Jerry Brown

I am trying to take better portraits of my grandkids and any body else who will sit for me. I read an article in Picture Perfect about taking better portraits; it all seemed pretty straight forward except for this statement:
More importantly,

when you come in close, instead of using a zoom,

you decrease the depth of field, which, in simple terms, is the length between your focus point and some point in the distance that is in focus. What this means is that when you come in close, you capture the face in sharp focus, but the closer you get the shallower the depth of field becomes. This, in effect, blurs out the background, and because our eyes always.

I understand everything except the section that I put in a space. I'll repeat my question; Is there a difference between zooming in and walking in.? The way I understand it is that there is, in that you lose your shallow depth of field when you zoom in.

right or wrong??

Rongnongno Loc: FL

Intimacy, contact with the subject.

Zoom/long focal is the way of the 'coward' afraid of connecting with the subject.

The dof observation is true as one of the factor is the distance.

Jerry Brown

LOL, OK then I guess that makes me a coward :D

Thanks for the reply and setting an old man straight.

KennyMac Loc: Lynchburg, VA

Jerry, as physical distance to subject decreases, DOF also decreases. Also as aperture opening increases, DOF decreases. This is very obvious in macro photography. Goto DOFMaster.com and plug in values to see this.

Bobby Deal Loc: Loveland Colorado

This is a topic that can get very confusing very fast. Focal length also has an effect on DOF. The longer the focal length the shallower the depth of field. For lack of a better more technical explanation if a lens has a 3x zoom factor it should have an equal 3x factor on DOF in that it should produce a DOF consistent with being physically 3x closer.

The difficulty in knowing exact differences comes from many variables.
1. What is the standardized point in focal length? I seem to recall somewhere that the human eye was effectively comparable to a 47 mm lens. If that is true then using the nifty 59 as a baseline would seem logical.

So in theory a lens of 50 mm at 10' and one of 150 mm at 30' should provide the same DOF at the same aperture setting.

2.. Focal length also plays a significant role in image distortion. Wide lens at short distances are much more likely to produce distortion than a longer focal length. Extension distortion, barrel distortion, pin cushioning etc are all more revel ant in wider lenses. You can combat distortion in wide lenses by maintaining level on all four points of axis but ideally the compression distortion inherent in a longer lens is preferable in portraiture than the various distortions that come into play with wide angle lenses. This is why lens recommendations for portraiture begin at roughly 70 mm and some of the most popular prime lengths for portraits at 85 mm 105 mm 135 mm and 180 mm

That is not to say you can not archive acceptable results with wider lenses but from a point of standardization these are the accepted portrait focal lengths.

In addition other factors come into play when comparing the use of mechanical zoom vs physical distance. Lens diffraction and field of view being a couple major ones. I am no expert on the inner working of a lens but I do know varying levels of diffraction can have significant impact on image quality.

Also one must take into account the digital sensor when considering focal length, the crop ratio of various DX camera sensors can have a significant effect on the effective focal length of a lens.

While the 50mm lens may not be the best choice for a head and shoulders portrait on a full frame camera'such as a D3 due to the potential of distortion from the need to get within just 3-4 feet of the subject to fill the frame at this focal length. The same lens may work wonderfully for you on camera with a DX sensor with a 1.5 crop factor such as on a D300 where your 50 mm effectively becomes a 75mm lens.

The other drawback to photographing people up close with wider lenses is simply one of physical comfort, not for the photographer but for the subject. Issues of distortion aside creating a portrait with a 28 mm lens on a full frame camera may require you to be at a distance of 24"-36" from the subject. For many people that is simply too in the face and creates an uncomfortable tension during the photographic process. Shooting from a longer distance with a longer lens eliminates the tension caused by having to be in someone's face to make their portrait.

Another factor to consider

Often when talking about depth of field people confuse bokeh as depth of field. Bokeh is not depth of field but rather is how a particular lens renders the out of focus areas, particularly the highlights in the background of an image. This is mostly a result of the aperture of the lens. A lens with 8 blades in its aperture will produce a much more pleasant bokeh than one with 6 or 7 blades.. Ultimately it is much more complex than just the number of blades and the shape they create but it is one of the key factors.

rpavich Loc: West Virginia

Yes...there is a difference.


DISTANCE is a large factor in depth of field or lack of it.

That's why the article said that there was a difference.

Aperture and distance account for depth of field.

It's one "tool" in your arsenal.

Framing, depth of field, composition, exposure, light direction, light quality...etc.

rpavich Loc: West Virginia

It seems that it DOES get confusing because this statement is false.

Distance and aperture account for DOF..not focal length itself.

http://www.cybercollege.com/myths.htm

Racmanaz Loc: Sunny Tucson!

Yes here we go again lol. Only 3 things affect the DOF, there are changing the aperture, changing the focal length and changing the focus distance. Subject distance really does not change DOF at all. :)

rpavich Loc: West Virginia

Wrong.

Aperture and distance.

focal length doesn't change DOF.

See previous link (or any other multitudes of links to be had)

Racmanaz Loc: Sunny Tucson!

Distance does NOT change DOF, only the focus distance changes the DOF in this instance. I can move my subject anywhere in the scene and it will not change the DOF at all, only when I change the focus will it change the DOF. Changing the focal length ALWAYS changes the DOF and moves it eaither back or forth. :)

Racmanaz Loc: Sunny Tucson!

Here's the chart which was proven to be true.

(Download)

rpavich Loc: West Virginia

Sure... you are right...but I guess when i said "distance" it was assumed that I meant "distance to subject which you focus on"

Sheesh....if you aren't focusing on the subject...what ARE you focusing on?

Focal length doesn't change depth of field...period...want some links?


http://www.bluesky-web.com/dofmyth.htm

http://www.cybercollege.com/myths.htm

http://www.luminous-landscape.com/tutorials/dof2.shtml

Racmanaz Loc: Sunny Tucson!

LOL I'm just playing with ya rpavich, don't mind me it' all in fun.

rpavich Loc: West Virginia

Now where are those blood pressure pills!!!! :)

Racmanaz Loc: Sunny Tucson!

I took them all already ;)