Louis D

I have the white light only version of that one.  It's a Cree type LED intended for tactical use.  I would try to locate a headlamp intended for astronomy use rather than try to dim this one.

10 minutes ago, John said:

I was quite impressed by the Aero ED 40mm clone that I had for a while. It was relatively lightweight for it's size, well corrected across the field of view even in my 12 inch F/5.3 dobsonian (although the exit pupil with that scope would not be the most efficient) and seemed to provide an AFoV which was the equivalent of the Pentax XW's (70 degrees).

Dang it, now you're making me want to hunt one down on the secondary market just to compare it to the 40mm Meade SWA 5000 and 40mm Pentax XW. 😉

1 hour ago, vlaiv said:

Image consists out of full moon in the center of the field and surrounding sky up to field stop (sky is bright enough against field stop so that you can easily distinguish it in each eye).

If focal lengths are the same - then moon will overlap perfectly from both eyes - there will be no double image of it.

If AFOV is the same - then field stops will align perfectly - there will be no double image.

You can have the same moon image and different surrounding sky images and you can have different moon sizes for same sky/field stop image. There are third and fourth cases - when both are the same and both are different.

This shows that AFOV and magnification are not effectively the same thing.

(you don't need the moon to compare AFOVs of two different eyepieces - you just need blank well lit wall - hold two eyepieces - each against one eye and let brain try to merge the image - if you have trouble and can't align field stops - that means AFOVs are different - and in fact, you can judge which one is larger by favoring each eye in turn).

You're assuming that distortion/magnification is the same across the field for the two eyepieces.  Let's say that they are both n millimeters focal length in the inner 10% of the field, then craters there will nicely merge in a binoviewer.  However, if distortion/magnification varies differently across the field, then craters further out won't merge because they are of different sizes at different positions in each field.  AFOV can be the same, but more or less of the moon might be visible due to differing distortion/magnification across the field.

I understand that there are two major types of distortion.  One where objects are the right size but positioned wrong across the field and one where objects are positioned correctly but vary in size across the field.  I'm asserting that at least the second one qualifies as magnification or focal length changing across the field.  I can't recall ever having an eyepiece that shows objects as the same size across the field, but moving them at differing speeds across the field during panning which the first type of distortion implies.  They always get bigger as they speed up toward the edge or slow down as they shrink toward the edge, but they never remain the exact same size from edge to edge as they speed up or slow down.

I guess it comes down to, do you mark them with the apparent field of view (AFOV) as seen by the eye or the effective apparent field (eAFOV) of view that allows the classic true field of view calculation to work.  Vixen used the first one initially until astro forum people loudly complained that it couldn't possibly have a 72° eAFOV (without even measuring the AFOV via projection before complaining), and then Vixen switched to the second one to shut them up.

I've seen a third method used to advertise AFOV, the comparative method.  The 35mm Baader Scopos Extreme is marked 70° despite having a 65°/66° AFOV and a 68° eAFOV due to its 41.3mm field stop diameter.  I guess they figured that since it has a slightly larger field stop than the 35mm Panoptic (38.7mm) and the same focal length, it must have a slightly wider AFOV (70° vs 68°), ignoring that it is the Panoptic's distortion that gets it to 68°.  The BSE 35mm is very sharp in the central 60%, has a slight blurring for some reason at midfield for maybe 10% that goes away if you tilt your head just right, and then sharpens up again toward the edge.  It really feels like a Pentax XL with that ~65° AFOV.  It feels a bit constrictive after using 70° to 78° eyepieces like the Pentax XW, Delos, and Morpheus.  On the other hand, distortion across the field is very moderate compared to a Panoptic.  It is a huge and heavy eyepiece, so there probably was just no saving it from discontinuation.

The 26mm (really 25mm) Meade MWA takes a similar approach.  Since it has the exact same 41mm field stop diameter as the 25mm ES-100, and the same actual focal length, it must also have a 100° AFOV by Meade's reasoning, and so they advertise it as such.  In reality, it has an 83° AFOV and a 90° eAFOV due to distortion of the opposite sign from the ES-100.  If it didn't have so much SAEP, it would actually have been a very good eyepiece.  It's pretty much sharp to the edge at f/6, but you can't see it unless you push in tight (10mm of eye relief) and lose the midfield part of the view.  If you hang back at 18mm of eye relief, you get a 79.4° AFOV and a very usable 37.7mm field stop diameter with only very moderate SAEP shadows.  Thus, it could be considered a good way to complete a Morpheus set with a 25mm version, but that's not how they marketed it.

How about kidney beaning (SAEP)?  It should be fairly strong in the redline and nonexistent in the LV (or is it SLV, you use both in your post)?  I have the original 9mm Vixen LV, and it has much better stray light control and much less scatter than my cheaper eyepieces.  Try hunting for the E and F components of the Trapezium with each to see which shows them the best.

4 hours ago, vlaiv said:

How can we be sure that all additional AFOV is due to distortion and not perhaps change in focal length?

As far as I'm concerned, they're the same thing.  If you increase image scale to stretch the image over a larger area, then you must have locally decreased the eyepiece focal length.  Vice versa, if you decrease image scale to squeeze more image into the same or a smaller area, then you must have locally increased the eyepiece focal length.  Is there another explanation as to how image scale can be changed in the apparent field of view without changing the local magnification power of the eyepiece across the field of view?

I've tried a bunch of microfiber cloths over the past 30 years and have come to prefer the Photo Clear ones in the 7"x7" size.  They're plusher than most MF lens cloths, have a serged edge to prevent fraying, and come in a handy plastic pouch to keep them clean while stored.  I have no idea if they're available in the UK, though.

13 hours ago, Merlin said:

Most of us use our ‘scopes for stargazing rather than research. It seems to a case of overkill to have a premium grade ‘scope for casual viewing.

A lot of folks who own premium scopes are far from casual with their observing.  Many choose to live in areas with very good seeing conditions, build roll-off observatories for their scopes, travel to multiple star parties each year, spend many days each year observing, spend entire nights observing and sleeping during the day, and are constantly searching out challenging objects.  For them, they want the best equipment to help them achieve their advanced observing goals.

You ought to take a picture of the lenses lined up in order and stuck to a strip of gaffers tape or similar for posterity sake.

In particular, are the central two lenses, L3 and L4 in the patent schematic, DCX (double convex) or PCX (plano/flat convex)?  The patent shows DCX while the TV diagram shows PCX.  Also, are they identical and interchangeable?  L3 and L4 are shown in the patent as unique.  If they are PCX and identical, that vastly simplifies reassembly to only one possibility.

TV freely acknowledges that they partner with Astronomik for their Bandmate filters, if that makes a difference in your decision.

ebay is my goto for hard to find used and new repair parts and new old stock vintage items available from within the US.  I rarely buy new items from there, especially from China.  Returns are impossible and refunds are a pain as a result.  Counterfeits are abundant as well.

Search for Nagler eyepiece patents on Google.  I don't think he ever assigned them to Tele Vue (he owns the company, after all, so he doesn't have to).

The 17mm Redline has some chromatic aberration in the last 25% of the field along with astigmatism.  The 13mm has much more radial chromatic smearing, among the worst I've seen.  It makes stars into pretty rainbows, though.  The 22mm only has slight astigmatism in the last 5% to 10% of the field and no chromatic smearing.

Here's the schematic for the original Panoptic from US patent #4525035:

Despite the 41mm being a slight redesign of the Panoptic, along with the 24mm, it should still be similar in lens shape and ordering.

On 06/12/2021 at 14:49, Thomas Burgess said:

If so I assume deep red as that's what the phone apps use, don't know the science behind it though.

Purely red light does not cause rhodopsin to decompose, so your rods can continue being sensitive to dim light.  Ideally, you would want a far red, long pass filter on the light to prevent higher frequency light from leaking through.

On 02/01/2022 at 18:29, Broadymike said:

All joking aside that's exactly what I do! Once I've got my eyes adapted to the dark if I need to go in the flat I really do put an eyepatch on. My flatmate thinks it's hilarious. 

Arrrgh, make 'em walk the plank, matey, for their insolence. 🏴‍☠️

If eye relief is a thing for the wife, I'd get the 24mm APM UFF or one of the more recent brandings of the same optics.  The 24mm ES-68 doesn't have quite enough eye relief for eyeglass wearers, but the APM has plenty and is just as well corrected.

I'd probably get the 17.5mm Morpheus, though, since it would better complement the BHZ without being too close to the 32mm ES-62 in power.

Another long eye relief option with excellent optics at a reasonable price is the 22mm Omegon Redline SW and other brandings of the same optics.  I find it better corrected across the field than the 24mm APM UFF while showing slightly more true field of view, but not quite as good as the 22mm Nagler T4.  You do have to screw off the stiff eyecup to get enough eye relief for eyeglasses; but if you hover above it, lens scratching has never been an issue for me.  You could always replace the eyecup with the newer Morpheus eyecup which is sold separately, has the same thread, and is pliable enough to fold down flush.

You might get a 4.5mm to 6.5mm eyepiece to complement the BHZ at the short end.  The 5mm BST Starguider is pretty decent, and has almost enough eye relief for eyeglass wearers.  If you can suffer through the kidney-beaning, the 6mm Svbony Redline and similar are supposed to be pretty decent performers for cheap while having decent eye relief and a wide field of view.  If you throw eye relief out the window, orthoscopics are good at the shorter focal lengths.  If cost is not an issue, the 5mm Pentax XW is a great performer while being very comfortable for eyeglass wearers.

As for narrowband filters, I'd start with 1.25" filters to see if you like using them.  I've compared a Lumicon OIII with a Zhumell OIII, and it was no contest.  The Lumicon actually works to show otherwise invisible nebula like the Veil while the Zhumell acted like a weird green filter and didn't really help with the viewing.  The Zhumell OIII is more like a light pollution filter than an OIII filter.  However, I only paid $16 shipped for it on clearance, so I'm not too unhappy with it.

1 hour ago, Cook-net said:

The unit is very finicky about voltage and even some power tanks cause the scope to lose it's mind.

It's too bad they saved a few bucks by not adding a proper voltage regulator which would have taken care of this problem.

The difference in optics mostly shows up at high power on low contrast objects like Jupiter.  Fine details like festoons become visible.

However, it's the attention to the mechanical details that makes custom Dobs so special.  The balance is right, the sticktion is right, the mirror cell is right, the secondary holder is right, the materials are long lasting, the focuser is a dream, DSC or goto integration is right, etc.  You don't have to spend your own valuable time trying to make it right, it just is from the start.

I suppose it's entirely possible for a 40mm 1.25" eyepiece to have a 52° apparent field of view (AFOV) if it has enough edge distortion to stretch the outer regions far enough to fill the extra 8°.  After all, the 25mm ES-100 and 26mm (really 25mm) Meade MWA have roughly the same true field of view (TFOV), but the ES shows it in a ~100° AFOV while the Meade shows it in a ~82° AFOV.  That's a massive difference in edge distortion for the same TFOV.

However, I don't think the 40mm Meade Plossl in question has that amount of edge distortion.

2 hours ago, Splodger said:

I think I would be getting to the point of diminishing returns if I were to go down the route of converting it.

If I didn't already have a bunch of 2" eyepieces and 2" diagonals, I probably wouldn't have bothered with them on my 127mm Maks, but since I did, it was low risk to shell out $50 for a 2" SCT visual back and the Mak to SCT thread step ring.  Luckily, it worked out for me.

If I were in your situation, I'd get an 80mm to 100mm ED refractor to take in the wide true fields you're after.

21 hours ago, Broadymike said:

Was just wondering if others have had similar issues with local big businesses wrecking their enjoyment of such a fascinating pastime?

In the 28 years I've lived in my current house, I've gone from Bortle 3/4 skies to Bortle 5/6 skies, or worse, depending on the direction.  When we moved out here, we had about 50 houses within a 4 mile radius and no businesses, just farmland surrounding us.  Now, we have at least 10,000 houses in that 4 mile radius, a 1000 foot wide tollway 1200 feet from my house, a major tollway interchange 2 miles southwest, a high school and middle school with regularly well lit athletic fields just 2.5 miles south, several gargantuan shopping plazas within a 4 mile radius (most SW to W to N), several all night big box stores with well lit parking lots, and two giant car dealerships that keep their lot lights on all night 5 miles to the northeast.  Only my eastern skies are still reasonably dark.  We're planning on moving once the wife and and I retire in a few years to someplace quieter and darker, but still reasonably near to the kids/grandkids.

As if light pollution wasn't enough, there's a neighboring city's amphitheater 2 miles NE that regularly hosts concerts that shake our houses.  That has gotten complaints, enough so that that city has tried and failed repeatedly to remediate the noise issue.  Unfortunately, I'm the only one complaining about the light pollution locally, so nothing happens on that front.  Nobody here but me wants to drive dark roads and walk through dark parking lots to the store.  It's so brightly lit that many folks forget to turn on their headlights while driving at night.

9 minutes ago, JAC51 said:

https://www.cloudynights.com/topic/498028-meade-lx70-150mm-f12-maksutov/

Has a thread on this telescope which would seem to confirm that, although a good telescope, it is limited to using 1.25” eyepieces only.

I stand corrected thank you gentleman.

Admittedly, if your 150mm Mak has a 25mm rear baffle, it's going to be a bit tighter than the 27mm rear baffle in my 127mm Synta Maks.  However, I'm able to use 2" eyepieces in my 127mm Synta Maks with about 40% light loss (vignetting) at around 90% to the edge as shown below.  You would just experience a bit more vignetting in your 150 Mak.  Both images taken from the same distance with the same diagonal, so the focal length is a bit longer than if I were using a 1.25" diagonal.

In real world use, I find the expanded true field of view with 2" eyepieces to greatly outweigh the outer field vignetting.

16 minutes ago, Don Pensack said:

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.

I was just going by the specifications on Meade's webpage for the LX85 which states the following:

Not just a 2" diagonal but also a 2" visual back as well.

I checked the US description of your scope, and it was supposedly packaged with both a 2" diagonal and visual back when new.

All sorts of widest field 2" eyepieces in the 35mm to 42mm range should work quite well in your scope.  f/12 is not very demanding as others have pointed out.  You could even go with a 48mm to 56mm eyepiece for widest field without exceeding a 7mm exit pupil.  At f/12, there are lots of lower cost options available.