Dof and focus point

Gavjenks

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Riiiiight. Is that why you posted a link earlier in the thread to a multipage article full of complicated graphs and tables and lens diagrams and circles of confusion? Because you wanted to communicate that depth of field is oh so simple?

It ISN'T simple. Pretending it is simple does nothing but cripple a photographer by making them not bother to learn the information they need to harness it to their advantage fully.

The stuff in your article was important. So was the 3 part visual diagram. So is understanding that creamy-looking backgrounds are not the same thing as DOF.
 

Derrel

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Riiiiight. Is that why you posted a link earlier in the thread to a multipage article full of complicated graphs and tables and lens diagrams and circles of confusion? Because you wanted to communicate that depth of field is oh so simple?

It ISN'T simple. Pretending it is simple does nothing but cripple a photographer by making them not bother to learn the information they need to harness it to their advantage fully.

The stuff in your article was important. So was the 3 part visual diagram. So is understanding that creamy-looking backgrounds are not the same thing as DOF.

What gavjenks is talking about is called "background blur". Background blur is different from depth of field. Lenses with physically larger lens openings, give greater background blur. So, let's say we have three different lenses, set to f/2.8 in each case. Lenses are a 50mm lens, and 85mm lens, and a 135mm lens. Go here and take a look at the example photos.

compare2.jpg

And then read the article. Bokeh and Background Blur - Bob Atkins Photography
 
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ndancona

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Background blur is what I was after. Now I need to master how to maintain background blur and keep both subjects which are on the same focal plane in focus. The child in my original post is visibly out of focus and that's what bothers me most about the image.
 

kay1547

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I recently bought a nifty fifty f1.8 and I'm enjoying playing around with shallow depth of field with the lens wide open. However, I am getting a lot of focusing issues. My line of focus tends to be extremely narrow. I've tried changing the autofocus settings and experimenting a little but can't seem to resolve this issue. Is this just a short coming of the lens or a drawback to shooting wide open? Any tips on how I can resolve this problem?

The image attached is an example of what I'm talking about. The guy is in focus, in fact his right shoulder seems to be the most sharp, but the child is out of focus.:grumpy:
View attachment 56280

try downloading the DOF depth of field calculator app so you'll always have it with you, you'd be surprise how shallow f1.8 really is. I find using the center focus point helps me choose exactly where i want the focus which helps when using such a shallow depth of field. you've already gotten great tips from other in this thread, but if you haven't already try these 2 tips, im sure it will help.
 

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The child in my original post is visibly out of focus and that's what bothers me most about the image.

Focus on the eyes.
 
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ndancona

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Is center focus point the best option in this case? With two people standing side by side, I've got to focus on the eyes of one of them, which will throw the other one out of focus. Is this assumption correct?
 

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If your camera doesn't have enough focus points, then focus on the eyes using the center point, and then lock focus before you re-frame the shot.
 

Gavjenks

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Background blur is what I was after. Now I need to master how to maintain background blur and keep both subjects which are on the same focal plane in focus. The child in my original post is visibly out of focus and that's what bothers me most about the image.

You need a much longer lens like 200 from 4x further AND a slightly smaller aperture like 2.8 to address both issues at once.
 

table1349

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Riiiiight. Is that why you posted a link earlier in the thread to a multipage article full of complicated graphs and tables and lens diagrams and circles of confusion? Because you wanted to communicate that depth of field is oh so simple?

It ISN'T simple. Pretending it is simple does nothing but cripple a photographer by making them not bother to learn the information they need to harness it to their advantage fully.

The stuff in your article was important. So was the 3 part visual diagram. So is understanding that creamy-looking backgrounds are not the same thing as DOF.

Actually DOF is quite simple and purely a product of physics based on individual focal length, distance to subject and f stop. The only other by product to this equation is the sensor size of the camera being used. If it inside the prescribed DOF area for a particular focal length, at a prescribed distance, using a particular f stop then things inside that DOF range will be in focus. Those things that are outside that range either in front or behind that DOF range will be out of focus. Not too tough. And as you noticed then even included a simple fill in the data calculator to tell you what the DOF will be based on focal length, distance, f stop and sensor size.

As to the quality of that out of focus area, ie., Bokeh, then that is a different matter based upon construction of the lens. You keep talking about using a 200mm lens. I can achieve the same quality of Bokeh with my 85mm f1.2 at a much more reasonable working distance.

Of course I am still trying to figure out what all the stuff about eyeball resolving and printing has to do with DOF. As stated DOF is purely physics.
 

Derrel

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Moral of the story????? Wide-open aperture is for experts. And for those who like to live on the bleeding edge. And can burn you just as easily as reward you. Especially when used at close distances. This was shot with a 200mm f/2 lens outdoors offhand, at a wide aperture. The DOF is placed pretty well, for my purposes. The lips and teeth are focused, as is the near side of the head. The guy's a well-known local sprinter, and this was a shot of him I grabbed for our paper's "headshot files" of top local area athletes. $DSC5743_fornewsprint.jpg

Heck, I was even able to crop it to a horizontal extreme close-up.

$DSC5743_fornewsprint-HORIZ.jpg

This lens has superb background blurring capability AND exquisite bokeh. And, when used this way, it also has selective focus. And shallow depth of field. All FOUR buzzwords, all from one lens.
 
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table1349

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Derrel, on a side note, just because I know that it is one of your favorite things. tonight we had BACON for dinner. :D FYI nice shot.

We now return you to your regularly scheduled comments.
 

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