[Birdbox]

Are any of the quality Opticron eyepieces compatible with the not so quality Classic IF 75? Would the addition of one of them alter the scope's performance much.

[Malcolm Stewart]

Hope this response isn't too late.

I have an old HR60 EDs which has Imperial threads for the eyepiece socket, and isn't compatible with modern metric threaded eyepieces. The solution offered on my visit to Opticron in Luton wasn't attractive to me as it would have involved alteration to the 'scope. However, the InFocus people at Martin Mere offered the modern SDL eyepiece which screws onto the outer (cap) threads, and works very well, albeit at a price.

[Birdbox]

Thanks for that. Does the modern eyepiece alter performance much?

[Malcolm Stewart]

My old eyepiece is fixed magnification, and the SDL is a zoom, so I suppose it's a dramatic change!

What's nice about the SDL is that the eye-end collar is adjustable in length from the mounting threads, and this helps optimise the view through the zoom eyepiece at different magnifications. Whether younger viewers would benefit as much as myself, I've no idea. I'm 70 and my optical accommodation is miniscule, and being astigmatic I wear bifocal specs all the time. My normal eyepiece is a 20x and I think the SDL gives me from 15x upwards with my 60mm aperture 'scope. I find I quite often use the wide end of the SDL so as to make use of the wider field of view.

Using the higher magnification naturally reduces the diameter of the exit pupil, and the brightness of the image. Focusing gets to be more critical and stability of support is much more important, as is the accuracy of aligning one's eye with the exit pupil. I think my old ED glass 'scope is just good enough to make full use of the SDL, but having looked through an 80mm aperture 'scope a few weeks ago, I've been checking prices and piggy bank...

(Both of my eyepieces are clean and surfaces unscratched.)