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glowingturnip

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glowingturnip last won the day on March 19 2014

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About glowingturnip

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  1. glowingturnip

    Help! Is it my DSLR or Newtonian?

    if you do the above ccd inspector test with the camera in different orientations, does the centre move around ?
  2. glowingturnip

    Help! Is it my DSLR or Newtonian?

    when I first saw this thread, I thought it would be collimation, I'd had similar issues and found my secondary was well off-centre along the focuser axis, and tilted. However, as you say, if the coma rotates with the dslr, then it's not anything to do with the scope or the focuser collar.. Is it possible that the lens of a dslr is off centre to the sensor ?? I'd say it's definitely worth re-checking the spacing of the cc though, I eventually found I needed a whole mm longer than the recommended spacing for my baader mpcc and I still have a slightly off corner
  3. glowingturnip

    Narrow band filter ratio

    I'm currently in the middle of processing my first ever SHO image. There's an excellent Pixinsight tutorial on combining the channels, whilst avoiding magenta stars, here - http://www.arciereceleste.it/articoli/translations/75-narrowband-color-composition-eng From my *very* limited experience of narrowband, the Lagoon is good in Sii (though maybe a bit low and late in the year now), and the Eagle is rubbish.
  4. glowingturnip

    Focusing

    +1 for a bahtinov mask - used with bahtinov grabber I can get critical focus within a minute, and without subjectivity. You can make your own bahtinov mask here - http://astrojargon.net/MaskGenerator.aspx?AspxAutoDetectCookieSupport=1 - I cut my first one with a craft knife from stiff black card, then 3d-printed my second one. Bahtinov grabber is free software which works a treat, here - http://www.njnoordhoek.com/ though I think APT now has the same functionality.
  5. glowingturnip

    130pds v 150pds for imaging

    I know you've ruled it out, but I love my 200pds for imaging. I like going in for the details in a tight crop rather than a wide view of the whole area, so probably suits my style, and it does seem to be giving me the quality I want. Downsides would be - it was poorly collimated when I got it, had to spend an hour or so with a cheshire and a laser to get it right, there's lightspill around the mirror end, so I wrap a piece of black-out cloth round it when I'm imaging, I replaced the stock focuser, which wouldn't be strong enough to hold my CCD, it is big for imaging, you'll probably need a stepladder and a steadying hand if the eyepiece is pointing upwards, and lastly I can't carry my kit all in one piece any more, have to take the ota and weights off to move it. But all that aside, I still love it, honestly !
  6. glowingturnip

    A question of balance

    I suspect that's not an argument that I'm going to be able to win without calculating the torque required to accelerate the rig's moment of inertia by at worst case 2x guide speed for one guide pulse (for a fast correction from one side of the mount to the other, full aggressiveness and no hysteresis in the guiding program) compared to the torque that the stepper motors are capable of delivering, and those motors are no slouches - lower rated motors are used in some very 'jerky' precision applications like 3D printing, laser etching, etc. I think the maths is going to be beyond me though, so we'll have to agree to differ However, isn't there a case to say that you would prefer a smooth acceleration for a guiding correction, that you would get from a motor that is under load, rather than a jerky acceleration followed by a jerky deceleration and possible overshoot that you would get from a motor that is under very little load ? Actually, I think the answer is going to be in the aggressiveness and hysteresis settings that we all tune in PHD - different torques and inertia loads will result in different tunings, and I think you'd be really struggling to spot the difference between the results from separately well-tuned guiding sessions for different inertia load-outs.
  7. glowingturnip

    A question of balance

    I think the moments of inertia calculation are for the effort needed to accelerate the angular velocity of the mount around one of the axes. When the mount is stable and guiding, there is no change in angular velocity, so it doesn't matter then whether you have a small weight far away or a big weight closer, or for that matter how far away your scope and camera are away from their joint c.o.g. However, when the mount is slewing, that's when it's accelerating, and that's when it could put strain on the motors depending how far away your weights are. Mind you, I do most of my big slewing with the eyepiece in and balanced for that, so no biggy. Same principal how iceskaters accelerate when they pull their arms in btw. Wikipedia - When a body is free to rotate around an axis, torque must be applied to change its angular momentum. The amount of torque needed to cause any given angular acceleration (the rate of change in angular velocity) is proportional to the moment of inertia of the body. Moment of inertia may be expressed in units of kilogram meter squared (kg·m2)
  8. glowingturnip

    decent HSO targets in Sagittarius region ?

    any ideas ? will be my first dabble in Hubble palette - keen to have a good target to try
  9. Hi all, So after rather a long wait, I finally received my new SII filter today, just in time, since I'm heading to southern Spain at the end of the week and will be able to do some imaging. What would people suggest are targets in the Sagittarius region, or up to Cygnus I guess, that have decent signal in OIII and SII as well as in Ha ? Last time out I took some OIII of the eagle nebula, yet to be processed, but just on visual inspection nowhere near as much signal as in the Ha I took last year, despite longer integration time. I'd like to do some Ha of the Lagoon, but don't know whether there's enough OII and SII in there too ? Any suggestions gratefully received, Cheers, Stuart
  10. glowingturnip

    an odd dark image

    it's light-spill round the base of the tube, I get the same with my 200PDS, took me a while to figure out what it was. I solved it for me by getting a square of black-out-blind material off amazon, and then when I've done collimating i wrap it round the base and hold it in place with a bungee cord of the right length.
  11. glowingturnip

    The joys of an F5 newt instead of an F4......

    I've certainly no complaints with my new-ish f5 200pds. Out of the box it wasn't very well collimated, the secondary was longitudinally out of place in the tube and a bit squint too (but I did buy it in Spain - maybe they dropped it), but after an extended session with the cheshire lining it all up it keeps collimation well now. I set up and tear down each session, and only need a quick laser collimate to get it all back in line again. My coma corrector MPCC III spacing was a headache though, I've ended up a full mm longer than the recommended 57.5mm spacing for M48 threads and it's nearly all gone, just a tiny bit of coma left along one of the edges, but any more spacing and I wouldn't be able to screw it all together.
  12. glowingturnip

    Horsehead nebula in Narrowband

    love it, really like the colours. I'd echo the comments on the flame though, looks curiously flat and yellow compared to the rest of the image
  13. glowingturnip

    M16 from Astro campsite

    there's another, frankly very strange, filter you can do to your photos - here Sorry Carole !
  14. glowingturnip

    M 16 Ha

    no no no, I think yours is very good, not a lot between them to be honest. It just struck me as funny that we had almost exactly the same pic. But I think we both owe it to ourselves to get more data :-)
  15. glowingturnip

    M 16 Ha

    it was 9x600s Ha, darks flats and bias, equipment as per sig, Pixinsight. - only 9 exposures, hmm, didn't realise it was so few, I definitely need to revisit then. I'd normally want over 20. my initial thread was here: and then I had fun with star removal here:
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