Don Pensack

On 09/11/2021 at 18:46, Louis D said:

I'll have to check my $50 2" dielectric Amazon diagonal against that one.  The biggest problem with it is that the 2" compression ring is mounted too high and forces eyepieces with undercuts up at an angle.  Otherwise, it works just fine.

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.

On 26/10/2021 at 06:49, fireballxl5 said:

Having the FS60CB with Extender-Q already, is there a preferred binoviewer that works well with this scope?

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.

23 hours ago, Louis D said:

Maybe in that case (like the 14mm and 20mm Pentax XWs) it would be.  In my experience, the 10mm Delos, 9mm Morpheus, 30mm ES-82, both ES-92, and 9mm Vixen LV all appear flat to my eye.  The 27mm Panoptic might have a bit as do some of the Nagler T4s (17mm springs to mind).  The 14mm Morpheus has a bit as well, although Don P. doesn't see any in his copy.  The worst are the 80 degree, 30mm WideScan III clones.  They have several millimeters of curvature center to edge.

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.

15 hours ago, badhex said:

Interesting! I don't know much about these, although I'm sure I read a thread somewhere that they aren't true orthos, but not sure of the design. I could be mistaken though. Either way, definitely interested to hear more about them!

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.

5 hours ago, F15Rules said:

Well, I took the plunge yesterday afternoon and decloaked the Axiom 31mm!.

It's completely reversible including the Celestron round stickers this time, as I knew what I was doing and managed to prise the labels off intact.

I think the 31mm looks great decloaked too, and saves very significantly on weight. Also, by coincidence, the top cap from the 23mm uncloaked fits on the top of the decloaked 31mm!!

Very happy so far, and hope to try it tonight if it clears as per forecast. Fingers crossed!

 

Dave

 

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.

5 hours ago, Art McConnell said:

Thanks for that info. Didn't know about in-travel adapters. I now know my 2" to 1.25" adapter is a High Hat, which is supposed to give a 16.5mm rise, but my dial calipers show me a full 19mm rise in my own adapter.

So that should fix me up with my Newtonian, which has a 2", low profile helical focuser. I built that scope, and chose that focuser because I wanted a wide(er) field of view for objects such as Andromeda galaxy. I was not disappointed....

But as for my BT-70s, might I find a different (brand? magnification?) reticled eyepiece that will perform better in them? Otherwise, it's to the machine shop with my Sbvony.....

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.

1 hour ago, Stu said:

There are some focal lengths in stock at FLO at £188 currently, 6.5, 14 and 17.5mm that I could see. Hope they don’t go up here as they seem excellent value for money.

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

1 hour ago, Louis D said:

In that case, it's cheaper to just buy them locally in the UK for £249.

I'm still seeing quite a few places selling Morphs over here for $259.

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.

4 hours ago, azrabella said:

Can anyone advise as to whether a 25mm BST Starguider (Explorer) will work reasonably well in an f/8 Dob? I have conflicting reports on this puppy. I have the 12mm version and that works very well indeed.

Yes at f/8

No at f/5

21 hours ago, Louis D said:

The illuminator sticking out to the side may limit the use of the negative profile adapters.

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.

16 hours ago, Louis D said:

Since the eye lens is about the same diameter for both (~30mm), I wouldn't doubt you would be able to see at least as much of the field in the XWA as in the NT4 (~82°) while wearing eyeglasses.  However, can you actually see the entire 100° of the XWA with eyeglasses?  I can just take in the 92° field of my ES92s by resting my glasses against the folded eye guard of each, and they each have a 43mm diameter eye lens!  I tried an Ethos at a star party while wearing eyeglasses and could only see the inner 70° or so with ease, and it also had a ~30mm diameter eye lens.

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.

Since the filter is soft aluminum (usually 2014 or 2024), it can be chased using the "Dutchman's Thread Chase".

Basically, you sit in front of the TV and thread the filter in till it stops and tweak it tighter an infinitesimal amount more, then thread it out until it feels loose.

Repeat, each time threading it in a tiny bit more.  After 100 iterations, the filter will be threading in much farther than it did originally.

If you feel like it, keep doing this until it hits the stop (though catching only a couple threads is sufficient to hold the filter in).

I would suggest doing this on an eyepiece with a chromed-brass or steel lower barrel, as doing this to an aluminum eyepiece could be chasing threads in the eyepiece

as well as the filter.  The process is a lot faster in an aluminum barrel, though.

Several years ago the people at Lumicon tested almost 200 2" eyepieces.

They found so much variation in diameter that they realized that if they held their filter threads to extremely tight tolerances

that they could only fit about 50% of the eyepieces.  25% were so large the filter would simply push in without catching a thread or be so loose it would fall out.

25% would thread in maybe 1/2 thread or not go in at all.  And some were not round!

The rest varied from extremely tight to extremely loose, but at least the filter would stay on the eyepiece.

48mm x 0.75mm is the standard, but just like when you use a tap, there will be a big difference between threading the tap in part way or all the way through.

So you are merely dealing with +/- tolerances here, and wonderful Chinese quality control (which barely exists, if at all, on eyepieces at this price point).

It isn't just filters, it's everything threaded from China.  

37 minutes ago, Andrew_B said:

Thank you, that's useful advice about the eyepiece retention system. Saved me getting the wrong thing.

I saw a a few models that looked like that Antares BV which came with a pair of Barlow lenses (1.85x and 3x). I suspected that their quality can't have been up to much given what the entire package was selling for.

Good to know. I ended up ordering a binoviewer sold under the Sky Rover brand who also have a few nice eyepieces that look the same as more familiar offerings from OVL and APM. I chose it mainly because it comes with a proper case but it also includes a 1.6x nosepiece in addition to the standard one so I wonder if that's the same model that W.O. were selling? I'll try it out and if it's junk it hardly matters for what I paid.

Sky Rover is the In-House brand name for United Optics, from whom come many many brands of eyepieces, including APM, Meade, Celestron, etc.

14 hours ago, Louis D said:

Just make sure the BV you choose has locking collets instead of thumbscrews.  Because the latter push the eyepiece off center to the side, merging can become an issue with them.

I have the Arcturus BV with two useless Barlows (both induce the weirdest linear instead of radial coma) but without the eyepieces of the current version.  I've never had trouble with the locking collets with smooth side eyepiece barrels.  I use the nosepiece from a Meade 140 2x Barlow to reach focus, operating at 3x.

I also tried inserting my BV into a Parks GS 2x Barlow (also known as Celestron Ultima and Orion Shorty Plus) and saw pretty much identical performance, so there are multiple options to reach focus.

Collets do really well on eyepieces with smooth barrels, but not eyepieces with conical tapered undercuts.  On those, the simple thumbscrew works best because the thumbscrews pull the eyepieces down into tight contact with the top of the 

eyepiece insertion tubes.  Ideally, a centering binder would be best, but centering binders don't work well on eyepieces with barrel undercuts.

9 hours ago, Louis D said:

I just measured the Sirius and GSO 32mm Plossl field stops directly using digital calipers after unscrewing each lower barrel to get clear access them.  I got 27.2mm for the former and 27.1mm for the latter.

I then did a comparative photographic analysis of each to the 27mm Panoptic accepting TV's 30.5mm FS diameter as gospel and arrived at 27.1mm for each.

At no point was there a doubt that they have at least a 27mm diameter field stop diameter, the only quibble would be about that last 0.1mm.

Good.  Then they have changed over the years.  That is compatible with a 50° field and edge distortion of 3%.