Focusing range for dual use Astrophotography and eyepieces

[a_q]

Well I have put together a prototype newtonian which we took travelling on our holiday in scotland this summer. Nice dark skies but cloudy too so didin't get much use.

Eventually I want to put the mirror to use in a more permanent lightwight aly frame. However my first experiments with the prototype revealed that the change in focus distance between eyepiece use, and digital camera use, was around 3.5", which is beyond the range of my current focuser tube.  I could just get focus in both use cases when the eyepiece (a Seben 8-24mm zoom) was hanging off the end of the focuser to give extra distance, and then removing the clamping ring on the focuser for camea use. Neither was very satisfactory  because the eyepiece was a bit precarious, and I couldn't really attach the camera tube properly.

The mirror is 10.5" diameter, 60" focal length. I currently have a 1.25" dia focuser and a (quite small) 35mm secondary. But I definitely plan to get a bigger secondary.

So I am wondering how best to get focus for both uses, my ideas so far are:

1. Use an extension tube for eyepiece use - but unless the focuser is large diameter (2"?) there may be vingetting of the image for wide field use.

2.  Shift the focuser and secondary relative to the primary - but this will be hard to keep in collimation.

3. Use a barlow lens for astrophotograhy - at some expense for  a decent one. I have been playing with the lelments out of a second hand photographic teleconvertor to prove that focus can be achieved. Plus this gives 2x image - good for planets, not so good for wide field. Some loss of definition I expect.

4. Use two different positions for the focusser/mirror  - will definitely work and be cheap but the penalty is re=collimating each time I want to switch uses.

Any other ideas - what works well to solve this problem? And isn't too expensive!

[ronin]

The "normal" approach seems to be to set it up for imaging, then add an extension tube for visual.

You can add the extension tube easily, what you cannot do is cut a chunk off the focuser when imaging - well only once.

An extension tube is easy and cheap and no adjustment of anything like mirrors.

[Laurie61]

I would agree with Ronin's comments above, adjust scope so camera can be focused and then add an extension tube for eyepiece use. I would also think about fitting a 2" focuser at some point as this will hold the camera more securely and give you the option of 2" eyepieces. If you have not already discovered it this is useful for working out secondary sizes and other aspects of newt design.

https://stellafane.org/tm/newt-web/newt-web.html

[a_q]

Thanks for the replies - the extension tube appoach does have the other benefit of making the scope shorter by a few inches too.

Yes I have played with the newt-web program before and it seems to agree a 2" focuser is the way to go.