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About rl

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    Star Forming

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    pershore, worcestershire, uk
  1. To answer the OPs exact question...I've owned both the Paracorr MK1 and the ES HR coma correctors..at the same time. Mainly using a CT8 f/4.5 scope, sometimes a 12" f/4, I always felt the Paracorr had the edge over the ES for visual use...the image was a little cooler and more transparent (the ES added a very faint sepia tint). The ES slightly but noticeably degraded the image on-axis at very high magnifications using a 4.7mm Ethos eyepiece, but to be fair you don't actually need the correction at this magnification and are better off without either. But it can be nice just to keep it in the focuser to maintain balance or avoid faffing around swapping with extension tubes. Both are very well made. Both give good correction with a 21 Ethos at f/4.5 and f/4. If you buy the ES secondhand make sure it has both the camera adapters. ES don't sell them as spares...I found out the hard way. The adjustment thread on the ES is very fine in comparison to the twist-and-lock on the paracorr, making it a bit of a pain to make large adjustments for perfection with different eyepieces, but to be fair the correction is good enough over a wide range of adjustment so as to just leave it set for your favourite low-power eyepiece. For photography I preferred the ES; the fine adjustment with an accurate scale then becomes a benefit. And the field is certainly very, very flat. It's as good as the Skywatcher aplanatic in this regard. In the end I sold the Paracorr simply because it raised more money and there was little point in keeping both. .
  2. I'm a big fan of the ST120 for widefield visual use on deep-sky. I've owned two; I regretted selling the first and eventually replaced it. The example I have now is quite acceptable on planets at *120; the previous one was not so good so either there is some production variability or they've improved the OG design on the later ones. But they're not a good option for serious astrophotography....the 72mm will be the better all-rounder.
  3. Proof of how powerful a scope the underrated 6" reflector can be in the right hands... well done RL
  4. It is my unfortunate duty to report that losing the will to live is something of a rite of passage with all this computer-controlled stuff...after much bad language, most of come out the other end with something approximating to a working system. I found the videos on the ascom website reasonably helpful. Take heart from the fact that someone, somewhere has got through the same issues..usually on this website!
  5. Yep, I saw that one as well. I would have gone for it had I been in the country at the time...I knew it would be gone by the time I got back.! Congrats on a great buy. RL
  6. Yep, that's about par for the course for me with similar kit! Did you select off the best 25% of the frames in autostakkert, or is it the whole lot?
  7. Can't comment on the 20mm but I have the 3.5mm which I picked up on ABS for a price which would have been rude to walk away from. The 110 deg field is very well-corrected to the edge, but, having compared the two side by side, it is rather spanked by the TV 3.5 equivalent on contrast. On the moon the shadow areas are dark grey as opposed to black. You still get the spacewalk experience, just with the tiniest bit of mist on the porthole...but for the money they're great. I haven't felt the need to upgrade and I am a TV fan
  8. Chromatic aberration is not the only issue with cheap short-focus crown/flint refractors. A lot of them suffer significant amounts of spherical aberration as well, and the field curvature might be a lot less predictable/ correctable. Alacant's suggestion with a Wratten #8 is worth a punt but that's about as far as I'd go. A least from the theoretical point of view, your Newt is a known quantity...any coma corrector to suit the f-ratio should be giving very acceptable results out of the box assuming the spacing is correct. We are taking it as read that you are looking to do deep-sky work here..I don't think it makes it clear in the initial post. A decent long-focus achromat is capable of very reasonable results on planets/ moon with nothing more than a cheap UV/IR filter. Are there any other ways you could optimise your results from the newt, at minimal expense? Are you using a Bahtinov mask to focus? Is the CC spacing optimised? Would a cheap LPR filter help? Processing? If you're determined to go the refractor route, the old blue Skywatcher ED80s often change hands for about £200 secondhand...mine did! They are a very good start, if a bit slow. The focal reducer is a very worthwhile addition. I've been doing astrophotography for 40 years and I'm still amazed at my own talent to mess it up completely either by clumsiness or forgetfulness. Given the infrequent good nights, anything that makes the data aquisition simpler and more reliable has to be a good thing. A small ED frac can be a big step in this direction providing it suits your chosen targets (wide field); easier to mount (half the weight, half the focal length, less than half the wind sail area), don't go out of collimation. They are about the closest thing in astronomy to kit which "just works". It might be worth saving up....optimise the return on those precious hours spent outside. RL
  9. Is this camera still for sale? RL
  10. I can fully relate to the op's comments....lost track of the number of times I've packed up the AP kit on a good night after achieving nothing due to some minor procedural oversight. The sheer simplicity of kit without wires or batteries is an underestimated pleasure too often forgotten.
  11. Not on the eq8 in mild breezes....both the mount and tripod are incredibly solid. The tube rings are far apart and the dovetail is pretty chunky all of which helps a lot. I can have the mount/ota assenvbled from scratch in about 25 minutes aligned but it's not for the faint-hearted. I hope one day soon for a permanent obs. RL
  12. I'm not an expert in correctors but the big 3" Wynne works excellently as far as I can tell but I don't have a full-frame camera. Personally I'm not a perfectionist and don't lose sleep over marginally un-round stars right in the corners but mine covers the field virtually perfectly (always a dangerous word) Having said that I 've had equally good results in 2" format with a skywatcher aplanatic coma corrector, and the ES 4-element jobbie on an APSC sensor. Both admittedly in a slightly slower f/4.5 Newtonian. A lot of issues with these scopes arise either from miscollimation or not having the camera square-on to the optical axis. F/4 is very unforgiving in more ways than one..the depth of the focal plane is tiny. I've been lucky in not needing a tilt adjuster (or maybe I'm just not critical enough?) One other thing; I was told an EQ6 would be ok for an AG12.....NO WAY! It might just about cope with the naked OTA but add in the rings, Wynne, Atlas focuser, filter wheel camera, finder and I was up to nearly 30kg. You are talking about only a 10" but I suspect an EQ8 may be on the cards if you go the full nine yards in 3" format. My EQ6 is just fine with my 8" f/4.5 and 2" kit....
  13. I'm running a very similar rig; a secondhand OO 12" AG12 with a 3" Wynne corrector and FLI Atlas focuser, which is theoretically capable of a 60mm diameter corrected circle at prime focus. It will cope with bigger cameras than I'm ever likely to be able to afford. But the cameras I currently use have an APSC -size sensor which would be quite happy with a 2" coma corrector and fittings. They'e also lighter which is a consideration, not requiring extra support rings on the focuser. The matching filter wheel that came with it takes 2" square filters which is better than a 2" system will do but still would vignette a 60mm circle. I use the big celestron OAG which again vignettes. You can get bigger ones at a price... 3" sounds very good but there is not a lot on the market for spacers, adapters, reducers etc. A lot of stuff has to be custom made which is slow and expensive. You need a friend with a lathe. Just collimating the scope requires a 3" to 2" reducer; one is available off the shelf from TS at 93 euros..... If I were buying new again I would not get the 3" option but settle for the best quality 2" setup I could get. One reason slightly off topic to go for the AG series or TS equivalent is the collomation stability; the spider is machined from solid aluminium plate. RL
  14. With due respect to Nikon (some of whose kit I also own) your lens may prove to be a slight disappointment as a scope even if you can find a short enough diagonal to make it work at all. I don't know this particular lens but I expect it's built to produce excellent colour correction and minimal distortion over a 44mm circle compromising absolute resolution on the process; the design tradeoffs with camera lenses usually give the best resolution when stopped down to about f/4 to f/8. Your lens has the additional design constraint of being a zoom..getting that right will mean the resolution probably is at its best over a limited range of focal lengths. Run fully open at f/2.8 the resolution probably won't get anywhere the Rayleigh limit since the camera pixel size will always be larger than the theoretical spot size wide open, and you will need excellent eyepieces to cope with so wide a cone angle without some horrible off-axis aberrations. Even TV only test to f/4. The usual advice using camera lenses for astro use is to stop them down 1 stop to improve the resolution ans star shapes in the corners. Astro telescopes are built to optimize resolution first, and trade off flatness of field Baader do a fairly comprehensive range of adapters; I don't know if they do a Nikon female to T-thread. They do a helical T-thread to 1.25" focuser which would open up the possibility of straight-through viewing. For low power-wide-field use you might be on to a winner capitalizing on the flat field assuming the eyepiece has an equally flat field. Regards, RL
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