Manual vs Autofocus for camera scanning

[Grim Tuesday]

Where do people fall on this these days? I remember it used to be everyone agreed manual focus is best. Set it at the beginning of the day and you're gold. I've recently seen reports from people who are fans of autofocusing on each frame, especially with cameras that have very precise autofocus, like the Nikon Z cameras. I haven't seen any direct comparisons on Youtube or elsewhere. Where do folks on this forum fall on this? Is it worth going out and buying an autofocus macro lens when I already have a manual focus one?

 

[Steven Lee]

There are several variables in play. Maybe so many that it's fair to call this a subjective matter. For example:

• Camera resolution. Taking advantage of 50-100mp sensors, especially with pixel shift involved, shifts the bottlenecking onto optics and its focusing accuracy.
• Film flatness. If your setup allows for absolutely consistent field of focus from frame to frame, then it's easy to manually focus just once and not touching the lens for the entire roll.
• Lens aperture. If you're at f/11 the focusing accuracy is not as critical. But this is closely related to sensor resolution. High-res sensors benefit from high-end lenses. And high-end lenses are at their best at wider apertures, often f/5.6 and sometimes even f/4.
• Fatigue. If the bullet points above push you to refocus for each shot, I would argue that a human can't compete with autofocus on consistency: some shots won't be optimally focused.

So I am unsure what a Youtube comparison video can possibly demonstrate here. I can share my variables if that helps. To take advantage of the 50mp sensor in my Sony A7R IV, I have a razor sharp Sigma 105mm Macro Art with an optimal aperture of f/5.6 (diffraction becomes noticeable at f/8). My film holders are Negative Supply and as film goes through the holder I can see variable grain sharpness from frame to frame, unless I refocus. So in my situation manual focusing would have been painful which leads to the fatigue concern.

BTW the old habit of manually focusing in shallow DOF situations stems from the SLR technology where AF sensors were never 100% precisely aligned with a film/sensor plane. Modern on-sensor AF in mirrorless cameras does not have this problem.

 

[sojournermike]

There are several variables in play. Maybe so many that it's fair to call this a subjective matter. For example:

• Camera resolution. Taking advantage of 50-100mp sensors, especially with pixel shift involved, shifts the bottlenecking onto optics and its focusing accuracy.
• Film flatness. If your setup allows for absolutely consistent field of focus from frame to frame, then it's easy to manually focus just once and not touching the lens for the entire roll.
• Lens aperture. If you're at f/11 the focusing accuracy is not as critical. But this is closely related to sensor resolution. High-res sensors benefit from high-end lenses. And high-end lenses are at their best at wider apertures, often f/5.6 and sometimes even f/4.
• Fatigue. If the bullet points above push you to refocus for each shot, I would argue that a human can't compete with autofocus on consistency: some shots won't be optimally focused.

So I am unsure what a Youtube comparison video can possibly demonstrate here. I can share my variables if that helps. To take advantage of the 50mp sensor in my Sony A7R IV, I have a razor sharp Sigma 105mm Macro Art with an optimal aperture of f/5.6 (diffraction becomes noticeable at f/8). My film holders are Negative Supply and as film goes through the holder I can see variable grain sharpness from frame to frame, unless I refocus. So in my situation manual focusing would have been painful which leads to the fatigue concern.

BTW the old habit of manually focusing in shallow DOF situations stems from the SLR technology where AF sensors were never 100% precisely aligned with a film/sensor plane. Modern on-sensor AF in mirrorless cameras does not have this problem.

I agree with all of this. I posted in another thread that I am using the Sigma 105 macro art with my S1r. I use an essential film holder and now tend to refocus every shot with af. It is much more consistent than I can manage over 5 rolls of 35mm.

As for your DSLR point, I was tempted by a very sensibly priced Pentax K1 I with 24-70 the other night. However, I recalled that sold my last one, and last DSLR, because I couldn’t get the thing to focus reliably other than with the (aps-c) 40/2.8 pancake. That list of failures included the rather wonderful sigma 50/1.4 art.

 

[runswithsizzers]

I have never used autofocus when digitizing film, so I cannot make a direct comparison. Based on my limited experience - about 50 rolls of 35mm film - manual focusing works fine, and I do not feel like I would gain anything by switching to autofocus.

My Fuji X-T1 has a Focus Assist button that zooms in the viewfinder, and it can show in-focus areas with highlight peaks in white, red, or blue. When the film grain is in focus, featureless areas of the negative twinkle in the highlight color like stars in the sky. Sometimes I set the camera to monochrome, so the red-colored peaks are more visible against the gray background in the viewfinder. (The RAW file, of course, still captures any color information.)

When I first started copying negatives, I was checking the focus for every frame, but I soon realized that was not necessary. Now, I might check the focus once every 6-8 frames, and when I check, focus adjustments are rarely necessary.

For the past two years, I have been using the Skier Sunray Copybox and negative holder. The Skier negative holder is designed so film strips can be fed through a channel which appears to be about 1mm tall. So the film is not really clamped down, but still, I don't see any signs of bowed film in my results. Before I got the Skier Copybox, I was using the negative holder that came with my Minolta film scanner, and that worked too.

My casual testing indicated I could see a slight softening of fine details due to diffraction starting around f/13, and it was quite noticeable at f/16. So at first I was stoping down to f/11. But later, I discovered f/8 gives me enough depth of field.

 

[cliveh]

Autofocus, wash your mouth out with soap and water.

 

[xkaes]

Another consideration is what gear you have. If you have both AF and MF, you can choose, of course, but if you only have AF or MF, the decision might be already made. You might not want or be able to go to the other option.
All my macro & micro gear is manual focus. Auto-focus macro is a waste of time in my book, and I don't find manual focusing difficult -- I routinely use a 2X magnifier.
So for my scanning/digitizing, I just slap on a manual-focus process lens and fire away -- but I always check the viewfinder to make sure the image is in focus, opened up. And it usually is, but I do a lot of cropping, so that changes things.

 

[250swb]

I start by setting the image up with AF because I scan multi formats and the copy stand is inevitably in the 'wrong' position next time I use it. But after setting everything up I switch to MF for what I think is a very practical reason, if I start with the green box in the centre of the frame and the lens wide open I can move the box around the image and see if it flickers or goes out of focus, but that is more important with a 6x12 neg than a 35mm neg. I then know everything is set up square and I can stop down and carry on scanning.