fmazzanti I was getting horrible light leaks that emerge as clear patterns.
As with all EFW from ZWO (not just one model), you can't expect to use them without mitigating the light leaks yourself.
This is especially true with the ones where you remove the tilt plate from a camera, and replace the tilt plate with the EFW.
If you look at a camera tilt plate, you will notice a foam annulus that is countersunk into the tilt plate. The foam compresses and form a light shield for the sensor. There is no such countersunk "moat" in the EFW, so light simply leaks at the interface between the bolted EFW back and the camera body.
For these, you need to use black electrical tape (both light blocking and stretchable) and do something like this:
Take special care where the flat part of the EFW does not overlap the flat part of the camera (on the right in photo, hidden from view) since that part will leak the most light.
You can avoid this by using threaded spacers, in which case the tilt plate would still be in place.
The other place you need to tape is the circumference of the stepper motor (white disk, used to say Made in Japan, now Made in China). That really leaks light. Just tape it off like this:
Do not tape over the bearings. Notice I left a gap in the tape.
There are also 4 small screw holes on the OTA side of the newer EFW plate. Tape them off too. At least the older versions don't have these screw holes. The problem with light leaks is getting worse (they are not reading this forum), not getting better with newer models. I don't know who came up with the idea on how to mount the stepper motor; they keep repeating this mistake for many versions of the EFW in spite of long standing complaints at sites like Cloudy Nights.
I don't think ZWO folks actually use their own EFW; everyone else seem to notice the leaks. If they had tested it, they would have noticed the light leaks right away.
Chen
