Zermelo

I've just noticed, while revisiting Ernest's review of the SV215, that he has updated it (on Feb 26th) with a second review. He has now obtained a production release specimen (the original review was based on a pre-production sample). The new review is posted immediately below the original one in this thread (English, translated from Russian). He has expanded the table of nominal vs measured attributes, to cover the additional click-stops on the production model. Also, some of the measured values for those focal lengths that were included in the first report have changed in the new one. The concluding assessment now reflects the production version, and is more positive in some respects than the original review: "The glare noted in the pre-production sample has ceased to appear, light scattering still seems to me increased, eye relief is still not the most comfortable. Interestingly, the angular field of view of the eyepiece, as well as the diameter of the effective aperture, is slightly larger than stated. But the real focal length of the eyepiece (and, accordingly, the increase) at the short-focus end does not fall far short of 3 mm. ... The mechanics of the serial sample has been noticeably altered: the landing sleeve has been shortened, intermediate stops have appeared at 7 and 5 mm focal lengths, and the distance that the eyepiece extends during zooming has been reduced. The optics remained almost the same, although the enlightenment seems to have been improved. In general, the eyepiece is quite worthy to be at hand for the owner of a moderately fast telescope when observing the planets. I recommend"

I spent a week there once, really enjoyed it, but didn't see a single star.

Welcome to SGL.

Will you be imaging or visual only? There are a few discussions over on CN, for example: https://www.cloudynights.com/topic/611308-new-skywatcher-eqm-35-progoto/ https://www.cloudynights.com/topic/752028-eqm-35-vs-eq5-for-130pds-eaa/ https://www.cloudynights.com/topic/714047-skywatcher-eqm-35-pro-or-eq-5-pro-for-astrophotography-with-guiding/ https://www.cloudynights.com/topic/726414-skywatcher-heq5-vs-eqm35-pro/

Also this: http://www.deepsky-brothers.de/SinnvKombiTEL_Monti.htm

Let's call the whole thing off.

My next scope purchase might be a 10" Dob, so I was interested in the discussion of GSO's tolerances. The Stellalyra Dobs don't quote any, and I found quite a few other GSO ads that didn't specify. But this one does quote "Diffraction Limited Optics (1/12 Wave RMS)", and the GSO mirrors sold here say "1/16 wave RMS at least, and often better" (I'm not sure how "better than 1/16 wave" helps, if 1/12 wave is already diffraction limited). I'm also aware that unqualified statements like this are ambiguous at best. Does anyone have any definitive info on GSO mirrors? Do the same tolerances apply to all of their output, or do they vary?

FLO do sell the 150PL on an EQ3-2, so it's obviously not an unreasonable match. The performance of increasingly heavy OTAs on a specific mount does not have a sharp transition from "OK" to "not OK", it's a gradual decline. I couldn't see a weight on FLO for the 150PL, but elsewhere it's quoted as 5.9kg. The stated max for the EQ3-2 is 5kg, so it's pushing it. And that's before you start adding a Telrad, better optical finder, heavier eyepieces, etc. The other factor with the 150PL is its length. It has a greater moment of inertia than a shorter OTA of the same weight, which affects its stability on a borderline mount. It also makes it more vulnerable to disturbance from wind. Obviously you just need to try it on your mount first a few times, especially in a breeze. A 6" F/8 is a classic configuration and a good all-rounder, and for visual only, you may find it works for you. If you need to get a heavier mount, you might be better off looking for a second hand EQ5.

oooh, now there's a challenge https://warwick.ac.uk/fac/sci/maths/people/staff/robert_mackay/isostaticmount8.pdf

Hello, and welcome to SGL. To get useful responses, you will need to say a bit more. How much do you want to spend? Do you have any prior observing experience? Have you done any research to identify the kind of scope, or features that you are interested in? Will this be for visual use, or for photography? Will it be just you using it, or will you be observing with anyone else? Do you have somewhere convenient to store it, and will it be easily transportable to where you will use it? (i.e. not down three flights of stairs) Do you think you will be using it away from home much (i.e. do you have decent skies where you live?) Do you have any other constraints?

Some of the testing that I did for this review was using a 150mm f/5 Newtonian.

I've seen this argument in previous threads, and I think I buy it, however: with star groupings, there must be some transition between the two behaviours? A nearby open cluster behaves, under increasing magnification, as a bunch of (essentially point-like) stars, but a distant galaxy will behave more like an extended diffuse nebula, at least in amateur kit? Do globulars (those belonging to our galaxy) behave more like open clusters, or more like distant galaxies? Or perhaps both - is it possible that an unresolved core behaves like an extended source, but the resolved outer regions like individual stars?

That's good news, then. When you check CO on Tuesday morning, the green will have moved to Wednesday. The bad news is that on Wednesday it will have moved to Thursday.

Some more: https://www.cambridge.org/turnleft/tables https://www.astroleague.org/observing.html https://telescopius.com/ https://tonightssky.com/MainPage.php https://stargazerslounge.com/topic/43881-object-list-indexed-by-constellation/

Have a look here:

Yes, a bit niche, but see https://www.cloudynights.com/topic/441767-good-objects-for-observing-with-the-h-beta-filter/

That's a real goldmine

Interesting, thanks. By co-incidence, just before I saw this thread, the subject of "Mary's Room" came up in my news feed. I hadn't heard about it before that. Funny how that happens.

I think we're only a cigarette paper apart, Jim. I'm a materialist at heart, and I think subjective sensations are emergent properties of complex systems. Until we understand how that happens, though, I'm not sure we can be confident that people with identical stimuli will experience identical sensations.

... and synesthesia has already been mentioned, which Wikipedia tells me is still not understood, but there appears to be one theory that there are physical differences in the brain that allow different regions to communicate in some people, and another theory that the sensory response is the same, but the "semantic interpretation" differs.

I agree with all of that, but arguably it still leaves open the possibility that subjective "redness" to one person isn't the same as it is for another. It could be considered an aspect of the more general problem of explaining how consciousness arises. As I said, from a scientific perspective it can justifiably be ignored as irrelevant. A positivist would no doubt dismiss it as literally meaningless.

I think two different things being discussed. (1) The question as to whether the internal sense experiences (qualia) of different people with equally competent senses are the same, for example when perceiving a green object. I maintain that there is no way of knowing, because there would be no functional (external) difference in how those people would behave (for example, if asked "what do you mean by green?" they might both answer that green is the colour of that grass, there", whatever their respective sense experiences). I do agree, though, that this is a philosophical rather than scientific concern - by definition, there is no experiment that could reveal such a difference; the different internal sense models would be at least isomorphic, if they weren't identical. (2) Differences between categorization of sensory experience. Such differences might occur because of differing sensory competence (e.g. colour blindness), or varying scope of terminology in different languages (apparently, the Dani people of New Guinea have only two words to describe colours, mili for darker/cooler colours and mola for lighter/warmer colours), or different cultural/historical choices. In these cases, the models are not necessarily isomorphic, and so are amenable to research and experiment, and have been studied by Brent Berlin, Paul Kay, Chad McDaniel and others. This is just one example of how categorization in general varies with culture/language/history. I've lifted it from Women, Fire and Dangerous Things by George Lakoff, which I just dug out, and see that I need to finish.

We can all agree on the name to give light of a certain frequency, but of course I can never know that the sensation I experience as green is the same as yours, and not instead the one that you experience as red. Some philosophers talk endlessly on that point. On another point, I think it's likely that our reasoning on fundamental matters like space and time is "tainted" by the niche we inhabit in the universe, in particular our scale. Our brains have evolved to deal with objects of the same scale as us, that behave in certain ways, and that is one reason why QM and relativity seem counter-intuitive to us.

I have the LIDL one and it works well. You might need to tape something over the display to dim it if you're using it during a session.

The strawberry fiasco continues. https://www.somersetlive.co.uk/news/somerset-news/anger-pink-franken-fruit-lights-8210277 But different lights now, apparently.