Binoculars from two Pentax 80EDs (1 Viewer)

[btschumy]

I am investigating mounting a pair of Pentax 80ED spotting scopes side-by-side to build a pair of astronomical binoculars. There are two features of this scope that make it particularly attractive for this project:

1. Uses standard 1 1/4 inch eyepieces
2. The scope can be rotated about its axis while mounted using the "click-stop rotation mechanism".

The reason #2 is important to me is that I'm considering using this feature to adjust the interpupillary distance between the scopes. Since the eyepiece rides above the optical axis, rotating the left scope clockwise and the right counterclockwise should reduce the IPD when two scopes are mounted side by side.

For this to work in my application, this rotation mechanism needs to be pretty precise. If there is any slop, the collimation of the two tubes will be affected. It is also important that the "click-stops" be fairly fine grained so as to give me enough precision in the IPD adjustment. I would get that I would need somewhere in the vacinity of 60 clicks per 360 degrees rotation.

So for those of you that have this scope, is the mechanism precisely designed and fine-grained? The best way to determine the precision would be to use a reticle eyepiece, center it of some spot far away and rotate the tube. If the reticle crosshairs remain centered on the spot then all is well. I understand that not many of you will have a reticle eyepiece, but maybe you could still comment on the precision.

Also, is there a release mechannism you have to disengage to rotate the tube, or does it just rotate with a little force. From pictures it appears there may be a release mechanism on the left side of the tube. If so, and if I have two tubes mounted close together, how hard will it be to get to the release on the right tube?

Thanks for any help you can give me.

 

[possum]

I am investigating mounting a pair of Pentax 80ED spotting scopes side-by-side to build a pair of astronomical binoculars. There are two features of this scope that make it particularly attractive for this project:

1. Uses standard 1 1/4 inch eyepieces
2. The scope can be rotated about its axis while mounted using the "click-stop rotation mechanism".

The reason #2 is important to me is that I'm considering using this feature to adjust the interpupillary distance between the scopes. Since the eyepiece rides above the optical axis, rotating the left scope clockwise and the right counterclockwise should reduce the IPD when two scopes are mounted side by side.

For this to work in my application, this rotation mechanism needs to be pretty precise. If there is any slop, the collimation of the two tubes will be affected. It is also important that the "click-stops" be fairly fine grained so as to give me enough precision in the IPD adjustment. I would get that I would need somewhere in the vacinity of 60 clicks per 360 degrees rotation.

So for those of you that have this scope, is the mechanism precisely designed and fine-grained? The best way to determine the precision would be to use a reticle eyepiece, center it of some spot far away and rotate the tube. If the reticle crosshairs remain centered on the spot then all is well. I understand that not many of you will have a reticle eyepiece, but maybe you could still comment on the precision.

Also, is there a release mechannism you have to disengage to rotate the tube, or does it just rotate with a little force. From pictures it appears there may be a release mechanism on the left side of the tube. If so, and if I have two tubes mounted close together, how hard will it be to get to the release on the right tube?

Thanks for any help you can give me.

Sorry this is a bit late, you probably know all this by now.

I have a PF100 ed scope and recently I've been thinking about doing the same, but using another 100mm scope.

The Pentax optics are fabulous, and I use mine for digiscoping as well as direct observation.

I use the rotation of the telescope to provide additional space between the Pentax scope and a 6-24x by 50 rifle scope that I use as a view finder for digiscoping, and which for compactness is mounted to the left of the Pentax.

I align the rifle scope to the Pentax on a distant object, say 450 yards. Rotation of the Pentax of 120 degrees about its objective optical axis, results in misalignment of about 4 feet at 450 yards.

There are three errors to consider, the concentricity of the optical axis of the Pentax with repect to the machined axis of its mounting collar, the angular alignment of the same, and lastly, and less importantly, the parallelism of the machined base of the Pentax mounting shoe with respect to the optical axis.

This last error is easily compensated by the mounting adjustments incorporated in any proposed mechanical layout. For me it required a small amount of shimming to the mounting of the rifle scope's dovetail slide, in order to produce proper collimation.

The IPD might be a problem, as the minimum is determined by the diameter of the collet locking wheel used to secure the eyepiece.

This results in a minmimum separation of 66 mm, 2.60 inches, between the eyepieces, OK for me, but too wide for my wife. For me, I find that having the interocular eyepiece distance set some 2 to 3 millimetres smaller than distance between my pupils provides me with the best view. ( Maybe I have a problem).

The rotation system of the scope is not a series of fine detents, but a continuous and smooth rotary mount, but provided with predetermined detents at 45 degree intervals. However I find that it is easy to set and forget the alignment, there does not appear to be much , if any, creep. The feel is smooth and fairly weighty, but this is readily altered using a different viscosity of lubricant, as in fluid heads.

The little thumbwheel locking screw is small and I can see no problem with reaching the right hand one as it is set well inside the throw of the optical crank defined by the prism assemblage.

I would encourage you to try the 100 mm scope, it is a total revelation, and combined with the wonderful Pentax eyepieces, represents astounding performance for the money.

Hope this helps

 

[Humboldt Jim]

Large binoculars

An interesting project, particularly if you have a small machine shop.

What I don't understand is why you don't just get some Fujinon 80, 100 or 120 mm astronomical binoculars? All of the features that you mention are on at least one model and there is no fiddling around with alignment.

Unless you are doing this as a hobby project, you would probably be time, mney and quality ahead by choosing big astro binocs.

Just my two bits worth.

 

[ranburr]

You may want to look over on swfa.com click on optics talk. There are several people who have don this with Swarovski spotters.

ranburr