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bobro

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About bobro

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    Star Forming

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    Isle of Wight
  1. Following the strange dark red/yellow sky in the southern UK on Monday, I captured additional subs of M33 later that night to add to some taken a couple of days before. Next day I had trouble with the colour of M33 - rather purple looking. I think this means an absence of green - same effect as during the previous day with the curious skies making green plants lack colour. The subs from Monday are certainly different from the previous ones, so something changed. Image is 42 subs @ 240 secs with 650/130 reflector on CG5 (cropped). Tried to get the colours a bit better. Anyone else have this problem?
  2. m33

    Lovely image, especially as I've just imaged M33 for the first time with much inferior results. What #subs and exposure length did you use? (Quite surprised to see my GIMP stacking demo showing a noise reduction demo referred to here - someone must have looked at it! )
  3. Deep sky, planets, viewing, astrophotography - very different requirements and one setup won't do it all. As advised above, best to do more research and decide which requirement is most important to you. You may then find that £1k doesn't go very far, especially for astrophotograhy.
  4. I had these on my CG5 (same as EQ5) but have just replaced them with belt drive NEMA 14 stepper motors due to general slack in the SkyWatcher motors making guiding a bit less accurate. They are a straightforward way of getting guiding going though. I used them with AstroEQ as a simple and low cost way of having goto (with EQMOD and Cartes du Ciel) but I couldn't get DEC dithering to work due to a combination of motor and mount backlash.
  5. Another go at Dumbbell Neb

    Image seems relatively small (doesn't expand when viewed) so difficult to comment on it.
  6. Not Brilliant Guiding

    Thanks @alacant. Note - APT supports dithering via PHD2 (this is what I use). I probably didn't explain my question well - my question about dual axis dithering was more about settling. E.g. if single direction DEC guiding is being used with a PA offset to induce drift, this will require DEC MinMov to be smallish to prevent a large DEC sawtooth. When DEC dithers backlash will come into play, possibly making settling time very long (if at all) as DEC hunts around trying to settle within MinMov and possibly overshooting. Perhaps I'm missing something?
  7. Not Brilliant Guiding

    This post is interesting as I have been working on the same DEC backlash problem with my recently acquired CG5. With my EQ2 (not much DEC backlash as not a worm drive but a paddle) I made use of dual axis dithering and wanted this to work with the CG5. Initially backlash was very large with the SkyWatcher DEC motor so I changed it for a NEMA14 stepper motor with belt drive. Although there is still significant (though reduced) backlash, I've found a solution that works by having a large MinMov DEC setting and very accurate PA. The large DEC MinMov setting allows for a reasonable DEC settling time after dither - it doesn't matter where it settles, as long as it doesn't move much during an image due to accurate PA. DEC error is typically in the 0.6-0.7 arcsec range. I wonder if the single direction DEC guiding you guys are trying out will support dual axis dithering? I can't work out how it will - perhaps someone can explain. As for CG5 RA guiding - let's just say another stepper motor is in the process of being fitted to the RA axis.......
  8. Fixing these star trails?

    That's a very neat way of diagnosing a polar alignment issue!
  9. Fixing these star trails?

    Sorry - was in a bit of a hurry this morning and forgot you had already mentioned no guiding. 1) Drift alignment is a very good way to achieve accurate polar alignment and especially useful as you have a permanent setup and won't need to keep repeating it. 2) Yes, this is coma. Just for fun a piece of cardboard can be used to reduce coma - see my post for info which shows the same image with and without coma : Regarding using the webcam for guiding, yes it can be used (I started out using a Microsoft webcam for guiding) though lack of sensitivity can be a problem with needing to rotate the guide camera in order to find a guide star. Depending how you feel about cost and DIY, a sensitive guide camera can be made from an AR0130 module - this is what I use and it finds a star without needing to be rotated. Good guiding can't make up for poor polar alignment though as rotation would be the result. Info on a guide camera : You've probably guessed by now I like coming up with ways of making things - I made my own coma corrector as it's difficult to find one for a 1.25" focuser : https://stargazerslounge.com/topic/288608-diy-125-coma-corrector/?tab=comments#comment-3163837 Hope you get the alignment sorted out.
  10. Fixing these star trails?

    Certainly coma (stars towards corners having tails pointing away from the image centre). Also looks like polar alignment error - this results in rotation about where the guidescope is pointing as guiding ensures the guidestar stays in the same position. A shorter exposure will reduce the rotation, but of course better polar alignment is necessary. How are you achieving polar alignment at present?
  11. What is wrong with my Flats

    Keep banging away! (I'm doing that trying to improve RA guiding - on my 3rd stepper motor!) To my eyes the lighter patch isn't central. As @alacant requests - a flat frame will show collimation.
  12. Fixing these star trails?

    I agree with @alacant : there are round stars so tracking isn't suspect. More likely an optical issue such as collimation, coma or coma corrector alignment, possibly in conjunction with polar alignment. To eliminate tracking and polar alignment just take a short exposure (e.g. 20 sec) at a high ISO of somewhere in the Milky Way to ensure there are lots of stars. No processing required - just a jpeg of the image.
  13. The Pleiades

    I think you have a sound understanding John. Longer exposures may not always be the best solution. FYI - I have a CG5 (same as EQ5) and am using AstroEQ for goto. Whilst AstroEQ is a great product, you have to be a bit careful with the stepper motors used. I started with the SkyWatcher motors supplied with the simple hand controller. The results were ok, though the DEC motor backlash was too much so I replaced it with a better motor. Now I'm in the process of replacing the RA motor to reduce RA guiding jitter. This means understanding a bit more about how microstepping works - so far I'm on the 2nd stepper motor type and think this is ok. A bracket will soon be made for testing. A DIY approach is great fun but has its challenges! Bob
  14. The Pleiades

    Stretching an image in software is basically doing the same thing as increasing the camera's ISO - amplifying the image. So, ignoring effects such as read noise and dynamic range, changing ISO / stretching in software do basically the same thing. So you have more than just exposure time and ISO - stretching amount is another variable under control. Stretching a histogram cannot clip the black point as stretching applies amplification (like increasing ISO), making image points brighter. As you say, ISO800 is a good compromise setting for a 1000D.
  15. The Pleiades

    The ISO setting makes no difference to the image captured by the sensor. It controls the 'amplification' used when the image is read from the sensor. So there is no need to double the exposure time when ISO is reduced. Image processing software is used to set the final brightness. As @John78 points out, read noise is lower at ISO1600 for a 1000D, though dynamic range is better at ISO800. Noise in your image is due to sensor pixel variation. This is best reduced using dithering - trying looking up 'Walking Noise'. HTH
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