View Full Version here: : 14mm UWA

02-10-2006, 11:00 AM
John.....speaking of the 14mm UWA series 4000, I recall going to a dark sky observing session with some friends from the Hamilton Amateur Astronomers club here in Hamilton with my previosly owned 12" GSO reflector.
I was looking for NGC-6946 in cepheus http://www.wodaski.com/wodaski/images/new/NGC6946-6939.SUM.jpg . I had made a map at home, (like the one in this link), of the surrounding area and started the hunt in the field with my 30mm 1rpd just to get in the general area.
I then zeroed in with the 14mm UWA and used my averted vision to detect this face-on elusive galaxy.
I did see it, but it was on the verge of detection, and it was extremely faint in the 14mm 4k UWA. I'm just wondering if it would have been easier to see in a 13mm TV Nagler with it's newer coatings, etc.
I did read that shootout you did in the forum, but just wanted to tell you about my experience with my 14mm UWA EP and experience in finding that faint galaxy, and get some input from your experienced eyes.

8" F/6 Antares Dobsonian (completely flocked and modded)
Looking for a 30mm Ultima
15x70 Celestron Skymasters
10x50 Magnicon binos
Meade 14mm series 4000 UWA
8mm Baader Hyperion (on the way)
2" Barlow
Sony Dig 4.1 Mp Camera

Don Pensack
04-10-2006, 02:26 AM
I recently did this comparison and the 13mm T6 won the contest. I reported my findings in a thread on CloudyNights.com. The 13mm did show fainter objects, but I cannot say with total authority that it was not due to the increased magnification.
There is more to viewing than merely transmission, however (the Pentax XW would also beat the 14mm Meade 4K). There is comfort of use, related to eye relief, head positioning, edge sharpness, etc.
Having spent two long all-night sessions comparing the 13mm T6 and 14mm UWA, I've decided to retire the 14mm UWA. It's very close, but I haven't found a single category in which the 13mm doesn't "nose out" the 14mm Meade.
Well, maybe one: I have to remove the counterweight to use the 13mm, and put it back on when I use my 17mm T4. That's a pain.
But I also own and use the 9mm T6, 7mm T6, and 5mm T6, and am in the process of comparing those to the equivalent UWA 4K's (8.8,6.7,4.7). It is beginning to look like the T6's are just better.
But it's not a "slap you in the face" difference. Just subtly sharper, less aberrated, and better transmission of faint objects.
The 4K UWAs fare remarkably well considering how long ago they were designed and manufactured. And they are easy to use.

04-10-2006, 09:27 AM
Don (or others),

As I am a bit lazy and have not yet read your comparison over at CN, I was wondering if you included the Pentax XW 14mm in the comparison as well or were just adding your observation with respect to the expected light transmission?...

I have a couple of XWs and beleive without personal comparison versus the 14mm UWA that your statement is likely correct...As I've found with an effort to discount for magnification differences I believe it to be true (more transmission of light with the Pentax) in my Pentax XW 10mm versus my 11 mm T6 Nagler...but I do like my T6 too...

Don Pensack
04-10-2006, 10:38 AM
I didn't compare the Pentax 14mm, as my comparison was only between the 14mm Meade and the 13mm T6 Nagler.
However, the Meade has 8 elements in 5 groups: 10 air-to-glass surfaces, and some of them appear to be completely uncoated. And some tests show transmission below 90%.
The Pentax 14mm has 7 elements in 6 groups, for 12 air-to-glass surfaces, but all are super multi coated, and the transmission of the eyepiece peaks at 96% at 550nm (green) which is nearly theoretically perfect for that many surfaces. All tests and observers have commented on this, so the difference between the XW and other widefields is likely to be real (but see my later comments).
The 13mm Nagler T6 has 7 elements in 4 groups, for 8 air-to-glass surfaces, all of which are multi-coated. I would expect transmission to be closer to the Pentax figure than the Meade's.

Though I believe people see differences between these eyepieces in regard to what they see, it may not be transmission that defines the difference. If it is, I have no explanation for that because controlled lab experiments show the human eye to be nearly blind to a difference in brightness of 10% (about 0.1 magnitude, which the AAVSO also holds as nearly the minimum identifiable difference under exceptional circumstances), so I suspect the differences are related to other factors, like surface polish, scattered light, exit pupil issues, internal baffling in the eyepiece, the frequency of greatest sensitivity of the eye vs. the eyepiece, etc.
But, if you add a small difference in transmission to those other factors, it probably adds up to what people see and have commented about.
The 14mm Pentax, for what it's worth, and the 40mm, are the only 2 XWs that I've never looked through.

04-10-2006, 12:47 PM
I agree...my perception of light transmission is likely impacted by what I am calling transmission...it might not be actually be light transmission at all (it is hard to argue with "science") and is as you mentioned is most likely a combination of things...

It might very well be the difference in color (warmth or coolness) that these different eyepieces impart (or don't impart) or some other factor.

Regardless of what it actually is users do see "some" difference...or at least some of us "think" we do... Cheers!