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mikeDnight

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About mikeDnight

  • Rank
    Sub Dwarf
  • Birthday 04/02/62

Profile Information

  • Gender
    Male
  • Interests
    Lunar & planetary , binary stars & comets.
    Visual astronomy in general and an advocate of sketching as an aid to observing.
    I also have a passion for refractors and optics in general, and have a deep interest in the history of amateur astronomy, the astronomers and their scopes and observatories.
  • Location
    East Lanc's

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  1. I've absolutely no idea about the strehl of the FC100D series. Tak seem to leave it to the individual, or indeed the forums to debate. The SW 120ED's are superb scopes, of that there is no doubt! The differences between the SW ED and the FC100D are not immediately that noticeable or obvious. You'd notice a reduction in brightness by moving from 120mm to100mm, but you'd also notice a lack of any visible CA in the Tak. As regards strehl, the Tak must be very high I'd imagine, as on a steady night it will just keep taking magnification, without any image breakdown, until you run out of exit pupil, or at least that's how it seems. I also think you'd notice an improvement in contrast and definition of lunar and planetary detail. Considering that the Tak will not show more detail at high power than any other apo of the same aperture, as its limited by its resolution, you could argue why bother to change scopes? For me its the higher quality of optical finish that appeals, as I'm able to increase the image scale of a tiny object like Mars, which I'm still observing, and see detail on its surface with relative ease. May be also, the 100mm aperture is better suited to my local seeing conditions. I've owned bigger Taks that haven't had such a pull on me as the FC100, possibly due to its minimal build I'm more inclined to observe at a moment's notice. A couple of nights ago I'd given up on doing any observing, so i had a shower and lounged around in my PJ's and dressing gown. Just before bed time my wife informed me that the skies had cleared, so.....
  2. I've read the same information somewhere, probably in a review about diagonals. However a couple of years ago, a group of friends and i had our scopes set up for a side by side compare. One of the scopes was a Takahashi Sky 90. We spent the evening looking at the moon, Venus, Jupiter and numerous star images to try and define any differences. The Sky 90 was the weakest of the scopes as it just seemed to lack the punch of the other refractors. Part way through the session, I suggested to my friend who owned the Sky 90 that he should try a different diagonal. Without giving any consideration to the short F ratio of his scope I handed him my Tak prism to try. The planetary performance of the Sky 90 with regard to the level of detail on Jupiter was instantly, and very noticeably enhanced. He chucked his mirror in the bin and bought a Tak prism. Now I'm not suggesting that the same result would occur on other short refractors. It may be that the Tak Sky 90 is a special case, as its lens configuration is different from the similar looking but longer FS series. On the Sky 90 the two elements have a greater seperation than the Fraunhofer FS. This was done i believe to allow better correction of various aberrations that would normally occur in such a short focus scope. The Fraunhofer lens design of the FS series of fluorite refractors reach their lower limit at F8, as any shorter and the level of CA would be unacceptable. By altering the lens design slightly and widening the seperation between the elements, the Sky 90 still maintains excellent control of CA. The alternative would have been for Tak to have used a Steinheil design for the lens, which allows excellent colour correction at shorter focal ratios, as in the modern FC series. I have seen some truly awful diagonals in my time, most of which were prisms made by or for Celestron, so i suppose prism quality could play a very important roll in short refractors. Mike
  3. The trick is not to have a diagonal that's a weak link! ☺ From what I remember of Bill's review, the Tak prism came a close second to the Baader Zeiss prism, and was better than any of the mirrors. All I can say for certain is that mine deliveries textbook star images even at very high power, and planetary detail is impressive. I could be coaxed into using a Baader silver diagonal, if someone would like to buy me one. Mike
  4. A Hargreaves Strut may work well, adding to the rigidity of the set-up. Mostly used with long refractors, there is no reason why the HS wouldn't work with a Newtonian. Mike
  5. I used to view straight through nearly all the time for lunar and planetary, but it meant having my scope mounted high up. However, after a short time at the eyepiece, discomfort from being in an unnatural position detracted from the enjoyment of observing. Still I was a stubborn devil and persisted observing that way for years in the belief I was getting a better view. I was not, and now I've a bad back and a creaking neck, dry rott and wood worm, that I'm putting down to bad observing posture. After spending quite some time observing straight through with my latest scope, and then comparing the diffraction pattern both inside and outside focus, as well as comparing planetary detail, I am totally convinced there is zero difference in image quality between the straight and diagonal view. I honestly believe that a modern, good quality diagonal, mirror or prism, will not degrade the image. Also, any perceived improvement in the diagonal free view is probably illusory. Discomfort will cause an observer to see less over time. Conversely, a comfortable observer is likely to see more. Attached is my silly straight through set-up from ten years ago , and my more sensible and comfortable set-up that I use today. Mike
  6. The glass doesn't do nothing. It's the accurate figure on the concave mirror surface that forms the image. The aluminium coating merely enhances reflectivity. Mike
  7. Superb report! You sound like you had much better seeing than I did, but I managed to see much of what you describes through the wobbly seeing. I'm glad you mentioned the dark southern edge to the GRS as I sketched it in my wonky, rapid eyepiece sketch before the clouds headed in again. Mike
  8. Laughing is usually preferable to crying. You could do both of course! 😂😂😂 Newton, a great british scientist, designed and created the Newtonian reflector, and James Nasmyth a great british astronomer, designed a superb altazimuth mount. Dobson, an american, invented half a box! If only Nasmyth had been called Dobson!
  9. Here's a thought Alan, You could collect the entire set of LVW's as they come up second hand from time to time, and resolve your rebalancing issues by doing so. There are few things as mouth watering as a fine, matching, set of quality eyepieces, or am I just really sad!? Mike
  10. Hi John, Sometimes the area in the armpit of the festoon can appear noticeably brighter and can appear to be a white oval. This can especially be the case where the festoon reattaches itself to the equatorial belt, creating a garland. Mike
  11. When I first built my 7'×8' run off observatory some six or seven years ago, I used a Helix Hercules altazimuth fork with a Equinox 120ED mounted on a central steel pier. I can't find any photos from back then, but it was an ideal set-up for sweeping. I've attached a image of the mount but it was on a field tripod at the time, and also one of the obsy, but now there's a GP mount in place of the altaz. Mike
  12. The 10mm XW is a wonderful eyepiece for DSO's in the FC100, very transparent, very sharp and comfortable to use. Personally I'd avoid the 11mm Nagler as I feel its not in the same league. Ive had all the Naglers in the past and found they varied greatly in performance and comfort, and all gave a warm colour cast to the image. Also, if youre using the Tak prism, the horrid deep undercuts on the Naglers can be troublesome. I've not yet used a Delite but have heard good things about them, though they too will suffer from the undercut issue and will be no better than the XW's optically. You'll have no such difficulty with the Pentax XW undercut as its not nearly as savage as Televue's. Mike
  13. Oh, youve just been spoiled by all that aperture, light grasp and resolution Mike! Or it could be over exposure to all that UV from distant starlight in your 20" has damaged your retina. 😎 Mike
  14. Hi Kerry, I find that rotating the diopters merges or demerges the image in my binoviewers, so i first merge the image, focus the scope so that one eye comes to sharp focus, then retract the out of focus eyepiece slightly until its in sharp focus, then lock it down. I noticed on another binoviewer belonging to a friend, that the locking screw seemed to push the left eyepiece out of true, and demerging the image in the process. There are generally three screw holes, if your bv uses locking screws, so you may try using alternative holes if you find its the locking screw pushing on the eyepiece that's causing a problem. Ive placed the screws on the inner holes of my bv. Mike
  15. You could always sell that DL thingy and buy a DC. That would give you the slightly lower power you're after. I'm here to help!