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Chipela

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  1. I've been observing for a year now and I'm considering to upgrade my gear. I currently have SW 150PDS and since I constantly feel it limits how much I can see of the deep sky objects, I'm considering to buying a bigger Newtonian. There just seems to be quite many options and I'd like to ask some info about a couple of tube parameters. 1) f number Considering purely visual observation, what difference does the f number make (e.g. between 8" f/4 and 8" f/5 tubes)? I know that a lower f number is more demanding for eyepieces and correct collimation. But is there anything else? Assuming that I adjust my eyepiece collection so that I get the same magnification (e.g. 50x would require 16mm EP for f/4 and 20mm EP for f/5 scope) is the resulting image similar? Or is it brighter or otherwise different with one of the tubes? The reason I'm asking is that my Televues should be able to cope with f/4, and a 20-25 cm shorter tube would be very tempting, but I'd like to know if f/4 is inferior in some area. 2) Aperture Does 8" give a considerably brighter image compared to my current 6" or should I jump to 10" to get a real visible improvement? 10" is not that much more expensive but it would mean that my EQ5 which should still work with 8" for visual observation would be too light to be used with 10" tube and suddenly I'd need to upgrade the mount too. (And dobsonian does'nt feel like a good option, equatorial breaks to small pieces and is easier to move around.) Thanks!
  2. I went through exactly the same thinking, I was about to build a setup using SW150PDS + Televue 4x PM + Canon EOS body. The problem seems to be how to record 1:1 video which is essential in planetary imaging. Full view recording on Canon EOS doesn't capture all individual pixels but downsamples the image quite badly. A better solution would be to enable liveview, zoom it to 5x/10x and record the liveview image via USB cable using Backyard EOS or similar application. The resulting video should be 1:1 containing a central crop of the EOS sensor output. I strongly considered this option but had suspicions that the camera or recording software are not necessarily well optimized for planetary imaging. Televue's 4x PM is also quite expensive and not so versatile in other uses. I ended up buying Televue 3x Barlow, 35 mm extension tube and a special planetary camera ZWO ASI120MC with approximately the same money that 4x PM + Canon EOS adapter would have costed to me. They have already given me very good results. The capture application (freecapture) has all needed planetary imaging related settings and the 3x Barlow is also useful with my eyepiece collection to fill some gaps. So all in all I'm very happy with the purchase. Any way you go, the T ring and 2" adapter should be ok because in planetary imaging, only the central area of the frame is interesting and the clear aperture of T ring is more than enough for that.
  3. Thanks for all nice comments and special thanks to knobby, CraigT82 and Michael for pointing out the option to add distance between Barlow and sensor. I have seen the graph by Televue (linked to by CraigT82) but somehow overlooked it because my thinking has been that proper focusing dictates the distance of the elements of the optical train. It's kind of a new concept to me that magnification can be adjusted by an extension tube and focus can still be reached.
  4. It's amazing what one can do with quite modest equipment! I think the biggest single factor (with this image) was great seeing, I was able to keep 50% of the 5000 image stack so there is quite much fine detail.
  5. One thing about the conditions: I live at 60 degrees north so Jupiter doesn't rise that high, current maximum is about 36 degrees
  6. I started practicing planetary imaging just a few days ago and this is my second try on Jupiter. First night didn't go that well but I think this came out very nicely, what do you think? Two questions: Do you think Powermate 5x would work with my 6" scope and give a bigger and better image or would that just lead to a bigger but softer image? I.e. is my setup already resolution limited? Do you see any immediate problems in post processing? Best regards and thanks! -- Very good seeing, Skywatcher 6" f/5, Televue Barlow 3x, ASI120MC, Firecapture + AutoStakkert + RegiStax + Photoshop
  7. Thanks for a very clear answer. I did some math to find out the size of Jupiter in pixels when selecting the Barlow so that the sampling is optimal for the resolution of my scope. -- CN has a formula for optimal focal length: FL(mm) = 3.6 x Pixel Size (microns) x Scope diameter (mm) For 6" tube and suggested cameras (3,75um pixel size) the formula gives 2025 mm. A suitable barlow would thus be 3x (3x*750mm = 2250mm). The vertical FoV would be (considering that the height of the 1/3" sensor is 3.6mm): FoV = 2 * atan (sensor size / FL / 2) = 5.5' Considering the size of Jupiter just now (44.5") that would mean that the diameter of the disc of Jupiter on the image would be: 960 pixels / 5.5' * 44.5" = 130 pixels Just makes me wonder if this is too small size to be appreciated (assuming that each pixel has information, i.e. capturing conditions and processing are perfect).
  8. What would be the most practical way to extend my visual-only rig (EQ5 + SW 150PDS) to do specifically planetary imaging: * attach my Canon EOS 100D * get a web camera * get a color CCD camera or something similar As far as I have understood correctly, I'd need a coma corrector, barlow lens and adapters in all options. What is the practical focal length for planets? Is it impractical to try to reach those numbers with a relatively short OTA (f = 750mm). Thanks a lot!
  9. Well, let's just say that planetary imaging would be so much easier for me compared to DSOs because I could do it even from my backyard which has quite a lot of LP!
  10. Chipela

    Horse head and Flame

    I like the image, also the noise. Noise is not necessarily desirable in astro images but it gives this shot a nice, ethereal feeling!
  11. A quick question: How can I calculate the effective focal length of the optical assembly when capturing a photo through eyepiece? By effective I mean the required focal length of an OTA (x barrow multiplier) needed to achieve the same FoV if attaching the camera directly to the OTA. I guess that it might be (OTA focal length * (camera focal length / eyepiece focal length), e.g. 750mm * (24mm / 4.5mm) = 4000mm but is that correct at all?
  12. Thanks Neil! The technical data is: Equipment: SkyWatcher 150PDS / Televue 4.5mm / Canon EF-S 24mm 1:2.8 / Canon EOS 100D (handheld against the eyepiece) Exposure: 1/80, F3.5, ISO800 Processing: Cropping, levels, removed some jpg noise
  13. Another clear night! I observed exclusively Jupiter for an hour or so. This time there were no clouds suddenly covering the sky and ending the session. To my eye, the sky was at least as good as in my original observation report. And this was the first time I saw the great red spot! I even snapped a photo of the great sight. (Through eyepiece, no stacking, jpg original, so not that great quality but hey, it's my first one! )
  14. Thanks for answers. I see that my question was over simplistic, I assumed that scaled designs would be more common. The references you provided look interesting, thanks for those as well!
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