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Everything posted by brianb

  1. I regularly use Meade series 5000 super plossls (60 deg) & prefer them to the Televue Plossls ...
  2. But the field is actually limited by the baffle tube .... Using a focal reducer with a SCT for visual work is pretty pointless, just more glass to soften the contrast ... when imaging with a small chip, a focal reducer makes a lot of sense!
  3. Much, much better than Brian Cox's series - and I would guess cost only a small fraction of our money to make - the locations were less exotic but effective enough, there was plenty of enthusiasm on show, it seemed to be pitched at a reasonable level yet still covered more ground than Cox's programmes in less than half the time, there was good occasional use of a second face. Looking forward to the second part where Jim should really be in his element.
  4. Superb work! Yeah, I've never seen anything like a diffraction ring with my C11 & only a trace with 8". I used to see complete diffraction patterns with 6" fairly regularly when I was in Derby ... some sites just seem to have bad seeing ...
  5. Actually it will work with any well-corrected eyepiece. There is a positive benefit in the small increase in focal length, it makes life easier for the eyepiece designer - even Al Nagler has difficulty designing an eyepiece that waill work well at f/4, f/4.5 is much easier to work with.
  6. No filter will make a huge difference. A better eyepiece might.
  7. 4x is better ... I have doubts about this project; 60mm is just too small to show much detail (except on the moon). And a refractor tube should IMO be white, or polished shiny metal, for the simple reason that a refractor works better in daytime observing conditions because the light only goes down the tube once, and it's better still if the tube isn't getting hotter than it needs to by absorbing solar radiation.
  8. Seeing can be a major issue. Shorten exposures as much as possible - even if it means turning up the gain. Do not use in camera noise reduction, it's crude & will cause image blurring if the seeing is at all wobbly (and it almost always is for solar). Try a deep red filter - it helps steady the seeing down. Clean the sensor! and use a clear glass "filter" (Astronomik Klar Glas) fitted permanently to the nosepiece to keep the dust bunnies at bay.
  9. Yes, you can get a 2" visual back which will screw on in place of the 1.25" one. There is no point whatsoever in doing so. The field of view is restricted by the internal baffle to a bit less than is available in an "optimum" 1.25" format eyepiece (e.g. a 32mm 60 deg AFOV Plossl). The extra optical length of a 2" diagonal will result in the focal length being increased (if focus is still obtainable, which it probably will be), this will reduce the actual field of view. The weight of the 2" diagonal & eyepiece will result in the centre of gravity being even further back than it is normally, making it hard or impossible to balance the tube (without a counterweight system). A 2" visual back is worthwhile with SCTs of 8" aperture and above but not for smaller scopes.
  10. The 1919 solar eclipse expedition which proved gravitational deflection obeys General Relativity was done with a very modest instrument, many of us have kit which is more capable. Light arcs from gravitational lensing in galactic clusters are small and faint, probably requiring apertures in excess of 0.5 metres to record convincingly.
  11. Here's something different - gonna have to work on the technique though ... False colour image, heavily oversaturated: the "red" image was made through an infra-red pass filter (Astronomik Planet Pro 807), the "green" imaged through a standard Wratten #58 green filter and the "blue" through an Astrodon UVenus filter. Each image is a mosaic of 6 frames, this is I think why there is a colour gradient across the image ... Images made between 2256 & 2314 UT, 2011 March 18th. William Optics FLT 110, prime focus, Imaging Source DMK41 camera.
  12. Yes but finding it might not be. Do NOT use the finder unless the sun is screened from the observing site. A good goto scope or a properly aligned equatorial mount with setting circles is very helpful indeed, in fact pretty near essential for Mercury - you can often get away without for Venus which is also best observed in daylight for the same reasons.
  13. Nice "straightforward" moon shot! Filters don't help much if at all ... when you get to a longer focal length so that seeing wobbles are an issue, a red filter does help ... but only when used with a monochrome sensor! Try reducing the exposure a bit, the brightest patches are getting very close to "burning out".
  14. Very nice indeed! That 925 is working well for you...
  15. Differential atmospheric refraction - when you look at objects low in the sky, the atmosphere is acting as a prism ... it's not Mercury, or your scope. The only things you can do are to observe when the object is higher in the sky (which means in full daylight for Mercury) or to use a coloured filter to kill the dispersion - red is helpful as the seeing is steadier in red anyway.
  16. Well that's 2.25x per mm of aperture, and 1.2x per mm is a good "rule of thumb" as to the maximum useful magnification! The PST is very tolerant of eyepieces - chromatic aberration cannot exist in a monochromatic solar scope, and the f/10 working focal ratio is tolerant of just about any design on the market. A simple eyepiece (few lenses, few surfaces) usually works better than a complex one as the contrast is higher; a wide field of view is not required, the 5mm blocking filter in the PST restricts the field width to not much more than the diameter of the solar disk.
  17. Here's my image of The Beast (SW) taken at 0937 UT this morning (March 19th) - the mono version is "raw" & shows just how bright the prom was at that stage!
  18. Wow! I thought it might blow ... & the clouds came across so there was obviously some action to hide ?8-/
  19. Indeed - the one on the SW limb is exceptionally bright - looks like the sort that might "lift off" (turn into a coronal mass ejection) but timing is very unpredictable. Do watch it if you have clear skies ... I got a quick look but the skies are now clouding over 8-(
  20. Should be more than adequate, unless you have the gain / ISO turned up too high.
  21. Can you operate them in the light? My efforts have always resulted in fumbled chopsticks, dropped food & amused oriental observers
  22. You need an image scale large enough to resolve galaxies before the surface brightness figure matters. Very distant galaxies will appear as faint stars. Seeing smears reduce the resolution below what you would expect by applying Dawes Limit, except in the smallest scopes ...
  23. Moths are very nutritious I tend to go inside for a break (lights stay off) cereal bar, mug of coffee & 10 mins nap to refresh myself when getting tired.
  24. Yes, it's definitely related - but whether the theory holds water or not depends on dark matter being (mostly) composed of WIMPs, and the WIMPs themselves are theoretical objects rather than things that have experimentally verifiable properties. There's as much experimental evidence for the dark matter being unicorn poo as there is for it being composed of WIMPs. Now I fully accept that WIMPs are rather more likely to account for dark matter than unicorn poo is, but I think you'll get my drift.
  25. There have been a few issues like this raised. Previously they've been "answered" by a recalculation of the distance of the star, or the discovery that what was thought to be a single supermassive star has turned out to be a pair of very massive stars. I don't think the derived mass of R136a1 is as accurate as the article suggests. The physics of radiation pressure on low density gases at moderate temperatures is however very well known and it's that which determines the maximum mass that can be accreted as a single body.
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