Over the last 50 years I've owned about 16 Pentax SLRs. This includes 9 Pentax dSLRs: 7 APSC dSLRs and 2 FF dSLRs. I still have several of them.
My SFX and Z-1P cameras.
Over the last 57 years I've also owned several mirror-less cameras; Pentax and non-Pentax. Sometimes I use both [d]SLRs and mirror-less cameras in parallel on the same occasion for their different benefits.
I sometimes mix different viewing technologies on a camera to try to get a superset of their benefits.
I've experienced the evolution of various viewing technologies over all this time. This thread summarises their advantages and disadvantages for me.
My history:
I started with a Brownie 127.
In 1963 (while still at school) I bought a Werra 1c. It was little more than a 35mm box camera, with a decent lens and in-lens shutter and a simple optical viewfinder.
I soon had some photos taken with it published, and I won first prize in a photo competition in a weekly photographic newspaper.
Over about 7 years I used my Werra 1c in about 7 European and Scandinavian countries, mainly successfully shooting black-and-white and colour-negative film.
All I really needed was a box with a light-sensitive recording medium and a way of pointing it in the right direction.
In 1967 a friend lent me his Pentax S1A to try. I suddenly realised what I had been missing:
- Parallax-free viewing!
- [Manual] Through the lens focusing on the viewfinder screen!
About 1970 I bought two Pentax SP500s. Since then, Pentax [d]SLRs have been my main top-end cameras, giving me:
[1] Parallax-free viewing.
[2] Manual, then later automatic, focusing.
[3] Manual, then later automatic, exposure control.
My two SP500s. I still sometimes pick them up and wind-on and press the buttons!
Those three features (plus image quality) are what I typically want in my main cameras. [2] is the most important, because if it fails, the image it typically lost.
Experience with 35mm film, then Pentax FF dSLRs, tells me that full-frame is best for my more serious photography.
My typical airshow or motor-sports or bird-in-flight kit.
I always want to have a smaller lighter camera available. So I typically have a mirror-less camera of some sort alongside my [d]SLRs. An example was a fixed-lens 35mm AF camera such as the Pentax Espio 120. From 2009 my smallish mirror-less cameras have been digital.
Such cameras are less "imposing". (And quieter, which can be important in some situations, such as bird-photography). They are convenient as "carry around" cameras. I often use them for context setting. And if the worst happens, they provide (very limited) back-up.
I now own mirror-less Pentax Qs, Panasonics, and Ricohs. I'm comfortable with using Electronic Viewing within its limitations at the time. My current small, digital, mirror-less, "carry everywhere" camera, is the Ricoh GRIII, which I hang off my belt when outdoors.
My Ricoh GRIII "carry everywhere" camera hanging on my belt.
Each of these is "a box with a light-sensitive recording medium and a way of pointing it in the right direction".
Mirror-less cameras allow better designs for wider-lenses: they can avoid the need for an "inverted telephoto" design, allowing lighter, cheaper, and potentially better quality lenses. They also avoid the need for AF Micro-adjustments.
This identifies problems introduced by the use of a mirror.
"Photography" doesn't need mirrors. Mirrors are simply one way of doing some of the preliminary actions that some of us demand in order to eventually capture an image. Mirrors introduce problems of their own!
Now consider burst-mode!
I've consistently found over years that the visual effect of mirror-flipping in burst mode has an adverse impact on my action photography. I want my future burst-mode photography not to involve mirror-flipping.
I hope this 5.2 MB video can be seen:
www.barrypearson.co.uk/top2009/downloads/00000.MTS_1.wmv
This is not a criticism of "Pentax". It is a criticism of "mirrors", whatever the brand.
I've spent time and money on two main ways to avoid this problem:
- A Red Dot Sight. (I have two of them).
- A supplementary optical viewfinder on the flash-shoe.
My first Red Dot Sight
My second Red Dot Sight
I find aligning my Red Dot Sights with the lens-axis too fiddly and error-prone. I'm unlikely to use them again.
Setting the alignment of a Red Dot Sight; in my garden, not even in the field.
Use of a supplementary viewfinder, fitted into the flash-shoe, works for aiming purposes, not for composition purposes. But when I'm (say) shooting aircraft in flight, "aiming" is what I'm doing! It is relatively easy to have an optical viewer intended for a Ricoh or Pentax-Q camera in the flash-shoe.

I've had a 50-year love-affair with Pentax [d]SLRs!
But we have become incompatible.
I've used mirror-less cameras for 57 years.
It is time for me to become mirror-free.
I'm currently gaining experience with an FF mirror-free camera.
This is "work in progress": so far, so good.
I hope to be ready for airshows on 18, 19, and 20 September.
Sooner rather than later, burst mode won't be a problem for me.