More analog DOF?

cmo · Jun 30, 2009

Yesterday I used a bellows for some real macro photography for the first time. It's a good equipment: Olympus 3.5/50mm with a 25mm extension ring and an Olympus 4.0/80mm bellows head, attached with an adapter to a Canon EOS 1v. Since yesterday I admire the handiwork of macro photographers... OMG, this is difficult. It starts with the wind shaking the leaves, focussing is a nightmare even with a loupe, and DOF just doesn't exist, even at f22. I asked a friend and his recommendation to gain more DOF was "Stack several images"... of course he assumed I am using a digital camera. 'Stacking' means to combine several shots of the same image with different focus settings into one new digital image.

So, is there an "analog way" to get more DOF in macro photography?

E76 · Jun 30, 2009

The only way to get more DoF is to use smaller apertures or less magnification. Depending on the bellows, it may be possible to use tilt to achieve more DoF (by taking advantage of the Scheimpflug principle). I know at least one particular Nikon bellows unit allowed this.

Ross Chambers · Jun 30, 2009

I'm not sure how macro I achieve, but sometimes I move the camera back and plan on cropping the print which gains some DOF.

If the leaves (petals etc.) shake about I pick the foliage and bring it inside to a windfree environment.

There goes my credibility!

Regards - Ross

AgX · Jun 30, 2009

A multiple exposure technique using staggered focussing is used in analog macro photography too.

However, not complete images are overlayed. Instead only parts of the object corresponding to the plane of focus are photographed. This is achieved by lighting the subject by means of slit lighting in the plane of focus. After each exposure the subject is moved by the width of that lighting.

cmo · Jun 30, 2009

AgX said:
A multiple exposure technique using staggered focussing is used in analog macro photography too.

However, not complete images are overlayed. Instead only parts of the object corresponding to the plane of focus are photographed. This is achieved by lighting the subject by means of slit lighting in the plane of focus. After each exposure the subject is moved by the width of that lighting.

Wow, I did not expect that. But it sounds very complicated.

AgX · Jun 30, 2009

It is not that complicated.

There have been setups using a sturdy tripod for the camera, some slide projectors for slit lighting, all based on scissor type lab-elevators for height adjustment, and the object itself too on such an elevator.

And once there was an all-inclusive device for doing such photography.

keithwms · Jun 30, 2009

There's no law against taking your shots on film, scanning them, and using the available software to do a combination.

Bear in mind that when you refocus with the lens, you will get small changes in perspective & magnification- the distance between the front element and your subject is changing. This could be important when you are focusing so closely. The software is probably correcting for that as well as doing the simpler image combination.

But personally I think front-to-back sharpness is far overrated. Why not use the out-of-focus transitions to convey dimension, and use tilts to place the plane of focus wherever you wish.

DannL · Jun 30, 2009

Ross Chambers said:
I'm not sure how macro I achieve, but sometimes I move the camera back and plan on cropping the print which gains some DOF.

If the leaves (petals etc.) shake about I pick the foliage and bring it inside to a windfree environment.

There goes my credibility!

Regards - Ross

Here's an example of Ross's "pulling back to gain depth of field". It's by far the simplest method I know. A silver finger ring.

David A. Goldfarb · Jun 30, 2009

Good demo, DannL.

Sirius Glass · Jun 30, 2009

Or use film with a higher ASA/ISO/DIN.

Steve

Galah · Jul 2, 2009

David A. Goldfarb said:
Good demo, DannL.

Hey David,

Your food shots have given me an apetite

wayne naughton · Jul 3, 2009

Bear in mind that when you refocus with the lens, you will get small changes in perspective & magnification- the distance between the front element and your subject is changing. This could be important when you are focusing so closely. The software is probably correcting for that as well as doing the simpler image combination. Current HDR software will even compensate for small amounts of movement

lxdude · Jul 6, 2009

cmo said:
It starts with the wind shaking the leaves, focussing is a nightmare even with a loupe, and DOF just doesn't exist, even at f22. I asked a friend and his recommendation to gain more DOF was "Stack several images"... of course he assumed I am using a digital camera. 'Stacking' means to combine several shots of the same image with different focus settings into one new digital image.

Also remember that even stacking digitally would give problems if the wind is shaking the leaves- the images won't be in register.

Q.G. · Jul 7, 2009

As Wayne wrote, stacks have to deal with such problems anyway. Refocussing will change magnification (creating a strange distortion), and when the lens to subject changes too (very probable), perspective will as well.

So the stacking software will have to deal with this.
It however is not hard to do: just find, for each point in the image, the image in the stack in which that point is 'sharpest' (by comparing contrast to neighbouring points), and put that in the combined image. Move on to the next point, etc.
Completely ignoring distortion and such issues will produce surprisingly good results.

richard ide · Jul 7, 2009

I think the digital aspect of this discussion is seriously misplaced. The easiest way to gain DOF is to use a longer focal length lens although this introduces a size of eqipment problem. At 1:1 a 420 mm lens at f32 gives a DOF of about an inch (COC .1 mm). In the next couple of weeks, I will do some tests at higher magnifications and smaller aperatures and post them in this thread.

Q.G. · Jul 7, 2009

That fickle thing called DOF...
If it were easy to have sufficient DOF, we would not all be chasing after it all the time.

At the same magnification and f/stop, DOF is the same too, no matter how long (or short) the lens.

You could permit larger CoC's in your equation, but that doesn't change actual DOF.

Backing away, and enlarging more will also not increase DOF per sé. It will change how parts of the image look relative to another (i.e. show less difference in sharpness). But at the price of absolute sharpness.
I.e. the gain in DOF is not achieved by getting more sharp, but by reducing the sharpness of the sharp bit so that the difference with the less sharp bit is less obvious.
As the example shows, it works. But it also does not increase DOF.

If analog only, the only real way to increase DOF is the slit light method: move the subject through a very shallow 'plane' of light, positioned where the plane of focus is, exposing only the bit in focus.

The hybrid way, stacking, works, and is much easier.
Perhaps we analog photographers should not always want to be 100% pure?

richard ide · Jul 7, 2009

The hybrid way belongs in a different forum.

EASmithV · Jul 8, 2009

Lee L · Jul 8, 2009

Q.G. said:
At the same magnification and f/stop, DOF is the same too, no matter how long (or short) the lens.

This is not true. http://theonlinephotographer.typepa...er/2009/06/depth-of-field-hellthe-sequel.html

Lee

Q.G. · Jul 8, 2009

It is.

The thing that changes with focal length is the rate at which focus changes, i.e. the amount of blur outside the DOF-zone.
But at the same magnification and f-stop, DOF itself is the same, no matter what focal length.

People keep using formulae derived from hyperfocal distance formulae.
In which the focal length figures twice (as F(ocal length) and as M(agnification), though noone can explain why.
They may work for hyperfocal distance calculations, i.e. when DOF is infinite. I don't know. But not for DOF

Every bit of 'proof' offered for the assumption that DOF is different when focal length changes, yet scale remains the same makes use of those same old formulae.

None (not a single one) of the proofs offered on the site linked to holds any water.

cmo · Jul 8, 2009

EASmithV said:
f64

Welcome to diffraction wonderland. Been there, got the t-shirt. Even at f32 images are A LOT less sharp than at f16.

Sirius Glass · Jul 8, 2009

Lee L said:
This is not true. http://theonlinephotographer.typepa...er/2009/06/depth-of-field-hellthe-sequel.html

Lee

Sorry Lee, you are wrong on this. When I first started working at Kodak and I was studying optics, I asked this question based on experience. One of the optical engineers sat down with me and Smith's book on optics and started with two equation. Substituting one into the other, with in two lines, the focal length drops out of the equation. I wish I had taken notes on it, but the bottom line is that for the same image size [magnification] the focal length is not a variable and the theoretical depth of field is the same for all lenses.

Search my posts, I have covered this in great detail in the past.

Steve

richard ide · Jul 8, 2009

I have to agree. The 420mm lens I am using gives a long working distance between lens and subject only. DOF does not change. I checked my SPSE handbook and lens focal length is not used in the equations.

Lee L · Jul 8, 2009

OK, let's try this one on for size: using the Schneider DOF spreadsheet calculator and two lenses, a 50mm focused at 50 ft, and a 100mm lens focused on the same subject, but from 100ft away to provide equal magnification. ( http://www.schneideroptics.com/software/DOF_Calculator.xls )

The Schneider DOF calculator (which I keep set for my preference of a CoC of 0.028mm) yields:

50mm lens focused @ 50 ft @ f:5.6
Near 25.56 ft
Far 1132.62 ft

100mm lens focused @ 100 ft @ f:5.6
Near 67.66 ft
Far 191.54 ft
100mm DOF distance from 50mm shooting position (subtract 50 feet from near and far DOF)
Near 17.66 ft
Far 141.54 ft

So the 100mm lens DOF extends from about 18 ft in front of the 50mm lens to 141 feet in front of the 50mm lens. The 50mm lens DOF extends from 25 ft to 1132 feet from that same reference point. This is at the same aperture and same subject magnification with the same plane of best focus.

The results reflect the same kind of relative front/rear shift in depth of field that Ctein shows in his photographic results and his chart when going from longer to shorter focal lengths.

Arthur Cox, pages 76-77, Photographic Optics, 15th ed, Focal Press, poses the question:

"A scene is to be photographed in such a way that the depth of field is to be a maximum. Is it better to use a long focus lens and make a contact print, or to use a short focus lens and make an enlargement?
The answer is in favor of the short focus lens."

He then goes on to show the depth of field with a 2 inch lens enlarged by a factor of four has greater depth of field than a contact print from a negative shot with an 8 inch lens, both shot at f:4, with the shorter lens having a DOF that is just over 4 times greater than the longer lens when both are focused on an object at 10 feet.

This agrees with Ctein's assertions. I searched for a while for your applicable APUG post Steve, but failed to find it. APUG needs a better search engine.

Lee

More analog DOF?

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