Posts Made By: Mike Hosea

I think it would be easier to supercede the Radians with 68-70 degree models, although this will probably push their diameters out to Pentax XW size, or possibly the Type 6 Naglers could be a starting point for a new line that adds eye relief and has smaller apparent field. I actually find that the eye relief of my Type 6 Naglers is already very Radian-like when I take in only 60-70 degrees.

The Panoptic design is a "scaled" design with eye relief that is a fraction of focal length. There's not much potential for this design to be scaled to shorter focal lengths than it already is.

Also, the short Pentax XWs and XLs are very nice.
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Mike

I've often thought about it, but one thing I rather dislike about it is needing both Powermates, but it can't be helped using the Plossls. The 5x will leave the mid-range with a hole, the 2.5x will leave the high end off. Swapping isn't that awkward, however, because the Powermates are not alternated for any sequence of increasing magnifications.

I've been experimenting with a 5x Powermate for very high magnifications. I have a 20mm Tele Vue Plossl, and I thought about getting the 15mm, but I remember that I used to get eyelash oil on that one regularly, and I decided instead to give the 21mm, 15mm, and 12mm RKEs a try. It sure is expensive to buy these directly from Edmund, but I wanted to see first-hand what the quality of new ones was like rather than taking my chances (and time) tracking them down used.
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Mike

I thought I might run out of space. What I was going to add was that in addition to running up the magnification to about 529x with the Powermate and RKEs, I couldn't help but push it further with the 11mm, 7mm, 5mm, and yes, the 3.5mm Nagler Type 6's in the 5x Powermate viewing Saturn. 1814x in a 10" Teleport might be some kind of record. I saw Saturn with the Cassini division and Crepe ring, but the view was much better at lower magnification (1270x) with the 5mm Nagler in the Powermate. ;-) Still no Encke. :-( But at least I know it wasn't there to see if only I could magnify the image a little more (too much scintillation).
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Mike

I've tried one thanks to Chuck Hovatter, who loaned it to me just so I could try it. I've also read the article. My only complaint was the field curvature. The designers argued in the article that up to x amount (the exact amount I do not recall--I want to say 1 diopter) was okay, and the eyepiece did seem to have about the amount they designed in. Unfortunately, for me it was just more than I would like. I don't like focusing the edge at infinity and accommodating the center of the field, so in using the eyepiece I was continually tweaking the focus. I didn't have a chance to compare the two, but with or without coma correction, I strongly suspect a 24mm Panoptic would outperform it to my eyes in my 10" f/5. The only thing I can say for certain at this late date is that my test drive of the Pretoria didn't leave me wanting one, and when I got a 24mm Panoptic I was entirely satisfied with it. YMMV.

One suspects that there is a niche market for affordable coma-correcting eyepieces, but the Tele Vue Paracorr has to some degree removed the large Dob market, and it must be hard to work up the courage even to try to service the remnant with specialized eyepieces, as it is just a fraction of a fraction of the overall eyepiece market. Nevertheless, there are plenty of smaller Dobs for which a Paracorr is a para-pain because of its weight and possibly in-focus requirement (potentially troublesome for optimized Newts with low-profile focusers).
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Mike

I'm not familiar with the CAA, but I gather it takes up enough in-travel that you don't have enough left for the 4mm ortho. If most of your other eyepieces do reach focus, I would think that you are not far off. If your 2" to 1.25" adapter is flat across the top, you might be able to solve your problem by just buying a different 2" adapter, i.e. one without a thumbscrew and with a recess on top. For example, you could buy the Tele Vue converter CEA-2125 to mount permanently on the 4mm.

You might also consider the 4mm Radian and the 3-6mm Nagler zoom. The 4mm Tak HI ortho is good but the focus position depends on the 0.965 adapter used. Unfortunately, most 4mm eyepieces without a negative field element are going to require a similar amount of in-travel as the circle-T.
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Mike

Well, the summit craterlet on Mons Gruithuisen Gamma is usually obvious in my 10" f/5 Teleport, and it was always invisible in my old MK-66 DX. Also, I don't recall seeing the two side-by-side craterlets in Plato as bowls in the MK-66 DX, whereas they appear that way under suitable illumination in both my 10" f/5 and 7" f/6.7 Newts. With Jupiter's type of detail, the contest sometimes seemed closer, however.
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Mike

I've had both and compared them directly in a 10" f/5 Newtonian and a 7" f/6.7 Newtonian. IMO, 5mm Nagler Type 6 is at least as good as the Radian in every respect. Certainly I saw no evidence whatsoever to support the idea that the Radian was sharper in the least. The Nagler is quite a bit superior in having less lateral color on a degree-for-degree basis. Eye relief isn't all that different on a degree-for-degree basis. At this price point I think the $40 price difference favors the Type 6 Nagler.

There are some measurements scattered here and there. I've never seen anything comprehensive. For example, there are some field stop measurements in this article:

http://www.cloudynights.com/eyepieces2/seven.htm

Note that to get a measurement when the focal plane is "internal" (e.g. behind a built-in Barlow or some such), you really can't make use of a direct physical measurement without taking the power of the field group(s) into account. A reasonable way of making an approximation is to measure the true field of view in a telescope of known focal length, F, by drift testing. The approximate field stop diameter for use with other scopes (not much point in using it with the scope that you already have a direct TFoV measurement for) is

field_stop = TFoV * F / 57.3 .

The point is that any time you can run across a situation where somebody has given you a directly measured TFoV and the focal length of their scope, you can compute a decent approximation of field stop diameter. When all else fails, you might use

field_stop = 0.95 * eyepiece_fl * AFoV / 57.3

The 0.95 here is arbitrary, but if you don't put something less than one there, you'll just be computing a fictitious field stop diameter that, when used to calculate TFoV, will be equivalent to TFoV = AFoV/mag, and we should all know that that formula usually over-estimates the TFoV (since pincushion distortion is more common than barrel distortion).

All I can tell you is that the 24mm Panoptic is much better in every respect than the 24.5mm Meade SWA in my Newtonians. It is my understanding that, in general, the Series 4000 SWAs are more on a par with and were contemporaries of the Tele Vue Wide Fields, i.e. a generation before the Panoptics at Tele Vue. The Panoptics represented a big step up in edge performance on faster scopes.

First perhaps it might be helpful to point out that all conventional Barlows are variable to some extent, and the 2x Ultima Barlow is biased towards higher magnification (up to 2.2x in common practice). The point is that ensuring equal magnification requires some effort to achieve.

Secondly, what is "bright"? I mean this as a rhetorical question. Eyepieces do not transmit all frequencies of light evenly, so every eyepiece is at least a weak color filter. The eye is not very sensitive to blue, but eyepieces that transmit more blue/violet than yellow/red appear whiter, and in laboratory experiments I think it is very likely you could fool people into thinking that a dimmer view was the brighter one by manipulating the spectrum just a little bit if the difference in overall brightness was not large. For some reason, the view in Tele Vue eyepieces appear a little yellowish compared to eyepieces such as UO Konigs and orthos. Frequently this is intepreted as a brightness issue, but I suspect the transmission in the critical green area of the spectrum is on a par, and even if the Tele Vue eyepieces are disadvantaged in the blue/violet end of the spectrum somewhere, these frequencies are not very useful scotopically, anyway.