Brightest of the 60s (1 Viewer)

Leif.
I think that the Diascope has a Pechan prism, and as Henry has mentioned a modified Pechan on the angled. Its looks as though it has been rotated. Coatings, well I would suppose that this is a well kept secret amongst manufacturers. Leica has a Porro, and looking at it, it would appear that the new Swaro, also has a Pechan / Schmidt prism.

mak said:

Leif.
I think that the Diascope has a Pechan prism, and as Henry has mentioned a modified Pechan on the angled. Its looks as though it has been rotated. Coatings, well I would suppose that this is a well kept secret amongst manufacturers. Leica has a Porro, and looking at it, it would appear that the new Swaro, also has a Pechan / Schmidt prism.

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Thanks!

Henry: I know that manufacturers do not always want us to know what they are doing. One story I heard was that at the end of the nineteenth century Carl Zeiss (the man and the company) started producing microscope objectives that stood out from the crowd. It turned out that he had invented the apochromatic triplet using flourite for the low dispersion element. He kept quiet for obvious reasons and it took a few years for others to catch on. Phase coating was invented IIRC in the late 80's and I'm sure the inventers tried to keep the details secret. I read somewhere that it took a while for the Japanese to learn the tricks. I suspect that a lot of the time manufacturers want us to think that they have some neat trick that no-one else has. I'm sure 'Hilux' or 'Swarobright' sound more appealing than 'dielectric coating'.

mak said:

Leif.
I think that the Diascope has a Pechan prism, and as Henry has mentioned a modified Pechan on the angled. Its looks as though it has been rotated. Coatings, well I would suppose that this is a well kept secret amongst manufacturers. Leica has a Porro, and looking at it, it would appear that the new Swaro, also has a Pechan / Schmidt prism.

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I am not sure if this (http://www.roesener.com/pdf/prodinfo_fern_spektive.pdf ) marketing material can confirm anything, but it does mention Schmidt-prisms in the Diascope.

I also found an interesting Dutch test report on "apochromat" scopes (http://www.vogelbescherming.nl/documents/Telescoop test 2003.pdf ). I jumped over most of the Dutch text, but in the end of the report there were tables and diagrams showing the light transmission-% as a function of wavelength. This kind of analysis - I think - tells quite a lot about the "real" color cast issues and maybe also about the scope's behaviour in different lighting conditions. Looks like Swarovski have found a coating that gives a very even light transmission (85%) in the whole spectrum - clearly more in the blue end than the tested competitors (Nikon was not in the test).

Ilkka

The Dutch information is excellent. I wish more such tests were being done. I notice a couple of things, very large transmission differrences between the two Zeiss scopes even though the optics are almost identical, suggesting large sample variation. I wish they had also tested the straight versions of the Swarovski and Leica which should have higher transmission than the angled. Also too bad Nikon wasn't included.

henry link said:

The Dutch information is excellent. I wish more such tests were being done. I notice a couple of things, very large transmission differrences between the two Zeiss scopes even though the optics are almost identical, suggesting large sample variation. I wish they had also tested the straight versions of the Swarovski and Leica which should have higher transmission than the angled. Also too bad Nikon wasn't included.

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An interesting link! I am now convinced that most top end scopes use roof prisms!

Henry: Don't forget that the two Zeiss scopes have different objectives - a three element one in the 65 and a 4 element one in the 85 - and of course the thicknesses of the glass elements differ, so those differences might well account for the differences in transmission as a function of light wavelength. It is though fascinating to see how large the differences between the instruments are, with Leica of all things being the least impressive!

I certainly agree that this kind of information is useful. But I do wonder whether the % transmission is directly related to how bright the image 'looks'? This might seem a really stupid question to some people but I know that apparent brightness is not the same as measured brightness.

Interestingly he mentioned sharpness (centre and edge), contrast, brightness and distortion but missed out correction for chromatic aberration (assuming my Dutch translation was accurate). I thought the Zeiss 85 was easily the best corrected with no CA seen, followed closely by the Leica with a faint trace at the field edges, and finally the Swaro 85 HD and Nikon 82 ED with a quite noticeable but not serious amount of CA. (It's minor but I have heard several other people comment on it, so I'm sure it's there.)

I still reckon that a prospective buyer should try shortlisted instruments out in the field in typical conditions, preferably in good and poor light.

Leif, Notice that the small differences in the Zeiss scopes' optics actually favor the 65, one less element in the objective and thinner glass in its smaller elements if there is any significant difference in thickness. Prisms and eyepieces are exactly the same.

Here's a way to think about the relationship between light transmission percentage and "brightness". Each 2% change in light transmission is about the equivalent in "brightness" of a 1% change in objective diameter. Henry

henry link said:

Leif, Notice that the small differences in the Zeiss scopes' optics actually favor the 65, one less element in the objective and thinner glass in its smaller elements if there is any significant difference in thickness. Prisms and eyepieces are exactly the same.

Here's a way to think about the relationship between light transmission percentage and "brightness". Each 2% change in light transmission is about the equivalent in "brightness" of a 1% change in objective diameter. Henry

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Henry: I'm talking about apparent brightness ie. how bright the image seems to the observer. To my eyes the Nikon 8x32 SE has similar brightness to top of the range full sized roof prism binoculars such as the Leica 8x42 BN despite the much smaller objectives. I have heard enough similar reports from others to believe what I see. (I was rather surprised.) In practice the transmission % for the Nikon and Leica instruments is probably similar, with the Nikon probably transmitting ~90% and the Leica ~86%. This 4% difference is small when compared to the difference in objective area i.e. (42/32)^2 ~ 2. I don't know the explanation but it might be due to differences in optical quality and optical design between the two instruments rather than due to an increase in % light transmission. I presume the same arguments could also apply to scopes which are from an optical point of view similar. In other words the % transmission figures do not directly tell you the relative apparent brightnesses of two optics.

henry link said:

Leif, Notice that the small differences in the Zeiss scopes' optics actually favor the 65, one less element in the objective and thinner glass in its smaller elements if there is any significant difference in thickness. Prisms and eyepieces are exactly the same.

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You've got me there squire! I was just pointing out the differences in the objectives. Yes I agree that the differences in light transmission between the Zeiss 65 FL and the Zeiss 85 FL are surprising. Let me know when you have the answer.

You have probably seen the Alula review which found large differences in sharpness between multiple samples of the same scope, and one or two lemons, including one from Leica. (A rather disconcerting finding, to me at least.)

Incidentally was the light transmission measured for the scope plus zoom eyepiece at some common magnification, or for the objective on its own?

How did you translate a .pdf file, Leif?

scampo said:

How did you translate a .pdf file, Leif?

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Steve: Use the selection tool to copy up to 150 words at a time, and copy the text to the translator. It's tedious but it works. Sadly the translation is far from good, but it gives an idea of what is being said.

You'll like the review. It slags off the Leica APO 77 something rotten.

I do wonder who the reviewer is.

Interesting scope review. From the tables i can see that the transmission in the yellow/red part of the light spectrum is favored by both leica and zeiss. I guess this explains the slight yellow "color cast" and the slightly better contrast in low light situations for these scopes. That the increased contrast is favored before total color fidelity is a optical design decision I would assume. But the APO scopes do have an extra lens or two..with more light loss as a result. I would have been interesting to se the Nikon scopes in the review.
The Zeiss FL65 actually has the largest exit pupil (at 15x) and a large FOV...so it looks pretty good for digiscoping to me even if eye relief could be better (longer)...in the Alula test the zeiss zoom were pretty out of focus though...due to lack of a flat field it seemed...or was it just a lemon...?
Experiences of the Zeis 65FL would be interesting to hear!

What is interesting is that this objective test shows such different results from the highly subjective recent Bird Watching review which claimed the Zeiss 85 was not the brightest - here they show that the Zeiss is the uncontested winner in light transmission.

But... it might be lost in the translation, they seem to have ignored the fact that the Zeiss zoom allows you to see much more of what you want to see - almost 50% more area than the Swaro zoom - now isn't that a key requirement of birding optics?

I looked for a good time today through two Swaro 80s - one with zoom, one with 30xW. The zoom does look somewhat tubelike once you compare it with the Zeiss; but the 30xW was truly a delight in every way. In fact, the guy with the zoom said he was going to buy a fixed 30xW tomorrow on the basis of what he saw.

As you say, it was a shame the Nikon was not included.

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scampo said:

What is interesting is that this objective test shows such different results from the highly subjective recent Bird Watching review which claimed the Zeiss 85 was not the brightest - here they show that the Zeiss is the uncontested winner in light transmission.

But... it might be lost in the translation, they seem to have ignored the fact that the Zeiss zoom allows you to see much more of what you want to see - almost 50% more area than the Swaro zoom - now isn't that a key requirement of birding optics?

I looked for a good time today through two Swaro 80s - one with zoom, one with 30xW. The zoom does look somewhat tubelike once you compare it with the Zeiss; but the 30xW was truly a delight in every way. In fact, the guy with the zoom said he was going to buy a fixed 30xW tomorrow on the basis of what he saw.

As you say, it was a shame the Nikon was not included.

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Steve: The Alula, BVD and Porters subjective tests also showed that the Zeiss was the brightest of the scopes tested (Zeiss vs Swaro ATS 80HD in the case of BVD). It does make me wonder what the BW magazine testers were up to.

If only manufacturers would bring out a wide field zoom with decent edges at low powers. Even if it cost £400 I think it would sell as it would replace the 30xw + zoom which together cost ~£400. After all, if someone is willing to pay ~£1500 for the Swaro ATS 80 HD with zoom eyepiece ...

I think you're right on that zoom idea although it still surprises me that Zeiss didn't push that aspect of their zoom harder. As you say, I feel sure such a zoom would sell despite the cost as, once the scope has been purchased, the extra outlay becomes less significant.

I have to say, though, that while looking for the local red-rumped swallow recently over a reservoir, the fixed 30x eyepiece really does come into its own. Those birders with narrow zooms really were really struggling to locate the bird, but with a wide angle, it was quite easy.

Trouble is, looking at something like distant waders or waterfowl, a zoom is a real boon to have even if it has a narrow fov.

Leif said:

Steve: The Alula, BVD and Porters subjective tests also showed that the Zeiss was the brightest of the scopes tested (Zeiss vs Swaro ATS 80HD in the case of BVD). It does make me wonder what the BW magazine testers were up to.

If only manufacturers would bring out a wide field zoom with decent edges at low powers. Even if it cost £400 I think it would sell as it would replace the 30xw + zoom which together cost ~£400. After all, if someone is willing to pay ~£1500 for the Swaro ATS 80 HD with zoom eyepiece ...

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Yes that would be interesting, but would we pay the extra? I must say that I am interested to know how Henry and you came up with the light transmission figures, because I would really look forward to seeing the light transmission on binoculars. It would be a real eye opener (excuse the pun).

mak said:

Yes that would be interesting, but would we pay the extra? I must say that I am interested to know how Henry and you came up with the light transmission figures, because I would really look forward to seeing the light transmission on binoculars. It would be a real eye opener (excuse the pun).

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Regarding eyepieces, many people seem to have the ~30xw and the zoom. Now the question is would us birders be willing to pay up front ~£400, or would we continue to spend two smaller sums spread over time? After all, two small purchases hurts less. ~£200 could just about be written off as an expensive impulse purchase, but ~£400 feels more serious. I suppose it would be a risk for any manufacturer to introduce something so out of kilter with the rest of the market that it might not sell. But then again, that is what Swarovski did when introducing even more expensive kit. Us birders could have said "Cor blimey, that's expensive, not on your nelly" so they took a gamble. I would assume that any half decent manufacturer would do product research to determine the expected demand and hence the viability of a product. (Which probably means that they already have, and concluded that it would not sell!)

My own figures for transmission come from the Zeiss site and from figures I have seen elsewhere. I believe ~90% for high quality porro and Abbe-koenig prism binoculars is reasonable and ~86% for a high quality roof prism binocular. Assuming two objective lens elements, 4 eyepiece lens elements, two porro prisms with two air glass surfaces on each, this gives ~16 air glass interfaces. Assuming ~0.5% loss at each air glass surface and zero loss at the prism reflection (total internal reflection is IIRC lossless), leads to ~8% loss. This is not far off the 90% transmission I gave. (I'm talking slightly rough estimates here. I have ignored losses in the glass which I assume to be negligible.) In the case of non-Abbe-Koenig roof prism binoculars there are some reflections off mirrored surfaces which introduce extra losses, and hence the lower value for a roof prism binocular. I suspect the loss is ~1% and I think there are ~5 reflections giving an extra loss of ~5%. Again these are rough back of an envelope figures. Of course you might be better informed than me and hopefully in that case will enlighten me!

Never mind eye-opener, typing the above is rather an eye closer. Especially given the hour!

Leif said:

Again these are rough back of an envelope figures. Of course you might be better informed than me and hopefully in that case will enlighten me!

Never mind eye-opener, typing the above is rather an eye closer. Especially given the hour!

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Many thanks.

Your figures must be very close, and no doubt the transmission figures are reduced as the light diminishes going into the twilight hours. So to achieve over 90% transmission at both day and twilight would be exceptional.

mak said:

Many thanks.

Your figures must be very close, and no doubt the transmission figures are reduced as the light diminishes going into the twilight hours. So to achieve over 90% transmission at both day and twilight would be exceptional.

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I would have used a slightly different method to arrive at them , but I agree with Leif's figures. I've also seen the same Zeiss information on their website. Sometimes the manufacturers seem happy to put a transmission figure in their promotional material. Other times they act like its a big secret.

The best light transmission information I've seen an optics firm provide came from Fujinon in the form of a graph plotting the light transmission curve across the visible spectrum of their 7x50 FMT-SX compared to four other 7x50's, including the current Zeiss 7x50 IF porro. Of course the Fujinon plot looked the best, very linear at around 95% from 680nm to 520nm and still above 90% at 425nm.The Zeiss was second best peaking at 90% around 570nm, but falling to about 75% at 450nm.

I might write this off as so much advertising hyperbole except that in my experience the Fujinon FMT-SX really are as bright as binoculars get and also as color neutral. The Nikon 8x32SE appears to use exactly the same coatings and produces an image that is virtually identical to the Fujinon 8x30 FMT-SX in brightness, contrast and color neutrality.

I'm still a bit skeptical of 95% transmission in a binocular. That's not a bad figure for a complex eyepiece alone. An independent and impartial test of the same sort would be very interesting. Henry

henry link said:

Sometimes the manufacturers seem happy to put a transmission figure in their promotional material. Other times they act like its a big secret. Henry

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I am sure that the manufacturers would not show their transmission figures, if it showed that their binocular was not as high as their competitors.

It would be interesting, especially for users with tinted specs (Product X is best and always will be, because everyone says so mentality (or loyalty)) to see that their binocular is not as good as everyone thinks it is. Yes I know that the binocular most suitable to the individual is best, but it would show how good a companies marketing message is, to sell a model that has a low transmission figure.

CDK said:

I am sure that the manufacturers would not show their transmission figures, if it showed that their binocular was not as high as their competitors.

It would be interesting, especially for users with tinted specs (Product X is best and always will be, because everyone says so mentality (or loyalty)) to see that their binocular is not as good as everyone thinks it is. Yes I know that the binocular most suitable to the individual is best, but it would show how good a companies marketing message is, to sell a model that has a low transmission figure.

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That's true, but transmission is only one of many factors that determine how well an optic will perform. Contrast and resolving power are also important and vary greatly between instruments. Even resolving power is not as simple as might be thought as it varies with image contrast. [Note added later: I originally said 'image brightness' which was an accident. I meant to type 'image contrast'.] One characteristic of a quality instrument is high resolution even in low contrast lighting. (I suspect Henry will have something to say on this, given his astronomical interests.)

Incidentally several people have mentioned that the Zeiss 85 FL is class leading in terms of brightness and sharpness. However Stephen Ingraham mentioned that the resolution of the Zeiss and the Swaro 85 HD were in low light comparable, due to the superior contrast of the latter.

Some camera manufacturers - e.g. Canon - publish calculated MTF curves for their photographic lenses. These give an idea of the optical performance of each lens. 'Sports optics' manufacturers could also do this and the results would probably be a real 'eye-opener'.