Andrew_B

28 minutes ago, LDW1 said:

Why do companies of that stature publish incorrect numbers that are that far off ? Surely they must know that some ........ will check them and will make sure the incorrect whatevers are brought out for all potential customers to see ? Especially if practically every measurement is wrong, it doesn't make sense or maybe ? What other industry, company does that with their products for the world to see ? This doesn't make sense or maybe ....... !

You'd be amazed at the mistakes that make it through to publication. I've seen scientific papers about medical research that have passed peer review and been accepted by major publications that had basic errors in arithmetic which hadn't been caught until it reached me. One of them looked at the effects of weight on diabetes risk in overweight and obese individuals. Out of the 50 people in the study group, 29 of them were classed as overweight while the remaining 22 were classed as obese... 

You would expect school kids to catch something as obviously wrong as that, but a lot of very smart people had read it and not noticed.

Marketing materials and spec sheets are even more error-prone. They're often written by very busy people and any proof reeding is likely done in a hurry by a single person so it's easy for a typo or a misread detail to be missed, especially if it's not very obviously wrong. I wouldn't be surprised if mistakes are actually less common in this industry than in many others due to the relatively knowledgeable customer base and the closer relationship between them and small retailers and manufacturers.

The best thing to do if you see a mistake is to send a polite message with a link to the offending page together with your correction, and ideally a link to a source for that info.

On 12/12/2022 at 18:02, Deadlake said:

APM has a limited time of exclusivity until copied:

https://www.cloudynights.com/topic/562562-apm-new-ultra-flat-eyepieces-30-mm-70-degree/?p=7635881

I would expect that such an arrangement meant that APM could secure better terms with KUO and/or Mark Ackermann.

Two years gives APM a decent amount of time to sell their versions, while making the eyepiece range available to other brands after that would mean higher sales for KUO (and possibly greater royalties for Mark) without necessarily costing APM too many sales by widening retail availability and brand recognition. APM could also benefit if increased production resulted in KUO reducing their wholesale prices.

I've got a few eyepieces from the range (Svbony and Sky Rover branded) and I've been impressed by the quality and value for money. Haven't tried the 30mm yet but everything I've read suggests it's the pick of the bunch.

I'll add my vote for the Baader ClickLock mirror diagonal. As well as being high quality, it has a modular construction and can be configured in different ways so for example, if you were bothered by field curvature visible at low magnifications, you could take the nosepiece off the diagonal and fit a field flattener like the TSFLAT2 in its place by using a suitable M48 to SCT thread adapter.

It's always frustrating to get caught by a price hike but we've been overdue one given the soaring inflation we've seen on top of less favourable exchange rates.

I managed to be lucky for once and decided to bite the bullet and invest in a Nagler zoom just before prices went up. One of the things that convinced me to buy said eyepiece was the excellent review by @DirkSteele in which he quotes the price it was going for back in May 2020 and it's the same as I paid a bit less than 3 weeks ago. When you consider how much everything else has gone up over that period, this recent increase seems pretty modest and I'm surprised it didn't happen earlier.

18 hours ago, Zeta Reticulan said:

I agree it's a pretty reasonable price for an Ohi ortho'. Although I don't see any real difference with TS Optics. FLO is much more convenient for UK customers of course. I'm hoping one day the Chinese will learn how to make orthoscopics properly.

I'm pretty convinced this was made in China. Could do better lol. They'll probably get there eventually.

Is that one of the Kson orthos?

I've got a pair of the 16.8mm ones for my binoviewer and I was pleasantly surprised by the image quality. The main negative point is that they could probably do with better control of stray light as there can be a halo outside the field stop when viewing bright objects. If I was feeling brave I'd consider taking them apart and applying a bit of matt black paint to see if that helped but it's not a showstopper and I don't want to end up making things worse. They're not going to trouble a good Japanese ortho but the pair only cost me £52 so I'm not complaining!

On 15/08/2022 at 19:31, Don Pensack said:

The argument for single layer coatings has to do with axial light scatter, not transmission.

Transmission with single layer coatings is likely to be ~93-94% at best.

With multicoatings on all surfaces, it could be ~97-98%.

The biggest difference is in the UV-deep violet, where the difference is larger.

That difference is completely unimportant unless the greater internal reflection causes ghost images.

Otherwise, a 4% difference is in the low hundredths of a magnitude, especially unimportant for lunar/planetary usage.

Note, however, all the ultra high-end planetary eyepieces have been multi-coated, so a single layer coating is more likely to be a cost-cutting decision.

 

Do you know if anyone has examined the issue in detail to measure differences in scatter or other properties between single and multi-coated eyepieces?

My understanding is that a good broadband AR coating requires quite a few layers, the thickness of which can vary enormously and must be precisely controlled not only to perform as designed but also to prevent irregularities in the surface from multiplying. If that's the case then I can see how a single coating might be preferable to a cheap and poorly done broadband coating but I can't remember seeing an in-depth comparison to back this up.

The Takahashi FSQ models are apparently superb wide field scopes due to their short focal lengths and flat image fields. Adding a matching focal extender can sharpen them up even more and make them into good planetary refractors. Only downsides are their weight and high cost.

Scopes like those and the TeleVue Nagler-Petzval models (Genesis, NP-101, NP-127, etc) are a bit like regular refractors with the addition of a permanently built-in reducer and field-flattener. For imaging you can achieve something similar by adding a reducer to a standard doublet or triplet design but this combination often aren't practical for visual use because there isn't enough back focus to accommodate a star diagonal.

Borg do some very lightweight fast focal ratio doublets (72mm, 90mm, and 107mm all f5.6) that would make great RFTs but they're not cheap. Field curvature might be an issue depending on your choice of eyepiece and how sensitive you are to it, but you can add a non-reducing flattener that would solve the problem and could be used visually.

It's worth checking out eBay. I picked up a full spectrum-modded 24MP Fuji mirrorless camera for £150 and it's great.

On 16/02/2022 at 17:33, johninderby said:

Reminds me of the old joke about guitar players. They spend half their time playing out of tune and the other half tuning. 😁

That’s the greatest weakness of the SCT design at least in the medium and bigger apertures. Keeping one in perfect collimation all the time is the problem.

It seems to be that when you make an optical system better by adding more lenses or mirrors, it also becomes more sensitive to being out of collimation on top of there being more elements to become misaligned or out of place.

Reminds me of an article I read about how they make the very high performance optics for photolithography stepper-scanner machines that are used to produce microchips. The tolerances are so fine that individual lens elements (and there might be 25 of them in a purely refractive system) have their supporting rings attached to actuators which alter their position to account for changes in the refractive index of the air caused by variations in barometric pressure! On top of that, the structures being created are so tiny and precise alignment of the lens and the silicon wafer is so critical that engineers have to account for the time it takes light to pass through the optics even though it's no more than a few nanoseconds, and they use adaptive optics to correct waveform deformations introduced by absorption-induced zonal heating of individual elements.

Thank goodness amateurs don't have to deal with any of that, but I liked the idea of the corrective adaptive optics - could be a great way to get around the problem of cool down time!

On 16/02/2022 at 09:33, Mike Q said:

800x is a dream.  My skies in Ohio limit me to about 300x on the best of nights.  

Sounds like you don't have the skies that would let a premium Dob show its quality. The larger scope would obviously show more which would mainly be an advantage when viewing DSOs, but that would be the case whether its optics were inexpensive or high-end and it would be very high magnification viewing of the planets that you'd need to see the difference from having a premium mirror.

On 16/02/2022 at 03:30, jetstream said:

Depends on whether the mass produced optic is a " good one" - scatter (roughness) can be an issue in some. Many mass produced dobs benefit from stray light control -actually many high end structures do too. Controlling stray light in a dob is very high on my priority list.

But then, we pull out the Heritage 130 and observe so many DSO with this scope.... M33 a bright puff ball, M101, M51 The Flaming Star neb, California neb, Lagoon, Rossette, Barnards Loop and on and on.

I think this kind of points out the fact that dark skies are more important than the scope for DSO.IMHO.

I think I read a comment by Roland Christen that said figure and polish were everything for high magnification planetary observing and other aspects of the design were relatively unimportant, while for DSOs those qualities don't matter very much (so long as they're not terrible) and its light control through properly blackened and baffled tubes that makes the difference.

On 06/01/2022 at 12:32, Merlin said:

Most of us use our ‘scopes for stargazing rather than research. It seems to a case of overkill to have a premium grade ‘scope for casual viewing.

Even top of the range amateur scopes aren't even close to the production standards or cost of the kind of high end optics used in research and defence applications. Have you ever heard of amateurs using silicon carbide mirrors or three/four mirror unobstructed anastigmat reflectors with optics that have been ion-beam polished?

Whether it's worth the investment in a Zambuto mirror over a mass-produced optic of similar aperture if you're just doing relatively low magnification DSO observing, I don't know.

1 hour ago, Mike Q said:

I have had the opportunity to run my 10 inch Orion Skyline next to Teeter 20 inch.  I had my Orion eyepieces and he had his TV eyepieces.  Now there is no doubt that his 10k dollar scope performed better then my thousand dollar scope.  But the question is was it 9000 dollars worth of better?  For me, the answer is no.  We swapped around different eyepieces in both scopes and as expected the TV eyepieces were better in both scopes, but we're they so good that I would spend 700 bucks on a 31 Nagler to put in a 1000 dollar scope?  Not a chance.  What we all concluded high end eyepieces are at their best in higher end scopes.  My Orion eyepeices held their own and gave me roughly 90 percent of what the TVs showed at a price point that I can afford, and I am good with that.  In the end, it's to each their own.  

What sort of things were you looking at and to what extent were you being limited by seeing? My understanding is that if you live somewhere like Florida then it's worth having a large Dob with a premium mirror because you'll have seeing good enough to view the planets at 800x magnification or higher, but in most other places you'll never get to push the limits like that.

5 hours ago, vlaiv said:

Contrary to popular belief - even for astrophotography, bigger is better.

You will usually hear that for astrophotography, size does not matter and you can image everything with even modest 80mm scope.

While that is true - more aperture means faster imaging time as speed of system is best defined as "aperture at resolution". Larger scopes simply have more aperture and hence for given resolution / sampling rate - they will be faster. Another point is that larger aperture telescopes can image at higher resolution than small telescopes.

This is very pronounced in planetary imaging, but also holds true for long exposure deep sky imaging. In long exposure imaging aperture is not sole factor for resolution and things of course depend on mount used and sky conditions, but at smaller side of things, resolution does depend on aperture size (below 8" or so) significantly.

Above is of course related to proper imaging telescopes.  Using achromatic refractor adds quite a bit of twist to the whole story as chromatic aberration is kind of a blur and reduces resolution of telescope further.

Learning astrophotography is a lot easier and less expensive with a small scope though, and going big makes the mounting requirements even more demanding and expensive than they already are.

You might sometimes encounter Arca Swiss dovetails as well which is mainly used in photographic equipment for things like tripod heads but turns up in some astro gear as well. They're a similar width to a Vixen dovetail and you can find both types on different sides of the same dovetail - William Optics sell them for example.

On 21/01/2022 at 11:28, Nik271 said:

I've been tempted by the 8 inch edge HD in the past but considering its price bracket I think the StellaLyra RC is the better choice. 6kg vs 8kg is not a big difference, you still need a 10kg class mount to use them comfortably. There is now 8 inch carbon fibre RC which is a kilo lighter but a bit pricier. 

As far as I see the only slight disadvantage of the RC is that its collimation is tricker than a SCT. But there are many online manuals on collimating it nowadays so should not be a big deal if you store it in one location.

RCs also have a very large central obstruction (often around 50%) which reduces overall light gathering and puts a lot of light into the diffraction rings rather than the central Airy disk which reduces contrast for lower frequency detail so they're not a great choice for things like planetary observing or imaging. Apparently you also get a lot of field curvature and astigmatism and as has already been mentioned, an RC is somewhat more sensitive to miscollimation than a Classical Cassegrain, and far more sensitive than a Dall-Kirkham.

I forgot to say that I have a pair of them which I use in both cyclops mode and with a binoviewer.

It's a lovely little eyepiece that's bright and sharp and I think you'd struggle to find anything significantly better without spending a lot more money. That said, I haven't got all the experience of looking through high-end eyepieces that some SGL members have so I can't make specific comparisons.

They are still available through Svbony's own website (along with the 18mm UFF) and the price is pretty good.

Takahashi FC-76DCU - incredible optical quality in a beautiful and very lightweight package.

It's far from cheap but it's not silly money either and is normally in stock, although I notice that at the moment FLO are quoting 7-10 days waiting time for orders.

21 hours ago, HollyHound said:

Awesome scope… thanks for sharing 😀

Interesting commentary in the advert about the (presumably new) usage of Fluorite in refractors… presumably Takahashi, or were others using it too 🤔

Although I actually have the space for a scope like this, it would have to be permanently installed, otherwise it would be a struggle to setup every night 🤣

Takahashi have been selling fluorite refractors since 1977 I think, and the FC-series was launched in 1981 but they were a lot more expensive than they are now adjusting for inflation. I notice the ad talks about the delicate nature of fluorite and its vulnerability to acids - it's actually much more acid resistant than typical ED glass and it's alkalis that you need to avoid when cleaning fluorite lenses.

It's funny to think that Astro-Physics scopes started out as an inexpensive alternative to more established brands, but over the years they've gone up in price (relatively speaking) while the competition has got cheaper. No surprise really when their reputation is so good and demand for their scopes means that even at today's prices demand far outstrips supply.

On 14/01/2022 at 02:24, Louis D said:

Aren't there any European made focusers to compete with the Feather Touch?  It seems like there are plenty of high end machine shops over there that could do it.

I'd imagine it would be hard to sell enough of them to make it worthwhile given that they would cost as much as a Feather Touch but wouldn't have the brand and reputation behind them.

1 hour ago, 883 said:

Also in my opinion the answer of Al Nagler was incredible. But that was exactly what he said.

Again, I think that TV is now focusing only on eyepieces and imagers. For visual purists there is only Takahashi IMO. AP and TEC are too expensive and with too long waiting lists, TAK FC series is instead affordable.

Al knows the business reality that there's too much competition for a normal visual doublet like the TV-102 to be able to keep charging the prices they'd like.

By all accounts they're very well made scopes, but at those prices you'd need to be getting optics that were at least as good as the Tak FC-series. The TV-85 is currently retailing for over £200 more than the FC-100DC and almost as much as the DF. Granted you get a case with the TV-85 and a dual speed focuser as standard but when a larger aperture fluorite apo looks like a bargain in comparison, it suggests they're asking a bit too much for it!

3 hours ago, F15Rules said:

Interesting Mike.. last night I used my 2" dielectric diagonal Cyclops with some large 2" eyepieces for the first half of the session.

Looking at M42 with the dielectric and an excellent 23mm Axiom LX eyepiece, I could look to the North East of the Trapezium (right way up reversed diagonal view) and see the two faint stars immersed there in the nebula..the "right hand side" star was visible with direct vision, the left hand side star was visible only with averted vision.

Half an hour later, I switched to my Revelation binoviewer in a Baader Zeiss BBHS T2 prism and a pair of Kson 16.8mm orthos, and was very surprised to see both these stars, very clearly, with direct vision!

To be fair, I was using a higher magnification with the bv, which made the contrasting sky background darker, but set against that, the binoviewer is usually held to lose around 0.5 to 1.0 order of magnitude due to the light beam splitting..so, I tend to think that the BBHS prism was reducing light scatter and possibly having better transmission than my dielectric diagonal? I believe the Baader website claims 98% transmission for the BBHS T2 prism..I don't know what the claimed transmission of my Astro Tech diagonal is though..

Dave

 

I suspect the difference is mostly down to the mirror having more scatter and reducing contrast as a result. The eye isn't very sensitive to small brightness differences so I doubt that's what you're seeing.

Good point Stu about the extender changing the back focus. I haven't used that combination with my binoviewer or been able to find any figures for the DCU with the extender, but when it's used with the FS-60CB it shortens the metal back focus distance by 3.6mm so perhaps something similar is going on with the FC-76.

I've used my binoviewer with my 76DCU which also has a FTF2025BCR. It won't work without a Barlow but there's no problem getting it to work with one. I use a Baader 32mm T2 prism though with a 2" nosepiece and a 1.25" T2 ClickLock adapter, and it seems that the prism has an 11mm shorter optical path (not including attachments) than the BBHS T2 mirror diagonal.

If I want to use that prism in cyclops mode then I've got a 50mm extension which I need to add otherwise my eyepieces won't come to focus.

I put a tiny amount of Loctite Super Lube on the threads of the CQ 1.7x Extender to help protect them from wear and stop them sticking. It makes a big difference but make sure that it's only a tiny amount and clean off any excess.