Dismiss Notice
New Cookie Policy
On May 24, 2018, we published revised versions of our Terms and Rules and Cookie Policy. Your use of AstronomyConnect.com’s services is subject to these revised terms.

Nebula's Astronomy Den

Discussion in 'Observing Celestial Objects' started by Nebula, Feb 2, 2018.

Nebula's Astronomy Den

Started by Nebula on Feb 2, 2018 at 8:12 PM

566 Replies 63505 Views 5 Likes

Reply to Thread Post New Thread
  1. Mak the Night

    Mak the Night Well-Known Member

    Joined:
    Jul 10, 2016
    Posts:
    4,681
    Trophy Points:
    113
    I think balance is as important. A lot of scopes intended for AP seem to be rear heavy and have limited back-focus.

    80ED.jpg

    My SW 80 ED DS Pro is really well balanced even with the aftermarket focuser. Shown here with a Takahashi diagonal and Takahashi 'before the diagonal' Barlow. I'm using a 3x SvBony Barlow housing (minus the element) as an ersatz extension tube. This way, the balance is still excellent and vibration is at a minimum. The Barlow needs an extension to achieve focus.

    80ed2.jpg

    I think the perfect Strehl number is 1.0, although apparently it can never be achieved. So, the nearest to 1.0 is the best number. According to Wiki:

    "The Strehl ratio S is frequently defined as the ratio of the peak aberrated image intensity from a point source compared to the maximum attainable intensity using an ideal optical system limited only by diffraction over the system's aperture."

    Strehl.jpg

    So, your guess is as good as mine lol.

    starwave.jpg

    I want to get the 102mm Altair Starwave out soon as well. This balances well with 1.25" accessories on a Porta II/TL130. I'm pretty sure the Starwave and the EDF are made by Kunming United Optics. They both have excellent FPL 53/lanthanum glass.
     
    Nebula likes this.
  2. Nebula

    Nebula Well-Known Member

    Joined:
    Aug 5, 2016
    Posts:
    1,621
    Trophy Points:
    83
    Quite an experiment with the SW 80 ED DS Pro, long chain with the barlow housing before the diagonal. Can you reach focus with such a long train?

    How is the Takahashi diagonal compared to the others in your collection. I don,t remember the Tak from your past publications, is it a new acquisition?

    (pretty high end? )

    ***
    Wow ok for the Strehl number, I'll leave the comprehension of that to others!
     
  3. Mak the Night

    Mak the Night Well-Known Member

    Joined:
    Jul 10, 2016
    Posts:
    4,681
    Trophy Points:
    113
    The Tak' Barlow is a bit sui generis in the fact that it was deliberately designed to be used in front of a 1.25" diagonal for 2x and to be used conventionally in a 2" diagonal (in an adapter) for 1.6x. It can't be used conventionally in a 1.25" diagonal.

    tak1.jpg

    The field lens is a diameter that would miss most safety shoulders and contact the prism/mirror. It was also designed to be used with an extension, ostensibly for a Tak' f/7.5 refractor. The 80ED is f/7.5.

    tak2.jpg

    It can dampen vibration this way, if the eyepieces are small. The diagonal prism is very high quality, the only thing better is the Baader BBHS. Unfortunately the housing is like it came out of a Christmas cracker. Although I've been reliably been informed it's strong enough to hold a bino. The twistlock is fussy with undercuts. I discussed it here:

    https://astronomyconnect.com/forums/threads/1-25-prism-comparison.13091/

    The diagonals are about a hundred quid (£) here. Tak' are basically giving them away. I believe they're more expensive Stateside.
     
    Nebula likes this.
  4. Nebula

    Nebula Well-Known Member

    Joined:
    Aug 5, 2016
    Posts:
    1,621
    Trophy Points:
    83
    @Mak the Night

    Very interesting information about the Tak diagonals

    "Unfortunately the housing is like it came out of a Christmas cracker."
    = LOL

    Its true that it looks cheap.. what material is that, not painted steel? and how are these Abbe eyepieces from Takahachi? Did you test them against the Fujiyama Orthoscopic eyepieces ?
     
  5. Mak the Night

    Mak the Night Well-Known Member

    Joined:
    Jul 10, 2016
    Posts:
    4,681
    Trophy Points:
    113
    I think the Tak' prism housing is light gauge pressed aluminium. It's stronger than it looks but the twistlock is a bit fussy with undercuts. The prism itself is excellent though. The Ohi ortho's are 42° whereas the Tak' ortho's are 44° as they have a bigger field stop. They are still only really 42° though, the extra 2° is probably to aid target acquisition. The Tak's have better contrast but less overall transmission; so basically a case of 'swings and roundabouts'.

    takstoo.jpg

    Also, the 4mm is ergonomically easier to use than the Ohi equivalent and there is a unique 32mm Takahashi version. FLO are selling Ohi ortho's now:

    https://www.firstlightoptics.com/ja...anese-genuine-abbe-orthoscopic-eyepieces.html

    They are sold under different names but they're all made at the Ohi factory in Tokyo.
     
    Nebula likes this.
  6. Nebula

    Nebula Well-Known Member

    Joined:
    Aug 5, 2016
    Posts:
    1,621
    Trophy Points:
    83
    @Mak the Night

    hello, back again.. it took some time to reply, I caught the Covid last Monday and was very sick.. I am just starting to feel better today, Friday...

    Holy wow! that is an amazing collection!! gee, you really are serious about testing eyepieces. So the Tak have better contrast but less transmission then the Ohi ok.

    Ohi is the same thing as Fujiyama with another name.. first time I see them.
     
  7. Nebula

    Nebula Well-Known Member

    Joined:
    Aug 5, 2016
    Posts:
    1,621
    Trophy Points:
    83
    I watched the video of the re-coating of one 8 meter mirror from one of the very large telescopes in Chile.

    Old stuff but fantastic stuff.

     

Share This Page