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michael.h.f.wilkinson last won the day on May 22

michael.h.f.wilkinson had the most liked content!

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About michael.h.f.wilkinson

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    Neutron Star

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    Astronomy, computer science, photography, wildlife, cookery, life the universe and everything
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    Groningen, The Netherlands
  1. michael.h.f.wilkinson

    best illuminated reticule eyepiece

    I have a very similar one (rated at 22mm focal length) which I can use readily with my glasses on.
  2. michael.h.f.wilkinson

    Smoke, Wind & Fire Prom on SW limb.

    Stunning image. Sorry to hear your family has been so badly affected by the fires. Hope they are safe
  3. michael.h.f.wilkinson

    Do I need one of these?

    For visual work, I would not use a coma corrector. I used a much faster Dob (not mine alas), and did not find coma much of an issue, even in ultra-wide-field EPs
  4. But as I point out even small, bright galaxies have lower surface brightness than planets, and almost all planetary nebulae (apart from one or two near stellar ones, like Jonkheere 320 an d 900 in Orion and Monoceros respectively) have distinctly lower surface brightness than planets. The effect of going from 130x to 260x means losing two full stops in terms of surface brightness (a factor of four), and going to 520x means a reduction of 16x with respect to 130x. These numbers correspond to 25% and 6.25% transmission filters, which is more like a moon filter than any LPR filter I have ever used. LPR filters have transmission curves like the one found here https://www.firstlightoptics.com/light-pollution-reduction/idas-p2-light-pollution-suppression-filter.html
  5. michael.h.f.wilkinson

    Prom on SW limb November 11, 2018

    Nice one! No luck here at the moment, alas
  6. When observing planets, much does indeed depend on the seeing conditions. With my F/10 8" SCT I generally start out with the 14mm Delos (145x), which is generally good, except on nights of really bad seeing, and move up to the 10mm Pentax XW (203x) which is often OK, but you may have to wait for moments of good seeing. On good nights, the Delos 8mm can be used (254x), and on really good night I use the XW 7 mm (290x), but again, you need to wait for moments of good seeing. I also have a Pentax XW5 (406x) which I have occasionally used on the moon, but in practice I only use it regularly in my 80mm F/6 scope, where it produces a very usable 96x. I am sometimes tempted when a second-hand XW3.5 turns up, which would yield 137x in the 80mm F/6 triplet, but as I do not use that for planetary viewing much, I would be better off saving money for that big, fast Dob I am longing to get. Once I have that, I will have an excuse to get that XW 3.5
  7. Sorry, not correct. Planetary nebulae and galaxies are particularly unsuitable for higher-than-rated magnification. They have far lower surface brightness, and far lower contrast than planets or the moon, so the loss of brightness you incur when going to high magnification means you lose much more than when observing high surface brightness, and high contrast features on moon and planets. Planetary nebulae can in some cases handle higher magnifications, because but only those with comparatively high surface brightness. I have used 245x on the Eskimo Nebula with my 8" scope, and that worked surprisingly well. On the Helix, which is huge and has low surface brightness, I used just 65.5x in my 8" scope for my best view. Anything higher and it seemed to fade away. On galaxies, higher magnification does not work well at all, and an exit pupil of around 2mm (one quarter of the maximum rated magnification) is generally advised.
  8. The image does become larger, but also blurred and much dimmer. What is still useful to you as observer depends on the contrast and brightness of the object (moon and Mars readily take more magnification than Jupiter, I find), and on your own visual acuity. I have a visual acuity of around 1.7 (well above average), and therefore the blurring becomes apparent at lower magnification than if you have more average visual acuity. Having said that, using a 5x Barlow and 2mm lens in a 130mm F/5 yields 1,625x magnification, which will certainly show the blurring effect, and the image will become very dim indeed. I once pushed my Celestron C8 to slightly more than the official maximum (406x) to about 450x on Mars, and that did sort of work, but showed no more detail than at 290x, I felt. I think the Stellarium simulator just adds magnification, and doesn't take the resolution of the scope into account
  9. michael.h.f.wilkinson

    UV/IR filter required with 80mm frac and Quark

    Note that a Combo Quark is meant for SCT with off-axis ERF, or refractors slower than F/15. Your ES 80 mm triplet sports the same F/6 optics as my APM version, I believe, so you will need a separate tele-centric lens of 2.5x or larger magnification. I use a Baader TZ-4 4x tele-centric, and a full aperture ERF with my Solar Spectrum H-alpha filter. The ERF might not be needed for the tele-centric lens used, in the case of the Combo Quark, but I am not sure of that. In summary, you should NOT use the combo quark without tele-centric lens in F/6 optics. Even if it might stand the heat, the wide light cone means you do not get the narrow band pass
  10. michael.h.f.wilkinson

    November 9, 2018: First M31 with APM 80mm

    The top has too much red, the bottom too little, it is difficult to get this balance right with so little data, I find. Much also depends on monitor calibration.
  11. michael.h.f.wilkinson

    November 9, 2018: First M31 with APM 80mm

    Reprocess, using median stacking rather than average, to get rid of hot pixels not removed by my older bad pixel map. I will make a new one, and new darks and flats to get rid of them. Quite noisy, but that is to be expected, but I am happier with the colour.
  12. michael.h.f.wilkinson

    November 9, 2018: First M31 with APM 80mm

    Managed only 1 h of data with the APM 80mm F/6 and Tele-Vue TRF-2008 0.8x reducer. Guiding was not good on the EQ3-2, so I used 60 60s subs. Used 60 darks and flats, but fogot to use the bad pixel map I have for my EOS 550 D. Not bad for so little data and rather hazy suburban skies. I am restacking the data with the bad pixel map, and will try to get he colour better. I also got one or two frames with comet 64P/Swift-Gehrels in it, which I will process tomorrow.
  13. michael.h.f.wilkinson

    Revisited an old image, from back when the sun was active

    I used my APM 80 mm F/6 triplet, with Beloptik tri-band ERF, Baader TZ-4 tele-centric lens, Solar Spectrum 0.3 Å H-alpha filter, and ASI174MM camera. This is a mosaic of some 45 panes, as I recall.
  14. Being bored, and browsing through some old data, I noticed a reprocess I did of an image I shot on my brother's birthday in 2015. I had it printed on a large format and gave it as a birthday gift. Boy was the sun more active then
  15. michael.h.f.wilkinson

    New Comet

    Very interesting stuff.

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