SuperflyTNT Loc: Manassas VA

In my experience with cameras that do focus bracketing you can set the shift amount and the number of shots. The shift differential is a relative number, not a fixed distance. I’m guessing it may take the aperture setting into account when calculating the actual shift.

jackm1943 Loc: Omaha, Nebraska

Based on Superfly's comments, I did something very drastic...I downloaded the camera instructions and took a look. They make it very clear that the amount of focus shift is automatically adjusted based on whatever f stop is selected. I'm embarrassed that I didn't check that out before but it just didn't occur to me these cameras would be that smart. Thanks to everyone who commented.
JackM

Grahame Loc: Fiji

In addition there's 'Exposure Smoothing'.

(Download)

jackm1943 Loc: Omaha, Nebraska

Thanks Grahame, I noticed that also. That could be quite useful when using this technique outdoors.
JackM

fetzler Loc: North West PA

If your lens has no markings, focus the lens to infinity and select the minimum aperture and note its value. Next, focus the lens to 1:1 and select the minimum aperture note its value. If the two apertures are different then your camera behaves like the Nikon. At !:1 there will be a two stop difference.

jackm1943 Loc: Omaha, Nebraska

[quote=fetzler]If your lens has no markings, focus the lens to infinity and select the minimum aperture and note its value. Next, focus the lens to 1:1 and select the minimum aperture note its value. If the two apertures are different then your camera behaves like the Nikon. At !:1 there will be a two stop difference.[/

My Tamron 90 macro can be set to f2.8 at 1:1 thru infinity. It's internally focusing, the length of the lens doesn't change. Some macro lenses get much longer as they approach 1:1. Maybe that's the difference?

User ID

Its partially the difference. The FL of an IF lens is decreasing as you focus closer. A rough guess is that your 90/2.8 becomes a 60/2.0 when focused to 1:1. Since the lens doesnt move closer to the focal plane as the FL shrinks, it winds up focused to a closer distance. Sticking with the idea of it being a 60/2.0 then its effective f/stop at 1:1 would be f4.0 cuz the 1:1 f/stop is always two stops slower than the physical f/stop.

The subject to focal plane distance is always 4x the actual FL. If the lens is really a 60/2.0 when the IF mechanism reaches 1:1, then you could measure from the subject to the FP marker and it would be 240mm.

You can thus determine what FL results from dialing the IF to 1:1. Simply measure from subject to FP marker. That measure always equals 4x the FL. (Knowing the shift in FL acoarst also provides you with the f/stop shift.)

A non-IF 90 would still measure 4x its FL from subject to marker, and that will be 360mm. IF always reduces your working distance cuz its mechanism shortens your real FL. BTW, dioptre lenses are cousins of IF. They shorten the real FL without moving the lens closer to the FP, resulting in close focus ... same principle as IF.

jackm1943 Loc: Omaha, Nebraska

Thanks UserID. I'm aware of how the apparent f stop changes as magnification increases but I don't pretend to know the physics behind it. I pretty much rely on the equations and formulas in extreme-macro.co.uk to determine what focus step increments to use with my various setups. When using a macro lens, or any regular camera lens, I think that we pretty much have to do some basic tests on each of our applications to determine the optimal f stop to use. I like to photograph a metal millimeter ruler for this purpose.
JackM

fetzler Loc: North West PA

At infinity focus the minimum aperture will likely be f/22 or perhaps f/32. When you focus at 1X magnification the camera will either show the same apertures as infinity focus or will show two stops smaler (i.e. f/45 or f/64).

The following shows how to choose optimal apertures (numbers in bold) for Nikon like cameras and cameras like Olympus and manual lenses for given magnifications. Recall Olympus cameras always display infinity f numbers.

https://www.zerenesystems.com/cms/stacker/docs/tables/macromicrodof?s[]=macro&s[]=depth&s[]=field

jackm1943 Loc: Omaha, Nebraska

Thanks fetzler. Zerene is my processing app of choice and I'm familiar with the charts. I just find the ones in extreme-macro.co.uk a little easier to use. I do understand that at 1:1, the f stop shown on the camera display isn't the true f stop. That's why it's important to actually do some tests to determine the limits of your system. It does get complicated but that's what makes it enjoyable (to a point).

amfoto1 Loc: San Jose, Calif. USA

No, the Canon M6 Mark II has "focus bracketing" (as well as "exposure bracketing").

User ID

Many formulae are for non-IF lenses.
The most important key I gave you for figuring out IF lenses is that ALL types of lenses, inclusive of adding a dioptre to the mix, have an effective FL thaz 1/4 of the subject to marker distance at 1:1 ("unity magnification").

You can mix tubes, dioptres, and IF. Jockey it all to 1:1 and you can find the working/effective FL (and calculate the effective f/stop).

BTW, at 1:2 (half life size) the subject to marker distance is verrrry close to 3x the effective FL.

Capn_Dave

To add to this all of the Canon R series have both