The idea when focusing is to hit the 'sweet spot' as seen on screen, the resolution of the 'live image' isn't important
If I may quibble here: if you mean that if the microscope is focused to show a sharp image on the monitor screen, it is unimportant if the view through the eyepiece is sharp, then I'll have to say that this is to a certain extent true but only for low power/small aperture objectives. With objectives with NA of 0.3 and above, if both camera image and view through the eyepiece are not in focus at the same time, then the camera image will suffer spherical aberration (as though one is using the wrong cover glass thickness), and the effect increases rapidly with increase in objective NA.
No, what I mean to say, assuming parfocality of the camera and objective (i.e. the view on screen and the view through the 'scope's eyepieces) has been set, as in my system by use of the focusing optics between the camera and the 'scope, the 'live preview' picture seen within Toupview may be set to a lower resolution than the camera's maximum. This will give a real-time response when focusing the 'scope as seen through the eyepieces or on screen - they are parfocal, that will exhibit a 'sweet (i.e. focused) spot that is passed through as the focus is moved to-and-fro whilst watching any part of the image being used as a focus reference, for example a cell-wall, nucleus etc..
The 'snap resolution' is however to be set and left at your camera's maximum
, and this is the resolution that your pictures will have
as captured. The lower resolution is only used for the 'live-view' screen. How
sharp it appears to be
on-screen during focusing isn't important, the important factor is that it's at the 'sweet-spot' that is the sharpest
position during focusing. Your captured image will be full-resolution and sharply focused, as with my 2mp Toupcam used in this way and seen in all my pictures.
It's just a manifestation of the lower video frame-rate of the higher mp Toupview (USB) cameras, this video frame-rate being that used to focus on screen, not the same resolution in which pictures are captured, much the same as my bridge-camera used for all my other pictures (i.e. not micrographic images) as taken in the lab etc, the live-view screen on the back of the camera is nowhere near the same resolution of the captured image (16mp).
Here's a screen-grab of Toupview using full-res 'live-view' for focusing, giving a slight lag from 'scope's image...
ws_tv-high-res-live-view.jpg [ 296.89 KiB | Viewed 7582 times ]
This is how I use Toupview, with 'live-view' in a lower res which gives smooth focusing whilst capturing images in full res
of my 2mp Toupcam by virtue of the setting of 'snap' resolution to the camera's 2mp maximum...
ws_tv-low-res-live-view.jpg [ 295.3 KiB | Viewed 7582 times ]
Hope this helps, but of course your camera and 'scope's images are far better parfocal I'm certain.