Don Pensack

5 hours ago, Mr Spock said:

That isn't the finding of people who are using it. I find it just a little behind the 3.3mm TOE at the 3mm (3.5mm) setting.

The center and 50% points are very good.  It's only at the edge the eyepiece image quality suffers.

As exemplified by the Moon photos and Ernest's measurements.

However, the figures at f/10 are very reminiscent of many inexpensive eyepieces.

It's only by f/4 (and likely f/5) that the eyepiece really falls down in edge quality, and then, likely outside the center 50% of the field.

1 hour ago, Louis D said:

Has anyone discussed theories on the optical and mechanical organization of the Televue Nagler Zooms and the Svbony 3-8mm zoom?  My theory, they have a 4 element image forming positive group up top and a 2 element negative, Smyth, group down in the insertion tube.  To increase magnification, they simply move the two groups apart like a varifocal eyepiece such as my Speers-Waler 5-8mm "zoom".  This also maintains the size of the AFOV as in the S-W.  The mechanical trick to maintain near parfocality is to move the negative lens group downward during zooming in (higher power).  I have to do this with the focuser knob to maintain focus while zooming in with the S-W.

In order to maintain parfocality, the upper and lower sections must move apart but one moves up while the other moves down.

That's why they look like mushrooms at the shortest focal lengths.

The Nagler Zoom has 5 elements in a 3 segment upper and 2 segment lower.

Al Nagler told me once that he could make a 15-30 zoom with an 82° field in the same manner, but it would be too expensive to sell, too heavy to use, and very fragile.

From Ernest Maratovich's test of this zoom:

The first column shows the focal lengths at the click stops (actual measured focal lengths in parentheses).

The next column is the field stop at each click stop.  No mystery here, because focal length = field stop at 57.3° apparent field, and this is very close.

The next column is calculated field stops based on stated (and actual) focal lengths with no distortion.  You can use these figures in Astronomy tools to get an accurate answer, or in TF = AF/M.

The next column is the measured apparent field (what we actually see). Roughly 57-60°.

Then 3 columns of spot size at f/4 (center/mid/edge) and 3 columns of spot size at f/10 (center/mid/edge). 5 is considered by most books to be perfect.  10 is fine as long as the spot stays round.  15 is OK and like many eyepieces at the edge. >20 is so-so.

The last column is the nature of the aberrations at that focal length, listed in importance from most to least, followed by a distortion %, if measured.

Conclusions: FC dominates from 5-7mm settings. Astigmatism is present from one end to the other.  Distortion is fairly high for the narrow fields.

f/10 performance is better than f/4, but not remarkably so except from the 3mm to 4mm settings.

It has much better performance than most inexpensive eyepieces except at the 3mm setting.

4 hours ago, Highburymark said:

Yes indeed Don - but this has always made me wonder why we don’t see more people having field curvature issues with the many brands of flat field eyepieces (APM, Altair, Lunt, SVBony etc)? As there’s field curvature inherent in many telescopes. I haven’t used any of that range myself, and I don’t doubt they are excellent, but why buy flat field eyepieces unless your scope has a perfectly flat field?

One reason I can think of is to reduce the amount of visible field curvature.

| + ) = )  You might be able to focus half way to the edge and accommodate the entire field.

| + | = |  This is ideal, and reflectors of 1200+mm focal length are pretty flat, so this will work.

) + ) = |  And this works if the eyepiece and scope have nearly identical curvatures,

) + ( = bad field curvature, and this can happen with a mismatch of eyepiece FC and scope FC.

Since we don't know (the manufacturers don't tell us) whether the FC in an eyepiece is positive or negative, the lowest risk is a flat field eyepiece.

But, alas, to the owner of a flat field scope, it doesn't matter whether the FC in the eyepiece is positive or negative--it'll be curved.

But, like the person with a flat eyepiece and curved focal plane scope, it might be possible to accommodate the curve, so the degree of FC is important as well.

I don't really under stand how short f/ratio refractors of 50-80mm don't see serious FC with nearly all eyepieces, though.

My 12.5" has a radius of curvature of ~1600mm.  An 80mm f/6 refractor has a ROC of 160mm!!  How any eyepiece wider than an ortho functions in such a scope is a mystery.

One note: please go down the page to the next time the Buyer's guide was posted, as it contains some new entries.

These are not new in the world.

Most resellers sell them as "Premium Flat Field" eyepieces.

Look up reviews on the Astrotech PF eyepieces to see some comments about them.

They are also sold by Artesky, Astromania, Astrotech, Auriga, Lacerta, Omegon, Sky Rover, Tecnosky, and Telescope Service.

FLO has a good price.  

5 hours ago, stormioV said:

I have just noticed these

https://www.firstlightoptics.com/ursa-major-eyepieces/ursa-major-fmc-flatfield-eyepiece-25mm.html

Would this be to similar to what I already have? 

I'm still thinking uff 24mm or es68 24mm would be better option.

Argh! Another new eyepiece!

These are the same eyepieces sold by many companies as "Premium Flat Field" eyepieces.  FLO is selling them at a good price.

20 hours ago, Highburymark said:

I’m not picking up much field curvature at all - maybe it complements the opposite field curvature in my scopes? The 3-8 works well in all three of my refractors in this respect. In the F/6 60ED for example, just a tiny shift of the focus is needed at 3.5mm to make edge stars sharp. 
On the issue of parfocality, it’s very close to parfocal through the range. I don’t need to refocus between 8mm and 5mm, but below that, a small tweak required.

It is when curvatures match that you see a flat field.  When curvatures are opposite, the edge is far out of focus when the center is focused.

FC is always more of a problem with larger field stops, too, so FC will be less visible at the 3.5mm end than at the 8.1mm end.

https://astro-talks.ru/forum/viewtopic.php?f=32&t=1483#p101290

Yup.  3.5-8.1mm

Review:

https://astro-talks.ru/forum/viewtopic.php?f=32&t=4585&p=94406#p94406

And yet, people heat their secondary mirror or corrector plates or eyepieces to prevent dewing.

A very slight change in the optical image is preferable to the problem of opaque optics.

On 16/04/2024 at 10:01, Zermelo said:

It may or may not be relevant to the decision that the Altair version (I have this one) has a steel body, and is heavier than some of the others.

[EDIT]  I just looked it up, 331g

The Altair Astro version is heavier than 331g.  In an early thread about the green eyepieces, someone quoted the actual weight, but, alas, I can't remember what it was.

The APM, with aluminum lower barrel, is 331g.

I sold APM eyepieces for years.

On my gram scale the 24mm UFF was 331g without eyepiece caps.

I have just posted the new 2024 Eyepieces Buyer's Guide here:

https://www.cloudynights.com/topic/919099-2024-eyepiece-buyers-guide/?p=13395818

Place a bright star at the edge of the field, then look direct at the center of the field.  If you can catch the bright star in your peripheral vision, you are seeing the whole field.

If you want to look at the edge of the field with direct vision, and you simply move your eye to do so, and the eyepiece is wider than about 70°, you will move your eye's pupil away from the eyepiece's exit pupil.

In order to look directly at the edge in an 82° eyepiece, you need to roll your head over and look through the eyepiece at an angle, whether using glasses or not.

21 hours ago, stormioV said:

Thank you.  24mm uff looks great on the ruler matrix . My 25mm Starguider not so good.

If I struggle with long eye relief with my 32mm plossl, would that be similar  case with 24 uff?

Possibly.  Though that depends on how recessed the eye lens on your 32mm Plössl is.

I' have see 32mm Plössls with very deepset lenses which reduce the effective eye relief significantly and are not usable with glasses.

The 24mm UFF has a tall eyecup and a deeply recessed eye lens.  Its 29mm of eye relief is reduced to about 7mm with the eyecup in the up position.

So it's likely you wouldn't have any issue with the large eye relief, especially with the eyecup flipped up.

I sold a 21mmEthos and went to the 22mm Nagler due to needing glasses at the eyepiece.

I preferred the larger field, but glasses use dictated what happened.

FWIW, I don't feel deprived.

2 hours ago, stormioV said:

Thank you for your help so far. It seems this version of uff is best priced in UK @£109

https://www.altairastro.com/altair-24mm-ultraflat-eyepiece---precision-barrel-stainless-steel-237-p.asp

With field stop of uff being 27.66 mm compared to 27.2mm, of ES does this mean UFF will have a slightly larger /very similar fov?  I thought UFF was 65 and ES68?

 

It means the Altair Astro 24 will have a larger True Field on the sky, but a slightly smaller apparent field.  This is because distortion characteristics are different among the choices.

The difference in apparent field is small, and the extra true field is a nice bonus.

4 hours ago, Second Time Around said:

I bought the 22mm/70 Deg Omegon Redline.  Everyone's different but I preferred it to the much more expensive 22mm Nagler.  It's supposed to be not quite as sharp as the Nagler at the extreme edge, but the shape of my eye sockets means that I can't see the very edge of many wide angle eyepieces anyway.  I also found the Redline very comfortable as well.  A further advantage is, as Louis kindly pointed out to me some years ago, it can take a Dioptrx astigmatism corrector that I prefer to wearing glasses.

It's currently £162 including VAT plus shipping from £6.90.  Go to https://www.omegon.eu/eyepieces/omegon-redline-sw-22mm-eyepiece-2-/p,33239

It's the same eyepiece as the Astromania 22mm for $128.99 (£103.54).  Even with VAT, it'll be cheaper than the Redline.

https://astromaniaoptics.com/products/astromania-2quot-22mm-70-degree-super-wide-angle-swa-mean-you-always-enjoy-a-huge-field-of-view?VariantsId=10092

Also sold as Arcturus Ebony, and Omegon Redline.  You might find a used one sold as an Astrotech AF70 or Olivon 70.

3 hours ago, groberts said:

If I may, a couple of questions:

1. What's the eye relief of the APM?

2.  Looking around, I see that using the APM as 1.25" can be a problem - any thoughts?

1. 18-20mm over the range.

2. Correct.  It's focal plane is very high in the eyepiece.  It will be easier to focus in most scopes if used as a 2" eyepiece.

It is usable as a 1.25" eyepiece if you have the large amount of in-travel required to get it to focus (it's over an inch).

The field stop in the eyepiece only requires a 1.25" barrel, so there is no difference in the image or apparent field if used as a 1.25".

I owned all the Ethos for years, and found the most-used one was the 10mm.  In my 12.5" scope, it had better contrast than either the 8mm or 13mm.

But the sharpest one of all, for Moon, planets, double stars, star clusters (especially small globulars) was the 6mm.  I call it my "100° ortho", LOL.

3 hours ago, stormioV said:

I'm looking for an upgrade eyepiece for my LX90 ACF 8inch at 24mm to get maximum fov for 1.25 fitting. I do not wear glasses. Currently i have BST Starguider and Meade 4000 SP 32mm. I don't really get on with the Meade Plossl, I struggle with eye placement with this eyepiece. Optically it is great. 

I am willing to spend up to £200 new for this. I am thinking about either

ES68 24mm

Stella Lyra(APM, Altair, Celestron) UF 24mm ,

Baader Hyperion 24mm

 

I do use a 2 inch diagonal with 1.25 adaptor so it is an easy switch.  My only 2inch is ES 68 34mm which I find stunning. 

Would I be better looking at 20mm 2 inch such as Stella LYRA 80/Founder optics or stick with my original 1.25 upgrade idea.

Thanks.

 

 

 

 

It sounds like you struggle with the Meade 32mm because of its long eye relief.

You probably need an eyepiece you can get closer to without experiencing blackouts.

That makes the two in the price range most likely to satisfy the 24mm UFF (27.6mm field stop) with eyecup flipped up, and the 24mm ES 68° (27.2mm field stop).

Hmm.  Long focal length, high power, narrow field scope paired with a short focal length, low power, widefield scope--a great combination.

Another report:  I wear glasses and can easily see the entire field of the 22mm T4 Nagler, glasses touching the rubber.  Strange that Mark can't.  His glasses must sit farther from his eye.

I can verify that by putting a brighter star at the edge of the field and then looking direct at the center of the field.  The bright star at the edge is still there in my peripheral vision, as well as the field stop.  Mark should try that.

It is an optical illusion that, somehow, the field looks a lot narrower when staring at the center than it does when you roll your head over to look directly at the edge.

I notice this in all eyepieces wider than about 70°--the field looks wider when you look directly at the edge.  I wonder if that is due to rectilinear distortion in the eye.  Possible.

My scope has over 10x the radius of curvature of his 60mm, and I see no field curvature whatsoever, so it will depend on the scope type and its focal length to determine whether you see FC in a 31.1mm wide field stop. 

9 hours ago, Louis D said:

The Long-Perng made 80 degree series have gotten good reviews in the 14mm and 20mm focal lengths in Orion LHD, SL 80º LER / UWA, and other liveries.  To get long eye relief though, you have to completely remove the eye cup as Don says above.  You might be able to find an alternate eye cup to slip-fit in place of it.

The Founder Marvel Ultra Wide version is also available from FLO for £20 cheaper if you can live with its green instead of red color.

If you're not hung up on 80º and could live with 70º, the 22mm Omegon Redline and its rebranded bretheren is very well corrected, eye glasses friendly with the eye cup removed, and not too heavy.  I have the discontinued Astro-Tech AF70 version.  I retired it only after acquiring a 22mm NT4, but am quite content to use it when I only have my B-Team case available.  The Baader Hyperion M43 screw-on eye cup fits it nicely as an eyeglasses friendly eye cup.  The original eye cup is far too thick and stiff to fold down.  This eyepiece used to be only $99 10 years ago, but it appears to have doubled in price since then.  Unfortunately, it's not such a bargain anymore.

I concur on the 22mm Redline.  It is far better than its price indicates.  The cheapest version of it seems to be the 22mm Astromania SWA 70°, which is about USD$130.  Last I checked, it was available under several different labels.

9 hours ago, groberts said:

In an attempt to broaden my interest in astronomy and occasionally share my hobby with the family and grandchildren (who are already interested), I recently acquired a Starfield 102 f/7 refractor.  I intend to use it for some of the larger / brighter DSOs and variable stars etc but especially for the family and therefore expect the planets, moon and solar will be their most favorite targets.

As we all know in the UK, it's not been the best for clear skies recently but I have managed a couple of short sessions using the Starfield and after a gap of 10-years have enjoyed getting back to observing, though,not surpringly I still struggle with some of my eyepieces to get the best of views, almost certainly because I wear spectacles and in most cases  (I suspect) find the FOV and eye relief inadequate. My signature below lists my current eyepieces, of which I really only get on with the 20mm & 32mm plossls and the Ultra-wide + Long eye relief 6mm.

I would appreciate any recomendations for maybe a couple of other eyepieces that would improve my viewing, bearing in mind the above objectives and problems (planets and spectacles).  I believe since I last did any observing there are some very good eyepieces now available that might be better suited to my needs?

Graham 

        

Graham,

Here are some suggestions:

Baader:  Morpheus eyepieces--all focal lengths

APM: Ultra Flat Field 30mm/24mm/18mm (also available as Celestron Ultima Edge, Meade UHD, Stellalyra UF, Tecnosky UF, Svbony UF, Sky Rover UF, Altair Astro UF, etc.)

Pentax: XW 70° all

Tele Vue: Plössl 25mm and longer;   Delite--all;   Panoptic 27mm and longer;   Delos--all;  Nagler--30mm, 22mm

Long Perng UW/Orion LHD/Stellalyra UW 80/Founder Marvel: all ,but only IF the eyecup is removed and a shorter substitute eyecup is used

Vixen: SLV--all, NPL--any of >25mm

Explore Scientific: 92° 17mm/12mm;   82° 30mm (barely);  68° 40mm/34mm/28mm;  62° 40mm/32mm/26mm;  52° 40mm/30mm 

My personal favorites are the Morpheus eyepieces in my 102mm f/7 apo.

Just really easy to use with glasses on.