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Everything posted by brianb

  1. Yes - if you're like me, things only work properly when you're not thinking about it ... so you have to practice enough to make the physical act of capturing the images unconscious, which means a lot of "wasted" sessions in poor to bad conditions. I'd notice from the preview screen if the filter wheel jammed, the planet just looks different in different wavelengths; in fact I'd even manage to tell you which filter was in from the monochrome preview. Takes practice but familiarity sometimes breeds success.
  2. It's working focal ratio that's the determining factor, not aperture - more aperture just gives a bigger image at the same focal ratio. 1/30 sec works for me with a C11 but only barely so with the blue filter & not at all with a IR pass filter. The IR image I posted a couple of days ago was taken at 1/15 sec. Fortunately the seeing is usually steadier in longer wavelengths! Moot for me - solid high cloud, last night was NBG here with very hazy skies (cirrostratus sheet, looked as though it was contrail derived)
  3. At the relatively low magnifications used for DSO work the diffraction pattern modification caused by the central obstruction has no impact at all. The central obstruction reduces the light transmission but less than you'd think - a 33% by diameter CO reduces light by only 10% (square rule) which is the same as reducing the aperture by 5% ... and about that amount of light will be absorbed going through the relatively thick lens elements in a good refractor of any size.
  4. The altaz fork mount that came with it. It's OK for unguided short exposures.
  5. The expensive bit is the etalon - the external Ha etalons are at least 50mm aperture, the PST contains special telecentric lens groups which allow the use of a small etalon (15mm) which makes manufacture much cheaper. There is a tendency to "sweet spots" with the sub-aperture etalon but the cost is a major factor. The PST is a great bit of kit for visual use but the Lunt 60mm Ha scopes (which also use a sub aperture etalon) are much better for imaging, mostly because of the convenience. To image at prime focus with the PST you neeed a low profile shoulderless nosepiece for the DMK (or other C mount) camera ... afocal imaging is possible but attaching a DSLR really isn't going to work (even with the anti-alias filter fixed to allow Ha through to the sensor). Second hand PST or Lunt 35 is a good taster. Try before you buy if you can - Ha instruments or filter sets that have been treted roughly won't work well even though they may look pristine. The main issue here as that you will get hooked & the really serious kit costs serious amounts of money!
  6. Good result for average / poor conditions. 1/30 sec exposure at 30 fps maximizes photon capture; 1/60 sec at 60 fps just doesn't work for Saturn because there's not enough light even with the gain turned right up.
  7. Very nice result ... especially for a single frame. Why waste time & effort when a simple push of the button works as well as this?
  8. That's a nice set of images! I find it remarkable how the sum of the R G & B images always seems to be better than the best of the individual ones. Do I take it you're using a combination of IR, R & G as luminance? I've found that using just the red channel works best & now shoot in the sequence G, R, B to minimise the rotational smearing between the individual channels and the "luminance" channel.
  9. Welcome! Which filter? A CLS / didymium glass type filter will reduce the sky light but your problem is more likely to be local light overspill which requires shielding. Tell your local authority that you're having trouble sleeping because of light spill from the street light and they should screen the thing for you. Tell them that you're an astronomer & they'll ignore you ... it has to be a health & safety issue before they'll act.
  10. The joke's on them .... Get it certified as sufferring from Sudden Oak Death Syndrome, or Dutch Elm Disease. Or invent a new reason to exercise your axe next time the weather is uncooperative.
  11. Very nice! Did you try mosaicing with the barlow?
  12. Good details captured on the globe ... the colours are not that far out either, try reducing the blue about 10% and then reducing the saturation slightly. This sort of image is much more valuable if documented with the exact date and time (to the nearest minute is good enough).
  13. Tape the top of the cable to the fork arm so movement doesn't strain the connector.
  14. Well a UV/IR bblocking filter would help ... but so would imaging Saturn when it's at a decent altitude. For most of us it still gets to over 30 degrees when due south.
  15. If the tube is slipping, the focus lock bolt won't help. Get instructions & adjust the focuser so it doesn't slip so badly. I say "get instructions" because doing the job incorrectly can permanently distort the focuser tube, making it impossible to work smoothly without slipping over the whole range of travel. Why don't the Chinese use a rubber-coated friction roller as per the original Crayford design? Smooth metal on metal is just asking for slippage even if the action is smooth & light.
  16. There's not a lot of saturation in the colours of stars ... there are a few that sort of pop out but the colours are mostly rather pastel. V Cyg is one that always looks like a glowing coal to me, even when it's faint. Astigmatism affects low power views much more than high power views. You can probably get away without using your glasses when using eyepieces shorter than about 12mm unless your astigmatism is very severe. "Better eps" don't help correct your eyes; you can get an attachment for some TV eyepieces (Dioptrix) that adds astigmatism to the EP to correct your astigmatic sight, enabling you to do without your glasses, but most people either don't need it or find it convenient to keep their glasses on when using low power EPs which usually have masses of eye relief.
  17. The latitude scale is an indication for a very rough alignment, that's why you have a polar scope and/or drift align the thing. Being several degrees out is common.
  18. The odd occasion when Moreton waves are detected using amateur equipment, surely the solar imaging section covers it. Seismic events on other stars are not, so far as I know, recordable with equipment likely to be accessible to amateurs. We even have difficulty with variable star observations, a very accessible field to amateurs. What do people do when they get bored of yet another image of M42 or M31? Sorry guys but I want DSO images that show transient events & I don't really care if they're rough. Yes, we've all got to learn & the old warhorses are good yardsticks for measuring progress in refining your technique, but I'd like to see people moving on to new ground (or sky) - there's plenty out there!
  19. The contrast features on Saturn's disc are very subtle, you need as much contrast as possible. If the planet is too bright (because of the dark background) observe in twilight or use a filter. To get more contrast (visually) use a lower magnification. Of course this makes the image smaller too, which is why larger scopes give a more detailed view - when the unsteady atmosphere allows them to work to their capability.
  20. Try sharpening it a bit ... the wavelets tool in Registax can work very well, but the results can be ugly if it's overdone.
  21. This is the first time I've tried to make a mosaic at this scale with such a thin crescent. Worked fairly well I think. 2011 Apr 07, 2001 - 2009 UT. William Optics FLT 110 4.3" f/7 fluorite triplet refractor, 2x Powermate, Wratten 29 (deep red) filter, Imaging Source DMK 41 camera - 5 frame mosaic. 25% resize; full size version here. Diameter 30.39 arc min; colongitude 322.7 deg; illumination 15.8%; libration in latitude -01 deg 55 min; libration in longitude -06 deg 34 min; altitude 30 deg. Transparency moderate with slight cirrostratus; seeing fairly good with slight boiling. Temp +08C; wind NW force 3-4; baro 1029 mb, steady.
  22. Very nice sharp image, just a touch of chromatic aberration on the "edges" but the natural colour in the maria offsets that beautifully.
  23. Here's my effort at using a barlow ... my "1.5x" actually gives closer to 2x & deteriorating seeing meant it wasn't very successful. Only the red channel was good enough to use & even that is very little if any better than the prime focus image. Still, I've managed to capture the crepe ring fairly successfully. 2011 Apr 08, 0057 UT. CPC 1100, 1.5x barlow, Astronomik red colour seperation filter, DMK21. Transparency good, seeing moderate with significnt boiling. Temp +03C; wind calm; baro 1030 mb, steady.
  24. Dark sky & wobbly seeing is a good night for "faint fuzzies". Bright moonlight & haze can be good conditions for observing planets, double stars & other relatively bright objects, especially if the air is steady. If you wait for good transparency and steady seeing, and you aren't at a major professional observatory site, you'll probably find your beard polishing your shoes before you're satisfied.
  25. Hyperion seems to be easiest when it's near elongation & Titan is nearby to act as a pointer. But it's really hard - unless you can get the planet out of the field the glare makes it impossible to see a mag. 14 object! The object I've recorded is a field star which is at least a couple of magnitudes brighter than Hyperion! Mimas was easy for me last year but the extra glare from the rings has made it harder this year. Iapetus is no problem to me, my image missed it because it didn't fit into the small field of view.
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