I posted a reply to this question over on DPReview just a few minutes ago
For reference, here's what I wrote :-
The K100D is a fairly basic camera, by today's standards, so LiveView (and tethering) was still some way in the future when it was designed.
So, it's back to basics!
A right-angle viewfinder will help enormously, especially one like the "Ref A"
https://www.bhphotovideo.com/c/product/41121-REG/Pentax_30148_Right_Angle_Finder_A.html? ... it has a prism internally so the image isn't laterally reversed (cheaper devices use a mirror and can be a pain with a moving subject), it also has a built-in 2x magnifier which helps as well.
Mine has been in regular use since I bought my
*ist film camera, when it was VERY expensive, although these days I will admit to using the tilting screens and LiveView on my K-70 and KP as well
The big advantage of the viewfinder is the lack of reflections, as experienced with a LiveView screen, so I won't be retiring mine anytime soon, indeed, it's in my bag permanently!
Good luck
Afterthought : However, you do have the opportunity to utilise "Digital Preview", which may help in some circumstances. This involves configuring the camera to make a "test exposure" and display it on the screen when the Depth-of-field preview switch is operated - see p.152 in the user manual