? for the flower shooting guru's...

07/22/2009 10:39:22 AM · #26

Originally posted by mercitrois:

I am curious about the reply by Bear Music and the link to xoomer.virgilio, etc. I opened that like and it was greek to me. Can you explain it in more simple terms. I have a Canon 5D and a 28-105, f/4, a 20mm f/2.8 and a 100 macro. Always had a problem with DOF until someone said to stop down as far as I can and focus on a point 1/3 of the distance from the subject and the camera. I tried that yesterday and seemed to work.

In general, DOF is a function of the size of the aperture you are using; the smaller the "hole in the lens", the greater the DOF. There is an allied concept called "circle of confusion", but it is very abstract and you can ignore it for now, except to be aware of its practical aspect: at very small apertures, you begin to see the effects of a process called "diffraction" that begins to rob your image of acuity, of perceived sharpness. But for broadly practical purposes, the more you "stop down" the more DOF you get; f/22 has more DOF than f/8, because it represents a smaller hole where the light passes through.

Likewise, in broadly practical terms your DOF extends 1/3 in front of the point of focus and 2/3 behind it. In other words, if you have 9 feet of DOF with a given lens at a given aperture. and your subject is 9 feet deep, you want to focus at a point 3 feet "into" the subject in order to have the entire subject in focus.

So both pieces of advice you received are good, practical advice.

Nevertheless, the concept "DOF" is in some ways a vague one, because it is basically subjective in nature and is dependent upon variables such as the aforementioned CoC (circle of confusion, which varies from camera to camera depending on the structure of the imaging sensor) and on the actual distance between the image and the viewer. Ever notice that a particular image may appear sharp in thumbnail, but is disappointingly not-sharp when viewed at a "normal" size? In just such a way a very large print might seem to be sharp throughout when viewed from across the room but the DOF might seem inadequate when the print is viewed from a closer distance. IN short, "DOF" is a subjective evaluation, based on what our eyes are willing to accept as "in focus".

Finally, DOF at a given angle of coverage will vary from camera to camera based on sensor size; a "telephoto" shot on a pocket-size P&S camera will have MUCH more DOF than the equivalently-framed image made with a "normal" dSLR, and the same-framed image on your 5D will have even shallower DOF than that. As sensors get smaller, the focal length required for a given angular coverage (tele vs wide angle) gets shorter and shorter. Since f/stop is a ratio between the physical diameter of the aperture and the focal length of the lens (a 25mm aperture on a 50mm lens is f/2; on a 100mm lens it's f/4, on a 200mm lens it's f/8, and so forth...), basically whenever you are shooting at f/8, say, and zoom from the wide end of your lens to the tele end, you are decreasing your DOF as you zoom.

I donno if this is "plain English" enough for you, but it was fun to write :-)

R.

Lutchenko

Sigma 24-70mm f/2.8 EX DG Macro for Nikon

07/22/2009 11:05:42 AM · #27

Great explanation Robert, many thanks.

I'm so glad I listened in physics classes at school because having a handle on this stuff from a physics standpoint makes photography much more
understandable, enjoyable and less hit and miss.

A question, you mention how a pocket size P&S can give a much greater DOF then say a dSLR for an equivalently framed image, but is there anyway to simulate that
DOF on a dSLR other then simply stopping down as much as possible and even resorting to focus stacking?

I ask as I see so many wonderful images here where the degree of focus from foreground to the farfield is staggering.

07/22/2009 11:28:25 AM · #28

Originally posted by Lutchenko:

A question, you mention how a pocket size P&S can give a much greater DOF then say a dSLR for an equivalently framed image, but is there anyway to simulate that DOF on a dSLR other then simply stopping down as much as possible and even resorting to focus stacking?

I ask as I see so many wonderful images here where the degree of focus from foreground to the farfield is staggering.

With a tilt lens you can do some dramatic things with DOF, that's the only other variable that comes to mind.

R.

Lutchenko

Sigma 24-70mm f/2.8 EX DG Macro for Nikon

07/22/2009 11:34:42 AM · #29

Originally posted by Bear_Music:

Originally posted by Lutchenko:
A question, you mention how a pocket size P&S can give a much greater DOF then say a dSLR for an equivalently framed image, but is there anyway to simulate that DOF on a dSLR other then simply stopping down as much as possible and even resorting to focus stacking?

I ask as I see so many wonderful images here where the degree of focus from foreground to the farfield is staggering.

With a tilt lens you can do some dramatic things with DOF, that's the only other variable that comes to mind.

R.

Wow I just looked that up. Very clever stuff, and non too cheap either

omg check this out lol DIY Lens Tilt Adapter

Message edited by author 2009-07-22 11:45:36.

07/22/2009 12:07:32 PM · #30

Originally posted by Lutchenko:

omg check this out lol DIY Lens Tilt Adapter

LOL, that's basically a DIY Lensbaby...

R.

MistyMucky

Nikon AF Nikkor 50mm f/1.4D

07/22/2009 12:10:57 PM · #31

Originally posted by Lutchenko:

You could use a shorter focal length and crop your image.

Lutchenko

Sigma 24-70mm f/2.8 EX DG Macro for Nikon

07/22/2009 12:35:36 PM · #32

Originally posted by MistyMucky:

This is very true

mercitrois

07/22/2009 12:43:59 PM · #33

By the diaphragm are you referrring the the distance of the lens from Point A, B or both or are you referring to making Points A and B closer or points A and B closer and the lens closer to point A assuming the point A is the vertical line closest to the lens.

I will send a photo taken with the 28-100 f/4 stopped down to 22 and at zoomed to100 mm. I used the rule of thirds and focused at 1/3 of the way in from the farthest flower of the left.