Louis D

8 hours ago, Franklin said:

the OIII can be used with smaller scopes.

Indeed.  It's exit pupil based.  The problem with smaller scopes is image scale.  At the preferred exit pupil, the nebula image will be smaller than in a larger aperture telescope.  If you're willing to live with a smaller image scale, the OIII will work fine in smaller scopes.  In fact, you might be able to detect large nebula regions thanks to the wider field of view at larger exit pupils.  By contrast in larger aperture scopes, you just can't get the magnification down low enough to do edge detection on these same regions.  You end up looking straight through them as if they were mere sky glow.  You might detect them with careful sweeping of the area, but detailed observing would be difficult.

8 hours ago, PeterC65 said:

The TV Bandmate OIII looks like it has a 12nm passband (see here) and is almost identical to the Astronomik OIII.

Not surprising.  It says right on the linked webpage:

Designed and manufactured exclusively for Tele Vue by Astronomik. 

4 hours ago, badhex said:

What's the difference between the regular and quartz Louis? 

About $14 at today's pricing here in the States (see added links above).  Less facetiously, I quote from the quartz diagonal's description linked above:

High quality diagonal mirrors are usually made of BK7 glass. Quartz glass goes a notch higher - it offers greater thermal stability, resulting in minimal thermal expansion and contraction as compared to other glass types. The result is a minimal, if any, shift in focus due to temperature changes over long observation sessions, making this quartz diagonal ideal for photographic and imaging applications.

I can't say that I've ever noticed the difference.  I just picked up the used quartz version because it was being offered for the same price as the used regular glass version.  I wouldn't have picked it up otherwise.

Who would image through a diagonal?  Who observes long enough at one focus setting to notice thermal shift?  If the difference is only $14 at the retailer, it's probably much less at the manufacturer and could become the standard if used in all diagonals which would further drive down the price differential through economies of scale.  However, it's a case that no one would ever notice the difference; so why drive up the price, even slightly, for every diagonal just to have quartz in it?  It's just a marketing ploy in my opinion.

Theoretically, as long as the passband is perfectly centered on the emission line(s), the narrower passband filters should simply exclude more stray light increasing contrast.

However, you run into the problem that there are two OIII emission lines, a brighter one at 500.7nm and a secondary one at 495.5nm.  Most visual OIII filters attempt to pass both while most ultra-narrowband imaging filters only pass the former.  It would be great if the filter could pass each with a 3nm passband, but that's not really possible as the two passbands would be touching at their bases, and it would be super expensive to manufacture.  Instead, most use a 12nm to 15nm passband for visual to pick up both bands to increase the signal being fed into the eye at the expense of passing more sky glow noise.

6 hours ago, Don Pensack said:

The inside of the housing needs to have the same blackening the insides of the barrels do.

That is really reflective.

I have the same diagonal in both regular and quartz, and I have never had any issues with stray reflections on bright objects causing odd halos or other artifacts as they enter and leave the field of view.  On the other hand, I do need to flock the rear baffle tube of my 127 Mak because I do get odd halo inducing reflections off of it with a 2" diagonal as bright objects pass the edge of it.

Maybe you'll say the surfaces cause some amount of contrast decreasing scattered light, but so do the shiny filter threads on many eyepieces, and I've never heard of anyone calling for a ban on shiny filter threads.  Some others start out blackened, but it grinds off pretty quickly using filters regularly.

I'll take my chances with stray light with these GSO diagonals over having a restricted light path with my widest field eyepieces in those other diagonals of unknown manufacturer (Synta?).

2 hours ago, doublevodka said:

Only info I can find directly about the process on BSTs is on another forum which I'm not sure is allowed, but I'm sure you could google it if needs be

I can't get the BST Starguider/AT Paradigm eyepieces to decloak.  The eyecup just pulls right off, and the lower ring and color ring unscrew easily enough, but the big metal band that twists the eyecup support up and down seems stuck in place.  If you come across detailed instructions, I'd appreciate it.

2 hours ago, chrispj said:

the Delite looks and feels like there should be no problem to use as a pair

There's a thread on CN about decloaking them for binoviewer usage.  IIRC, It's fairly straightforward to unscrew the lower ring of the adjustable eyecup, and then just lift off the rest.  It helps those with deep set eyes and tall nose bridges like myself.

15x long eye relief microscope eyepieces are about 17mm while 20x ones would be about 12.5mm.  They're designed for binoviewer usage and very slow f-ratios (f/18, IIRC).  Some Leica and Zeiss eyepieces have excellent polish and correction.  You would just need to adapt them to a 1.25" barrel.  I have been using a pair of vintage Bausch & Lomb 15x WF eyepieces in my binoviewer to good effect for years.  I had a machinist make 23mm to 1.25" adapters for me.  3D printing would also work well for this purpose.

A pair of zooms would be another option.  Eye relief might be a little tight, but you can easily change magnification to match seeing conditions.

19 hours ago, Fedele said:

I bought a TS 70/420 ED for some tests. As soon as I arrived it became normal for me to mount it very quickly in parallel to my FS60CB (60/360).

In visual the CB wins

Can I ask why you bought another scope barely different from the FS60CB aperture-wise?

For my second refractor after my 72ED, I went with a 90mm APO FPL-53 triplet, and it made a big difference in reducing spurious color at high powers.  However, cool down time increased dramatically.  I really like the R&P focuser on the APO for securely lifting heavy loads at high altitudes as well.  The smooth Crayford focuser on the 72ED slips horribly with 3 pound loads in it no matter how much I try to tension it.

I can't get my fairly narrow nose bridge between a pair of eyepieces in the Hyperion width class, so double check your width tolerance.

I'm surprised the Plossls aren't sharp at f/10.  Most Plossls are pretty decent at f/6 and really good by f/12.  Perhaps it's the level of polish on them that makes the difference in your case.

I would probably start with a pair of longer eye relief 22mm to 26mm Plossls or similar and put a 1.6x to 2x Barlow nosepiece or similar OCA/OCS/GPC on the front of the binoviewer to get to higher powers.

The 130PDS would probably be excellent for wide field viewing, but the 5" aperture would be a bit limiting on DSOs.

At f/5, collimation will be more critical.

The secondary is oversized for visual use to avoid vignetting while imaging.  As such, it will decrease planetary contrast somewhat.

If you go the EQ mount route, don't forget how top heavy they get with an OTA and counterweights attached.  It makes moving the fully assembled system about the yard to avoid trees, bushes, and houses really difficult compared to a similar weight Dob.  You just pick up the bottom heavy Dob and hug it close to your body while penguin walking it about.  I once looked at buying a used 127 Mak on a smallish EQ mount and couldn't believe how heavy it was fully mounted.  I went the alt-az mount route instead to avoid counterweights.

38 minutes ago, malc-c said:

It was fun and exciting at the time, but I lacked the funds to patent the concept and at the time none of us ever thought that belt drive would be so popular

Since your work was published in Astronomy Now well before the Rowan kit was offered, it is now prior art; and Rowan would have to limit the scope of any patent because of your prior work.  Kudos to you for keeping your efforts in the public domain.

On 04/04/2022 at 14:29, Roy Challen said:

SLVs are also undercut free☺️

Interesting.  Their LV and NLV predecessors both had undercuts.  I guess when they moved production to China, they also removed the undercuts.

Yes, it does work to use 2" accessories on a 127 Mak.  You do get gradual vignetting toward the edge as is visible in the Meade 40mm SWA part of the image below.  You do get a much wider true field of view than is possible in a widest field 1.25" eyepiece as with the 24mm APM UFF part of the image.  The eye is very forgiving of gradual vignetting.  I do get an odd reflection from bright objects once they pass the edge of the rear baffle tube.  I need to flock the inside of it to see if will suppress this artifact.

The telescope does not suddenly become an all-rounder, you'll just be able to draw upon a degraded, wider field of view occasionally for large objects and for centering objects.  It is not the same experience as using an unvignetted refractor view.  Even many Newtonians will have some vignetting due to undersized secondaries, but no one complains about it visually.

True, but the true field of view would only be 8% narrower in the 10-30mm if all the focal length and AFOV values are accurate.  By the time you get to a 40° AFOV, it's feeling mighty narrow.  33° will be worse, but you're already deep into the uncomfortably narrow zone anyway.

How about the Svbony SV170 10-30mm zoom eyepiece?  It's only $50+tax over here direct from Svbony's store, and £59.99 on Amazon UK and £55.99 on ebay UK.  I couldn't locate a Svbony storefront in the UK.  At least one person on CN likes theirs.  Svbony also sells the 9-27mm zoom for about $90 to $100 +tax over here.

Recently, I measured the actual focal length of my Surplus Shed 7.2-21.5mm zoom and came up with 7.4-20.6mm, so a bit short on both ends.  It's not as bad as my Celestron Regal 8-24mm zoom, though.  It measures out to be 8.2-21.2mm!  All I'm saying is, don't bet the farm on the 9-27mm zoom being 27mm at the long end.  It probably will be pretty close to 9mm on the short end, though.

Also, remember that many 2x Barlows are closer to 2.1x to 2.4x in your calculations, depending on where the eyepiece focuses relative to the Barlow's shoulder and the native power of the Barlow if the eyepiece reference plane is exactly at the shoulder.

What about using a hyperwide 9mm eyepiece like the APM XWA for general viewing?  You'd get plenty of dwell time at a reasonable power.  I see you have some 82° eyepieces in that range already.  Is this more about putting together a travel kit or trying to chase the optimum power in real time?

More than likely, no, it won't noticeably impact viewing for the time being.

Because Pentax eyepieces are weatherproofed, the threads are threadlocked and are nearly impossible to loosen without strap wrenches.

Pentax eyepieces are supposed to be weatherproof to protect against this very problem.  You might want to check with Pentax Europe first.  Here's their warranty in the US:

PENTAX

THE PENTAX "WORRY FREE" WARRANTY

The PENTAX "Worry-Free" Warranty is available on all PENTAX Sport Optics products purchased in the United States, on or after March 1, 2006, from an authorized PENTAX Sport Optics dealer.

PENTAX Sport Optics products are of the highest optical and mechanical quality. If your PENTAX Binocular, Spotting Scope or Riflescope purchased in the USA from an authorized PENTAX Sport Optics dealer requires repair, PENTAX will repair or replace it to the original purchaser (even if damaged by fault) for a charge of $19.95, to cover handling and return shipping.* This warranty does not cover cosmetic damage, theft or loss. (Replacement may be with comparable model at PENTAX's discretion if the original model is no longer available.)

*Applies only to unmodified equipment or product with modifications performed by authorized PENTAX repair personnel.

If you have a Tele Vue eyepiece, their online specs are quite accurate in my experience.  You can start with that eyepiece as the baseline for your measurements.  First, setup a ruler or yard/meter stick a good distance (20 to 40 feet minimum) from your telescope.  Next, put the TV eyepiece in the focuser, focus on the ruler, and note the left to right distance from field stop edge to field stop edge.  Next, substitute your unknown field stop eyepieces and measure the displayed distances.  Since it's a direct linear relationship between distance on the ruler and field stop diameter, all you have to do is divide the TV field stop number by the distance it showed on the ruler.  This becomes your conversion coefficient from ruler distance to field stop diameter.  Now, just multiply each ruler distance by that coefficient to calculate each eyepiece's field stop diameter.  Due to measurement errors, you shouldn't expect FS diameter accuracy better than about 0.3mm in my experience.

This method is completely independent of eyepiece magnification distortion across the field of view or location of the FS within the eyepiece.  If you don't have any TV eyepieces to boot strap the process, you might try a 32mm Plossl which generally has a ~27mm field stop diameter and is completely measurable with calipers to get better accuracy.  In fact, any simple positive-only eyepiece like a Plossl, Kellner, Ortho, Huygens, RK, RKE, etc. will work as long as you have calipers accurate to sub-millimeter distances to generate your baseline coefficient.  In fact, if you have multiple coefficient measurements from multiple eyepieces, you can average them for better accuracy.

That's why I only cap eyepieces in my airtight cases while outside.  The air sealed inside is very dry and only slowly humidifies long after the eyepieces have warmed.  Eyepieces, diagonals, finders, and OTAs not sealed in airtight cases are left uncapped in open cases to warm up to prevent fungal grown.  20+ years of practical experience later, and I've not had any evidence of fungal grown on anything.

Those low cost 0.5x FRs impart loads of field curvature to the image, so not very useful in my opinion.

If you go with a 2" visual back, 2" diagonal, and 2" widest field eyepiece, you'll see an improvement in true field of view similar to below with gradual vignetting:

It does help when centering bright objects in particular given how narrow the true field of view is.

I put my Paradigm (Starguider) eyepiece collection in a B&W Type 1000 case.  Of course, I picked it up for only $10 on sale at Fry's before they closed up for good a few years ago.  They're quite a bit more expensive nowadays.

I thought the SVBONY CLS looked pretty decent under Bortle 9 skies in that filter review.  In a 1.25" size, they're only $30+tax shipped here in the States.  At that price, you don't feel too bad if it doesn't get a lot of use.

2 hours ago, Mike Q said:

Yes the cap screws on and off.  I don't know if I like that or not.

Check to see if the eye cup is 2" in diameter.  The one on my Celestron Regal zoom is, and a soft plastic 2" cap fits over it perfectly:

You could then store away the original thread-on cap in the original eyepiece box if you want to resell it later.

First off, what f-ratio is the scope you're going to be using it in?  Second, will you be using a Barlow to boost the power and/or reach focus?  It makes a difference in the required quality of the eyepiece for wide fields of view.  The NPL being a Plossl should be fine at f/6 and above.  I don't know if they're worth about twice the money of the Astro Essentials or Revelation 20mm Plossls.  Has anyone compared them to see if the lens polish, coatings, and stray light control of the NPLs are that much better than budget Plossls?

I use a 2x Barlow nosepiece operating at 3x in my binoviewers, so I have an effective f/18 focal ratio or longer in my scopes.  As such, a pair of SVBONY 68° Ultra Wide Angle 20mm eyepieces work great for me.  They just about max out the unvignetted field in my BVs.  I wouldn't recommend them for scopes below f/10 natively, though.

I wrote up my thoughts on the SVBONY below: