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TAL UWA 24mm Eyepiece
The following field testing was done comparing the new TAL UWA-24mm ultra-wide eyepiece to the Apogee WideScan II 30mm, and a Meade SWA-24.5. Some comparisons were also made to other eyepieces but were not the subject of this test.
Weight of the UWA-24 is the same as 30mm Wide Scan or 40mm MK-70 class eyepieces. The size is slightly more compact than these two others. Coatings look to be fully multi-coated of a Russian variety - which is to say, good.
There is a notable degree of amber tone through the glass. This is a bit more so than the "tinted" Tele Vue Radian product, in comparison. From what I've heard it said, this is by way of a larger amount of elemental barium common to Russian glass. In my opinion, this point is the only seemingly significant drawback to the eyepiece.
What happens is that the thick cross section of glasses, using this high content of barium, somewhat alters color transmission, brightness and contrast of integrated light going through it. In a direct in-the-field comparison, a 6-element Meade 24.5mm Super Wide Angle gave brighter and whiter views with a bit more detail seen in nebula.
However, the larger true field size provided in the UWA-24 is a major advantage over the narrower one with the Meade SWA. Add to that, the ability to swing the eye in the viewing field is at an excellent level compared to most other similar 80 deg. type eyepieces. For reference, comfort with the UWA-24 was noted better in this regard than the 30mm Wide Scan II, when under a test to eye sweep two stars "right to left", without blackout, when they were both far outboard of center axis.
There are similar spacewalk characteristics in this UWA-24 as to a 20mm T2 Nagler eyepiece. What I refer to here is that it gives a "wow" feeling of panoramic involvement to the human eye. Many ultra-wides don't have as much of this effect in comparison. This has a lot to do with how the eye favorably corresponds to (and hence, works in conjunction with) the lens system itself. Part of that effect is how easily (or not) the eye can comfortably pivot around and appreciate the very wide provided view. Often the easier it is, the better this effect becomes. In this regard, the TAL UWA-24 is an eye-friendly design with a high visual impact.
The axial (center) sharpness in the UWA-24 is excellent. The field area sharpness is fair-to-good and is acceptable even used with an f/5 achromatic refractor. There is sharpness fall off at 45% center-to-edge with the f/5 achromat. In comparison, there is 50% with the Meade SWA and 55% with the Wide Scan in the same test scope. The center sharpness is very slightly better than the Wide Scan and is about the same as the Meade SWA. There is a bit more lateral color than the Meade SWA when used with a fast f/5 achromat.
With an f/6 Newtonian reflector, the *good* field sharpness reaches to approximately 55% center-to-edge compared to 60% with Meade SWA and 66% with Wide Scan. Eye relief about 12mm in the UWA-24. There is a very minor ghost seen produced off from Saturn when beamed through large aperture (17.5"). This is not totally unheard of especially with wide FOV designs like this, and is not an issue in this case. There was no flare or ghost produced with bright Jupiter when placed outside of the field stop. This is good.
There is some barrel distortion visible in the UWA-24. But, it is, for the most part non-distractive even while sweeping rich starfields. It is a very good eyepiece design and overall likely quite useful as used with many differing telescopes. For reference, the point of focus for this new ultra-wide is acheived 1/8" outside of the 30mm Wide Scan when used in a 500mm FL instrument.
|UWA 24||SWA 24.5||Widescan II 30||Nagler 22||Radian|
|Focal Length (mm)||24mm||24.5mm||30mm||22mm||misc|
|Eye Relief (from top)||10mm||12mm||3mm||-||-|
|View Comfort||Very good||Good||Good||Fair||Good|
|Major dia (mm)||55mm||45mm||59mm||-||-|
|Eye Lens dia (mm)||26mm||25mm||38mm||-||-|
|Axial sharpness||Excellent||Excellent||Very Good|
|FOV field sharpness||Excellent||Excellent||Very Good|
|FOV field sharpness f5||45||50||55||-||-|
|FOV field sharpness f6||55||60||66||-||-|
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