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

    sgl_imaging_challenge_banner_lunar.thumb.jpg.ef4882eb5fb3610f8a68e5e6913de0e3.jpg

YKSE

Advanced Members
  • Content count

    2,689
  • Joined

  • Last visited

Community Reputation

2,089 Excellent

About YKSE

  • Rank
    Brown Dwarf

Profile Information

  • Gender
    Male
  • Interests
    Bridge, badminton, mushroom picking.
  • Location
    Gothenburg, 57°, Sweden
  1. There's this site for Messiers in binoculars: https://www.astroleague.org/al/obsclubs/binomess/binomesa.html Here's their list of 76(!) doable Messiers with 7x or 10x binoculars: M1 is challenging, but doable. Those who have some experience with telescopes will notice directly that M57 (ring nebula) is not in the list, it's simply because 7x or 10x is just to low magnification to identify M57.
  2. Yes, "Turn left on Orion" seems to be a very popular book. but I don't have the pleasure to read it before and after these years observations. I was quite attached to the simple planisphere I had in youth, just used it to guide me around the sky. You can easily download and print it out to make your own. With zero cost and get a basic intro as how the constellations get around. In most light polluted area, it's good enough to find your way around, IMHO
  3. That's it! I had very much difficulty in my light-polluted, backyard (arorund mag 4.7), couldn't see M1 with 130P, just made it with C8, but in my dark sites, a pair of 10x50 binoculars did it.
  4. These eyepeices are scale design, meaning eye relief(ER) is proportional to focal length, about 0.7, so 40mm has 28mm ER, enough for glass-wearer. You may even feel too long with 40mm Maxvision if you don't twist up the eye guide, you can find out youself. Please be careful when twisting up the eye guide, you may unscrew the 2" barrel (since you're holding it) that lenses fall out of the housing. edge correction should be very good for your f6 200P (noticeable better than BST e.g.). Did you do the comparion head-to-head or to memory? This is the test done by Ernest in optical bench with his standarized methods and his comments on 28mm MV and ES:
  5. The ES 68° are essentially the same (except the 28mm) design as the Maxvision, with soft eyecup, ES has reduced the weight compare to MV. 28mm are different where Maxvision 28mm has noticeable better image quality. Of the other focal lengths, 16mm and 20mm are best, work well even in f4 scopes, the others are more suitable for f5 or slower as recommended by ES.
  6. I made this Xcel file some time ago based on the actual spectrum measurement of nebulas, OIII is clearly the most useful one for planetary nebulas.
  7. This is my one case of mismatched eyepieces, which has been stable for some years except the pair of binoviewing zooms 10 different brands
  8. Stu, I think it sound correct putting the 1.25" in the focus plane, you'll get TFOV of about 27mm field stop; using T2 to 1.25" adapter to 2" barrel is quite close to focus plane, therefore you'll get quite hard vignetting, but I'd still expect the TFOV is still slightly wider than true 1.25" 40mm plossl (maybe you can verify it in some way)? Using the filter in front of the diagonal, it becomes so far away from focus plane(field stop), it should behave like 37mm baffel diameter in C8, i.e.e there is vignetting for sure, but it's so gradually, that our eyes just don't really see it unless you look for it very carefully.
  9. From what I can get from Tammy's measurement, all the Nikon NAV-SW are par-focal within 1mm, and all Pentax XWs from 3.5mm to 40mm are par-focal within 1mm if the 2" to 1.25" adapter doesn't add any length).
  10. 11.5mm exit pupil is exactly the same brightness in any scopes sizes. If we look at visual without NVD, larger scopes will always give higher magnifications (i.e. larger image scale) over the smaller ones, as exit pupil is defined as exit pupil=telescope Aperture/magnification (Check the followed link if you want the details). As to visual without NVD, a large scopes delivers larger image at the same brighteness as a small one(We're talking about extended objects only, i.e. nebulas, galaxies and faint GC, not the points sources like stars, bright OC and GCs), it is similar to looking at a small picture on a well-litted wall, at 10m distance(like a small scope), you mayhardly see any detail, but moving in to 5m distance (= a scope of twice aperture of the small one), you'll be able to see more details, and there's no brightness change in these two cases, only the image scale.
  11. How about these? http://www.russell-optics.com/two_inch.html http://www.siebertoptics.com/
  12. Yes, the long eyepiece is used to speed up the scope, i.e. to let the NVD to get larger exit pupil for more lights, therefore brighter image. It's not for increasing TFOV, because the NVD ifself can't get larger TFOV than its less than 1" field stop. AMaybe we can consider a practical example? a comercial 10"f4.7 and 8"f6, both have fl 1200mm, you'll get 44x with a NVD, so the same image size. If you add 54mm eyepiece to 10", and 81mm to 8", which one will get brighter image? My understanding is (can be wrong of course) that the 8" will show brighter image, because the exit pupil is 13.5mm in 8", and 11.5mm in 10", that's about 38% more area= 38% brighter image. Besides, f6 scope is more tolerant to off-axis aberration, and more less coma from the scope will be seen than f4.7 scope, and 8" is much less bulky and costly than 10" too. What do you guys think? BTW, there're some small eyepiece manufactures do these long eyepieces, and it doesn't cost a fortune.
  13. Thanks for the helpful info Garvin According to Peter's decription, it seems to me that a long focal length EP is a very good to increase image brightness when using a relatively long focal scope, a 72mm or 85mm eyepiece should reduce your scopes' fl to about 1/3 of original, thus much brighter image, does it sound correct?
  14. OK, does it mean that it's kind of like astrophotography? i.e. faster scope gives brighter image, and longer focal length gives larger image scale?
  15. Just a stupid question, since a 54mm ep works as 0.5 focal reducer, shouldn't a 9mm EP works as 3x magnifier?
×