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Old Wednesday 10th October 2012, 23:58   #1
henry link
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Resolution and Star Tests of ATX Scopes

I had an opportunity to do resolution and star tests of several ATX modules in a store recently. Three objective modules were available (two 85mm and one 95mm) and two prism/eyepiece modules. I set up a USAF 1951 resolution chart and an artificial star and, for comparison, I brought along a reference scope with essentially perfect optics, an Astro-Physics 92mm Stowaway APO. For testing purposes I was able to boost magnifications up to 180x (85mm) and 210x (95mm) using a Zeiss Tripler, which happily fits the ATX eyecup perfectly with the FL binocular eyecup adapter.

When star tested all three of the objective modules proved to be very well corrected for spherical aberration, probably around 1/6 wave. In my experience thatís considerably better than the average expensive spotting scope specimen. In fact itís close to cherry territory, which I wouldnít expect from three randomly selected samples. The 85mm modules showed a little more chromatic aberration in out of focus diffraction patterns, which fits logically with their slightly lower focal ratio.

There were some minor optical defects in each of the objective modules. All were slightly comatic and the 95mm also showed some astigmatism and pinching. None of the defects appeared to be associated with the prism modules. Each objective showed the same defects regardless of which prism it was matched with.

Since they were pretty mild and the spherical correction was good the defects didnít appear to have much effect on the resolving power. The 95mm could resolve the same element on the USAF chart as the Astro-Physics Stowaway though not as cleanly. I wasnít able to easily move the scopes for a more precise measurement, but I would estimate that this particular 95mmís resolution falls between 1.25-1.3 arc seconds. Both 85ís resolved one element larger, about 1.4-1.45 arc seconds. These are very good figures for spotting scopes. The 95 has the best raw resolution Iíve measured for a birding scope although itís no better per mm of aperture than the best Kowa 883 Iíve seen. A 95mm module this good without any astigmatism would probably do a little better.

I didnít have time to test any eyepiece characteristics, but I found the new zoom very comfortable to use, with none of the blackout problems Iíve experience with the 25-50x Swarovski zoom. The zoom ring was a bit harder to turn than the focusing ring, but its motion is smooth enough. In the latest scope catalogue I notice that Swarovski claims that the difference in effort is intentional to make it easy to differentiate between the focusing and zoom rings by feel alone.

Overall, it looks to me like Swarovski has, once again, come up with some very desirable new products. Even if the modular feature (which doesnít interest me at all) is ignored, this specimen of the 95mm ATX is the most optically capable spotting scope Iíve seen thanks to its large aperture, low aberrations, high resolution and a wide angle zoom eyepiece with (almost) enough magnification to show the full resolving power.
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Old Friday 12th October 2012, 09:06   #2
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Henry,

Thanks for your careful observations. I'll add some of my own experiences with these scopes, these are from a few weeks back and you have read them already but other readers on BF have not.

"On monday and tuesday I got to try these at the local shop. We had the 95 set up on an outdoor balcony with some views extending a mile-and-a-half, alongside with my Nikon ED 82 A and a very good sample of the Zeiss 85 older FL with a 20-75x zoom. Later, we had these and a Kowa 883 on the yard, with some resolution charts posted on a pole nearby. In this latter setting, we also tried the 65 & 85mm front ends, and did a sloppy "NEED" -test where we just quick & dirty set each scope standing at the distance from the chart where we could just resolve a particular pattern of lines in four different orientations. (The target was Jan M:s photochart I have).

The short story is that the ATX is very impressive, and the 95mm front-end certainly works well. It was undoubtedly the best scope there, and the difference in resolution, brightness and color was quite obvious. Unfortunately, a proper star-test was not possible due to a lack of a suitable glitter point. The best I could find was a reflection from a chromed bicycle part about 30 meters away, but there was enough heat haze to prevent fine analysis. However, the 95 front end/ATX body we had showed very good star-test performance for a Swaro, with good symmetry inside and out, with easily visible ring patterns on either side. The contrast of the rings was not quite as good as in the best scopes I have seen, including mine, but much better than usual. Best focus pattern was a bit difficult to assess due to the conditions, but seemed very good, with perhaps a wee bit more flare than there should be, but essentially with an Airy disk and a first diffraction ring visible. Of astigmatism, I cannot say whether there was a bit or none, but certainly not more than a bit. Both the 65 and especially the 85 pretty clearly showed some moderate decentring in ring patterns, and relative to the other scopes did less well than the big monster.

On the test target, at identical distance, the 95 resolved 1-2 patterns better than the other scopes, mostly one step, but the separation of the lines in the finest resolvable pattern was much easier to discern than in the other scopes. The image also looked very clean. Brightness at maximum magnification was very impressive, and in a flock of wagtails and yellow wagtails on a field some 600m away, picking up birds that did not happen to move was clearly easier in the 95. I tried to assess the maximum magnification against the Nikon's 75x by seeing what the booster field incorporated through both, and the Swaro at max was very similar, only a hair wider, so it seemed that my guess of ca 72x is probably pretty close. Anyway, it was clear that the Swaro at max shows more than the Nikon (or Zeiss) at 75, the only question is whether it shows as much more as it should given the aperture difference.

The eyepiece gives a very good and expansive view, but feels very similar to the Swaro 25-50x WA zoom in that it is somewhat critical of proper eye-placement and kidney-beans a bit more easily than most. Zoom control is somewhat stiff and takes unnecessarily much twisting between the extremes. Since it is not crucial to zoom to an accurately defined magnification between the extremes, a faster gearing would be welcome. Focus was very smooth and precise, with a decidedly low gearing which in my view suits a high-magnification scope well. it takes almost three full rotations of the collar to go from minimum (which was probably under four meters) to maximum (beyond infinity), but the first two rotations are for the first five-seven meters. Focusing from 30m to infinity is plenty fast enough, while there is enough rotation needed for fine-tuning at distance that you don't have to play infuriating "nudge back-and-forth" games with it. The scope is well balanced and does not feel as big as it is. Weight was some 40g over the specified."


"Have now seen two more 85's and one more 95 ATX.

Image quality in the second 95 looked just as good if not a bit better even than in the first 95. I only tested it indoors today, at the shop where I don't know the exact distance to the target. The target is the Edmunds glass slide, mounted in front of a white sheet of paper (but not against it) with a window behind and a halogen desk light illuminating the slide from about a 40 degree angle from the front, about a foot from the slide. They have used this setup to check a lot of scopes, and I have checked perhaps a half-dozen there this way. Kowa 883's can let you see the orientation of the line pattern in group 3/elemnt 6 there providing the sample is good, but only barely. Other scopes are considered good samples if they make 3/5. The 95 makes 3/6 easy, and 4/1 can be resolved to my standard of what I consider resolved. The 85 there today struggled with 3/5 but resolved it. My Nikon (did not have it today) has also barely resolved the 3/6 there. Unboosted star-testing with giny glitter points on a chrystal/gold Swarovski miniature binocular bling-bling item showed ecellent symmetry in diffraction patterns, easily discernible rings either side of focus already at 2-3 rings, and no other defects besides some triangularity that resembles slight pinching, but fortunately with no flare from the roundish corners. Trying the same objective with the back that came with the 85 added an ever so slight bit of astigmatism, just enough to prevent seeing the orientation of the horizontal 4/1, and made the focus a tad more difficult to achieve. The 85 showed a more messy diffraction pattern, but still good by most standards. The 85 that I saw at another store last Thursday was significantly better, about as good relatively speaking as the two 95's. All of the ATX's I've been able to look at diffraction-patterns with have exhibited tiny amounts of coma as well, but in only one 85mm was it enough to begin to compromise the image a little."

So, my observations are very similar to yours, and put together they give a very favorable first impression of the general quality of these unusually complex scopes. I was certainly worried about excessive sample differences, but our admittedly small sample has not yet included any lemons.

Kimmo
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Old Friday 12th October 2012, 10:21   #3
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Henry and Kimmo,
We calculated the real magnification of the ATX-85 and ATX-95 from the sample that we received for a very short time:
ATX-85: 25x=24,2x and 60x=58,5x
ATX-95: 30x=27,9x and 70x=73x
Gijs
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Old Friday 12th October 2012, 10:35   #4
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Henry,

...our admittedly small sample has not yet included any lemons.

Kimmo
This is good news all round. I can add the 85mm sample I have seen at my at my local reserve shop as being also certainly not a lemon. I don't think I can see all I need to when star testing and need a booster/camera but from what I could see,it showed a good centred pattern both sides of focus. I personally found the eyepiece easier to use than the 25-50 zoom.

Not that I can see myself upgrading anytime soon but is there a cheap booster available to use on scopes for testing or would it be cheaper to get a cheapish compact to examine diffraction patterns?
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Old Friday 12th October 2012, 11:19   #5
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Allthough I have already mentioned some of our data in another discussion topic, it may be worthwile to repeat them here:

Our measured light transmissions:
ATX 85: 500nm= 86,2%, 550 nm=86,9%. Values in Swarovski flyer: 86%
ATX 95: 500 nm=86,2%, 550 nm= 87,6%. Values in Swarovski flyer: 86%
From these values a perfect colour reproduction is to be expected, which is confirmed by visual observations.

Weights:
ATX 85: 1931 g. Value in Swarovski flyer 1910 g
ATX 95: 2194 g. Value in Swarovski flyer 2150 g

Gijs
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Old Friday 12th October 2012, 11:42   #6
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Kimmo,

Thanks for posting your experiences.

Gijs,

Something might to be off with the magnification measurements. Shouldn't the zoom ratios be identical?

dipped,

I'd go for the Bushnell doubler. To my knowledge it's the only inexpensive booster with phase coating.

Henry
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Old Friday 12th October 2012, 17:28   #7
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Henry,
I looked into the measurements again, but I can not make anything else of it.
Gijs
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Old Friday 12th October 2012, 20:00   #8
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Gijs,

I must assume there is a margin of error in the magnification measurements. From the numbers you give, the 95 would have a ratio of 2.616 between the lowest and the highest magnification, and the 85 would have a ratio of 2.417. Since the eyepiece is identical, the ratio should be identical as well. Or, if you used a different prism/eyepiece assembly for the two objectives, then there would need to be a rather large difference in the zoom ratios of the two eyepiece modules.

Just out of curiosity, what is the method you use for determining the exact magnifications?

Kimmo
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Old Friday 12th October 2012, 20:22   #9
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Kimmo,
I use an electronic ruler to measure the objective diameter 9accuracy 0,01 mm) and a compact measuring telescope (Ramsden dynameter among others described in "Lehrbuch der praktischen Physik" by F. Kohlrausch, 16th edition, page 361), which has a built-in micrometer to measure the width of the exit pupil. The instrument is also suited to measure the eyerelief of a binocular. (The measurement set-up is placed on an optical bench for optimal stability during the measurements). The dynameter is especially constructed for that purpose by an optical company, which was specialised in the production of binoculars and microscopes. With the measured values one can calculate the magnification.
Gijs
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Old Friday 12th October 2012, 20:37   #10
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Gijs,

Sounds convincing, assuming that the objective diameter that you get this way is the effective objective diameter and not just the diameter of the exposed glass of the objective front element. For most top-quality scopes, these two are the same, but it is not a given, since there may be an internal obstruction that makes the effective aperture smaller than the front lens diameter.

But, assuming that there is no mistake in your measurements, how do you explain the difference in zoom ratios? Did you measure each objective with the same or a different eyepiece/prism unit?

I'm not trying to criticize your work by any means, only trying to understand a finding that is contrary to my expectations and for which I don't know the explanation. Moreover, if it did turn out that some of the zoom/prism units had a zoom ratio of 2.6x and others only 2.4x (as calculated from your magnification results for the two tested scopes), I would surely want to get a 2.6x one, and I would probably not be the only one.

Kimmo

Last edited by kabsetz : Friday 12th October 2012 at 20:39. Reason: Additional info
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Old Friday 12th October 2012, 20:59   #11
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Kimmo,
I used the same prism unit for the ATX-95 and the ATX-85. And I looked as carefully as I could to measure the real optical opening of the objective. Of course there is a level of uncertainty in the measurements. The electronic ruler has an accuracy of +/- 0,01mm and the Ramsden dynameter of +/- 0,05 mm. I have no explanation for the difference in zoom ratio's, I take it as measured. I do not take your questions as criticism I understand why you ask since it is puzzling.
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Old Friday 12th October 2012, 21:08   #12
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I don't know how I missed this thread Wed and Thursday. I sure would like to visit proudpapa56 about now. I just read that he sold the only 95mm in Central Pa., to a long range shooter at that. I can understand the fellow wanting the 95mm scope for that use.
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Old Friday 12th October 2012, 22:00   #13
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Originally Posted by Gijs van Ginkel View Post
Kimmo,
I used the same prism unit for the ATX-95 and the ATX-85. And I looked as carefully as I could to measure the real optical opening of the objective. Of course there is a level of uncertainty in the measurements. The electronic ruler has an accuracy of +/- 0,01mm and the Ramsden dynameter of +/- 0,05 mm. I have no explanation for the difference in zoom ratio's, I take it as measured. I do not take your questions as criticism I understand why you ask since it is puzzling.
Perhaps neither or only one scope was pre-focused at infinity when the exit pupil measurement was made?
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Old Saturday 13th October 2012, 07:02   #14
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Kimmo and other readers,
I looked in my notes from the magnification measurements of the ATX telescopes and the calculations were OK. However it is possible that I made a reading error of the micrometer,used to determine the size of the exit pupil since reading the smallest values can be tricky if the telescope with its 45 degree configuration is not perfectly aligned with the measuring setup and a reading error of 0,1 mm in the small exit pupils is already sufficient to explain the difference in zoom ratio. I will check that. To avoid lengthy discussions on this forum I propose therefore that my data on the measured magnifications are ignored until I have repeated the measurements to be absolutely sure.
That may take some time, since it is not easy to get hold of the telescopes long enough to do these measurements.
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Old Saturday 13th October 2012, 07:58   #15
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Gijs,

Thanks for the explanation. As you used the same prism back for both, it seems that margins of error in the measurement are the likely explaining factor for the differences in magnification ratios. I'll see if I can get around to doing some magnification measurements next week. I will use a measurement of booster field-of-view through the telescope at constant distance from front lens to a ruler, which will yield a very accurate magnification ratio result and allow comparing magnifications between different scopes, but getting a precise figure for what the actual magnification is, is not quite so accurate. If I get this done, I'll post the results here.

For checking the real aperture of binoculars and scopes, I have been using a simple but effective method described some years back by J-C Bouguet on these forums, where you place an adjustable rectangular obstruction centrally over the objective lens and determine what is the width of the obstruction that just stops the exit pupil. If the obstruction is even a millimeter narrower than the true aperture, you will see a sliver of the exit pupil on both sides of the obstruction when you view the exit pupil axially about a foot or more from the eyepiece. I have found this method cheap, fast, easy and repeatable. Will do this to the ATX's also.

Kimmo
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Old Saturday 13th October 2012, 14:12   #16
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dipped,

I'd go for the Bushnell doubler. To my knowledge it's the only inexpensive booster with phase coating.

Henry
Thanks Henry, I'll have a look out for it in the UK though one retailer was quoting over £250 - not exactly cheap in my book!
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Old Saturday 13th October 2012, 16:55   #17
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dipped,

Looks like it's discontinued. See this thread:

http://www.birdforum.net/showthread.php?t=214376
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Old Sunday 14th October 2012, 16:39   #18
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Perhaps neither or only one scope was pre-focused at infinity when the exit pupil measurement was made?
That's a good advice. Such measurements should be always done with the instruments pre-focused at infinity.

BTW, thanks to Gijs and Henry for providing such informations of high interest.

Steve

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Old Monday 15th October 2012, 21:04   #19
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Gijs, Henry, all interested parties,

Today I went and did the measurements explained in post #15 above. One prism unit, one 85mm objective module and one 95mm objective module & my Nikon ED 82 A with a 25-75x zoom EP as a reference.

The short version is that these measurements confirm most of Swarovski's specs, the only notable exception being the maximum magnification of the 95mm unit, which is ca. 72x rather than 70x.

For the more detail-oriented readers: I first measured the effective apertures of the two objective units. The scopes were focused at 200m. For the 95mm, the reading I got was between 94 and 94.5mm, and for the 85mm between 84 and 84.5mm. These measurements were done with good time and several repeat measurements, and have a margin of error I would estimate at 0.5mm. To me, they mean that the effective aperture is essentially as specified, possibly about 1% smaller, but that could very well be a result of this unconventional measuring method.

For the magnification measurements, I had a steel millimeter ruler placed perpendicular to the optical axis ca. 10 meters from the telescope front lens, each scope taking their turn for the same spot. I then measured the number of millimeters visible within the field stop of a 3x Zeiss auxiliary telescope attached to the eyepiece. This was measured both for the minimum and for the maximum zoom setting for all three scopes. For the Nikon @25x nominal magnification, the visible field was 81mm and for 75x 26.5-27mm. For ATX 85, @ 25x nominal, the visible field through the booster was 80.5-81mm and at nominal maximum magnification of 60x 33.5-34mm. For ATX 95, 68mm at minimum X and 28mm at maximum X. The alternative readings represent my best efforts of rounding to the closest 0.5mm on a ruler that has markings at 1mm intervals, and below I have given the calculations for all the taken readings.

The zoom ratio that can be calculated from these results for the Nikon is 81/27=3 (81/26.5=3.06) and for the Swaro ATX 85 it ranges between 2.37 and 2.42. The ATX 95 figures yield a zoom ratio of 2.39-2.43.

To me, these results leave the specified zoom ratios of these scopes (3x /25-75x for the Nikon and 2.4x/25-60x for the ATX 85) comfortably in the very middle of the probable margins of measurement error. Also, the 25x of the Nikon is essentially the same as the 25x of the Swaro. In order to have been able to measure the exact magnifications, I would have needed to set up a much wider measurement track for measuring the field width of the 3x booster alone at an identical distance, and that was impractical today.

For the ATX 95, the math gives a minimum magnification of 29.6-29.8x and maximum of 71-72.8x. Again, this is in good accordance with all the other measurements and supports the specified 30x-70x figures except that, since the zoom ratio must remain constant irrespective of the objective unit, the maximum magnification is ca. 72x (30x2.4=72x), not 70. For those who object that the minimum magnification figure I got for the ATX 95 is too low, I will point out that a 0.5mm lower reading for the minimum magnification booster field width would have given exactly 30x to the 25x of the other two scopes, so it is also comfortably within possible margins of measurement error.

Hope this helps and is of interest to you.

- Kimmo
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Old Wednesday 17th October 2012, 12:24   #20
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Kimmo, Henry and other readers,
As promised I have remeasured the magnification values of the Swarovski ATX telescopes using the measuring set-up described in post 9. The set-up was modified in that sense that the telescopes and the measuring equipment were perfecty aligned on an optical bench construction and the construction allowed a high degree of reproducibility. Moreover the readiblity of the scale of the measuring microscope(or telescope as I called it before) was enhanced, by using a magnifier.
Altogether six instruments were investigated each with its own prism/eyepiece module.
Alle measurements were performed with the telescopes put at infinity and at close focus.
No difference in the values of the objective diameter or diameter of the exit pupils was found between close focus or infinity and as a consequence the magnification values were the same wether we put the telescopes at infinty or at close focus.

ATX-95 nr.1:
30=29,7x and 70x=70,3x and zoomratio 2,37
ATX-95 nr. 2:
30x= 29,5x and 70x=70,3x and zoomratio = 2,38

ATX-85 nr. 1
25x=24,6x and 60x= 60,6x and zoomratio = 2,46
ATX-85 nr. 2
25x= 24,8x and 60x= 59,8x and zoomratio 2,41

ATX-65 nr 1:
25x=24,5x and 60x=59,0x and zoomratio = 2,41
ATX-65 nr.2
25x=24,8x and 60x= 59,0x and zoomratio = 2,38

These values are circling around a zoom ratio of 2,4 and, considering the uncertainty in the measurements, which will be in the range of +/- 3% it seems to me, that the quality control by Swarovski is allright.
Gijs
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Old Wednesday 17th October 2012, 14:10   #21
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Off topic. I so envy you the Astro-Physics Stowaway.
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Old Wednesday 17th October 2012, 14:36   #22
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Michaelboustead,
I am not bright enough to get your point.
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Old Wednesday 17th October 2012, 16:53   #23
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Kimmo and Gijs,

Thanks for your efforts. I think we can now almost put to rest the question of magnification variations in the different models. I say almost because it would still be interesting to see how the ATX-95 Nr.1 and ATX-85 Nr.1 in Gijs' tests would measure with their eyepiece modules exchanged.

Gijs, I think Michael is referring to the scope I mentioned in my first post. If you're not familiar with it, Astro-Physics is a small company in Illinois owned by the master telescope maker Roland Christen. He produces some of the world's best astronomical APO's. Production numbers are very small, so to buy a scope you must place yourself on a waiting list and be prepared to wait for at least several years.

Henry
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Old Wednesday 17th October 2012, 17:10   #24
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Henry,
Thank you, I did not know the company Astro-Physics.
If I have time left I will see what happens when the eyepiece models of the ATX number 1 measurements are exchanged, but I immediately admit that it is not high on my priority list.
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Old Wednesday 17th October 2012, 18:11   #25
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Gijs, Henry,

I noticed there was a slight omission in my data in post #19. The maximum magnification reading for the ATX 95 had a range of 28-28.5mm, not just 28, which is why there was a range for the zoom ratio for that scope also. With single figures, there would of course have been a single zoom ratio.

Gijs,

With your new measurements, and especially taking into account the margin of uncertainty in them, I concur with your conclusion that we may take Swarovski's published data as being accurate. But, since 2.4 x 30 = 72, the maximum magnification figure for the large scope seems to be rounded down in the Swarovski literature.

Thanks for going through the trouble of measuring so many scopes again.

- Kimmo

Last edited by kabsetz : Wednesday 17th October 2012 at 18:12. Reason: addition of essential info
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