Telescope Reviews: T Ring for micro four thirds camera

I'd be surprised if you can find what you are looking for. camera T adapters are supposed to have the far end of the adapter a specific distance from the imaging plane. That's why yours has such a long barrel. If the distance from the front flange to the imaging plane is a fixed distance; then any "lens" designed to attach to a T adapter will have a "fixed" back focus. This makes it easy to calibrate the lens with focus distance markings and the manufacturer knows that the lens will work on any camera with its specific T adapter.

You might be able to take your long monster and ship it to one of the machining companies to have them shorten it and put new threads on the far end. Your description of the problem sounds like your scope doesn't have enough back focus to support AP using a camera and a T adapter.

One thing you could try is to remove the mirror assembly and use the collimation screws to move the mirror as far as it will go up the tube. This will increase the back focus at the eyepiece. You may get enough to focus your camera. You will need to collimate the scope after doing this. If this doesn't work; you can try using longer bolts for the collimation screws and locking bolts. Sears Hardware stores are a good place to buy small quantities of both metric and SAE bolts. Collars and washers will also let you use your existing collimation springs.

The main problem with moving the primary mirror is that you may start loosing light from the edges of the primary because the secondary is too small to catch the (larger) light cone as the primary is moved closer to it.

You'll also be limited to relatively short exposures because you have an Alt-Az mount. Imaging with this type of mount quickly shows the effects of using a mount that doesn't have one axis aligned with Earth's axis of rotation.

The easiest imaging technique available to you is afocal imaging. Use your camera, with its lens focused at infinity and attach it to an eyepiece that's accurately focused. I believe that ScopeStuff sells an adapter that attaches to an eyepiece and has male T threads on it. This can be attached to a female T adapter and step up/down rings that end up matching the filter thread of your camera's lens. You can also get camera holders that attach around the focuser and have a 1/4-20 screw to hold the camera at the eyepiece.

You might also be able to use an eyepiece projection adapter and one of your eyepieces to image with your camera without using the camera's lenses. This is usually done to enlarge the image from the scope but the correct choice of eyepiece focal length and distance of the eyepiece's optical center from the imaging sensor can use the eyepiece projection unit as a relay lens to improve back focus. The amount of focuser travel will also effect your ability to do this.

Phil