Jason,
I agree about the highjacking of the thread, so if you would like to further pursue this we can start another thread on this subject of photography technical formulaes. I am assuming that this is what your point is regarding:
"Close-up
When the subject distance s approaches the focal length, using the formulae given above can result in significant errors. For close-up work, the hyperfocal distance has little applicability, and it usually is more convenient to express DOF in terms of image magnification. Let m be the magnification; when the subject distance is small in comparison with the hyperfocal distance,
\mathrm {DOF} \approx 2 N c \left ( \frac {m + 1} {m^2} \right ),
so that for a given magnification, DOF is independent of focal length. Stated otherwise, for the same subject magnification, all focal lengths give approximately the same DOF. This statement is true only when the subject distance is small in comparison with the hyperfocal distance, however.
The discussion thus far has assumed a symmetrical lens for which the entrance and exit pupils coincide with the front and rear nodal planes, and for which the pupil magnification (the ratio of exit pupil diameter to that of the entrance pupil)[4] is unity. Although this assumption usually is reasonable for large-format lenses, it often is invalid for medium- and small-format lenses."
Now I'm not a very formula oriented type of guy and I'm sure a lot of people here viewing this thread isn't either. But if you could explain in laymen's terms on how the formula will help in understanding macro photography better, it would be greatly appreciated. At this point, I've figured myself to be a decent photog and actually took 2 years of photography school but frankly you've gotten me quite confused.
From my understanding of photography, and there are many links that I've provided to support my claim, f-stop DOES play an important role in DOF.
Other factors that influence DOF are:
Focal length
Subject distance
Film or Sensor format
Here is another website that explains my theory in laymens terms with photo samples:
http://www.dpreview.com/learn/?/key=depth_of_field
All lenses have the ability to allow you to change its' aperature therefore allowing you to control the amount of light entering the lens. Because of this control, it causes the lens to change its' point of focus due to the adjusted lens elements focusing onto the film or sensor plane. The smaller the aperature ie f/8-f/22 the greater the focus range. The larger the aperature ie f/1.4-f5.6 the shallower the focus range. Please correct me if I am wrong here.
Macro lenses are specialized lenses that are constructed in a way that allows the photographer to get closer and focus closer to an object that most conventional lenses will not let you. True macro lenses also magnify at a ratio of 1:1 meaning that the lens will reproduce the image to full life size as the photographer is seeing it through the lens. Some lenses advertise that they are macro but are only 1:2 meaning that they will focus close but will only magnify half the life size of the object that it is focusing on. Please correct me here if I am wrong.
Wider lenses ie 28mm have greater DOF sometimes up to f/32 however they also have an aperature ring that will allow you to control DOF. Meanwhile telephoto lenses may have shallower DOF but most have minimum of f/16.
You are saying that the higher the magnification the greater the DOF? Is there something else besides a formula that can explain this?
From my experience shooting with a prime Nikon 105 macro f/2.8 and a Nikon macro 80-200 f/2.8, I can tell you that I see a difference in my DOF when I am shooting aperature priority. Do I know the manufactures specifications on how my lens works, No. All I know is that I control light entering my camera so that I can take a photo but manipulating the lens' iris and my cameras' shutter. Because of this manipulation, there are other factors that need to be considered ie DOF, Bokah, Cirlce of Confusion etc...Unless you are striving to become Annie Lebowitz or the next Ansel Adams most amateur photogs just want to know what they can do to take a better photo. A formula with no explanation will not help them IMO.
Photography is best learned through trial and error. Formulas in my opinion does not really help in understanding how the camera and lens work together.
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BMW R47