AstroDude42 Interesting, that it leaks light "by design". I will use it and fill the screw holes as you pointed out.
Lots of ZWO products are flawed "by design." Hiding a WiFi antenna inside a metal Faraday cage is a glaring example. Just ignorance of fundamental principles, and how devices are used by real hobbyists.
You can probably just use electrical tape over the holes. Even on the underside, since a small tilt is not going to be a problem. But even with tape on the upper surface, you will not be touching the tape since after assembly, it is all enclosed in a M42 tube.
And do yourself a favor and not succumb to any ZWO or SVBONY glass filters. But you don't need to use premium filters either in this application. For 685nm IR pass, I use a cheap Antlia at 1.25", and a cheap Optolong at 2".
Another light leak source is the way the new ZWO filter wheels are held on the camera body using screws, after discarding the tilt plate. The light leak from that is atrocious. You should see all the ugly tape I have to keep light off -- must have used a quarter roll of electrical tape :-). Another light leak is with their original filter drawer, where they saved a few pennies and made the cover plate too short. They saved a few pennies, but it translated to many dollars of frustration for the customer.
What would be a better one? Something like the William Optics Uniguide series (32mm or 50mm)?
Almost any other optics would be better. But don't get the 130mm one from QHY either. That one has optical quality almost as poor as the ZWO one. And speaking of weight, I could swear that my Borg 36ED is lighter weight than the ZWO guide scope even after you remove the mounting bracket. With the Askar 230, I am discarding the heavy reducer (so it becomes 275mm focal length) and the obnoxiously heavy tube bands -- I replaced them by a pair of (third party) Canon tripod rings that happens to have a diameter of 66mm. The tripod rings are also black instead of ugly red, but that does not make it work any better, just less unprofessional. To reduce the weight of all of my guide scopes, I use ARCA Swiss to mount them. The RST-135 is so resistant to third axis balance that I had a thick aluminum plate fabricated as a dual saddle with a Losmandy dovetail clamp for the main OTA, side by side with a set of ARCA Swiss clamps for the guide scope. (Between them are a power hub and a USB hub.).
That is something i did not know.
Should be quite obvious when you think about it, no? The sensor size does not change when you bin, so the FOV stays constant as long as focal length stays constant. Now, on another thread, someone was complaining that the sensor size of a different camera changed by a couple of pixels after binning -- we are talking about loss of a couple of arc seconds, and dithering has bigger loss! Silly complaints when there are much bigger problems with that camera :-).
As long as the star size (plus influence by atmospheric turbulence) is larger than a super pixel, there is no downside to binning that is immediately obvious to me. Your stars will have better SNR, and the guiding rate is faster. The read noise is higher when you use higher frame rates, but that is not directly caused by binning, but by reducing the exposure time.
Do try 2 FPS since the RST-135 should benefit from it. By the way, surprisingly, your ASI178 should also be capable of 2 FPS when it is binned. But the near IR performance is no good. I did a FPS check with my dozen or so ZWO cameras after the ASIAIR attained the capability of binning during guiding.
Chen
