Don Pensack

On 03/09/2020 at 12:00, Rob_UK_SE said:

A quick update...

Firstly, thank you all for sharing your insight with this. I ended up making the decision to close the gaps in my available focal lengths (expanding on the 21E, 13E, 8E and 6E quartet) and, in particular, have something else to complement the 21E for lower power / wide field views. Below is the updated case which now includes a 30mm XW and a 10mm XW. This will be my main case as it covers focal lengths from 30mm to 3mm.

 

After spending some initial hours with the XW eyepieces, I have found them to be extremely comfortable and very easy to use in terms of eye placement. I will evaluate their optical performance over a series of nights and don’t want to jump to conclusions, but I have certainly been pleased with the views, so far. For the reasons of comfort and accessibility primarily (so that my son can enjoy higher power views too), I have decided to expand my higher magnification set and complement my 3-6mm Nagler zoom with the XWs. I’m starting to see why you enjoy using these eyepieces with your refractors, John.

This arrived today. Can you see the emerging theme here... (another case might be required)😀

Ironically, my observing partner (who also reads through the posts on SGL) ended up purchasing your recommendation, Don, for the 30mm APM ultra flat. I had, regrettably, already ordered the 30mm XW before your recommendation. I will therefore look forward to a bit of a ‘shoot out’ between these two heavyweights: the 30mm XW and the 30mm ultra flat.  

Ferrari is better than Lamborghini.

No, Lamborghini is better than Ferrari!

What about a Bugatti?

Or a McLaren?

When you're at that level, little nuances in character determine what you do or don't prefer.

And, at low power, contrast is probably more important than sharpness, since our eyes have limited resolution with night vision.

But here's some things to look for:

Date__________________Scope______________

Eyepiece_______________________________Day  Night

1.       spherical aberration_________________________________________________________

2.       coma_____________________________________________________________________

3.       astigmatism________________________________________________________________

4.       field curvature______________________________________________________________

5.       distortion--type and amount___________________________________________________

6.       chromatic aberration--axial and lateral___________________________________________

7.       apparent field_______________________________________________________________

8.       eye relief___________________________________________________________________

9.       light scatter control--field and star outside field (glare)______________________________________________________________________

10.   SAEP_______________________________________________________________________

11.   CAEP_______________________________________________________________________

12.   Tint________________________________________________________________________

13.   Vignetting___________________________________________________________________

14.   Transmission_________________________________________________________________

15.   thermal issues________________________________________________________________

16.   field stop focus_______________________________________________________________

17.   impression of contrast_________________________________________________________

18.   EOFB_______________________________________________________________________

19.   Sharpness on axis/50%/edge____________________________________________________

Other comments about eyepiece____________________________________________________

_______________________________________________________________________________

_______________________________________________________________________________

_______________________________________________________________________________

1 hour ago, Stardaze said:

Interesting Don! Out of interest, having got the APM 20 and 13, how improved did you find the Ethos variants? 

The 21mm Ethos has a bit better star images and contrast than the 20APM (it's not 3x greater, though)

The 13mm Ethos was definitely sharper than the 13 APM, but contrast was the same or even maybe a tad better in the APM.  It was hard to tell.  They were close.

By the way, there is a 7mm APM XWA coming in December (+/-).

I never took to the 21mm because it had a slightly poorer outer field correction in the 12.5" than the other Ethos focal lengths.

Axial sharpness was excellent, as was contrast but it was obvious to me why TeleVue didn't stretch the focal length past 21mm.

Even using my glasses to completely correct astigmatism (I see none at 31mm with the glasses on), the edge of the field displayed some visible astigmatism when running through

focus from one side to the other.

Granted, it is WAY out in the field, but the 17mm was simply sharp to the edge, as was the 13mm.

Compared to the 22mm Nagler, the Nagler seems to have a flatter field (not field curvature per se, but the presentation of the field to the eye), and a slightly easier exit pupil to acquire and hold.

I just find the 22mm more comfortable to use.

I find it ironic that in comparisons I've done of all the focal lengths in the ES 100° series and the APM XWA series, that the poorest edge correction in each of those lines is with the 20mm as well.

[well, except the 25mm ES 100°, which is a "bridge too far" in my opinion]

I don't really expect perfection in an eyepiece, but I came to the 21mm Ethos after 12 years with the 22mm Nagler, and just never got comfortable with the 21mm Ethos.

In contrast, the 17mm was an example of everything an eyepiece should be.  It ended up being my most-used low power eyepiece. Because of the nature of the targets I observe,

which are usually small, my most-used eyepieces are in the 6-11mm (166-304x) range, so I use any eyepiece in the 15-30mm range primarily for the very largest targets at low power.

I certainly recommend the 21mm Ethos over those other two, and I used it for 10 years.  It was only when I found I needed glasses to observe that I went back to the 22mm Nagler.

Otherwise, I'd still be using it.  A 95% score is still an A grade.

If the purpose is for lunar or planetary visual use, you won't like the scattered light in the ES focal extender.  The FEs work fine for deep sky, but they aren't well baffled for bright targets like the Moon

or planets.  As for imaging the planets, you should be able to with eyepiece projection, and the focal extender attached to the camera would also work.

I am not certain the correct adapters are available for direct attachment of FE to camera, but a 1.25" nosepiece on the camera will work if the scope has a reasonable amount of in travel available in the focuser.

Read the replies to your query on the other thread on the same subject:

The faster the scope (the lower the f/ratio), the more obliguely the rays at the edge of the light cone enter the eyepiece at the edge of the field.

An eyepiece designed to handle light rays at more parallel entry angles sometimes have problems with the lateral light rays.

This results in astigmatism in the star images in the outer field.

Now, some eyepieces just have astigmatism, period, in all focal ratios of scopes.

Others are good down to some Critical F/ratio, which is almost never specified by the maker, since they don't want to lose a lot of sales by being honest their eyepieces don't work in dobs.

But, if you want to correct the astigmatism at the edge of the field in short f/ratio scopes, it can be done.  It entails adding more lenses in the eyepiece to control it.

It entails using more expensive glass types.  Or it entails making the field much narrower.

Because wide fields are more popular these days, the more expensive glass types and more elements routes are the methods followed.

The problem is that very few manufacturers actually make astigmatism-free designs (or have astigmatism so low you don't see it).

The absence of lateral field astigmatism is one of the reasons TeleVue is such a popular brand.  I have also seen some recent eyepieces from APM, Baader, Pentax, and Explore Scientific that addressed

the problem.  Note that it isn't every eyepiece from any manufacturer that is good down to f/4.

The issue grows worse the longer the focal length of the eyepiece and the shorter the f/ratio of the field.

If you want an astigmatism-free 30mm eyepiece for an f/4.7dob, you have a choice of maybe 3 eyepieces in the entire market.

If, on the other hand, you want a 3.5mm eyepiece for that same dob that is also free of lateral field astigmatism, you have many choices.

Eyepieces that come free with scopes won't likely be as well-corrected as eyepieces you buy in the after-market.

If you see astigmatism in the center 50% of the field, it is likely in your eye and you may need to wear glasses at the scope.  There is an easy way to tell if wearing glasses will improve the image quality:

Take a star in the center of the field and defocus it.   If it becomes oval when out of focus, and becomes oval at an angle 90° from that on the other side of focus, you need to wear glasses to eliminate the astigmatism caused by your eye.

Note that this will not correct the astigmatism in the eyepiece, just that caused by your eye.  But I have several eyepieces for which all astigmatism over the entire field disappears with glasses on that are horrible without them.

That is certainly not the fault of the eyepiece.

Just remember, 2" caps are 50.8mm.  48m is the filter thread size.

Of course, top caps vary all over the place.

AgenaAstro.com in the US sells these.  And, they sell to the UK.

However, it wouldn't be cost-effective unless importing a hundred of them.

Can you get them at FLO or RVO?

The 13mm Hyperion has severe edge of field brightening--the worst in the entire Hyperion series.

The ES 82s do not, and would be a better choice.

Bear in mind, the ES cannot be used with glasses.

10 hours ago, Stardaze said:

I think that’s handy as I’m sure you would have the option of using either sized filter. Might actually save a bit of money and buy the 1.25” baader Contrast boost filter as that will only be used for planets with the 8mm and 6mm (when I add one). 

The 1.25" filters will fit all the Ethos eyepieces except the 17mm and 21mm.

18 hours ago, John said:

In my case, I only use the barrel extensions to enable me to use 2 inch filters with the 13, 8 and 6mm Ethos. Otherwise the 2 inch barrels work fine with no extensions IMHO.

 

 

 

I put all my 2" filters on the front of the Paracorr.

5 hours ago, RickEm said:

Don, in the above explanation, were the 10 and 13 Ethos being used as 2” eyepieces?

Yes, they were. Sorry.  They could be used as 1.25" eyepieces.  I use a Paracorr, and they cannot be used as 1.25" eyepieces in the Paracorr, but they certainly could without it.

I don't know where they would focus though.  It's outside the range of +0.3" to -0.4" from the focal plane, for sure.

4 hours ago, Connor brad said:

Hi, I have a 200p skywatcher explorer I was seeing astigmatism when looking through the eyepiece I got tested and they found astigmatism in my eyes anyways they provided me glasses but I'm still seeing the same distortion sometimes the stars look like a deformed diamond or a elongated kite a bit like the umbro symbol at the egdes they look a bit like seagulls anyone know what it could be could be because I have cheap eyepieces I use the eyepieces that came with the scope or could it be a collimation problem? 

There are aberrations, and there is distortion.

Aberrations you might see include:

--astigmatism at the edge of the field.  The star goes from --- on one side of focus to | on the other, with best focus looking like a +  Not all eyepieces work well below f/7-f/8.  If you have a short f/ratio, the number of eyepieces that won't show astigmatism is a highly reduced number.

--coma.  This is from the scope, not the eyepiece.  It makes stars at the edge appear a little like fans, with the point closer to the center of the field.  If this is a problem, a coma corrector becomes a needed accessory.

--chromatic smear.  the star appears to spread with red/orange on one side of the star image and violet/blue on the other.  Some eyepieces have more of it than others.

--light scatter.  the star images are surrounded by a small fuzz of light, which grows brighter as the star grows brighter.  Some eyepieces have superior light control and some don't.

--field curvature.  Usually from the scope, but also possible in the eyepiece.  The stars at field edge are out of focus when the center is focused and vice-versa.  The key is to focus half-way from center to edge to reduce this to the amount your eye can accommodate.

--edge of field brightening.  The edge of the field appears to have a brighter sky background than the center.  Not all that common, but endlessly reported if it's there.

Distortion you might see:

--rectilinear distortion (RD).  Makes a straight line running across the center of the field change as it does.  Pincushion (positive RD) looks like ) | ( across the field.  Barrel distortion (negative RD) looks like ( | ) across the field.

--Angular magnification distortion (AMD).  Makes things appear smaller in the center or larger in the center than the edge of the field, like A A A   or A A A.  It's most commonly the latter and looks like the field is rolling over a ball or globe.

Orthoscopic means without distortion and since distortion increases with the width of the apparent field, keeping the eyepiece to 40° or so is just about the only way to make an eyepiece orthoscopic.  All wide eyepieces have distortion and the preferable type for astronomy is RD because it is the least injurious to the image we see.

4 hours ago, Louis D said:

So pretty similar to the 12mm NT4 at 0.78" OUT.  I had to add five 4mm thick O rings and a 20mm 2" extension ring to the 2" skirt to make it roughly parfocal with my other eyepieces that focus near the shoulder (reference surface).  It was practically unusable otherwise because it required so many turns of the focuser to reach focus.

I found it just simpler to use them as 1.25" eyepieces and reduce the necessary range of the focuser.

Of course, using a Paracorr, they are all parfocal anyway.

If you mount tracks, then a narrower eyepiece would work fine.

If your mount doesn't track, a wider eyepiece will help keep the planet in the field.

If you wear glasses, you have no choice and need more eye relief.

If you don't wear glasses, eye relief only gets annoying when your eyelashes brush the lens all the time.  A 12-12.5mm Abbe ortho won't be an issue there.

If you want an eyepiece ONLY for planets, then the narrow high resolution eyepieces work fine.

If you want an eyepiece for multiple kinds of objects, then a wider eyepiece would be better.

You can sort of get the best of both worlds with eyepieces like the TeleVue Delite.

But, if looking for a planets and deep sky eyepiece, I'd look seriously at the Baader Morpheus 12.5mm, TeleVue Delos 12mm, and APM Hi-FW 12.5mm eyepieces.  All are 1.25" eyepieces.

Helpful information about focus positions:

21mm and 17mm Ethos:  0.4" IN from the focal plane of the scope (i.e. how much in travel is necessary when the focal plane of the scope is right at the top of the focuser)

13mm and 10mm Ethos: 0.3" OUT from the focal plane

3.7mm and 4.7mm Ethos (used as 2" eyepieces with included adapters): 0.3" OUT from the focal plane.

6mm and 8mm Ethos (used as 2" eyepieces with barrel extenders added): 0.7" OUT from the focal plane.

Used as 2" eyepieces, the Ethos eyepieces focus up to 1.2" apart!

Any of the above used as 1.25" eyepieces: focal position will vary according to the adapter used.

For example: 6mm and 8mm Ethos used as 1.25" in the Paracorr adapter: 0.3" IN from the focal plane.  If you used an adapter 10.5mm thick, then they would focus 0.6" IN from the focal plane.

Lift the eyepiece up, and more IN focus is needed.  Drop the eyepiece down and the eyepiece needs more OUT focus.

That's logical, right.  And it means that with a selection of 1.25" adapters, you can come close to parfocalizing all your eyepieces.  Adapters come with heights from -0.5" to +0.6".

One more thing: the T6 9mm Nagler focuses 0.25" OUT from the focal plane.

I regularly observe at a cold high altitude site.  It's not uncommon for temperatures to reach 3°C in August and -18°C in December.  Eyecup up, eye nestled into cup, is a prescription for immediate fogging of the cold eyepiece.

If it still fogs with the eyecup in the down position, I remove the eyecup altogether to allow more air to circulate in between the eyepiece and my eye.

[I also keep a Japanese folding fan in my pocket to wave at the eyepiece to quickly evaporate any fog on the eyepiece in the event it does fog up.  Don't laugh.  It works.]

I spent 12 years with a 22mm Nagler and loved that eyepiece like a well-broken-in old shoe.

Then I replaced it with a 21mm Ethos.  Excellent eyepiece, but I never warmed up to it quite the same way.  I ended up preferring and using the 17mm Ethos a lot more.

Then my vision changed and I needed to wear glasses down to about 10-11mm focal lengths, so I started experimenting.

So, after a 10 year segue with the 21mm Ethos, I'm back to the 22mm Nagler, and I simply had forgotten how enjoyable a low power eyepiece can be to use.

The 22mm is spending a lot more time in the focuser than the 21mm ever did.

So here's the point: you have to spend time with an eyepiece to really know it well and to understand all its strengths and weaknesses.

And sometimes what's new and shiny doesn't really match your needs.  That takes time to find out.

I never was a fan of the Moon & Sky Glow filter on the Moon, though I think it does well on Jupiter and Saturn's rings.

With the additional minus violet feature of the Contrast Booster (essentially a M&SG with minus violet added), it works well on Saturn's disc

and improves contrast on Mars without affecting the coloration of the planet, like turning up the contrast without changing the image otherwise.

It's possible the M&SG might bring out limb clouds and polar caps on Mars a tad better than the CB, but with a notable bluer tone to the image.

Both filters do great on dust storms, light colored features, and enhancing the dark markings.

1 hour ago, John said:

Not sure. I like all the ones I've owned / currently own. The 10mm is the only one that I have not owned or used - perhaps that's the best one !

If Don Pensack sees this thread his opinion would be valuable I think.

 

My favorites in the Ethos eyepieces were the 17mm, 10mm, 8mm, 6mm, 3.7mm, though they were all a bit different.

I never really took to the 21mm, and ended up preferring my old favorite 22mm Nagler.

The 13 was very very sharp, but I never felt it had the contrast of the 17mm or 10mm.

The 4.7mm isn't as sharp as the 6mm or 3.7mm in my 12.5", though I couldn't tell you why.  Perfect focus at 400x is often tough,

but why, on the same night, the 3.7mm was sharper at 500x indicates the internal configuration might be a little different.

Some day I'll do a comparo of 4.5-5mm ultrawides as I've done at several other focal lengths, though I think the 5mm Nagler will win--that eyepiece even tests better than the others. 

Anyway, Ethos:

17mm--excellent contrast, sharp stars, great step down from 30-31mm.  Could be a low power eyepiece for me most of the time.

10mm--excellent contrast, a very sharp view, very low aberrations of any kind.  perfect magnification for most DSOs in my scope.  Perhaps my most used eyepiece.

8mm--easiest exit pupil of the series to acquire and hold--like the 11mm Apollo, just an easy eyepiece to use.  I use this one a LOT.

6mm--Is this an ortho?  Fantastic contrast and sharpness.  Close to having no flaws at all.  Stunning.  Beats all the other focal lengths in superb seeing.

3.7mm--not used that often, but rendered moons of Uranus and Neptune as tiny pinpoints and even allowed me to see a white stripe on Uranus.

Used a month ago on Mars with a Baader Contrast Booster--OMG.  Mars at 500x--incredible.  My go-to planetary nebula, smallish planets, eyepiece.

On 20/08/2020 at 11:00, Rob_UK_SE said:

Thank you for these suggestions.

John, it’s interesting to read that you tend to stick with your Ethos set for the 12” dob. I was assuming that your XWs might have some benefits in the dob too (in terms of light transmission, scatter control, object framing etc.)? I have certainly been very pleased with the Ethos quartet and don’t plan to part with them - especially for DSOs. I think we are all, to some extent, eyepiece addicts on this forum!

Don, I have checked the magnification steps, based on your suggestion, and can see that the biggest gap does indeed appear to be between the 13mm and 8mm Ethos. In the 12” the spacing is 73x between these two; it is 43x in the 130mm APO. Given the current UK price for Ethos I can’t -regrettably- stretch to a 10mm now, but could go for an XW, Morpheus or similar. Reflecting on this focal length a little more, in the 12” it would result in 152x (2mm exit pupil) and 92x in the 130mm APO (1.4mm exit pupil). I think both of these magnifications and exit pupils would be useful. 

The views of both parts of the Veil (in the 12”) are lovely, but it does struggle -even with the 21mm Ethos- to frame the eastern part properly. When using the 21mm in the 130mm APO the exit pupil is down to 3mm which may well account for the dim view which isn’t nearly as immersive. One of my biggest regrets in this hobby was selling my 31mm Nagler, but it is now too expensive to be replaced for only occasional use. Further to your suggestion and linked to the 10mm, perhaps a 30mm XW or APM UF is indeed needed too? With an exit pupil of 6mm it could still be useful (at dark sites) with the dob.

Baz, your point is one I have wrestled with for quite a while in this hobby - wanting to spend more time observing than auditioning eyepieces.
 

Decisions, decisions...

I recommend the 30mm APM UFF for a lower power with a somewhat wider field than the 21mm Ethos.  The 30mm's field is ~5% wider.

It's not quite as wide a true field as the 31mm Nagler, but then, is way less than half the cost.

Between the 10mm Delos and the 10mm XW, I would pick the Delos.  I found it sharper than the XW AND the Ethos (though, of course, the field of the Ethos is a lot wider).

The Delos 10mm measures a 73° field and is stunningly sharp--I've looked through orthos with softer star images.

Look at the specs here:

http://astro-talks.ru/forum/viewtopic.php?f=32&t=1483#p41976

1 hour ago, Rob_UK_SE said:

Hello all,

I am toying with the idea of filling in some gaps within my current eyepiece collection. For some time I have tried to simplify things by owning fewer eyepieces that would, in theory, spend more time in the focuser. The current focal lengths are 21mm, 13mm, 8mm and 6mm plus a Nagler zoom (for higher power in a refractor). The scopes used are a 12” f5 dob and a 130mm f7 APO.

 

Living relatively near to the coast, the atmospheric conditions can be quite unpredictable which has resulted in me wondering... should I ‘fine tune’ things a bit to achieve more optimum views? Excluding the 6mm, the 21/13/8 trio follows a spacing of 1.6, but -perhaps- I am trying to cover too much ground with just these focal lengths and two scopes. Have others (that have adopted 100 degree eyepieces) also ended up reducing their originally planned eyepiece spacing due to this?

In summary, I am considering purchasing a 10mm Pentax XW to both try out this much praised Pentax range as well as to start filling in the current gaps.

Is this unnecessary madness, a case of ‘eyepiece addiction’ or have others ultimately found it useful to have closer focal lengths? Is there a general consensus on a ‘goldilocks’ (not to short/large) eyepiece spacing when you use more than one scope?

 

Thanks.

Rob

if you arrange your eyepieces to have constant jumps in magnification, i.e. 60x/120x/180x/240x etc., they grow closer in % as the magnification goes up.

If you are trying to beat the seeing conditions, then those jumps will allow you to creep up on the highest magnification you can use.

The thing is, the jumps should probably be smaller for the 130mm than for the 305mm.  A 60x jump is probably fine for the 12", where magnifications up to 300x will be used all the time.

But on the 130mm, it's not likely you'll use magnifications over 200x much and jumps of 40x make more sense.

So you need to see if the eyepieces you have will provide the jumps you need.

In the 12", you are lacking a 10mm Ethos (assuming you want to stay with 100° eyepieces), which I found essential in between the 13mm and 8mm in my 12.5" dob.

[I went from 140x to 228x in one jump and it was often too large a jump.  The in-between of the 10mm at 183x was perfect.]

You're also missing a really low power eyepiece, like a 30-31mm.  Perhaps your light pollution doesn't allow for that, but that low power would be wonderful on the Veil Nebula, North America nebula, Praesepe cluster,

Perseus double cluster, M31, etc.  I ecommend the APM 30mm UltraFlatField or its Altair UltraFlat twin.

6 hours ago, Andy38416 said:

I’m giving it a day time try out as we speak, the 18mm and 15mm seem ok and manageable. The 8mm however I’m struggling with, I just can’t seem to get it where no black area is appearing in the field of view. 
 

naturally it makes me wonder if I should have got the celestron xcel lx EP, but it might just be me struggling. I will keep trying, hoping for clear skies later too.

 

The Celestron X-Cel LX would have been worse because the eye relief is a bit longer.

I agree that you are simply getting too close to the eyepiece and getting blackouts from being too close to the lens.

The Binoculars example in the video is apropos.

4 hours ago, JeremyS said:

Quite so, John 🙂

Do we know anyone on SGL that has bought one?

I've been using the Apollo 11 since December.

I wrote some comments here:

https://www.cloudynights.com/topic/687544-televue-apollo-11-reviews-here/?p=10009894

The 2 most cost-effective suggestions are the 12.5mm Baader Morpheus 76° and the 13mm APM XWA 100° eyepiece.

The Morpheus actually measures about 78°, so it would have the most similar apparent field to the Nagler.