This is meant to be a "road test" thread to describe how the cameras handled and what the results were like.
The photo below shows the three folders I tested. From left to right, they are a Zeiss-Ikon Ikonta 521/16 (6x6) with a 75mm f/3.5 Novar, a Zeiss-Ikon Nettar 515/2 (6x9) with a 105mm f/6.3 Novar, and a Zeiss-Ikon Nettar 515 (6x4.5) with a 75mm f4.5 Novar. All had the flip-up type finder on the body, no rangefinder, and no exposure meter. Each was purchased on the auction site for under $40 and is routinely available in this condition for that price. I did a basic CLA of the shutters and some minor repairs to get them in working trim.
I intended to shoot color positive film exclusively and brought along a supply of Astia 100F, Provia 100F, and Velvia 100. Shooting slide film with old folders is tricky because it is so unforgiving of exposure errors, but it's what I like and I have worked out a method to get decent results. The first important thing is to know what shutter speed you are shooting at. Even after they have been CLAd by the experts, folder shutter speeds are not accurate in the sense of matching up with the indicated speed on the dial. But they are reliable in the sense that you do get the same (inaccurate) shutter speed very repeatably. I made one of those DIY shutter speed testers that works with your PC's sound card for testing the shutters. At first I took the average of five trials at each indicated speed to determine the actual shutter speed, but soon I realized that three trials was plenty and really even one or two would be enough. For each camera, I measured the actual shutter speed for each indicated speed. Then, by moving the dial to intermediate positions (e.g. halfway between '25' and '50'), I tried to see how close I could come to the standard shutter speeds of 1/30, 1/60, 1/125, and (if the camera was capable of it) 1/250. Then I made up a little card for each camera like this:
I keep that in my breast pocket when I'm shooting. Note on this card, typically of many folders, that while all but the top speeds may lag, the very top speed is often close to or even faster than the rated speed. The reason for that is that on these old shutters, the top speed actually bypasses the geared escapement that times the other speeds, simply springing closed as fast as it can. So if the gears have picked up a little extra resistance over the years, it won't affect the top speed.
Often, the nature of the speed cams inside these shutters, which tend to increase in discrete steps, makes it impossible to get very close to a desired speed such as 1/60. In such cases you have to get as close as you can and live with it. To simplify things, I tend to settle on a speed that works well for a camera, say 1/125, and shoot at that all day, to the extent I can, varying the aperture rather than the shutter speed.
Besides knowing your shutter speed, the other good rule for slide shooting with folders is to meter accurately, using something like an SLR. Pulling out one of those old selenium meters may look very butch and old-school, but it introduces too much imprecision for slide shooting. Save it for when you're doing negs. Most of the time, I used my SLR for focusing as well, reading the distance off the SLR lens barrel and transferring it to the folder. My usual procedure was to meter and focus with the SLR, usually shoot an insurance shot with it, then transfer the settings to my folder and make the real shot.
I brought along my RB67 to serve as a benchmark for the folders. This of course is a classic in its own right, especially my old Pro model.
With the RB67 you get that wonderful Mamiya glass with all that contrast, sharpness and tonality, it's just an amazing camera. I knew the folders weren't going to be THAT good. But, dollar for dollar and ounce for pound, could they hold their own at least a little?
First up was the 6x9 Nettar 515/2. With its slow 6.3 lens, this is about the lowest-end folder that I have (unless you count my Kodak Tourist II which lacks such refinements as the ability to focus), and I have better 6x9s but I wanted to see what this very basic camera could do. These were the first rolls of film I ever ran through it. I used a tripod and cable release for all shots with this camera because of the big image size and slightly awkward handling. As with all of the folders, I tried and was generally successful at staying in the lens's sweet spot of f/8 to f/16.
This camera produces large, eye-popping transparencies. There is just nothing like the wow factor of 6x9. On closer inspection, the images were surprisingly good. (I'm showing all of the folder photos with borders so you can see the variations in how straight and clean the image edges are.)
Sharpness of the slides viewed through a loupe was quite nice. Small stencilling painted in 1-inch-high letters on the sides of 30-foot-long aircraft were easily legible, even when the whole aircraft was in the frame. In the biplane picture above, there are some college buildings on a hillside in the background about 2 miles away, and with a loupe, you can make out the individual panes in their windows. So that little Novar doesn't give away much to the RB67 in sharpness!
(By the way, all of these MF scans are from my crappy Epson 4180 Photo scanner, and are retouched by me to look reasonably like the original slides. The scan itself tells you nothing about what the film looks like, I'm just using them for illustration.)
The Novar also had no problem producing accurate and pleasing color rendition. I did not use a lens hood with any of the cameras, but had no flare problems.
The problem that I did have, as you can see in all of these scans, was brightness fall-off from center to edge. I don't think "vignetting" is the right word for this, it's just -- fall-off. In the transparencies themselves it is not very noticeable, but it is definitely there. Scans seem to accentuate this problem, as I have also noticed with scans of my 35mm film shot with cheaper lenses. The amount of it that is present with this camera can be eliminated almost without artifacts by any of the common PS plugins, but still, it is disappointing.
My next folder was the 6x6 Ikonta 521/16. This was an easy-handling camera with the welcome feature of multiple exposure prevention. On cameras without this feature you can try to avoid multiple exposures by establishing a routine where, for example, winding the film is always the last thing you do before you shoot, but then there are always times where your picture goes away at the last moment, you give up and walk around some more, then you can't remember whether you wound or not. I erred on the conversative side and always wound again when I wasn't sure, and ended up with no double exposures but a few mixed frames. Except with the Ikonta. That was nice.
Photos with the Ikonta were also very nice and sharp. I was pleased with both the resolution and contrast that I was able to get.
Exposures and focus were accurate. Composing the picture through the flip-up viewfinder, however, was tricky. A few, but not all, of my photos have more sky at the top and less earth at the bottom than I remember composing.
I used this camera on a tripod sometimes and handheld other times, and generally, the ones I took on a tripod seemed to come out more accurately composed. So maybe the trick to using these flippy finders is just taking your time and making sure your face is square with the camera.
This is my first 6x6 camera, and about the third roll of film I've put through it. I enjoy the challenge of the square composition. Airplanes are inherently horizontal subjects, so the square encourages you to find an interesting composition in part of the airplane. I enjoy that.
Note, though, the issue with the frame edges with the Ikonta. The sides cant inwards at the top of the frame (and also less noticeably at the bottom). The edges toward those corners are fuzzy. Maybe the bellows are intruding into the frame a bit? And the other issue is that there is a darkening in the corners -- and this I would really call vignetting, in contrast to what happened with the 515/2. Also, unlike the 515/2's brightness fall-off issues, which occurred at all apertures, the vignetting with the Ikonta seemed to go away as the lens was stopped down.
The solution to this, I guess, is to compose the picture conservatively, allowing a margin around the edge that can be cropped off. There's still plenty of real estate on the neg/slide to play with.
The third and final camera for this jaunt was the Nettar 515, truly a delightful little camera with a 6x4.5 image size. It is more compact than any high-end SLR, and so easy to handle that it just begs to be treated like a 35mm camera, especially with 16 frames per roll to play with. So, that was what I did.
I didn't get this camera on the tripod at all. It would have been awkward anyway, since the photo format is vertical when the camera is right-side-up, and it doesn't go on a tripod easily when held sideways. But mainly it was just too much fun.
Essentially I treated this camera like a super 35mm, using it whenever I would have used my 35mm but found a shot that would benefit from just a little more resolution. Actually, I had never shot 6x4.5 before and was surprised at the amount of extra punch you get compared with 35mm.
Once again, the Novar lens proved more than capable of handling color, controlling flare, and making Velvia look like Velvia. Also, this camera displayed nice clean, straight edges and no vignetting or light fall-off.
One thing about this camera, though, was that composing through the flippy finder was dodgy. I found that the actual image area captured was rather smaller than what I had seen through the finder, and also biased a bit to the left. As a result, the left edge of some of my subjects was snipped off, or nearly so.
This made me think that with cameras with flippy finders, it is a good idea to calibrate the finder somehow. Maybe in much the same manner as calibrating the focusing element, put magic tape or a groundglass at the film plane, hold the shutter open and compare the image through the finder with that through the lens.
Or another answer is simply, again, to compose conservatively and leave a little margin around the edges, recognizing that the flippy finders are just not very precise. At any rate, this is a small quibble. It created issues for only a few images. Overall, I was more pleased with this camera than with either of the other two, and it is so handy that I will be carrying it with me often.
So that is an account of shooting slides with the old folders. Perhaps not adequately stressed in this road test is how darned much fun it is walking around with a bag full of these things and snapping away. It would almost be worthwhile even if the film didn't come out. Except it's expensive, so I'm glad it did.