Don Pensack

Jeremy,

A clarification: the 24mm Panoptic has a flat field and near zero field curvature.  The edge stars are sharply focused at the same time as the center, even at f/4-f/5.

What you're probably remarking about is its positive rectilinear distortion (i.e. pincushion distortion), which is noticeable if the eyepiece is panned

or if the telescope has a long enough focal length the passage of the field is fairly rapid.  It results in straight lines moving across the field as ) | ( 

That the eyepiece has, in abundance--perhaps stronger than other eyepieces in the size.

The 41mm is the same design, just larger and with a wider field stop.  If the RD in the 24mm bothers you, the 41 might not be the best choice.

Though, the much lower magnification does mean that field drift through the eyepiece is a lot slower, so it largely depends on whether the eyepiece is panned across the sky.

It does depend, also, on what you want the eyepiece to do.  If you want a good eyepiece for terrestrial use, suppressing rectilinear distortion and allowing some angular magnification distortion may be a better choice (e.g. 24mm APM UFF).

Or, for use in an astronomical scope that tracks, the RD would be unnoticeable (just as AMD is unnoticeable (e.g. 12.5mm Docter/Noblex).

But, in a scope that doesn't track, many people would prefer a smaller amount of RD. 

You're not going to beat the sharpness of the 41mm Panoptic at its focal length, though.  So it does depend on the observer's preferences.

The design has visible astigmatism at f/10 and probably shouldn't be a top choice below f/8.

There are better designs at that focal length, but probably none so inexpensive.

Easy enough on those to take them apart and blacken lens edges and spacers.

https://www.cloudynights.com/topic/821853-finally-a-killer-zoom-for-binoculars/

Read the whole thread.  The review gets more in depth.

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

Reviews:

https://www.cloudynights.com/topic/692020-orion-linear-binoviewer-mini-review/

https://www.cloudynights.com/topic/739149-ok-so-i-bought-an-orion-linear-binoviewer/

https://www.cloudynights.com/topic/615344-orion-premium-linear-binoviewers/

https://www.cloudynights.com/topic/643840-orion-binoview-any-opinion-or-actual-usage/

Filters have a lot of coatings and can be easily scratched.

I would go with Lumicon's recommendation to never use anything stronger than isopropyl alcohol.

Pure ethyl alcohol would work too but it is illegal for sale in many places since it can be consumed.

Something strong enough to remove mould, like MEK or a solution of sodium hypochlorite would likely damage the coating.

I have had eyepieces for >20 years that I sold that looked brand new.

I clean them by:

1) blow off all debris to avoid scratching.  I have an electric blower (no propellant or oil) that blows just about everything off.

2) I add 1-2 drops of fluid to a Q-Tip, and, while the Q-Tip is wet, make a spiral pass of the entire lens surface, starting in the center, then quickly flip the Q-Tip and repeat with the dry end to mop up the residue.

3) I quickly grab a 2nd Q-tip (cotton only, no additives) and, moving from edge of lens to just past the center of the lens, rotate the eyepiece under the Q-Tip until the whole lens has been brushed twice.

I then flip that Q-Tip to the clean end and repeat the spiral pass.

When done, no streaks, no residue, and a clean lens.

One way you know the lens is very clean is that the resistance to the movement of the Q-Tip on the lens disappears during the process, as if the lens is teflon coated.

6 hours ago, LDW1 said:

I am looking for a recommendation for a 42-50mm eyepiece, from actual experiences, with as wide a FOV as possible.  Cost is not an issue.

If cost is no object: TeleVue Panoptic 41mm.  You won't find a better eyepiece, optically, in or around that focal length.  It has a 46mm field stop.

17 hours ago, cajen2 said:

Yours doesn't look much like the StellaLyra Barlow (the usual equivalent to Orion US here).

https://www.firstlightoptics.com/stellalyra-eyepieces/stellalyra_2x_2_barlow.htm

This is a good one, though, with ED glass. It's a 2", please note.

The StellaLyra is a GSO-made, and a good one.  It's a conventional telenegative Barlow.

The one in Mike Q's post is made by JOC, the maker of Explore Scientific, Maxvision, et,al. and is a 4 element telecentric Barlow.

You can look up "telecentric Barlow" to find posts explaining the difference.

A couple reviews so far, but mostly from daytime users.

I think more will have to be in the hands of users to get better information on aberrations and eccentricities.

On 04/06/2022 at 10:15, jetstream said:

What type of distortion are we talking about?

TV uses pincushion distortion and a whole pile of it in some of their eyepieces, very noticeable. The Docter 12.5mm is pretty much orthoscopic except for a bit of barrel distortion right at the edge.

All of the eyepieces I tested (a pile of them) showed a variety of distortion including "moustache" distortion.

I wonder how many have tested for distortion or know about the effect?

Some say pincushion is "astro" friendly distortion and some say "barrel" is for daytime use... I like a minimum of distortion- I really dislike watching the moon "turn into an egg"  from "astro friendly" pincushion in a widefield eyepiece.

So what type of distortion does the APM zoom actually have? Is there a lot of it?

If it does have barrel distortion does it induce the "globe effect" when panning?

You cannot simultaneously remove both rectilinear distortion (RD) and Angular Magnification Distortion (AMD).

The way to have very small amounts of distortion is to keep the eyepiece apparent fields narrow, since distortion increases with apparent field.

If any eyepiece with more than about 40° of AFoV has zero RD, it will have a lot of AMD, and vice versa.

In daylight use in spotting scopes, reducing RD to keep straight lines straight seems important.  And if this means the magnification at the edge is not the same, it's not a problem, since you can simply move the object viewed to the center. (no RD, let AMD be larger)

In astronomy, though, having a different magnification at the edge is a problem (for many reasons I won't go into here), while there are no straight lines to keep straight, so having a more uniform magnification across the field is better (no AMD, let RD be larger)

Here are the curves for RD and AMD and you can see how apparent field affects the amount of distortion seen:

12 hours ago, IB20 said:

I have some BVs, but right now with my set-up they aren’t quite working meaning they’re a bit of faff. The thing I don’t have time for right now is faff. Maybe when I don’t have a toddler swinging from my ears I can invest some time in sorting it out. 👍🏻

What is noted is that reducing the brightness a bit on a planet or the moon can make things easier to see because the image isn't so bright it washes out by dazzling the eye.

One easy way to do that is to add a 50% transmission neutral density filter to the eyepiece, or to double the magnification (which reduces brightness by 75%).  If you are already at high power, the ND filter makes a lot of sense.

One of the reasons my best view of Jupiter ever was with a Paracorr + PowerMate + Ethos eyepiece was the 18 lens elements in the optical train in the focuser.  It was also a high magnification (456x, 0.7mm exit pupil).  The light loss due to magnification and several inches of glass and innumerable air-to-glass surfaces was just enough to make the image look photographic and not even a bit washed out.  Having superb seeing didn't hurt.

20 hours ago, sorrimen said:

Hi everyone,

First off, I understand that there are lots of topics out there very similar to this, but for whatever reason getting people replying specifically to my queries makes me feel a lot more comfortable (I’m sure some of you understand)

Anyway, I’m a new 8” dob owner (1200mm fl) and have just got a set of 8, 12, 18, 25mm BST Starguiders. Living in London, I feel as though planetary and lunar will make up a lot of my observing so I think I would like a 6mm for 200x. Would you guys recommend any specific 6mm? Alternatively there is a BST Barlow for a good price. The barlow would also give me 300x for lunar and maybe planetary on exceptional occasions. Might I add, I’m really not looking to spend much; £40 new or used is about my limit (already spent the cost of the scope in EPs, cleaner fluid, collimation tools, chair etc). 

Essentially, is the barlow (with the additional 300x) or a 6mm eyepiece on its own going to be better, and what are the recommendations for either? 
 

Thanks ever so much!

Your choice of a 2X Barlow was a good one.

With the eyepieces you have (also good ones), you now also have 9mm, 6mm, and 4mm.  The jump from 200-300x might seem large, but here is the thing:

on the nights when a 200x image is clean and sharp and not scintillating, it is likely 300x will be usable too (Moon, double stars, Mars at opposition, Neptune, Uranus).

And on a night where 200x is really pushing the limits imposed by Seeing conditions, even 250x won't be usable.  So the 100x jump a the high end is likely to be fine.

It's the same reason why, in my 12.5", I have smaller steps to 300x, then jump to 400x and 500x.  On the nights when 300x is clean and sharp and still, 400x and 500x are usually usable.

Bill Paolini reports:

On 29/05/2022 at 02:06, Franklin said:

Just found this from Astromart 3 years ago. K40mm is from 1980 and made by Carton Optical-Japan.

So your K18mm is definitely later.

 

A 40mm eyepiece is useful in a long f/ratio scope, to achieve a larger exit pupil and a brighter image--always a good possibility for long f/ratio Maksutovs.

But in 0.965", the apparent field will be 32-33°, so that is one narrow eyepiece.

Still, likely the true field maximum limit for the scope.

A lot of people who owned those scopes added hybrid 0.965--1.25" diagonals to be able to use 1.25" eyepieces.

But with a complete set of Japanese-made 0.965" eyepieces, few would bother.

12 hours ago, Louis D said:

I've noticed the red and blue ends of the spectrum don't focus at the same point radially in my 30mm ES-82.  On Jupiter, I could literally see fully separated red and blue versions at the edge.  I was mystified why there were no other color versions in between, though.  The 30mm APM UFF does not suffer from this artifact.

6 elements versus 9 elements.

And 82° versus 70°.

But, you make a strong argument in favor of the APM.

That is one of many reasons I use that eyepiece for my lowest power.

14 hours ago, Dave scutt said:

Last night was the first clear night in a while, at 11.15pm it still wasn't dark I could only see Vega and Arcturus.

It was the first time using yhe ES 82 degrees 30mm and its a beast weighing in at 1kg I thought I would have had balanced issues but the dob moved around perfectly .

 

I didn't have much time to explore as I  had an early start in the morning so stayed around Vega, I've been using the skywatcher 28mm since I've got the dob and was I in for a treat, I could see so much more with the 30mm stars where sharp but not to the very edge of the fov.

It was so much easier finding objects with such a large fov I just pointed in that area moved around a bit  and it was there,  I moped up all the Open Clusters and Globular Clusters in that area, the ring and owl nebula,  then m81 m82 and then m51, noticed on my phone there was a comet  c/2017 k2  I've never seen a comet before tried searching for a while didn't know what I would expect to see  (something like a photo) but had no luck finding it. 

It was a lot easier holding my phone over the ep for photo's and took this one of m13.

Dave

Oof.  Bad seeing.

The "not sharp at the edge" could be coma, and the eyepiece has a tiny bit of unresolved astigmatism near the edge as well.  You don't say whether you are using a coma corrector in the dob or not.

Good luck finding the comet.

https://en.wikipedia.org/wiki/C/2017_K2_(PanSTARRS)#/media/File:C2017_K2_skypath.png

It's a tiny fuzzy star at the moment.

Here is the ephemeris:

https://in-the-sky.org/ephemeris.php?objtxt=ck17k020

Your best bet is to plot it on an atlas so you can find it easily by star hopping from a nearby naked eye star.

If you have a computer atlas, you can print the page where it is and mark it in.

23 hours ago, markse68 said:

Hi Don,

I was quite clear when talking to Baader, and have mentioned in this thread that this IS for a finder- not a main scope. Magnification will be 8x. Given that, do you see any reason that it should be acceptable in an f4 finder but not in an f3.3 finder? If the prism is big enough, why would you get vignetting?

PS the optics I want to use for the finder are from porro binoculars- so they were used with prisms and worked excellently before.

Mark

It should work equally as well or poorly in an f/3.3 finder as the typical f/4 as long as the clear aperture is adequate for the fatter light cone.

7 hours ago, markse68 said:

Hi Dave, I have read a few differing explanations of why phase coatings improve the image in roof prism bins but this one seems typical. Here they say this:

“One remedy is to silver the faces of the roof prism, as Buchroeder found experimentally in 1982. An even better way is to apply dielectric phase-correcting coatings. Zeiss Oberkochen started doing this in 1988, and other firms quickly followed suit.“

https://skyandtelescope.org/astronomy-resources/astronomy-questions-answers/why-do-the-best-roof-prism-binoculars-need-a-phase-correction-coating/

Still am left wondering why it’s deemed acceptable to use amici prisms (are they phase coated? unlikely- are they even silvered?) with f4 finders (Baader even sell one!) yet it won’t work at f3.3. At what focal ratio does it stop working?That may well be the case but i’d like to understand why.

Mark

 

It works in finders but that's because of the extreme low powers.

And, if you really analyzed the finder like you do a telescope, you'd find excessive astigmatism, spherical aberration, chromatic aberration, vignetting, and a darker image than should be the case.

So in an f/3.3 scope, you'd not only get a loss of brightness, you'd have excessive lateral chromatic aberration, serious vignetting, a visible line in the field, and likely a poorer quality axial image.

In general, prisms of any kind are not recommended below f/8 because the lateral rays enter at too oblique an angle, yielding significant chromatic aberration.  And, if the clear aperture is insufficient, vignetting. 

1 hour ago, Louis D said:

Definitely not me.  My kids accuse me and the wife of being hoarders.  I've still got 20+ year old digital cameras that are so obsolete I can't even read their memory cards anymore or get their batteries to charge, and yet I haven't chucked them for unknown psychological reasons.  I even boxed up my 200 and 300 CD changers and put them away just in case I ever want to go back to playing CDs instead of MP3s.  What is wrong with me? 🤪

On the plus side, my grown son has eyes on my old 1980s turntable to play his, and my, vinyl records.  It still works great and wasn't cheap to buy back in the day.

Here's proof of my eyepiece hoarding:

I did pass along the BST/Paradigm and HD-60 sets to my grown daughter now that she and her husband bought a house in a semi-rural area.  She also got some of the lower end 2" eyepieces for widest true field of view use and a couple of the reticle eyepieces for the 60mm RACI finder scope I loaned her.  I hadn't used that finder scope in 20 years, and yet I held onto it.  Now I know why. 😁

If I'd saved every eyepiece I've ever owned, you'd need to shoot the portrait in Panorama Mode. (over 350 at this point).

I just unloaded 10 of them, so I'm down to only 12.  How long that will be the case, I have no clue.

And one reseller in the US is selling these under the manufacturer's name.

4 hours ago, badhex said:

I got both in the end. Hard to take a photo but even visually the aperture difference between this and the (synta) ones is significant. 

I hadlve had first light with it (last night) and so far it seems very well built piece of kit. One minor niggle is that the 1.25" EP adaptor gets a bit stuck sometimes on insertion, and a couple of times I nudged the scope enough to lose my current target. Hopefully with use it will insert a bit more smoothly. 

Looks like the one on the left in the bottom photo has a noticeably larger clear aperture.

8 hours ago, FLO said:

Not yet but I don't see any reason we cannot. I will look into it then let you know 🙂 

I confess I only became aware of the other version yesterday when I saw Don bashing the original (Don is an APM dealer).

Our customer feedback for the original is excellent and - so far - not a single customer return so I was not expecting to read such a full-on attack. 

Steve

I don't sell to the UK. Nor do I sell this tool.

I merely reported my experience with the tool. something, I believe, an amateur astronomer can report, based on experience and not hearsay?

I have used nearly every collimation tool there is over the years, and most have their ups and downs.  FLO, BTW, sells an incredibly nice combination Sight tube/Cheshire:

https://www.firstlightoptics.com/other-collimation-tools/stellalyra-premium-cheshire-collimating-eyepiece.html

Here in the US, there ae several very poorly-designed collimation tools that are sold, but sales don't necessarily equal good design.

I try new tools all the time to stay up on collimation trends.

As for the Concenter, I've stated my experiences with the tool, which I obtained at retail from the EU.

The new one doesn't solve problem G--you won't be able to get the pupil of the tool down to the focal plane of the scope.  In the case of the new one, perhaps not down to the apex, even.

The new design would seem to solve several of the other issues I saw with the tool, however.

Here are some things I noticed about the Concenter.  This is the version I had:

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p5506_TS-Optics-Concenter-2--Collimation-Eyepiece-for-Newtonian-Telescopes.html

1) It does agree with other tools once you have collimated with the other tools. Read on as to why the "AFTER" other collimation tools is necessary.
2) However, it suffers from multiple problems:
a. it's too short. I couldn't focus on the rings even with reading glasses because they're only ~3" away from the eye.
b. I could not adjust the focuser to get even one ring to correspond to the outer edge of the primary mirror OR secondary mirror, even running my focuser from one end to the other. They're spaced wrong for my f/5 setup.
c. the rings are very broad and not particularly sharp in execution
d. the center hole in the reticle is larger than the hole in the center marker, but smaller than the Hotspot, so it isn't visible at all. It would collimate a mirror with a Sharpie center dot kind of like a collimation cap can, but wasn't useful in my scope for primary adjustment at all.
e. but the biggest problem and one that makes the tool completely worthless, is the terrible problem with parallax. The center hole isn't large, but with such a short distance to the rings, they wandered all over the place. I tried to stabilize my head by sitting and putting fingers on tool and cheekbone, but that didn't help at all. The wandering rings problem makes the tool worthless unless following after some normal collimation tools are used. I had no such problem with the Astrosystems LightPipe, even though it has a larger center hole than the Concenter.
f. The eye relief of the tool is perhaps 8mm to see all the rings and the outer inside edge of the tool. At that distance, I couldn't focus on the rings at all--they were just a blur. When I put my bifocal reading glasses on and looked through the bifocal section to focus on the rings, I couldn't even see my entire primary mirror.
g. When my focuser was nearly all the way in, I was at the apex for my mirror because the pupil of the Concenter sits almost 1.5" above the shoulder of the tool. I couldn't even get the pupil TO the focal plane of my scope, which is 0.75" above the racked in focuser.

Just a horrible execution of a decent idea.
It needs to be a longer tool--a LOT longer.
It needs to move the pupil in to about the top of the focuser so the entire field can be seen.
I have no idea how to solve the problem of the invisible center hole in the reticle. Maybe make it a lot smaller or larger?  Or make multiple f/ratio versions?

TeleVue is in the process of eliminating all the 0.25 sizes

Currently, the quarter diopter sizes are only available in: 0.25, and 2.25

Otherwise, they are now only available in half diopter increments.

I suspect the 0.25 diopter one won't stick around, either, as most with that little astigmatism see no need for glasses at the eyepiece.