Aperture? (Page 3): TSHDGTL posted about exposure elsewhere so it's safe to assume that he is now asking about DOF.

selmslie Loc: Fernandina Beach, FL, USA

N4646W wrote:

May I ask what information prompted you to ask this question? That way maybe we can get your topic back on track. Hopefully someone can help with out hijacking your thread.

Ron

TSHDGTL posted about exposure elsewhere so it's safe to assume that he is now asking about DOF.

Dikdik Loc: Winnipeg, Canada

N4646W wrote:

May I ask what information prompted you to ask this question? That way maybe we can get your topic back on track. Hopefully someone can help with out hijacking your thread.Ron

Not far off... and, all seems to be relevant.

Dik

N4646W

Dikdik wrote:

Not far off... and, all seems to be relevant.

Dik

Yes, if we assume he is asking about depth of field. There have be discussions about light refraction and diffraction off of the aperture blades at small f#, discussions about heat and humidity affecting sharpness over long distances and in studio use. Who knows what he has read on this forum or others that has him asking a question, and looking for clarification? The OP, as I read it, did not specifically ask about depth of field, he asked about light "quality or characteristics" at f stops. Until he chimes in, this is moot.

Ron

rmalarz Loc: Tempe, Arizona

Well, looks like I'm not going to loose. My 50mm f/1.4 Nikkor has marked feet and f/stops. Let's pick f/16.

If I focus at 10 feet, the near footage aligned with the nearside f/16 mark is approximately 7 feet. The far distance aligned with the far side f/16 is approximately 30 feet. That equates to things at 10 feet being in focus and things as close as 7 feet, 3 feet in front of the focus point to things at 30 feet, 20 feet past the focus point, being acceptably in focus. That a total of 23 feet for the total DOF.

If I set the focus at 5 feet, the near distance is 4 feet, the far distance is 7 feet. again using f/16 marks. That's 1 foot in front of the focus point to 2 feet behind the focus point. This shows the distribution to be smaller in front of the focal point and larger behind it. This isn't an opinion. It's an optical fact based on markings on a lens made by a reputable lens manufacturer.

The only correction I'd make is that the DOF scale numbers are closer to each other towards the infinity side of the scale. I believe I stated the opposite earlier.
--Bob

selmslie wrote:

You would lose that bet as I just showed.

For starters, take any full frame 50mm lens and place the infinity mark at the f/16 mark. You will find the focus point at around 16 feet (the hyperfocal distance) and the near DOF mark over the other f/16 mark at around 8 feet. The calculated DOF would be somewhere between 1390 to infinite.

That's not 1/3-2/3 (1:2). It's closer to 8:infinity.

TSHDGTL

N4646W wrote:

May I ask what information prompted you to ask this question? That way maybe we can get your topic back on track. Hopefully someone can help with out hijacking your thread.

Ron

Was wondering if the aperture was near the focal point of the lens. If so, the in-focus image passes through a small point and the farther you get from this point the less focused the light would be. Hard to find reliable information on the subject. Maybe someone who understands lens design can chime in.

selmslie Loc: Fernandina Beach, FL, USA

rmalarz wrote:

Well, looks like I'm not going to loose. My 50mm f... (show quote)

Anyone with a DOF calculator can figure that out.

I guess you lose.

Not even close - 3.8:15.9 is not 1:2

(Download)

Focus distance about 1/3 of hyperfocal distance - I predicted earlier it would be close

(Download)

selmslie Loc: Fernandina Beach, FL, USA

selmslie wrote:

Anyone with a DOF calculator can figure that out. ..

Now focus at 2 feet. The ratio is 0.21:0.26
At 15 feet - 7.21:188
At 17 feet - 8.31:infinity

You really don't understand DOF at all!

tdekany Loc: Oregon

selmslie wrote:

Now focus at 2 feet. The ratio is 0.21:0.26
At 15 feet - 7.21:188
At 17 feet - 8.31:infinity

You really don't understand DOF at all!

Cheese and rice! Why not focus stack?

mwsilvers Loc: Central New Jersey

TSHDGTL wrote:

My understanding is that a smaller aperture blocks out of focus light. Does this mean wider apertures are using out of focus light to brighten the image?

This thread has gone off on a tangent that really doesn't address your confusion. Both of your statements are incorrect and you may have misunderstood or misinterpreted something you heard or read. Light is neither in nor out of focus. A larger or wider aperture (smaller f number) lets in more light. A smaller aperture (higher f numbers) lets in less light. A lens wide open may be less sharp than when its stopped down a bit due to the geometry of the lens. Lens are often at their sharpest 2 to 3 stops down from wide open. When sufficiently stopped down lens may suffer from a phenomenon called diffusion which may render images a bit less sharp, but none of this has anything to do with blocking out or allowing in out of focus light.

N4646W

TSHDGTL wrote:

Was wondering if the aperture was near the focal point of the lens. If so, the in-focus image passes through a small point and the farther you get from this point the less focused the light would be. Hard to find reliable information on the subject. Maybe someone who understands lens design can chime in.

No, the aperture is not located near the focal point of the lens. It is in most cases located between the front element (light gathering element) and the primary focusing element. It controls the volume of light entering the optical elements. Depending on the design of the aperture or it's quality, it can degrade an image to the point where it "may appear" out of focus, (This is entirely a separate issue). This in most cases appears in extreme light conditions (mostly brightly lit environments) at numerically high apertures. The actual focus point of a lens occurs at a distance between the rear element of the lens and the camera sensor or film plane.

Hope this helps, if not, keep asking.

Ron

selmslie Loc: Fernandina Beach, FL, USA

rmalarz wrote:

... The only correction I'd make is that the DOF scale numbers are closer to each other towards the infinity side of the scale. I believe I stated the opposite earlier.
--Bob

You even got that wrong.

The distance difference is greater. After all, infinity is pretty far away. It's just the marks that might get closer together.

The marks are farther apart between 1.7 and 1.5 feet than they are between 20 and 7 feet.

TSHDGTL

N4646W wrote:

No, the aperture is not located near the focal poi... (show quote)

Thanks for replying to my original question Ron. This all stems from my desire to use unusual aperture designs and the effect they would have. What if the aperture blade weren't totally opaque but started off transparent and gradually became opaque what effect would that have on bokeh. Is this how STF lenses work? I'm under the impression there is a focal point where the image converges and this would be an idea place to place such an aperture. Just my 2 cents.

rmalarz Loc: Tempe, Arizona

Apparently, you don't know how slide rules work either.

That aside, you failed to address the fact that there is a ratio between the distance in front of the subject to the distance behind the subject.
--Bob

selmslie wrote:

You even got that wrong.

The distance difference is greater. After all, infinity is pretty far away. It's just the marks that might get closer together.

The marks are farther apart between 1.7 and 1.5 feet than they are between 20 and 7 feet.

biry

Bob, if you posted that the sun rises in the East and sets in the west as a general rule, somebody here would dispute you. Its a little north or south of East and West. Probably go into Earth inclination, rotation, on and on. You are a good teacher and try to help folks (like me) understand photography. A fine photographer, too. Appreciate you.
Bill

rmalarz wrote:

"Is depth of field equally distributed in front and back of my focus point?

No, it’s usually about one third in front and two thirds behind your focal point, but as your focal length increases, it becomes more equal".- https://digital-photography-school.com/understanding-depth-field-beginners/

Again, for the average beginner, which this post seemingly is by, the 1/3-2/3 is good enough. I didn't wish to extend that to a detailed treatise on optics.
--Bob

selmslie Loc: Fernandina Beach, FL, USA

rmalarz wrote:

Apparently, you don't know how slide rules work either.

You know I do. They are based on logarithms. What’s the logarithm of infinity?

DOF scales are not based on logarithms.

rmalarz wrote:

That aside, you failed to address the fact that there is a ratio between the distance in front of the subject to the distance behind the subject.
--Bob

That’s all we have been talking about. Look at the DOF calculator screen shots. They tell us more about the ratio.

Now use the f/8 marks on your lens. Set one on the infinity mark. Can you read the hyperfocal distance? The near focus distance? Hint: it’s half the focused distance.