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rotatux

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About rotatux

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    Star Forming

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    France
  1. The EQ3 DSO Challenge

    Beware that if you use a fixed delay in the sleep, this kind of loop has inherent timeshifting builtin because of various lags in execution. Unless it's already the case, you should aim for fixed average frequency, by using the builtin clock to compute the next delay each cycle. I mean something like: avgPeriod = CONSTANT target = clock() + avgPeriod while (tracking) : step() sleep(target - clock()) target += avgPeriod NB: BTW, this kind of code works very well even without any interrupt handling, it will absorb and correct minor local variations of time and execution as long as your clock is stable enough.
  2. Thanks vlaiv, exactly the kind of answer I was looking for. So rays of too wide an angle wrt optical axis are supposed to end absorbed by baffling or coating. Now I can tell where and how my 130PDS has a problem for flats: the painting inside is dark but reflective, and diffusion of strong lights can be seen too just by eye through the focuser without eyepiece. I already made a DIY flocked dew shield, now I need to use it for flats too, and add flocking in the OTA at least under the focuser.
  3. I'm thinking about trying a bias+flats based process rather than my current darks based one. Bias is no problem. Now I'm thinking about the most simple and hopefully successful way of making flats. In case this matters, I will need to make flats for my proper scopes (130PDS and 127MAK) and also some traditional lenses. I have searched and read a bit. I consider the following techniques would be accessible to me: white tee-shirt / plastic bag, LCD screen, and light/flat box. However what striked me is that all those techniques make light sources which are very close to the scope's objective (whether reflector or refractor). At first this seems wrong with the intention of correcting images of light sources at a (relatively) infinite distance, because then the incoming light rays certainly aren't parallel and will also illuminate unexpected places on the camera sensor. I didn't find discussion on that subject. So, what's the trick I missed, and how (and if, after all) can those techniques actually produce good enough flats ? Thanks for reading me.
  4. The EQ3 DSO Challenge

    Nice M1... I personally struggled to frame it (too weak and too small) last year in my H-LP sky and abandonned, so that's some achievement Oh and question about your HH+Flame: what filter did you use ? your colors look like what I get with my UHC...
  5. Weather seems as difficult as here, judging from clouds ;-) Sad you could not track and try longer exposure... However even at F/2.8 I can spot cross-shaped stars at edges and corners, which IIRC means astigmatism. The brightest stars are elongated too, meaning some coma. It could be more clear with a higher exposure. Also remember CA in my tests appeared more easily in long subs or with more stretching, since its intensity is quite low relative to star's peak brightness. FWIW I'm afraid it confirms the difficulty to find a good wide-field lens. But I must also say this Takumar seems to perform way better than my Helios-44M 58mm/2, which I also have some shots at 3.2s in my gallery, showing huge coma.
  6. First Milkyway

    Good first. That hardware can give you plenty. You will get more and more goodies as you learn the (not so difficult) technics. Clear skies!
  7. No all images are uncropped unscaled. Sure but the fast modern primes come with a high price. For the price of a Panasonic 25/1.7 or Sigma 60/2.8 I can have at least 5 if not 10 "good old" lenses. Initially I got into the old lens market because no money for modern lenses, plus they are generally too much closed on focal ratio. For example it's almost impossible to focus manually with my kit zooms 14-42/3.5-5.6 or 40-150/4-5.6. Meanwhile it's quite easy to find open primes within old lenses. However I come to realize that most if not all old lenses suffer from annoying aberrations, and modern optics formulas are much better (though often still debatable IMO). Coming Christmas may help but until then, still trying to find proof of the good old lens.
  8. Hi, a few days ago I posted a 135mm battle. Now here's another one at 50mm. Same kind of procedure, except here 2 different subjects were chosen, which could make a comparison difficult, but both are star-rich fields. Both 20s subs at 3200 iso with E-PL6 on Nexstar SLT, 22x for one, 26x for the other, and darks. First is Perseus double-cluster + Heart & Soul nebulas with MD-Rokkor 50mm/1.7 at F/2.8. Second is Cygnus region around Deneb and Sadr with OM-Zuiko 50mm/1.8 at F/2.8. What do you think ? The Zuiko shows good colors but a very big and entering coma. The Rokkor has less good colors but much less coma. I also like the handling (ergonomics) of the Rokkor more, but I just wonder if the coma of the Zuiko would go away at F/4. I tried to search references on astrobin but it's difficult to tell if cropping occurred or not to mask its coma.
  9. Imaging with the 130pds

    You definitively have some valuable data in that sub : Some nebulosity and nice colors. Your sub is not that much overexposed, I would say it's reasonnable, so that was your stretching. You will do better focus / tracking next time, learning one step after the other (live view focus, exposure settings, stacking, etc.).
  10. Old 135mm battle

    In fact I don't like closing too much as my sub times are limited with an AltAz. Anyway that's another story. If that qualifies, the narrower I have is a UHC which I tried first last year with the 130PDS. It proved to eat most of red and green (and Ha, though I have doubts), to the point I could not equilibrate colors in post-processing. So I'm reluctant to waste my few clear nights retrying it. I may be tempted however to give it a go again, since the PL6 seems more sensitive to reds. You think it could help with red CA ? but then Ha would be even more diffracted than reds, so I doubt it. Or you mean even narrower than this, such as Ha/O3/S2/etc ? No I don't have any.
  11. Old 135mm battle

    Yes exactly: a bit different stretching levels. There was 48min between the 2 shot runs (Oly first), and M31 was resp. 60 and 66° high. I like the Oly for it has a very uniform behavior across the whole frame. However I dislike it's stronger blue CA, and much stronger red CA, over the pentacon. I like the Pentacon for it has much less CA, especially in red. However I dislike it has a stronger coma from 1/2 or 2/3 of the frame. Between the two, maybe the Pentacon's coma is more acceptable than Oly's whole-frame red CA. Just thinking loud: Could a star-6 or -8 photo filter, that I would rotate in small steps every few shots, diffract out the color aberrations to spikes, which could then be eliminated by sigma clipping ? Then Oly would win...
  12. Imaging with the 130pds

    I wish I had my first at it that good Though that's strange all your stars are already burnt at such low ISO, did you use RAW or a cam-produced JPEG ?
  13. The "No EQ" DSO Challenge!

    While zooming you even get the start of a hint of the Flaming Star Nebula. I like this subject, already had a go at it with an old 135 last year, but being a smaller frame it was more on the center part and only catched the top cluster. Not sure I will have the night to retry it this year :-/ You say 75mm and F4.5... is it a prime or a zoom ?
  14. Hello, one (rare) clear night after the other I test my lenses to try to determine which ones to keep and which one to sell back. I find it could be interesting to compare such old lenses (mean: manual, before numeric) by pairs or more to find out what people think of their optical pros/cons. Nonetheless I have a case of mixed feelings about those two I submit. I'm not totally decided because pros/cons balance each other. Maybe I could gather advice and opinions here. I shot the same subject (M31) with both and same settings (12-13 subs x 20s x 3200iso, F/3.7 with ring adapters masking) and setup (E-PL6 on Nexstar SLT). I intended to push processing as far as possible to get most of what could be had from each lens, but it ended with a very close process, maybe only stretch level and color processing differed. First is Olympus OM-Zuiko 135mm/3.5, Second is Pentacon M42-long 135mm/2.8. What do you think ?
  15. Very nice subs, stars are ok now. Next step you want to learn stacking
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