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Old Wednesday 19th October 2016, 19:45   #1
Fedster
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fixed 30x sw brightness

Hi All,

aside from birding I enjoy looking at mammals. Mammals are often crepuscular, and thus I use either 10x56 or 8x42 binoculars to observe them. I also have a Swaro STS 65 HD with the 25-50 wide zoom. My problem with the spotter is that is is nowhere as bright as the binos (which is not a surprise just by calculating the pupil size). Nevertheless I was wondering whether anybody had direct experience comparing the 25-50 wide zoom to the fixed 30x SW eyepiece, in case the fixed 30 is brighter than the zoom, especially in fading light. If that is the case it might be worth for me to get a used fixed eyepiece for twilight spotting (I mentioned the 30 because the 45 would be darker and greater reach means nothing if cannot see...).

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Old Wednesday 19th October 2016, 20:46   #2
SteveClifton
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Can't comment on the relative brightness, but Swaro also used to make a fixed 20x SW eyepiece. Now discontinued but still available used.
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Old Wednesday 19th October 2016, 20:53   #3
Fedster
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Can't comment on the relative brightness, but Swaro also used to make a fixed 20x SW eyepiece. Now discontinued but still available used.
I read about the 20 though I was thinking the 30 would (possibly) be the best compromise between magnification and brightness.
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Old Wednesday 19th October 2016, 22:29   #4
jring
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Hi,

forget about the 30 fixed with a 2mm exit pupil being anywhere near as bright as big bins with over 5mm in anything than bright sunlight. If you want that, you either need to reduce magnification to 15x (20x might come close since the larger objective means that more light is concentrated into the exit pupil) or increase aperture quite a bit.

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Old Wednesday 19th October 2016, 22:36   #5
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You have to consider the twilight effect also. Where mag plays a role helping the decreasing resolution in the eye in low light.
I definitely "see more" with my scope (25-50x + ATS65) than with my bins in low light.
Don't think the 30x would add much in transmission (might even be worse with older coatings...). And EP will be smaller than at 25x.
The 20-60x zoom might help with relative brightness a bit at 20x, but not sure how many minutes of viewing you will get extra. And it's not even a full f-stop (56%) so it might not even be noticeable.
When it comes to transmission the Swaro scopes are very good, 85% and quite flat transmission curve. Very good in blue/violet spectrum that is important in twilight.

Last edited by Vespobuteo : Wednesday 19th October 2016 at 22:42.
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Old Thursday 20th October 2016, 08:44   #6
Fedster
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You have to consider the twilight effect also. Where mag plays a role helping the decreasing resolution in the eye in low light.
I definitely "see more" with my scope (25-50x + ATS65) than with my bins in low light.
Don't think the 30x would add much in transmission (might even be worse with older coatings...). And EP will be smaller than at 25x.
The 20-60x zoom might help with relative brightness a bit at 20x, but not sure how many minutes of viewing you will get extra. And it's not even a full f-stop (56%) so it might not even be noticeable.
When it comes to transmission the Swaro scopes are very good, 85% and quite flat transmission curve. Very good in blue/violet spectrum that is important in twilight.
would you say going up from a 65 to an 80 would make a huge difference? I hike a lot and while it's a difference of 300 grams and 3 cm in length, the lighter and more compact the better for me -- I would need a very obvious improvement in low light performance to justify the kerfuffle of selling a body/buying another one and carting around the extra weight.
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Old Thursday 20th October 2016, 10:59   #7
Vespobuteo
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would you say going up from a 65 to an 80 would make a huge difference? I hike a lot and while it's a difference of 300 grams and 3 cm in length, the lighter and more compact the better for me -- I would need a very obvious improvement in low light performance to justify the kerfuffle of selling a body/buying another one and carting around the extra weight.
With the 80mm scope you will get the same exit pupil (1.6mm) @50x as the 65mm scope have @40x (same relative brightness). So the 80mm will be more slightly more usable at 50x.

It's not a huge increase IMO (1/2 stop of light). For me it was not enough so I went with the more compact and lighter 65mm.

But I think you have to try to see for yourself. You might experiment by cutting out a 53mm hole in cardboard and put it infront of your lens. The you get that 1/2 stop difference compared to 65mm. Or just zoom up from 25x to 30x-31x, the exit aperture difference would be about the same. The current light level and your eye pupil size will affect the result of course.

I might consider a larger scope some day, for more stationary use, but then I will get a 88mm+ scope.

Last edited by Vespobuteo : Thursday 20th October 2016 at 11:08.
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Old Thursday 20th October 2016, 22:12   #8
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I did a test tonight 30 minutes after sunset and I did not perceive any dimming between 25 and 40 (the magnifications I would most likely use to look at mammals at sunset). I will ask around friends to see if there is a Swaro 80 to directly compare with, but I am quite happy with what I have.

Now if I could figure out the best harness I can make for the scope to use with the Y stick (http://www.birdforum.net/showthread.php?t=332193)...
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Old Friday 21st October 2016, 08:50   #9
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The swaro 65 has the same focal distance as the 80,with a much smaller objective...Its aperture value is f/7.4 versus f/6 for the 80 mm...the swaro is one of the few makers,with nikon and dont know if others,that designed their 65 model to grant high magnification at the price of relative brightness ..most mid size scopes stay at the f/6 value reducing the magnification of the zoom ,usually from 20-60 to 15-45...So if a very portable scope is a must and low light viewing is going to be its main use,another 65 mm model could be more convenient,in theory...
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Old Friday 21st October 2016, 08:56   #10
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The swaro 65 has the same focal distance as the 80,with a much smaller objective...Its aperture value is f/7.4 versus f/6 for the 80 mm...the swaro is one of the few makers,with nikon and dont know if others,that designed their 65 model to grant high magnification at the price of relative brightness ..most mid size scopes stay at the f/6 value reducing the magnification of the zoom ,usually from 20-60 to 15-45...So if a very portable scope is a must and low light viewing is going to be its main use,another 65 mm model could be more convenient,in theory...
Thanks for the info! I presume Swaro aims at birders first and foremost, who are more likely to use their spotters in decent light. Having said that it seems to be just a matter of magnification -- if the Swaro had a lower magnification eyepiece it would most likely do as well or better than otehr scopes.

One question: how do I get info on the F stop values for scopes? it's an info I do not seem to find.
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Old Friday 21st October 2016, 21:54   #11
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The swaro 65 has the same focal distance as the 80,with a much smaller objective...Its aperture value is f/7.4 versus f/6 for the 80 mm...the swaro is one of the few makers,with nikon and dont know if others,that designed their 65 model to grant high magnification at the price of relative brightness ..most mid size scopes stay at the f/6 value reducing the magnification of the zoom ,usually from 20-60 to 15-45...So if a very portable scope is a must and low light viewing is going to be its main use,another 65 mm model could be more convenient,in theory...
At 25x the relative brightness will be the same for all 65 mm scopes...
The swaro 20-60x zoom is an alternative if you want a larger exit pupil.
But the twilight factor says higher mag will help..

Swaro scopes have the highest transmission in the blue/violet spectrum in the class,
important for mesopic (low light) vision.

http://www.houseofoutdoor.com/testra...telescopen.pdf

Last edited by Vespobuteo : Friday 21st October 2016 at 22:10.
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Old Friday 21st October 2016, 22:24   #12
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Originally Posted by Vespobuteo View Post
At 25x the relative brightness will be the same for all 65 mm scopes...
The swaro 20-60x zoom is an alternative if you want a larger exit pupil.
But the twilight factor says higher mag will help..

Swaro scopes have the highest transmission in the blue/violet spectrum in the class,
important for mesopic (low light) vision.

http://www.houseofoutdoor.com/testra...telescopen.pdf
I tried the 20-60 eyepiece but the FOV is far too narrow for me -- I hated it.
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Old Friday 21st October 2016, 22:44   #13
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One question: how do I get info on the F stop values for scopes? it's an info I do not seem to find.
Hi,

the focal ratio, as it's called with telescopes is again focal length divided by aperture - in this case of the objective lens and not some diaphragm.

Since the focal length of a body is often unknown with spotters, it is not that easy to determine - sometimes it can be found by searching the web, sometimes educated guesses help (standard zooms with 3x zoom range are usually 8-24 or less frequently 7-21mm) and sometimes there's little hints like the number in the Kowa fixed mag eyepiece type names is the EP focal length which allows together with the known magnification in some body to calculate its focal length - Fep * Mag = Fbody.

The ATS bodies have a focal length of 460mm which makes the ATS65 a rather relaxed f7 while the ATS80 is quite fast for an ED doublet at f5.7. The smaller instrument will have better color correction and less problems with axial CA at the high end of the zoom range. On the other hand there's more light and higher resolution due to the bigger aperture - pick your poison...

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Old Friday 21st October 2016, 22:47   #14
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Thanks for the info! I presume Swaro aims at birders first and foremost, who are more likely to use their spotters in decent light. Having said that it seems to be just a matter of magnification -- if the Swaro had a lower magnification eyepiece it would most likely do as well or better than otehr scopes.

One question: how do I get info on the F stop values for scopes? it's an info I do not seem to find.
Yes, scopes are most likely optimized for daylight viewing, a too large exit pupil is not of any benefit in day light as your current eye pupil size sets the limit for how much light reaches the retina. Around 3 mm seem to be the "optimal".

Last edited by Vespobuteo : Friday 21st October 2016 at 22:56.
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Old Friday 21st October 2016, 22:54   #15
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The ATS bodies have a focal length of 460mm which makes the ATS65 a rather relaxed f7 while the ATS80 is quite fast for an ED doublet at f5.7. The smaller instrument will have better color correction and less problems with axial CA at the high end of the zoom range. On the other hand there's more light and higher resolution due to the bigger aperture - pick your poison...

Joachim
Lower CA was one of the reasons I picked the 65mm over the 80mm.
In larger scopes, I actually prefer the Kowas for the superior CA correction.

Last edited by Vespobuteo : Friday 21st October 2016 at 23:16.
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Old Friday 21st October 2016, 23:15   #16
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I tried the 20-60 eyepiece but the FOV is far too narrow for me -- I hated it.

Hate is a strong word...but I agree that the view is more tube-like in the 20-60x.
Wide angle zooms like the 25-50x have a more immersive view.
The AFOV in the 25-50x is pretty much perfect for my taste.

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Old Saturday 22nd October 2016, 09:35   #17
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Lower CA was one of the reasons I picked the 65mm over the 80mm.
In larger scopes, I actually prefer the Kowas for the superior CA correction.
Yes, with a CaF2 doublet f5.5 or so still works pretty well - I love my old Kowa too.

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Old Tuesday 25th October 2016, 12:56   #18
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A colleague who owns a 30xSW just told me it is much brighter than either 25-50 or 20-60 zooms. As he owns a 80 ATS HD and the full set of optics we are going to do a side-by-side dusk brightness test late in November (because we can do the tests just after work...). I will report back.
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Old Wednesday 26th October 2016, 01:29   #19
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Fedster,

I owned both the 30x and the 20x60x zoom for several years (I still have the 30x). I spent quite a bit of time trying to determine if the 30x had any optical advantage over the zoom set at 30x, besides the obviously wider field and longer eye relief. My eyepieces were bought about the same time, so they came with the same generation of Swarovski coatings.

Extensive side by side testing convinced me that the 30x was not perceptibly brighter than the 20-60x set at 30x. How could the 30x have been "much brighter"? Both eyepieces had the same coatings and the same number of lens elements. The 20-60x zoom is at a very slight disadvantage because its seven elements are in five groups rather than the 30x's four groups, but the two extra glass/air surfaces couldn't possibly reduce its light transmission by more than 1% compared to the 30x, probably less.

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Old Wednesday 26th October 2016, 07:08   #20
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Hi Henry,

thanks - that's what I see with my Kowa too - exit pupil wins, coatings second and number of elements is not very noticeable. There's a good reason why spotter manufacturers with good wide-angle zooms discontinue the 30 wide EPs.

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Old Wednesday 26th October 2016, 09:28   #21
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Fedster,

I owned both the 30x and the 20x60x zoom for several years (I still have the 30x). I spent quite a bit of time trying to determine if the 30x had any optical advantage over the zoom set at 30x, besides the obviously wider field and longer eye relief. My eyepieces were bought about the same time, so they came with the same generation of Swarovski coatings.

Extensive side by side testing convinced me that the 30x was not perceptibly brighter than the 20-60x set at 30x. How could the 30x have been "much brighter"? Both eyepieces had the same coatings and the same number of lens elements. The 20-60x zoom is at a very slight disadvantage because its seven elements are in five groups rather than the 30x's four groups, but the two extra glass/air surfaces couldn't possibly reduce its light transmission by more than 1% compared to the 30x, probably less.

Henry
Well, I am reporting something I was told (please note that the colleague in question is an experienced birder -- he is in fact making a living out of it in a way -- hence why I take his opinion seriously). That's why I mentioned we are going to do side by side testing in poor light[1] to sort the issue out!

[1] poor light brightness is the only thing I care about -- for midday birding the 25-50 is perfectly fine.
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Old Wednesday 26th October 2016, 09:33   #22
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Fedster,

I owned both the 30x and the 20x60x zoom for several years (I still have the 30x). I spent quite a bit of time trying to determine if the 30x had any optical advantage over the zoom set at 30x, besides the obviously wider field and longer eye relief. My eyepieces were bought about the same time, so they came with the same generation of Swarovski coatings.

Extensive side by side testing convinced me that the 30x was not perceptibly brighter than the 20-60x set at 30x. How could the 30x have been "much brighter"? Both eyepieces had the same coatings and the same number of lens elements. The 20-60x zoom is at a very slight disadvantage because its seven elements are in five groups rather than the 30x's four groups, but the two extra glass/air surfaces couldn't possibly reduce its light transmission by more than 1% compared to the 30x, probably less.

Henry
Incidentally I do not mean to discount your experience and I value your feedback -- it is perfectly possible that I will not see any perceivable difference between the fixed 30 and the zoom set at 30 in terms of brightness (in the same way I might feel that any brightness advantage of the 80 vs 65 body is not worth the extra weight)...

A used 30xSW is still a good deal of cash so I'm not desperate to impoverish myself to get a trivial benefit in terms of low light visibility.
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Old Saturday 10th December 2016, 17:14   #23
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Hi All, apologies for the long delay but I did check. Specifically I used a Swarovski ATS 80 HD bought in ~2006 and a 30 SW eyepiece (date unknown).

1) I did not detect any brightness difference on my 65HD or on the 80HD at 30x irrespective of whether I was using the 25-50 eyepiece at 30x or the fixed 30x
2) In fading light, looking at a 50x50 cm square white sign (at the back of it, at ~ 800 metres) I stopped being able to tell whether I was properly focused on it or not with the 65HD while at the same time I could see the white square clearly (and see if I was properly focused on it or not) with the 80HD -- so the larger front lens did make a difference I could perceive.

Conclusion: the fixed eyepiece did not give any advantage while the larger front lens did.

My experience also showed me that past a given (not measured alas) point in terms of available light both scopes were equally good or bad -- it was really a matter of fading light after the sunset that made me see a difference.
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