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  • Re: Communal Night-Sky Photography Thread

    Originally posted by MikeOxon View Post
    very crisp and contrasty. What are the exposure and processing details?
    It's actually 3 shots taken hand held using my 300mm plus MC14
    ISO 250, f/5.6, 1/250th sec.

    I stacked them in PS and sharpened a touch thats it.

    The sky was crystal clear for a change.
    Dave

    My Flickr

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    • Re: Communal Night-Sky Photography Thread

      Needle Galaxy. NGC4565. Monochrome so far.
      No Oly kit used so not sure if I should post.

      Last edited by wornish; 14th April 2019, 02:02 PM. Reason: changed image
      Dave

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        • Re: Communal Night-Sky Photography Thread

          Yes nice to see it whatever you took it with. Just out of interest could you have done that with your Oly kit?
          http://www.flickr.com/photos/flip_photo_flickr/

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          • Re: Communal Night-Sky Photography Thread

            Originally posted by Phill D View Post
            Yes nice to see it whatever you took it with. Just out of interest could you have done that with your Oly kit?
            Dave

            My Flickr

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            • Re: Communal Night-Sky Photography Thread

              Originally posted by wornish View Post
              Needle Galaxy. NGC4565. Monochrome so far.
              No Oly kit used so not sure if I should post.
              I find your deep-sky photos inspirational and they have persuaded me to buy a tracking mount, to see what I can do with my E-M1-ii with various lenses, especially my trio of f/1.8 primes (17, 45, and 75mm)
              Mike
              visit my Natural History Photos website:
              http://www.botanicdesign.co.uk/Natur...story/home.htm

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              • Re: Communal Night-Sky Photography Thread

                Originally posted by wornish View Post
                ......... and to some extent the ability to use autofocussing............

                Am I missing a point? I would have thought that all night sky objects are effectively at the same distance - infinity - wrt a camera lens. If I focus carefully on a bright star, why isn't this setting ok for everything else?
                Mike
                visit my Natural History Photos website:
                http://www.botanicdesign.co.uk/Natur...story/home.htm

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                • Re: Communal Night-Sky Photography Thread

                  Originally posted by MikeOxon View Post
                  Am I missing a point? I would have thought that all night sky objects are effectively at the same distance - infinity - wrt a camera lens. If I focus carefully on a bright star, why isn't this setting ok for everything else?
                  You are right in one way that all stars and planets. are from the point of a camera at infinity. But...... and there is always a but.

                  The infinity mark on a lens is not accurate, most lenses, in fact, allow you to rotate the focus dial beyond infinity!

                  So yes once you manually set it by looking at a bright star using maximum digital zoom and getting it to be as small as possible you are OK its a very sensitive adjustment. Remember your depth of field is very small. Then if the temperature changes a just few degrees so will the focus. You end up with bigger stars than you expected. Not the end of the world as you can, in fact, shrink them in post-processing.

                  It seems you are where I was a few years ago when I started with my EM5 with a 12-40mm zoom mounted on a low cost tracking mount on my basic tripod. It of course worked.

                  One thing to think about is battery life. Taking long exposures eats battery life. I could just about get an hours worth of use from a single fully charged battery, then had to change it. So I recommend having a second fully charged battery to hand, its amazing how time flies when you are out there!
                  Dave

                  My Flickr

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                  • Re: Communal Night-Sky Photography Thread

                    Mike you've done what I've been pondering for a while. What tracking mount did you get?
                    Oh and did you see the recent comment I put on your mount images in the Panasonic 100-400 problem thread?
                    http://www.flickr.com/photos/flip_photo_flickr/

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                    • Re: Communal Night-Sky Photography Thread

                      One thing to consider when choosing a tracking mount is polar alignment.
                      The accuracy of polar alignment is a critical aspect of taking long exposure astro pictures. Assuming that you are in the Northern hemisphere it's important that you can see Polaris from your chosen location. If it's blocked from view there are workarounds but they can be very time-consuming.

                      If the tracking mount has a polar scope that's a good basic start, be prepared to get down on your knees Using a polar aligned tracking mount you should be good for at least 5-sec exposures maybe even 30-sec or more.

                      To go beyond that guiding is necessary especially when using telephoto lenses for a narrow field of view, so before choosing a mount check that it can be externally guided.

                      For guiding, you need a webcam attached to a small finder/guide scope and have to start using software. Many people use PHD2 which is free
                      Dave

                      My Flickr

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                      • Re: Communal Night-Sky Photography Thread

                        Dave appologies if this is a daft question but what's the difference between tracking and guiding?
                        http://www.flickr.com/photos/flip_photo_flickr/

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                        • Re: Communal Night-Sky Photography Thread

                          It's not daft at all.

                          Tracking is when the mount moves the attached camera or scope at a fixed rate across the sky entirely under its own control, rotating the camera at the same time. Normally there are three main options:-

                          Sidereal rate - The rate the earth rotates causing the stars to move.
                          Lunar rate - the rate the moon moves across the sky
                          Solar rate - the rate the Sun moves across the sky.
                          then, in addition, there are some faster rates to allow you to slew the mount quickly to point at a specific target.

                          Most entry-level and some professional mounts do this using worm gear drives with attached encoders for better control. The more you pay for the mount then usually the tolerances and gear accuracies in the drive train are higher. Handling backlash in the gears as the mount traverses the sky and the weight on the gear drive changes is another challenge.

                          Good tracking mounts are not bad at keeping track by themselves but even small errors add up. Unguided the average error can be in excess of 10 - 20 arc seconds ( 1 arc sec = 1/3600 of a degree) over a modest angular change. I know it doesn't sound much but it becomes a big issue especially when at longer focal lengths and/or taking long exposures. For short or wide field shots its less of an issue.

                          So the answer is to use guiding, which is basically a method of using feedback to try and lock the mount on a specific target (guide star) so it keeps pointing exactly at the same place to an accuracy of between 1 and 3 arc seconds. Remember how small a single pixel is on modern cameras, it doesn't take much to move a photon from hitting one pixel to the next. Guiding makes use of a small CCD camera to do this and some clever software (like PHD2) that calculates the chosen stars exact position in the guide cameras field of view and then sends short correction pulses to the mount control to make it speed up or slow down and correct for any small changes.

                          Hope that makes sense. Its all good fun - honest

                          There apparently is a saying amongst experienced astrophotographers that it's better to spend more on your mount than on your scope or camera!
                          Dave

                          My Flickr

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                          • Re: Communal Night-Sky Photography Thread

                            Dave, many thanks to the responses both to my question and to that from Phill D, which was a help to me, as well.

                            I think I read somewhere that many tele lenses do not have a 'hard' infinity stop, to allow for both manufacturing tolerances and the effects of temperature. I have tended to assume that temperature would not change much during a viewing session but I guess this may not be true for those very extended sessions, sometimes spreading over several nights. It is my practice to use manual focus with a magnified image displayed on the camera's rear screen.

                            I have seen the term 'focus adjustment' apparently being confused with 'tracking adjustment', when the user applies adjustments to correct for any tracking errors that cause loss of sharpness in star images.


                            You mentioned the difficulty of getting down on knees, to use a polar scope. I read a suggestion to use a right-angle finder, so I intend to adapt the one from my old Nikon system, to help my ageing knees!

                            You are right to assume that I am at a very early stage in my exploration of night-sky photography. I can see your point about battery life, which, I assume, applies to the tracking mount as well as to the camera. I also note your comments about sensor temperature. I wonder whether the Olympus freeze-proof claims would allow dunking the camera in liquid nitrogen? (only joking)
                            Mike
                            visit my Natural History Photos website:
                            http://www.botanicdesign.co.uk/Natur...story/home.htm

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                            • Re: Communal Night-Sky Photography Thread

                              Originally posted by Phill D View Post
                              Mike you've done what I've been pondering for a while. What tracking mount did you get?
                              Oh and did you see the recent comment I put on your mount images in the Panasonic 100-400 problem thread?
                              On the basis of advice from this forum and other sources, I bought a 'Sky Watcher' Star Adventurer Pro Kit. This seems to represent an excellent compromise between cost and quality of construction. The Kit includes a polar scope and equatorial wedge, which I mount on my Manfrotto MT294C3 tripod, which normally carries a Manfrotto 498 ball head, with quick-release fitting for my camera.

                              The tracker itself provides all the tracking options described by Wornish in his posts. There is also a socket to receive correction signals from a guiding system but I have not investigated this yet.
                              So far, I have done very little with this equipment, apart from checking that it works - too many other commitments at the moment.

                              I saw your comment on the 100-400mm thread and it seems to point the finger at the screws used on the Panasonic mount - the plating on the screw heads looks to have been rubbed so, perhaps, they protrude very slightly above the mount surface. I shall have a closer look, when I have time.
                              Mike
                              visit my Natural History Photos website:
                              http://www.botanicdesign.co.uk/Natur...story/home.htm

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                              • Re: Communal Night-Sky Photography Thread

                                Added RGB last night to NGC4565. Full moon and High cloud made the image worse in the end but thought I would share anyway.

                                Dave

                                My Flickr

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