Don Pensack

You won't pay a tariff on 2 small pieces of rubber.

If you buy used, look for an older 4-element Celestron from when they were made in Japan.

I compared it with the Meade back then and the Celestron was better in every way--sharpness, contrast, correction, vignetting, etc.

I have not used the newer Chinese-made one.

I have not used the Starizona or the Optec, both of which were a lot more expensive.

58 years of telescope observing under my belt and I've never seen an issue caused by heat in the eyepieces.

Mirrors, objective lenses, corrector plates, yes.  Eyepieces no.

Easy to see: defocus a star and look for movement of small air pockets in the out of focus star image.

Looks like a can of worms when I try this before the mirrors cool down.

If I try this with eyepieces straight from the box, which don't feel cold to my bare hand, after the mirror is fully cooled, 

no noticeable movement in the out of focus star image.

I have.  It's 7x in my 4" apo and has a 11° apparent field.

The field looks like it is way off down a tube.

But, the true field is only 1.5° in that scope with the 100mm..

Since my 24mm APM yields a 2.2° field at 30x, I see no value in the Vixen eyepiece as a replacement for a finder scope.

In contrast, my 8x50 finder provides a 6° field, about 4x wider than the Vixen eyepiece.

It's not as wide as a typical finder scope in an 80mm scope with a 480mm focal length (2.3°)

This is one of those, "You made what?" products.

I may not have pointed this out before, but the field stop diameter will equal the focal length (+/-) if the eyepiece has a 1 radian apparent field (57.3°)

and will be larger if the apparent field is larger and smaller if the apparent field is smaller.

Some examples:

18.2mm Delite, 62°, field stop 19.1mm.  Field stop is 0.9mm larger than the focal length, or 4.9% larger.  Apparent field is 8.2% larger than 1 radian.

20mm Plössl, 50°, field stop 17.1mm.  Field Stop is 2.9mm smaller than the focal length, or 14.5% smaller.  Apparent field is 14.6% smaller than 1 radian

21mm Ethos, 100°, field stop 36.2mm.  Field stop is 15.2mm larger than the focal length, 72.4% larger.  Apparent field is 74.5% larger than 1 radian.

Of the 3, the one with the largest discrepancy is the 18.2mm Delite.  Either its apparent field is wrong or the field stop is wrong.  I suspect it's 60° or a hair more.

On 04/03/2021 at 10:24, vlaiv said:

Your astigmatism is going to affect all stars in the field equally, so that is not it, but it can possibly be coma?

In F/6 scope - you don't see much of it and only time it can be seen is with wide field eyepieces with this one.

@Carl Au

Nice report. Any chance of field stop measurement?

This eyepiece has residual lateral field astigmatism, so that is probably what he is seeing.

22 hours ago, Louis D said:

Since the OP didn't really specify cost, I took the topic's debate to be between wide field and narrow field eyepieces in general.  At the high end, narrow field eyepieces like the ZAOs, TMB monos, TAK TOEs, and Vixen HRs still outperform their similarly or lower priced wide field competitors.

Though people vote with their wallets.

Three of the 4 eyepieces you mention are discontinued and only available used.  And every time new eyepieces get added to my Buyer's Guide, they seem to be widefields.

You can download the Buyer's guide here:

https://www.cloudynights.com/topic/758306-2021-eyepieces-buyers-guide/

On 27/02/2021 at 00:13, Deadlake said:

Is the Stellarvue a clone of the XWA design, just a baffle and a steel tube on the bottom? Shame not available outside of US.

Stellarvue differences:

--stainless steel lower barrel

--metal focal length badge

--ozone and UV-resistant rubber in the eyecup and gripper

--slightly different focal lengths claimed.  The APM 5mm is a 4.77mm according to the factory specs, so Stellarvue's 4.7mm is closer than APM's 5mm.

Stellarvue says 3.6mm, APM says 3.5mm.  I'd put money on it being 3.55mm.  LOL.

Stellarvue says 13.5mm, while APM says 13mm.  That is odd, but they are the same, so I don't know which is accurate or if the truth lies between.

In my dob, that's a difference of 5x, which is unnoticeable, and even less so in shorter focal lengths.

Same eyepiece, different top: SkyWatcher Myriad 20mm

Also available as:

Antares XWA 20mm (same top as APM)

Stellarvue Optimus 20mm (same top as APM)

Telescope Service XWA 20mm (same top as Myriad)

Many retailers in the US ship to the UK, but the shipping and importation charges would be prohibitive.

I guess that's the same now when buying from the EU.

APM will have more in late March.

4 hours ago, jetstream said:

I wonder who makes this zoom?

Kun Ming United Optics.  May be available as soon as  June if everything goes right.

On 24/02/2021 at 10:40, vlaiv said:

Here is simple method of doing it (at least I think it is simple).

Requires way to measure distance and white circle on black background.

Test is conducted by standing in front of the wall with circle on it at some distance so that circle is approximately the size of quoted FOV. Now take eyepiece and place it in front of one of your eyes - as if you are observing thru it. You should see field stop of the eyepiece and out of focus light in FOV. Keep you other eye open and move forward/backward until two circles overlap.

Measure distance from your eye to circle on the wall and use diameter of circle to calculate angular diameter of circle at that distance.

This technique can be used to compare fields of view of two eyepieces. You don't need circle - just a blank white wall or any other background that will illuminate FOV properly. Place each eyepiece on respective eye like when binoviewing. You should be able to instantly tell which FOV is bigger since circles will overlap but have different sizes (or same size if FOVs are equal).

I find this technique works well at 50-70°, but is difficult to gauge with 100-110° eyepieces.

10 minutes ago, Louis D said:

And take manufacturers claims of eye relief with a large dose of skepticism.  Most quote designed eye relief to the center of the eye lens, which can be much less than the usable eye relief if the eye lens is deeply recessed or deeply concave.

Wouldn't it be nice if eye reliefs were stated in terms of the optical configuration (from the glass) and the ergonomic configuration (from a horizontal line across the top of the eyepiece).

I would argue the 2nd eye relief should be measured from the folded down rubber eyecup, and not the aluminum below it.

8 hours ago, Aquavit said:

Some very helpful replies, thank you.

Last night I adopted the advice given and enjoyed what was my best yet observing session, comfortably seated, telescope at the right height for viewing the Moon near to the zenith and the Mak mounted on an alt az rather than the usual EQ mount - this made a big difference in ease of use. I also adapted my viewing approach to suit the eyepiece rather than fighting it, this was better although still not ideal but, as has been said, I may get used to it over time.

Interesting point Vlav makes about the design of the Mak 102 possibly contributing to this effect, it will be interesting to compare the EP performance in my 80ED when I get it. 

For the inexperienced, it seems eyepiece selection is something of a lottery with potentially frustrating and expensive consequences. I wonder if there is a formula for determining an individual's EP eye relief requirements?

No formula, but 10-15mm eye relief is comfortable without glasses, and 18-24mm with glasses.

Eye reliefs in excess of 24mm or shorter than 10mm are a problem.

Yes, it is the long eye relief on the eyepieces that is causing you a problem.

First, observe seated.  You can hold your head steady much more easily.

Second, perhaps look for eyepieces with less eye relief in the future if you prefer to bury your eye in the eyecup.

With the overall aging of the astronomy population, there is a lot of pressure on eyepiece companies to produce long eye relief eyepieces for eyeglasses wearers,

but there are still a lot of (still the majority) eyepieces with less eye relief.

As you get used to holding your head steady, this problem will go away.

In use, how to approach an eyepiece is this:

Start from too far back and approach until you begin to see the field of the eyepiece.

Get closer until you *just* see the edge of the field in your peripheral vision.  Stop there.

That is the "working" distance for that eyepiece.

If that seems too far out from the eyepiece, you can look into raising the eyecup with an eyecup extender, or get a longer eyecup from a dealer who sells such things.

Or replace the eyepiece with one having less eye relief.  Or get a long eye relief eyepiece that has an adjustable eyecup that can be raised sufficiently to make it comfortable to use.

There is always more than one way to get to the goal of comfortable observing.

21 hours ago, KeithP22 said:

Could anyone tell me if I would be able to use a celestron nexyz with BST starguider ep's or are they too big for the phone mount. 

They're the wrong shape.  The phone adapters all require more cylindrical eyepieces.

I wonder if the exteriors of the eyepieces could be removed?

16 hours ago, HollyHound said:

I’d agree with that Don 👍

I’ve tested the Morpheus 14, XW14, Delos 14 and DeLite 13 in both an 80mm f/10 refractor (focal length 800mm) and 10” f/5 dob with ParaCorr 2 (focal length 1460mm).

Field curvature was very noticeable with the Morpheus and slightly more so with the XW,  but not visible with the other two, when used in the refractor.

Field curvature was (barely) noticeable with the Morpheus, again slightly more so with the XW, and not visible with the other two, when used in the dob.

I’ve just bought and tested (once) an Ethos 13 in the dob, and no field curvature is visible at all.

I find coma very noticeable with all these eyepieces if the ParaCorr is not used, so that stays in the dob for all sessions, but I’m aware some don’t find it objectionable.

The Delos 14 is my most used eyepiece in the dob for DSOs, but as the Ethos is the same quality with a wider FoV, it will likely replace it for most sessions. I have sold the Morpheus and selling the DeLite, but retaining the XW as it fits my XW set and still gives a superb relaxed central field view 😊

And my own dob has an 1826mm focal length, so is even flatter.  Since the longer the focal length, the less FC is seen in the 14mm Morpheus, does that mean its focal plane is completely flat?

Because if focal plane | is mated with (  you get ( in the image.

More likely, it's focal plane is curved slightly in the same direction as the scope's so ( + ( = < (really strongly curved)

And as the focal length gets longer, the 2nd curve gets flatter, reducing the impact of the ( in the eyepiece.

We all have the ability to tolerate a very slight FC, but not when the scope compounds the problem.

That's the issue, for instance, with the 14mm Pentax XW, which I also see as fine in my dob, yet that eyepiece has a ton of reviews describing FC in the eyepiece.

All from telescopes with more strongly curved focal planes.

29 minutes ago, Louis D said:

First, does your scope use 23mm or 30mm barrelled eyepieces?  This is what ultimately limits the true field of view of any eyepiece in a microscope.  You can't see what's beyond the barrel.

Second, microscopes operate at high f-ratios (f/13+ as I understand it).  As such, they're not very demanding on eyepieces at the edges.

Third, I love my 23mm Aspherics in my binoviewer when barlowed to f/12 in my Dob or natively at f/12 in my 127 Mak.  It's super easy to get my nose between them and sink them deep into my eye sockets thanks to their diminutive size.  Being super light also makes scope balancing easy; although this isn't an issue for microscopy.

I also remembered I have unprocessed/unreleased 127 f/12 Mak images for several of the eyepieces I've mentioned here.  I whipped together a new composite image below for three of them.

As you can see, all perform really well at f/12 which is comparable to a microscope as compared to with the f/6 flattened ED refractor in the earlier image.

Though I notice that, par for the course, all have a fair amount of rectilinear distortion in the form of pincushion.  You could tolerate that in a microscope, but it wouldn't be preferable to an eyepiece with lass or none.

3 hours ago, Thalestris24 said:

Hi again

I suppose the main difference, visually, with a microscope that the view is almost just 2D so very little depth that's in focus (depending on objective power). In that case it's just rectilinear, chromatic and spherical distortion one wants to minimise. The spherical and chromatic distortions comes largely, if not wholly, from the objective (I think!). So for the EP it's really just the rectlinear distortion one wants to minimise though a small amount is still acceptable. One does want good contrast. It's like with engineering generally - good enough will do! The imaging side is naturally a bit more demanding but, even so, most of the time you end up cropping around the subject of interest which will likely be occupying the central area of the (objective's) fov. Still, having an EP with a largely flat field makes everything nicer and easier. At the end of the day, as with astro observing (which I've done very little of!), one just wants a pleasant experience   Oh, it's easy to 3D print appropriate adapters. For the EPs I can remove the 1.25" barrel from the astro EP and connect the optical part with the microscope via a 3d printed adapter (threads can be challenging and it usually takes me several goes before I get it just right!). The imaging train keeps the 1.25" barrel and connects via a1.25" astro helical focuser, and then a 3D printed adapter that connects it to the trinocular port. All seems to work ok  .

Louise

One thing: the 27mm EF eyepiece has about a 10% wider field stop than the 25mm Paradigm/Starguider.

That wider field could be a problem if there is any field curvature in the objective.

But Vlaiv's summary of why you might not want a telescope eyepiece for microscopy is relevant.

You should be looking at microscope eyepieces.  Yes, I know they cost more, but they are optimized for that usage.

Any telescope eyepiece will be a compromise.

Bear in mind there is a difference in apparent field, the 27mm being 53° and the 25mm being 60°.

7 hours ago, Carl Au said:

Interesting the clone I have has 6 elements: https://www.teleskop-express.de/shop/product_info.php/info/p2335_TS-Optics-30-mm-2--UFL-Eyepiece---69--Field-of-View---6-Element-Design.html 

That's because that's a completely different eyepiece internally, not merely a rebranded clone.

The clones are from Meade, Celestron, Altair, APM, Tecnosky.

I love the 14mm Delos, and almost bought one.  But I loved the 14mm Morpheus more.  Both are quite usable with glasses.

I use a coma corrector on my 12.5", so it's f/5.75 and has a fairly flat focal plane, so I don't see any issues with the 14mm Morpheus,

Some people with much shorter focal lengths who do not use a coma corrector have had issues with FC in the 14mm.

As I read people's remarks, the dividing line appears to be about 1200mm, with longer focal lengths giving it great reviews.

That's the shipping weight.

9 hours ago, Stardaze said:

For what it's worth I have the APM 20 and 13 and think they're great EP's, certainly not bettered for the money imo. I do hanker after the Ethos 13 at times but honestly, the APM 13 still blows me away when I use it, they are my go-to EP's and get used most nights unless it's lunar and planetary viewing of course. 

I have also debated the APM 30 for a while, it won't give me much extra in terms of FOV but the exit pupil would be 6.04mm in my 10" dob over the 4.03mm the APM 20 currently gives me, which may be useful with a filter purely for nebula use. My skies are 20.54 so quite average and it's this that keeps me sitting on the fence. Just one point though regarding the APM 30, it is over 1kg in weight. I've skim read the thread so that may have been pointed out already, but that's significantly heavier than the APM 20 and might be tricky to balance for you? The XW30 is only 740g by comparison. I don't think you'll go far wrong with anything you've mentioned to date.

The APM 30mm UFF is only 556g.

3 hours ago, John said:

I'm sorry - I missed this question.

17mm is my most underused focal length. I replaced the Ethos 17mm with an ES 17mm / 92 because of this and I've thought about letting my 17.3mm Delos go as well but I keep finding excuses to hang onto it, usually after I've read a report from someone else saying how much they like the eyepiece

I guess a 17.5mm Morpheus would fill the gap very adequately but, as I tend to move directly from 20-something mm eyepieces to 13mm / 14mm eyepieces the poor 17mm's get overlooked so the Morpheus would get similar treatment I expect.

Other than that, I think my current Tele Vue's are "keepers". Probably .......

There are a few out there that might be a touch better in certain focal lengths but they cost even more than the Ethos's do.

 

 

I have 30mm (UFF), 22mm (NT4), 17.5mm (M), 14mm (M), 11mm (Apollo), for glasses, and  8mm (E), 6mm (E), 4.7mm (E-SX), 3.7mm (E-SX), without glasses, in a scope with an 1826mm coma-corrected focal length.

I tend to use them in "sets", i.e. 30, 17.5, 11mm one night, and 22mm, 14mm, 11mm the next night.

It depends on what I am observing, whether I'm using a filter or not, whether I want the extreme low power of the 30mm, how good the seeing is, 

the darkness of the sky.  

I can't say I ever use all 5 eyepieces of 11mm and longer on the same night--I don't need the magnifications that close together.

So you could justify keeping the 17mm or 17.3mm if there are times it gets used along with the next jump down or up.

But if it's never used, it should get a new home where it will get a lot of love.

On 14/02/2021 at 14:19, Deadlake said:

Would it make a difference with a 40 mm 1.25” vs a 2” ep?

Sky brightness in the eyepiece, no.  The same.

Field size, huge.  The 2" would have nearly 3x the area of field.