It’s interesting to see how the term viewfinder is now used for small monitors rather than monocular viewfinders or shrouded dedicated viewfinders. Unless the a monitor screen is properly shielded from external light then you can only guess at the contrast and brightness of the images feeding it in anything other than a dim/dark room.
This is one of the key reasons why for decades viewfinders have been in fully shrouded hoods, snoots or loupes. As one of the key roles of a viewfinder is to show how your recordings will look for exposure assessment, if it doesn’t have a full shroud then in my opinion it isn’t a viewfinder, it is simply a monitor and exactly what your images will look like is anyones guess depending on the ambient light conditions. Furthermore even a young person with perfect can’t focus properly at less than 6″/150mm and that distance increases with age or in low ambient light. So most people will need a loupe or magnifying lens to be able to make full use of a small HD LCD for critical focus. In order to be able to see the sharpness of an image you need contrast, so an unshaded LCD screen on a sunny day will be next to useless for focus – perhaps this is why I see so many out of focus exterior shots on TV these days?
To be truly useful a viewfinder needs to be viewed in a controlled and dark environment. That’s why for decades it has been normal to use a monocular viewfinder. The eyepiece creates a tightly controlled, nice and dark, viewing environment. This isn’t always convenient. I will often flip up or remove the eyepiece for certain types of shot. But – if you don’t have the option to fully shade the viewfinder – how do you work with it on a sunny day? On a camera like the FS5 I often find myself using the small, enclosed viewfinder on the back of the camera when the sun is bright. These tiny built in viewfinders are not ideal, but I’d rather have that than a totally washed out LCD or trying to shoot with a jacket over my head as my only option.
So next time you are looking at upgrading the monitor or viewfinder on your camera do try out a good 3rd party monocular viewfinder such as the Zacuto Gratical or Zacuto Eye. Perhaps consider a Small HD monitor with the Side Finder option. Or an add-on monocular for the existing LCD panel. Without that all important shading and magnification it isn’t really a viewfinder, it’s just a small LCD monitor and in anything other than a very dim environment it’s always going to be tough to judge focus and exposure.