Don Pensack

Tele Vue eyepieces are made in Japan or Taiwan. Not one is made in the U.S.A.

It has been the source of more than one call, over the years I was in business, of how to remove an eyepiece stuck inside a Click-lock. In every case, it was an eyepiece with a conically-tapered undercut, like the ES.

Tele Vue is never going to remove the undercuts on barrels. It's pointless to ask. As they say, colloquially, in the south of the US, "That dog don't hunt". Where Tele Vue is concerned, it's a moot point. I notice they asked whether we considered it important which country was the source of the optics. Hmmm.

That's not a "simple" eyepiece, i.e. an all-positive design with the field stop below the field element. Field stops in 2" all-positive designs max out at ~46.5mm. What do you mean by "bare upper section? Did you remove the field lens? ES says the field stop int he 12mm ES92 is 19.6mm, i.e. the eyepiece has a "virtual" field stop that can't be measured by measuring an internal stop.

Without distortion, the apparent field at 80mm and a 46mm field stop would be 32.1°. Field stops in simple eyepieces don't exceed 46-46.5mm in a 2" eyepiece. Add a typical 4% distortion and you get about a 33-1/2° field.

I don't believe the Takahashi Barlow is telecentric. I think it is a standard telenegative design, which means the magnification will vary with distance from the lens. So I don't think it is Takahashi's answer to the PowerMate. I've seen telecentric Barlows from TeleVue, Explore Scientific, Harry Siebert, and Astrotech. JOC, who makes the ES stuff, also makes the same telecentric Barlows for other brands, like Bresser, et.al.

Possible the best I've found to hold 1.25" eyepieces is the Twist-Lock adapters. They are not all the same. The best ones tighten with the least rotation and have internal compression rings (they truly are compression rings as they compress all the way around simultaneously) that extend all the way to the opening of the adapter (so they grab that short section of 1.25" barrel above the undercut), have smooth sides with no undercuts, and are threaded for 2" filters. Example: Olivon Twist-Lock adapter. I retouched this image to see the length of the internal 'collet'. This is not the only such adapter, but it is one of the best. I added an extension on the bottom so a Barlow wouldn't hit the 2" filter. Forgot: I painted the inside with Black 3.0 paint to eliminate reflections. In the picture, you can see the bottom, where the filter has removed the paint, but the area above that is very very black.

No, it clicks as you tighten it. You can super tighten it--to the point it is hard to unscrew.

Alternative: Baader Morpheus eyepieces. A bit wider than the Delos and just as easy to use. Also, slightly smaller and less expensive.

Do not use this type on an eyepiece with a conically tapered undercut--the rods will bend out of their holders and it will ruin the binding system. At worst, they will catch, making the eyepiece extremely difficult to remove.

He makes a really big deal about the fact the Baader Click-Lock does not center the accessory inserted. However, being shoved off center by 0.002" to 0.004" (0.1mm) at most is really not a problem. Even a coma corrector's sensitivity to being off center is minimal. Focuser axis error tolerance for high power collimation is 0.002D with a Paracorr 2, where D = diameter of the primary objective. In a 10" scope, that is 0.508mm, where the off-centering due to being shoved to one side never seems to exceed 0.1mm in well-machined focusers. So, whereas he was disappointed the inserted accessory didn't stay centered in the Click-Lock mechanism, the issue is really not an issue. Even if the focuser has sloppy machining and the shove is 0.2mm off center. Astrophotographers can correct with flats, and visual observers will never notice.

That is true of the 2" to 1.25" Click-Lock adapter as well.

Though this would change the magnification factor of the Barlow by pulling the eyepiece back from the lens. By how much, I don't know, but it would likely increase the Barlow's magnification by 1.15-1.25x.

Easy enough to replace brass or steel screws with nylon ones, or teflon-tipped steel ones. You only need two screws with large heavy eyepieces. Otherwise, one screw is enough. As an aside, though, if it leaves a mark on the eyepiece, that will affect its optics exactly zero. It might net you a trace less in re-sale, but do you buy every eyepiece with the presumption it will be resold? As for tilt, you can perform this experiment--tip the eyepiece ever-so-slightly as you tighten it down. Can you see a difference in focusability? Unlikely. And a brass split ring shoves the eyepiece against one side of the focuser or accessory no differently than a thumbscrew directly on the eyepiece. A brass split ring is not a collet, and it does not tighten down around the eyepiece uniformly, nor hold the eyepiece in the center. It is merely a way of putting a brass surface between screw and eyepiece. If you want to center the inserted accessory, then you need a Twist-Lock system.

Generally, additional back focus means the same as additional IN focus. When an adapter is used with an eyepiece that pulls it out more from the focuser, additional in-travel of the focuser is necessary. 0.965" (24.5mm) eyepieces are typically so short, though, that only a trace of in-travel is necessary, if any.

That calculator uses the inaccurate TF=AF/M formula to compute true fields. The actual difference is a 36.3mm field stop versus a 34.8mm field stop, so the true field of the 30mm UFF is 4.3% wider than the 20mm, a bit more than shown in the illustration. With a 1200mm focal length, the true fields should be ~1.73° versus ~1.66°, so your point is valid--the 4.2' difference isn't significant. For the Pleiades, though, the lower magnification makes the cluster appear more "cluster-like". For the Pleiades, the view in an 80mm refractor at 15-20x is really the best way to view the Pleiades. It looks a lot more impressive with 2.5° and more in true field. M44, though, would be very nice in either eyepiece, though it, too, looks better at a low power.

An eyepiece can have any apparent field of view you want, from 20° up to 100-120°. The True field on the sky that you see in the eyepiece is dependent on an inside focal plane diameter called the Field Stop. Field stops get smaller with shorter focal length. Once the field stop easily fits inside a 1.25" barrel, it is no longer necessary to make the eyepiece in a 2" diameter. And as the apparent field gets larger, at any given focal length, the field stop grows as well. With currently-produced eyepieces, the transition point between 2" and 1.25" is: 41-40mm at 40° apparent field. 41mm and longer will be 2" eyepieces because the field stop will be too large to fit in a 1.25" barrel. 33-32mm at 50° 27-26mm at 62° 25-24mm at 68° 17-16mm at 82° 14-13mm at 100° So you don't need 2" eyepieces to get a large apparent field and large true field with shorter focal length eyepieces.

Step 1 is to learn the sky, i.e. learn the constellations and the names of the 30 or so brightest stars. To help out with that: skymaps.com monthly maps (which show the planets) a David Chandler two-sided planisphere and, use the "nightly Tour" in your telescope's hand controller.

Bortle 9+. You need to understand that once you get to a 10mm eyepiece, anything shorter will heavily depend on Seeing (atmospheric turbulence). The less air movement there is, the higher the power you can use. Just stay away from nebulae and galaxies for a while, as they are the hardest things to see in the night sky. Try star clusters, because no two look alike, and there are thousands of them visible in a 6" scope. Urban astronomy can be: Moon Planets double stars (many are quite lovely, and do display striking colors) carbon stars (large red giants near the ends of their lives) Variable stars Bright open star clusters Bright globular star clusters The cores of the brightest galaxies The brightest emission nebulae (using a nebula filter) Then, when you get to darker skies: Galaxies, Emission nebulae, dark nebulae, reflection nebulae, supernova remnants, all star clusters, telescopic comets, and everything seen in the city. Your term "smudges and blurs" is a good one to describe how nebulae and galaxies appear in a scope. The words "faint fuzzies" are often used. We do not, by and large, see colors, or see the details in photographs, so put that out of your mind. It can be exciting to see a small faint fuzzy when you know it is a galaxy of billions of stars 250 million light years away and that the light you are looking at was emitted back before the dinosaurs walked the Earth.

A note: the field stops of 100-110° eyepieces (and anything narrower in apparent field) fit inside a 1.25" barrel at any focal length shorter than 14mm. So you don't get any wider a field with a 2" barrel below that point. 2" may be convenient, or support a large heavy eyepiece more safely (e.g. 9mm 120°), but to all intents and purposes, 1.25" eyepieces can be as wide as they get when the focal length is shorter than 14mm. If the goal is nice "framing of DSOs at shorter focal lengths", one needn't use a 2" eyepiece to attain the necessary field.

Maximum magnification depends on Seeing (atmospheric turbulence), which varies from night to night and even from hour to hour. For a 6": 21-60x is considered low power 60-120x is medium power 120-180x is high power 180-300x is ultrahigh power. At a useful minimum, you want to have eyepieces that yield one low power, two medium powers, and one high power, maybe 40x/80x/120x/160x, or eyepieces of 38mm, 19mm, 12.5mm, 9mm Your environment is heavily light-polluted, so the 40x is likely only going to be used on large open star clusters on the very clear nights. That does not mean you wouldn't want more eyepieces eventually, since 200x ( 7.5mm) is often a useful magnification for a 6" scope. You will likely have to observe often to get skies steady enough for 200x, or even 160x for that matter. Pay attention to collimation (SCTs don't go out of collimation easily, but excellent collimation is critical for high power), Cooling of the optics (the scope will not yield sharp high power images when first taken outdoors, but images will get better over the couple hours the scope will take to cool down to the ambient temperature, and the conditions of the night sky. I refer to this as the three "C"s. Seeing at high power will be better when the jet stream is not overhead, 2-3 days after the passage of a front, when the wind has died and the air seems thicker and harder to breathe. You want non-moving, stable air. To see deeper in magnitude, you want the front to have just passed, when the air is very transparent and clear and light scatter of the atmosphere is at a minimum. I live in L.A., and right after a front has passed, and there is no moon in the sky, I have seen magnitude 5 stars at the zenith. On the days of really good seeing, I can barely make out Polaris and magnitude 2, and the air is thick.

Then a compromise: the 30mm 70° UltraFlatField from United Optics. It's available for £179 from FLO as a Stellalyra Ultra Flat Field: https://www.firstlightoptics.com/stellalyra-eyepieces/stellalyra-30mm-ultra-flat-field-2-eyepiece.html Magnification won't be too low, so the field won't be completely washed out. The step to the 17.3mm is a good jump up in magnification. It's one of the finest 30mm eyepieces out there today. I find it sharper than every other 30-31mm eyepiece except the 31mm Nagler. The true field is 34.4% wider than the 24mm Panoptic. In a typical 8" dobsonian, 1.73°.

See: https://www.cloudynights.com/topic/862337-2023-eyepiece-buyers-guide/?p=12473522 Here is what is available in 6mm (you can scroll the list): [It is plenty of choices!]

The black section containing the lens is smaller in O.D. than the 1.25" barrel above it. That does not augur well for the threads on the lens portion to be the 28.5x0.6 filter tread. Highly unlikely, I'd say.

Simply use a 2" barrel extender threaded to the skirt and you have a 2" eyepiece. If the 2" skirt is not threaded to accept barrel extenders, then an attached adapter works. The eyepiece is usable as 2" in base form, but it takes 1.25" filters.