Louis D

I read Don's write-up of the 23mm XW and concluded that I'll soldier on with my 26mm (really 25mm) Meade MWA in my quest for an ~80° long eye relief eyepiece with good correction in the 23mm to 26mm range.  If I back off a bit (maybe to 17mm eye relief) to avoid severe SAEP, I can comfortably take in 79° wearing eyeglasses with just a hint of SAEP shadows.  Pushing in hard with eyeglasses (just 10mm of usable eye relief) to see all 83° results in massive SAEP making it impossible to take in the entire FOV at once.  As Don said in his piece, some flawed eyepieces that make up for it in performance just grow on you over time.  The Meade is surprisingly well corrected and flat of field to the edge despite its usability warts.  I've never tried to judge it for EOFB or contrast.

@Don PensackHow much of the new Pentax's FOV is visible when backed off to a comfortable eye relief distance for wearing eyeglasses?  How much does SAEP intrude at that point?

15 hours ago, cajen2 said:

High magnification! 🤣🤣🤣 In what?

In a 14" Celestron SCT?  Given its 3910mm focal length, a 27mm eyepiece would yield 145x.  Not super high power, but decently high power.

I wonder if the 28mm Pentax XL which has a 55° AFOV has more distortion to account for its wider AFOV.  Has anyone ever done a shootout between these two to see if they have the same TFOV?

15 hours ago, Alan64 said:

In the end, what is needed are purchasers and testers of these latest models.

Don't look at me. 😁  I just picked up a used 6" f/5 GSO Newt this fall and haven't had a lot of quality time with it.  I wanted a decent dual speed 2" focuser for my big glass.  It definitely benefits from a coma corrector with my 70 to 92 degree AFOV eyepieces.  Of course, these Ursa Major scopes target an entirely different clientele.  I doubt they'll be dropping in Nagler or Ethos eyepieces anytime soon after purchase.

I got initial through-the-eyepiece images and measurements taken with the Svbony 3-8 zoom in my f/6 72ED field flattened refractor.  Here are my preliminary thoughts and findings:

• AFOV is pretty consistently 60 degrees, give or take a degree or so.  If you zoom fast enough and only pay attention to the illuminated circle, you can see it subtly changes.
• Usable eye relief is pretty consistently 8mm from the top of the folded down eye cup.
• Every clickstop focal length is within 0.1mm of the claimed focal length.  That is mind boggling given how far off I've found most zooms are from their marked focal lengths.
• The clickstops and zoom action shouldn't cause too much of an issue while viewing and zooming.  I didn't need to hold the eyepiece while zooming.  The 2" GSO diagonal's 1.25" eyepiece adapter's compression ring held it tightly without allowing rotational twisting.
• Focus is pretty much parfocal between any two clickstops.  I tweaked focus at each focal length to be certain of the best image possible, but it might not have been absolutely necessary.  I didn't try racking from one end to the other to check for end-to-end parfocality.  I also did not check for parfocality with other eyepieces known to focus at the shoulder.  I'll try to remember to do this the next time I have it out.
• You can't easily read the focal length scale if you have a GSO style 2" to 1.25" adapter that partially submerges the eyepiece's upper barrel to keep 1.25" eyepieces parfocal with 2" eyepieces if they all focus at the shoulder.  To be certain of which focal length I was at for each photo session, I racked the zoom collar back to 8mm and counted clicks downward from there.
• In the same holder, it's a bit difficult to grab the zoom collar and not the eye cup collar instead.  You have to get used to where it is, right at the top of the adapter.
• Zooming in while viewing to the 4mm and 3mm settings can be disconcerting as the top of the eyepiece lunges upward toward your eye.  I certainly was unprepared for this the first time I zoomed while viewing.
• There's no sign of SAEP (kidney beaning) or oddball edge artifacts at any focal length.  It made taking quality AFOV images a breeze.
• The fieldstop is nice and sharp throughout the focal range.
• It is a noticeably sharp eyepiece except maybe in the last 10% of the field near the edge at the shorter focal lengths.  Even then, it's relatively unobtrusive in daytime testing, and I wouldn't have noticed it without specifically looking for it in my photos.  I'll have to star test when the Holidays are over, and the sky clears, to confirm field sharpness at each setting.
• I started to come to the realization that this eyepiece might be a great eyepiece for newbies trying to populate their high power collection.  If eye relief isn't an issue, it can easily replace 3.2mm, 4mm, 4.5mm, 5mm, 6mm, 7mm, and 8mm TMB Planetary eyepieces along with 3.2mm, 5mm and 8mm Starguiders/Paradigms without giving up anything except eye relief.  That makes it a bargain at its current price.
• As I became more accustomed to it, I really began to appreciate what an optical engineering achievement this little eyepiece really is.  It took the 3-6mm Nagler Zoom as a starting point, lengthened the focal range upward to 8mm and widened the AFOV by 10 degrees, all while maintaining very good optical quality at an exceedingly affordable price point.  That, and the mechanical aspects are top notch as well.  It just exudes quality and attention to detail.

Bear with me through the Holidays.  It takes significant time to edit and composite the images for my test reports, time which is scarce right now.  I just wanted to give y'all a heads up that this eyepiece appears to be the real deal, and to snag it at the current discount if you want a good self-present for Christmas.

After rescuing my Svbony package from the wrong community mailbox by catching our postman late this afternoon (holiday substitutes don't know the route), I have the Svbony 3mm-8mm in hand.  It's very nicely built with a smooth zooming action despite being about 6 °C straight from the mailbox.  I've never felt such a mechanically precise click-stop action.  It feels like a fine piece of machinery.  The upper part barely moves upward zooming to the 7mm and 6mm positions, then starts accelerating faster and faster toward 3mm position.  It increases a lot in length from 5mm to 4mm to 3mm.

Some quick measurements with a flashlight indicate it has about 8mm to 9mm of usable eye relief throughout the range with the eye cup folded down.  I can't even come close to seeing the entire field with eyeglasses when holding it up to my eye and viewing a lamp sans telescope.  Perhaps at the smallest exit pupils I'll be able to get away without eyeglasses despite having 2.5 diopters of astigmatism.

The eye cup folds down very easily without wanting to flip by itself like the original Morpheus eye cups.

The insertion barrel is about 36mm long.

I'll try it out in my normal testing rig when I get the chance.  For now, it feels way more expensive than it is.  I probably won't be able to get it out under the stars for a while given our extended forecast and Christmas.  After all, it has to go in my stocking for a few days. 😁

16 minutes ago, FLO said:

Though today I have been extra quick because I am in bed with a laptop recovering from Covid.

I had the alpha variant back in 2021 before I was eligible for a vaccine shot.  It was not fun.  I wish you a speedy recovery.

@FLO Is it possible someone has already bought one expecting it to have a parabolic mirror?

I use the optics section of a Meade 140 2x Barlow on my Arcturus BV to reach focus and boost power by about 3x.  Most commonly I use 20mm Svbony UWAs and  vintage/adapted 15x (16.7mm) Bausch & Lomb microscope BV eyepieces.  I have also used 32mm Plossls and 23mm 62 degree Aspherics with varying success.  For me, I need long eye relief so I can wear eyeglasses due to 2.5 diopters of eye astigmatism which limits my choices.  I've tried larger wide angle eyepieces, but I couldn't fit my nose comfortably between the eyepieces.  The key thing is that the above eyepieces work well at f/12 and above.  Thus, I need the 2x Barlow to boost f/6 scopes to above f/12 (f/18 actually).

BV collimation is less critical with lower power eyepieces, so getting to higher powers with a Barlow, GPC, OCA, OCS, etc. and lower power eyepieces is preferable to using a pair of high power eyepieces without one.

If it ever arrives from China, I'm going to give the Svbony UHC a try.  For only $19, I figured it was worth a go.  Based on Star Hunter's light pollution filter test, it appears to be about the same (with a bit less blue) as the Baader UHC-S for a fraction of the price.

No filter:

Baader UHC-S 2″:

Svbony UHC 1.25″:

Spectra:

Those are physical field stop numbers.  The effective field stops as I measured them photographically are 27.5mm for the 24mm (it gets fuzzy, so a bit of a judgement call) and 36.4mm for the 30mm (nice and sharp).  You could probably extrapolate the 15mm and 18mm to have approximately 17.8mm and 21.3mm diameter field stops, respectively, since the 15mm, 18mm, and 24mm all appear to be scaled versions of the same design.

On 13/12/2022 at 16:24, great_bear said:

I took a S5000 Plossl apart (not the 40) and it wasn’t like that at all on the inside. Are you going by documentation or have you taken a look yourself? 
 

Mine was basically an Erfle variant. 
 

The 26mm would be a mess at F6. It wasn’t that great at F15 to be honest. 
 

However, apart from minor eye-glint, the 20mm and 14mm are essentially perfect in an F15 Mak - I wouldn’t swap them for anything. The glass has a breathtaking coolness to it. I’ve used mine in a WO Binoviewer for several years now, and nothing has beaten them. 
 

interesting to hear they’re back in production. I saw that range and wondered if those might be them redesigned. 

No, I haven't taken mine apart.  It's way too nice sharpness and contrast wise in the central part to do that to it and risk ruining it or getting dust in it.  I was just going by the general consensus online that since it was referred to as a Plossl and contains 5 elements, it's based on the older 5 element "Plossls" or Pseudo-Masuyamas I mentioned.

I put together the following comparison of the 40mm Meade 5000 Plossl with my 38mm Rini MPL which has 5 elements and my 42mm Rini Erfle which has 6 elements.  I don't know that Paul ever disclosed the design of his MPL anywhere besides declaring it has 5 elements.  It was probably his most successful effort.  It is probably two doublets and singlet, with the latter possibly in the center.  He did tell me that the Erfle was 3 achromats.  I'm guessing 50mm binocular objectives or similar.  It was not a very successful design.

The Meade has a 61 degree AFOV as I measured it.  The MPL has 66 degrees and the Erfle has 68 degrees.  Field stop diameters are 42.7mm, 42.4mm, and 46.0mm in the same order.  Measured focal lengths are 40.4mm, 37.1mm, and 40.8mm (same order).  Radial edge magnification distortion is 21.2%, 20.8%, and 47% respectively.  This last one makes me think the Meade and MPL share a common design philosophy since the two distortion amounts are nearly identical.

Clearly, the Meade is probably the best, followed by the MPL and then the Erfle.  Given that the Meade performs closer to the MPL than the Erfle, I always thought of it as a 5 element "Plossl".  The Meade was a good deal for the $50 I paid for it.  I definitely would not pay the $289 for the 40mm ES-62 version.  The 40mm Lacerta ED is a way better deal performance and price wise.

2 hours ago, Space Hopper said:

I've tried varifocals, but couldn't get on with them at all.

I never tried them after a friend of mine tried them and got queasy from wearing them.  He did eventually get used to them, but I don't like the idea of the constantly changing correction amount depending on where I look through them.

I've been wearing bifocals for about a decade now and have gotten completely used to them after tweaking a few things about them:

• Get big frames to push the close distance part completely below your forward line of sight, yet leaving a large enough area to be useful for close-up work.  Nothing is more annoying than having to tip your head down just to look straight ahead at a distant object.  This gets really tiresome driving in a hurry.
• Back-off the near focus distance from 8 to 12 inches to about 20 to 24 inches.  Now I can clearly see my car's dashboard, read printed material on a tabletop, and read store shelves from a normal stand-off distance.  Luckily, I have 20-15 corrected vision, so I can read a bit further out than most folks.  Also, stairs are not completely blurry with the greater focus distance which freaked me out the first time I wore bifocals with normal reading distance (8-12 inches) correction.

For astronomy use, I wear single vision distance-only glasses.  I can't stand seeing the bifocal line of my daily wearers in my ultrawide field eyepieces.  The pair is only used for astronomy, so it doesn't accumulate microscratches from cleanings and daily abuse.  I got them in the lowest index plastic lens available to reduce chromatic aberrations with off-axis rays.  I bought them from an online retailer for a very reasonable amount out of pocket.  So far, I have no complaints about them.

I will admit I am lucky in that my uncorrected, yet fixed, focus distance is about 12 inches, so I can just look under my distance only glasses to read the large, blocky characters on my DSC screen.  I'm just dealing with astigmatism blurring at that point, which I can squint out in large part.

1 hour ago, Don Pensack said:

I just wish I could get glasses made to that level of polish and coating.

That would be nice, but they'd be heavy (glass).  I wore glass eyeglasses back in the early 80s, and they were always slipping down my nose.  I will admit to taking my uncoated distance-only glasses off sometimes to see if reflections are coming from my cornea, eyeglasses, or eyepiece.  Often, it is the eyeglasses, and I have to cup my hands to block the external light source.  At a truly dark site, I would imagine this to be far less common.  Yes, there is the issue of transmission; but again, you could flip your glasses off to see if there's a brightening in the field due to a DSO not visible with eyeglasses on.

On 13/12/2022 at 11:20, FLO said:

There can be no doubt UK Royal Mail service is exceptionally good, when they are not on strike.

Lucky you.  Our USPS system is a joke.  The regular employees are pretty good once they've been on a route a few years, but their substitutes are complete morons.  Mail is continually being misdelivered because of turnover and substitutes not knowing their routes.  There are no repercussions for poor job performance because there's no way to complain to the local post office.  All complaints go to a centralized call center.  Package delivery is very slow and expensive.  Tracking and delivery confirmation is extra.  When your group post office boxes in your neighborhood are broken into with crowbars to steal mail rendering them unusable, they pass the buck on replacing them saying they have to be paid for by the subdivision.  When the sub tries to replace them, they're told by the USPS that only they can replace them once they've ordered the replacement and its been paid for by, you guessed it, the subdivision.  USPS owns the boxes, but we pay for them.  Where's the logic in that????  On top of all that, they raise rates while extending delivery times to much longer than couriers for similar prices.

Couriers by contrast (UPS, FedEx, and increasingly Amazon) are in a state of competition and know their business can go elsewhere, so they tend to have on time deliveries, tracking and delivery confirmation are included with every package, and they rarely misdeliver packages, at least in our area.  It is true they do have to leave packages on your doorstep leaving them vulnerable to porch pirates, but many drivers will ring your doorbell to alert you.  Lately, USPS has been leaving parcels at our doorsteps once their parcel lockers are filled for the subdivision.

Look to camera lenses to see what the future may hold for eyepiece design.  They use many different sorts of dispersion glass types and hybrid glass/resin aspherics.  Perhaps they will trickle down to astro gear.

1 hour ago, ollypenrice said:

I don't understand the second part of this (ie 'compressing the image circle.')

I'm just pointing out how focal reducers work from a layman's perspective.  Also known as telecompressors, they compress the image circle into a smaller area, increasing the photon flux per unit area, simultaneously reducing image scale.  As you say though, what good is a faster acquired image if it is tiny on the sensor?  However, if someone is after large, expansive, low resolution sky survey images acquired in the least amount of time possible, then perhaps the Starizona solution is for them.  It's similar to a Schmidt camera which is used for such purposes.

1 hour ago, Vulisha said:

It is spherical aberration together with coma, mirror was not polished perfectly.

Thanks for the info.  I wonder what its wavefront error measurement is.

If the weather ever clears up here, I'll try to do a careful star test on the GSO 6".

2 minutes ago, ollypenrice said:

The effect of focal reducers on light gathering can be stated with absolute certainty. It is zero. How can a lens at the back of the lightpath increase the amount of light going in at the front?

It can't, but it can increase the amount of light per unit area on a sensor by compressing the image circle as with a refractor.  I get the whole pixel business, but if you take the imaging device out of the equation and simply look at the optics, the light flux per unit area at the imaging plane has increased.

5 minutes ago, ollypenrice said:

What Starizona should do is stop comparing a Hyperstar with the scope it was originally, since it is now a totally different kind of scope suitable for totally different targets.

Hopefully their customers who are willing to pay their prices are savvy enough to understand this trade-off.  If it was a $100 device, then I would be concerned about noobs being misled.

2 minutes ago, LDW1 said:

Why would most sellers hesitate to sell to Europe, as in Canada the seller shouldn't have to worry or get involved because normally customs does not release the item to the buyer until any accessed sales taxes are paid upon release ? Amazon / eBay is a different story due to their size, their sales volumes. Thats the reason for the customs declaration on the outside of the package clearly identifying the actual cost of the item(s) for tax purposes. All non paid but taxable items are also supposed to be declared at tax time up here in Canada but the amount, the cost of those items have to run into the high tens of thousands before they bother ie an in home seller business not the back and forths like most of us ! When I buy from Agena Astro, B&H, etc. they don't collect my Canadian sales tax, they leave it up to Customs on behalf of my government. Amazon or eBay do through a legal agreement with the government incl. audits.

Ask @Don Pensack why he quit selling into Europe.  I may be mistaken, but I recall reading a post of his where he decided the cost and overhead of VAT collection for EU sales to be too much for too little benefit in additional sales over US-only sales.  He may still sell into Canada.

4 hours ago, Vulisha said:

My heritage has some aberrations so it cannot achieve perfect picture anyhow

I'm curious what they are.  Certainly there's uncorrected coma since 1.25" CCs are hard to come by.  Are there others?

I had thought about getting a Heritage 150, but decided I'd miss 2" eyepieces and CCs too much, so I recently picked up a used 6" f/5 GSO Newtonian with the dual speed focuser.  I have been impressed with the quality of the mirrors.  Our weather has been terrible, so it's been difficult to critically evaluate it, but so far it exceeds my expectations for about $300.

54 minutes ago, ollypenrice said:

nonsense like this, just copied from the Starizona website; The HyperStar 8 lens converts a standard Celestron 8" SCT from f/10 to f/1.9, making the system 25 times faster.

Are you also saying focal reducers are nonsense and don't actually reduce exposure time while simultaneously reducing focal length?  I thought if aperture remains constant but focal length decreases, f-ratio must go down as well.  When the f-ratio goes down, the exposure time required for the same exposure density also goes down.  The HyperStar gets rid of the 5x magnifying effect of the SCT secondary mirror, reducing the focal length and f-ratio by 5x in the process.

57 minutes ago, ollypenrice said:

It doesn't do any such thing. To make the system 25 times faster you would have to increase the area of the telescope objective by 25 times.

You're assuming the focal length remains constant, which it does not; and they make no claims that it does.  Further down, they show the decrease in both in a table:

The 25x comes from the squaring effect of f-ratios on light gathering.  I think it is really 2**5 or 32x, actually.  That much they did screw up.

1 hour ago, great_bear said:

Oh, it is for those of us in the UK - it's just that by law, UK web sites have to show prices with the sales tax ("VAT" at 20%) already baked in.
(typically, the final sales invoice will break out the tax separately to make it clear that qualifying businesses can claim it back)

I'm pretty sure if folks in the UK buy from overseas, someone from the government collects VAT upon arrival of your item in your country because it's a fixed nationwide tax similar to tariffs.  That doesn't happen in the US.  Americans are expected to keep track of sales for which no sales tax was collected and submit use tax instead on their own to their state and local governments since sales tax is not a nationwide tax.  That pretty much never happens, though.  It would cost too much in labor and overhead to create the government bureaucracy in every state and local taxing entity to collect the small amount due since the vast majority of Americans buy goods within the US.  The exception are online marketplaces like Amazon and ebay which do collect sales tax for sales into the US on behalf of overseas sellers ever since the 2018 US Supreme Court ruling South Dakota v. Wayfair.  By contrast, European countries are now requiring overseas sellers, not just online marketplaces, to collect and remit VAT on behalf of customers, creating a lot of undesired and expensive overhead, so many non-European sellers have simply quit selling into Europe.

I think the OP was asking, "Why do we put up with long f-ratio scopes just for high power usage?  Why not just buy shorter f-ratio scopes and use Barlows or short focal length eyepieces to get to higher power."  And the partial answer is, that would be great if optical quality didn't suffer at shorter f-ratios, particularly in refractors.  However, as I stated above, shorter f-ratio scopes of high quality get real expensive real fast.

There are very short focal length Dobs made to be more ergonomic to observe with.  Here's a Webster 28" f/2.7:

Is this what you are suggesting?  The problem is that it is difficult to make short focal length scopes with the same optical quality as longer focal length telescopes.  As a result, they are more expensive aperture for aperture.

That's at least $85 cheaper than buying it here in the US.  Add in the fact that sales tax isn't collected by FLO, and the deal gets even better.