Louis D

Nice work @vlaiv.  Your next experiment is to confirm if eyepiece aberrations are reduced when using the phone camera versus the DSLR lens.  I theorize there is no difference because the eyepiece sees only the telescope and the camera lens can't undue aberrations once introduced into the image train regardless of combined working f-ratio.

I will admit that the enormous depth of field of wide angle phone cameras will compensate for image field curvature.  In particular, the 30mm WideScan clone eyepiece has tremendous field curvature to my presbyopic eyes, but it looks really nice in a phone camera image.  It's the Agena UWA 80° 30mm below.  Notice how readable the rulers remain so close to the field stop.  When viewing with my eyes, those edge images were a blurry mess until I refocused for the edge.  As such, you cannot judge field curvature of eyepieces using these phone camera images.  Your f/1.4 image would probably reveal how it really should look to the human presbyopic eye.

Notice how the strong astigmatism in the Rini MPL 29mm and chromatic aberration in the Kasai Super WideVue 90° remain even in the phone camera images?  No improvement.  That's pretty much what my eye saw through each eyepiece.

Another option would have been to try and locate a used 18mm Meade 5000 UWA in 1.25" barrel to get the widest field possible at about the same exit pupil as the 16mm ES-68.

13 minutes ago, johninderby said:

VAT registered individuals / business however are subject to VAT on the sale of used goods.

Same for registered individuals/businesses who collect sales tax on new items as well as used items.

However, ebay and other online peer to peer marketplaces are now collecting sales tax on all sales, foreign and domestic, by registered and unregistered sellers.  Is this happening with VAT as well in the UK?

53 minutes ago, Goldfinger said:

OMG 😳😳😳 I didn't realize binoculars could get so big. I'm so used to seeing the field binoculars that are used by bird watchers or fans at sporting events.

Those are huge and no doubt have a huge price tag as well.

You asked.

Hidden VAT is not an issue in the US.  Prices are always listed before sales tax is added.  Keep that in mind when comparing US to UK astro prices.  That might explain why some folks in the UK price their used gear significantly higher than Americans even when exchange rates are accounted for.

Are UK individuals (sellers or buyers) required to collect/remit VAT on used gear sales?  Technically, individual American buyers are supposed to remit the appropriate sales tax on items bought from other individuals or from overseas sellers, but literally no one does this, and there is no enforcement effort anywhere except for private used car sales.  Sales tax in that situation is paid when and where the vehicle is registered.

Gasoline, cigarette, and liquor excise taxes are hidden, though.  I find it interesting that most other countries hide their consumption tax.

On 31/05/2021 at 07:58, Goldfinger said:

I never thought of that. What is the highest power binoculars you can purchase?

Perhaps not the highest power, but often thought of as among the nicest large binoculars, the Fujinon LB150 Series – 25×150 MT-SX Binoculars:

APM in Germany sells all sorts of giant binoculars including several variants of this Fujinon if that sort of thing interests you.

If you like looking at pictures of giant binos of the past and present, here's a page full of them at Oberwerk.

2 minutes ago, vlaiv said:

Well, I guess that test is in order tomorrow.

I have all the equipment needed and I'll happily test this with DSLR, fast longer FL lens (85mm F/1.4 Samyang), small scope, two or three eyepieces with different magnifications and eye reliefs as well as AFOVs.

And pull out your cellphone/smartphone (UK mobile?) camera for comparison shots with each eyepiece.

8 hours ago, carastro said:

Ditto.  

I have also had a few silly offers from people trying their luck, which I have declined. 

Carole

If I see something expensive I want, but can wait on buying, I'll let it sit on CN classifieds for 2 or 3 weeks and make an offer for about 80% of their asking price.  We generally move toward 90% of asking price, but I insist they eat the PP and S&H fees at that price.  I end up saving hundreds of dollars in those cases.

Check out my first look of the SVBONY 68° Ultra Wide Angle 20mm eyepiece:

Based on a recent comment by another SGL user that the SVBONY 68° Ultra Wide Angle 20mm eyepiece was sharp and gives very clear images in an f/6 Dob, I thought I'd get one to try out in my field flattened f/6 AT72ED refractor to see if somehow this repackaged $30 eyepiece is working some kind of miracle at that price point.

I measured it to have a 67° AFOV, a 68° effective AFOV (eAFOV) due to slight edge distortion, a 23.7mm field stop, 14mm of usable eye relief, a 24mm diameter eye lens, and 3.1 ounces (88g) in weight.  As such, it lives up to the ad for the most part.

Since it has been raining almost constantly here for the past 4 weeks, I haven't been able to get out and observe at all.  I think the night skies cleared up by early morning once during that time.  As a result, I'm constrained to indoor testing for now.

It's a bit shy on eye relief for me when wearing eye glasses.  I need about 2mm to 3mm more eye relief to see the entire field comfortably.  However, I would estimate I can see about 80% of the field while wearing eyeglasses.  It's easy enough to tip my head slightly to take in the edges.

The eye cup snaps up and down with relative ease, and yet it stays up when used without eyeglasses.  It's very similar to many budget Plossl eye cups.

The center appears to be sharp, but the edge sharpness falls off noticeably in the last 25% of the field.  Refocusing did not improve things, so it appears to have a flat field insofar as I can tell in an f/6 field flattened scope.  I'm guessing astigmatism is the primary cause of edge unsharpness since I didn't see any appreciable chromatic smearing.  It is not sharp edge to edge at f/6, but it is pretty sharp over the central 67% (45°) of the AFOV.  As such, it performs as well as a 20mm Plossl while providing more context.

Here's a couple of group beauty shots of the SVBONY alongside its more expensive competitors.  It certainly is a handsome looking eyepiece in gloss black, textured grip ring, engraved white lettering, and snazzy red anodized beauty rings.  It's much nicer looking than the earlier incarnations of this line of eyepieces such as the Orion Expanse and other 66° UWA variants.  It looks much more expensive than it's price tag would suggest.  It's also very compact for what it does.  It's fairly dense, though.  I was surprised by its heft in my hand.

Here's the updated 18mm to 22mm comparison image taken through the eyepiece of my standardized rulers target.  I've included the original eyepiece group shot for context.  I didn't feel like digging out all the other eyepieces to reshoot it.  Just imagine the new SVBONY slotted between the generic reversed Kellner and the Orion Centering SWA eyepieces.

As can be seen above, the SVBONY holds its sharpness farther off axis than the 20mm Orion Centering SWA, but it is not as wide in AFOV or TFOV.  It also has 3mm more usable eye relief which is quite noticeable.  I did not notice any SAEP kidney beaning in daytime usage.  The view is quite easy to acquire and hold.

It is head and shoulders better than the 20mm generic reversed Kellner in all respects except for physical size.

The SS zoom is incredibly sharp at 21.5mm, but also incredibly narrow in AFOV and short on eye relief (11mm).  Since the SVBONY can't zoom, it's not a relevant comparison.

It performs slightly better off axis than the 19mm GR Konig, but it is only marginally wider in AFOV.  I think the SVBONY is likely an improved Konig variant based on tear downs of the 20mm Expanse I've seen on CN.  There's a slight chance this version has been redesigned, but I'm not disassembling mine to find out.

Both the 18mm Meade HD-60 and AT Paradigm (BST Starguider) hold their sharpness better to the edge, but both have noticeably narrower AFOVs.  The HD-60 also wins out on usable eye relief at 19mm versus only 12mm for the Paradigm.

The 22mm AT AF70 holds its sharpness much farther off axis and is slightly wider in AFOV.  It also has more usable eye relief (16mm that feels more like 18mm in use).  It isn't much of a surprise it's better given how much bigger and more expensive it is.

And of course the 22mm Nagler T4 rules them all for sharpness and AFOV width, but at a significant size, weight, and price premium.  It's also a bit tight on usable eye relief at 14mm, although it feels like 16mm in use.

Once I get some time under the stars with it, I'll report back.  If I like it enough, I may get another for binoviewer usage.

1 hour ago, rl said:

Sadly no longer available new, Maxvision were rebadged Meades as a result of some contract mess-up, but I think the same optical design has been cloned several times over and is probably still out there as a badge-engineered new product .

It is optically the same as the 24mm ES-68.  However, it has better eye relief due to the eye lens being less recessed.

1 hour ago, JamesF said:

The unintended consequence being that lots of trees get cut down as soon as they reach 18" in diameter?

James

Actually, they're quickly cut down by crews of unregistered immigrants working for cash.  Grind the stump, and there's little evidence of what happened.

A nearby city has an ordinance protecting trees with trunks greater than 19 inches in diameter at 4.5 feet off the ground from being cut down without council approval even if dead.  Generally, they require them to be moved if they impede construction.  This can cost $125,000 to $250,000 per tree and take weeks of preparation.

5 hours ago, Mr Spock said:

Being a photographer I can say for certain my DSLR will not image an eyepiece with a lens attached. All you will get is an out of focus image of the eyepiece top and its surroundings.

It will do eyepiece projection of course but I have no means to connect it.

Thank you for the confirmation.

All you have to do is look at the geometry to see that camera lens will be looking well past the edges of the eye lens unless it's a long telephoto lens, and therefore it can't possibly image anything other than the very center of the field of view.

8 hours ago, Kon said:

When I thought I had made my mind.....I will see if any of these might come as second hand as well and if not, then make a decision which one to buy new.

Good idea.  I picked up my 24mm APM UFF second hand for $130 3 years ago.

17 minutes ago, Don Pensack said:

Sale or no sale, I just wish they were available, period.

There is so much pent-up demand.

It's got to be killing your business if you have no stock to sell.

3 hours ago, Kon said:

Thank you all for the links, comparisons and personal experience with different EPs. After reading the links and careful consideration, I am thinking of going for the ES 24mm (68°) (ouch, that's a lot higher than my initial budget). Several of you suggested it.  I realise that I use my 25mm EP quite a lot so getting an EP that will deliver hopefully sharper images is worth it. I will try see if anything might come on second hand market otherwise I will be placing an order soon.

For the same money, the various 24mm APM UFF class eyepieces have a similar performance level to the 24mm ES-68 at the same price, at least here in the US.  They are also more readily available.

Look for the 24mm APM Ultra Flat Field, 24mm Altair Ultraflat, 24mm Meade 5000 UHD, 24mm Celestron Ultima Edge Flat Field, and 24mm Orion Ultra Flat Field.

Below is a comparison image of my various ~24mm eyepieces, including the 24mm APM UFF, in an f/6 field flattened 72ED refractor:

I don't have either the 24mm ES-68 or Panoptic for comparison due to their tight eye relief.  The Panoptic, at least, would be similarly sharp to the 27mm Panoptic shown near the bottom.

If the focuser can accept a 3" diagonal, the 30mm ES-100 comes into play along with custom Siebert 3" observatory eyepieces.  Many refractors intended for astrophotography come with 3" or larger focusers, so there might be some options there if there is enough back focus, which there should be since they're intended to accept filter wheels, OAGs, and other gear in between the focuser and camera.

18 hours ago, Cosmic Geoff said:

If you want to take spiffing colour images of deep sky objects you will need one of those GoTo mounts you say you don't like - they are needed for precise guiding and tracking.

Folks were taking well guided astro images using ordinary tracking mounts long before goto mounts came to be, so they are not a prerequisite.

If using an image intensifier, the 40mm will allow for a larger field of view than will the 32mm if it has an angle of view of less than 43 degrees.  Obscure reason, but it might apply someday.

On 22/05/2021 at 02:21, Cornelius Varley said:

Afocal photography and eyepiece projection are two separate things. Afocal uses a camera with a lens to image through an eyepiece ie smartphone or compact camera whereas eyepiece projection images directly onto the sensor from the eyepiece.

Eyepiece projection might be possible with that camera, an eyepiece, and an eyepiece projection adapter of the proper type now that think about it.

The Mak will need a mount and tripod, so you'll need to budget for that.  The mount is built into the Dob.  I find Dobs easier to track with than alt-az mounts on tripods and are better at resisting diving when changing out heavy eyepieces.

1 hour ago, Ags said:

But now I will have to wait longer for the Morpheus 17.5. 

Maybe it will go on sale in the interim?

1 hour ago, vlaiv said:

I still don't get this part - isn't lens entrance pupil in fact its aperture for collimated / parallel rays (object at infinity)? If so - large fast lens will have aperture much larger than exit pupil of eyepiece.

Next chance I get, I'll dig out my Sigma 50mm f/1.4 lens (with 1.6x DSLR crop factor on my Canon Rebel T3i) and try to image a typical eyepiece's AFOV just to illustrate the result for you.

1 minute ago, vlaiv said:

I'm not sure that I ever had a chance to look thru astigmatic eyepiece when my pupil was smaller than exit pupil of eyepiece.

For that I would need really fast telescope and long focal length eyepiece - or perhaps really destroy my night vision with flash light to conduct a test?

Sometime try looking at a bright star at the edge of a low power Erfle, Kellner, or other poorly corrected eyepiece, and then swing the scope over to the full moon and observe for a while.  Now, quickly swing the scope back over to the bright star.  Does it look sharper at the edge now?