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About alan4908

  • Rank
    Proto Star

Contact Methods

  • Yahoo

Profile Information

  • Gender
  • Interests
    Astrophotography ! ....at the moment I'm concentrating on deep space imaging
  • Location
    East Sussex
  1. The SW 80ED DS Pro is excellent value for money and has excellent optics. From an imaging perspective, yes, it does have some CA but I'd be amazed if you will be able see it in your images - this is because your post processing skills will need to reach a certain level before they become noticeable. When your skills have reached that level then you can easily correct for any CA by various post processing techniques. From an imaging perspective, I'd say that the weakest element of this scope is not CA but the focuser, which whilst adequate, it is not great. However, if this becomes an issue for you, then can easily upgrade, as I did - which allowed me to go down the auto focusing route. If you want to have a look at some images taken with this scope, have a look in my gallery pages on this site. Overall, I would definitely recommend this scope. Alan
  2. Deep Sky III

    Images taken with a Trius 814 and a Esprit 150
  3. Messier 78 - a dusty favourite

    An exceptional image Barry - well done ! Alan
  4. NGC891

    Thanks for the comment Alan
  5. NGC891

    This is a reprocessed LRGB image was that originally submitted in the Deep Sky section. It was taken with an Esprit 150 on a GM1000HPS and has a total integration time of about 12 hours. I was very happy with the amount of details resolved in the main galaxy. The starfield was processed separately from the galaxy, with the purpose of minimizing the effect of the quite bright red/yellow stars, however, I still highlighted the various small background galaxies. Alan
  6. M81

    This is my first attempt at M81 with my new imaging set up (SW Esprit 150 on a 10micron GM1000HPS). The combination of the scope and the camera (Trius 814) yields 0.7 arc seconds per pixel which seems to work well on this object. The following is an LRGB image, processed in PI and PS and represents just over 12 hours integration time. I do like the colour of the galaxy arms and I was impressed with the details of the Ha regions, given that I did not use an Ha filter. Alan
  7. NGC891

    Hi Tom No I wasn't using PI but a PS tool that I believe uses the liquify and pucker tools within PS. If used correctly, then it does not cause any problems, if you set it at too high a strength, as I did, then you can get issues. Thanks Olly ! Thanks Steve - however, please don't think that you should never shrink stars - just when you do, don't over do-it and double check that everything is OK ! Alan
  8. NGC891

    In order to track down where the vertical star elongation in the star cores came from, I decided that I needed a software tool, so I decided to program CCDstack to highlight the areas in the image where the pixels where either at or near saturation. Using this technique, I went back to my subs and then tracked these through the various processing stages. Although the stacked FITS subs do not give perfectly round stars, they are not the source of this vertical elongation effect, which largely eliminates tracking and optics. Loading the various stages of my processing into CCDstack, I discovered that my experiment with a global star shrink operation introduced the effect. I think the effect is hidden from some people (including myself) and the various software programs (Pixinsight, CCDInspector and MaximDL) because the star halos are rounder than the core - I tend to use separate processing techniques on the halos. So, it would appear that this mystery is solved. Alan
  9. NGC891

    Thanks Dave - the unprocessed star definitely looks rounder to me than the processed version ! Yes - I can see this too. Yes, I think the core and halo have different aspect ratios, with the saturated core being worse. Yes, it is interesting that all the software programs MaximDL, CCDInspector and Pixinsight believe that the stars are quite round. I presume this is because they as looking at both the core and the halo and then they have a weighting about how much each contributes to the roundness. Olly Thanks for performing this analysis, I do like this methodology. Just to let you know that I repeated this myself with PS and CCDStack and obtained slightly different results but perhaps this is because I measured something slightly different ! In PS, I set the eyedropper to point sampler mode and looked at the information window where it gave a saturated (255/255/255) reading. Using this method, I measured the saturated core at 7 pixels top to bottom and 6 side to side. On the halo, I programmed CCDStack to reject all pixels between 50k and 60k ADUs, which gave an annulus of rejected pixels within the star, since CCDstack marks rejected pixels in red, I then simply measured the height (12 pixels) and width (11 pixels) of the outer annuls. Although the numbers do slightly differ from yours, they do lead to a similar conclusion (at least for this star), that within the processed data, the saturated core roundness is slightly elongated in the generation direction seen by some. This elongation appears to be lower if you take both the core and part of the halo into account. You may be correct about the cause being a some form of tracking or optics error, however, I think it is more likely to be due to the way that I've processed the data. I shall investigate. Many thanks for your help and assistance. Alan
  10. NGC891

    Thanks Tom - I'd be interested to know how this star looks on your screen without any or minimal processing (see above post for the info). Alan
  11. NGC891

    Hi Olly, Tom and Dave Since I have a suspicion it has something to do with the way I've processed this, I thought it would be useful to do some measurements at the early stages on the same star. So, firstly, an unprocessed and unstretched RGB TIFF image in MaximDL (showing the star roundness at about 4%) A crop of the unprocessed and unstretched RGB TIFF image (this is the same star as the crop of the fully processed result) RGB unprocessed star crop.tif MaximDL screenshot measurement - still unstretched but after applying DBE, Photometric Colour calibration and SNCR Green (showing star roundness at about 7%) Alan
  12. NGC891

    Dave No, I don't wear glasses (hence my use of a magnifying glass to hopefully eliminate this aspect !). Personally, to solve the problem, I think we need to eliminate the human and screen resolution effects and just try to measure something with a software program. Hi Olly - yes, on the wierness scale I think this is pretty bizarre ! Here, is a TIFF crop of the star that I pointed MaximDL at: Star crop.tif Hope this works since I never attempted to upload a TIFF before. Alan
  13. NGC891

    Thanks John !
  14. NGC891

    Thanks for the information. My screen resolution is 2560 x 1080, I changed it to 1920 x 1080 but I still cannot see any star elongation. I then went around various PC's of various screen resolutions but still nothing was revealed. I then thought perhaps it's my eyesight, so to hopefully eliminate this aspect, I took a magnifying glass and started peering at the screen Unfortunately, I still cannot see anything odd. What I really don't understand, is related to the point made by Dave - how is it possible to see the elongation when zoomed out but not when zoomed in ? I've also found star elongation, more easy to see when zoomed in. Anyway, all very interesting, although I am puzzled. Alan
  15. NGC891

    Hi Dave Thanks for this - this does seem very bizarre. What screen resolution you are viewing the image at ? Alan