Light and aperture

How does the aperture modify the quality of light?why a small aperture cauze a more directional light?I talk about the light touching the subject,if you use a small number,larga aperture the light îs soft,if you use a narrow aperture,big number the light îs more punchy and directional..

A small aperture may cause diffraction:

https://www.cambridgeincolour.com/tu...hotography.htm

The questions can not be answered with a simple post because a scientific understanding of optics would be needed to correctly answer the questions as they were written (i.e. "how", "why"). It would be better to Google for papers about diffraction, lens aberration and theories of light, both quantum and wave theory.

Quote:

---

Originally Posted by costasd68

How does the aperture modify the quality of light?why a small aperture cauze a more directional light?I talk about the light touching the subject,if you use a small number,larga aperture the light îs soft,if you use a narrow aperture,big number the light îs more punchy and directional..

---

Most is explained by the aperture blades and their shape.

Hi @ costasd68,
This pic is shot at f/22 with a flash in M mode. I wonder it says something for you

http://www.flickr.com/photos/ndk277/...n/photostream/

Tks

Not quite sure what Y! is asking but hard and softness comes from the size of the light source in addition to whatever aperture is being used by the lens. Direct sunlight/overcast Spotlight/broad etc.

Good afternoon OP (costas, Y),
I read your post as asking about the size of the light source lighting the subject rather than the size of the aperture in the camera. Aperture and size of light source are two rather different things.

Assuming a single light source shining onto a subject, you have three phases to consider. Shadow (full shade, umbra, where no part of the light source can be seen from this area), lit areas (no shade, where ALL the light source can be seen), interface (partial shade, penumbra, where only part of the light source can be seen).

As such, a small light source (from the point of view of the subject) will have a sharp transition (narrow penumbra) between the lit area and the full shadow. Usually considered as hard light. Easy to tell (from examination of a photograph) where the light is coming from.
A large light source (from the point of view of the sbuject) will have a longer transition (broad penumbra). Usually considered soft light. More difficult to tell the direction of the light source.


As an example, bright sunlight. The sun, from this distance, is close to a single point, so the transition from shaded areas to lit areas is very narrow (hard light, easy to tell direction of the light). In cloudy weather the clouds modify the light so it seems to be coming from a very much larger area. The transition from shaded areas to lit areas is very broad (soft light, difficult to tell where the light is originally coming from).
Hope I understood your question correctly.
The aperture in camera has little discernible effect on the hardness/softness of the light.
Graham

Interesting name, that: http://cdn.cambridgeincolour.com/for...c/im_yahoo.png reminds me of the "artist formerly know as . . ."

I wonder if we are misreading the question and should replace the work "aperture" with "size of the light source".

A small light source, like a small flash or even the sun is highly directional, i.e. light travels in a straight line and causes harsh shadows.

If you take a large light source, like an overcast day or a softbox that is close to the subject, light travels in all directions and any shadows that are cast tend to be fairly soft. That is why I have never understood people that use softboxes that are really far away from the subject. They start to act like a point source and all benefits of a soft, diffuse light source are lost, and harsh shadows occur.

Thankyou Manfred ... you have caused a penny to drop for me :)
Never owned or used a soft box though have hung muslin curtains in front of lights on occasions I have wondered at the ability of the cheaper flash units like YungNuo to be used with a softbox or reflector as opposed the the hard light of being used directly and realise that if the unit is used close to maximise the softness the loss of effective output is compensated for by the reduced distance of flash to subject.

Re-reading Y!'s question I think the effect is the lens working in a crisper manner when only the centre of the lens is used comes from the lens itself rather than the aperture ... at least with older lenses or those not designed to be used wide open ... it is often suggested that rather than working wide open one should close down to a middle point in the range of available apertures.
Here I am equating soft/hard with crispness/quality in the end result, a soft result is usually frowned upon these days and everything has to be brittle sharp to be accepted.

Though of course the smaller aperture gives greater depth of field which could lead to greater aceptance due to less out of focus areas in the image.

Quote:

---

Originally Posted by xpatUSA

Interesting name, that: http://cdn.cambridgeincolour.com/for...c/im_yahoo.png reminds me of the "artist formerly know as . . ."

---

That reminds me of Yahoo...

Quote:

---

Originally Posted by GrumpyDiver

I wonder if we are misreading the question and should replace the work "aperture" with "size of the light source".

A small light source, like a small flash or event the sun is highly directional, i.e. light travels in a straight line and causes harsh shadows.

If you take a large light source, like an overcast day or a softbox that is close to the subject, light travels in all directions and any shadows that are cast tend to be fairly soft. That is why I have never understood people that use softboxes that are really far away from the subject. They start to act like a point source and all benefits of a soft, diffuse light source are lost, and harsh shadows occur.

---

A good point. In watch photography, the use of diffused lighting is common - usually in the form of light "tents" - sometimes to excess, IMHO. The rounded metal or glass surface reflections from a watch act to concentrate incident light which, if already from a point source, guarantees blown highlights in the image.

I find that it is best to be able to move the lighting and diffusers relative to each other and to the subject. That allows adjustment of the diffusion "factor" to an extent. Lighting far from the diffuser gives a flat-looking, low contrast image. Lighting near the diffuser, image is vice-versa. I keep a Maglite handy to apply "spot" highlighting if needed, usually on dials.

http://kronometric.org/tcw/mec/vintage_V/an512.jpg

Not the best shot, just showing off the watch really . . :-)