Great info Jon - though you don't mention which RACI you use And just as you do, my intent is to add a wide angle EP to see more of the sky. I'm still learning my way around - I know most of the northern constellations now but not nearly to the detail to get around without help - and help is necessary with the contortions of the EQ. Still, I am determined to master it - with a bit of help.
Do you glue the cross-hairs into the barrel (obviously not touching the glass) and what do you use for material?
I have settled on a Stellarvue F050W2 - it has great reviews and interchangeable EPs. I guess the unknown is how much capacity there is for reaching focus with other EPs: I may have to find a high FL to match. Maybe they can help me.
I presume I can use the RACI as a finder when I move to photography too...
"Still, I am determined to master it - with a bit of help."
I like your attitude. If there is one virtue, one trait, that is required to be an amateur astronomer, it's perseverance, there are many obstacles and overcoming obstacles, whether it's the clouds, the cold weather, light pollution, bugs, humidity.. it's a big part of amateur astronomy.
And having the right equipment to star hop successfully, that is also important. So many are dismissive of star hopping,particularly under light polluted skies. If one wants to do it, it can be done. I do it because I love doing it.
I did mention I use a Stellarvue 50mm RACI finder.
Eyepieces for finders, the short story:
To start out, I would just use the eyepiece that comes with the finder. I calculate that the eyepiece that came with my SV RACI 50mm provides a 6.0 degree TFoV, that's generous and if you find you want more, that's the time to decide modify an existing eyepiece.
The long story:
As far as the cross hairs. It's pretty tricky. First, it only works with some eyepieces.
Eyepieces have a field stop, it's what you see at the edge of the field of view when looking through the eyepiece. With many eyepieces, if you turn the eyepiece over, you can see that ring. It's at the focal plane of the eyepiece and since you want the cross hairs to be in focus, they must be attached to the field stop. Not all eyepieces have field stops that can be seen or that are accessible. That's the first requirement.
The second requirement is that the field stop be wide enough to glue to. Eyepieces that maximize the field of view have very large field stops, just a fraction of a millimeter narrower than the barrel, there's not much to glue to. And the diagonal of a finder doesn't have the full 27mm of clear aperture to avoid vignetting. A field stop of about 25mm is about right about right, enough to glue to, not to wide to vignette.
The third requirement is that eyepiece must focus in the SV finder.
And finally, the eyepiece needs to be reasonably well corrected in the F/4 finder.
Such eyepieces are expensive.. From what I can see, I I think the 20mm Explore Scientific 68 degree would be about the best choice. I would provide a 6.5 degree TFoV at 10x, it has a 22.8 mm field stop and should be quite sharp at F/4. But it costs $152..
When I decided to do this, I had an old 24mm TeleVue Wide field that had seen better days and so that is what I used. It has a near perfect 24.7mm field stop so it provides a 6.8 degree TFoV.
I use 0.004" hard brass wire for the cross hairs. I have a large stock of it and can slip some in an envelope and send it if need be.