Don Pensack

Not everyone thinks the 12.5mm Noblex was all that great an eyepiece. It's angular magnification distortion made it unusable for me. The 12.5mm APM Hi-FW is better in that regard and equally sharp, but has edge of field brightening, another issue I can't live with. I find the 12.5mm Morpheus better than both of them. However, I don't use that much, preferring the TeleVue Apollo 11.

That difference would be invisible in smaller scopes.

You're right. It would be great to get some in-depth lab testing, but there isn't enough money in it to pay for the lab equipment. If such occurs, it is usually an amateur astronomer working for a large optical lab doing government work.

The answer to your question is no. It is a threaded-on eyepiece and not 1.25". The likely focal length is 22-23mm to yield 9x in a 200mm focal length front lens. Reticle (note spelling--reticule is a seldom-used variant and usually refers to a small drawstring bag) eyepieces in 1.25" are available quite cheaply on eBay and Amazon. Stellarvue produces a small finderscope with a 1.25" eyepiece, as does Antares, but they are rare birds. Most dedicated finder scopes (not 50mm refractors repurposed as a finder) do not use 1.25" eyepieces.

The difference in transmission is likely to be on the order of 2%, if that much. That is ~0.02 magnitudes. It would take a spectrophotometer to see that difference. Both Delos and XW are BBAR coated on all surfaces, even the cemented ones. There is a difference in correction of astigmatism at the edge in faster f/ratios, and in the spectrum of transmission (the XWs were a tad yellower in my color test), and in flatness of the field. Those differences are unlikely to matter for something on axis in a tracking scope. If you are looking to see deeper, eyepieces are not the place to look for that. Larger aperture is. As for the latest technology in lens materials and surface polishes, unless suddenly the eyepiece market is willing to cough up $1000 or more for every eyepiece, we aren't going to see it. High end camera lenses for professional use are mostly above $10K. Most of the posts here on SGL are arguing about whether this $100 eyepiece or that one is better. A Nikon engineer told me they can get 99% transmission through a 20 element lens, but the coating on each lens surface costs about $300. We will never see that. Still, there are differences in eyepieces that can be measured. Here are a couple links to peruse: https://web.archive.org/web/20110622011950/http://cieletespace.fr/files/InstrumentTest/201102_test_oculaires.pdf https://web.archive.org/web/20130829052725/http://www.cieletespace.fr:80/files/InstrumentTest/201306__6_oculaires_10mm.pdf

Delites are also Japan.

Deep Space Products sells a 3" to 2" drop-in adapter: https://www.deepspaceproducts.com/product/reducer-adapter-for-3-0-compression-ring-opening-to-accept-2-0-accessories

With some people reporting vignetting on the 17mm Ethos in the P-II, I looked for it. It certainly wasn't severe if it is there at all. I'm not as sensitive to vignetting, I guess, as some people, since I regularly used a 41mm Panoptic in an 8" SCT and eyepieces that yielded up to 1.3° at f/5.5 in the same scope. I didn't find either the 17 Ethos or 21 Ethos had notable vignetting. Currently, my largest field diameter eyepiece has almost exactly the same field diameter as the 21mm Ethos, and I see no vignetting in that eyepiece. That would not carry over to a larger field diameter such as those in the 31mm Nagler, 30x82ES, 41mm Panoptic, 40x68 ES, 35mm Panoptic, 34x68 ES, 36mm Hyperion., all of which have larger field diameters.

Different eyepieces focus at different points. I've had sets of eyepieces that focused 1.2-1.4" apart at times. They will focus that far apart in a coma corrector too. It's why I suggested parfocalizing your eyepieces with the in-most focusing eyepiece, since that one has its focal plane the farthest from the bottom of the eyepiece and needs to be closer to the CC lens. How close is that? It would depend on how far in the eyepiece focuses. The size of the spacer in the GSO Coma Corrector that would be added would depend on how much infocusing that eyepiece needed, and whether or not you wanted that eyepiece to focus the CC + eyepiece ensemble perfectly when sitting in the CC without any parfocalizing ring. The key is to achieve the correct placement of the CC in the light cone of the scope and that will be done when the focal plane of the eyepiece is the working distance from the CC lens. I described a method for determining what that spacer length should be in my previous post. It could be short, or, as in your case, it could be longer. With a few eyepieces, that spacer might be quite short or even removed. I have had eyepieces with focal planes 0.5" to 0.7" above their shoulders that required a lot of infocusing.

No. Your extension tube pulls the eyepiece out of the focuser a minimum of the length of the bottom barrel of the eyepiece. If that works, then fine. it might not work for other eyepieces, though. Most of the time, you won't need that much pull-back distance, but only, say, 1/2", which is much shorter than the length of the lower barrel on the eyepiece. In that case, adding a barrel extender (it merely extends the barrel of the eyepiece, but it is the same diameter as the barrel) works better, since you can simply pull the eyepiece out 1/2" and tighten it down and know there is enough barrel down inside the focuser for safety.

No. it is not a simple "drop the eyepiece in" device. At least, not without first adjusting the eyepieces. I'll explain: A coma corrector has an operating distance, wherein the focal plane of each eyepiece needs to be a set distance from the CC lens. If your eyepieces focus at different places in the focuser travel, they will also be at different distances from the CC lens. As I understand, the top of the GSO coma corrector is not long enough to place the CC's focal plane far enough away from the CC lens, hence the spacer. Now, no spacer is necessary if the barrels of the eyepieces are long enough you can pull them out of the CC to the correct point, but that is less likely. What is typically done is to find a spacer that puts the opening of the CC at the correct working distance away from the lens. That information is online many places. Translucent scotch tape is placed in an X pattern over the hole sans eyepiece. The scope is pointed at the Moon and the moon is focused on the tape by moving the focuser. The focuser is then locked in place, the spacer is removed from the CC, and every eyepiece is inserted until it is in focus and the distance above the CC the shoulder of each eyepiece is is recorded. If all eyepieces focus when pulled out of the CC by over a certain minimum amount, say, 14mm, that spacer's length can be inserted into the CC between lens and upper. Done right, your in-most focusing eyepiece will be perfectly in focus at that point, when simply dropped into the CC. All other eyepieces should have parfocalizing rings added to them so that when they are dropped in they too are in focus. Essentially, you have parfocalized all your eyepieces. [You can do this in advance by starting with your in-most focusing eyepiece] When starting out for the night, any eyepiece, then, can be inserted in the CC, the ensemble put in the scope, and the scope focused, knowing that so doing puts the CC lens in the exactly right place in the light cone of the primary mirror to correct coma. Every other eyepiece inserted will encounter the CC in its optimized position and will be in focus when dropped in (or very close). You only have to do this once. Any new eyepiece, just insert the new eyepiece and pull it out until it is in focus and that will be the optimum position for that eyepiece. Parfocalizing rings are a nicety. You can, of course, merely pull the eyepiece out of the CC until it is in focus and simply tighten it in place. After this is done, you will still need a mm or two of focuser travel for the very best fine focus, but that's all. Moving the CC back and forth more than that results in poorer correction. I suggest you read the long thread I linked to earlier. Complicated? Not really. Time consuming? A bit. This is one of the reasons why the ES and TeleVue CCs are more expensive--they have helical tops that replace the necessity of parfocalizing rings.

One should remember that no matter how short the upper section of an extension tube is, it will still raise the eyepiece out of the focuser by at least the full length of the lower barrel of the eyepiece. That will require a LOT of in travel at the focuser to get back to focus. So if you need 1/2" of out travel to focus, it may not be the best solution. It might be better, where focus travel is more limited, to utilize a barrel extender that threads onto the eyepiece but which still inserts fully into the focuser, and then pull the eyepiece out to the focus point, knowing there is still enough in the focuser for safety. I know this does not solve the problem of moving a filter from one eyepiece to another, but does get around the huge refocusing problem when an extension tube is used. Creative solutions to the hassle of transferring filters from eyepiece to eyepiece (as a side note for the above): --filter on the front of a coma corrector or Barlow. This applies to newtonians or any scope with a Barlow. --filter on the bottom of a 2" to 1.25" adapter. This is a preferred method for planetary filters, where multiple high power eyepieces might be used. --filter on the front of the star diagonal (refractor, SCT, MCT)

Ah, the Omegon re-badged GSO unit. One of the starting points for use as a visual corrector is to add a 19mm spacer between the upper barrel and the lens housing. One very easy way to use it is to parfocalize all your eyepieces first to your eyepiece that needs the most in-travel at the focuser. Here is a long thread on optimizing the GSO coma corrector for visual use: https://www.cloudynights.com/topic/462985-setting-up-the-gso-coma-corrector/

As I said--a lot of adapters out there. You can pretty much choose where you want the scope to focus.

If you get the shiny spacer, this happens on the Moon or as a bright object approaches the edge:

1. The amount of infocus varies according to the scope's f/ratio. The Paracorr is ~14mm, and the MPCC seemed to be less when I was fooling around with it. 2. The knurled ring is for certain camera adapter attachment. It is removed for visual use. 3. you don't. One of the accessories needed for the MPCC is the 1.25" adapter which allows 1.25" eyepieces to be used with the 2" MPCC. You do need a 2" focuser--there is no 1.25" MPCC. 4. I saw a lot of spherical aberration in the out of focus star images, so I think it would be wise to remove it at high powers for planet viewing. However, you will also need to have a tracking mount, then, as only the center of the field will be coma free. This makes the ES HRCC and TeleVue Paracorr better, since they do not add spherical aberration. And, they add a bit of magnification as well, not a bad thing for planets, Moon, double stars, planetaries. 5. I didn't see any evidence of field flattening. In my f/5 dob, the 35mm Panoptic has a slightly curved focal plane, so a different focus in center and at the edge. I saw the same thing when the MPCC was used. 6. I agree the GSO is a better choice and easier to optimize for all eyepieces. It's 1.1x also has some field flattening.

It is hard to use--it attaches directly to the eyepiece, but to get it the required distance from the focal plane of each eyepiece, it's necessary to have a different length of spacer stack attached to every eyepiece. The easy way to do that is to optimize the spacer stack on one eyepiece and focus the scope. Then, add or subtract spacers from every other eyepiece until it is parfocal with the first eyepiece you optimized without using the focuser of the scope. You won't be able to perfectly parfocalize all the eyepieces, but if you get them all within about 2mm, you're OK. There is also a 1.25" adapter it can attach to that, because most 1.25" eyepieces are closer to the same focus, can be used with parfocalizing rings on the eyepieces themselves. If all the spacers are correctly chosen, all the eyepieces will become approximately parfocal. Typically, you leave the spacers on the eyepieces and merely transfer the CC to the next eyepiece like a filter. The GSO coma corrector is easier to use, and the Explore Scientific and TeleVue coma correctors require no spacers and are the easiest to use. If the scope is f/5 or faster, you'll want coma correction at all powers. At f/5, only the center 2.2mm of field is coma free otherwise, and it's only 1.1mm at f/4. 1) the working distance between lens and eyepiece focal plane (or chip) is ~55mm. It requires a placement closer to the mirror than the focal plane of the scope, so the focuser may move in some while the eyepieces move out. 2) The Morpheus eyepieces cannot be used in 2" mode with the Baader MPCC--you'll never get the eyepiece far enough away from the CC lens. You must use them as 1.25" eyepieces. 3) It does not change the focal length of the scope and has negligible effect on field flattening. It will also add some spherical aberration on axis, so might be a negative for planet viewing at high powers. 4) Yes, it will correct the visible coma down to about f/4.5 in a full-field eyepiece. Below f/4.5, the field size corrected shrinks. The aberration you see in the outer field could be astigmatism combined with coma. The MPCC can correct the coma, but won't help the astigmatism.

At that apparent field, figures as high as 10% are not uncommon. 4% is close to the figure found in many 55-60° eyepieces.

They are all nice eyepieces. The Delos is probably the sharpest of the bunch at the very edge, but it requires even more in focus than the 17.5 Morpheus. The ES 92° is a very nice eyepiece and has a comfortable eye relief, but I found the exit pupil more finicky to attain and hold compared to the others. It's now by far the most expensive of the 3 here in the US, recently going to $800USD (only £410 in the UK) versus $259 (Morpheus) and $352 (Delos) It's also by far the heaviest. of the 3. And I see a little edge of field astigmatism at f/5.75 and f/5.18. I haven't used it in a faster scope yet. The "Critical f/ratio" at which the eyepiece begins to perform more poorly are f/3 (Delos), f/4.5 (Morpheus), and f/4.75+/- for the ES. They can be used at shorter f/ratios, of course, but with lesser edge performance, even in a coma corrector. The respective weights are: Morpheus--305g Delos--409g ES 17x92--1159g

Not necessarily. 2" to 1.25" adapters come in many different heights, from -12.7mm to +16.5mm So you could change to a lower height adapter and get the 1.25" eyepiece just as close as the 2" eyepiece. Ultimately, though, there is nothing prohibiting you from using the eyepiece as a 2" in the scope without the adapter at all, and using the 2" adapter when using the Barlow. The focuser works without the 2" tall adapter. You could even use the telescope as a 2" without any adapter and drop a normal 1.25" adapter into the focuser if you needed a lot of in-travel.

Yes, it's been independently measured and no, it doesn't match specs claimed. The 23.55mm field diameter they claim turns out to be ~21.7mm and the apparent field about 74° instead of 76 (all the other focal lengths are 78-79°). Still, use the eyepiece, and it is so nice and pleasant to use, and sharp, and has such superb contrast, that that simply won't matter. It became a favorite from the first hour I used one. If you don't wear glasses, the 17mm Ethos is a tad better, but then, it's, uh, a bit more expensive.

Too early. It's still not safe due to the spiking infections in most of the US. Even fully vaccinated people are getting it, though vaccinated people only represent 1/10000 among the hospitalized. But infected, but fully vaccinated, people can carry the same load of virus as the unvaccinated. They've just approved of a 3rd dose of the Pfizer vaccine for the high risk individuals. I'd wait until the case load on this current spike diminishes substantially before I'd even think about visiting the US. https://www.nytimes.com/interactive/2021/us/covid-cases.html

Not a nuisance at all. The Morpheus eyepieces come with an eyeguard extender, and you can even add another extender. If you did that and used the rubber eyeguard in the UP position, you'd need to press hard into the eyeguard to even get to the exit pupil. With Morpheus eyepieces, never a need to hover.

So use the eyepiece as a 1.25". It's really a 1.25" eyepiece anyway.

A couple notes: 1) The UK now requires that an American merchant collect the VAT at time of sale and pay the British government the tax separately upon shipment. So all US prices exclude VAT but it will be charged. Any American seller selling to the UK now and not charging VAT on top of the price is probably selling below his cost. I have given up selling to the UK because of this. 2) I'm in CA, and when I sell to the other 49 states, I need not charge sales tax. So the price listed, which does not include tax, is what the consumer pays. In CA, I not only charge tax, but there are 509 separate tax rates for residences in my county, so the tax charged is not only not standardized, it varies according to zip code! I have to note that when I pay sales tax collected to the state. 3) Merchants in other states with Sales Tax (not all states have a sales tax) also charge their local state rate for purchases made in state but do not charge sales tax for purchases from out of state. 4) Because of the internet and many/most people buying from out of state to avoid the sales tax, local governments are missing billions of dollars in revenue that they got before Covid-19 when a lot more sales were in local stores. There is, because of that, a move to require all merchants to collect sales tax for purchasers in all the states that have a sales tax, and pay sales tax to each state. That would be such a nightmare that a very large number of retailers would simply close up shop rather than have to pay 4 dozen separate taxes monthly or quarterly. That is why it has not be instituted. But if sales continue to shift to the internet and away from stores (a shift that started long before Covid), that may happen. The possibility is to devise a central bureau to receive all the sales taxes for all 50 states and distribute it to the separate states for the merchants. At a cost, of course. One other thing that has kept this collection of taxes from happening isn't logistical, it's the long history of anti-tax sentiment in the US. The obvious answer is a VAT that covers all 50 states, but this would cause a revolution in the US, so it won't be done. Remember George III and the tea tax? Also, there is a substantial argument this affects the poor more than the rich, which isn't viewed as fair, and a VAT percentage cannot be computed based on one's income. I could really get into the weeds with this since a very good friend is a tax attorney and we have debated this for decades, but I won't. To get back to the price of the 31mm Nagler, any UK denizen buying from the US should add 20% to the purchase price and not forget that shipping is now quite expensive compared to only 5 years ago. So $666 = $799.20 and there would be at least $75 for freight and insurance (maybe more) = $874.20, which is £630.67 So UK prices are in line with US prices.