25mm viewfinder accuracy.

[andephotographic]

I'm selling the viewfinder that came with my 25mm Snapshot Skopar and a buyer has asked me if the framelines in it really are 25mm. I only have nothing to compare it to really so wondering if anyone here knows?

(I know, maybe dumb to split the lens and vf up but I don't see me selling the lens and I use it on the R-D1s which has a built in finder with 28mm lines and if I get a film body it'll be an R3a or R4a so never use and never see that I will use the 25mm finder.)

 

[Richard G]

Tell him they really are 25mm. There's naturally some variation in coverage, depending on camera and distance. I don't quite know what he means by his question. They really are in the sense it is not another focal length. And they really aren't if he means does what the finder shows exactly match what will appear on the negative.

 

[andephotographic]

He says he wants to use it on a Sigma DP1X. The lens on it is 28mm equiv so not sure why he is so bothered about the accuracy to 25mm.

I think what you are saying is that unless the viewfinder was made specifically for a particular camera the view through it won't exactly match what's on the neg (or sensor) right?

 

[sevo]

I think what you are saying is that unless the viewfinder was made specifically for a particular camera the view through it won't exactly match what's on the neg (or sensor) right?

Well, the finder can only be accurate to specification for cameras with a hot/coldshoe position (relative to the lens) identical to the one it was made/adjusted for.

But given that parallax can only be compensated for flat field subjects in one single distance, specifications are far from general, and it might still be accurate at some other distance - and parallax corrections only work within sometimes impractical constraints in any case. Even the best parallax-compensated brightline rangefinders are only a very coarse framing guide once you get to close-up work in a three-dimensional world - if you need high precision framing, there is no way around a (SLR/view camera/live electronic) finder using the image from the main camera lens.

It is trivial to test whether a given auxiliary finder will work for you - move the finder by the difference of hot shoe positions between the original and your camera, and it will become evident whether and for which distances it is relevant...

 

[Richard G]

My film Leicas have a narrower view for a particular frameline or external finder compared to the M9. The field of view of finders is affected by the distance from the subject. The precise alignment of the mounting shoe, with the differing offsets of that to lens axis, and the vagaries of manufacture, even with Leica's exacting standards, means that there will be some natural variation from camera to camera of the same make and even model, and from one 25mm lens from one manufacturer and another manufacturer's lens. So the guy either wants an SLR or he'll be happy with your 25mm finder's field of view.

 

[mdarnton]

It depends on the finder. Your purchaser may be very observant. I had one of the plastic 25mm finders, an early one, and it was very apparent that the view through the finder was not in 3:2 proportions. I checked the coverage against my negs carefully and discovered that the window was slightly squarer than a 35mm frame, and that the sides and bottom were fine--by which I mean the view was proportional and spaced correctly. However, there was a lot of extra on the top in the finder, above the real photo, and the coverage was definitely not a 3:2 ratio. I don't know if this persisted through all of the plastic finders, of whether it was just an early thing, or maybe just a fluke (that, I doubt) but it was definitely there.

Easy to check, by the way: find something in real life that's 3:2, and see how it fits in the lines.

I also had 15mm and 28mm versions of the same black plastic finder, and they were fine. I'm absolutely neurotic about tight and balanced composition, and that weirdness was one of the reasons I got rid of the 25mm lens--not the accuracy of the view, but the lopsidedness of it.

I guess a lot of people wouldn't/didn't notice. . .

 

[Lss]

He says he wants to use it on a Sigma DP1X. The lens on it is 28mm equiv so not sure why he is so bothered about the accuracy to 25mm.

I had the original DP1 and used a Voigtländer 28mm finder on it. Unless you really want to sell your viewfinder to this guy, tell him to go with the 28mm finder instead.

 

[andephotographic]

If it doesn't sell it doesn't sell, I'll advise him to go with a 28mm if he can find one.

Cheers.

 

[Phil_F_NM]

Remember there is focus breathing too. The field of view will range around the nominal focal length of the lens according to where it is focused so it could be anywhere from 23mm to 27mm depending upon the lens and how close it focuses.

Phil Forrest