Posts Made By: Greg Nowell

I probably won't understand the answer to this, but here goes....

When you push a four inch refractor (but this applies to any scope design) to around 50x per inch you get for sure the Airy disk and it's plain and easy to see. So there is a point source of light and something happens to make that effect. It is more readily viewed on bright stars.

If you look at TWO adjacent stars, very close, you will see TWO Airy disks.

When you put the same scope at the same power on something like Jupiter the view is peachy keen. One would think that Jupiter can be thought of as a mass of adjacent points. If two stars give you two Airy disks, one would think, that this point over here on Jove would give an Airy, and so would this one over here, and that one, and the result would be an indistinct mass with no contrast. Or perhaps an Impressionist assemblage of pointillism. There's plenty of brightness, just as bright stars show an Airy more readily.

I've never seen anyone ask this question before so I'll put it out.

thanks

Greg N

http://www.astromart.com/articles/article.asp?article_id=716

I submitted this article last night. There were some technical issues in the picture sizing, the webmaster fixed that, but the pictures are out of order. I don't think it matters, most people will pick up a thing or two about Pentax XLs and XWs from this article.

thanks for your interest,

Greg N

http://www.astromart.com/articles/article.asp?article_id=718

Y'all very smart people and if I need my head bashed in I know it's going to happen anyhow so I'll put this latest piece of writing out there in case y'all find serious issues and want to complain to me whilst I am inclined to pay heed.

It's not like I won't hear from you anyhow, one way or t'other.

Nonetheless I think this article is "overdue" and if it needs rewriting I will do so. I put it together after reassembling my 8" SCT which I had apart recently.

regards
Greg N

Eyepieces in thirty years have reached an apogee of development never before reached in the previous 400 years of telescope use. The wide field has been developed and explored, e.g. the Televue Naglers and Ethoses etc. The ultra-precise moderate wide field has been brought to a high level, my beloved XWs. The tiny glass options have reached an extraordinary level of development: ZAO, ZAO II, AP, XO, etc. Coatings are amazing.

What will make these great eyepieces look as backwards in thirty years as my 1965 Swift Kellners look today?

I'm thinking that some fundamental development in real time imaging, like the I3: an order of magnitude improvement in pixel resolution, true color transmission so space is black etc., and some of kind of projection technology that is subtle enough not to blast your eye dark adaptation.

In other words, I'm suggestion that glass may have "peaked" as a technological option, and taht what remains is for electronic imaging to catch up to the subtlety and clarity of what we experience when looking through glass. So that in thirty years all these glass eyepieces will resemble the high fidelity phonographic equipment from the 1970s: there will be some people clinging to it and saying it's really the best, but the world will have moved on.

I find it difficult to think of a world where Ethos, Naglers, XWs and such are lying around in attics and more and more frequently turning up in landfills. But I'm trying to imagine "where it would go" if the next thirty years brought real-time observing "at the scope" as far along as the past thirty years have.


I can even see antique telescope society people demonstrating the views through XWs and Ethos eyepieces as "glass views" that are "representative" of the "era of glass"--as if Huygens and ourselves were all lumped together in one generic technological period.

I also think it is not out of the question that some kind of amateur level interferometry would have us setting up two c8s at different ends of a field and getting the resolution of a 50 meter scope possibly with some sort of real time stacking that amounts to adaptive optics "in the field."

Sounds whacky, but if in 1965 I had said that people would be routinely capturing 90% of the light that goes through their scopes and taking pictures out of a 6 inch apo or c14 that blow away the 200 inch on Mount Palomar, that would have seemed silly too.

Comments?

regards
Greg N

Roland suggested in the humongo thread on "what is an apo" that when you're evaluating color correction not all scopes perform the same with all eyepieces; that orthoscopics can introduce false color below f/8.

Now the ZAO II series is a cool $2400. We are getting into the cost realm where the tale might wag the dog. That is, suppose you have these eyepieces and you're a precision optic fetishist. Your name finally comes up for an f/6 130mm from AP.

Should you stick with your f/8.1 FS128 because it's a better match for the premium eyepieces? Should one apologize to discriminating viewing guests for offering a view through a ZAO II in an F/6 AP refractor saying, "I wanted the f/8 AP but it didn't work out"???

I lie awake at night pondering these issues.....

But I think not a few people on this list have more into their eyepieces than many other amateurs have into their OTAs, and it does raise the question of whether one might want to purchase the OTA as a function of the eyepieces, rather than vice versa.

Or should I make a virtue of necessity (my name never destined in reality to come up on the AP list) and say: "I passed over AP when they called about my f/6 because I just KNEW this here FS128 is a better match for these here ZAO IIs"!

But one final point a bit more serious: at the level of color correction that we are talking about in these fine refractors, if one is a visual observer and paying these premium prices, isn't it a bit odd not to consider the eyepiece's contribution to color in the final view?

regards
Greg N

(Public note that is)

Greg S I see from your profile that you have a Vixen ED102SS f/6.5. I'd be interested to know your assessment of its color correction vis-a-vis the Traveler and your thoughts about it generally (I have one). The objective size and FL are closer. If you have data on an NP101 4" I'd like to see that too.

thanks
Greg N

I have been disconcerted to see that UO has discontinued all of its Japanese wide field options; its only Japanese line these days appears to be the regular orthos and the HDs.

The Mk-70, the MK-25, the 32mm 82 degree, I had thought these were fairly regular staples of the market.

So is UO's cheap chinese crap any better than any other cheap chinese crap? They have a number of inexpensive wide fields.

thanks
Greg N

FS 128 FL: 1036 mm
3.5 XW: 296x
4 mm ZAO II: 259x
5 mm XW: 207x
6 mm ZAO II: 173x
7 mm XW: 148x

I deployed the FS128 vs Jupiter and its impact spot last night (morning of 28 July east coast time). Several other scopes were present including a 10" Meade SCT, a 14" T-scope, and an AP 130mm Gran Turismo.

Seeing was better than average and views were on the whole steady though during some periods seeing made it difficult to focus. The FS128 shows a good view at 296x. The GRS was plainly visible and splits and details in the SEB and NEB also were present, including a "dark spot" very near and trailing the GRS which is easy to mistake as the impact spot (further south and trailing by much more).

The impact spot itself was "easier to detect" as a tight dark elongated spot at lower powers then at higher ones, even though the higher powers were giving good views of Jupiter. In the 5mm XW and the 6mm ZAO I thought I could see wisps of blue festoons which I will have to corraborate against a picture. Usually I don't pick up planetary color in my refractors. The 7mm XW view closely approximated Sue French's AP GT view. She had stuck in the 130 to 140x range due to eye troubles, and I note that at the higher powers it was not always easy to get a clear view due to floaters.

As I have noted in the past, the eye relief and "big glass" of the XWs made them significantly easier to use, but I split the time between them and the ZAO IIs. Since I spent a good deal of time in the various magnifications (I had determined that seeing the Jupiter hole was my #1 priority and blew off dsos) I used the ZAOs quite a bit. And for comparison there was an AP refractor albeit at lower powers.

My general observing sense was one of classic "less magnification means tighter view." Every time I decreased magnification the view got a bit tighter and the impact spot a bit more contrasty and easier to detect even if it is "shriveled" at lower magnifications. At higher magnfications it the impact spot fuzzed at more in interludes of bad seeing.

I can't honestly say that the ZAO IIs kicked XW butt. What was evident to me mostly that a good comparison is impossible because the differences in magnifcation were palpable: 4mm ZAO was crisper than 3.5XW, 5XW was tighter than 4mm ZAO II, 6mm ZAO tighter than 5mm XW, 7mm was tighter than 6mm ZAO II. But by then magnification was halved.

So my overall impression is that rather than providing an air tight case for ZAO IIs, this observing session merely demonsrated that ZAO IIs, combined with XWs, give a very high quality stepwise progression from 3.5mm through 7mm. The effects of changing magnification dominate the view of Jupiter, the XWs are always like "islands of viewing ease" compared to the small ZAO glass and lower eye relief. There is also a palpable "floater relief effect" which for me kicks in at about .5mm or .6mm exit pupil (a very standard view). The 3.5 is an exit pupil of .43mm and the 4mm ZAO II is .49mm.

So my sense is that it may not be possible, using the FS128 and the eyepiece series above, to make meaningful comparisons that isolate issues of design from the effects of changing magnification and diminishing eye strain due to increasing exit pupil as one shifts to lower magnification.

In the past, I dealt with this issue by "bracketing." When I had a 6mm radian, I tested it by comparing it to the 5mm XL and the 7mm XL. If I found the views in both eyepieces superior, then I faulted the radian (which is what happened). That at least controls for exit pupil and magnification effects. When doing "bracketing tests" of one series vs. another I usually consider the more difficult test to be the one at higher magnification; that is, one normally expects a 4mm to give a bit of sharpness up to a 5mm. If one finds the view in 5mm superior in comfort and clarity to another eyepiece at 6mm then generally one can conclude the 6mm isn't up to snuff.

In this case the bracketing failed to reveal differences "on both sides". The ZAO IIs appear to be performing *at least* up to the XW standard, so when one brackets a 4mm ZAO II with a 5mm and 3.5mm Pentax there is no visible superiority among the three. I like the ZAO IIs and intend to keep them for the time being, but it is clear that if the 4mm ZAO is going to kick XW butt by, for example, outperforming the 3.5mm AND the 5mm XW, that "it has its work cut out for it."

The ZAO IIs may actually reveal superior performance under some conditions, but last night was pretty much "as good as it gets" around here. Jupiter offered good views at all powers up to 296x, the FS128 was doing nicely, the impact spot was readily visible, and all the equipment performed. Since I write too much this is unlikely to be my last word on the topic of ZAOs and XWs, but for now I'm sticking to the view that ZAO IIs are nice to have, but are definitely the kind of thing one budgets when the other important stuff has been acquired.

I can do an apples to apples comparison of the XW10 and ZAO II 10mm, but in the FS128 this is only 103x and therefore not a tough test, in the C14 both eyepieces give 390x and at that power, seeing limitations dominate the evaluation, it being very easy to mistake a view of this or that detail as rendered by the eyepiece rather than a moment of exceptional seeing.

regards Greg N



ps I was at this for 3 hours, much longer than previous comparisons.

A remarkable 48 hours:

Sunday I caught a 2 p.m. show of Shakespeare's "Twelfth Night." This was in Lenox MA at the Shakespeare and Co. theater complex which has become one of the leading Shakespeare centers in the nation. I know of nothing else like it. Excellent performance.

Monday, painting the house.

Monday night: Tanglewood in MA, James Levine and the Boston Symphony Orchestra playing Mozart's Don Giovanni. I've wanted to see this opera for about thirty years. Wow! We got hit by heavy rains, flash floods, and thunder during the performance.

About 80 miles to the W all was calm and some of my observing friends had set up for an impromptu star party. I had pre-packed the car with the FS128 and after returning the missus back home and paying the baby sitter headed out to catch photons.

We have had so much rain this month that I had given up any thought of being able to catch the impact spot. But lo and behold, we had good seeing and clear skies and caught it.

So: Shakespeare play, Mozart Opera, and the Jupiter impact spot: something of a personal trifecta, I never thought I'd pull that off within 48 hrs.

regards
Greg N

About two months ago on a rare clear night I noticed that in focus star images on my C14 were showing flare with a 40mm eyepiece and also were showing classic oblong shapes at 90 degrees to one another on both sides of focus.

I felt a sinking feeling and concluded that somehow the secondary must have got loose on the corrector. The secondary mounting is generally snug, rotates with hand pressure, but I was thinking, well, maybe some ignorant person turned it at a star party, or I twisted it by accident, or something.

So I proceeded to evaluate the secondary mirror different positions, moving 1/8th turn each time.

(Meantime everyone around me is having observing fun.)

I was at position #6 and thinking the view was pretty good when perchance I came at the eyepiece from a different angle and noticed that the astigmatism was differently skewed.

Then came the DOH! moment.

My 40mm Pentax XW has a dioptrx on it. And I ain't just anyone. I'm the guy who wrote and posted the article on how to put a dioptrx on an XW40.

The scope was never showing any astigmatism, and the eyepiece only showed it because I had put an astigmatic corrector on it to counteract my eyeballs.

I lost about an hour to all this. It shows the terrible effect that long weather-enforced abstinence from viewing can have: one's equipment becomes a stranger. I forget what I have, and also how to set up what I have.

regards
Greg N