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12-21-2014, 02:02 PM   #1
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DOF shooting at 1.8

So here's three pictures I took earlier today. All taken with da50 1.8 @ f1.8. Why do they all look so different? The one with the fence looks good, the one of the path isn't horrible but the one of the moss is. The bokeh is terrible and there's pretty much nothing in focus. I'm guessing its because each shot was different distances from the camera. The fence was the farthest, the path was a little closer, and the moss was the closest (about 5 feet away). Shouldn't 1.8 be 1.8 no matter the distance? And the moss and path shot are not that different in terms of distance from the lens. So why does the background (trees) look so much better than the moss shot? Shouldn't they be completely blurry since theyre so far away?

---------- Post added 12-21-14 at 02:06 PM ----------




Last edited by Another dyemention; 12-21-2014 at 02:07 PM.
12-21-2014, 02:07 PM   #2
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No pics.

And even without pics your distance to subject is one of the most major factors in determining depth of field.

At f1.8 and a subject 5 foot away with a 50mm lens you have about 2 1/2 inches in focus.

Not much wiggle room there.
12-21-2014, 02:21 PM   #3
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Put em on flickr and post the links. It's easier. At least for me. Thats what I do.
12-21-2014, 02:23 PM   #4
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Online Depth of Field Calculator


And then there is the APP:
https://itunes.apple.com/us/app/depth-of-field-calculator/id356339910?mt=8

12-21-2014, 02:29 PM   #5
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Can you confirm you have reduced the picture size to conform with the forum settings?
12-21-2014, 02:44 PM   #6
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As others have said, yes f/1.8 is f/1.8 but no, it won't give the same results at different focal distances. Depth of field expands along with distance to the subject. With a close-up shot, f/1.8 might give you a depth of field of only a fraction of an inch. With a telephoto shot at hundreds of feet, the DOF might be dozens of feet. That is why macro shots are almost always shot at f/22 or so - to expand DOF to something usable. Distance matters.
12-21-2014, 02:56 PM   #7
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QuoteOriginally posted by alamo5000 Quote
Put em on flickr and post the links. It's easier. At least for me. Thats what I do.
What he said. Flickr makes it easy.


Steve
12-21-2014, 02:59 PM - 1 Like   #8
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Yes, focal length, aperture, and distance from subject is what gives different apparent DoF. DoF is most shallow at nearest focus, smallest f-number, and highest focal length.
Keep in mind that bokeh is not the same as DoF. Bokeh is the character of the blur. Other than the previously mentioned factors, bokeh is also determined by lens design and background (well-lit or dark, with lot of detail or little, point light sources,..).
This is why using f1.8 takes some skill. You need to know what kind of result you want, and then use the appropriate aperture. f1.8 is not useful for landscapes, architecture, most nature photos, documentation, macro, and product photography. f1.8 is good for portraits, moody empty photos, subject isolation, and so on. Photography is a balance act, each setting has effects, and you need to select the three settings, as well as place yourself and take aim, in the way that will give results that you want to see. Good luck.

12-21-2014, 03:00 PM   #9
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QuoteOriginally posted by abmj Quote
it won't give the same results at different focal distances.
It also won't give the same results at different magnifications. I don't remember what aperture was used for my avatar picture, but here is a larger version. Hint: DOF for this photo is even less for a full-resolution crop.




Steve
12-21-2014, 03:06 PM   #10
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QuoteOriginally posted by Na Horuk Quote
This is why using f1.8 takes some skill.
...and is possibly why so many people complain of excessive softness with the DA 50/1.8 wide open. DOF at 3 feet and f/1.8 is less than an inch and that is the range for "acceptable" focus.*


Steve

* Acceptable focus is somewhat loosely defined. IIRC it is an 8x10 enlargement viewed at 24 inch distance. That is not exactly pixel peeping with today's camera resolutions.

Last edited by stevebrot; 12-21-2014 at 03:12 PM.
12-21-2014, 05:01 PM   #11
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trying this once more

so ill try this once more. if it doesn't work, I'll put them on my flickr

---------- Post added 12-21-14 at 05:06 PM ----------

I get the whole distance thing. I suspected it as soon as I seen my photos. But what I don't get is the background on the third pic. how can it be so drastically diferent than the other two? oh.. oops. the second pic is 2.5. jeez I feel like a dumbass now.

---------- Post added 12-21-14 at 05:08 PM ----------

Thanks for your help everyone. I don't know what id do without this forum and all of you helpful people. I really appreciate it.
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12-21-2014, 06:08 PM   #12
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I can see the pics... now other than knowing that you used a super thin depth of field, what are you wanting to know?
12-21-2014, 06:21 PM   #13
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Why the background is so bad on the third pic compared to the others.
12-21-2014, 06:31 PM   #14
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QuoteOriginally posted by Another dyemention Quote
Why the background is so bad on the third pic compared to the others.
Bokeh can vary by the characteristics of the background. With some lenses (I have a few such) a busy background can result in "nervous" bokeh at some apertures.


Steve
12-21-2014, 06:33 PM   #15
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The reason why the OOF background is so different-- the difference in lighting, and the background itself. The third picture has a bright/light background and has less contrast versus the area in focus. The first two have more distinctive contrast between the OOF area and the area in focus.
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