopes mounted on a suitable steady tripod, which is a completely different game. This still leaves the question of brightness of image which I can demonstrate hardly affects the viewer at all in any practical way.
Our goal was to give birders a scope with both a super-large zoom range and a super wide field of view, for all of the practical advantages that come from these, and also a constant angle of view for maximum viewing comfort and pleasure. This could only be done by zooming with the objective lens group, resulting in some (for a telescope) insubstantial vignetting of the objective for just about 40% of the zoom range at the lower end. For sure we knew exactly what we would get and we made the design having in mind some inspiration from the old well-respected Zeiss-Jena Asiola scope, fitted with the 16mm eyepiece. This gave a magnification of 26x and an exit pupil of 2.4mm which was found to be very effective because the human eye is best able to perceive details when the pupil is between 2 and 2.5mm. By the way, Holger Merlitz mentions this fact several times in his recent book although the principal was mentioned by e.g. König and Köhler in 1959. We made sure that the modestly reduced exit pupil at the lower magnifications is within this bracket, and it is actually between 2.5 and 2.2 mm, in the band from 23x to 40x magnification, above which the full objective size is used by the system
Look, the reason for doing this was to achieve a super-wide zoom range with a super wide field. In fact the 3x zoom range is the biggest wide angle zoom range on the market today. As a birder myself this gives me a big choice in magnification and a really tremendous field of view, especially in the low magnifications sector which I use intensively to constantly find birds, or follow flying birds, during the whole observation day.
At the lowest magnification the field of view is wider than any other wide-angle zoom scope today. If you compare with other zoom-scopes at 30x, the Harpia at 23x gives you a 2.8 times bigger area of field of view, that’s almost 3x bigger, which is an enormous help to find birds, and with the bigger depth of field this really helps with identifying flying birds big time.
I can’t think of any habitats where these two things don’t give me positive advantages, and the fact that the angle of view doesn’t change is a nice bonus and makes it so pleasant it encourages you to all the time use the full range of magnifications without any hesitation or reluctance. Once you have experienced this it is disappointing to go back to conventional scopes.
By designing the system to give an EP of 2.5mm at the lowest magnification we made sure that the system would deliver the best image for the human eye and brain to process at this point in the zoom range.
T: OK, but before we examine this question further, when you zoom up from 23x at what magnification do you begin looking through the full objective diameter?
D: From about 40x upwards to the highest magnification the system uses the full objective diameter. This is about 60 Percent of the zoom range.
T: OK, back to the exit pupil at lower magnifications, doesn’t this put Harpia at a disadvantage compared with competitor scopes?
D: The disadvantage is more theoretical than practical, but I am happy to deal with this question full in the face. Only at low magnification there is a minor reduction in brightness restricted to a few minutes at dusk and dawn without practical significance. However the wide field of view (and also the bigger depth of field compared with scopes with a lowest magnification of only 30x) are of much bigger advantage in low light conditions anyway. You can find your subject in the super wide field much quicker, then zoom to about 40x magnification and you get the full objective size with a bigger field of view so you can see the detail you expect from the rules of twilight observation, when high magnification is very well important. If you need the full objective diameter it is there waiting for you to select by zooming to a higher magnification within a second of time.
I have used the scope a lot and from a birder’s point of view the 2.5mm maximum exit pupil at low magnification is of no practical significance because it may appear a little less bright for maybe 10 minutes of the day, compared with the other 710 minutes in a 12 hour day, during which you constantly benefit from the luxury of a 3x super wide-angle zoom range and the bonus of a constant angle of view. And as I said you can get the full objective any time you like by increasing the magnification.
Anyway, most people prefer binoculars for twilight observation and spotting scopes are hardly ever used for night observation, except for some expeditions using spotlights, where you see no difference in brightness anyhow but again benefit from the big field of view.
Second I explained already that there are also compensations coming with the 2.2 - 2.5mm EP in that this is the pupil diameter at which humans can see most detail and at 23x magnification the resolution delivered by Harpia is absolutely better than the human eye can resolve. From 23x to 40x the exit pupil is quite enough and you can see this is correct from your experience of the many variations of well-respected 65mm scopes at around 30x magnification. These 65mm scopes are very popular because they perform nicely even down to an exit pupil of less than 2.0mm for good reasons, but from 40x upwards a larger objective becomes necessary for performance and comfort. At high magnification level the Harpia performs extremely well and gives you much more power than a 65 mm Scope when you need it.
Third, another thing to consider, as I mentioned right at the beginning, is that although small exit pupils can cause difficulties with binos, this is hardly true at all with scopes which are mounted on suitable tripods and not subject to hand shake.
T: OK but as you are mentioning ‘real life’ and ‘practical benefits’ can you give me some examples from real life?
D: Yes and since we are talking about performance at the bottom end of the zoom range I give you two short stories about this. I live in the south of Germany and within reach of the big lakes like the Federsee and the Lake of Constance. So down I went there with some image-stabilised binos and the Harpia, and I wanted to see which was best for viewing the Hen Harriers that roost there, about 50 of them, in the winter time. It is easy to know the males of course but if you want to try to tell the adult females from the young females and young males you need a lot of experience and good optics. A few of the harriers perched on the bushes about 150 to 300 m away, where the high magnification performance of Harpia allowed me to see the face pattern well enough. In between studying these birds I was able to quickly zoom to low magnification and use the big field of view to catch the incoming flying birds before they dropped down into their roosting place among the reeds and to study them while they were still flying. With the binos I couldn’t see enough details on distant birds, but it was very effective to stop panning the Harpia, back off the magnification slightly to 23x to get the full field of view, and take my hand off the scope, and just watch the harriers fly gently across the field of view which was super. In these circumstances and with this technique the Harpia simply out-performed the stabilized binos. With the 23x magnification and 2.5mm EP and the wide field I could see what I needed. I used this technique in summer when I saw a large grey tern at another lake. The question from its size was: is it Gull-billed or Sandwich? It wasn’t behaving like a Gull-billed, it was dipping down to the water then up again and then down.
T: So it was not flying low but rather high?
D: Yes, exactly, and if it would be Sandwich this would be really exciting so far inland. I couldn’t see the bill detail at first and then used the same technique of lowest magnification and maximum field and depth of view and then just watching it fly across. A long black beak with yellow tip made it into a Sandwich Tern and I was really pleased to make this identification making full use of Harpia’s dynamics and agility. By this I mean the ability to go from 23x to 70x magnification and back again, with just a twist of the zoom ring, and no need to swap eyepieces. More birds till the end of the day – this is what counts.
This kind of technique is possible because if you compare it with other zoom-scopes at 30x, the Harpia at 23x, gives you a field of view of 2.8 times bigger area, that’s almost 3x the area of view, which is an enormous help to find birds, and with the bigger depth of field this really helps with flying birds. One more thing. In the south of Germany near these lakes, we often have rain, maybe not so often as in UK but it can be even heavier. A bonus of the 3-times zoom ratio from 23 to 70x is that you have a big choice of magnification without needing to change eyepieces or add a converter which is very convenient when it rains.
T: Tell us more about the big zoom range and how it is achieved.
D: (Sighs) This is not cheap or easy. Moving the objectives to achieve a high quality wide-zoom range is harder than making an eyepiece zoom, but we have a lot of experience with the Photoscope and we have been able to make the system better. To answer your question in detail about how this is done, you would need to be very familiar with the mechanics of how lenses are moved inside optical tubes. The main thing is that over a full day using the scope you appreciate the big choice of magnifications and the comfort from the constant wide angle of view makes you want to stay out longer. Nothing beats the Harpia in dynamics and versatility and this is what makes the whole birding day most successful.
T: What is Harpia 95’s eye relief and does it change with magnification?
D: Good question to ask! It is 18 mm and it does change, but so little it is hardly measureable.
T: Normally low focal ratios can result in serious chromatic and spherical aberration. How well are they controlled? And what can you tell us about perceived sharpness?
This is correct but we have bench-marked opposition scopes and we have worked very hard to achieve a good control of these aberrations and our control of chromatic aberration is absolutely best in class and spherical aberration is at least as good as the best in class, as is the sharpness and contrast. We don’t give these figures out to make it easy for the competition but I am more than satisfied by the results and the market will soon be able to check this.
T: Why no straight eyepiece version?
D: It is governed by demand. About 90% of scopes bought are angled, and some of this is driven by social birding where a group of people is using the same scope. Even tall people can bend down to view through an angled scope but people who are not as tall cannot suddenly grow upwards to look through a straight scope, so the height of the tripod has to be adjusted all the time and this is not popular.
T: Would Harpia eyepiece work on other scopes?
D: We haven’t tried this and it probably works but how well it would work I can’t say because the eyepiece was designed to work with the whole Harpia optical system. The eyepiece isn’t for sale separately.
T: Would astro eyepieces work on Harpia (with suitable adapter) and what magnifications could you expect?
D: Yes, and to achieve something like 105x you would need a 5mm eyepiece.
T: Can you tell us the light transmission achieved by Harpia?
D: Yes, daylight transmission is 88%, helped by our use of High Transmission glass.
T: The Zeiss website said more accessories are coming. What are these?
D: A smart phone adaptor, and adaptor for camera lenses which will allow the fitting of lenses with threads of 49, 52, and 58mm. With standard step rings you can fit other lenses but you need to check if they would work optically
T: Finally, when will the Harpia arrive at the dealers?
D: My latest information is that Harpia will begin arriving in stores starting in September.
T: Herr Dobler, thank you taking time out from your schedule for this interview.
D: You are welcome and I should say Birdforum is welcome. It is the top birding forum in the world and I am happy to make this contribution. As usual I will be at the British Bird Fair in August with the whole Zeiss team and Birdforum members are welcome to visit our stand. Will you be coming to Bird Fair?
T: Definitely, I booked my hotel room last year, for this year’s Bird Fair. So I will see you there and hopefully meet other Bird Forum members.
Lee
I am grateful to the Copyright holder of the photo below, Melissa Penta, for her permission to use it here. She tells me the photo of the Barred-Puffbird was taken at maximum magnification and has not been cropped, using an old iPhone 6.
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