Recently I photographed some eyewear with my "Canon 24-70 2.8 L" at 70mm (70 mm decision is for a matter of correct ratio between filling the format with subject and it's perspective rendering the client asked for). But, even closing down to f22 the depth of field turns out to be a little too shallow for my needs. Please, do you know if using "Canon 24-70 2.8 L II" or "Canon 24-105mm f/4 L IS II" I could improve DoF? Or, any other Canon lens that could do better at 70mm? Thank you!
Have you considered spending less & achieving more?
You then wouldn't also be fighting the diffraction limit you get at narrow apertures.
11 layers, stacked
I've got better at it since this, but this one shows quite an extreme effect, front to back.
Time taken to shoot approx one minute; to stack, approx one minute - it really is quite a quick process once you got the hang of it.
For something as large as glasses, you could probably do it at f8 in 3 or 4 layers.
You can either pull focus, pull zoom, or get a macro rail thereby moving the entire camera back & forth. I've tried all three & I can't make up my mind which is actually best. After each pull I wait a couple of seconds to reduce any potential shake in the tripod, then have a 1s mirror up delay. I also use a wired release.
Another way is to use a tilt-shift lens, and tilt the lens to have a focus plane that is not parallel to the sensor. To quote this page:
Product photography is a great use for the Canon TS-E 90mm f/2.8 Tilt-Shift Lens - Especially medium and small-sized products such as plates of food, model cars, bottles ...
If a 70mm focal length and the distance to object are absolutely required for correct framing, then, aside from aperture, the other variable you can change is the sensor size - smaller sensors give more depth of field with all other variables constant.
If all you really need is a specific framing of the subject, a longer lens, and an increased distance to the subject can give you the same scaling of the subject (although foreground, background, and perspective will be correspondingly different) at the plane of focus, and correspondingly larger depth of field.
Usually, I would say:
It's not the camera, it's the lens.
However, now I say:
It's not the lens, it's the camera.
Some newer cameras have a focus bracketing feature. You take a number of shots with automatically set focus. The feature is fully automatic. Later, you can use focus stacking to combine the focus bracketed shots into one.
The reason you have the difficulty is that you are taking macro shots of a small object. At macro distances, the depth of field is very shallow even if you use a small aperture.
If third party lenses for the canon system are acceptable there are a couple that go to f32
For example • Sigma 24-70mm F2.8 EX DG Macro - discontinued but can be found used for £450 • Tamron Di SP AF 28-75mm F/2.8 XR - costs €270 new
That should give you a bit more depth of field, if it is enough will depend on your subject of course.