Just wanted to share some experiences on the performace of multi vs few element eyepieces. As you may have noticed, I'm all for fewer elements these days. Recently when Mr Harlequin came over for a quick saturn ob session, I got to try his 4mm UO ortho and compared it to the 4mm radian. With 4/2 elements/groups vs 7/5 in the radian, I was expecting the 4mm UO to trounce the radian and it came close to it. The image of saturn was noticeably brighter than in the radian, through sharpness was still close. Furthermore, the UO gave a cleaner image as compared to the radian's slight brown tinge, and was possibly slightly more contrasty. It resembled a more magnified view of the 5mm LE (5/3), bright and clean. Overall, the view through the radian looked as if you were looking through sunglasses (with brown tinge and dimmer image, analogy much exaggerated of course). I should also add that the UO was not perfectly sharp in the last 10-20% of the much smaller 40+ deg field whereas the radian was sharp up to 99% of the 60 deg field. The UO at 3mm eye relief was quite a pain to use as compared to the best-in-class 20mm in the radian.
Comparison 2 : 20mm Televue plossl vs 20mm Pentax XW
Bought a TV plossl on astromart to try it out. The 20mm TV has only 4/2 vs 6/4 on the xw. The TV plossls are known to be perhaps the best mass production plossls in the market, very sharp, contrasty and with over 98% peak transmission. Can the xw's proprietary SMC coatings undo the damage of 2 additional elements / groups? Tried out on M45 and M42 at 63x with the rising moon blocked out behind buildings to reduce glare. My first impression was --- no difference. Even after swapping the eyepieces 20+ times back and forth on M42, I could not discern any difference in the quality of the image. I could not see a larger M42 in the TV (which would indicate better contrast / light transmission). The trapszium was just as sharp in either ep. The slight reflective nebulae in the running man nebula was equally subtle. The structure in M42 was also somewhat similar. By the end of the night, I got the impression that the TV was just a hint brighter and more contrasty than the XW (this difference is far smaller than the difference between the UO and the radian in brightness-- that difference was obvious) but I can't be sure since it could have been biased by my expectation anyway. Overall, the much larger FOV of the XW and longer ER made it the obvious winner against the TV on deep sky. So it seems that Pentax's SMC coatings are pretty good. While the 20mm XW may be good, the rest of the XW line has more elements, up to 8/6. The 20mm is the only one with 6/4. I would like to try a 8/6 XW to see how good SMC really is.
I leave you to draw your own conclusions.