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About Ikonnikov

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    Star Forming

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    West Yorkshire
  1. What you don't show/mention is the quality of the in-focus image; if that's good after adjusting with the star test then why worry about the Cheshire? Personally I would use mechanical alignment as a starting point and always fine tune collimation with star testing when possible; with an RC scope you can follow the procedure below for adjusting your primary and secondary with your imaging camera attached to get very accurate collimation. Since it also relies on images of (slightly) de-focused stars you don't need amazing seeing to get a good result. https://www.deepskyinstruments.com/truerc/docs/DSI_Collimation_Procedure_Ver_1.0.pdf Paul
  2. Great first light with your new camera, agree that the OIII filter is very likely the cause of the halos. I wonder if you might be able to get even better signal to noise using longer sub exposures since the KAF16200 sensor has quite high read-noise; certainly I find that 30 mins per sub helps with the Moravian G3 camera and 3nm filters even on an Epsilon at F3.3 (although I've not gone beyond this so far for reasons of pixel rejection, imaging time wasted by spoiled subs etc). Paul
  3. Using various online calculators (e.g. the Wilmslow Astro website) the airy disk size for green light (510nm) at 80mm aperture comes out at 3.2 arcsec and for red (650nm) as 4.1 arcsec i.e much larger than typical guiding error and larger than typical uk seeing. This being the case then wavelength would have more of an effect on the final image fwhm between oiii and Ha filters than you suggest above. I still typically see smaller star sizes with shorter wavelength filters when imaging with a mirrors only 250mm RC scope (where the airy disc size is in the order of 1 arcsecond for green and 1.3 for red) suggesting some effect of wavelength on fwhm even at larger apertures. Paul
  4. As you mention above, shorter wavelengths will intrinsically give higher resolution images (with a smaller airy disk and therefore star size) than longer wavelengths. The theoretical airy disk size for Ha emission wavelength is 31% larger than for for OIII primary emission wavelength so could this not account for the differences in star sizes? I appreciate that bad seeing affects longer wavelengths less but i don't know at what point this would outweigh the intrinsically larger airy disk size. From experience I've consistently seen smaller star fwhm measurements for OIII over Ha with reflectors and refractors. Paul
  5. Hi Richard, this article might be worth looking at as it highlights some of the potential problems with star shapes that can arise in the esprit scopes: http://interferometrie.blogspot.com/2014/08/esprit-tuning-how-we-finetune-esprit80.html I was going to hold off on my own Esprit experiences for now but since it seems relevant to this thread I'll continue... TLDR is, (especially if imaging in colder weather) it can be a delicate balance with these scopes between preserving element centering/collimation and preventing some pinching of the optics. I bought a new Esprit 120ED last autumn and although perfectly collimated I noticed some funny star shapes & (asymmetric) diffraction spikes in images appearing only when the weather is colder (below about 4 or 5 C) suggesting mild pinching by one or more of the element centering screws (e.g. below). p Seeking perfection (foolishly perhaps) I decided to very slightly loosen the centering screws for the front element (WARNING this is a high risk procedure!!!) The good news is that I managed to isolate the screw causing the problem and stop the uneven spikes regardless of temperature. The bad news is that I managed to very slightly de-centre the element which has made the star halo slightly asymmetric and resulted in a slight lateral colour shift. I can get good star shapes now if I combine subs from each side of the meridian flip as the distortions essentially cancel each other out (see below) but this is hardly ideal. Also aligning RGB channels is problematic. I figured I had two options from here, admit defeat and fork out to have the scope sent back to Es Reid or attempt more advanced adjustment techniques. Since there was no guarantee that pinching wouldn't result again in cold weather after the scope was recollimated I figured it would be better (and more fun!) if I could attempt this myself at home as required. At a not inconsiderable expense I've managed to put together a double pass autocollimation setup with a beam-splitter, focuser-insertable artificial star and optical flat as described in the Teleskop Austria article above and the test setup seems to check out on my (well collimated non adjustable) Tak FC76. Next step is to try it out on the Esprit... Paul
  6. I'm guessing the signal to noise for the short exposures required in this study wouldn't be high enough using a smaller aperture system (with much lower limiting magnitude). Camera lenses have been used in other professional setups I've seen e.g. http://mascara.strw.leidenuniv.nl/technical/ and https://www.canonwatch.com/canon-ef-400mm-f2-8l-ii-lenses-used-discover-new-dark-galaxy-dragonfly-telephoto-array/ although in the latter one, each lens costs the same as 3x 11" RASA scopes! ?
  7. An interesting study published in Nature Astronomy using amateur off the shelf gear for some occultation photometry (alas full article requires online purchase or journal subscription but abstract, figures and raw fits data available here https://www.nature.com/articles/s41550-018-0685-8). In essence they’ve done a lot of high-speed photometry using two identical setups situated on opposite sides of a building roof in Okinawa (both observing the same region of sky) and looked for occultations of any stars with the appropriate decrease in magnitude for the appropriate duration (up to around 1 second for ~1km diameter object) recorded simultaneously with both scopes (to rule out non-astronomical interference like birds/bats etc). To record such a fast transit with enough (temporal) resolution they had to use very short exposures (~65ms) which requires a very fast optical system to gather sufficient light. To achieve this, they used a Celestron Rowe Ackerman 11” scope (already F2.2) and made it even faster with a DSLR to M43 Speed Booster (Metabones 0.71x) and acquired images with a ZWO ASI1600 CMOS camera. Crazily they can get a usable signal for stars down to magnitude 13 with these very short exposures. Unfortunately for the budding amateur scientist, what is described in the paper as an ‘extremely low cost’ system still comes to $16,000 per setup, but nonetheless it’s interesting to see what can be done with gear that people do own here on SGL (albeit not usually in duplicate!).
  8. Thanks for your reply Peter. Yes, on balance I think a small roll off is probably the best option for me all things considered. The functionality of a dome is attractive and the price of the basic small pulsar within reach, but I think the added cost to allow full automation and the appearance in my smallish garden make a ROR option my preferred choice. Paul
  9. Hi Folks, I've been thinking for a while about trying to increase my imaging time by either using remote scope hosting or getting my own observatory and am leaning towards the latter currently (if only I had the dosh to do both...). I currently image from a concrete-mounted metal pier in the corner of my back garden (mount/pier covered with a Telegizomo 365 when not in use) so was thinking of putting a simple small obsy over this (no requirements for warm room or doing visual from it). I don't have the time or skill level required to build my own (certainly to the quality I would be happy with!) so I'm looking at commercial options. After some internet searching I came across the 'Astro Booth' http://astrograph.net/epages/www_astrograph_net.sf/en_GB/?ObjectPath=/Shops/www_astrograph_net/Products/AGOABOOTH which seems to meet all my requirements and be reasonably good value compared with similar alternatives, being fairly compact/robust, relatively easy to construct myself (and dismantle if I have to move house) and with a motorised roof and delivery included in the price. I've only come across one account (at least in English) of someone buying one and they seem to like it, although they used it in Spain so might take a bit more of a battering/soaking here in Yorkshire. Would be grateful if anyone else has encountered one or has any thoughts/opinions on it (good or bad) from the website material etc. Cheers Paul
  10. Very nice Barry. This remote imaging thing is looking increasingly tempting!
  11. When I bought the RC second hand it came with this corrector https://www.teleskop-express.de/shop/product_info.php/info/p2646_TS-Optics-PHOTOLINE-Full-Frame-APO-Corrector---Flattener-for-astrophotography.html (if I remember correctly) which is supposed to be very good for RC from reading around and looks the same as the one you're referring to. Unfortunately with my modified backplate/replacement TS focuser I didn't have enough in-focus when using it at the correct spacing distance. Instead I have this now https://www.teleskop-express.de/shop/product_info.php/info/p4006_TS-Optics-2--corrector-for-GSO-Ritchey-Chr-tiens-w-o-focal-reduction.html (and also this https://www.teleskop-express.de/shop/product_info.php/info/p5120_Riccardi-0-75x-APO-Reducer-and-Flattener-with-M63x1-Thread.html which I'm currently trying out with an Apo refractor), both are small enough to insert inside the 3" focuser drawtube so I can achieve focus ok with them, also they're big enough to avoid significant vignetting on the 16200 chip. Obviously this applies to my 10" RC so things might be different for a 12". Definitely handy if you can fit your corrector in the focuser though.
  12. You can utilise the NIR preflash feature (followed by some CCD clear cycles) as indicated in the image on the Moravian instruments website for the G4-9000 camera, but the default for the G3-16200 is to have 0 sec for NIR preflash (i.e. no preflash) but 2 for Num clear (i.e. 2x clear cycles) so I assume the clear function is important regardless of whether or not you do the preflashing. The KAF9000 chip is very prone to RBI so the preflash is almost a must for this camera but the KAF16200 (and closely related 8300) show virtually no RBI signal down to at least -25C in my and others' (e.g. see Cloudy Nights forum posts) experiences.
  13. Here's an integration and simple stretch of a dozen or so lum frames from the same imaging session (where I managed to guide keeping the target in the centre of the frame). You can see the off axis aberrations in the corners which the field flattener should take care of.
  14. Thanks Richard, no I haven't got round to sorting out the secondary recoating yet, been distracted by various things including deadlines for work and another telescope purchase of the refracting variety (on which I'll post something eventually...).
  15. Thanks Dave. There's a fair bit of distortion in the corners with this set up but overall the uncorrected field is surprisingly good. These images are substantially cropped but not entirely central crops due to position of appropriate guide stars in the field. I'll try to remember to post an uncropped lum sub later. The quality of the stars across the same sized chip should be better in the 12 inch version. I have a 2"TS rc flattener but not bothered to use it yet as i needed to get collimation sorted without it (and also is a hassle to fine tune the spacing). I also now have the small riccardi reducer/flattener to try which gives a slightly less oversampled 0.75 arcsec per pixel along with correspondingly larger fov.
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