[miro]

[quote name='Lomskij' timestamp='1301136339' post='7102']

Hold on, the DOF difference between FF and 1.5x crop is exactly 1.5x, or at least online DOF calculators show that. One aperture stop is 1.4, which affects DOF exactly in the same way - 1.4x. So 1.5 crop is slower by 1.5/1.4 = 1.07 stop, not a huge difference.



For nitpickers - I know that Nikon's crop is nearly 1.52x, however one aperture stop (sqrt 2) is not exactly 1.4 either <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/cool.gif' class='bbc_emoticon' alt='B)' />

[/quote]





Well,

I don't agree with your calculation.

The DOF function on Squire of Distance

While Aperture affect DOF linearly.

Mathemathical writen is



DOF = f(D^2, A)



while

D - distance to subject

A - apeture number



for example if you shoot subject from 5 meters and you have DOF 1m.

If you shoot the same subject from 10m at the same focal length and aperture you will have DOF 4m.







For simplicity I assume that we work with fixed focal length lens.



What does it mean?



It remembers me one of my first photographic lessons. The master explain us how to change the DOF.

If you want shallow DOF

- first you have to go as close as possible to the subject.

- secondary you have to choose the appropriate aperture.



As technical aware person I ask the teacher about how DOF is affected by camera formats.

He answer - well the larger the format the shallower the DOF you acheve, BUT you have to remember first you have to be as close as possible.



That is the answer of artist. Later on I found the mathematical equation and I understood what did he said.



greetings,

miro