PDA

View Full Version : More analog DOF?



Pages : [1] 2

cmo
06-30-2009, 02:49 AM
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
06-30-2009, 03:10 AM
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
06-30-2009, 03:52 AM
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
06-30-2009, 04:01 AM
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
06-30-2009, 06:56 AM
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
06-30-2009, 07:44 AM
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
06-30-2009, 08:40 AM
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
06-30-2009, 11:32 AM
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
06-30-2009, 12:02 PM
Good demo, DannL.

Sirius Glass
06-30-2009, 01:19 PM
Or use film with a higher ASA/ISO/DIN. :)

Steve

Galah
07-02-2009, 08:04 PM
Good demo, DannL.

Hey David,

Your food shots have given me an apetite:D

wayne naughton
07-03-2009, 09:30 AM
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
07-06-2009, 04:52 AM
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.
07-07-2009, 11:26 AM
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
07-07-2009, 02:25 PM
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.
07-07-2009, 02:50 PM
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 sť. 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
07-07-2009, 03:15 PM
The hybrid way belongs in a different forum.

EASmithV
07-08-2009, 01:05 AM
f64

Lee L
07-08-2009, 08:03 AM
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.typepad.com/the_online_photographer/2009/06/depth-of-field-hellthe-sequel.html

Lee

Q.G.
07-08-2009, 11:15 AM
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.