Posts Made By: Larry Stedman

What's the best way to compare and judge the quality of barlows?

I've ended up with several that are similar mag factors (2x, 3x) and would like to run my own comparative "shoot-out".

Are there particularly good test objects--planets, certain DSOs, the Moon? Particular aberrations to look for?

Should I only test on pristine nights? Would it matter which scopes I'm testing on--or would the results transcend type of scope?

To pose this question a different way: How did you decide which barlows to keep and which ones to sell?

Saw this pair for the first time yesterday night. At first, I had too much power and was looking at one of them thinking it was the globular and that the planetary was going to be one of the "stars" in the fov. Scratched the head, put in the O-III, thought one of the stars was more distinct. Nah!

Tried using the DSCs to find the other... sure enough, it was in the fov one over. So, went to lower power to see both... quite nice. Now, the Night Sky Observer's Guide says that the nebula is half the size of the globular... yet, they looked about the same size to me and if either had an edge in size, it was the planetary! What have other people seen as to size comparisons? (I suppose it depends on aperture and sky conditions...)

When I put in the O-III one became more distinct, the other seemed to have stepped behind a veil (no pun intended!).

Am I right that the northernmost one is the planetary? And that it indeed is shaped something like M27, the Dumbbell Nebula, that is, rectangular? Or to put this a different way, in a reflector, the glob would be on the right when looking South and sitting on the West side of the scope?

Yes, I should simply double-check NSOG or my Planetarium program... but what fun would that be, when I can easily ask here for expert advice about their appearance, too?!

Okay, so I knew that getting a larger scope would help a lot with globulars (going from 7" to 12.5")... and it really has. Even the smaller "guys" glitter, sparkle... the mid-range ones are bright and resolve nicely, and the superstars are a marvel (I mean 133x and no eye strain, no averted vision, just straight-forward real sparklers). M22 had its streamers and pinpoints everywhere; M13 was, well, globular in all its glory. I even toured the host of mini-globs in Sagitarrius. Wonderful with the bigger scope.

But I was totally unprepared for the impact of aperture on nebulae! We can sometimes get caught up in equipment details so much that we forget that the real point of it all is the views! I should have known something was going on when, even under moonlight the other night, I had my best views of the Ring Nebula ever. Large and bright, a major ring, simply glowing in spite of the moon drenched brighter skies. Then, last night, without the Moon, and with pretty good transparency, the views of nebulae were absolutely stunning.

The Swan Nebula truly looked like an observatory photo... simply huge, bright, and awe-inspiring. The Dumbbell showed off its structure, large & luminescent. The Ring Nebula... well, I was ready to wake up the neighbors with shouts of joy.

And this was from small city suburbia with limiting mag prob about 4.5. (Maybe I will have to try dark skies some time!)

The incredible thing about the larger aperture is being able to use high power and have the images be bright and the objects huge... I'm sure that's because of the magnification being higher, but also because of greater light gathering. And I still haven't viewed many of the other major nebular showpieces, e.g., M8 and M42, nor looked at the large retinue of planetaries, the host of blue-green shells floating out there.

I can sum up my reaction with an overused 3-letter word: WOW!

Symptoms: excessive star flaring throughout much of the field of view.

Patient: Astroscan f/4.2 with an intake of a 14mm Epic.

Tests so far: Gave patient 22mm Epic, symptoms largely vanished. Tried a regimen of Televue Radians... 1 dose of 18mm, no symptoms to speak of. Switched dosage to 12mm... better than when on 14mm Epic, but still some problems. Tried 2nd round with different 14mm Epic (in case there was a problem with that batch of medicine), but symptoms returned.

Consulting physician Dr. Rank suggested combining his known patent med cure with Dr. Barlow's home remedy. Gave patient mixture of 1 part 28mm RKE and 1 part #126 Meade barlow. (Which is roughly equivalent to 14mm Epic). Symptoms largely vanished except in outer extremities. Main torso in better condition by a bit than with 12mm Radian. Similar findings with 22mn Epic and barlow.

Instrument calibration: switched eyeglasses to see if problems were being caused by new prescription. Similar findings.

Observations: What gives here? I always thought that coma (an obvious issue at f/4.2) is more of a problem with longer focal length, wider field eyepieces. And that because the fov would be larger. Here the reverse is happening. The 22mm is excellent, the 14mm is where the flaring appears. (Does this have something to do with star images being larger? The effects are most noticeable on brightest stars.)

Questions for residents: The barlow cure suggests that astigmatism is what is showing up in the 14mm Epic (yet it looks decidedly like comet flares pointing away from the center of the fov). If so, then what is showing up in the 12mm Radian? Some coma?

Can seeing issues bring out the coma more? (Mars looked like the Olympic rings).

Overall diagnosis: The 14mm seems to be a pretty good eyepiece otherwise, with good contrast and shows DSOs well even at f/4.2. The 14mm is also better at f/5.4, quite acceptable, but still shows some flaring away from central area.

Notes: Any insights from attending physicians would be appreciated!

Is there any way of setting things so that one receives an e-mail notification if someone responds to a thread one started or responded to?

Just in case anyone's interested, here are some rough summary statistics on what was posted in that incredible 3 most used eyepieces thread. With multiple entries, I usually selected only one set of 3 eyepieces, and that was for the dob... (personal bias). A couple of smaller refractors got dropped entirely if the longest focal length was something short, e.g. only 9mm. Clearly averaging choices together is fraught with problems, but here are the results anyway!

Average focal length for 3 most used -- 27, 14.9, and 8.2

Median for 3 most used -- 26, 14, and 8.8

We can use the results to pick a gold winner set!

At the high $$ end, it looks like a 26mm Nagler, 14mm UWA or Pentax XW, and 8.8 UWA!

Or a 27mm Panoptic, 14mm Pentax, and 8mm Radian.

For much less money: 26mm Meade Series 5000, 15mm Vixen or 13mm Stratus, and a 9mm Expanse or 8mm X-cel.

Obivously one's choices depend on the scope's focal ratio, tolerance for sky brightening, and the type of objects being viewed, but the choices were surprisingly similar and largely independent of scope focal ratio.

By the way, the SDs were 5.6, 3.1, and 2.4 Shows that there is definitely some variation. (This is partly because some picked a 30-35mm 1st then jumped to the 20-24 range which was other people's first choices)

Using ± 1 SD, we'd have about 21-33, 11-17, and 6 - 11 which reflects the variation and overlap in choices.

Astronomy magazine recently published a "new" DSO observing list:  the Bennett Catalog.  (It's a compilation of prior lists by Bennett.)  The catalog appears in the article "A southern-sky Messier catalog" by Michael Bakich, July 2006, pp. 76-81.

While the object lists were developed in South Africa by comet hunter Jack Bennett, most of the objects are viewable by observers living in the Northern Hemisphere.  

I have received permission from Astronomy magazine to distribute adapted versions of the catalog.  I took their PDF document and converted it into an Excel spreadsheet.  I then streamlined that, retaining all objects with declinations more northerly than -40.  That produced a list with 100 objects!

I call it the "Bennett 100".  It is designed for northern observers (even those observing as far north as 50 degrees latitude). 

I also created an Excel version of the full Bennett catalog, which you can sort by declination for your latitude and observing horizon.

The files are .xls documents, but are openable in AppleWorks, too. I've created a web page where you can fetch them. It's

http://home.roadrunner.com/~lstedman/

Both are simple files with columns for Bennett number, Messier/NGC number, type of object, constellation, magnitude, RA, and declination. The Bennett numbers are those from the original Astronomy magazine article. 

The document is ordered by RA.  I've added several columns that break the RA into hours and minutes and Dec into degrees and minutes for sorting purposes.
 
Hope you all find them useful!

Greg, I have the makings of a similar addiction. It took me years before I broke down and bought a 21mm XL. The views and comfort were incredible. That got me over the psychological barrier of spending real $$ on an eyepiece, and so a 14mm XL joined the ranks soon after.

Then for a few years, barlowing kept me from buying more as I figured I was saving $. But recently I've started getting a little tired of barlowing and pondered getting a used 10.5mm XL. Instead an Astromart 10mm XW called me first!

Now the flood dam may be broken!

I'm wondering whether you ever barlowed the XLs or not. Did you try it and not like it? Was there too much strain on the diagonal? (I only used the Pentaxes in dobs myself as the couple of times I tried my Pentax in a spotting scope my worries about the potential twist, plop, & CRASH overcame any appreciation for the wonderful views!)

I, too, would be interested in hearing more about the XLs vs. XWs, especially on field curvature in the longer focal lengths (same? worse?) (I know the technical curves and user experience sugest the XWs have it, too, but was wondering the comparative amounts!). I do wonder whether to replace the 21/14 XLs. Although any replacement would have to be clearly sharper over a wider field of view and have similar comfort!

Oh, my aching wallet! 8)

Just found this here on AF

http://www.astromart.com/forums/viewpost.asp?forum_post_id=449006&poll_id=&news_id=&page=

I see on the TV site that there are instructions for tightening the Instadjust

http://televue.com/engine/page.asp?ID=164

But no pictures. Is this something that someone who is a klutz do successfully?

I have an 18mm Radian that has the proverbial drop syndrome. Lift it out of the case and it slips all the way up. But the views are spectacular and I'd hate to do something BAD to the eyepiece!

I've read with interest the various threads about optimal exit pupils. There seems be a consensus, albeit with some variation/dissent, that a 2mm exit pupil is about ideal for much DSO observing.

Have an f/5.4 dob. Ended up with 12mm and 10mm eyepieces, which give me exit pupils of 2.2 and 1.85. In other words, straddling the "ideal".

In your experience, which will serve me better? Would you go higher or lower for your workhorse eyepiece?

How much depends on sky conditions? I preume that darker skies would tolerate the smaller e.p. better, but I'm under small city suburban, semi light polluted skies, perhaps mag 4.5 skies when transparent with Milky Way somewhat visible.

I also presume that one's eye make a difference... young eyes with bright pupils probably can go deeper, with smaller exit pupils, and see more with darker, more magnified views. Old geezers, which is more what I am, probably do better with larger exit pupils and less magnified and, therefore, brighter views.

I'll likely keep both, but as they are $ eyepieces, I may replace one of them with a less expensive eyepiece in the same f.l. or barlow another premo eyepiece to get to the f.l. of the one I'd sell.

The question arises from an observing session early this morning in which I was struck by how different the Ring Nebula appeared in 14mm, 12mm, and 10mm. I found it at 26mm, jumped to 10mm, was initially impressed by the view, but then the 12mm really knocked my socks off with a real glowing ring. The 14mm was a pale third, showing a smaller, less distinct object. (Of course, I discovered later this morning that the 14mm had some minor, left over condensation on it from a session a week ago. That may have dimmed the views.)

Any thoughts?