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Photography Q&A
Help me understand DOF a little better
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<blockquote data-quote="Bob Blaylock" data-source="post: 501540" data-attributes="member: 16749"><p>Who's that on the bed, then?</p><p></p><p></p><p></p><p></p><p> Let's see if I understand correctly, as much as you've said so far…</p><p></p><p> The brassiere, hanging on the doorknob, you want in sharp focus; the bed and the woman thereon, you want out-of-focus. You used a 17-50mm ƒ/2.8 zoom lens to take the picture shown here, and the bed/woman is in much sharper focus than you want.</p><p></p><p> Am I right, so far?</p><p></p><p> Much is missing. You mention having taken pictures at 17mm and at 50mm, but have not indicated at which focal length the picture you've shown was taken. I assume this picture represents, more or less, the field of view that you want.</p><p></p><p> If you get a view that is acceptable with the lens zoomed at 50mm, then your 50mm ƒ/1.8 prime should give about that same field of view, and allow you a wider aperture, with less depth of field. If the 50mm is too narrow, then perhaps your 35mm will be fine.</p><p></p><p> You also did not say what camera you're using, or what settings you're using on the camera.</p><p></p><p> For future reference, if you upload a picture that is larger than 1000 pixels on the longest side, this site will scale it down to 1000 pixels,and in so doing, will strip all the EXIF data therefrom. Upload a picture that is 1000 pixels or smaller, and the site will keep it unmolested, EXIF data and all. The EXIF data can help the rest of us to see what settings you used, and to better help you.</p><p></p><p> In general… <ul> <li data-xf-list-type="ul">The longer the focal length, the narrower the depth of field.</li> <li data-xf-list-type="ul">The wider the aperture (the smaller the ƒ/ number) the narrower the depth of field.</li> <li data-xf-list-type="ul">The closer the point of focus, the narrower the depth of field.</li> </ul><p></p><p></p><p> First of all, it seems we need to make sure that whatever lens you're using, that you start with it at its widest aperture. Whatever your camera is, however it it takes settings, you should probably set it on aperture-priority exposure, if not full manual; and make sure it's set to the largest aperture setting available. You'll want to make sure that the camera is focusing on the bra, not on the bed/woman. If possible, moving the camera closer to the bra will also help to put the more distant subjects more out of focus, as long as the focus remains on the bra; even if that means going to a shorter focal length (which increases depth of field) you'll still narrow the depth of field by focusing closer, and the distant bed/woman will be farther out of the focus range.</p><p></p><p> In the example picture that you posted, it appears to me that the lens is stopped down significantly from its maximum aperture, and it looks like the camera was focused somewhere farther forward than the bra. The woman on the bed looks like she is in sharper focus than is the bra.</p></blockquote><p></p>
[QUOTE="Bob Blaylock, post: 501540, member: 16749"] Who's that on the bed, then? Let's see if I understand correctly, as much as you've said so far… The brassiere, hanging on the doorknob, you want in sharp focus; the bed and the woman thereon, you want out-of-focus. You used a 17-50mm ƒ/2.8 zoom lens to take the picture shown here, and the bed/woman is in much sharper focus than you want. Am I right, so far? Much is missing. You mention having taken pictures at 17mm and at 50mm, but have not indicated at which focal length the picture you've shown was taken. I assume this picture represents, more or less, the field of view that you want. If you get a view that is acceptable with the lens zoomed at 50mm, then your 50mm ƒ/1.8 prime should give about that same field of view, and allow you a wider aperture, with less depth of field. If the 50mm is too narrow, then perhaps your 35mm will be fine. You also did not say what camera you're using, or what settings you're using on the camera. For future reference, if you upload a picture that is larger than 1000 pixels on the longest side, this site will scale it down to 1000 pixels,and in so doing, will strip all the EXIF data therefrom. Upload a picture that is 1000 pixels or smaller, and the site will keep it unmolested, EXIF data and all. The EXIF data can help the rest of us to see what settings you used, and to better help you. In general…[list] [*]The longer the focal length, the narrower the depth of field. [*]The wider the aperture (the smaller the ƒ/ number) the narrower the depth of field. [*]The closer the point of focus, the narrower the depth of field.[/list] First of all, it seems we need to make sure that whatever lens you're using, that you start with it at its widest aperture. Whatever your camera is, however it it takes settings, you should probably set it on aperture-priority exposure, if not full manual; and make sure it's set to the largest aperture setting available. You'll want to make sure that the camera is focusing on the bra, not on the bed/woman. If possible, moving the camera closer to the bra will also help to put the more distant subjects more out of focus, as long as the focus remains on the bra; even if that means going to a shorter focal length (which increases depth of field) you'll still narrow the depth of field by focusing closer, and the distant bed/woman will be farther out of the focus range. In the example picture that you posted, it appears to me that the lens is stopped down significantly from its maximum aperture, and it looks like the camera was focused somewhere farther forward than the bra. The woman on the bed looks like she is in sharper focus than is the bra. [/QUOTE]
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