jackm1943 Loc: Omaha, Nebraska

A few months ago, I purchased an inexpensive mirrorless camera (Canon M6 Mark 2, 32 meg APS-C sensor) just to do focus bracketing. I’ve been very happy with it so far and did some tests yesterday to determine what minimum F stops I need to use to keep everything in focus when shooting stacks using my Tamron 90mm macro lens with and without a Raynox 250 attachment. I found the results very surprising and am wondering if they are normal for this type of use.

What I found was that somehow the camera knows to make different lens focus adjustments depending on what f stop I use. With the camera set to take the maximum number of pics (smallest increments), the lens set to 1:1, and the f stop at 2.8, the camera took 148 pics to move the focus point one centimeter. But, at f4 it took only 91 pics to move it one centimeter. At f5.6 just 72, at f8 just 54, and at f11 just 40. With the increasing DOF, the focus coverage appeared to be similar in all the examples.

I got similar results with the Raynox attached with the number of pics required to move the point of focus 0.5 cm ranging from 296 (f2.8) to 71 (f11) and, again, there seemed to be full focus coverage with all.

I would have thought that the same number of pics would be taken regardless of the f stop used, just more focus overlap as the f stop increased. I don’t know if it’s something in the camera’s computer chip or some optical physics I don’t understand. The camera does have focus peaking, maybe it automatically adjusts how much it moves the focus ring based on how wide it senses the DOF to be? If so, this little thing is a heck of a lot smarter than I thought.

Hudsonwi Loc: Wisconsin

watching topic

lamiaceae Loc: San Luis Obispo County, CA

Interesting, the camera can do that. Interesting the camera even has internal automatic focus stacking.

jackm1943 Loc: Omaha, Nebraska

Yes. I purchased it because 1) it focus brackets, 2) was inexpensive, 3) it has a large 32 meg APS-C sensor, and 4) it has a relatively updated processor. I have the EF to M adaptor so can use my EF lenses. And, it will still autofocus the macro lens with the Raynox attached, allowing it to focus bracket that way.
JackM

Just Shoot Me Loc: Ithaca, NY

Yes I think you are mixing up "focus stacking " with "exposure bracketing."
All the same it is a nice camera.

Ron

Manglesphoto Loc: 70 miles south of St.Louis

I use a Nikkor 200mm f4 macro and shoot at f32 -f45 and can get a flower with a front to back measurement of 1" in focus with four shots.
However I have read/heard somewhere some if not all are not as sharp as they could be at small apertures and have lens flare which I have not experienced since I have had and used this lens.

Capn_Dave

I gotta watch this Interesting for sure

wireloose

Optical diffraction is an issue at high f stops, see http://www.earthboundlight.com/phototips/diffraction-small-apertures.html and there have been lots of posts on UH about this. I rarely go past f11 (Sony A1/ A7R3) for that reason, it is sensor dependent though- the smaller the pixels the earlier you get diffraction

jackm1943 Loc: Omaha, Nebraska

No, it does exposure bracketing also. It focus brackets. I've done quite a lot of that with the camera and was surprised to see it can vary with whatever f stop is used. I think it's probably because it also focus peaks and somehow knows just what is in focus at each setting.

I've never tried exposure bracketing macro shots, I'm not sure if anyone does that.

jackm1943 Loc: Omaha, Nebraska

Thanks for the info. I've looked at my setup (Tamron 90 plus Raynox 250, aps-c camera) and f11 is as far as it can go. Noticeable diffraction is present at f16 and is really bad at f22.
JackM

jackm1943 Loc: Omaha, Nebraska

As I mentioned above, f11 is as far as I can go with the 90 plus Raynox 250. I try to not go above f11 with or without the Raynox.
JackM

User ID

Sadly typical UHH "expert commentary".
Can *sometimes* be cured by reading more slowly, and by reading aloud to a cat (dogs are too attentive).

fetzler Loc: North West PA

No the op has it right. Many mirrorless cameras have both focus bracketing and focus stacking. On Olympus cameras focus stacking produces a jpg file with limited options regarding the number of exposures. Focus bracketing is more flexible and can produce a set of RAW images that are then stacked using external software.

fetzler Loc: North West PA

Lets take a moment to examine the problem a bit more. The f number inscribed on your lens if they are present is the f number when the lens is focused at infinity. In general photography this is the only aperture that one needs to consider.

If I attach enough extension tubes to reach 1X magnification the aperture becomes two stops smaller. A lens set to f/8 on the barrel is f/16. The effective aperture is the one of concern for diffraction.

When a macro lens is mounted on Nikon cameras, the display shows the effective aperture and not the infinity focus aperture. Olympus cameras do not display the effective aperture only the infinity focus f number. For diffraction considerations one must consider the effective f number. What does your camera do?

The displayed settings would be different on my Nikon camera and my Olympus camera for the same subject and same lighting.

Close-up lenses (like Raynox) do not change the effective f number. In this sense such lenses offer an advantage - more magnification with less concern for diffraction. Cheap close up lenses are of poor optical quality and this advantage is not realized but Raynox lenses are of rather good quality.

My Laowa 25mm macro lens is a manual lens that takes photos at 2.5 -4 X. It is effectively a lens on extension tubes thus I use either f/4 or f/2.8 as marked on the lens to avoid diffraction as the effective f number is much smaller that the one marked on the lens.

jackm1943 Loc: Omaha, Nebraska

Thanks Fetzler. The Tamron 90 is rated at f2.8 but has no markings on the lens itself, I have to rely on what the display says. All the above tests were done at the closest focus distance (1:1). With the Raynox attached it's slightly more than 2:1. One thing I really like about this setup is that the lens internally focuses so the lens length does not change when the focus changes. For 4:1 and higher, I use microscope objectives. I don't have anything for around 3:1 but I do have a Nikon 50mm enlarger lens I might try reversing at some point in the future. One of those Laowa's is on my wish list, I read lots of good things about them. Boy, this macro stuff gets difficult at an exponential rate eh?
JackM