I’ve just finished my first build of the microscope (v7). However the objective is about 3mm above the top of the stage, have I bought an objective that’s too long?.
Total length is just below 50mm, and the length from the “pupil plane” to the end of the objective is 45mm.
I thought I’d try taking the motor off and manually cranking Z down as low as it would go and then manually focusing. Managed to get an image out!
That is what I would have suggested. To manually bring the objective down until you get an image.
I am glad that you have been able to get to focus. Now that it is in focus, could you post a picture looking in at the nut slot in the z-actuator column. The z-axis should be close to the central position, where the nut slot is lined up in the actuator and the casing, as it was when you put the nut in.
I think this is what you mean?
If I slide the allen key along the bottom of the slot it fits under the cap head of the nut.
I was meaning the nut on the screw actuator, at the left of your picture, not the screw holding the optics module. It is not quite clear, but it does not look as though the actuator is central.
When you said your objevtive is 50mm, is that the total length including yhe screw thread length? It should be 45mm from the shoulder of the screw, where it meets the top of the optics module, to the focal point. It looks as though you haxe a x40 lens, so the focal point is very close to the lens. The lens body would be a bit over 44mm from the shoulder to the lens end.
Second attempt (thanks for this help)
When you said your objevtive is 50mm, is that the total length including yhe screw thread length?
Yes, 50mm is the total size including thread. I’ve made a more careful measurement from the shoulder to the tip of the objective and it’s just less than 45mm (maybe ~44.9).
That is then a standard 45mm par-focal objective. In the picture the nut slot is a little up, so the objective has been moved down a little, but not much.
It all looks correct. 
