Art McConnell

On 25/10/2021 at 13:42, Don Pensack said:

The reticle is at the focal plane of the eyepiece and, obviously, fairly high in the eyepiece, so extra in travel of the focuser is necessary.

this is not unusual for reticle eyepieces.

If your scope has a 2" focuser (your 8" probably does), then the answer is simple.

The average 2" to 1.25" adapter is about 9.5-10.5mm tall above the focuser.

There are lower height adapters.

The Howie Glatter Parallizer adapter is 0mm tall, which would gain you about 10mm of in focus.

TeleVue has an In-Travel adapter that is -1.5mm tall, which would gain you even more.

And Astrosystems has an adapter that is -12.7mm tall, where you would get so much in-focus you might need to move the focuser out from its normal position.

The lower adapters would solve the problem in the 8", but it won't solve the problem in the bino-scope since it only has 1.25" eyepiece capability.

Lower height adapters solve many in-travel problems.

Thanks for that info. Didn't know about in-travel adapters. I now know my 2" to 1.25" adapter is a High Hat, which is supposed to give a 16.5mm rise, but my dial calipers show me a full 19mm rise in my own adapter.

So that should fix me up with my Newtonian, which has a 2", low profile helical focuser. I built that scope, and chose that focuser because I wanted a wide(er) field of view for objects such as Andromeda galaxy. I was not disappointed....

But as for my BT-70s, might I find a different (brand? magnification?) reticled eyepiece that will perform better in them? Otherwise, it's to the machine shop with my Sbvony.....

I bought a Sbvony illuminated double reticle 12.5mm Plossl eyepiece and I can't get  the star to focus. Eyepiece all the way in, focuser all the way down, and with the reticle focused clearly and I have a star image that is useable for centering but still quite out of focus. If I then run the reticle focuser in, the star image comes into clearer focus, but never sharp.  At some point the reticle becomes useless, and I try to split the difference. I get this same behavior with this eyepiece in both my BT-70 binoculars and my 8" Newtonian. Is it me or the eyepice? I'd like to use this eyepiece for viewing also, but it needs to focus.

5 hours ago, jjohnson3803 said:

Interesting!  When I was researching mirror mounts for binos, I seem to recall a lot of insistence on 1/4-wave mirrors, which were really cost prohibitive, so I dropped the idea.   I'd be using it with only 15x70s, but tilting my head back can be problematic due to some old injuries so a look-down would really help.

How did you calculate the size of your mirror?

I had a large non-first surface mirror on it first, cut a cardboard template to cover all but what was needed. 6x9 was as small as I could go, and still use my laser pointer, which had a slight vertical offset from my optical axis.

I had my 6.3mm plossl in it this morning, and the moon was as clear as I could expect it to be. With a F/L of 400mm, it would have been about 63x. Just fine for deeper wide field viewing.

The mirror was $79 plus shipping, less than $100. I got the mirror here:

https://firstsurfacemirror.com/glass-first-surface-mirror/ 

with

Except for the price of the binoculars and a good mirror, mirror mounts are easy and cheap to build. Since one advantage of binos is the wide field of view, the limited magnification of less expensive mirrors ( I got a one wave for under $100) is not so much of a disadvantage for wide field wiewing.  The ease and speed of sweeping through a dark star-filled sky makes my mirror mount a joy to use.

This is what I did with my BT70 binoscope (everything but the mirror and binos came from my scrap pile):

The pedestal is height-adjustable (one pipe in another), and mounted on a lazy susan-type turntable off an old swivel chair, rotates 360 degrees.

I just came in from viewing the moon at 63x, and was pleasantly surprised at the clarity of the image my 1 wave mirror produced.