Louis D

Are you pulling back too far from the eyepiece to take in the entire field of view? You might also be too close, but that's less likely, especially with the 10mm. Try moving your eye position in and out with respect to the eyepiece when you notice this happening. Not likely because you would see an overall cloudiness of the image, not a black ring.

Aren't there any European made focusers to compete with the Feather Touch? It seems like there are plenty of high end machine shops over there that could do it.

Here's another test of the two eyepieces. Move the moon and/or a bright planet or star just outside the field of view. Which does a better job of suppressing stray light not in the field of view? Of course, if your scope's tube isn't well baffled/flocked, any eyepiece differences may be drowned out by it.

I have an 8" dovetail on my 72ED and a 14" dovetail on my 90mm APO triplet to get the CG far enough back to use heavy 2" eyepieces and binoviewers with both. I do have to be careful with the focuser knob's orientation, or it will either touch the dovetail or be behind it, depending on the scope. I suppose dovetail flex would be an issue for imaging, but it's not an issue for visual observing.

Not really an option for Dob users with no view of Polaris and no EQ platform like myself. Unless the star is perfectly centered, you can't easily distinguish decentering from bad collimation; and since it drifts off axis fairly quickly, it doesn't leave much time to adjust collimation. It's mostly useful as a quick confirmation of decent collimation before the star drifts off axis.

I only use my laser to get my secondary pointed back at the primary's center after loosening everything up and starting over when something seems amiss, but I can't quite nail down where. I have to be very careful not to lase my own eyeball while looking down the front of the tube to get the laser off the tube wall and back to the mirror. After that, I mostly use a cheshire sight tube with crosshairs and an Aline cap to finalize everything.

What about something similar to this to keep everything dry?

The Baader Neodymium cuts out a good chunk of the yellow part of the spectrum where there is a lot of light pollution. This also increases the contrast between blue-green and red-orange planetary features much like a magenta or salmon filter operates.

And if it's the Synta focuser I think it is, don't put the 1.25" adapter in the 2" adapter, you won't be able to reach focus. Replace the 2" adapter with the 1.25" adapter. Synta alone uses this scheme. Every other 2" focuser uses 2" eyepieces natively, and then you insert a 2" to 1.25" adapter into it to step it down for 1.25" eyepieces As @John points out, 2" eyepieces are best for low power, wide angle views. I'd recommend picking up something in the 35mm to 42mm widest field range just to help center objects before moving to higher powers. Of course, with Synta's focuser, this isn't as quick and easy to do as with other focusers. Take a picture of the primary mirror to help us get an idea of how dusty it is. It has to be really grungy to warrant a cleaning. Cleaning microscratches are worse than dust because they cause light scatter. Dust just tends to attenuate the brightness a bit. You'll want to at least collimate the primary with something like a Rigel Aline to make sure you're getting decent views. This assumes the mirror has a center marking ring, which it should have from the factory.

Here's an article with suggestions for more appropriate astro headlamps.

I have the white light only version of that one. It's a Cree type LED intended for tactical use. I would try to locate a headlamp intended for astronomy use rather than try to dim this one.

Dang it, now you're making me want to hunt one down on the secondary market just to compare it to the 40mm Meade SWA 5000 and 40mm Pentax XW. 😉

You're assuming that distortion/magnification is the same across the field for the two eyepieces. Let's say that they are both n millimeters focal length in the inner 10% of the field, then craters there will nicely merge in a binoviewer. However, if distortion/magnification varies differently across the field, then craters further out won't merge because they are of different sizes at different positions in each field. AFOV can be the same, but more or less of the moon might be visible due to differing distortion/magnification across the field. I understand that there are two major types of distortion. One where objects are the right size but positioned wrong across the field and one where objects are positioned correctly but vary in size across the field. I'm asserting that at least the second one qualifies as magnification or focal length changing across the field. I can't recall ever having an eyepiece that shows objects as the same size across the field, but moving them at differing speeds across the field during panning which the first type of distortion implies. They always get bigger as they speed up toward the edge or slow down as they shrink toward the edge, but they never remain the exact same size from edge to edge as they speed up or slow down.

I guess it comes down to, do you mark them with the apparent field of view (AFOV) as seen by the eye or the effective apparent field (eAFOV) of view that allows the classic true field of view calculation to work. Vixen used the first one initially until astro forum people loudly complained that it couldn't possibly have a 72° eAFOV (without even measuring the AFOV via projection before complaining), and then Vixen switched to the second one to shut them up. I've seen a third method used to advertise AFOV, the comparative method. The 35mm Baader Scopos Extreme is marked 70° despite having a 65°/66° AFOV and a 68° eAFOV due to its 41.3mm field stop diameter. I guess they figured that since it has a slightly larger field stop than the 35mm Panoptic (38.7mm) and the same focal length, it must have a slightly wider AFOV (70° vs 68°), ignoring that it is the Panoptic's distortion that gets it to 68°. The BSE 35mm is very sharp in the central 60%, has a slight blurring for some reason at midfield for maybe 10% that goes away if you tilt your head just right, and then sharpens up again toward the edge. It really feels like a Pentax XL with that ~65° AFOV. It feels a bit constrictive after using 70° to 78° eyepieces like the Pentax XW, Delos, and Morpheus. On the other hand, distortion across the field is very moderate compared to a Panoptic. It is a huge and heavy eyepiece, so there probably was just no saving it from discontinuation. The 26mm (really 25mm) Meade MWA takes a similar approach. Since it has the exact same 41mm field stop diameter as the 25mm ES-100, and the same actual focal length, it must also have a 100° AFOV by Meade's reasoning, and so they advertise it as such. In reality, it has an 83° AFOV and a 90° eAFOV due to distortion of the opposite sign from the ES-100. If it didn't have so much SAEP, it would actually have been a very good eyepiece. It's pretty much sharp to the edge at f/6, but you can't see it unless you push in tight (10mm of eye relief) and lose the midfield part of the view. If you hang back at 18mm of eye relief, you get a 79.4° AFOV and a very usable 37.7mm field stop diameter with only very moderate SAEP shadows. Thus, it could be considered a good way to complete a Morpheus set with a 25mm version, but that's not how they marketed it.

How about kidney beaning (SAEP)? It should be fairly strong in the redline and nonexistent in the LV (or is it SLV, you use both in your post)? I have the original 9mm Vixen LV, and it has much better stray light control and much less scatter than my cheaper eyepieces. Try hunting for the E and F components of the Trapezium with each to see which shows them the best.

As far as I'm concerned, they're the same thing. If you increase image scale to stretch the image over a larger area, then you must have locally decreased the eyepiece focal length. Vice versa, if you decrease image scale to squeeze more image into the same or a smaller area, then you must have locally increased the eyepiece focal length. Is there another explanation as to how image scale can be changed in the apparent field of view without changing the local magnification power of the eyepiece across the field of view?

I've tried a bunch of microfiber cloths over the past 30 years and have come to prefer the Photo Clear ones in the 7"x7" size. They're plusher than most MF lens cloths, have a serged edge to prevent fraying, and come in a handy plastic pouch to keep them clean while stored. I have no idea if they're available in the UK, though.

A lot of folks who own premium scopes are far from casual with their observing. Many choose to live in areas with very good seeing conditions, build roll-off observatories for their scopes, travel to multiple star parties each year, spend many days each year observing, spend entire nights observing and sleeping during the day, and are constantly searching out challenging objects. For them, they want the best equipment to help them achieve their advanced observing goals.

You ought to take a picture of the lenses lined up in order and stuck to a strip of gaffers tape or similar for posterity sake. In particular, are the central two lenses, L3 and L4 in the patent schematic, DCX (double convex) or PCX (plano/flat convex)? The patent shows DCX while the TV diagram shows PCX. Also, are they identical and interchangeable? L3 and L4 are shown in the patent as unique. If they are PCX and identical, that vastly simplifies reassembly to only one possibility.

TV freely acknowledges that they partner with Astronomik for their Bandmate filters, if that makes a difference in your decision.

ebay is my goto for hard to find used and new repair parts and new old stock vintage items available from within the US. I rarely buy new items from there, especially from China. Returns are impossible and refunds are a pain as a result. Counterfeits are abundant as well.

Search for Nagler eyepiece patents on Google. I don't think he ever assigned them to Tele Vue (he owns the company, after all, so he doesn't have to).

The 17mm Redline has some chromatic aberration in the last 25% of the field along with astigmatism. The 13mm has much more radial chromatic smearing, among the worst I've seen. It makes stars into pretty rainbows, though. The 22mm only has slight astigmatism in the last 5% to 10% of the field and no chromatic smearing.

Here's the schematic for the original Panoptic from US patent #4525035: Despite the 41mm being a slight redesign of the Panoptic, along with the 24mm, it should still be similar in lens shape and ordering.

Purely red light does not cause rhodopsin to decompose, so your rods can continue being sensitive to dim light. Ideally, you would want a far red, long pass filter on the light to prevent higher frequency light from leaking through.