Don Pensack

Yes, this chromatic aberration of the exit pupil, or CAEP, is common in longer focal length ultrawide eyepieces, making them less appropriate for daylight or lunar observing. Fortunately, those are two uses less likely with long focal length eyepieces in astronomical telescopes.

Boy, has there been a lot written on how to choose magnifications for a scope! One way is to have a range of exit pupils, but which? Another way is a % step between magnifications. Another is to have even steps from a low power up. I side with this latter approach for a couple reasons: --it makes the highest powers closer together, %-wise, which is useful when bumping up against the ceiling of your seeing conditions --a smaller % jump at the high end is necessary to not make the magnification jumps too large. a 40-60x jump at low power is very close together. The same % could be 400-600x and that is a huge jump So, what is the even magnification jump to favor so that low powers aren't too close together and high powers aren't too far apart? I think it varies by scope size. If you have a 20", it wouldn't be outside the realm of utility to have a 100x jump in between magnifications, i.e. 100/200/300/400x and so on That wouldn't work for a 4" refractor, where jumps of 30x might be more rational. So, it seems to me, from owning 31 scopes so far, that a 1X/2X/3X/4X sequence is reasonable, where x = a number appropriate for a certain size of scope. Perhaps, 50 for an 8", 60 for a 10", 70 for a 12.5", and so on. And if the jump at some particular place in the sequence seems too large, then fill in with a 0.5x in the middle, like 1x, 2x, 2.5x, 3x, 4x, etc. So, in answer to your question, and having owned an 8" scope for 11 years, I think you do not need a magnification in between 50 and 100x, but each observer has a favorite power that just feels right. If you are constantly finding 50x too low and 100x too high for some preferred targets, you might definitely add one in between. What i would do, though, is just to get a wider apparent field at 100x. The objects would stay in the field longer, and the desire to have a lower power might evaporate. I think having jumps of 50x on your scope is pretty close to perfect, and the wider field may make the 100x eyepiece more usable and desirable. Make your 9mm a 100° eyepiece and the 20mm might get a lot less use.

The SSWs should be OK. Just be aware of the fact they have a lot more spherical aberration of the exit pupil than the Type 6 Naglers, which are their direct competitors. And slightly less well corrected for lateral field astigmatism than the Naglers, though this varies across the line. There is a good review of the SSWs here on SL. Over here in the US, the SSWs are actually more expensive than the Naglers, but that may be different in the UK.

There is more to focal length than AFoV. Longer focal lengths yield larger exit pupils and brighter images. The 21mm also has a 4mm wider field stop than the 17mm, so yields a larger true field, regardless of apparent field. That's what makes a 40mm Plössl a good eyepiece for a small, long f/ratio, Maksutov. Yes, it has the same TFoV as a 32mm Plössl, but it has a larger exit pupil and a brighter image, as well as being lower power, important for some objects. I doubt anyone would buy both the 21mm and 17mm Hyperion anyway, as the magnifications would be too close together.

Just got an updated list from Baader in Germany. They haven't updated their site yet. They say: 4.5mm--358g 6.5mm--326g 9mm--328g 12.5mm--315g 14mm--363g 17.5mm--305g. That is very close to JOC's weights. Excellent.

The fields of view are wider, but though that might be enticing, they are not all equal. The 24 is poorly corrected in an f/5 scope. The 21mm and 17mm are good. The 13mm suffers from edge of field brightening. The 10mm is fine. The 8mm is just OK, while the 5mm is a bit better. I don't have experience with the 3.5mm. I could see buying the 21mm, 17mm, and 10mm, but I'd skip the others. Your Zoom has the flaw of having a wide field below about 14mm, but a narrow field above that. Were I to suggest supplementing the Zoom, I'd say add a long focal length with a wide field. If 24mm is enough, try an APM 24mm UltraFlat field for glasses, or an Explore Scientific 24mm 68° if you don't wear glasses. If you'd like a maximum field eyepiece, then go for a 30mm 2" design, like the APM UFF 30mm, or the same from Altair.

OK, I will have to re-weigh them all again. I just weighed my personal 17.5mm at 305g, the same as JOC. And I got 320g for the 12.5mm. For now, trust his figures. They are likely to be accurate for current production. I'll have to ask Baader for clarification.

Odd. I measured them on my gram scale only about a month ago and got: 4.5mm--370g 6.5mm--350g 9mm--360g 12.5mm--345g 14mm--360g 17.5mm--312g. I rounded off, but I was within a gram of Baader's quoted spec sheet weights. I wonder if they have thinned the barrels and lightened the eyepieces?

Yes, on a gram scale. The amount of astigmatism in the SSWs depends on the f/ratio of the scope. At f/5, they are just OK, not perfect. At f/8, they're nearly perfect. The SSWs also all have spherical aberration of the exit pupil, but its effects diminish with focal length. By the shortest focal length, it would be hard to notice.

12.5mm is 345g. Nope, the latest one weighs 320g.

Try a 30mm APM UltraFlat field eyepiece to round out the set. Then your training will be complete.

For low power, a 30mm APM UltraFlat Field eyepiece is a winner. It's lighter and smaller and as sharp as the 31mm Nagler and 30mm Pentax XW, with which it competes. And compatible with glasses. The next one needed is something like the 17.5 Morpheus. Wider, which befits a higher power, and also compatible with glasses. If you don't need glasses, the TeleVue Nagler Type 6 eyepieces could round out the higher powers (down to a 3.5mm eyepiece). The APM 100s are a good value, too, and the shortest focal lengths are the best-corrected, I've found. It makes sense to go wider in apparent field as the magnification goes up, to keep the field from shrinking too much. Especially in an undriven dob, where things can go whizzing through the field and a wider eyepiece gives you more time between nudges. Russ, though the Morpheus can be used as 2" eyepieces, you should think of them as 1.25", because if used as 2", they require an enormous amount of out-travel at the focuser. They are closer to parfocal with a lot of other eyepieces if used as 1.25". There is no harm in using them that way. All the eyepieces I've mentioned except the 30mm APM can be used as 1.25" eyepieces.

The primary thing to do in an urban LP environment is use a bit higher powers than normally used at a dark site. Yes, this will dim the object as well as the background, but the larger size and darker background will make most extended objects a bit easier to see. For any star or star cluster (open, globular), higher power yields improved contrast and allows you to see fainter stars. Many if not most beginners use too low a magnification for most objects and that's OK in dark skies, even though they'd see more at higher power. With most DSOs (not the largest objects) observed in an urban setting, you probably shouldn't go lower in power to view them than 0.5D in millimeters, i.e. a 10" scope at 127x, or a 6" scope at 76x. The lower powers can be quite nice, but not particularly when the skies are light-polluted.

I seem to recall some early Questars, Bushnells, and even a Celestron with threaded-in eyepieces. But I haven't seen one since the '80s.

Just posted the 2020 Eyepiece Buyer's Guide https://www.cloudynights.com/topic/700069-2020-eyepieces-buyers-guide/ Enjoy.

Sorry, just saw your question. The Paracorr's top is not smooth enough to be used for fine focusing. What you do is focus with it (after setting the Paracorr with an eyepiece that you know the setting for and focusing the scope) when you insert eyepiece B just to find out what the proper setting is for eyepiece B. Write it down. Next time, before inserting that eyepiece, dial the top to the setting you discovered, then insert the eyepiece. It'll be really close to focus and only a tiny touch up of the fine focus knob will be necessary to achieve pinpoint focus. Even with knowing the settings for every eyepiece in your collection, you will still need about a 1mm range of focus in your focuser. As for figuring out what eyepiece to start with, if you own a Paracorr 1, you should not use a 31mm Nagler, or 21mm or 17mm Ethos or a 20mm ES 100° as your starter eyepiece, as these do not have optimum settings in the range of the tunable top. Use another eyepiece you know the setting for. The eyepieces I mention will all use Setting 5 (all the way down on the Paracorr 1 ), but that setting is still a tad short of optimum. Because they are not at the optimum position relative to the CC lens, if you focused using the tunable top on another eyepiece, it, too, would be at the wrong position for optimum correction. So, an 8mm Delos uses the Paracorr 1.25" included adapter and the 14mm and 17.3mm use the in-travel adapter to make them parfocal with the 12mm and shorter Delos, all of which are parfocal.

The visibility of coma is apparent field related, i.e. you WILL see significant coma in a 13mm 100°, whereas it will be substantially less in a 72° field eyepiece. I don't really understand why you don't use the Paracorr for all your eyepieces as it not only eliminates coma but also slightly flattens the field. The 13 APM has a small amount of induced astigmatism at f/5 which will be worse at f/4. The Delos will have a far better edge, where star images are concerned. As for not fiddling around with Paracorr settings, perhaps you aren't aware you needn't do that. The Paracorr will parfocalize all eyepieces, i.e. simply insert eyepiece B after eyepiece A is properly set in the Paracorr, and focus eyepiece B using the Paracorr's top. The setting that results in focus is the setting for that eyepiece. That's no more complicated than moving the focuser. Even if you insert a 1.25" adapter, the process is the same. You may still need to fine focus with the focuser, but a half millimeter of focus travel is about all you'll need. The 14mm Delos, however, will need the TeleVue In-travel adapter (AIT) to be parfocal with the 8mm Delos when the 8mm Delos is used with the Paracorr adapter.

Add the additional eyeguard extender. That will solve your problem.

From hours in the field: Mars: Contrast Booster stupendous--simply the best Mars filter out there. Jupiter--Moon and Sky glow filter better, though CB helps a little. Best is no filter and high power. Saturn--Yellow #12 or #15 enhances shadow details in rings. Otherwise, like Jupiter--high powers with no filter is best. M&SG not much help at all.

Some possibilities compatible with glasses: Baader: Hyperions, Morpheuses Explore Scientific: 30x82, 28-40x68, 12-17x92, 26-40x62, 30-40x52 TeleVue: Delites, Deloses, 32-55 Plössl, Apollo 11, 27-41 Panoptics, 22-31 Naglers, 17 Nagler marginal (a bit tight) Olivon (BST or Barsta): 70° Series, 58° series (marginal--a bit tight) Pentax: XWs, XFs APM: 12.5x84, 24x65, 30x70 Vixen: 2.5-25 SLV There are others, but that gives you some choices.

Since you can have an exit pupil larger than your pupil in a refractor (it only sacrifices some light, but the magnification is really low), I've tried a 55mm Plössl in my 4" refractor and got to 13x and a field of 3.7°. It's not quite large enough a field for using the scope itself as a finder (my finder is 8x and a 6° field), and the magnification is barely more than my finder, albeit with a significant jump in aperture. "Context" views for objects like the Pleiades or M31 do require massive fields of view. My best view of those objects with context is something that yields ~10-20x and a 4.5° field, like a 31mm Nagler in a TeleVue NP101 refractor. I've regretted selling mine for several years.

For me, yes, 44x is low enough as a low power. I don't need for my refractor to duplicate a binoculars power or field size. IF you seek a really wide field and really low power, then perhaps it makes sense, but I really see very little reason even then to have a magnification below about 5X/inch (5mm exit pupil) That would be a 23mm eyepiece. Yes, the image is brighter at low power, but star clusters will be poorly resolved, and galaxies really small so unless you really enjoy the "context" view, I wouldn't bother. The largest eyepiece I use with my 4" refractor is an 18.2mm yielding 39x. My most-used eyepiece is an 11mm (65x) or a 7mm (102x).

I used a #30 magenta on Mars for a while, but a friend suggested the Baader Contrast Booster. it is simply the most amazing Mars filter I've ever used, and I've had about 9 other specialized Mars filters over the years, including the TeleVue Mars A and Mars B, the TeleVue Planetary filter, the Orion Mars filter and the Sirius Optics Mars filter, a #23a, a #25, a #21, and the #30 magenta. None gave the incredible images of the CB. If you have one, try it on Mars. You'll be amazed.

Except the UHC. Astronomik's UHC filter passes the H-α wavelength at a high percentage, whereas TeleVue's Nebustar II (their version of the UHC) has no red transmission at all. Star images in the Astronomik have a bit of red tint to them, where the stars in the TeleVue are the usual blue green seen in a filter lacking red transmission. The current Lumicon Gen.3 UHC has the same profile as the TeleVue, while the DGM admits a much broader patch of red than the Astronomik.

The 11mm was the poorest selling Nagler, maybe the same as the 2.5mm (also discontinued). Everyone who bought the 13mm skipped to the 9mm as the next size. The Apollo 11 eyepiece was designed to commemorate the moon landing of the LEM of the Apollo 11 mission. So of course it had to be 11mm. It almost missed the 50th anniversary year because of some changes after the prototypes. The Nagler wasn't discontinued because of the Apollo 11 eyepiece, but because of sales. And if TeleVue came out with a long eye relief line of T7 Naglers, I'd suggest they skip 11mm.😀