I have a Sony A7r3 with Sigma 105 1:1 DG DN macro lens on a copy stand with the film in an EFH. I put the film carrier on the copy stand base, make sure it’s stable and leave it alone. I put a small level on the carrier to get a stating point and angle the camera to same level point.
I place the carrier under the camera so its in the central part of the viewfinder as close as possible, as seen through the viewfinder screen. I make sure the camera is close to the cropping point you want for your film carrier.
I put a small flat mirror right over the same spot where the film is exposed for the camera lens. I set camera to a small aperture, f16, and the focusing point is set to the smallest central spot. I arrange the flip up viewing screen so I can see it sitting next to the camera. The mirror shows the reflection of the aperture blades. I manually focus to see when it’s sharp and fine tune The X, Y axis so that the small f16 aperture opening is inside the central focusing spot. I tighten everything down and recheck for any movement. The camera is now focused on the exact center of the camera sensor.
After putting in the film to be scanned all you have to do make any minor focusing adjustments for your particular film and you’re all set.
If you have a solid setup, it doesn’t require rechecking between rolls of film.
If I have to move anything then rechecking is fairly simple. My scans show consistent edge sharpness. This method was initially time consuming but can be easily repeated anytime without expensive equipment.
Well I’m not sure thanks in order, I don’t seem to have made things any easier for you! I haven’t watched that video yet but in terms of your method I must admit that I don’t attempt to go to that level of precision. Actually it would be interesting to use your screw method to your satisfaction and then confirm it using your precision mirror method. The only difference with what I do is that I estimate when the centre AF focus point on my screen is at the centre of the filter thread of the reflected lens, for me that’s enough, I don’t feel the need to see the stopped down aperture but that’s just me and it is borne out by confirmation with Vlad’s Test Target, the Siemens Stars towards the corners are great for that. Still I am using 24MP so when you start using cameras with 45-61MP or beyond as @Mark_Segal does then maybe one does have to be more precise, but I haven’t been there!
The method that @fwolff describes doesn’t seem too onerous though. He is using the EFH which is a kind of flat pack of layers so it is easy to be sure that a mirror on top will be aligned with the film and as I said before I use a 2"x 2" mirror in the slide holder of my adapted clamshell enlarger film holder. You do of course have to be sure that whatever you rest your mirror on does represent the true plane of the film. Mind you that was one of my reservations about the ‘screw’ method. A mirror has long been used to photograph flat artwork, but it needs adapting for the miniaturisation required for film.
…actually now I come to think about it I light up the AF selection spots and see how the pattern fits inside the reflected filter ring of the lens.
Hi Mark - yes, correct, I am using a Sony a7r4 which is 61MP. I’ve set my Stackshot to move up or down at 2-micron increments. It can do 1-micron intervals, but that isn’t necessary. I find that there is indeed very little leeway - at most 4 microns in either direction before one begins to see a change in the definition of the dye clouds at the 11.9x magnification that this camera allows Sony’s Remote tethering app to show on a Retina display. While numerically higher f/stops increase depth of field, they also increase the risk of diffraction, so one needs to find the sweet-spot. I’m using a Schneider Apo-Digitar Macro 80mm, f/5.6 lens, which Schneider, based on their MTF readings, recommends using wide open. Perhaps with other lenses the recommendation would differ, I don’t know, but the principle of needing to balance DoF against diffraction risk is probably generally valid even though it would play differently with different lenses. Trials is the only way to parse it.
There is fairly exotic way of alignment routine. Place the mirror on the surface representing film plane and drop few sugar or salt particles on the mirror very sparse so each particle is separate. Now look in the viewfinder - the particles which completely mask their own reflection in the mirror are those which are on optical axis. The particles for which you see reflection because the line of sight (through the lens of course) is non at right angle to mirror surface. So if you see particles of sugar without their reflection in the underlying mirror in the center of viewfinder - you know you camera is aligned. Just try it -thus is truly simple!
