fixed 30x sw brightness (1 Viewer)

henry link said:

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

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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.

henry link said:

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

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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.

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.

Eye relief 30x

What about ease of view / eye relief esp for glasses wearers.

Scarletmacawdad said:

What about ease of view / eye relief esp for glasses wearers.

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I am far-sighted in my viewing eye with a +2 dioptre correction, so I need more eye relief than the short-sighted. Nevertheless, I extend the eyecup of the 30x W by a couple of mm when viewing with glasses and can still see the field stop. Viewing comfort is excellent.

John

Thank you all!