Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

  • Announcements



Advanced Members
  • Content count

  • Joined

  • Last visited

Community Reputation

1,163 Excellent


About DirkSteele

  • Rank
    Sub Dwarf
  • Birthday March 9

Contact Methods

  • Website URL

Profile Information

  • Gender
  • Interests
    Astronomy has been a part of my life since I was 3 years old, so I have been looking up for about 30 years, and using telescopes for about 25 years. My education followed a similar path and I left University having studied Physics and Astrophysics at both Undergrad and Masters level. I was also a founder member of the University Astronomy society and held the position of president in my last year of undergrad and continued on as treasurer in my masters year. My interest now is primarily visual astronomy.

    I currently own 7 telescopes, and the list clearly shows that I am a refractor man. The pride and joy of the collection is a 7" Triplet Apo (f/7) from APM in Germany, as well as 2 smaller Triplets (TMB 115 f/7 and the APM TMB 105 f/6.2 which is my primary travel scope). I also own three ultra portable Takahashi fluorite doublet Apos, the FS-60 CB & FS-60Q,as well as the FC-76 for those times when the 105 is a bit too large to take with me. Rounding out the collection is my oldest scope, the Celestron Nexstar 11 GPS.

    I love to cook (and eat!), and also collect retro video games, though prices recently have gone through the roof, so that has taken a bit of a back seat.
  • Location
    London, UK
  1. Harvest Moon

    Lovely shots. As someone who primary interest is DSOs, is it me or do we seem to get more clear nights (like last night) when the bright search light in the sky is up most / all of the night?! However, last night I was testing some new binoculars so a bright moon was useful to assess ghosting, flares and chromatic aberration.
  2. Nikon WX 10 X 50 IF

    There are a couple of accounts on line where some lucky individuals had some limited time with them and they are apparently spectacular. As one would hope for that price. It does seem as though Nikon have done a bit of a Bugatti Veyron in so far as hurdle all engineering challenges to make the ultimate example, but whoops it costs €4mn per car to build. However, they should be commended for doing so even if they are beyond the ability of most to own. Only problem I see with them is the weight. They are heavy and with my personal belief that bins best quality is hand held grab and go, potentially needing a mount for them to produce the best performance perhaps reduces the desire for a pair slightly (but only a bit... I would still love to own a pair!).
  3. Trying to compensate for something

    Yep, a good point. The Ethos 21mm is definitely the EP for scopes less than f/4. I lent mine to someone with an f/3.5 Dob once and almost had to wrestle it back from him! In your example it gives a 7mm exit pupil which works. If we were to compare this f/3 to say and f/5 which if I recall the big Obsessions were a few years ago, that same 32" scope would be best served by the 31mm Nagler (using the Tele Vue line up) with a 0.59 degree field (131x and 6.2mm exit pupil). However, nothing in their EP offering gets to the same max field available in the f/3 model without having to large an exit pupil. But it can obviously be achieved going down the custom route. Siebert Optics make some huge EPs (up to 110mm in a 4.3" body), just need a focuser that can accommodate them I guess.
  4. Trying to compensate for something

    When I first read @swamp thing comment, I thought yep I have been a fool and not thought about that properly, just seeing a very long telescope and thinking narrow fields of view. However, I have now thought about it a bit more and I am not so sure. Perhaps the practical reality is somewhere in the middle of the two statements made. But please tell me I am being an idiot if I am way off base here. Laying out a couple of critical formula to use: Magnification = Telescope Focal Length / Eyepiece Focal Length = Telescope Aperture / Exit Pupil Which can be rewritten as: Exit Pupil = Telescope Aperture / Magnification which also = eyepiece focal length / Telescope f/# True Field = Eyepiece Field Stop Diameter / Telescope Focal length x 57.3o True field can be approximated to Eyepiece Apparent Field / Magnification (though aspects like amount of rectilinear distortion can mean it is not quite precise, but field stop diameter is not always a known quantity). Let us consider two telescopes, both with a 50cm mirror (I want!) with one scope a step ladder requiring f/5 focal ratio and the other a fireman’s ladder inducing f/7 (perhaps unreasonable but helps to illustrate the point). Starting with the f/5 scope, using a 55mm Plossl such as the Televue would yield a 45.5x magnification and a true field of 1.1 degrees which is the maximum achievable with a 2” eyepiece in this scope. However, the exit pupil is an unusable 11mm, so your pupil diameter will stop down the telescope considerably. However, switching to a 31mm Nagler Type 5 (yes I am a disciple of the church of Tele Vue ) yields a magnification of 80.6x, true field of 0.96 degree and an exit pupil of 6.2mm. Now turning our attention to the f/7 scope, the plossl yields 63.6x at a 0.75 degree field and a slightly too large but arguably useable exit pupil of 7.9mm. The 41mm Panoptic yields the same true field but a better exit pupil of 5.9mm. Using the 31mm Nagler results in 112.9x, 0.69 degrees and an exit pupil of 4.4mm. So the maximum available field of view available is greater in the shorter f/# scope with production line available eyepieces. Of course, hypothetically two scopes of the same aperture can always achieve the same max field of view, but to do so in this example would require a custom made eyepiece (but if you can afford that monster, then a custom EP might well be within your means). In my f/7 example scope above, the field stop diameter would need to be approx. 59mm to yield the same field as the 31mm Nagler in the f/5 scope, so a 3” format eyepiece would be needed. That 30mm, 100 deg Explore Scientific monster 3" EP is not quite there at around 0.86 deg true field. I guess what I have also illustrated is just how important the development of eyepieces with very wide apparent fields such as the Nagler and Ethos are to the giant Dob mob. But as Steve says, when you start considering all other issues like coma, required collimation precision and fabrication difficulty (cost) you cannot quite have your cake and eat it!
  5. Trying to compensate for something

    Stubby all the way! If I were to ever buy a big dob (and I would have to get over my "mirrors are for shaving point of view") I would definitely go short and stubby. The advent of the very short focal length mirrors in the world of large dobs brings back into play the familiar favourites.
  6. Trying to compensate for something

    While I would love to have more than a peak through that monster, one issue I would think would present itself is the focal length. The big show piece objects (M42, M31 etc) just would not fit in the maximum achievable field of view so you would be unable to view familiar friends in a new light, thus forcing one to chase ever smaller, dimmer objects which perhaps negates some of the aperture advantage. However, being able to chase down stuff from the PGC catalogue would still be fun!!
  7. Travel scope or binos?

    How much are you looking to spend? There are advantages and disadvantages to both. The scope, even with the same size aperture will give more flexibility to view different objects optimally dues to varying magnifications available through taking different eyepieces. Binoculars you are stuck with one field of view. However, Bins are truly grab and go (the smaller ones at least) as they can be hand held. A scope will require a tripod and mount which adds to the equipment that must be carried. I travel a lot and prefer scopes, but I must admit I do find myself some times thinking that the ease of binoculars would be rather nice.
  8. Taking RC8 on airplane

    Who are you flying with? How heavy is the scope and what bag will you be transporting it in if it came in the cabin? Maximum dimensions and weight need to be considered. I have flown many times with scopes (all refractors of 4" an under) and I would would be pretty uncomfortable about leaving a scope at the mercy of baggage handlers. Always comes into the cabin with me. Some of the budget airlines will let you purchase a second seat for something that is over sized / over weight so that could be an alternative option.
  9. Best sky app

    I think Sky Safari is particularly good. There are three versions at varying price points, the Basic, Plus and Pro, which have varying levels of plotting accuracy (forward and back in time) as well as depth of the catalogue of plotted objects. Some versions also permit telescope control etc. I believe the Basic was offered free in recent days and it still might be.
  10. Lagoon, Trifid and Friends.

    Keeping the 30 second theme going I see! Very nice image. One of my favourite regions to explore visually. Love having both M8 and M20 in the same low power field.
  11. I cannot speak to that bag specifically, but I have one of the Geoptik bags that just holds the mount (rather than the tripod as well) and I was quite impressed with the quality and strength.
  12. Gary Fildes, inspirational book.

    I received this book as a gift on my last birthday. I really must read it. Thanks for reminding me.
  13. Ideally, the best stargazing is found in the period between when Astronomical Twilight ends in the evening and begins in the morning. Astronomical twilight is defined basically as when the centre of the Sun is between 12 and 18 degrees below the horizon. Once it is below that lower threshold, the sky can be considered properly dark. However, at such high latitudes as Elgin, a good portion of the summer months, that is never achieved (in fact not even Astronomical Twilight is reached). This link will show Astronomical Twilight times (and Nautical and Civil) for your location at any time of year. http://www.ukweathercams.co.uk/sunrise_sunset_times.php Of course in this fair land of ours with its wonderful weather, best advice is get out and enjoy the sky you have when ever you have the opportunity!
  14. Total eclipse in north carolina

    Definitely one of the most amazing sights you can witness. Lovely images.
  15. Astro Baby website back up

    Excellent!! Good to see it back.