Singularity Observatory
Telescope Mirror Flip Flop
Using new Celestron telescopes, how well do mirror locks work to reduce or eliminate the shifting of the mirror?
There are two specific conditions that affect SCTs with moving mirrors. The first is mirror shift that occurs when you are attempting to focus. The second is mirror FLOP, where the mirror moves as you cross the meridian or change orientation in altitude.
The mirror locks do absolutely nothing to control the shift that occurs when focusing. For visual use, they are not normally employed because you would have to unlock them every time you wanted to change focus.
If you are imaging, the locks are used to keep the mirror from flopping as the telescope changes orientation. For this, they are very effective. Once the mirror is focused and the lock knobs are tightened, the mirror will maintain its position and not flop around as the telescope is moved across the sky. Once you put your camera on and focus, you can move from object to object without fear of the mirror flopping to a different orientation.
Note: As soon as you adjust the focus using the mirror focuser you may introduce a shift in the mirror. The mirror locks do nothing to counter this. The mirror locks consist of small rods that are attached to the back of the mirror assembly and extend into the lock knobs. When the lock knobs are turned, they cause the mechanism to tighten around the shaft to hold it in place. The best way to avoid the flop issue, if you can do so with the back focus, is to use a rear cell Crayford focuser. That way you can lock the mirror into position and leave it there when collimated.
When dealing with flop, it may not be an issue when astro imaging with short exposures summed in a small time frame where the telescope will not cross the meridian or make large changes in elevation.
