When using manual lenses with manual aperture setting on the lens, the electronic viewfinder and the live view screen becomes very dark. This is due to the small aperture normally used in closeup to increase depth of field. Another reason for dark screen is use of extension tubes in order to increase magnification. At 1:1 there is already a loss of two steps of light, and the screen darkens even more with higher magnification. This makes focusing very difficult, and could force the use of artificial light for this purpose. This problem will also be present using reversed lenses. Live view focusing is the preferred way of focusing in closeup work, and for moving subjects flash is usually a necessity.
A solution with mirrorless
Sony a7 cameras have a menu setting for the live view function which lessens this problem and makes it easier to focus. Go to Menu – Cog wheel – Live View Display. Here, it is possible (on the a7R) with two selections: Setting Effect ON or Setting Effect Off. Choose Setting Effect Off. This will always give correct brightness of the live view screen, no matter what the manual aperture is set to. This means that it will be much easier to focus using small apertures and flash. The downside is that it will not be possible to see how the exposure will become in advance, like we normally do with mirrorless cameras. But for closeup work this setting is very helpful when we use flash exposeure. The other setting (Setting effect On) and flash exposure will give ghosting.