Brought this hefty multi-element lens some years ago from surplus store. There were a few of these around. Gives passable images in a temporary 25mm diagonal and 12mm eyepiece with limited field held together with plumbing fittings. I am interested in properly converting it to a grab and go with a 2" crayford. Are there old hands who remember these and know if they work OK or have field curvature with full field?
Appreciate any advice. There seems to be a lot of good quality but redundant old optics out there going to waste since digital arrived.
Regards
Greg46
More likely the focal length is 16", not the aperture ... that would be SOME lens !!
So 100mm F4 ... hmmmm, could be useful depending on all sorts of things.. Try it and see I say, mock it up with plumbing bits and cardboard tubes. Possibly make a good guide scope or widefield but coma\distortion may be an issue at that focal length.
I have attached photos of the lens which is a Taylor Hobson ortal complete with "sticky tape". The company was well known for TV and cine lenses.
On the subject of "beasties", there is an old World War 2 brass housed bomb sight eyepiece in the box. It is the biggest eyepiece I have seen and weighs 2.2kg. It has an enormous field and eye relief but absorbs some light and is about 30-40mm. You know, it is easy to collect junk over the years.
Would be interested if anyone has used one of these. I am planning to mount it on my new dob. Perhaps I should ask on a new thread.
Best
Greg46
Having played around with all sorts of video/camera lenses trying to make simple telescopes I would say that for a practical device you are wasting your time but for a bit of fun and experience it could be quite a useful experiment.
The biggest problem with these lenses is they are designed to come to infinity focus about 1" from the back of mount. An adapter can be made for a simple straight through eyepiece if you have access to a lathe or can find a suitable device but there won't be enough length to add a diagonal and still come to infinity focus.
Interestingly enough however many of the diagonals have a thread in the nose that will take the convex lens out of a barlow assembly and increase the focal length to a point where focus can be reached at the expense of doubling the magnification.
Thanks Barry for the advice. I have managed to get a decent but narrow field image with a 25mm diagonal straight at the back using the barrel as a draw tube to focus. As you say, adding a focusser would take it out of the focal plane (which may be curved). I will have a go with the barlow and see if it is any good.
All these quality optics lying around with no apparent use seems such a waste. You would think they could be reused for eyepieces, finders etc. I have a hope I can properly mount the old bomb sight eyepiece and re-balance my 10" scope. For the simple test I have done it really is like sticking your head out the window. A wide field and comfortable eye relief is what I am looking for to enable younger kids to get a good look.
that would be SOME lens !!
