Macro photography with the GX680
Tony Bamford
the 125mm lens I got with the "680 kit", my 80mm extender rails and
the wide/long bellows, I could get within about 4 inches of the
blooms. This gave me roughly (I guess) 1:1 on the neg - though the
thought of waving the flowers around the negs to compare sizes isn't
really appealing.
I noticed that my 65mm lens allows me to get about 1 inch away, but
the image *looked* the same size. I do have a 500mm lens, but didn't
even think of using that, as the closest focusing distance is
substantial.
My question is this: Is there some law of optics operating here that
keeps the image size roughly constant. So, if I bought a 250mm lens,
would my lens-to-subject distance double, keeping the image size the
same as with my 125mm lens?
Foto28
I've been doing a lot of flower macro work with my 680 lately. I generally use
the 100mm lens, since (along with the 80mm extension rails) it will give the
largest magnification that I've found to be usable. In testing the 65mm and
50mm lenses, working distance is so minimal that there isn't room to light the
flowers (i.e. studio setup using a softbox). I don't have the 80mm, but perhaps
it would be a fair compromise. With the 100mm and 80mm rails, I can get 1.38:1;
if I add a Canon 500D screw-in "filter style" macro diopter, a bit larger.
Per your question, it's not as simple as double focal length = double working
distance, since you're limited by bellows extension to a certain maximum
magnification that differs from lens to lens. Fuji's 680 brochure lists maximum
magnification possible with each lens, as well as associated lens-to-film
distances (but unfortunately not the much more useful working distance in front
of the lens).
===============
Danny Burk
www.dannyburk.com
John Yeo
The magnification would be: (i/f) -1, where "i" is the distance from the
lens to the film, and "f" is the focal length of the lens. I just worked
this formula out quickly, but i'm pretty sure it is correct. See how I
arrieved at this formula at http://www.enteric.org/optics/magnification.jpg.
Shorter focal lengths should yield larger magnifications, which has been my
experience with a 4x5 camera.
John
--
http://www.enteric.org/
"Tony Bamford" <tony_franc...@hotmail.com> wrote in message
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Denny
larger magnification, is that the shorter lens must be closer to the
object for any given magnification compared to a longer lens... The
limit is reached when the front glass of the short lens is touching
the object... At that point you have no alternative to a longer lens..
Denny
"John Yeo" <jon...@thegrid.net> wrote in message news:<a33w8.19301$3z3.1...@newsread1.prod.itd.earthlink.net>...
Bill Siler
focal length, and M = magnification. Thus for a 250mm lens to get 1:1
reproduction (M = 1), we must have v = 250(1 + 1) = 500mm. Note that at
infinity focus, M = 0 and v = F = 250mm. Another way to look at this is that
for any lens, to get 1:1 reproduction, the lens extension beyond infinity
focus must be = to the focal length, for 2:1 v = 2F, for 3:1, v =3F, etc.
Bill
"Tony Bamford" <tony_franc...@hotmail.com> wrote in message
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Tony Bamford
Thanks for your replies. Using a shorter focal length lens seemed
counter intuative, but I can see from the maths why this is so. I
guess I can't use this as the primary justification for buying a 250mm
lens ;-(
On a vaguely similar note, I remember from my 35mm days being told the
"ideal" portrait lens was around 135mm, as anything less tended to
introduce noticable distortions characteristic of wide angle lenses
(even though I wouldn't tend to think of anything less than 135mm as
"wide angle").
My guess is that even though I've jumped from 35mm to 6x8cm, I still
can't ignore this rule. Thus I will need something around 2.5 times a
"standard" lens, i.e. around 300mm in the case of the GX680.
Tony.
David Glos
Sorry, can't pass by that snippet of misinformation. ;-) Apart from
particular optical anomalies, a wide angle lens does not produce more
distortion than any other optic. Using a wide angle lens to record full
frame face shots, will result in an unusual perspective, although the
recorded perspective would be identical to that received by your optical
nerves if the subject was viewed at the same distance. Recorded perspective
is ONLY related to the camera to subject distance, and NOT the focal length
of the lens.
Hope that helps,
David Glos