I'm trying to tidy up my equipment cabinet, and of course, I want to play around with the stuff inside as well.
I tried to test my Borg 45ED II with different barlows and eyepieces.
My first target is a 2" Pentax SMC XL 40mm... the Pentax is so big that it's bigger than the objective end, the field is nice and bright as well as flat, no vignetting to my eye. Very sharp and no color, it's 8.125x...
Next is my 13mm Nagler Type 6. It reaches focus in the same 2" diagonal as well, the field again is nice and bright and flat, too. However, the Nagler is not really a day time eyepiece, the view is not easy to hold and you can see blackout rather easily. There were some color at the edge of very high contrast object, like the edge of some white wall, it's very low, and you can't see it unless you specifically look for them. It's 25x now.
Then I inserted a 5x Powermate there, it's nearly parfocal, I mean when I drop the 13mm Nagler back there, it's basically in focus. I tweaked the focus with my JMI controller, and it's very sharp and contrasty. There is no obvious color, but the exit pupil is getting small so that you can see floaters. Image is still solid, no sign of breaking down. Tweaking the focus reveals a tiny amount of image shift from the NGF-S, not a big problem here. It's 125x, i.e. 0.36mm exit pupil.
I went crazy and I inserted a 3x barlows between the 5x and the Nagler. To my surprise it's like parfocal too, tweaking the focus a little bit and the image is still quite solid!!! I can still see detail in the image, of course, it's too dim now and all the dust, floater jumped into the view. Again, no more color than before. It's 375x!!!! For that small objective, it means 0.12mm exit pupil only!
Modern objectives are so great that you can push as far as your eyes allow!