Don Pensack

Omegon Redline = Astromania SWA 70 = Astrotech AF70 = Celestron Ultima LX = Arcturus Ebony = Olivon 70 = Skywatcher SWA = Telescope Service Expanse. Some would be used, others new. Shop for price. However, the focal lengths all have different internal designs. 32mm--an average Erfle--best at f/8 or longer 22mm--very very good for a cheap price--a real bargain 17mm--the same as the 22mm, with just a *trace* of edge of field brightening. 13mm--Horrible. The worst edge of field brightening I've ever seen in an eyepiece, with 50% of the outer field looking like you're looking through a nebula. 8mm, 5mm, 3.5mm. Just average. Baader Hyperions are better. For f/6 and longer, they're OK.

The maximum without rectilinear distortion is 37.8° with a 27.4mm field stop. 4% distortion yields 39.3° 6% distortion yields 40.0° (the average 40mm Plössl) 10% distortion (very large for this type of eyepiece) yields 41.6°. You can see how unlikely even 43° is.

If they quote 52°, it is because they merely copied the information from a shorter focal length. The maximums are 43° on a 40mm, 49.5° on a 32mm, so if you see figures quoted that are larger, they are advertising figures, not actual.

I believe the instrument comes with a 1.25" star diagonal and visual back, but has a standard SCT thread which will accept a 2" visual back and 2" star diagonal. I don't think the scope comes with those, however. They would have to be added.

To clean the eye lens well on nearly any eyepiece, removal of the eyecup is desirable. However, ROR is very gentle and will not damage rubber or plastics, or your skin if you get a drop on it. I recommend the drip bottle. The spray wastes a lot of fluid and you cannot spray it directly on the lens anyway.

Baader is interested in selling Baader accessories. The Baader Zoom works fine fine many different Barlows, the TeleVue among them.

See: https://www.baader-planetarium.com/en/baader-2"-clicklock-eyepiece-clamps.html For sure it is not a T-Thread under the adapter. The I.D. of the 2" adapter is 48mm for 2" filters. The I.D. of the upper section is 50.8mm+ a bit. T-Thread is only 42mm, so it would make no sense to make this adapter with a 42mm choke point in the middle. Ergo, the thread in the middle, where the Click lock connects is probably larger than 50.8mm. The drawing implies at least 50.8mm.

I worked in a shop where we had to clean the eye lenses on binoculars every other day on all our demo models. We sold a lens cleaner that was basically alcohol, and it simply did not remove debris like mascara or fingerprints easily. We started carrying ROR and it was a godsend--it cleaned the lenses to, in some cases, cleaner than new, with only one cleaning, where alcohol required multiple passes on some lenses. We also had Nikon lens cleaner, which was pretty good, but ROR was the best cleaner we used. It even beat acetone and was less caustic to use. I figured out that it was primarily the tiny amount of soap and ammonia in the formulation that really did well to remove the stuff on the lens. ROR has, in addition, water, isopropyl alcohol, and salt. I'm not sure what the salt accomplishes, but the formulation really works. I'm sure there are other cleaning fluids that work well, but ROR works very well, and I've used it now for 20 years and it still is my cleaner of choice. There is one issue with ROR, and it deserves mentioning: you should not let it or any residue from it dry on the lens. It leaves a haze on the lens (probably the soap). It can be cleaned off easily enough, but it does mean that when you use it to clean a lens, you can't dawdle. Once the lens is wet and wiped, it's important to clean it off completely with a clean Q-Tip ASAP. My work station has an ultra-bright lamp on the desk, and if I hold a lens up to the light and tip it just right, I can see anything still on the lens, whether a streak, or haze, or dust particle. When the lens is really clean, passing a Q-Tip across the surface feels like moving on a teflon surface--there is no drag whatsoever. I've even cleaned brand new eyepieces (mostly from 2 Chinese factories whose names I won't mention) and made them noticeably cleaner.

I look in the APM and see the same thing. There are probably multiple baffles along the length, and a field stop somewhere above the field lens and a focal plane even higher in the eyepiece. The extra baffle in the 2" adapter is probably a good thing. It made a *slight* difference in the TeleVue Apollo 11, and lower baffles were built into the Vixen HRs and a few other eyepieces I've seen. So, whether APM or Stellarvue, I would use the 2" adapter if it has a lower baffle in it, or at least experiment to see if the baffle in the 2" adapter makes any difference at all. In the post to which you link, I was comparing the Ethos SX to the Stellarvue.

Both the APM and Stellarvue have the same baffle in the 2" adapter. The difference is that the bottom barrel of the eyepiece is stainless steel on the Stellarvue and aluminum on the APM.

Well, if the Ethos was a smidgeon over budget, the APM XWA would be within budget, and approximately 2 for 1 in price. If that is too expensive, well, there are a myriad of cheaper options.

Then the equivalent APM XWA in 4.7mm (labeled 5mm) and 3.5mm, both 110°.

Sure looks like it.

A very easy way: #1.Time the passage of a star across the field in the eyepiece. Convert to seconds. #2.Time the passage of the same star across the field with the Barlow in place. Convert to seconds. #1÷#2 (i.e.1/2) = magnification factor of the Barlow for that eyepiece. Since different eyepieces have their focal planes in different places within the eyepieces, the magnification factor will vary slightly for every eyepiece. Parfocal eyepieces will all have the same magnification factor.

Well, if you need glasses at the short focal lengths, then look for 18mm+ eye relief. But if you don't, 13.6mm is OK.

My double star/Neptune/Uranus/small planetary eyepieces are the TeleVue Ethos SX in 4.7mm and 3.7mm. Superbly sharp and I can watch the object drift across nearly the entire field before nudging the scope (almost a full minute at 495x in the 3.7mm). I also own the 3-4-5-7mm Delites and they are fine, but the longer drift time in the Ethos SX makes observing at high powers very easy. I wear glasses to obseve with 9mm or longer focal lengths, but not that at that small an exit pupil.

You missed some: --Barlow lens attached to bottom of 2" eyepiece. --Barlow lens attached to bottom of 2"/1.25" adapter --Barlow in its own tube in front of the star diagonal

What is the highest power usable on a given night in a given scope? 1) 350x. This is the usual maximum the atmosphere allows with average seeing, no matter what the scope size is. On average, which is when? LOL. 2) 50-60x/inch of aperture. This is predicated on excellent optics, excellent seeing conditions, and excellent vision. Is it usable? Sometimes, but not often. 3) the point where the scope reaches maximum resolution because the Airy Disc becomes visible with a size, usually around a 1mm exit pupil (magnification = aperture in mm). 4) The magic "eutectic point, where dimming due to increased magnification is offset by the increased size. Higher power makes the object less visible. This will be different for nearly every object. 5) The limit allowed by whatever the seeing conditions allow. Could be 200x, could be 2000x. 6) the maximum allowed by the optical quality of the scope. 7) the maximum allowed before floaters in the eye significantly interfere with the image. It will be higher with double stars, lower with the Moon. I simply cannot use 60x/inch any more except on a double star. Otherwise, whatever I observe is filled with floaters. I stop around 0.65mm in exit pupil (exit pupil = eyepiece focal length / telescope f/ratio). But I can go a lot higher on double stars, ~0.4mm exit pupil. I usually say to people, "Magnification range is from whatever eyepiece yields an exit pupil equal to the dark adapted pupil in your own eye at low power up to where floaters in your eye interfere with high power. Another way to look at it is: Low Power: 4-10x/inch of aperture. You may have astigmatism in your eye at these low powers. If so, use glasses or contacts to correct it and the images will be a lot sharper. These magnifications are limited by light pollution in how low you can go, because lower powers make the eyepiece field background brighter and reduce contrast. Medium Power: 10-20x/inch of aperture. The range where your vision will have its greatest acuity, where seeing will interfere very little, if at all, and where most deep sky objects will be visible easily. High Power: 20-30x/inch of aperture. You may be running into seeing issues here. Floaters in the eye may interfere with magnifications near the upper end. Usable many, if not most, nights. Best choice for planets and Moon IF seeing allows. Ultra High power: 30 to 50-60x/inch of aperture. Not typically usable every night, but can be used more often on double stars and small planetary nebulae than most other objects. My recommendation--use a Barlow to get here, using a lower power eyepiece in the Barlow.

That was a 2" Barlow with an ED glass lens from Barsta and sold under many many labels (Knight Owl, Olivon, etc.). It was one of the first Barlows in 2" that I saw that had a removable lens that could be threaded elsewhere. You could use it on the bottom of the eyepiece (1.5x), in its own tube (2X), on the front of the 2" star diagonal (2.6x) or in its own tube in front of the star diagonal (~3x) And, of course, threaded to the bottom of a 2"/1.25" adapter for 1.5-1.6x with 1.25" eyepieces. I agree, it was a good lens. I haven't seen them for a while. I wonder if they're being sold under other labels.

On the 40XW, in my 12.5" Dob with Paracorr 2 (so operating at f/5.75 = 1826mm focal length), I don't see FC in the 40mm XW, but there is a bit of astigmatism in the outer 5°+ of field. That may be what is blurring the edge in your photo. The resultant exit pupil was way too large for my older eye, and I didn't see any increase in brightness from a 27mm Panoptic. Ah, to have younger eyes and larger pupils. Too bad the 35mm Scopos is no longer available.

That looks like a re-badged GSO, and would be a good choice for an inexpensive Barlow. It also has the advantage of being able to have its lens unthreaded and attached directly to a 2" eyepiece or 2"/1.25" adapter for 1.5X magnification. The 2" 2X Explore Scientific would not solve your issues of weight and length.

What Louis said. If the scope is an f/6, and the pic looks a little like it is, then 42mm is the longest you want to go. That's OK, since 40-42mm eyepieces have the same size true fields in 2" as longer focal length eyepieces.

At f/5, yes, the Morpheus is sharper to the edge. At f/6, the difference is marginal. At f/7, it's getting hard to tell. At f/8, no difference to the edge. However, in my experience, the Morpheus have better contrast and a lot less internal scattered light.

The true answer is that only you can answer that with experience. The Starguiders will be wider in apparent field from 16-24mm but otherwise it's a toss-up. The zoom gives you the option of the perfect magnification for conditions, but the individual eyepieces will allow a change of magnification without all the in between magnifications you don't want. In other words, when you want to change the size of an object in the field by increasing magnification, you rarely want to change the magnification 5% or 10%--you want the change to be substantial and give you an entirely different view of the object. That can be nicely accomplished with, for example, a 40% change in magnification between eyepieces. The Zoom hits all the points in between and requires more adjustment to find the increase you were looking for. If you have a zoom from 24mm to 8mm, you have every tenth of a mm focal length in between. If you had a set, it might run 24mm--17mm--12mm--8mm. After a short while, you'd already know which other eyepiece to pick for the view you want. A zoom does mean you don't change eyepieces in the focuser, which keeps you in your seat with your eye against the eyepiece. But, doctors say we should get up and move around periodically for health, so there may be some side benefits from getting up, moving to a table, and selecting another eyepiece from your box. There is no really definitive answer here. For me, the narrow fields of view in zooms at low powers would keep me using fixed focal length eyepieces for much of the zoom range, and then what's the point of a zoom? My last point is that SCTs have very narrow fields of view intrinsically. I would argue that eyepieces even wider than the Starguiders might be a better match. I'd look for eyepieces of 68-70° at a minimum, many of which are available for modest prices. That way, the fields of view won't seem as narrow.

The APM 20 is a much better eyepiece than the ES in the outer 50% of the field. It is also sealed, just not submersible. There are differing degrees of waterproofing standards.