They were fine for what the camera was intended to be used for: a negative to give a positive contact print for a photograph album or a wallet. What's happening now is that people are trying to squeeze as much as they can from cameras which, at the time, did precisely what they were meant to do at the price offered. In the 1950s anyone who bought a Mess-Baldix or a Franka Solida, say - which, in today's terms, would equate to about £500 - would be happy with the result: a contact-print of their subject. It's no good using today's mores and ideals and technology to berate a camera which did precisely what it set out to do. You have to go back sixty-six years and look at it from a contemporaneous point-of-view.
We have a saying over here which describes the process of squeezing what you can out of something not designed for the job: 'You can't make a silk purse out of a sow's ear'. I've had more fun with that little folder than I have with any amount of digital auto-this-auto-that cameras, and am perfectly satisfied with my images, which knock the socks off 35mm negs. But that's because I'm aware of its limitations, including R/F limitations (been there; done that; what you describe about consistency has happened to me!).
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R.
No no, I’m not berating folders at all.
These folders, are from a time when contact prints were important as “what is on the roll at all”/“I just want some cheap photos to put in my wallet or put on my desk”, with full-blown use of enlargement for your favorites.
The original Brownies 6x9, 6x6 and other roll film formats, was clearly invented as a happy medium sub postcard size for contact printing, with enlargement as a distant possibility.
When we get up to Rolleiflex or 6x4.5, enlarging, projection and (stereo) magnifying slide viewers get more important and thus resolution and good focus.
Folders from the late thirties to sixties are not stretched beyond their ability all. They are used for exactly what they were meant.
The requirements are not that different from back then.
The last revival folders from the 80s and 00s might be able to pull out a few more lp/mm in the corners, but stopped down a great vintage folder from the last couple of decades of prime popularity, is about as good as it gets WRT IQ.
My point in this thread, is just that one should not put too much emphasis and trust on the build in rangefinder.
Sure, they where better than guessing for people with no sense of space and distance.
But, it’s much better to hone that skill.
It’s possible for just about anyone to learn.
Focus pullers on film shoots do it all the time.
Of course they also make use of pre-measured marks, which is another possibility for people photographing dynamic stuff. IE. measuring a mark and then waiting for the action to get to it.
BTW there is of course also quite good apps for distance measuring that work by triangulation and inclination.
For example:
https://apps.apple.com/dk/app/easymeasure/id349530105?l=da
With a light meter app you have just about everything you need (including image preview ;-)