this is for people who know how to use the 4by 5 camera?

Question

how do you calculate the magnification of the subject and how do you work out the exposure?

Answer 1

In terms of how to work out an exposure I am assuming that as a 4x5 user, you know the basics as to how to use a handheld incident light meter, or for that matter a reflective light meter to get an exposure. What it sounds like you are asking is a tricky things called exposure compensation which is typically calculated when either your lens or say your bellows are outside the standard measurements i.e, the standard focal length on a 4x5 is 150mm. However if this is not the case restate your question and I can tell you what you need to know. Also if you don't want to deal with math, I would suggest purchasing a polaroid back for your camera from KEH.com, at least it will give you immediate feedback as to your exposure, under or over.

Regaring exposure compenstion,in theory you need some exposure compensation when focused at *any* distance other than infinity, with *any* lens, but the amount of compensation needed is so slight at "normal" distances that it can be effectively ignored. How much compensation do you need? Well, that depends strictly on the ratio of the iris->film plane distance to the focal length:
effective aperture = (f-stop set on lens)*(F+L)/F, where F is the focal length of the lens, and L is the additional extension required to focus at the "non-infinite" distance you're working at. How does this relate to magnification? Well, magnification is given by the following
formula:

M = L/F

Since (F+L)/F = F/F + L/F = 1+M, the effective aperture can also be given
by:
effective aperture = (f-stop set on lens) * (1+M)

What does this mean in real life? Well, if you're shooting at a 1:1
reproduction ratio, then:

M = 1 = L/F, so L=F.

Your effective aperture (lets call this "A") is related to your indicated
aperture (let's call this "a") in this way:

A = a * (1+M) = a*2

So, if your indicated aperture is f/8, your *effective* aperture is f/16
and you need to apply 2 stops of compensation.

At half life-size, M = 1/2, so

A = a * 1.5,

So your f/8 indicated aperture is effectively f/12 and your compensation
is slightly more than a stop.

At M = 1/4.5 = 0.222, which is the closest focus for the 120,

A = a*1.222,

so your indicated f/8 is an effective f/9.778, and your exposure compensation
is a hair less than a half-stop (.4938, if you're terminally picky).

At infinity, your required compensation is always 0, since the effective and indicated apertures are identical. That's how all these compensation charts are calculated.

Answer 2

the mega pixels simply rely on how giant you desire to make it whilst you print it. in case your in need of a giant percent his is bigger. if u going for who has the bigger cam you simply desire to seem at percent satisfactory. they may be able to each be well satisfactory, however whilst you ship the one million.three in a textual content the probabilities are that if u ship it to any individual with a greater MP that it'll exhibit up small. so the five MP cam is prolly bigger.