Posts Made By: Jeff Young

Does anyone know where to find top caps to fit Tak LE's (specifically the 7.5mm and 5mm)?

I store my EPs in a custom machined tray, so I don't use bottom caps (but of course those are easy to find anyway). Of course, this also means a bolt-type case won't work for me.

Thanks,
-- Jeff.

There was an interesting question brought up on the Tak LE thread, but it didn't get answered there:

Will an eyepiece dew heater also prevent (or reduce) eyeball fogging, or are they only effective on dew resulting from heat-loss due to open sky exposure?

I'm upgrading my 8" SCT to a 16". My current eyepieces include:
Pan 27 & 19
Nag 11 T6
Tak 7.5 & 5

Obviously, with twice the focal length, the Nagler and Taks aren't going to be much use. So I can either let them collect dust (using them occasionally in the 8") and lay out a bunch of cash on a Pan 41 (and possibly upgrade the Pan 19 to a Nagler 16), or I could get something like Lumicon's Giant Richfield Viewer (an 80mm F/6.5 field flattener) and continue with most of my existing oculars.

Is the richfield viewer going to degrade my optical path noticeably? Any other thoughts or things I should be aware of?

Thanks, Jeff.

I'm building a 10' tall timber framed structure under a 10' ProDome, which will house a 16" SCT. I'm planning a concrete pier up to just below floor level (roughly 6' above ground level), with a steel pier for the last 30".

The original plan was to use a sonotube, but they're very hard to come by in Ireland in anything larger than 12". So the current plan involves an 18" concrete sewer pipe (with an outside diameter of 22") 8' in length, which will be set 2' deep into a 3' x 3' x 4' footing, and then filled with concrete.

The pipe will have a nicer finish on the outside, and should give me better rigidity (assuming the casting conditions are better controlled in the factory than in my field).

But it does have a smooth inside bore. I'm wondering if the poured core (which has the anchors for the metal pier on top) is going to shrink enough to give a tiny gap between the core and the shell, and therefore not make use of the outer shell?

I also wonder if I really need any rebar inside the core, or if the outer pipe provides plenty of strength.

Any help appreciated.
-- Jeff

I've come to understand that there's some adjustability in the Panoptic 41's eye-guard, but that it's not an instadjust. Someone suggested that the top metal cone unscrews upwards (from just above the finger detent?), but all the pictures I've seen show it down.

Could some please post a picture of one with the eyeguard adjusted all the way up?

Thanks,
-- Jeff.

Now that we're on to the timber framing, I've started a new thread.

Just to recap, the pier and pad design and construction were detailed in: http://www.astromart.com/forums/viewpost.asp?forum_post_id=355146.

Here's the result of that stage, and the foundation for the next:

I went out two nights ago at about 10:00, and contrast and light pollution seemed much worse than normal. It was first light on a new 16" SCT, so I wasn't sure what to expect, but the background was *very* gray.

I fired up trusty AstroPlanner this morning, and noticed that a 30% moon had set maybe an hour to an hour and a half before I went out. Would this still be scattering a bunch of light around the upper atmosphere?

Or was this just different atmosphere conditions than normal? It was my first night ever in Ireland with no dew, but I would have thought that would be indicative of better transparency, not worse... :S

Thanks,
-- Jeff.

Boy, the new scope has brought up all sorts of new questions....

I was under the impression that the amount of useful magnification was in proportion to the aperture, up to a fixed limit imposed by the seeing.

But my new 16" SCT seems to take more magnification than my 8", even when the seeing is limiting both to less than the 8's maximum. I had about Pickering 6 skies the other night, and the 16's image was fine at 360X, breaking down at 530X, and complete mush at 800X. Now, I didn't have the 8" set up the same night, but from memory, in similar seeing, I'd get the same results with the same eyepieces -- but since the focal lenght is 1/2, that would equate to OK at 180X, breaking down at 265X, and mush at 400X.

Am I suffering from wishful thinking (and a flawed memory), or is the limit imposed by the atmosphere also somewhat proportional to aperture?

-- Jeff.

I was out observing Mars the other night, and wanted to get the best view I could. I've been comparing a 7.5mm Tak LE with an 8mm RKE and an 8mm TV Plossl -- so these were my candidates. Seeing was fluctuating from minute to minute between a Pickering 6 and 8, so they were actually quite hard to compare.

Subjectively, three things pop up immediately. The RKE feels brightest. Now, I didn't do any limiting magnitude tests (my goal here was Mars, not an eyepiece review), so this isn't necessarily due to better transmission -- it could, for instance, be a result of more light scatter.

Next, the RKE has what I find to be a claustrophobic view. I just don't find 45° comfortable, whether it frames what I'm looking at or not.

And finally, the Plossl's short eye relief combined with its rubber eyeguard result in a lot of eyelash scraping and jamming for me. I don't think the RKE has any more eye relief, but the volcano top at least keeps my eyelashes out of the view.

Now, like I say, the seeing was fluctuating quite a bit. So I had to keep popping them all in and out to try and confirm any differences. I believe that I got crisper lines between the Northern lowlands and Southern highlands more often with the RKE and the Plossl, than with the Tak. But the view was pretty fuzzy in all 3 most of the time, and all three managed moments of great sharpness.

Just about the time this trade-off between obvious comfort (the Tak LE) and perhaps better views (the RKE and Plossl) was becoming a real delimma, the seeing settled down to Pickering 7 or 8, with moments of 9. Our three contestants were duly retired in favor of a 5mm Tak LE, and I was able to get on with viewing Mars without worrying whether or not I had the right occular in the scope.

The 5mm is that much better than the 7.5, you ask? No, there's just no competition at that focal length in my kit.

(It should probably be mentioned that the 8mm RKE and the 8mm TV Plossly each represent the shortest focal lengths in their respective ranges.)

-- Jeff.

This is Part III in a series.

Part I detailed my original questions (boy was I green back then) and all the foundational concrete work. It can be found here: http://www.astromart.com/forums/viewpost.asp?forum_post_id=355146.

Part II detailed the fabrication of a timber "kit" which was partially erected inside to fit everything. It can be found here: http://www.astromart.com/forums/viewpost.asp?forum_post_id=365122.

This part will describe the erection of the "kit" and the assembly of the dome. (Well, we'll see how long this one runs. Maybe the dome will end up as Part IV.)

This historical observatory in Armagh has become our inspiration.