Quote:
Originally Posted by Varangian
Hmmm, I wonder if I connect both the 14mm and 28mm finetuning rings and a 2" Baader neutral density filter to my 8mm Hyperion whether I will be looking at a 3.2mm eyepiece? This would be ideal for Lunar viewing, if it worked. Any one know or done this?  |
Can it be done? Yes
Will it work? Yes
Will it be usable? Depends.
I've got both fine tuning rings and have tried stacking. But you lose image quality. How much you lose or are willing to lose will depend on seeing conditions and your personal preference. You can do similar "cheap" tricks to extend the capabilities of camera lenses but the trade off is quality.
Optics are built with certain characteristics in mind with each lens element playing a part in reducing distortion and flattening out the image so that the photons entering the front exit the back at the same time in same relative position to each other. So by adding an extension ring you are increasing the gap between elements. So if the existing gap was, for example, 14mm and you add a 14mm extension ring you just doubled the gap. The spread of the photons (distortion) at 14mm might have been in acceptable limits to ensure a certain level of image quality for the assembly. By doubling the distance the photons will spread further, distorting more and the rest of the elements will only be able to counter that partly.
In practice I find the extension rings work best on the wide field eyepieces (above 20mm), where the distortion is so tiny its still un-noticable with the rings. But getting down under 10mm eyepieces the quality loss seems to be more pronounced. So its hard to tell where the practical limits will be. Each eyepiece will have its own characteristics (eg your Hyperions might be a tiny bit better than mine), each scope has its own characteristics, collimation, seeing...all these factors will compound the more you push the optics.
But you won't break anything by giving it a try
You could also "ghetto" an extension tube by using an empty toilet paper roll or something similar. Maybe (if its safe enough for you) you can undo the eyepiece (as if you were adding the extension ring), put the bottom part into your scope and carefully hold the remainder above and see for yourself what the distortion is like at different distances.
