Hello.
I am building a dob using the Kreige/Berry book as my guide, but got a little lost in the sections on eyepiece-exit pupil-secondary size relationships. sec 4.3 through 4.5.
I am building a 13.1" whose true focal length is 58.5".
I am super partial to Pentax XL eyepieces and have 3 already (14, 10.5 and 7) looking to add something in the 18-22 range and then later something closer to 28 to 32mm. These are all 1.25" EPs and I'm even wondering whether I should just stick to a 1.25" focuser to keep the CO to a miniumum and also the weight of my upper cage as low possible (both due to a light weight 1.25 focuser and a smaller secondary?) as my base is going to be low profile (portability, nestability is my priority) so I need as light weight up top as possible to stay in balance.
With all these factors floating around though, ALL I REALLY NEED TO KNOW IS WHAT SIZE SECONDARY DO I NEED FOR THESE PARAMETERS? D=13.1 FL=58.5...and EP preference as noted above.
Thanks!
Tom L.
I am building a dob using the Kreige/Berry book as my guide, but got a little lost in the sections on eyepiece-exit pupil-secondary size relationships. sec 4.3 through 4.5.
I am building a 13.1" whose true focal length is 58.5".
I am super partial to Pentax XL eyepieces and have 3 already (14, 10.5 and 7) looking to add something in the 18-22 range and then later something closer to 28 to 32mm. These are all 1.25" EPs and I'm even wondering whether I should just stick to a 1.25" focuser to keep the CO to a miniumum and also the weight of my upper cage as low possible (both due to a light weight 1.25 focuser and a smaller secondary?) as my base is going to be low profile (portability, nestability is my priority) so I need as light weight up top as possible to stay in balance.
With all these factors floating around though, ALL I REALLY NEED TO KNOW IS WHAT SIZE SECONDARY DO I NEED FOR THESE PARAMETERS? D=13.1 FL=58.5...and EP preference as noted above.
Thanks!
Tom L.
