New variable eyepiece 20-50x ASPH. (1 Viewer)

Hi !

New on this forum and first message.

Leica annonces a new variable eyepiece : 20-50x WW ASPHERICS.

Which concrete advantages can we hope of this technological option ?
Better resolution, better contrast, better ease of viewing, better flare and backlight properties, wider fields of view, better edge quality ... ?

Cordially yours,
Luc

New variable eyepiece 25-50x ASPH.

Oups... I mean the new variable eyepiece 25-50x ASPH.

But still the same questions...

Cordially yours,
Luc

Luc,

Welcome to Birdforum! I'll open the door to speculations about this very interesting eyepiece by offering a few of my own.

The only concrete advantage that we can be certain about from the specs is that the field of view will be wider than other zooms. As for the other items on your list, we can also be certain that resolution (in the center) will not be any better, because the current high quality zooms are already not limiting factors for resolution. Contrast is unlikely to be significantly better than other equally complex eyepieces with comparable coatings. Flare performance, as in any zoom eyepiece, will mostly depend on how well reflections have been controlled inside the tube and the moving field group at the front end of the eyepiece. The use of an aspheric element may improve the edge quality, but it might just function to keep the quality acceptable at the unusually wide 58-80 degree AFOV.

One thing you didn't mention is eye relief. The spec is 19mm, just like the 20-60x zoom. That is probably the maximum eye relief. All current zoom eyepieces suffer from a considerable dip in eye relief in the middle of the zoom range. We won't know until we see it if this zoom behaves the same way.

Henry

Hi Luc,

A warm welcome to BirdForum from me too.

After Henry's analysis there is not very much more to be analyzed. :t:
From my point of view the wide angle & long eye-relief at 25x has two extremely useful practical implications:
1) for birdwatching you will see more true FOV than with most other zooms at 20x. This makes it easier to get birds into the FOV and at the same time more power helps to ID them (without as much need to zoom in). This IMO is an example where less (zoom range) is more.
2) for digiscoping a long-ER, wide 25x is *very* close to ideal (more power than 20x, but brighter than 30x). It gives large exit pupils, causes very little to no vignetting - and permits the use of many different digital cameras.

Unfortunately and obviously there must have been some compromises made. In this case the large size and slightly lower max power have been the price that has been paid to achieve all the good things at low powers. It is interesting to see whether customers are willing to accept it... I know, I will.

Best regards,

Ilkka

Henry and Ilkka,

Thank you very much for your interesting and detailed answers!

For several years I have tried to find an upgrade to replace my old Optolyth TBS 80 (with a 30X fixed eyepiece).

I tested various kinds of spotting scopes with a zoom in the field and I was particulary impressed by the Swarovski ATS 80 HD and the Nikon 82 ED A.
But unfortunately, I do not like a focusing ring...

Moreover, I always kept in mind a comment of Jan Meijerink on a report published several years ago : "Leica APO Televid 77, Swarowski AT-80 HD and Kowa TSN 823" (www.tvwg.nl, 1998).


[...] "In het algemeen zijn deze diameters te klein om een goed beeld te kunnen geven bij vergrotingen van 60x of meer. De uittreepupil wordt dan kleiner dan ca. 1.5 mm. en dat kijkt onplezierig. Niet alleen komt er weinig licht in het oog, maar ook veroorzaakt de smalle lichtbundel een onrustig beeld. De fysiologie van het menselijk oog gaat meespreken. Elke "ongerechtigheid" in het oog wordt op het netvlies duidelijker zichtbaar, de haarvaten in het vaatvlies worden enigszins zichtbaar en veroorzaken een onrustig beeld. Dit probleem is slechts op te lossen door het toepassen van grotere objectieven met daarbij uiteraard een groter kijkergewicht en -volume, tenzij we overgaan naar spiegeltelescopen, maar die hebben naast een hogere prijs ook andere nadelen (maar ook voordelen).
Dat betekent dat een 50x vergroting bij dit type telescopen het maximaal haalbare is. De 60x geeft dus niet meer informatie dan de 50x. Het beeld wordt wel wat groter, maar tevens onscherper, minder contrastrijk en onrustiger." [...]

In a nutshell, a tube with a diameter of 80mm is generally to small to restore a good image with a magnification of 60x or more. The exit pupil becomes lower than ca. 1.5mm and the image becomes unpleasant and rough/unstable (I don't know the exact term in English) because the light transmission becomes to poor in consideration of the physiology of the human eye.
In conclusion, a magnification of 50x is the maximum usable limit for a 80mm diameter scope. A magnification of 60x does not give more information than a magnification of 50x : the image is bigger but less sharp, less contrasted and more unstable/rough!

According to these comments, a variable eyepiece 25-50x sounds to be a good idea ...

Which are your opinions about the Jan's comments ?

Cordially yours,

Luc

Oups ...

[...] According to these comments, a variable eyepiece 25-50x sounds to be a good idea ... [...]

I mean that such a variable eyepiece 25-50x ... with a wider FOV ... sounds to be good idea ... if magnification of 50x is the usable limit of tube of 80mm.


Cordially yours,

Luc

Gentilis said:

a magnification of 50x is the maximum usable limit for a 80mm diameter scope. A magnification of 60x does not give more information than a magnification of 50x

Click to expand...

That's bogus. A well corrected 80 mm telescope should provide additional detail and a beautiful image up to 150x or more. If birding scopes don't reach this limit (and they don't) it has more to do with their use of prisms (which introduce optical flaws) and their short focal lengths (which don't allow for optimum control of aberrations).

--AP

Alexis,

I was perhaps not rather precise. I speak of course about "traditionnal" birding scopes when I refer to this limit.
If not, we can consider the mirror scopes which in addition to their high price have also their disadvantages (eg. their weight), like their advantages (as Jan Meijerink says : "tenzij we overgaan naar spiegeltelescopen, maar die hebben naast een hogere prijs ook andere nadelen (maar ook voordelen)".

But considering the "traditionnal" birding scopes (generally lighter) do you agree whith this usable limit of 50x with tubes of 80mm ?

Best regards,
Luc

Gentilis said:

Alexis,

I was perhaps not rather precise. I speak of course about "traditionnal" birding scopes when I refer to this limit.
If not, we can consider the mirror scopes which in addition to their high price have also their disadvantages (eg. their weight), like their advantages (as Jan Meijerink says : "tenzij we overgaan naar spiegeltelescopen, maar die hebben naast een hogere prijs ook andere nadelen (maar ook voordelen)".

But considering the "traditionnal" birding scopes (generally lighter) do you agree whith this usable limit of 50x with tubes of 80mm ?

Best regards,
Luc

Click to expand...

As I said before, I agree that traditional birding scopes don't perform at high magnifications well, but not because of their 60, 77, or 80 mm tubes. A well built "traditional" long focal length refractor of of 70 or 80 mm can easily perform at these powers. Even shorter refractors (e.g. the Tele Vue scopes) can do very well at these powers if they don't use those image degrading prisms.

Even conventional birding scopes with prisms can do better than 50x. My trusty Nikon 78 mm ED does very well at 75x.

--AP

Luc,

There is no single answer for everyone and every telescope. To answer this you need to know two things; the resolution of the telescope and your eyesight acuity.

A "perfect" 80mm telescope will resolve about 1.5 arcseconds on a line pair resolution chart. A person with a visus of 1 or 20/20 vision can resolve about 120 arcseconds measured the same way on the same chart. So, for 1.5 arcsecond resolution to be barely visible to a person with eyesight acuity of 120 arcseconds requires about 80x (1.5 X 80 = 120) and the details would really be easier to see at 90-100x. If your vision is better than 20/20, then you can see the same 1.5 arcsec resolution at a lower magnification. For instance, if your eyesight allows you see 90 arcseconds then you could barely see the scope's 1.5 arcsec resolution at 60x. If the telescope is not perfect, then the magnification required to see all the detail it can resolve will be even lower. If the scope can only resolve 1.8 arcsec then the person with 20/20 vision can barely see the smallest details at 67x and the person with 90 arcsec acuity needs only 50x. So, if your eyesight is very good and the scope is not so good you might be able to see all the detail at 50x, but a really good scope and/or average eyesight will require higher magnification. I think magnification at least equal to the aperture in mm is more likely to allow most people to see all the available detail in a good scope and even a bit higher magnification makes it easier.

Henry

Gentilis said:

But considering the "traditionnal" birding scopes (generally lighter) do you agree whith this usable limit of 50x with tubes of 80mm ?

Click to expand...

Luc,

I have no doubt that the usable limit of a good 80+mm scope is more than 50x. But as you may have noticed I strongly prefer low-powers, wide-angles and good edge sharpness & eye-relief to theoretical max powers/resolution of the scope. I also believe Jan Meijerink's data has been collected in daylight, which probably resemble more normal birding conditions than clear starry nights required to determine the ultimate performance of a scope.

In my practical birding I have often seen that the weakest link in viewing is the unstable air between the scope and the bird - and THIS, in my experience, is the reason why powers of more than 50x seldom bring any benefit. However, there may be short moments in the morning or evening when the air may permit the use of higher powers. I have experienced a couple of situations when my 20-60x was not quite enough for ID, but someone's -75x Nikon or -70x Optolyth helped to spot a king eider in a group of common eiders. Now I carry a 3x booster for those rare situations.

Regards,

Ilkka

Alexis, Henry and Ilkka,

Thank you very much to have put my questions in a more appropriate context.

I must keep in mind that various kinds of extern factors (like air turbulences / atmospheric disturbances ...and our eyesight acuity) limit the theoretical maximum resolution of a scope (well described in Henry's post).
It is probably the reason why I often notice in my birding practice that a magnification of ca. 50x is frequently the maximum usable magnification.

So I am very eager to test the new Leica scope with the new variable 25-50x eyepiece ...

It is very interesting to read you and I'll surely be back with other questions!

Regards,
Luc

Post-scriptum (for Ilkka) : King eider is a very mystic bird for a Belgian birder ;-)

Hi !

A well-known dealer in Belgium (Leica, Swarovski, Zeiss, Optolyth, Kite...) advises not to buy the current Swarovski's zoom because he expects an counterattack of Swarovski on the new Leica's zoom...

Luc

I've very excited about the 25x-50x since that's usually the range that I currently use on the 20x-60x. I would like to see Leica offer a fixed 75 as an option for when conditions permit.