Adapting an eyepiece to fit. (1 Viewer)

[Cluster]

I have a B&L Premier HDR scope body (60mm) and have found that eyepieces are rare for this model/range. It has a bayonet fitting for the eyepiece and a 42mm (I think) threaded mount.
I may be able to find an eyepiece that will fit into the body, but without the bayonet and can work on a way to secure it, but...I probably can't get the eyepiece to sit at the same distance from the prism as the one made for it. Is this a drawback?

I notice that my Opticron threaded eyepiece fits the thread and gives a very good image at widest zoom, but degrades dramatically as the zoom is increased. Could this be because the eyepiece is not matched (positionally) correctly?

Dave

 

[Cluster]

To rephrase my question:

What happens to the image (or IQ) as the eyepiece is moved further away from the body of the scope.
I can see a small increase in magnification as I move my fixed EP out on its thread, but is the IQ degraded?

Dave.

 

[henry link]

Dave,

I have no experience with this particular zoom eyepiece, but I think the image degradation probably has nothing to do with eyepiece quality. It's much more likely that applying higher magnification is simply revealing the inherent optical limitations of the scope or possibly just the degradation imposed by some unsteady air when you tried it.

As for what happens to the image quality as the eyepiece is moved further from the body of the scope, the answer is "not much". Moving the eyepiece is not significantly different from simply changing the focus with the focusing knob. If you can still reach focus at infinity then the focuser has enough travel to compensate for the repositioned eyepiece field stop, so nothing much has changed. There could be a small difference in the way the prism housing vignettes the aperture of the objective over the focusing range, but that shouldn't have much effect on the image.

Henry

 

[Cluster]

Thanks for the info, Henry.

So, I should think of the light leaving the prism (or scope body) as a nearly parallel beam, so that the position of the eyepiece is not critical? Thanks, this explains a little of what I have seen when waving the eyepiece around the body (adjusting the position).
This then may allow the use of a range of eyepieces on the scope, provided that they can be mounted firmly......hence the multiple mount systems seen on my Opticron GS665 for example (two male thread mounts and one or two female threaded mounts).

The possibility of getting an eyepiece to work on the B&L scope is fairly realistic.

Dave

 

[Cluster]

Thanks again for the info. I've just received a nice 20x eyepiece of unknown origin that works pretty well with the scope. As you have said, it was just a matter of finding a new focus position for the eyepiece that is further away.
I just have to identify the thread size of the EP mount and buy a camera lens step up ring to get it to mount on the scope. The slight outwards shift of the EP is of little consequence.

Dave