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SJP

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About SJP

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    Kent
  1. For comparison (and I'm nowhere near as adept at astrophotography as the other contributors here), here's a comparison between techniques on M42 in my first month of astrophotography. Increasing sub exposure length and commensurate reduction in sensitivity (ISO) really improves the detail of the image, and you really need a motor driven mount for that. The longer focal-length and faster telescope gives a sharper and more detailed overall image. Getting light onto the sensor is the key, and for that a motor-drive is the cheapest and most effective option. First a simple 20 second exposure using a DSLR/Celestron 6" Newtonian Orion by S.J.P, on Flickr Now around 1 hr of 1 minute sub-frames using a DSLR/Sigma 150-500 zoom at 500mm (Forgive the colour-cast!) M42 Sigma Zoom by S.J.P, on Flickr Then 40 minutes of 1 minute sub-frames using a DSLR/6" Newtonion M42 Edited by S.J.P, on Flickr
  2. Be warned, this is a slippery-slope! I started with a DSLR/Lens and short-exposures, dabbled with a barn-door tracker, and ended up getting a cheap 'scope/drive/guider. Note that for anything other than the larger DSO's (such as NGC7000, M42, M31 etc) you'll need a longish focal length, and a decent, fastish (f/4-5.6), telephoto lens (300mm-600mm) which will set you back at least £500 (third-party such as Sigma/Tamron), possibly £1-5k if you go for the best marque brand glass. If you're chasing dim DSO's and you don't have a tracking-mount then you'll also need good sensor sensitivity to allow short exposures (particularly if you have a cheaper/slower lens) so you're then looking at full-frame cameras (Canon 6D or 5D) or the better crop-sensor models (70D or 7Dii) which will set you back another ~£750-£2,300. That's a lot of cash! Finding DSO's can be a right royal pain too as the live-view screens aren't that sensitive and taking a series of high-ISO 2-3 second exposures to locate your object is time consuming. Alternatively you can pick up a cheap 'scope with GoTo mount for ~£500 and then use GoTo to find you subject and the tracking to give exposures of 60-seconds or so allowing you to get by with less sensitive (and cheaper) cameras like the 1200D (£250). Add a guide-camera and finder for £300 or so and you'll be able to take 300-600 second sub frames at the cameras base-ISO for maximum quality, and the total outlay will be less than a decent telephoto lens! My advice would be to find a friendly local purveyor of all-things telescope and talk through your aspirations with them, I did exactly that and found their advice invaluable.
  3. Thanks for the suggestions guys. I'm not convinced the artefacts are entirely 'scope related though, as they're equidistant from the rectangular camera sensor corners. If they were entirely 'scope reflections I would expect them to be in a square pattern
  4. Since starting-out in astrophotography I've noticed at least one semi-circular artefact in the corner of my DSLR images, but usually it's cropped-out. This week I noticed three in this capture. I've (over) processed to bring them out, does anyone have any idea where I might look for the culprit? I'm using an unmodified Canon EOS 6D attached via a T-Mount to a Celestron 6" Newtonian. I usually use a 2" LP filter (which I thought may be causing the artefact (through internal reflection), but for this capture I didn't so I guess that precludes the filter as the cause! NGC7000 by S.J.P, on Flickr
  5. That sounds promising If yours is anything like mine, it'll work flawlessly from now on. It's so convenient when there's little observing time available for the 'scope to align itself (even during twilight) whilst I'm preparing for a session.
  6. CG-5's seem notorious for being problematic with Starsense. They require a splitter cable (around £25) and most require a specific modified splitter which doesn't seem to be generally available. I had mine shipped from Celestron in the states.
  7. What mount are you using? I had the same problem with my CG-5 until Celestron Support sent me a replacement splitter cable, that solved all my problems
  8. SJP

    Guiding

    The basic PA I've been performing (using a polarscope and iPhone polaris app) has been good for 60 second subs, and I've extended this to 600 seconds with the guider so I'm happy on that front. It's good to know that I'm not destroying my mount in the process though Thanks for allaying my fears.
  9. SJP

    Guiding

    I have a Celestron CG5-GT mount with a C6N (Newt) OTA with a 60mm (280mm Focal Length) ZWO guide-scope with Celestron's NexGuide attached. I was just concerned that frequent adjustments would wear-out the mount/motors!
  10. SJP

    Guiding

    Having only just made the jump to basic guiding (using a Celestron NexGuide) I'm somewhat ignorant of the intricacies so my question is, how often should the guider clunk the drive motors? The other evening after a basic polar-alignment, the guider was clicking the drive motors on/off something like every three to five seconds - is that normal?
  11. I tried fiddling-with and fettling my cheap Celestron focuser, I dismantled it, cleaned, regressed, shimmed, replaced the knobs and in the end became so disenchanted with the sloppy build quality and tolerances I replaced it with a lovely CNC machined Crayford focuser. Beware the road you're embarking on!
  12. http://stargazerslounge.com/index.php?/topic/222735-Telephoto-Vs-Telescope is the link to the thread Hobsey mentions.
  13. The Canon EF 2x iii is expensive, but there's a reason for that, it's bloomin' good! Coupled with a decent telephoto lens it will focus quickly (albeit slower than without it in place), it'll autofocus with a f/2.8 or faster lens (or with an f/4 lens on a 1 or 5 series body), and image quality will only be slightly inferior to a lens with the same native focal length. Using it with a less expensive telephoto lens, particularly those with apertures slower than f/4 won't be a particularly enjoyable experience though. The extended nosepiece on the EF 2x iii also prevents it being used with all but a select few lenses, so do check the Canon website for compatibility before investing. I've tried a cheap 2x T/C in the past and results were extremely poor and I'd avoid them like the plague. Having said that the Kenko Pro 300 DGX is fairly well reviewed, but at around £150 it's not exactly cheap, but is compatible with more lenses than Canon's version. Overall I think the options for a manual-focus long prime lens is probably going to offer the best bang/buck ratio.
  14. Very valid point! Widening your focuser hole isn't for the fainthearted, you can't use a hole-saw as there's already a hole there and a conesaw of a suitable size is difficult to come by and you aren't guaranteed a centralised hole. After contemplating a jigsaw, I finally went for a nibbler as the swarf it generates is larger and easier to catch than the dust from a cutting blade. Sent from my iPad using Tapatalk
  15. There are few lenses available which offer true rounded iris diaphragms, and whilst multi-bladed square edge blades improve upon versions with less blades they do still exhibit spikes when stopped-down. Here's an image taken at f/8 with a Sigma telephoto-zoom, its 9 iris-blades have given rise to eighteen-point stars
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