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  1. Past hour
  2. Oh, new version of that spread sheet, thanks for that. I was using V2.1 to do calculations for different configurations with SA200. This one has objective grating section as well. According to spreadsheet, with 6 lines/mm and 200mm aperture I'll be seeing limited in resolution. Total of 1200 lines would give me theoretical resolution of R1200, but star size for 2" FWHM would limit me to R384 if I use native F/8. Dispersion would be 3.9 A/pixel - which is quite enough to record 15.6A resolution (even binned to boost SNR). I'm going to see what difference makes using reducer, not sure if it will make any since it is objective grating - star size will be smaller, but so would be sampling resolution as well. Yes, not much difference, so no point in using focal reducer (except for boosting SNR of spectrum), but at a small cost of spectrum resolution - R343 with reducer. I have found a paper that describes using just the approach I came up with - printing with laser printer on overhead projector clear film. Author also concluded that 6 lines per mm is achievable with 600dpi laser printers. Here is reference: http://aapt.scitation.org/doi/abs/10.1119/1.2768688 and also from abstract: "A standard laser printer can print black lines (separated by a white line) at 60 black lines/cm (about 150 lines/in), which is a small enough spacing to produce a crude diffraction grating [see Fig. 1(a)] that is sufficient for the physics inquiry activities described in this paper" (not sure what that paper is about, I just read abstract and found confirmation that printed grating will work). So it looks like this could indeed be viable solution for ultra cheap way into spectroscopy. I just ran numbers for smaller scope - something like 80mm F/6, and results are still good - still seeing limited - R227 for 2" seeing, again using same 6 lines per mm grating. Probably only drawback of this method is efficiency - grating will not be blazed, so light will be equally spread on both sides of source.
  3. Cone Nebula

    Great image Billy, really like the colour balance you got. Jim
  4. Show us your Solar Observing Equipment

    Thanks Mark yes I had read about the problems with the double 80m stack and over on solar chat there a guy with the same set up using the 75m with great success So I'm hoping for good things
  5. Am I a dinosaur?

    Lots of interesting and passionate views on this one! I think its just a language thing. There is often more than one term used for things. As we become more and more technological though we tend to invent new and usually shorter words for doing the same thing. Imaging is shorter than astrophotographing, so easier to use and therefore may eventually replace it? In Fox Talbots time Louis Daguerre's rather better quality (Betamax v VHS of the 1840s) but rather vainly named daguerrotypes had already been demonstrated before Fox Talbot showed one of his. It wasn't as commercially friendly as Talbot's but maybe the name was part of the reason it lost out in the long run?
  6. Eyepiece for frac

    Baader Hyperion are the next step up or Explore Scientific 62/68 range . I have Baaders , ES 62 /82 and BSTs - and BSTs punch well above their weight .
  7. So, I bought a skywatcher 130p loved the images but hated the wobbly mount. Cashed it in for an st80 on a tripod, same issue and less "good" image (qualifier: me, my eyes, my preferences) Decided I needed a rock of a mount and found a bargain heq5, bought it, never used it due to the faff of storing it, setting it up and hoiking it to the garden. Moral of the story for me is I'm an occasional astronomer with a buying fetish. big heavy gear is a no-no. Still have the st80 which is perfect for my needs. I'm going to build a portable pier from plywood for stability and then geek out on a small head/mount, maybe a star adventurer, cos you know, why not. Have a think guys, sometimes all you will need is a small "toy" scope to sate your astro desires. Nick
  8. Heart ic1805 in Ha

    I see there is a 30 day trial, so I'll have a go soon I do like the pix insights way of doing it all, but it cannot be perfect on all types of processing, I guess.
  9. Could you post the entire first and last subs (rather than just crops) so that any change can be looked for? Thanks.
  10. Eyepiece for frac

    I have BST`s and they perform brilliantly in both my scopes a 8" F/5 and the Tal 100rs F/10
  11. Show me your eyepiece cases

    Stanley Tstack! I'll have to have a look and see if they're any cheaper than the DeWalt version. The drawer units in particular look useful as they would still be accessible while at the bottom of the stack.
  12. Spring narrowband targets?

    Galaxy season is definately upon us........
  13. My centre spot is very slightly off-centre and I was too tight to pay for another reflective spot so I'm putting up with it. I can get collimation close with the Cheshire then fine tune with a star test but the Cheshire seems to be good enough. There is a good tutorial for centre spotting the primary on the Astro-Baby website. http://www.astro-baby.com/TAL Telescope Rebuild/Telescope Mirror Cleaning.htm If you use the template just size it up against the mirror and take your time to line everything up before sticking the spot down. Good luck.
  14. M 51

    Thank you very much. Glad you like it.
  15. I have for sale my very lightly used 10mm and 20mm Orbinar plossl eyepieces. Bought new last year to pop in the case of my Equinox 80 as a grab and go complete set up when I'm on holiday, but I always find that I just take my eyepiece case anyway so end up not using these as I favour my BSTs. Nice clean pair of eyepieces for either a beginner or to use for outreach etc. Note: the 20mm has an end cap only as shown in the photos, however the 10mm does not come with any caps. They do not have bolt cases, and will be posted out well wrapped and protected. Would prefer to sell as a set, but will split if no takers on the two by the weekend. £20 for the two including 2nd class signed for delivery, uninsured. Thanks for looking Vicky
  16. Am I a dinosaur?

    My 2 pence Surface etymology is photo- +‎ -graphy, together meaning "drawing with light" or "representation by means of lines", "drawing". From φωτός (phōtós, “(genitive) of light”), and γράφω (gráphō, “I write”). I like this picture the Latin of the meaning of the word photography means. I Write with Photons! that is in my opinion a beautiful meaning of what our type of photography aims to do. Paint with light. I would much rather call myself a painter of photons or a writer with photons but I guess imager will have to do or astrophotographer. Gerry
  17. Eyepiece for frac

    Different scope, but I found nothing special when I used 'better' eyepieces on my scope. Like I said. different scope, f/6 but selling the better eyepieces says something about the Starguiders? Your 8mm should be ok on your f/7.5, but your nearing the limits for the scopes maximum practical power
  18. http://www.astrobuysell.com/uk/propview.php?view=134794
  19. Eyepiece for frac

    Thanks Rob, good to hear from you. How's the celestron cpc 11 going?
  20. Surely if the speed of light (that is to say the speed at which photons travel) were infinite (Can anyone actually comprehend such a speed?) surely Maxwell and Lorentz would be broken. Just sayin'
  21. Show us your Solar Observing Equipment

    Yes I can see a doublet may help with that, but surely that doesn't require ED glass?
  22. blue Star

    Really beautiful colour and diffraction patterns. However, the slightly triangular shape makes me think the telescope may have pinched optics... Correct me if I am wrong. Dan
  23. Eyepiece for frac

    Hi Steve, the eyepieces you have should be sufficient. But you could try a Baader Hyperion eyepiece, they are pretty good value, and decent eyepieces. FLO- Baader Hyperion
  24. Cone Nebula

    f3.8 carbon astrograph - that's why!
  25. Really nice winners, well deserved Fay
  26. Just joined the H alpha club.

    Still have not popped my Ha cherry. The Sun is just still too low from my location. Its blocked for the most part by trees. Ill wait til its higher.
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