Ruud

Ha! I have that too, but checked on google and saw the price, so decided not to mention it. It's very good, but not hundreds to a thousand dollars good!

I forgot to mention, if you can't find the Times Atlas of the Moon you can still enjoy its artful maps here: https://www.lpi.usra.edu/resources/mapcatalog/LAC/ I downloaded all the charts and reduced them to 50% and bundled them into a pdf. The charts are free to download. They are in jp2 format (jpeg 2000). Irfanview can't open them without a plugin, but Gimp, Photoshop etcetera can. I converted one of the maps to .jpg so that you can have a look. Try it at full size.

I just love the Times Atlas of the Moon. It's out of print, but there are still copies around. Also have a look here: https://svs.gsfc.nasa.gov/4442 Set date and hour, click on the preview and see what you got in your download folder. And this is nice too: Quickmap (sometimes a bit slow)

3D vision depends on parallax difference between the images the eyes take in. Astronomical objects, even the nearby Moon, have a minute parallax. Way too small for the eyes to make use of. Anyway, a binoviewer just splits one image into two identical ones. Both eyes view the same scene from the same angle and the binoviewer imparts no 3D information to the observer. If any 3D perception occurs, it does so in the imagination of the beholder. Now, if you have a set of eyepieces where one has a group of small prisms in the light path that shift parts of the image, you get a kind of artificial 3D effect in your binoviewer. It's a real effect, but not real 3D and really no more than a gimmick. Anyway, I imagine that with your lack of stereo perception even artificial 3D is going to be of no use. Finally, you can simulate the 3D effect of a binoviewer (one that uses normal eyepieces) by means of this naked eye method: look up at the night sky with both eyes open, cover one, look again with both. See any difference in 3D?

Once these new techniques are fully developed they will show live views of electronically captured images in user selectable bands from UV-b to near infrared that can (if the visual observer wants to) be stored as stills or video and shared. We'd better prepare for more abbreviations. I suggest we name them SBWREEVTs. That will impress people.

I'm buying a 70mm with a 2+1+1 design. Good for photography, excellent for birding I think. Robtics_robtics_70_mm_f5_4_element_flatfield_astrograph_quadruplet_nl.pdf

The knob is probably to prevent focus creep, but everyone else already said that. I have a question: I've been looking at this telescope. I thought I'd buy it for birding and as a super portable visual scope, as well as a bit of photography. Do you think this telescope would be a good choice for that?

A decade or so back, we had a year with many more good nights than I was used to. It felt like I could take out the telescope every night. There was a great increase in my observing, but after a few weeks I began to get bored! Too blase to bother. No chance of that happening these days in which sessions are so few and far between. I now feel I've invested in a hobby that can never wear out. Impossible at this rate!

Yes, a finder eyepiece with an incredibly small fov. I think Vixen's logic is in the calendar. It's the right day for a joke.

I like my SCT, I love my refractor. Tighter stars and less diffracted light just makes for a better visual experience. I saw an 8" refractor the other day. A CFF impossiscope. Cost €25,000 for the OTA, weight 23 kg. I suppose refractors are nice up to 5 or six inch, but beyond they make no sense at all. This one was sold but still in the shop, waiting for the buyer to finish the observatory for it. He also still had to decide on a mount for it. http://cfftelescopes.eu/refractor-200mm-f8-2/

I don't use one but I would certainly like to. Mine is metal and plastic. Wooden eyepiece boxes are so much more beautiful, especially handcrafted ones. Looking forward to the pictures.

The first Naglers (1980s) had spherical aberration of the exit pupil (SAEP). They were also the first commercially available UWAs that were sharp across the entire field. I still have one: the 4.8 mm. The smaller the exit pupil, the less problems you have with kidney beaning from SAEP. That's why I only got the 4.8 mm. That's a zero problem eyepiece even at f/5 when its exit pupil is 1.2 mm wide. I've never seen a kidney bean in it, even at daytime. With larger exit pupils, say 3 mm and larger, kidney beaning did occur in the first Naglers, especially on sunny days when the observer's pupil got narrower. In spite of their SAEP, the first Naglers were well received. Then already, they were the best around. NaglerT2 addressed the kidney beaning issue, T4 is a small series with long eye relief and very little AMD. A special series. Bulky though, and not everyone was prepared for a combination of ultra wide and long eye relief. The eye relief problem comes from having the eye hover over the eyepiece, missing the exit pupil from time to time. This you can see in the post above. The problem disappears with practice and if you have no control over it, a different eye guard will probably help. The wide angle issue occurs when you want to scan the entire field of an UWA eyepiece. For that you eye has to move. This is needed because while turning your eye from 41° left via straight forward to 41° right, the pupil changes position, and you need to compensate for that. It must stay on top of the exit pupil. You can see that here. The centre of the eyeball has to move from left to right as the eye scans from right to left. That some people need an eye guard for long eye relief eyepieces is not a design fault of the eyepiece. It's a motor control issue of the observer that can be remedied by an eye guard or practice. That the problem existed for some observers only became apparent after such eyepieces became widespread. Try before they buy and be prepared that you may have to get used to a new eyepiece. Having to keep your eye still enough and having to move it as well can be a bit tricky, but it can be learned! Here's the source file for the animation above: glasses and UWA.ggb To open it and play with the sliders you need to download the free app Geogebra from https://www.geogebra.org