Re: [Leica] Re: Re: autofocus macro

[Barney Quinn <barney@ncep.noaa.gov>]

OK guys, I'm going to jump in here. Everyone's sort of right. I have shot hundreds and hundreds
of both macro shots and close ups, usually of flowers, often with a 4x5 view camera. Life-size
is 1:1, meaning that if it's an inch tall in in life it's an inch tall on the film. A 35 mm
negative is what, an inch x an inch and 3/4? Something like that. Flowers come in all sizes, to
be sure, but most are larger than a 35 mm negative. The implication of this is that you're
frequently not using any magnification, and that you're typically working six to ten inches
from the subject. Mark and others are correct. This is technically a close up, not a macro
shot. Lea is right about auto focus under these circumstances. It works quite well. If the AF
doesn't get it the way one wants it is a simple matter to tweak the focus ring. Easier, in
fact, than racking  the lens back and forth over a lot of its range. And, in the case of
flowers in a garden they typically aren't located at your eye level. You're often down in the
dirt, twisting this way and that.

As you photograph smaller and smaller objects at closer and closer distances from the situation
changes. Let's say you are shooting something a half an inch high and you want to have it be an
image an inch tall on the file. This, if I remember properly, is a ratio of 2:1. The more you
magnify the image the more the whole system begins to act as a telephoto lens. Small changes,
vibrations, etc., begin to have more and more of an effect. It's like a lever with a long arm
and a short arm. The longer you make the long arm the more effect the same amount of motion has
on the shorter arm. Here the rest of the group is right. It's a real pain to have to move the
camera because it takes some hassling around to get it back the way you want it. Focusing does
become more critical, and depending on circumstances and equipment you may even be in a
situation wherein your AF doesn't work. Classic example is an extension tube without lens
coupling.

Most of my work is shot on E-6. For me the critical problem isn't focus control. It's exposure
control. The bit of automation which makes close and up macro work much easier for me is
actually built in metering. As you move the lens further and further from the film in order to
get more and more magnification less and less light hits the film. This is right out of physics
101. The TTL metering on a modern SLR takes care of this for you. It measures the light
actually hitting the film. It simply doesn't care how far you have the lens racked out.

If you are using a 4x5 view camera to take close ups or macro shots the situation also changes
quite a bit. For one thing you need more magnification. An inch tall flower shot life-size on a
35 mm negative fills the frame. In a 4x5 negative it's just a little one inch tall blob in the
center of the image. You have to move in closer to get a larger image if you want to fill the
frame. Now you've got a lot less light falling on the film, and you don't have a nice TTL meter
to help you out.

This is where the dreaded bellows factor comes in. It gives you a number which tells you how
much to increase the exposure. I think that there has been as much blood shed on the net over
this topic as almost anything else. Magnification is a function of how far you move the lens
from the film. It has nothing to do with format or file size. How it works is really quite
simple. The focal length of on ordinary lens is just the distance from the film to the lens
when something an "infinity" is in focus. For our purposes that just means a long, long, long
way away. Just to make the math easy let's say that we're using a 100mm lens on a 4x5 view
camera. At "infinity" the lens in 100mm from the film plane. Now, if we move the lens one focal
length more from the film the lens will be 200 mm form the film plane and the image on the film
will be 1:1, meaning life-size. This costs us two stops of exposure. If you use your light
meter to measure the subject and it says 1/100 at f8 you need to shoot at 1/100 at f4, or its
equivalent. Rule of thumb is that every time you advance the lens half a focal length past
infinity you cost your self a stop of exposure. I keep a small ruler in my view camera bag.
With a little practice you can estimate the bellows correction quite easily.

All of this, to me, presents a paradox. For close ups a modern 35 mm automatic camera with AF
works well and sure is easy to use. ( Before you start an argument on this point I invite you
to get down on your belly in a muddy garden with a 4x5 view camera and all the clobber you need
to make it work and shoot a few close ups. ) As you work with smaller and smaller subjects
requiring more and more magnification you quickly get to a point, IMHO, where the tool of
choice is a view camera, and at that point you've got automatic nada.

I think I've got my optical facts here. If I've messed up I invite Erwin or one of the groups
other technical wizzes to put me right less I mis-lead people.

Barney

Mark Rabiner wrote:

> ><Snip>
> > Lea,
> > Macro photography is usually defined as no magnification of the subject
> > (1X) to about 10 X magnification. That is STARTING at 1:1 subject size to
> > size recorded on film, as in a subject 1 inch tall being recorded on film
> > 1 inch tall - actual life size. More magnification than about 10X moves
> > into microphotography.
> >
> > Less than 1:1 is close-up.
> >
> > Welcome to the LUG, where no one escapes without a fight :)
> >
> > Henry
>
> The way i always understood it 1:1 to 1:10 was macro.
> 1:1 to 10:1 and more is micro.
>
> Actually in my own head i defined macro as photography which requires a bellows correction.
> I think this is right at 1:10 requiring a half stop correction. If you are
> shooting something ten inches tall and making it one inch on your you are at
> that point.
> If I'm being vague it's becuae i haven't a clue to what I'm talking about!!
> I think it's all semantics. I think I'm antisemantic!!
>
> Mark Rabiner
>
> Portland, Oregon
> USA
> http://www.rabiner.cncoffice.com/