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About Ikonnikov

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    Star Forming

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    West Yorkshire

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  1. No worries! I've had the secondary dew up a couple of times after several hours when it's been particularly damp and now use a large dew strap placed around the outside of the tube just above the primary (as recommended by folks on Cloudy Nights) on a low heat setting which works well without noticeably affecting the image quality. This isn't an option for the truss tube version if you're interested in that but you can get a dedicated secondary heater which fits under the mirror with the power cables going across one of the spider veins (to prevent them from creating unwanted diffraction
  2. Once you've done the fine tuning and are happy with it, it should hold collimation pretty well for months/years; I dismantle my setup after every imaging session and I've only had to redo it once after accidentally bashing the end of the scope on a door bringing it in the house.
  3. I have the old Altair Astro solid tube version of this scope and like it a lot, although it took quite a bit of work to get it up to scratch. I strongly recommend getting a version that has the primary mirror cell decoupled from the focuser (I think this is the case for the newer truss tube versions) otherwise collimation is very tough. Once you get the collimation close with tools (e.g. a cheshire) you can fine tune it with your camera attached by inspecting star shapes (see the DSI method on the web) to get it pretty accurate. Then it seems to hold pretty well. In answer to your questio
  4. If the reference scope is much larger in aperture than the test scope wouldn't this help to reduce the apparent error (assuming the lager scope was reasonably well collimated)? I seem to remember people on CN using big dobs for this purpose.
  5. Yes, its a reducer/flattener; as far as I know all Takahashi reducers are. You can see the optical diagrams here (under documentation): https://www.telescopes-et-accessoires.fr/fc-76dcu-ota-tube-seul-au-coulant-3175-pare-buee-non-retractable-c2x30343677
  6. I also had a go at a drizzle experiment recently, and came to a similar conclusion: Capturing subs on my E130D with a ASI290MM (giving 1.39 arcsec/pix image scale bin 1x1) with medium SGPro/PHD2 dither between each sub, using PI for (pre)processing. Capture 1: 64x subs bin 1x1 15sec exposure, registered with auto settings and integrated with default linear clipping rejection settings. Average FWHM about 2.8 arcsec by PI FWHM eccentricity script (Moffat 2.5), similar values by dynamic PSF of a selection of stars. Capture 2: (back to back with capture 1, no obvious change in sky
  7. These images have stars with low snr (especially Ha one) and a lot of hot pixels which are being picked up as stars by the PixInsight script and very significantly lowering the reported FWHM. Manually measuring each of the stars with dynamic PSF gives an average of about 5pixels (2.6arcsec) FWHM for Ha and 3.2 pixels (3.3 arcsec) for OIII, so I'm in agreement that by most measures you're considerably oversampling here. From my understanding, optimal sampling rate for DSO imaging (i.e. to record maximum detail without oversampling) is a continued source of debate on this and other astro f
  8. 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
  9. 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
  10. 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
  11. 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 reflecto
  12. 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 autu
  13. 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! ?
  14. 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
  15. 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
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