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About billyharris72

  • Rank
    Proto Star

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  • Gender
  • Interests
    Astronomy, climbing / mountaineering, chess
  • Location
    St. Arvans, Wales
  1. billyharris72

    I need a collimating tool!

    I'd second this option. It's as easy as it gets and for f5 or slower it's all you need, especially for visual. If you need to collimate the secondary (e.g. if you've had the scope apart for some reason) then I'd go for Cheshire. The laser is handy for the initial rough alignment, but the Cheshire (or sight tube) is the best tool for finishing. Bear in mind that with visual use of slower scopes the secondary has to be pretty bad to affect what you'll see in the eyepiece though. 90% of the time a collimation cap is plenty. Billy.
  2. billyharris72

    Magnets and miracles

    Worth bearing in mind that the bino alone would not be cheap. A low production run Zeiss bino with 60mm objectives probably isn't going to get you much (if any) change from £5k.
  3. billyharris72

    Magnets and miracles

    As I understand it, the magnets in these are not the core part of the stabilisation system, but are used to dampen the motion of a cardanic suspension system. So the prism assembly will be mounted using a 3x gimbal arrangement, with some sort of counterweight to stablise it, and the magnet is somehow used to damp any rocking (I don't know exactly how, but that's the principle). Quite an old system (I think it's how ship's chronometers work too, though I may be wrong). Billy.
  4. billyharris72

    Which scope to buy

    Bang for buck, I think it has to be an HEQ5 or NEQ6 (NEQ6 will handle up to 6 inches easily, and 8 at a push). If you're looking to do some imaging I wouldn't go below that, provided you have the budget (good things have been done with less so don't be put off if you haven't). For a scope, the Skywatcher 150 P-DS would be a good choice, I think. Reasonable aperture (more than enough for all the Messiers) and no chromatic aberration. For imaging with a one shot colour camera I wouldn't go for an achromat refractor, and for visual including DSOs I wouldn't go for anything below 150mm. For me, unless you want to spend a lot of money, that means a Newt (you could go for an SCT but the higher price, smaller FOV and larger central obstruction make this a suboptimal choice unless you are specifically interested in planetary photography or small DSOs like planetarty nebulae and distant galaxies). For cameras, you could do much worse than check out the ZWO section on the First Light Optics webpage. Billy.
  5. billyharris72

    Why on earth would I buy a DSLR for astrophotography?

    I'm with alacant on this. The cheapest dedicated astro camera I could find out there with a half decent sensor size(still smaller) was the ASI1600, which was about £1200 (maybe a bit cheaper now). That's by no means a bad deal (you get a lot of camera for the money) but still quite a bit more than the DSLR. Add to that the greater flexibility (are you totally sure you'll never use it for anything else) and I still reckon it's the best way to start out. Bear in mind also that you don't need to mod it, though you might want to. Clusters, galaxies and a lot of nebulae don't really need it - depends how much you want to image the fainter Ha emission nebulae. Billy.
  6. billyharris72

    SALE PENDING 12" f/5 Revelation dobsonian - £250

    PM sent.
  7. billyharris72

    32bit image in Ps CC

    Sounds good. Other option worth exploring is the new version of Gimp, which has 32 bit support (after years of being 8 bit only) and a great array of tools (comparable to though not as user friendly as PS, and without the PS astro plugins). You could try using Gimp for the initial stretch and then going back to PS for the rest of the workflow if you don't get on with it. Nothing to lose given that it's free. Billy.
  8. billyharris72

    Nikon d5600 for astrophotography

    Forgot to add - that's better than my first attempts were! Keep it up. Billy
  9. billyharris72

    Nikon d5600 for astrophotography

    What shutter speed did you use, and what lens setting? These will be recorded with the image. As a general guide, for a crop sensor DSLR like the D5600, divide the focal length of your lens into 275. That is around the maximum exposure you will be able to use before you get star trails (experiment to see what is acceptable to you). So about 15 seconds at 18mm. Hope this helps. Billy.
  10. billyharris72

    what am I doing wrong

    Hi Louiz: As above, try not to worry - I've used that scope and once you get the hang of it it will give decent views (the Moon will look good, it will show banding on Jupiter, the rings of Saturn etc and it will work for brigher nebulae and star clusters too). The finder, to be honest, is pretty rubbish - finding things with this scope can take a little more effort than with others, but agtain you will get beter with practice. The issue with the Moon was probably focus. Especially with reflectors, focus can be confusing at first - if you are very far out you will start to see the refelction of the secondary mirror and that can make you think you are in focus but that the scope is not working (this happened to me the first time). Be patient and try working through the full range of focus. At some point it should start to give a sharp image and you can fine tune it from there. Best of luck - let us know how you get on! Billy.
  11. Funnily enough I have the 65mm version of this and was just thinking about it. I went for that scope specifically because it does take 1.25' eps, and the zoom eyepiece it comes with is good (it's not their standard "astro" eyepiece, which is like the one they use on their budget spotters). Despite the smaller diagonal and erecting prism it far outperforms my ST80 on the moon, but the small aperture makes it very limited for DSOs obviously. Can be mounted on a light tripod and is comfortable to use even at high sky, but tricky to aim. Be aware that most spotting scopes (this one included) have small prisms which rules out sweeping wide angle views - I find it can do up to about 3 degrees or so. The alpha models don't have this problem, but for that price you could buy Tak. Overall I'm glad I bought it, but was intended for birding and general nature watching. It gets an occasional astro-outing if I'm in a rush but I suspect the new ED72 would be a better bet for that. Billy.
  12. billyharris72

    Naked eye view of Venus phase?

    Not the first time I've heard this. It's just about feasible depending on where Venus is and its angular size. It gets up to about 1'6", and the resolving limit of the eye is in that region also, so you may well have picked it up. I've certainly noticed in the past that it sometimes does not appear "disc-like" but would not say I could discern the phase. Billy.
  13. billyharris72

    Strehl - I don't Know???

    I'd agree that having an objective measure of quality may well be worthwhile, but having some trust in the manufacturer, looking at reliable reviews and actually using the instrument have to trump it. My concerns about using Strehl ratio (in isolation) is that you see it being used as a marketing tool as much as anything else. And it's susceptible to that for a few reasons. 1. How do you measure it? When you see a Strehl ratio in a scope advert, how many of those ads point out that there is no agreed standard for how Strehl is measured and that the results are both uncertain and sensitive to the approach used? The following paper sets out some of the issues https://www.google.co.uk/url?sa=t&source=web&rct=j&url=http://rohr.aiax.de/Is_that_really_your_Strehl_ratio.pdf&ved=2ahUKEwi9xoaezu_eAhVnCsAKHZSRA_0QFjAAegQIARAB&usg=AOvVaw13Tvw7ED6wKzu42eCp-hl0 2. Ever seen Strehl used for an astrographic scope? How many of the ads point out that Strehl isn't a meaningful measurement for instruments that don't have a theoretically anastigmatic PSF, which renders it meaningless for instruments with a flat field? Here's an example of a scope with a (measured) Strehl of >0.99 that was a bit of a duffer. It's an extreme example admittedly, but illustrates my point. interferometrie.blogspot.com/2015/01/orion-optics-24-research-grade-sad-story.html?m=1 I don't have a problem with people using Strehl as a means of measuring real vs theoretical PSF. But I do have a problem with marketing department misappropriating it to flog kit.
  14. billyharris72

    Strehl - I don't Know???

    I really wouldn't worry about the Strehl ratio at all. All modern optics (excluding the kind of junk optics you might find in a "department store" scope) are of pretty reasonable quality. This is usually equated with a Strehl of about 0.8, and incorrectly labelled diffraction limited- the definition of the Strehl ratio is such that diffraction limited is identical to a Strehl of 1. In practical terms, though, it's as good as diffraction limited, since seeing conditions will override any issues with the optics. If there is a problem with an optical system it's likely to lie in astigmatism, off axis aberrations, chromatic aberrations etc. These are very different in practice and some may be more acceptable than others. And none of these is adequately characterised by the Strehl ratio. It has it's uses - if you're a physicist or an optician. It can also be used to identify a dud. But for everyday purposes I wouldn't get too hung up on it. Billy.
  15. I reckon this isn't a sensor fault as I have a very similar issue (same camera with a SW 72 ED) with Ha images that doesn't affect LRGB images at all. I haven't got to the bottom it yet but suspect it's some kind of reflection artifact. Pretty sure it's not amp glow, as nothing like this shows up on my darks. Billy.

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