connecting CS mount video camera to scope

[Andrew C]

I have a Vixen Geoma 80A spotting scope, to which I would like to attach a CS mount astro video camera.

The scope body has a male M42? threaded flange over which the Vixen EP is screwed.

Superficially, it looks as though an M42 to C/CS mount adapter would do the trick for what I want to do.

The problem is that the back focus distance (flange to focal plane) of the scope body is very short, and it does not appear that the adapters (which seem from the photos to be fairly long) would allow the scope/adapter/videocamera combination to focus out to infinity.

The Vixen EP has a central section that actually fits inside the flange (presumably to keep the whole assembly compact), and this may be their proprietary solution to this issue.

Has anyone solved this one (narrow C mount teleconverter to fit inside the flange or some other solution)??

[Dennis]

Hi Andrew

I cannot offer any help with your specific problem, but double check your M42 assumption as a lot of my Vixen eyepiece adapter accessories are actually M43 for my Vixen astronomy gear.

And, the Vixen M43 is not the same as the Takahashi M43 – one must be 0.75mm and the other maybe 1.0mm thread?

I hope you find a solution.

Cheers

Dennis

[Andrew C]

Thanks Dennis,

The outer thread on mine is 1mm pitch, but I don't have anything in the way of an old screw mount Pentax lens to check it with at the moment. Will keep your advice in mind.

I did also send a query to Vixen in Japan, but am not sure whether they will respond (they may just say no or too hard).

Cheers,

Andrew

[iceman]

Have you tried asking Steve Mogg from moggadapters?

[Dennis]

Hi Andrew

My wife has a Leica spotting ‘scope and we tried afocal bird photography through the eyepiece and had some minor success, but it was difficult and unrewarding. Like the Geoma, the Leica eyepieces have lens elements inside a barrel that protrudes into the ‘scope body. I suspect that these ‘scopes are an F5 to F7 design and to allow for their close focusing, typically 3 metres, part of the eyepiece body has to protrude into the ‘scope body.

We also have the Leica photo adapter that converts the ‘scope to an 800mm F10.4 telephoto lens but this adapter is approx 6 inches long (150mm), placing the DSLR quite some way from where the eyepiece position normally is.

I think it is a tough ask unless Vixen have some accessory made for the job?

Cheers

Dennis

[turbo_pascale]

You could get Luke at http://starstuff.com.au/camadaptors.html to sell you one of his C/CS mount to 1.25" nosepiece adapters. That's what I use on my Imaging Source camera. If you can get an EP to focus, you can get one of these to focus.

[Andrew C]

Hi again Dennis,

Yes the Vixen is roughly an F5.6 (450/80). It wouldn't worry me too much to have to use a long extension photo adapter if Vixen had one at a reasonable price - I haven't seen one referred to but will have to ask them about that. I assume the Leica one sits in place of the EP, so it too presumably has a lens element very close to its front end much like the EP does, to meet the focal plane.

Cheers,

Andrew

[Andrew C]

Rob, the problem with this approach is that there is no 1.25" barrel on these spotting scope eyepieces - they (at least the Vixen ones) use an eyepiece socket with a protruding head having a male thread on the outside, and with a narrow internal diameter of about 28mm only. The EP itself has an external sleeve that screws down over the outside of the socket head.

Cheers,

Andrew

[Andrew C]

Will check him out thanks,

Cheers, Andrew

[Dennis]

Hi Andrew

Here is a photo of the Leica adapter indicating the position of the multiple lens elements.

Cheers

Dennis

[turbo_pascale]

Andrew,

Both Luke @ Starstuff and Steve @ Mogg Adapters could make something up for you - just work out who's going to be cheaper and who can get it made quicker! Both these guys are very busy beavers!

[Andrew C]

Thanks again Dennis. It looks as though the Leica scope design is similar in terms of the EP connection method, with probably somewhat more back focus distance than the Vixen, although still not a lot. As you said before, the only likely option is if Vixen themselves have an equivalent adapter.

Andrew

[Dennis]

Hi Andrew

With a full Moon it might be worth taking your spotting scope outside and pointing it at the Moon, without the eyepiece, to establish where the prime focus is. Use a small sheet of grease proof or transparent tracing paper so you can bring the Moon to focus.

At least this will let you know how close the focal plane is to the body of the ‘scope in case you decide to get an adapter made up.

I might just try the same experiment with ours, just for interest.

Cheers

Dennis

PS – I know that you know Andrew, but just in case someone else stumbles across this thread in the future, via a search engine – DO NOT POINT THE ‘SCOPE AT THE SUN – WITHOUT A FULL APERTURE SOLAR FILTER, YOU WILL SUFFER IRREPERABLE EYE DAMAGE.

[Andrew C]

Dennis,

It turns out that the focal plane is actually inside (!) the telescope body when focussed at infinity, so there was not much joy to be had there without the proprietary EP. Vixen confirmed this in a later email. I am experimenting with eyepiece extension instead.

Cheers,

Andrew

[Dennis]

Hi Andrew

Much as I expected. The Leica eyepiece barrels have elements that extend into the body of the ‘scope also, so I figured the focal plane must lie inside the body.

Cheers

Dennis