Pentax 20mm XW & Tak 5mm LE

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Pentax 20mm XW & Tak 5mm LE

Postby elton » Wed Oct 29, 2003 11:31 am

Back from japan with a couple of new toys... only 2 you may ask considering the other temptations there : the cute mini-Borg 45 mm ED (small enough to put into a deep trousers pocket), Tak Sky90 (this is such a cute sexy babe!! one day ...), the whole range of pentax XW and XOs, most of the remaining XLs at clearance prices (sadly no more 10 and 21mm), whole range of tak LEs, the Sphinx goto mount (sexy and small ) plus a lot of weird and wonderful vixens, meade, tak and other jap brands.

Anyway back to the star test last night. Comparing the 20mm XW to the 19mm Panoptic :
- I felt the XW was slightly sharper across most of the field. Remember what I said before about the 19 Pan being almost but not totally sharp over most of the field? The XW was sharp like a good plossl or ortho. period.
- There was coma towards the edge of the 1 deg FOV in both eyepieces due to the F5 newtonian but i thought the 20 XW was as good if not slightly better than the 19 Pan despite having a slightly larger true field.
- did not make any comparisons on contrast
- The 20mm eyerelief on the 20 XW made a large difference compared to 12mm on the 19 pan. 12mm ER for wide FOV eyepieces is not enough for pple wearing glasses to take in all at once without squishing your eyes into the glass. Same experience with the 9 Nagler T6, the large FOV is not obvious until you squish your eyes really close. The XW / XL at 20mm ER resembles more like a large picture window or large screen TV with a great wide view which you can enjoy leisurely.
- related to above, because of the long eye relief, the view through the XW / XL felt more detached, like you are looking at something as opposed to being immersed in it. In this respect the Pan (and nagler) had the advantage but this is subjective.
- also related to above, the XW having a large glass exposed also attracted more reflections from surrounding lights. should not be a problem at a dark site though.
- the XW's eyecups have improved substantially over the XLs, smooth but firm helicoid. I'm one of the few who prefers TV's instadjust though.
- the 19 pan has already found a buyer

Comparing the 5mm Tak LE ED (254x) and the 4mm Radian (318x) on Mars and Saturn :
- even with the magnification difference in mind, i still felt that the LE was brighter and contrastier than the radian. With the tak on mars, the features around syrtis major were reminicient of opposition days. These were quite a bit more difficult to make out on the radian, too large a gap even considering the 60x difference in mag.
- The view of saturn was also the same, bands were slightly better on the tak while ring structure was similar. I thought there was a bit more texture on the rings with the tak.
Please bear in mind that the seeing last night was only average and the higher powered radian would be more limited by seeing. This test needs to be repeated in good seeing for the results to be confirmed.
- as expected, 20mm ER of the radian made it more comfortable to view and the instadjust keeps you close and involved. keeping you comfortable at the eyepiece allows you to view for longer periods of time and see more detail (to catch moments of good seeing and your eyes slowly train to see more detail ) - a big plus for radian
- the 3D effect of saturn hanging in space was present more in the LE than in the radian, probably due to the tak's sharpness and brightness --- subjective.
Why the difference? Besides the difference in mag, the tak has 5/3 elements/groups whereas the radian has 7/5 elements/groups. This means that there are 4 more air/glass interfaces on the radian, more light and contrast loss. Frankly, I regret not getting the 5mm LE and another few-element eyepiece like the 3.8 XP for mars opposition, to think the radian already saw so much ......
So now i'm even more deeply in dilemma with regards to planetary eyepieces - comfortable eye relief or more contrasty views? The 2.8 LE has 4mm ER, tried it in the shop and found it too tight. Short FL orthos and TMB monos have even worse ER. Barlowing adds more elements. Looks like a trade off is inevitable. Anyone wants to buy a 4mm radian? :)

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