Andrew_B

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.

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.

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!

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.

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!

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.

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.

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. 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.

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.

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.