Wide aperture - Pictures out of focus

Started Aug 3, 2014 | Discussions thread
tedolf Forum Pro • Posts: 26,892
Less than $300.00.....

Truthiness wrote:

tedolf wrote:

Doss wrote:

tedolf wrote:

Doss wrote:

But it doesn't work well for beginners, or frankly most amateur photographers. And, you pay a lot of $$ for it. If a beginner can't really make use of it, what is the point of spending all that $$?

Yes...but - Having gone out and bought such a lens the first thing I would suggest to anyone (beginner or otherwise) is run a few tests shots and make sure it is usable wide open - for when you need it.

Well, I guess I wouldn't go out and buy a lens, especially and expensive one unless I knew it was going to work for what I wanted to do. DOF tables are not a secret (they used to be supplied with every lens) and are available on the Internet.

You can also compare systems by just taking advantage of the crop-factors.

We are assuming that the OP already has a camera and is now looking for a lens. Obviously that was the OP's situation here where he was trying out his new lens and was surprised by what it couldn't do!

Thus, before buying a fancy f/1.8 85mm portrait lens you would think that a person would look at a DOF table and say, "hey, this thing isn't going to work for tight head and shoulder shots wide open-the DOF is too shallow, maybe I would be better off buying an 85mm f.2.8 lens instead and save a few hundred dollars!".

Would you point out to me how many 85/2.8 lenses there are on the market which cost about 100 dollars or 200 dollars?



Less than $300.0 and that is new. Used it is less than $200.00




There are many others you can find, I will leave the exercise for the reader.

85mm f/1.8 lenses from Canon and Nikon are inexpensive yet optically very good. The CaNikon lenses in question cost 400-500 dollars.

The m43 45mm f/1.8, a two stops slower lens that the above FF lenses, costs 350 bucks.

It is exactly the same maximum aperture, not two stops "slower".

Please, F-stops are the mathematical ratio of focal length to lens diameter.

The 42.5/1.2 Leica/Panasonic is still a stop slower,

No, it is one stop faster.

yet costs 1500 bucks...

And you know, some people avtually shoot multiple kinds of subjects and multiple kinds of images, not just passport shots. I often shoot at f/2 and faster on FF without any DOF issues.

so do others, do you want a prize?

Let's get back on topic.  We are talking specifically about the image the OP tried to take.

but I don't think they were trying to get a desired effect,. I think they were just testing out a new lens and wanted to be sure they could get away with using it at f1.8 - which is the point of having a lens with that setting!

And he couldn't. And neither could I, and neither could you in that setting,

Erm - Yes, I most certainly could! Why do you not find this achievable?

Because for a tight head and shoulders shot at 10 feet, 85mm, f/1.8 the DOF is exactly 0.28 feet (about 3"). You can not get the entire head of a subject in focus. Can't. Period. Look at the DOF tables.

And maybe you don't want to get the entire head in focus

Oh, please.

Now you are just changing the issue.

Let's stay on topic-the OP's posted photo.

because most of it is not visible in the image anyhow... often all one needs is the closest eye to be in focus. Or the fact,not the back of the head

Not if the ears are out of focus.  If you have a paying client and you give them a photo like the OP took they are going to be extremely dissatisfied!

And that DOF depends on the output size btw, so it's not "exactly 0.28 feet". And please try to use metric units, after all we're no more in the middle ages

Really, just check the DOF tables.

What are you going to do, stand 12 feet away from an 8" x 10" print?

with that light unless you started using ND filters or something.

And why bring ND filters into the equation? I'm off! You're making me feel as confused as you sound

To still use f/1.8 and......oh, forget it.

You don't need any more ND filters on FF f/1.8 than on m43 f/1.8. Light per area is the same, light per photo differs by factor of four.

forget it, I don't want to explain it to you.  It is just going to get you off on a tangent.


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