Hey Jon, this is very insightful. Thank you. I agree with the cross hairs, I was looking at illuminating eyepieces, but I am a explore scientific kind of guy, and as of now I’m not aware of them offering such a thing. Orion seems to have one with a nice FOV would be interested in quality. Would love to know how / where you put in cross hairs on your eyepiece, have you tried the illuminated eyepieces? Also, I noticed your finder scope is located very very close to your focuser (nice configuration by the way). How do you like that position? Do you use your finder scope for any wide field viewing?
- I have owned a number of illuminated reticule eyepieces including the AgenaAstro version of the Orion 20 mm 70 degree. I dislike them. They illumination bleeds into the field, they're fragile and unnecessary. They also an Erfle derivative or something and quite a mess off axis.
The 20 mm 70 degree was my last purchase. After trying it out, I decided there commercial eyepieces were hopeless and decided I had to modify existing wide field eyepieces. The first one I did was the 24 mm TV Widefield. The cross hairs are placed at the focal plane so they're in focus. That means attaching them to the field stop. The field stop has to be wide enough to glue the wire to. Eyepieces like the 24 mm Panoptic barely have a field stop, too narrow. It's difficult work because you're working inside the barrel.
The usual problem with unilluminated cross hairs is that they disappear under dark skies. This is just because the cross hairs at too thin, bad design. Thicker wire, I use 0.004" hard brass EDM wire, is easily seen even under the darkest skies. Last week I was at the Navajo National Monument. Directly overhead was the Milky Way. Pointed directly at the Milky Way, I was reading 21.82 mpsas on my SQM. Pointed at the darkest sky, 21.9. I had no trouble seeing the cross hairs.
Positioning the finder relative to the focuser is important. It needs to be close so that it's easy to work between the main scope eyepiece and the finder but not so close that they interfere. I use 6 screw mounting rings so I can slide the finder in the rings to position the finder.
I do use the finder as a mini RFT, sometimes using filters. I use my refractors less now, the 50 mm does a good job.
Regarding finder aperture:
As I said, I have 50mm, 70mm and 80mm RACI finders. Both the 70mm and the 80mm were reworked so they operate at full aperture. The 70mm is an Orion Multi-Use finder with the objective replaced with a Japanese Carton 70mm F/4.5 air spaced objective from Sheldon Farowski. I am using AgenaAstro rings. The complete finder weighs 29 ounces minus eyepiece. Optically, it is very good (not many finders split the double-double) and with the 24mm TeleVue wide field, it provides a 4.5 degree field at 13x, it's really a very nice view.
The StellarVue 50mm finder weighs 19 ounces so that's only a difference of 10 ounces so it doesn't take a lot of counterweight to balance the scope. With an ST-80, you gain a little aperture but just the scope weighs 48 ounces and then with the diagonal and rings, it takes a lot of counterweight, at least 10 pounds with an Obsession style truss Dob.
I always take the 70mm with me and I do use it some but I find that the 6.4 degree TFoV at 10 inch shows me plenty of stars and the wider field is a real advantage, it just works better for me. But the 70mm, it's a good finder...