Jump to content


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


roof diopter moves but no change in focus

  • Please log in to reply
No replies to this topic

#1 LoveWillSteerTheStars



  • -----
  • topic starter
  • Posts: 1,078
  • Joined: 13 Sep 2022

Posted 07 June 2023 - 06:25 PM

Bushnell roof prism, Image View 8x30; two hinges with a camera in the center.

Left view is sharp, but the right is way out of focus and the diopter seems to not make any difference.

Glass is clean

It has a diagonal slot in the focus knob, which captures a pin that moves up & down, must be in a vertical slot.


So is the diopter not actually moving, or is there something out of alignment with the objective or ocular side, like the optics are not the correct distance apart ?


The objective housing has a very long threaded portion, maybe 2cm. 


Possibly it is to get the right distance from the ocular & not necessarily be screwed all the way in ?

EDIT - I think this is the issue.  This bin focuses by moving the objectives out & back.


Lots of physical interferences with turning the obj housings:

1) the beauty ring is a couple inches long, and tapers at the body.  So I cannot remove it to grab the obj housings.  Unless I remove the rings entirely.

2) the obj housings are conical, so any tool wants to slip.  Plastic, so fragile.

3) the gap between the beauty ring & body is narrow, 1/4" at best, so need a narrow plier type tool.

4) I think the factory set one obj much further back (from the front of the beauty ring) than the other, so the gap (3) does not tell me when each obj is at the same out/in point

5) To turn the obj I need to yank out the beauty ring until there is enough friction to engage the obj housing, then turn the ring.  But it does slip, so I can't count the number of turns reliably.


I can get frustratingly close to both sides focusing at the same distance, at a distance.

I'm starting with equalizing close focus, so I picked a reasonably close minimum focal distance.  But it stays in focus over a rather wide range of adjustments, starting from CF turned fully to the stop.  I can't see the whole wheel, only the top part.  Black plastic is hard to mark.


Then the "distance" focus happens at the mid-range of the CF wheel, instead of closer to the end of travel.  This strikes my as not right ???  I don't have a lot of "turns" available in the middle distance, where you want to dial it in.


Maybe I should remove the beauty rings to get them out of the way, so I can easily turn the obj housings.  But one is also dented, so need to iron that out to get the ring off. Then somehow mark their in/out point, to duplicate after putting the rings back on.


Its dark so I gotta wait until tomorrow, so hoping to get some ideas before then.

Edited by LoveWillSteerTheStars, 07 June 2023 - 07:37 PM.

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Recent Topics

Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics