Telescope Reviews: First look at the new Leica ASPH zoom

Two weeks ago I took delivery of my long (VERY long) awaited new zoom: Leica 25x-50x ASPH. The designation "25x-50x" refers to the available magnifications together with the Leica spotting scope's focal length of 440mm. I will call it 17.6-8.8mm.

General:
- Body dimensions: 59mm/2.3" diameter, 89mm/3.5" body length (without barrel)
- weight approx. 400g/14oz
- twist-up eyecup (3 positions, 9mm difference)
- comfortable eye relief (18mm)
- smooth zoom-ring movement

Having been a fan of my Leica zoom 22-7.3mm for quite some years my expectations were rather high. My benchmark was this:

ZAOII's vs. Leica 22-7.3mm

Fortunately the skies were cooperative at the very first evening showing a 12 day's moon with fairly good seeing conditions. I did compare the new zoom against the ZAOII's and the old zoom at different focal lengths of 16mm, 10mm, 8mm, 6mm, and 5mm. The main target for the higher mags was crater Gassendi. As reported in the given link the old zoom and the ZAOII's again were so close that it wasn't possible to see differences. The new zoom instantly could be seen as being on par with both. But after the comparisons had been performed for more than one hour it even seemed to excede both for coming slightly better into focus, not by a large margin but repeatedly so. It kind of looked a tad "sharper" which I did interpret as being may be even more contrasty. At any rate: it can easily compete for contrast, definition, and absence of stray light. And of course it substantially surpasses the ZAOII's for its huge AFOV and its generous eye relief.

This week the sun made for a very tough test target for stray light and ghosting. With a filtering of ND5 (100 000 times) the apparent brightness of the solar disk is still 1.6 magnitudes brighter than the full moon. Putting the sun just outside the field stop there could not be seen even the faintest glow. This is equal to the ZAOII's where the approaching solar disk can be seen already through the triangular cuttings without generating stray light within the field of view.

Saturn gave a very pleasing view with natural colors slowly drifting through the large field of view without the necessity to refocus. To conclude this little report: the double cluster looked magnificent at different magnifications displaying pinpoint stars up to the field stop. Finally, the E and F stars within M42 could equally easily be observed with both Leica ASPH zoom and the ZAOII's.

Pros:
- wide AFOV: 58.5° at 17.6mm up to 79.5° at 8.8mm
- virtually flat field (within my measurement uncertainty of 0.05mm)
- no astigmatism up to the field stop
- extremely sharp
- extremely high contrast due to complete absence of straylight and ghosting
- no eyeball reflections
- neutral color rendition
- parfocal
- no kidney beaning
- replaces three high quality eyepieces (even more with barlowing)
- barlows very well
- with a quality barlow lens element and extension rings it covers all focal lengths

Cons:
- expensive (800 Euros/1080 USD)
- 2"-adapter not yet available (I'm using a modified Baader adapter T2-#16)
- no click-stops (I don't need it: see below)

Summary: Is it the "ultimate" eyepiece? For me: YES. For others as always: YMMV (or better: YMWV). My UWAN16 and the old Leica 22-7.3mm zoom have been sold already, and eventually I will even sell my ZAOII's since I don't think them to be used often any more after – of course – much more comparisons. Together with a premium barlow lens (Baader VIP Modular) and a two-stage scheme of adding extension rings I have 3 barlow factors of 1.5x, 2x, and 2.5x. Thus a focal range of 17.6mm down to 3.5mm gives me everything I would need.

The attached picture gives an impression. From left: Zoom with 2"-barrel, barlow lens for 1.5x, 30mm T2-extension for 2x, 32mm T2-extension for 2.5x. The two combos 1.5x and 2x fit within the 2" eyepiece holder of my Baader Maxbright diagonal, the second extension will be placed outside the eyepiece holder. The white markings on the eyepiece body are little pieces cut from a nylon cable binder and glued onto small strips of transparent selfadhesive tape. They enable "feeling" the chosen magnification and are placed such that they give with my TEC140 mags of 60x, 80x, and 100x unbarlowed and the corresponding magnifications multiplied with the barlow factors.

Andreas