Loading ...
Sorry, an error occurred while loading the content.

Re: [tec-scopes] Re: flattener position and focal ratio

Expand Messages
  • Antonio Agnesi
    Lee, here is something different: I knew that flatteners typically increase the focal a little bit, but I wanted to know why someone ends up with f/7.2 and
    Message 1 of 8 , Apr 2, 2013
    • 0 Attachment
      Lee, here is something different: I knew that flatteners typically increase the focal a little bit, but I wanted to know why someone ends up with f/7.2 and others with f/7.4. Yuri did explain this clearly, saying that the native focal lenght of the APO140 is actually 980 mm with batch variations up to +/- 5%.
      I did not check the focal without flattener, since I lack the spacer allowing to reach focus. I am not that picky anyway: I am glad the scope + FF performs flawlessly, the 2% lower speed really does not bother me!
      Cheers,

      Antonio
       

      this question has come up in the ap-ug. roland indicated it is typical for a field flattener to increase the focal length 5-10%. i have seen that to be true in my own refractors.

      Lee

      --- In tec-scopes@yahoogroups.com, Antonio Agnesi <antoniangelo.agnesi@...> wrote:
      >
      > > Antonio,
      > > the focal length of the APO140 could be different from original +-5% depending on melts of the glass.
      > > I will check tonight about spacing vs. f/ratio.
      > >
      > Thanks, Yuri, that would be interesting! This tolerance is perfectly reasonable, for sure the slightly longer focal will not hurt high res work...
      > > The main thing is - "the field is perfectly flat with nice round stars"
      > >
      > Yes, any custom-made adapter is always a bet! If all tolerances add up with the wrong sign it is easy to be off by few mm. Luckily, it's allright!
      > I had only one clear evening in one month also for enjoying a magnificent moon sight, as usual for new scopes!
      >
      > Regards,
      >
      > Antonio
      >

    • Yuri
      Antonio, the ff increases the FL of the telescope on ~3%. Changing spacing (FF to focal plane) +-3mm changing focal length on appr. same amount. Going further
      Message 2 of 8 , Apr 2, 2013
      • 0 Attachment
        Antonio,
        the ff increases the FL of the telescope on ~3%.
        Changing spacing (FF to focal plane) +-3mm changing focal length on appr. same amount. Going further is not recommended.
        Sample:
        APO140 + FF w. back focus 85mm, the focal length of system is 1034mm
        APO140 + FF w. back focus 88mm, the focal length of system is 1037mm
        Regards,
        Yuri

        --- In tec-scopes@yahoogroups.com, Antonio Agnesi <antoniangelo.agnesi@...> wrote:
        >
        > > Antonio,
        > > the focal length of the APO140 could be different from original +-5% depending on melts of the glass.
        > > I will check tonight about spacing vs. f/ratio.
        > >
        > Thanks, Yuri, that would be interesting! This tolerance is perfectly reasonable, for sure the slightly longer focal will not hurt high res work...
        > > The main thing is - "the field is perfectly flat with nice round stars"
        > >
        > Yes, any custom-made adapter is always a bet! If all tolerances add up with the wrong sign it is easy to be off by few mm. Luckily, it's allright!
        > I had only one clear evening in one month also for enjoying a magnificent moon sight, as usual for new scopes!
        >
        > Regards,
        >
        > Antonio
        >
      • Antonio Agnesi
        Message 3 of 8 , Apr 2, 2013
        • 0 Attachment


          Il giorno 02/apr/2013, alle ore 20:17, "Yuri" <tec@...> ha scritto:

           

          Antonio,
          the ff increases the FL of the telescope on ~3%.
          Changing spacing (FF to focal plane) +-3mm changing focal length on appr. same amount. Going further is not recommended.
          Sample:
          APO140 + FF w. back focus 85mm, the focal length of system is 1034mm
          APO140 + FF w. back focus 88mm, the focal length of system is 1037mm
          Regards,
          Yuri

          --- In tec-scopes@yahoogroups.com, Antonio Agnesi <antoniangelo.agnesi@...> wrote:
          >
          > > Antonio,
          > > the focal length of the APO140 could be different from original +-5% depending on melts of the glass.
          > > I will check tonight about spacing vs. f/ratio.
          > >
          > Thanks, Yuri, that would be interesting! This tolerance is perfectly reasonable, for sure the slightly longer focal will not hurt high res work...
          > > The main thing is - "the field is perfectly flat with nice round stars"
          > >
          > Yes, any custom-made adapter is always a bet! If all tolerances add up with the wrong sign it is easy to be off by few mm. Luckily, it's allright!
          > I had only one clear evening in one month also for enjoying a magnificent moon sight, as usual for new scopes!
          >
          > Regards,
          >
          > Antonio
          >

        • Antonio Agnesi
          Thanks, Yuri! This definitely confirms that most significant changes come from focal variations batch-to-batch, rather than from exact position of the
          Message 4 of 8 , Apr 2, 2013
          • 0 Attachment
            Thanks, Yuri!
            This definitely confirms that most significant changes come from focal variations batch-to-batch, rather than from exact position of the flattener.
            Regards,

            Antonio

            Il giorno 02/apr/2013, alle ore 20:17, "Yuri" <tec@...> ha scritto:

             

            Antonio,
            the ff increases the FL of the telescope on ~3%.
            Changing spacing (FF to focal plane) +-3mm changing focal length on appr. same amount. Going further is not recommended.
            Sample:
            APO140 + FF w. back focus 85mm, the focal length of system is 1034mm
            APO140 + FF w. back focus 88mm, the focal length of system is 1037mm
            Regards,
            Yuri

            --- In tec-scopes@yahoogroups.com, Antonio Agnesi <antoniangelo.agnesi@...> wrote:
            >
            > > Antonio,
            > > the focal length of the APO140 could be different from original +-5% depending on melts of the glass.
            > > I will check tonight about spacing vs. f/ratio.
            > >
            > Thanks, Yuri, that would be interesting! This tolerance is perfectly reasonable, for sure the slightly longer focal will not hurt high res work...
            > > The main thing is - "the field is perfectly flat with nice round stars"
            > >
            > Yes, any custom-made adapter is always a bet! If all tolerances add up with the wrong sign it is easy to be off by few mm. Luckily, it's allright!
            > I had only one clear evening in one month also for enjoying a magnificent moon sight, as usual for new scopes!
            >
            > Regards,
            >
            > Antonio
            >

          Your message has been successfully submitted and would be delivered to recipients shortly.