Don Pensack

If you use the Barlow under the Binoviewer, the magnification will not be the stated magnification because of the large distance between the Barlow and the eyepiece. If you use a telecentric Barlow, like the TeleVue PowerMate, the magnification will barely change at all with distance from the lenses. If you use the Barlow under the eyepiece (you'd need 2!), then a Barlow would be fine. But most Glass Path Correctors (OCAs) used with binoviewers already impart a magnification. Typically, it's 1.6-2.5x. So a 24mm eyepiece will give you the magnification of a 15-9.6mm focal length. That's one of the reasons people don't typically use Barlows with binoviewers.

There is a lens tool you can buy on-line (it's cheap)--it's a small suction cup with a bulb attached. You can attach it to a lens to pick up the lens and place it in the eyepiece barrel without touching it with anything that will leave lint or a mark. Here is an example: https://www.amazon.com/SE-EL-VP6-7-Piece-Vacuum-Interchangeable/dp/B00XSDHPEK/ref=asc_df_B00XSDHPEK/?tag=hyprod-20&linkCode=df0&hvadid=309811990469&hvpos=&hvnetw=g&hvrand=15807450112636400556&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9030974&hvtargid=pla-570530083398&psc=1

If you were comparing to the Hyperion 24mm, you got the better of the 2. In the US, the Baader is now $169, while the ES is $269.99, so there is a much bigger difference in price.

Louis, I notice the right side of each image is in better focus than the left edge. Is your scope's objective tilted relative to the target?

Some notes: 1) the Sky & Telescope test of the 127mm showed the actual clear aperture is about 121mm because lateral rays from the corrector diverge enough to miss the primary (this kind of Gregory-Maksutov should have had a primary mirror about a half inch larger to field all the lateral rays from the corrector), and the measured focal length at the back with the provided 1.25" diagonal and provided visual back was 1540mm. That makes the as-delivered scope about f/12.73 2) the focal length grows on this scope with increased back focus distance. It grows by approximately 3.75mm for every mm of additional back length. So adding a 2" diagonal and visual back is probably going to add at least 80mm to the back focus distance (maybe more), so that means a focal length of about 1840mm, for f/15.2 3) Hence, a 40mm eyepiece would yield about a 2.6-2.7mm exit pupil. The way to increase the exit pupil and field size at low power is to use as short a visual back as possible and use a 1.25" prism diagonal AND use a 40mm 1.25" eyepiece. You can get the focal length as short as 1500mm that way (f/12.4), and get both a lower low power and a larger exit pupil.

The basic problem is that brass split ring binding is incompatible with safety groove undercuts, which were designed to be used with thumbscrews pressing directly against the barrel.

Yes. https://www.telescope.com/Orion-Premium-Linear-BinoViewer-for-Telescopes/p/130300.uts

The early ones (so: caution buying used!) had a bright shiny spacer under the eye lens that reflected the light of anything bright. Later versions more adequately blackened this spacer. I don't know when the change occurred.

The scope in question is a 1587mm focal length with a field-flattening coma corrector. Resultant focal length is 1826mm, and slightly flatter than a non-corrected newtonian with that focal length. If you look at field curvature in a newtonian, where the ROC = the focal length, anything longer than 1.5m is very flat. It is typically the shorter focal length refractors, with a ROC of 1/3 the focal length, that field curvature is an issue. Evaluating FC of an eyepiece in a strongly curved field telescope has to take the scope into account--otherwise the report of FC is simply confined to one observer on one scope. I've spent a lot of time now with the 9mm, 12.5mm, 14mm, and 17.5mm Morpheus eyepieces, and I see no obvious FC in any of them. Stars exit the field with tight focus. I do have to say, the 9mm is special--almost the RKE 28.7mm phenomenon--where the eyepiece disappears, leaving you looking at an image hovering about the scope. It's amazing.

A simple difference in the size and shape of the housing could account for it. The current ES 30mm has a conical machining that is absent from the 31mm de-cloaked Axiom. That heavy shoulder of aluminum could very well be a contributor, as well as a heavier aluminum wall.

orthoscopic means "without distortion". The 3:1 design for the Abbe orthoscopic eyepiece is only one of the orthoscopic designs. Though the Starbase orthos are a 2:2 design, that doesn't mean they're not orthoscopic. So long as the field is under 42-45°, many designs could be described as orthoscopic.

Looks like you still have the translucent plastic on the "C" Logo cap on the 31mm. You should peel that off so it looks better. After all--now the eyepieces are sleek and shiny. The logo on the cap should be too.

I've used all those eyepieces over time, but didn't compare them at one sitting. I would note that I use the 17.5mm, 14mm, 12.5mm, and 9mm Morpheus today, however, and that is by choice. Below 9mm, though, I prefer TeleVue Ethos and/or APM XWAs. If it weren't for astigmatism and needing glasses, I would only use 100° eyepieces.

Reticle eyepieces have to have their illuminators at the focal plane of the eyepiece. That means the focal plane cannot be located at the shoulder, where it is often located on non-reticle eyepieces, but must be placed higher in the eyepiece. Ergo, just about every eyepiece with a reticle will require at least 8-10mm more in focus than other 1.25" eyepieces. I don't see a solution for a 1.25" focuser that doesn't have sufficient in-travel.

Baader shows €245.00 for the Morpheus, or £208, so that may be the new price. I don't know.

Technically, $259 till midnight, then $299.

Don't know if UK/EU prices will keep pace, but as of today, the Baader Morpheus goes to $299 in the US. That's roughly £219 If you find a lower price, I'd jump right away, as you may see UK/EU prices jump as well.

As of this month, US prices are: TeleVue Delos $387 Baader Morpheus $299.99 Pentax XW $269 Looks like the budget one is Pentax.

Yes at f/8 No at f/5

Only the Astrosystems. The TeleVue In-Travel adapter won't.

The reticle is at the focal plane of the eyepiece and, obviously, fairly high in the eyepiece, so extra in travel of the focuser is necessary. this is not unusual for reticle eyepieces. If your scope has a 2" focuser (your 8" probably does), then the answer is simple. The average 2" to 1.25" adapter is about 9.5-10.5mm tall above the focuser. There are lower height adapters. The Howie Glatter Parallizer adapter is 0mm tall, which would gain you about 10mm of in focus. TeleVue has an In-Travel adapter that is -1.5mm tall, which would gain you even more. And Astrosystems has an adapter that is -12.7mm tall, where you would get so much in-focus you might need to move the focuser out from its normal position. The lower adapters would solve the problem in the 8", but it won't solve the problem in the bino-scope since it only has 1.25" eyepiece capability. Lower height adapters solve many in-travel problems.

Your choices in 24mm are, from smallest to largest: TeleVue Panoptic 24 Explore Scientific 24x68 APM/Altair 24mm Ultra Flat Field Baader Hyperion 24

Astigmatism can be seen at smaller exit pupils that it is bothersome in focus. I'll explain. Defocus the eyepiece on both sides of focus. Does the star image go oval in one direction and then go oval in a direction 90° away from that angle on the other side of focus? That is astigmatism. If I am fussy about having the out of focus star images be completely round, I can detect astigmatism down to about 4.7mm of focal length in my f/5.75 scope. But, if I evaluate astigmatism seen in the eyepiece IN FOCUS, I simply cannot see it below about a 9mm eyepiece. My prescription for correction of astigmatism says I shouldn't need correction below 11.5mm focal length, but I can see it down to 9mm, likely indicating that astigmatism with a dilated nighttime pupil is a bit worse than the daylight prescription I was given. So, there you go: what your prescription is, what you can see in focus, and what you can see out of focus--3 different levels. Technically, you want to correct all of them until all out of focus star images are perfectly round, but since we use our scopes primarily in focus, the second level is what to correct for.

Some better-corrected eyepieces in the focal length include: APM Ultra Flat Field 30mm 70° Pentax XW 30mm 70° These would also display less coma than 80+° because of the narrower apparent field. Yet, at that magnification, they'd still be acceptably wide.

I just tried a 20mm, and the eye relief was too tight to see the entire field with glasses on. The 22mm Nagler is no problem in that regard.