wolves3012 said:
Baselength isn't the only factor, RF magnification is too. Out of interest, I made a comparison (only approximate since I don't know the exact magnifications) and there's actually very little to choose on the accuracy of all the FSU RFs. The FED 3, 4 and 5 are slightly less accurate than the others, all others are almost identical. The Kiev, despite the longest baselength, is only marginally the best.
A long baselength isn't the same as higher magnification. A movement on one end results in a visible shift in the finder. Different magnifications can make the apparent offset in the finder similar, but the basic geometry makes a longer base more accurate, regardless of the finder mag.
Consider that any mechanism for syncing the rf to the lens focus has limits. A short base rf translates each degree of lens movement into a far smaller degree of mirror/prism/whatever movement than a long base rf. Any free play in the mechanism can result in no movement of the rf reflector even though the lens focus has changed. As your rf base increases, the tolerance for error increases - one degree of error in a short base can result in a large focus error, while the same one degree of error in a longer base will result in a much smaller error in focus. This is independent of finder magnification.
For example, my Canonet has a rf base of very roughly 30mm. At 1 meter, an error of 1/10 degree makes the focus of by almost 6mm. On my Kiev 4 with a rf base of very roughly 90mm, the same 1/10 degree error renders the focus off by not quite 2mm. At 5 meters, the error on the Canonet would be really close to 159mm, while the Kiev error would be only 49 mm. This addresses an error caused by a knock or drop that caused the same displacement on both rf mechanisms. The view through the finder would appear in focus. Errors induced by gear play would have similar implications. A small error in a long base rf has a minor effect, but the same small error in a shorter base does greater damage to focus accuracy, increasing as distance to subject increases. Finder magnification has no effect on this kind of error.
Obvously, error induced in an otherwise perfect rf mechanism by the user would have similar greater implications with a shorter rf base. But missed focus is missed focus
🙂 One might argue that higher finder mag helps the user more accurately focus, but we have already seen how slight errors in rf alignment results in smaller focus errors with a longer base. It really doesn't matter if the error is user induced or not. Higher finder magnification is only "better" when compared to equal base rf mechanisms, basically.
Higher finder magnification only makes the rf spot alignment easier to see. It doesn't change the basic accuracy of the mechanism itself. With a longer base, even a low mag finder can be highly accurate and easy to align. In practice,
assuming both rf mechanisms are accurate, higher mag on a shorter base is comparable to lower mag on a longer base. But if one has questions about the play in the mechanism or its current state of sync with the lens, a longer base is more forgiving of errors. The longer base can tolerate greater error between mount and finder spot with less focus error. As well as be more tolerant of eyesight failings.
With that said, I like my Kiev's because I like to use them, not for technical reasons. I was attracted to them because they were based on the Contax design vs. Leica. No dislike for Leica, I just made a choice I'm happy with. I have every intention of using something like a FED 2 and a Leica rf down the road, but it might be a longer road now that I have my Kiev's
🙂
