This is a bit unusual and one for the tinkerers that have to work to a budget. Very recently I had the opportunity to buy an f6.9 – 415mm fl / 60mm objective refractor from dhumpie (Darren) mostly because I am just beginning in backyard astro imaging and needed a finder/guide more friendly then the stock neck breakers that usually come with our scopes.
There seems to have been a bit of interest in these old but very affordable Japanese achromats of late for guiding, and one of the stumbling blocks is that they usually have 0.965 inch diagonals and eyepieces, which for astronomical purposes is generally inadequate, the 1.25 inch equipment is the standard and a decent 0.965 to 1.25 inch EP adaptor for these scopes is not exactly cheap.
Looking at the tiny 0.965” plastic standard eyepiece and glass prism diagonal, a thought occurred to me – if I unscrewed the barrel extension off one of my 1.25 inch EP’s, would it fit over the top of the diagonal tube in any way that would have it fit?
I chose the least used eyepiece in the collection, the poor orphaned 15mm GSO super view. Low and behold without its barrel extension the lens body fitted onto the 0.965” diagonal upright tube perfectly, the tube slipping very snugly into the body recess provided by the removed barrel.
It is still an ordinary view through this flawed 4-element EP, but it transmits lots of light and clarity on-axis and gives roughly a 60 degree field of view, in fact through this scope this eyepiece gives a 2 degree 26 arcminute true observable FOV at 28x magnification, not brilliant, but acceptable for my eyes and brain.
I suspect there are a few of these GSO SV 15mm EP’s lying dormant, and the astro shops are almost giving them away if you press them for a deal…. and here could be a use for them if you are willing to give away some outer FOV clarity with your guide scope.
It is even quick and easy to set up cross hairs between them and the 0.965” diagonal if required, the pics below show this using light fishing line as a knock-up, but finer gauge wire is available and less prone to misalignment.
Hope this info might be of use to someone somehow somewhere.
Cheers,
Steve.
