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Beg. questions F-stop - ISO
First of all.the term wide open.I'm assuming that refers to shooting at the lowest fstop. lets say f/4 on the 70-200/4 please correct me if I am wrong..

I know lower Fstops produce better bokeh, but I think I remember hearing that they also are not as sharp....

Also When shooting is it always preferable to have the lowest ISO number? I usually keep mine on 100 unless I need a faster shutter speed in lower light situations....

Comments (5)

Yates717 wrote:.

First of all.the term wide open.I'm assuming that refers toshooting at the lowest fstop. lets say f/4 on the 70-200/4 please correct me if I am wrong..

You are right.

I know lower Fstops produce better bokeh, but I think I rememberhearing that they also are not as sharp....

Not better. The quality of the bokeh is a constant of the lens, determined by the mechanical and optical design. Shooting wide open will give you less depth of field and more out of focus area. Yes, it can be softer, both absolute and perceptive..

Also When shooting is it always preferable to have the lowest ISOnumber? I usually keep mine on 100 unless I need a faster shutterspeed in lower light situations...

Think of iso as the pregain in a guitar amp. The higher it is, the more distortion you get in the sound..

/d/n..

Comment #1

Wideopen means that with 50mmf1.4 lens the fstop you are using is 1.4..

The lens itself however is giving up a lot of it's sharpness to shoot at f1.4. good bokeh will not matter is the scene is not sharp and in focus. max sharpness for lenses occur 2-3 fstop closed down from wideopen or f8.0(if you do not know). personally, for max sharpness on my lenses I just use f8.0 and not worry about it. if it is not f8.0 then any differences would be exremely minor..

It is also important not to close down too far. if you do you have diffraction distorsion, which is the way light rays(beams) behave when they go through a small hole. the smaller the hole the more they distort. for digital photography and c sensor you are talking about diffraction distorsion starting beyond f11.0. this does not means the images at f16.0 are bad, it is just there is some distorsion setting in. by all means if you have to have max dof use a high fstop.



One thing a newbie tends to do is crank the fstop to 16-22 because he thinks you have to have all that dof. not true. you are better off with your midrange fstops, say f5.6-11.0..

When shooting try to stay with the lower iso numbers. but if the light is dim then I have no qualms about cranking the iso to 800 or 1600..

If there is noise there are programs to get rid of it, like noise ninja or similar.taken at the detroit zoo iso 800 on a tripod..

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window.

Taken at the niagara falls butterfly conservatory. handheld. iso 1600..

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window..

Comment #2

Your specific questions are basically in the right direction, with minor quibbles on terminology. Some grounding on the basics will help you understand why you're right..

Http://halley.cc/photo/last.html.

[ e d @ h a l l e yc c ] http://www.halley.cc/pix/..

Comment #3

Yates717 wrote:.

First of all.the term wide open.I'm assuming that refers toshooting at the lowest fstop. lets say f/4 on the 70-200/4 please correct me if I am wrong.I know lower Fstops produce better bokeh, but I think I rememberhearing that they also are not as sharp....

Also When shooting is it always preferable to have the lowest ISOnumber? I usually keep mine on 100 unless I need a faster shutterspeed in lower light situations...

The smaller the f-stop number the larger the aperture opening and the more light will be let in. Think of your eye in bright light vs night time when it dilates letting in more light. Faster lenses have lower f-stops when wide open. The more wide open you shoot does decrease the DOF which means you really have to have your focus right on your subject. I don't think it makes the lens not as sharp. Each lens has it own sweet spot where it will be the sharpest..

Just like any other adjustable setting the ISO should be set to benefit the shot you are taking given the surrounding conditions... Use the lowest ISO you can for the conditions....Dennis..

Comment #4

You mentioned the 70-200 f/4L. It is one of few lenses that is fully sharp wide open. No matter which lens you are using, don't be afraid to use high ISOs. Lots of pros say to start at 200 outdoors and 400 indoors and then move up as needed..

Jerryhttp://jchoate.zenfolio.com/..

Comment #5

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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