EXIF and Depth of Field
Posted: Tue Aug 14, 2007 8:02 pm
Recent comments about EXIF (Exchangeable image file format) have got me thinking. I routinely save the original images as downloaded and before any cropping, etc. In this way, the date such as exposure, focal length, etc are preserved (EXIF). However, the merest modification, loses that data. So if you ever want to verify an original as being genuine, the EXIF data must be intact and that means keeping the unaltered basic image as well. I do that now that I have appreciated the situation.
However, it is unusual that a photo (of a butterfly) does not benefit from post processing, often a simple crop.
Now this brings me on to a point that was explained to me by Tim Munsey. I contacted Tim after I had come across his excellent website:
http://www.wildphotolife.co.uk/
and asked him for the benefit of his experience. Tim gave me one piece of absolutely invaluable advice about depth of field and that has transformed my photos. I'll try to explain.
If you completely fill the frame wingtip to wingtip you get a certain depth of field, let's say as an example, that depth of field is 2 centimetres. Now if you zoom out (or move further away) so that wingtip to wingtip only occupies HALF the frame, you get FOUR times the depth of field, ie 8 cms. But of course, your butterfly is half the size of the full frame image, so you probably need to crop.
However, if you want the butterfly the same size as that first full frame image, you will of course lose half that depth of field gain of four times, but even so still finish up with twice the depth of field. This does depend on having enough pixels to be able to tolerate such a crop, but I am perfectly happy to use say 1600 pixels width from my original width of 2800 pixels. (Not quite a gain of double the DoF, but certainly a noticeable gain)
This might sound a little technical and I admit that I don't understand the science behind it. But the point is it works.
So any image that I publish will not have the EXIF information but I do have that available on the original file. Earlier photos are not protected in this way as I simply had not understood the situation, but my later ones are.
Jack
However, it is unusual that a photo (of a butterfly) does not benefit from post processing, often a simple crop.
Now this brings me on to a point that was explained to me by Tim Munsey. I contacted Tim after I had come across his excellent website:
http://www.wildphotolife.co.uk/
and asked him for the benefit of his experience. Tim gave me one piece of absolutely invaluable advice about depth of field and that has transformed my photos. I'll try to explain.
If you completely fill the frame wingtip to wingtip you get a certain depth of field, let's say as an example, that depth of field is 2 centimetres. Now if you zoom out (or move further away) so that wingtip to wingtip only occupies HALF the frame, you get FOUR times the depth of field, ie 8 cms. But of course, your butterfly is half the size of the full frame image, so you probably need to crop.
However, if you want the butterfly the same size as that first full frame image, you will of course lose half that depth of field gain of four times, but even so still finish up with twice the depth of field. This does depend on having enough pixels to be able to tolerate such a crop, but I am perfectly happy to use say 1600 pixels width from my original width of 2800 pixels. (Not quite a gain of double the DoF, but certainly a noticeable gain)
This might sound a little technical and I admit that I don't understand the science behind it. But the point is it works.
So any image that I publish will not have the EXIF information but I do have that available on the original file. Earlier photos are not protected in this way as I simply had not understood the situation, but my later ones are.
Jack
