J. C. O'Connell:
Focal length differences are the same for macro as for regular shooting: a 100mm is going to give only half the angle of view as a 50mm, but there is one thing you have to keep in mind though and that is the effective focal length DOUBLES by the time you get to 1:1 vs. infinity, so a 50mm at 1:1 gives same angle of view as a 100mm at infinity. The other thing that focal length affects is the working distance. A 100mm lens at 1:1 will give you 400mm from subject to film plane while a 50mm will only give you 200mm from subject to film plane at 1:1.
I'm not sure that I follow you here. How will it affect the picture if I use the 50mm or the 100mm lens? Will I get the same thing but from different distances?
For comparison, the way I do macro shots now is that I have this bellows: http://anders.hultman.nu/kamera/makro-b.jpeg
When I connect a 50mm lens, it gives approx. 1:1 on the stort end and about 3:1 on the long end. It gives me sharp image at 75mm and 50mm from the front lens, respectively.
When I connect a 200mm lens, I have to back out quite long to get sharp images. More than half a meter. With the bellows on the short end and the lens focused the closest possible, the distance from front lens to subject is 600mm. The magnification don't get anywhere near 1:1, though. Rather approx. 1:2.3.
So, my question really is which of the two new Pentax macro lenses I should get if I wanted the largest possible magnification. They're both 1:1 but is it "the same 1:1" so to speak? I'm only used to using the bellows, and with that it really is a difference between a 50mm lens and a longer one.
With the bellows, the magnification setting effectively determines the working distance. The DOF is extremely short, and I have to focus by moving the whole camera back and forth.
anders ------------------------- http://anders.hultman.nu/ med dagens bild och allt!
