Getting to grips with aperture

[stugman]

I just got a T1i and just had my first weekend out taking pics. My first DSLR and I am having a lot of fun.

Is there an upper level of stopped down aperture that still gives apparent infinite dof?

Are there general rules of what to do?

I am just trying to work out whether I need to crank up to f10 or above to be sure say landscape shots are all in focus. I did a few test shots but not at each setting.

I realize that less light gets in so that also might be a restriction. Just trying to get ideas/concepts down.

[mike_d]

Smaller apertures (bigger number) gives more depth of field. I believe landscapes are commonly shot at f/16 or higher. Less light getting in isn't a problem because you'll likely be shooting on a tripod and you can leave the shutter open as long as it takes to get the desired exposure.

[stugman]

ok thanks for the f/16 hint.

I also found http://www.dofmaster.com/dofjs.html which is helping but also can get a bit confusing when I play around with the settings.

[WaltA]

Well, be careful about the above tip to "leave the shutter open as long as it takes to get the desired exposure". At settings above f16 you'll begin to lose IQ because of lens diffraction. Exactly at what setting and how bad depends on your lens - and you don't say what lens you use.

I would stay between f11 and f16 with most lenses and you'll get the best band for your buck.

check it out here ...
http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm

Also, every lens has its own "sweet spot" so you'll want to experiment between f8 and f16 and see where your lens is sharpest.

[DunnoWhen]

What I think you will find beneficial is to read up on Depth Of Field (DOF) and Hyperfocal distance. DOF calculator HERE (http://www.dofmaster.com/dofjs.html)

My starting point is to set F11, sub 25mm focal length and focus on anything 10 feet away. With those settings I know that, at worst, my DOF extends from 4.9 feet to infinity.

Buy the time I get to 17mm, the DOF is from 3 feet to infinity.

Using these figures, focusing beyond 10 feet won't change the far point being infinity, only the near point will move away from you slightly. The near point does not, however, move further away than the hyperfocal distance, which at 25mm is 9.62 feet or, at 17mm, is 4.47 feet.

IF I've remembered to carry my charts, I can be a more accurate but this suits me fine for remembered values. :)

[stugman]

I added my gear to my sig line.

For example with the 18-55 IS kit lens and a subject at 15 feet at 50mm f3.6 (although maybe at 50mm it might have to be f5.6 not sure) the DOF is 3.73ft and at 18mm it is 302ft.

Interesting so it seems that zooming in will isolate the subject more unless I am missing something else.

[DunnoWhen]

For example with the 18-55 IS kit lens and a subject at 15 feet at 50mm f3.6 (although maybe at 50mm it might have to be f5.6 not sure) the DOF is 3.73ft and at 18mm it is 302ft.

Yep, you've got it:)



Interesting so it seems that zooming in will isolate the subject more unless I am missing something else.

Again, yes.

DOF is a function of focal length AND aperture. So, zooming in will help isolate a subject but, more importantly, choose a large aperture (small f numbers). Oh, and don't forget to considering seperating/moving your subject away from the background.:)

[stugman]

Thanks for the reply. Now with a bit more understanding I can progress.

So for the most isolation (small DOF) you would zoom a large extent and try and use a low f stop.

[tonylong]

Thanks for the reply. Now with a bit more understanding I can progress.

So for the most isolation (small DOF) you would zoom a large extent and try and use a low f stop.

That and your distance from the subject. And, for the best effects, you want distance between the subject and the background. Each of these plays a part, and some times one thing can "trump" another -- for example, if you have a long lens and your subject is pretty distant from the background, you can have the creamy background even if you are a ways from the subject and you are shooting with a narrow aperture.

I personally don't give much "analysis" to my scenes, but rather approach things in a "rule of thumb" way, just knowing what range of aperture I want for a given subject and desired depth of field. It doesn't need to be overly complicated.

[DunnoWhen]

So for the most isolation (small DOF) you would zoom a large extent and try and use a low f stop.

.... and move your subject away from the background as best you can.

Yes. That's it:)

[stugman]

Thanks guys I get it.

Also that online calculator is useful although it is good to have the general concepts down because in real life you probably don't have a calculator available.

I'll do some testing now that I have a better idea.

[IslandCrow]

Also that online calculator is useful although it is good to have the general concepts down because in real life you probably don't have a calculator available.

Actually, you can with something like this: http://www.adorama.com/EXDOFN.html. Yes, before there were electronic calculators, there were mechanical ones. Of course, if you want to jump into the 21st century, you could always get one of those fandangled smart phones and download a DOF app.

But you're right. Having the concept down is the most important part. Even when I remember to bring my DoF calculator with me, I tend to use it mostly for macro photography where even an inch more/less DoF can make a really big difference. Otherwise, I tend to WAG it.