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Author Topic: Sharper Macro than Canon 5d2 and 100mm Macro?  (Read 9784 times)

Bart_van_der_Wolf

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Re: Sharper Macro than Canon 5d2 and 100mm Macro?
« Reply #60 on: April 23, 2015, 08:44:42 am »

Bart, thanks for the detailed reply. You mention Camranger, but did you mean Helicon Remote? Camranger does not calculate the number of steps, but rather relies on the user to input this datum.

I did indeed mean CamRanger, and I was indeed afraid it just uses the user input of step size and number of shots, instead of true steps. Helicon remote instead does calculate the actual number of required steps based on front and rear focus range limits, and then uses exactly that (tweaked by the correction factor).

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This approach is elegant, but I can foresee problems with my "macro" workflow, which is mainly closeup with a magnification of less than one. My MicroNikkor lenses are the G type which lack an aperture ring and the aperture is set electronically and with the effective aperture set by the in lens chip.

If the camera doesn't exactly use the user's input for fixed Aperture value, then one can also convert between Nominal (at infinity focus) and Effective (at nearer focus) Aperture, before plugging the numbers into the earlier formula.

Nominal Aperture = Effective Aperture / Log((1 + M/P)^2) / Log(2)
or
Effective Aperture = Nominal Aperture x Log((1 + M/P)^2) / Log(2)

where:
M = Magnification factor
P = Pupil factor

The formula is supposed to be exact, regardless of magnification factors being larger or smaller than 1.0, with the possible small inaccuracy of conveniently rounded aperture number representations. A nominal f/5.6 for example would actually be more something like f/5.65685424949238 .

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Furthermore, these lenses exhibit focus breathing with shortening of the focal length as one focuses nearer.

That would complicate focus stacking by electronic focusing, compared to using a rail.

I also have a small issue with the electronic focusing of my Canon EF macro lens, and that's to do with hysteresis caused by the focus drive direction. Switching the direction will shift focus, so one needs to account for that when determining the front and rear focus positions. When the camera returns to the start position, it may focus slighty in front or behind the earlier determined position, depending on the direction of approach. So it's wise to set the boundaries slightly wider than needed. Other than that, it works wonders, and saves time because I can do something else while the stack is being shot.

Cheers,
Bart
« Last Edit: April 23, 2015, 02:27:22 pm by BartvanderWolf »
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