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08-03-2016, 07:59 PM   #1
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Question about depth of field when shooting with a longer lens

So this is probably going to make me sound like and idiot ..... but. I am having trouble with why I am not getting a deeper depth of field (more of subject in focus when shooting at higher aperture settings). Is it because I am shooting with a longer lens? 100mm as opposed to the 35mm I am use to shooting with. Here is the dilemma ... working on a project where I am shooting animals .... I'm looking to have as much detail in the animals face .... from the snout all the way back to the ears and every thing between those two areas. I was under the impression that at higher aperture settings I would be able to get that highly detailed (in focus) look. Primarily I have been shooting at between F8 and F10. I focus on the animal's eye .... recompose... shoot ... the animals eye(s) which were the focus point are perfectly in focus ... the snout (of a dog in this case) is out of focus..... I figured at F10 if I focused on the eye ... it being somewhere between where the snout begins and the head of the animal ends that I would have the entire animals head in focus. Normally I shoot with a much shorter lens ... 35mm and have not had this issue ... is it that I am shooting with a 100mm telephoto that I am getting this effect? And if so do I need to step down to a shorter focal length to get the effect I am looking for? Or how do I make it work with a longer lens. Any advice or help would be greatly appreciated. Thanks!

08-03-2016, 08:16 PM   #2
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The longer the lens or the closer your subject, the shallower the depth of field.

If your subject was 10 meters away, at F10 your total DoF would be about 4m (i.e. things between 8m and 12m would be in focus).

But if your subject was only 3 meters away, your DoF would be very shallow- about 0.4m (i.e. things between 2.8m and 3.2m would be in focus).

I'd recommend taking a step back, as this will probably give you the results you are looking for.

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08-03-2016, 08:24 PM   #3
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Ditto on Adams suggestion. In fact I would use an even longer lens (say 200mm) and stop down (f11 to f16). Telephoto lenses compress perspective and from a farther distance, you should be able to get the animal's head entirely in focus and fill the frame with the telephoto lens. Instead of focusing on the eye, which is near the back of the head on snouted animals, focus on the middle of the snout. Remember, you have more DoF behind the point of focus than in front (in general, 1/3 in front, 2/3 or more behind).

With shorter focal length lenses, you have much more DoF, but you have to get closer to fill the frame with such a subject.
08-03-2016, 09:27 PM - 1 Like   #4
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Have a look at the DoF calculator on this site It will help demonstrate the principles involved.

Online Depth of Field Calculator

08-03-2016, 11:25 PM   #5
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I was shooting shipping at 300 mm f10 when this fella landed nearby so I swung round and shot with that. The DOF for f10 was a surprise at the time but as mentioned, the DOF calculator tells the story.
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08-04-2016, 07:55 AM   #6
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Yes, depth of field is one of those things that disappears quickly when magnification goes up - either by using a longer lens, getting closer - or by making a larger print. What looks sharp and in focus in a small image, can look a lot more fuzzy when blown up big.

I often hear beginners ask odd questions about depth of field - sometimes asking if there's a lens that will give them more depth of field for their macro photography. For instance, I've seen it asked if using a macro lens, extension tubes, or close up attachments will yield the most depth of field. Of course, at the same magnification, they should all be the same (image quality may be another issue).

But the telephoto issue is the big shocker, as the OP discovered. While we got used to big differences in depth of field when stopping down our normal or wide lenses from f2.8 to f16 - that difference isn't nearly as big when shooting telephoto. If you're doing bird photography, that bird has to be the point of sharpest focus (if not its eyes). Even stopped down to f10, you don't have an extra meter or two of depth of field to fudge the focus.
08-04-2016, 09:26 AM   #7
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Last autumn I was trying to get images of Lasioglossum bees (4mm, some smaller) on goldenrod. The 100mm lens wouldn't let me get a good DOF. Any tiny movement would render the image useless. I switched to the 28mm macro, stopped down to the same aperture (probably 13) and got good images even though I had to crop all the way. You can know the theory but until you really try it yourself it's hard to internalize.
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