Depth of field vs aperture sharpness: Hello Is there a difference in sharpness in the infinity range of a depth of field chart? For example, say a lens has its 70mm sharpness sweet...

Hamltnblue Loc: Springfield PA

Hello
Is there a difference in sharpness in the infinity range of a depth of field chart?
For example, say a lens has its 70mm sharpness sweet spot at f8.
The focus point of a shot is on an object at 100 feet with a background object at 5000 feet.

This shot is taken at f8 and again at f14.
The DOF charts indicate that the far plane at f8 and f14 is infinity.

The sharpness of the object at 100 feet would be better at f8. Would the sharpness of the 5000 ft object be better, worse, or the same with the focus point at 100 ft?

For reference thin of it being a pic of a person with a city background.
Thanks
Jim

sippyjug104 Loc: Missouri

I don't know the answer however I do know that there are 5,280-feet in one mile so 5,000 feet is WAY out there.

CHG_CANON Loc: the Windy City

You might want to look up the topic of lens diffraction.

Regarding sharpness, what are you, the photographer, trying to accomplish? First, did you focus specifically on the subject? Did you pick an aperture and lens and aperture for that lens on your camera that maximizes the sharpness of the subject of the image?

Next, how critical is the sharpness of the background? A natural fall-off of the background is how our eyes would see the scene when focused on a subject. But, a camera / lens can create sharp or out-of-focus backgrounds different than our eyes. What are you trying to accomplish?

Strodav Loc: Houston, Tx

The engineer in me had to look up the numbers. Using a DOF calculator for a FF camera with 70mm lens at f/8 with subject distance at 100' the acceptable sharpness range is 40' to infinity. Using f/14 you get 27' to infinity, but as CHG Canon implies, when you get around, or over, f/11 you end up with diffraction affects diminishing IQ. So, IQ will be better at f/8 for both the subject and background, but at a mile behind your subject the background will probably be very, very, very, very tiny, and acceptably sharp, but as sippyjug104 implies, you won't care if it's in focus.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

Hamltnblue wrote:

Hello br Is there a difference in sharpness in the... (show quote)

Focus on the subject, use F8 and don't worry about something that is a mile away. Atmospherics will disturb light transmission and along with it any chance of something being in clear crisp focus. Hyperfocal at F8 is 67 ft and 37 at F14 - if you want maximum depth of field with crisp sharpness and the hyperfocal distance, and "acceptable" sharpness within the range of 1/2 the hyperfocal distance to infinity. Many lenses show good sharpness at f11, and some are still ok at F14, but not great. Higher resolution cameras will show sharpness lost to diffraction at wider openings than lower resolution cameras. F8 would be the better choice with either camera.

kymarto Loc: Portland OR and Milan Italy

Hamltnblue wrote:

Hello br Is there a difference in sharpness in the... (show quote)

DOF always means "acceptable sharpness". There is only one point of maximum sharpness and steady softening on both far and near sides of that. The simple answer is that if the lens is focused to 100 feet any object beyond that distance will be defocused to some degree, though if the far distance is still conventionally considered to be within the DOF range, the amount of defocus will be minimal.

RLSprouse Loc: Encinitas CA (near Sandy Eggo)

kymarto wrote:

DOF always means "acceptable sharpness". There is only one point of maximum sharpness and steady softening on both far and near sides of that. The simple answer is that if the lens is focused to 100 feet any object beyond that distance will be defocused to some degree, though if the far distance is still conventionally considered to be within the DOF range, the amount of defocus will be minimal.

jlg1000 Loc: Uruguay / South America

Well... If you want ultimately sharp pictures of a far away subject regardless of atmospheric transmission or the internal focus transference function of the lens, you could just shoot a laser on the subject and correct later based on the laser spot.

User ID

Hamltnblue wrote:

Hello br Is there a difference in sharpness in the... (show quote)

If you had perfect optics and very sharp film and the atmosphere were gone, yes there would be a slight improvement at f/14 vs f/8 becuz the 5000 ft distance is not within the true in-focus plane, but is only within some degree of DoF.

That degree always varies by aperture. The improvement may require a good microscope to see it on the film but with perfect optics and no atmosphere it will be there.

So thaz how DoF functions in principle. Others have correctly informed you about reality, but I thought maybe the actual “mechanism” of DoF was on your mind as well.

Hamltnblue Loc: Springfield PA

Thanks All
I shoot a lot of land city scapes. Conventional wisdom tells us to shoot with a more closed aperture when trying to get the whole scene in focus. For that reason I typically shoot F11 to F16.

At the distances I gave the far point infinity for 70mm is f5.6, but I've read that just because F5.6 and F16 both have infinity as being in acceptable focus for infinity, they aren't the same. At some point I would assume there would be no change between the two. ( The moon and stars is a good example)

The attached shot was done at around f14.
The center point of the reflections is 4-500 feet away (focus point). The buildings are about a mile out.
Would the buildings be any more or less sharp with the shot done at F8(lens best sharpness), or a higher number?
Thanks

(Download)

jlg1000 Loc: Uruguay / South America

Hamltnblue wrote:

Thanks All br I shoot a lot of land city scapes. ... (show quote)

Why don't you just try by yourself?

Just put the camera in the "A" mode and shoot the same picture with each available aperture stop.

Later, pixel peep each photo and find out which is the sharpest one.

Each time I have such doubts, I just experiment to see what works best

Bo0mer

Nice shot!

Hamltnblue Loc: Springfield PA

jlg1000 wrote:

Why don't you just try by yourself?

Just put the camera in the "A" mode and shoot the same picture with each available aperture stop.

Later, pixel peep each photo and find out which is the sharpest one.

Each time I have such doubts, I just experiment to see what works best

Hi JLG
I have experimented some. I'm interested in what the science is from someone who has studied or taught it.
If the actual answer is that infinity is the same sharpness regardless of F stop, using the lower number would allow the exposure time to be reduced significantly.
If there is a cut-off point, experimenting with one scene would not provide a general answer for other shots.

jerryc41 Loc: Catskill Mts of NY

It's funny, but I was thinking about this morning. "Depth of field" should be called "apparent depth of field" because that's all it is: apparent. Regardless what focal length you use, the depth of field will be about the same. A tele seems to compress the area in focus, while a W/A seems to expand it. In reality, they are both just about the same. As the aperture gets smaller, the depth of field increases.

Very good article - http://www.joeenglander.com/documents/depth.pdf

Picture Taker Loc: Michigan Thumb

"CHG CANON" hit it on the head.