bodon Mount seems to slew to a bright star but I get plate solve error.
Keep in mind that a plate solve is simply the process of taking a photographic plate with stars in it, and then using the pattern ("asterisms") of stars in that frame, compare them to a database of asterisms to find out where the center of the plate is.
(It has no bearing on the mount, or your guide scope or guide camera.)
Plate solving has to first identify stars. Big blobs are not stars, they need to be focused well. Streaks are also not stars, so for longer exposures, be sure that you have tracking turned on. And as far as your "bright star" is concerened, it also cannot use that particular star, since that willl look like an overexposed big blob; it will just use the other stars in the frame.
As far as stars go, they usually have a wide spectrum. You can kinda assume that their spectrum is as wide as a typically sensor's sensitivity -- e.g., 400nm to 800nm, i.e., about 400 nm wide.
Your Optolong Ultimate has two passbands, each of 3 nm in width (I had bought one not long ago to test how it fares compared with something like the Radian Quadband). I.e., it passes 6 nm worth of spectrum from a wideband source (e.g., the 400nm I mentioned earlier). As such, a star will be roughy 50 to 100 times dimmer at the sensor.
Notice that an emission nebula that emits wavelengths that pass through your filter will only suffer about 15% loss, instead of 100x loss.
If 0.25 seconds was the minimum exposure time that you could plate solve a certain region of the sky without a filter, that exposure time with the filter now has to be around 12 to 25 seconds! Thus needing to make sure tracking is on. If your minimum before was 1 second, you will need to increase that to 50 to 100 second exposures.
Now, you can also increase the gain of the camera by a factor of 50 to 100 (to reduce tracking error). If you are using a ZWO camera, they use 0.1 dB per gain value. I.e., a camera gain of "200" will be 20 dB compared to a camera gain of "0". A gain factor of 20 dB coresspond to a gain factor of 10, so it will be rather limiting, but you can certainly try using as much gain so that the exposure time only needs to be lengthen by 10x instead of 100x.
Your original choice of the L-eNhance has a total passband of more like 35 nm instead of a total passband of 6 nm for the Ultimate, and would have required 6 times shorter exposure to plate solve.
If you can adjust the optical axis of your guide scope to be aligned to the optical axis of your main OTA, you can use that to plate solve.
Chen
