View Full Version here: : F/4 16" TV camera lens
21-06-2012, 04:59 AM
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.
21-06-2012, 10:11 AM
Can you upload a picture of that beastie?
21-06-2012, 12:37 PM
More likely the focal length is 16", not the aperture ... :eyepop: 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.
23-06-2012, 09:23 AM
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.
25-06-2012, 08:31 AM
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.
26-06-2012, 08:18 AM
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.
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