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

13443Re: [ETXASTRO] Entering seconds for custom object autostar 497

Expand Messages
  • Brian Straight
    Aug 15, 2013
      And yet again, for the umpteenth evening in a row, the clouds roll in again here in Indiana, rendering speculation on FOV irrelevant, at least for one more night....

      Brian

      Brian Straight, Ph.D.
      The Walnut Ridge Observatory
      40.389452/-87.044881
      West Point, Indiana


      On Thu, Aug 15, 2013 at 5:18 PM, Rod Mollise <rmollise@...> wrote:
       

      Whether a camera lens or a telescope objective (NO EYEPIECE), the focal length does indeed tell you about the field of view. There are other considerations that may limit that field of view, but, yes, the focal length tells you everything about field. A telescope objective lens or mirror is no different from a camera lens....focal length and f/stop (speed) tell you what you need to know.

       

       

      Rod Mollise

      Contributing Editor Sky and Telescope Magazine

      Uncle Rod's Astroblog:

      <http://uncle-rods.blogspot.com>

       

       

       

       

       

      From: ETXASTRO@yahoogroups.com [mailto:ETXASTRO@yahoogroups.com] On Behalf Of Chris Harvey
      Sent: Thursday, August 15, 2013 1:44 PM


      To: ETXASTRO@yahoogroups.com
      Subject: Re: [ETXASTRO] Entering seconds for custom object autostar 497

       



      I'm doing my best to get my head around this .. but also when applied to photography lenses and the angle of view, initially I thought a 10mm focal length lens was also telling you its apparent field of view, but when it comes to fish-eye or wide-angle lenses this isn't the case. I was considering the cheaper Nikkor 10mm lens as an alternative to the expensive 10mm wide-angle lens - but it turns out they have totally different fields of view, and the cheaper one does not get me a fish-eye lens, damn . ..
      This page has some very clever calculators; but I'm not claiming to fully understand it: www.tawbaware.com/maxlyons/calc.htm

      I still don't understand why Stellarium is showing equatorial lines spaced by 5mins; thus Pleiades looks like it is 5 arc mins across, yet SEDS says its 110 arc mins across .. ? 5 mins makes sense. What is SEDS on about exactly? I have Googled/Wikiepedia'd this but I'm travelling in a 'circle of confusion' (not good if you've had a beer).



      On 15/08/2013 19:03, Ron wrote:

       

        Sometimes discussions stimulate me.

       

        Here is an explanation of the difference of Apparent and True FOVs.  I will probably forget it in a few hours .

       

       

      Other times discussions make me believe in something.  I believe I will go have a beer.

       

      Ron

       

      From: Ron

      Sent: Thursday, August 15, 2013 12:50 PM

      Subject: Re: [ETXASTRO] Entering seconds for custom object autostar 497

       




      I meant to say has NOT reduced my enjoyment

       

      Ron

       

      From: Ron

      Sent: Thursday, August 15, 2013 12:27 PM

      Subject: Re: [ETXASTRO] Entering seconds for custom object autostar 497

       




        Similar if not the same information is in the back of the users manual for the LX200R and LXD75 under optional accessories with the Eyepieces.   It gives Power and Actual Field.  The ETX manual only gives the power.

       

        Not knowing the difference between Actual and apparent and other items about the FOV has reduced my observation enjoyment.

       

        Dr. Clay’s site provides a lot of helpful information and he uses ‘plain’ english.

       

      Ron

       

      Sent: Thursday, August 15, 2013 12:06 PM

      Subject: Re: [ETXASTRO] Entering seconds for custom object autostar 497

       




      Hi,

       

      I got the info from Dr. Clay's website where he lists ETX scopes and FOV for various FL eyepieces (very useful info).  For the ETX 125 and a 26mm eyepiece, his table reads:

      26mm - 73X / (42')

       

      The site can be found here:

       

      All the Best,

       

      Brian

       

      Brian

       

      Brian Straight, Ph.D.

      The Walnut Ridge Observatory

      40.389452/-87.044881

      West Point, Indiana

       

      On Thu, Aug 15, 2013 at 12:57 PM, Chris Harvey <chris@...> wrote:

       

      Ahh yea I see .. sorry .. just looking in Stellarium; it looks like the Plaiedes is aprox 5 arc mins square, for context.
      But SEDS says the Plaiedes has: Apparent Dimension: 110.0 (arc min)
      What have I got wrong?




      On 15/08/2013 17:39, Ron wrote:

       

        I am pretty sure he was saying the Field Of View of the 26mm is 40 odd ArcMinutes.

       

        That is how I read it.

       

      Ron

       

      Sent: Thursday, August 15, 2013 10:09 AM

      Subject: Re: [ETXASTRO] Entering seconds for custom object autostar 497

       



      Erm, are you saying a star takes 40mins to get accross the FoV on an ETX125 with 26mm? That canny be right... more like 4mins, if that ?!
      Sorry if I'm misunderstanding you . .. .
      (I have read the Weasner news, will read again properly later to understand further, you don't miss somet 'till its gone ..  . . .. . )

      Nothing to do with ETX, but check out my Perseids including an animation of the smoke from a fireball dying away over 14mins:
      www.flitemedia.com/photography/night-sky.php
      Cheers,
      Chris

      On 15/08/2013 15:56, Brian Straight wrote:

       

      ...and with a 40-odd-minute FOV at 26mm, not necessary...

       

      Brian

       

      Brian Straight, Ph.D.

      The Walnut Ridge Observatory

      40.389452/-87.044881

      West Point, Indiana

       

      On Thu, Aug 15, 2013 at 10:37 AM, BrianS <briansxx@...> wrote:

       

      OK--I'm sure this is a "dumb" question, but I'll ask it any way. I want to use my 125 to take a look at the new nova in Delphinus. I've created a user object, and I need to enter an RA of 20h:23m,30s, but the seconds only allows for single-digit entry, which seems rather strange. Maybe seconds is more resolution that is needed for the ETX, given the field of view, but any thoughts or help appreciated.

      Thanks and Best,

      Brian

       

       

       

       






    • Show all 22 messages in this topic