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_open_clusters.thumb.jpg.f534ff4cbeb9f1a55a0d894ac8bc190b.jpg

Louis D

Advanced Members
  • Content count

    2,154
  • Joined

  • Last visited

Community Reputation

1,213 Excellent

2 Followers

About Louis D

  • Rank
    Brown Dwarf

Profile Information

  • Location
    Texas, USA
  1. Nagler Type 4 question?

    Try a 17mm ES-92. No field curvature, no edge of field astigmatism, at least as pinpoint stars on axis, no finickiness holding the view with eyeglasses, longer eye relief, and 10 degrees wider. I've repeated compared them and retired the T4 to my 2nd tier collection of eyepieces that may end up being sold if they don't get used enough. I only keep it around for use on the ED72 that really doesn't like the weight or lever arm of the ES-92. The Dob has no issues with it until I get below 25 degrees or so elevation.
  2. I find it easier to pick out the GRS in my 72mm ED scope at the same exit pupil than with my 8" Dob. It's smaller, but it's more obvious. I can also pick out the E and F components of the Trapezium much easier with the frac than the Dob. Having any CO, no matter how small, limits how pinpoint each point of focus can be. Stars are more bloated as well in the Dob than the frac. It's not the mirror, it's a premium, hand figured mirror in the Dob with an 18% CO by diameter secondary. Part of it is surface roughness of the enhanced and dielectric coatings. Silver would be better, but no one does them for mirrors.
  3. I guess it's go big or go home for you.
  4. vlaiv is correct. To summarize, the smaller number is CO by area which affects light gathering and is the less important number. The larger number is by diameter and is the more important one as it affects contrast which affects perceived resolution. A typical SCT will have a 35% to 40% CO by diameter compared to a 20% to 25% CO for Newtonians. By area, it will be much less for both. Even getting above 30% CO, contrast will start to noticeably go down. By 40%, it's quite obvious in A/B testing with a low CO Newtonian on low contrast objects like Jupiter. Even at 20% CO, a Newtonian looks noticeably worse than an equivalent APO refractor when it comes to contrast. Of course, that APO will cost much, much more than the Newtonian on a per aperture basis. SCTs cost more than equivalent Newts as well because you're paying for the convenience of a folded, more compact light path which necessitates the larger CO. TANSTAAFL
  5. First buy help.

    I would avoid ebay as a beginner. You need to be quite a savvy buyer to avoid being ripped off there. Craigslist in the US can be a great place to locate a local, used 6" Dobsonian beginner's scope for under $200. There's also CN classifieds and Astro Mart, but unless you're close to the seller, you'll lose out big time on shipping fees for a scope. In the UK, there's AstroBoot and UK Astro Buy & Sell as well as ads right here on SGL.
  6. Nagler Type 4 question?

    But were they certified pre-owned as US used car dealers like to say?
  7. Folks on here and CN have reported good luck by marking where each leg of the tripod was placed and putting it back on the next outing in the exact same spot, coming out of hibernate mode, and being very close to aligned again.
  8. 4mm Ortho

    Well, according to John in this posting and seemingly confirmed by this posting on CN, the SLVs are now made in China.
  9. 4mm Ortho

    With the SLV line, production moved to China. Reports seem to indicate they got better, if anything, over the LV and NLV. I would definitely place the Pentax XL and XW line slightly above the LV line in terms of overall sharpness. The Delos and ES-92 are also right there for edge to edge sharpness. However, if you can pick up the LVs for $60 to $70 used, they're a great deal. I paid $90 in 1997 for my 9mm.
  10. I can't speak directly to the APM barlow to which you refer, but I've found that extending the distance increases the magnification with no appreciable loss of quality. Perhaps the exit pupil might become more difficult to acquire for some eyepieces, but that's about it. On the other hand, trying to mount the nose piece of a barlow directly to the filter threads of an eyepiece to yield a lower magnification factor never seems to work for me. The field of view is usually cut off well inside the natural field stop, and either field curvature or some other aberration gets introduced causing the outer part of the field to be distorted and/or out of focus.
  11. If I were to chop my Vixen 22mm LVW....

    Here's a link to Don Pensack's excellent post on the subject from 2013.
  12. Absolutely. I have no trouble leveling my tripod mounted alt-az grab and go setup (DSV-2B mount). The bubble level is built into the tripod. However, it has no electronics on it whatsoever. The reason I level it carefully is it will swing wildly in azimuth if it is the least bit off with an offset mounted telescope. With telescopes on both sides to balance it out, it's not quite as likely to swing around.
  13. Not on a dob without any way to adjust the height of individual feet under the ground board.
  14. Being a push-to, I slew manually to both stars. I didn't realize these goto mounts will do the slewing to the second star.
  15. Show me your eyepiece cases

    Some my reactions to your news:
×