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brianb

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Everything posted by brianb

  1. You don't need a barlow for visual ... modern long eye relief EPs mean that there's no benefit in them. Something similar is essential for increasing the image scale for lunar / planetary imaging. Don't waste money on anything but the best!
  2. Blunders of the Looney Verse, Shirley?
  3. Fiddling with ISO / exposure length will not change the signal to pollution ratio. Increasing the exposure time & reducing ISO to get the same image density will improve signal to noise. To improve signal to pollution, you need to find a darker sky or use a filter which will selectively remove pollution.
  4. brianb

    BST

    Not at all ... just grab an extra hour's kip whilst at work ...
  5. brianb

    BST

    Introduced during WWI to reduce the amount of time the oiks who worked in munitions factories were spending down the pub. Now that we have effectively got rid of closing time it no longer has any justification.
  6. brianb

    BST

    I'm going to forget deliberately, I don't do blumming silly time.
  7. Fact of the matter is, once you get near the top end, you pay increasingly large amounts of money for increasingly small increments in performance. If this scope has guaranteed superb quality optics (1/10 wave PV or better) then the price is very reasonable. If it's a run-of-the-mill 1/4 wave Chinese optics scope that just happens to be f/15, it is indeed expensive. Don't forget that a world class focuser costs pretty much the same as this does as a whole scope.
  8. Sunspots, faculae, granulation (with 4"+ aperture and steady seeing). It's 100% safe when used according to instructions. Like most things, it isn't safe if abused. Do remember to remove the finder, leave it capped or make it a solar film filter of its own. Inspect the film for splits / tears / holes before every use, and make sure the filter mount is attached firmly to the scope (so it won't accidentally fall or be blown off, and is unlikely to be disloged by stray fingers etc.)
  9. Interesting - I bought a couple of cheapo BP-511 clones from 7dayshop for my 40D & I reckon they outlast the genuine Canon ones by 50%. If you're a heavy battery user, the battery grip is worth having as it takes 2 standard batteries giving 3-4 times the life of a single battery in cold conditions.
  10. Why not? Take a 50mm camera lens stopped down to f/16. Its aperture is therefore just over 3mm. Nevertheless it manages to illuminate the whole area of the film gate / sensor - 36mm x 24mm ...
  11. Does you no harm to offer a few quid, & may soften his heart. Finding you on his ground without asking previously is very unlikely to result in being allowed to stay.
  12. OTOH the DMK cameras are easily available, cheaper, the software works & the performance is adequate if not leading edge. '31 & '41 probably the best choice for solar (or lunar) work. Get a clear glass "filter" (Astronomik Klar Glas) to keep the dust bunnies away from the sensor surface.
  13. That's a lot less dangerous than being trampled all over by a field full of bullocks ... cleaning the slobber off your precious optics would put you off trying it again. Seriously, though, if a farmer is receiving set-aside grant for land that is doing nothing and can get a few quid off an astronomer in "rent" (especially as a tax-free backhander) then he's going to jump at the chance.
  14. And the UV/IR blocking filter reduces prismatic dispersion in the atmosphere ... and having something stuck on the filter threaded end of the nosepiece helps keeps dust bunnies off the sensor.
  15. Yes.If you look at the research grade astro CCDs you will find that they're manufactured by thinning the silicon substrate and illuminating them from the back - that maximizes the sensitive area as the circuitry doesn't interfere with the detector sites. It's an expensive method of production as a large percentage fracture whilst being thinned, but it's how you get the very highest quantum efficiency at the blue end of the spectrum. The more silicon the light goes through before being detected, the more of the shorter wavelength photons are absorbed before they get there. Foveon is a clever application of this principle, but whether it has any advantages or not, it hasn't caught on ... possibly due to the pixel count of Bayer filtered sensors being higher for the same actual resolution (and people think a 12 MP sensor must be better than a 6 MP sensor ... even if they're not measuring in the same units) and possibly because colour balance has been as issue with Foveon sensors (varying between pixels in a random way, due to the absorbtion in the silicon not being absolutely uniform).
  16. Actually you get a true mono image if you isolate the signal from the top layer. The middle layer is "minus blue" and only records what doesn't get detected by the top layer. The bottom layer is "red" & only records what doesn't get detected by either the top or middle layers. There's no free lunch.
  17. Nice start ... if you tweak the tuning a bit you should be able to get the shading more even across the disc.
  18. You can think of the speed of light decreasing - that gives a good mental model though it's not accurate physically. Alternatively go back to the inflating balloon model. If a balloon is inflating at such a rate that a pair of points one millimetre apart doubles their seperation in a second, and the balloon is the size of the Earth (40,000 km in circumference), a pair of points in London and New York (5,000 km apart) will be moving apart at 5000 km/sec in the first second, 10,000 km/sec one second later, 20,000 km/sec two seconds later ... after only 6 seconds their mutual speed will have increased to 320,000 km/sec - more than the speed of light - so that they will no longer be in the same "universe" - yet neither has accellerated. Einstein's Theory of Special Relativity says that objects cannot accellerate through the speed of light. It does not say anything about space being warped. Neither does General Relativity set a limit to the rate at which space/time can be warped ... this leaves a (rather improbable) loophole for the designers of a inertia-free "space warp drive" similar to that apparently used in the Star Trek series; "compress" the space ahead of the ship and "stretch" it behind and the ship can be propelled at limitless speeds through the cosmos without having to accellerate at all, let alone break the "light barrier" in its local space.
  19. If using a narrowband filter, the CLS is not needed & may absorb a significant amount of the light you're wanting to record. (Depending on the wavelength, of course. CLS is fairly transparent to Ha.) If using RGB colour seperation filters, you will benefit from the CLS filter.
  20. Some things (red shifts, chemical composition of stars) very certain indeed. Some things (dark matter, dark energy) are rather tentative theories. Distances (of stars, except for the nearest ones), a few decades ago we could have been wrong by 50% - now we're sure fof distances to galaxies to the order of 10%. So it all depends what it is that we "know".
  21. Very nice indeed - you must have had pretty good seeing (by UK standards!)
  22. With a short focus achro 'frac, the semi apo/minus violet/contrast booster filter is practically essential ... a slightly better diagonal will make no difference without it.
  23. Realistically, the more light you get the better, so no filter (apart from UV/IR blocking) is going to work at least as well as any.
  24. Try Modern Astronomy, Bernard has managed to source some specialist filters for me in the past.
  25. No - it still needs to absorb light in order to get the colour data. The way to get high efficiency is to omit all the colour filtering i.e. a monochrome camera. If you really need colour data you can add your own filtering.
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