Louis D

38 minutes ago, PeterC65 said:

Perhaps, but 29mm of eye relief would be too much for me.

Due to eye lens recession, it has about 17mm of measured, usable eye relief.  This is about perfect for eyeglass wearers with the eye cup flipped down.

3 hours ago, Voxish said:

One of the most disappointing things, and something which ruins the  whole experience is that the contrast is, unless you are somewhere really dark is awful.

At the same exit pupil, the contrast should look the same.  It could simply be that your skies are incapable of supporting the Dob's higher powers necessary to equalize the exit pupil with that of the smaller refractor.  If you're looking for contrast on big objects like M31 that require lower powers to frame it properly as a whole; then yes, the smaller aperture instrument is the better choice.

3 hours ago, Mr Spock said:

A few nights ago I was looking at some doubles. One was 2.5" and separation was wide. The stars has small airy discs with a single faint diffraction ring. The diffraction ring is smaller than the airy disc of a 4"... How people can say the 4" apo has pinpoint stars when the airy disc is so large is another one of those baffling statements people made.

At the same exit pupil size, the refractor's star image will be tighter because there's no central obstruction or spider vanes reducing the central peak intensity of the Airy disk.  The following diagram from TelescopeOptics.net shows how as the central obstruction grows from 0% to 50% of the clear aperture diameter, so grows the bloat of the Airy disk.  This manifests itself at the eyepiece as bloated instead of pinpoint stars.  I can confirm that my ED and APO refractors show much tighter stars than my Dob or Mak at a given exit pupil.

It is entirely possible that it is impossible as you say to separate a given double star pair due to insufficient resolution as a result of insufficient aperture in a smallish refractor versus a large reflector.  It's just that the unresolved pair will look nice and tight in the refractor relative to the larger reflector's view at the same exit pupil even if resolved into two slightly bloated stars.

2 hours ago, mikeDnight said:

I've only once seen a Schmidt Cassegrain give a good planetary image. They invariably deliver bland, barely focused planetary images, with stars presenting as blobs rather than stellar points, and soft lunar views.

I looked through an 8" Celestron EdgeHD with a 10mm Delos at Jupiter a few years back at a star party, and it was astonishingly sharp.  Apparently, all that extra glass in the corrector puts all the errant SCT light rays where they belong.

2 hours ago, mikeDnight said:

However, if you know of anyone who would like to buy me a 12" Obsession I woul receiveit gladly. 

The 12.5" Mag-1 Portaball I viewed through about 10 or 15 years ago was a lot easier to move around the skies.  The Zambuto primary made Jupiter look like a photograph.  Being on a Osypowski  EQ platform made extended studying of the image a breeze.  Eyepiece balance can be an issue, though.  The owner was using fairly lightweight, but high quality, Plossls.

7 hours ago, mikeDnight said:

Hi Geoff,

 I'm talking about an apochromatic refractor such as Michael's lovely Starfield ED above. I've used many ED and Apochromatic refractors and they are in a different league to the SW achromats. I learned that the hard was back in January 2003, when my Helios 150mm F8 achromat was utterly annihilated by a Vixen 102mm fluorite apochromat. The difference was so stark that I never looked through the 150mm achromat again. A couple of years later at an Easter star party at my local astro club, an elderly man who'd looked through every other scope on the field, some very big scopes of every major design, came finally to the Vixen. He took a long look at Saturn, then asked "Why is this one so much better than all the rest"? So even a complete novice with no axe to grind could see the difference.   Back then there were only Vixen, Takahashi, Astrophysics and a new kid TMB. Skywatcher ED's were just about to take the astro community by surprise.

I had the opposite experience 20+ years ago at a local star party.  The Obsession, Starmaster, Star Splitter, Tectron, and Mag-1 Dobs with their premium, hand figured mirrors and hand built mounts were blowing away the Tak and AP refractors on Jupiter, to say nothing of SCTs.  I bought a Dob later that year and have enjoyed it ever since.  I only recently bought a 90mm APO refractor and quite enjoy it as well.  Yes, stars are more pinpoint in the APO, but aperture limits resolution under our steady Texas skies.  It's not unusual to push a 12" to 15" premium Dob to 350x and higher on planets and GCs revealing far more detail than a 4" APO at 200x.

1 hour ago, great_bear said:

Is a 24mm UFF likely to be better corrected at F5 than a 24mm SWA (Meade 5k)?

Here's what Ernest in Russia had to say (after Google Translate) when running the 24mm APM UFF through his testing:

Direct comparison in the focuser of a fast (1:5) 24 mm telescopeES68 and UFF showed that the quality of correction of field aberrations in UFF is better than in ES68. In fact, in the image that UFF builds, at 90% of the field of view there are only signs of small focus variations (higher-order curvature) - you can choose the focus at which the field of view looks very uniform and only at the very edge of the field diaphragm image quality drops sharply. But in ES68, visible manifestations of curvature and astigmatism start from about half of the field of view and gradually increase towards the edge of the field of view. Both eyepieces are excellently corrected in terms of chromatism. Straight line distortion is excellently corrected in UFF, angular distortion is better corrected in ES68. UFF is more massive and overall.
24 mm Panoptic lighter and more compact, in terms of monochromatic aberrations the field is corrected better than in UFF. But UFF and ES68 build an image more free from chromatism.
All three eyepieces have virtually the same effective field stop (TFOV) diameter.
Both Panoptic and ES68 lose a lot to this UFF in terms of eye relief.

1 hour ago, Don Pensack said:

Pressing that hard is what I have to to with the new Pentax XW 85°.  I'm on a search for a very low profile eyecup for those eyepieces, but haven't found one yet.

Sounds like a hard pass for me on the 23mm XW85.

The 22mm Nagler T4 was working well for me Saturday night despite not being the sharpest tool in the case.  Sure, it would be nice to have an improved version like a 23mm ES-92, but it doesn't seem like that is ever going to happen.  The XW85 could have been a contender were it not for the eye relief.

I will say I was enjoying the view through my 26mm (really 25mm) Meade MWA Saturday night.  Backed off to a comfortable eye relief distance, SAEP is not an issue.  AFOV is very similar to the 14mm Morpheus.  Sharpness is as well.  Moving your head side to side allows for seeing more field obscured by SAEP, just not all at once.  The Trapezium became difficult to split at 24x only in the last 15% of the field, which I consider a pretty decent showing.

On 08/01/2023 at 21:36, Louis D said:

There is minor yellow fringing at the 3mm and 4mm settings. I have yet to compare my 3.5mm Pentax XW to the zoom at these settings to see if the fringing persists. I do see similar fringing in my 2.5mm TMB Planetary clone, so it might exist independently of the eyepiece.

Finally compared the 3mm (really 3.5mm) setting to my 3.5mm Pentax XW.  There is no color fringing anywhere in the field with the Pentax, but there is in the Svbony.

After comparing images with my premium eyepieces, I'd say from 5mm to 8mm, the Svbony hangs with the best of them.  At 4mm and 3mm (really 3.5mm), image quality becomes second tier.  So, to get premium level performance from 5mm to 8mm at it's current price is a pretty good deal.  I'd consider the sub-5mm settings as nice to have, but not really showing any additional detail due to aberrations.

3 hours ago, Mr Spock said:

If you are looking at eyepieces under £100 then for me the best choice is the Nirvana https://www.firstlightoptics.com/ovl-eyepieces/nirvana-es-uwa-82-ultrawide-eyepieces.html They are a big step up from the BST but not really a lot more money.

I have all of them. The 13mm and 7mm would give x92 and x171 - very useful; or you could choose the 13mm and 10mm, plus x2 Barlow giving x92, x120, x185, x240 - I like the sound of that. As well as the obvious advantage of 82°, they are sharp and comfortable to use.

All well and good as long as you don't need moderately long eye relief.

5 minutes ago, Don Pensack said:

That 18mm UFF is only £109 from FLO.

That is very inexpensive for such a well-corrected 65° eyepiece.

However, once VAT is removed, shipping to US added, and GBP to USD converted, it comes out to within $10 of your 18mm APM UFF price.  The GBP is well off of its September 2022 lows.

3 hours ago, great_bear said:

What's the concensus on how the StellaLyra Kitakaru's perform at these tricky 18mm and 25mm focal lengths with F5/F6 scopes Louis - do you know?

Nothing more than what I've read on CN.  Probably best in slower f-ratio scopes based on that.

I just recalled another 18mm step-up eyepiece that had poor performance relative to its stablemates.  It was the 18mm 55° LER made by Long Perng and sold under many different names.  Again, it lacked a Smyth lens group and had really poor edge correction even in modest f-ratio scopes.  The rest of the line all had Smyth lenses and were well regarded.

On 22/01/2023 at 10:00, pipnina said:

I've done some fiddling with it in daylight and I think I've solved the coma issue in the center. But now that that's solved I think I've introduced astigmatism... or worse, it's there when the cell is properly tilt collimated, meaning the problem lies within the arrangement of the triplet of lenses within... Far beyond my ability.

Make sure the triplet is fully acclimated.  My 90mm triplet takes over 30 minutes to acclimate just 11 degrees C.  Until then, I see all sorts of star spikes.

Here's a comparison of premium scopes of different designs which sought to answer this very question.

The 18mm Meade HD-60 is similarly the weakest link in that line as well.

The problem is that all of these step-up 18mm eyepieces are positive-only designs with no negative Smyth lens group to improve correction in faster scopes.  The 18mm APM UFF and its brand-mates would probably be a good bet at that focal length since it is a negative-positive design.  Yes, it is considerably more expensive.

6 hours ago, PeterC65 said:

That's good to know. Their shipping cost to the UK is the same price as the eyepiece though!

I paid about $65 in shipping costs to the US; but on the plus side, FedEx got it here in 3 days.  Since I didn't pay the 25% special tariff, 8% regular tariff, or 8.25% sales tax, I was still paying about the typical used price for them in the US ($170).

6 hours ago, PeterC65 said:

Do you happen to know what the specified eye relief is for the Lacerta ED 40mm? I can't find it specified anywhere.

I measured 11mm of usable eye relief using the flashlight projection method.  The eye lens is recessed 7mm, so 18mm of design eye relief.

Believe it or not, but I've had no issues seeing the entire AFOV in the 40mm Lacerta ED with my eyeglasses on.  They do have to be in contact with the fully retracted eye cup, but it works just fine for me.  I reverified this Saturday night.  I can't explain this result any more than being able to see the entire AFOV of the Svbony 3-8mm zoom at 8mm with eyeglasses pressed lightly against the rolled down eye cup.  It has a bit less measured, usable eye relief than the Lacerta.

For comparison, I have to really cram my eyeglasses really hard into my 27mm Panoptic to see its entire AFOV, and it claims to have 19mm of eye relief, though I've measured just 14mm of usable ER.  The eye lens is barely recessed, so it must be down to its concavity.  I even scratched an expensive eyeglass lens on the exposed, metal retaining ring on the eye lens of that eyepiece.  I have had no qualms retiring it in favor of the 30mm APM UFF.  Had the UFF existed in the late 90s, I would have never bought the 27mm Panoptic in the first place.

That concave eye lens versus flat eye lens may be part of eye relief usability despite what the ER numbers say.  Eyepieces with steeply converging eye rays from concave eye lenses may be more difficult to use with eyeglasses than those with more gently converging eye rays from relatively flat topped eye lenses.

I have used a Moon & Skyglow (Urban Skies) Neodymium filter to slightly cut light pollution to enable better seeing of comets in the past.  Lumicon made a comet filter that passed the carbon lines associated with many comets.  Since they are just to the right of OIII lines, a UHC or light pollution filter like a CLS or similar might help as well.

As far as color filters, perhaps a light green or blue filter might help.  The problem is, you want a teal or cyan filter that cuts out yellow/orange/red light.  I don't know of a commercial astro teal or cyan filter.  It would sort of be the inverse of an orange filter (which cuts violet/blue/green light, the colors of most comets).

You really won't know until you try each on a particular comet.

6 hours ago, PeterC65 said:

Unfortunately the Lacerta 40mm seems to be in very short supply again, with little data available about it.

Try Budapest Telescope Centre.  They show low stock rather than no stock.  I've bought from them before without any issues.

3 hours ago, Franklin said:

I'll have to have a play with that, thanks. Do I need to adjust the spacing for different eyepieces? or do you I just go with the recommended "thread to sensor" spacing for scope focal length as given in the instructions?

I've found that if I add 15mm of extension to a GSO dielectric 2" diagonal along with an SCT to M48 thread adapter, I get pretty close to perfect results in either my 432mm 72ED or 600mm 90mm APO.  I tried removing the 15mm extension for the latter as suggested by the separation table, but the results were worse.

6 hours ago, PeterC65 said:

I'm assuming that the OEM eyepiece range from which the StellaLyra UFF is a branding includes the 35mm since other brandings (the TS-Optics one that I mentioned) seem to include longer focal lengths.

It's the same as the APM UFF line which includes 10mm, 15mm, 18mm, 24mm, and 30mm versions:

It could be that KUO makes the ED line as well as the UFF line, thus the similarity in appearance that you noticed.

You may also be confusing the 30mm ED with the 30mm UFF which are not the same design at all.  The 30mm and 40mm EDs were originally TMB Paragon designs.  The 35mm was introduced later after the death of Thomas M Back under other labels.

I see @badhex beat me to the punch, but on the next page of responses.

8 hours ago, Don Pensack said:

The 14mm Morpheus was seeing limited because of the magnification produced, but during some moments early in the evening I watched a star cluster leave the field still in tight focus with tiny pinpoint stars.

8 hours ago, Don Pensack said:

I trust that others do, but I just don't see it in the 14mm.  Is it the Paracorr that corrects the eyepiece to that level?  Or the f/ratio?

That is so weird that you consistently get these results with your copy, and I get my results with my copy.  It doesn't matter which scope I use it in or how much edge refocusing I do, the Trapezium clearly loses its distinctive shape nearing the edge in my 14mm Morpheus while the 17mm ES-92 at an even lower power and wider AFOV continues to show it perfectly to the edge without any focus futzing.  I even tipped my head to look straight at the edge to make sure my eyeglasses weren't causing the issue by inducing chromatic aberrations by looking through them off axis, but the view remained the same.

3 hours ago, PeterC65 said:

The StellaLyra UFF 30mm is tempting but just a bit too close to my existing ES 68° 24mm which I love. I wonder whether @FLO will also stock the 35mm variant in the future?

35mm variant of which?  The UFF series stops at 30mm and the ES-68 series has 34mm and 40mm members.

3 hours ago, PeterC65 said:

TS-Optics seem to offer a clone of the Aero ED 35mm but I would prefer to buy in the UK and I'm not completely sure this clone is the same as the well regarded Aero ED 35mm.

I have both the 35mm Aero ED and 40mm Lacerta ED versions of these eyepieces.  The 35mm has a wider AFOV, slightly smaller TFOV, and poorer outer field correction than the 40mm.  In fact, last night, I went back and forth between my 40mm ED and 40mm Pentax XW-R, and I think the ED had less field curvature and basically the same level of field correction.  The Pentax does have a larger AFOV due to greater distortion, but basically the same TFOV.  I thought about bringing out the 35mm ED last night, but the tighter eye relief and poorer correction put me off that idea.  I had lots of other comparisons of newer equipment to make that had been queued up for a while, so my time was somewhat limited for revisiting the past.

Basically, I'd say skip the 35mm ED and get the 40mm ED.  The difference in exit pupil and sky brightness is minimal.  I'm pretty sure you've seen my write-up of all of them, but it bears worth repeating for those who haven't:

Tonight I compared my new Svbony UHC to my vintage Lumicon UHC on the Orion nebula.  The difference was very slight.  Both helped to bring out nebulosity in my Bortle 6/7 skies.

My new Lumicon OIII performed about the same as my vintage Lumicon OIII except that it didn't leak any red, so stars were simply green, not green/red, which was less distracting.

Either Lumicon OIII worked better than my Zhumell OIII, but not vastly so.  Stacking them darkened the background even more.  Any of the OIII filters brought out more nebulosity extent than either UHC from the background sky.

In short, the Svbony is a great tool to have in your astro toolbox for a great price.  The Lumicon OIII is also a best buy at its current closeout price with the moving sale discount code from Farpoint.

I just got in from using my 90mm TS-Optics FPL-53 APO (f/6.7) with TSFLAT2 flattener on the Trapezium region, and I could only detect the very slightest amount of astigmatism and field curvature in the last 15% of the 30mm APM UFF's AFOV.  The 30mm ES-82 had vastly more astigmatism, and wasn't nearly as sharp on axis.  I had difficulty splitting the Trapezium anywhere in the field with the ES-82, but could split it everywhere except in that last 15% with the UFF.

My only two eyepieces that were absolutely sharp edge to edge without refocusing were the 12mm and 17mm ES-92s.  The 12.5mm APM Hi-FW was close behind losing just a bit of sharpness in the last 5% of the field.  The 14mm Morpheus had a bit more astigmatism and field curvature nearing the edge.

The 22mm NT4 was had noticeable astigmatism and some field curvature.  The 26mm Meade MWA was noticeably sharper on axis and held onto more of that sharpness nearing the edge without refocusing.