8x10 questions

[rbarker]

The area comparison is interesting with respect to grain, but doesn't that assume that the person will be holding the 40"x50" at the same 14" (let's say) viewing distance?

 

[David A. Goldfarb]

It's conventional to refer to an 8x10" print from a 4x5" neg as a 2x enlargement. That's just common usage in photography. If you go into a lab with a 4x5" neg and for some odd reason request a 4x enlargement (though every lab I've used asks for the print size, to avoid this confusion), you'll get a 16x20" print, not an 8x10".

It's similarly common usage in photography to refer to an image of an object that is, say 2 inches wide but appears 4 inches wide on the negative as a magnification of 2x or 2:1. The formula for bellows factor using magnification (as opposed to the formula that determines bellows factor from focal length and subject distance or from focal length and bellows extension) is--

exposure compensation required = (1 + magnification)^2

And this value for "magnification" in photographic textbooks is always going to be in terms of linear magnification, as are the values in photographic tables for exposure compensation for macrophotography. (So for a magnification of 2x, exposure compensation required is 9x or 3-1/3 stops).

Yes, obviously the relation between magnification and exposure is not linear, but in the context of photography, the value for magnification by convention is always expressed in linear terms, and the inverse square relation is built into the formula.

 

[isaacc7]

The area comparison is interesting with respect to grain, but doesn't that assume that the person will be holding the 40"x50" at the same 14" (let's say) viewing distance?

Yes it does. That's why I mentioned he should think about how far away his viewers will be and how much grain he wants them to see at that distance. Most people are self regulating when it comes to viewing distance, they'll stand at whatever distance the picture looks best to them. It is a lot of fun though to be able to get right up on top of the thing and still have it look good. I'm sure we're all familiar with how that goes with our 16x20 and 20x24 prints, it'd sure be cool to do that with a 40x50 print too Or is that too large format geeky?


Isaac

 

[Paul Ozzello]

Thanks everyone for the very helpful information. I'm going to do some preliminary tests using MF and determine what focal length(s) I'll need. If I don't have enough DOF, I'll probably resort to 4x5. I live in Montreal; the one shop that rents 8 x 10 equipement has one camera, but it's out of commission: the ground glass is busted and they can't get a replacement.


Paul

 

[isaacc7]

It's conventional to refer to an 8x10" print from a 4x5" neg as a 2x enlargement. That's just common usage in photography. If you go into a lab with a 4x5" neg and for some odd reason request a 4x enlargement (though every lab I've used asks for the print size, to avoid this confusion), you'll get a 16x20" print, not an 8x10".

Huh, I've been working in labs (from the mundane to the rather esoteric) for over 10 years and have never heard of anyone ask for this, but I'll come back to the reason why...

similarly common usage in photography to refer to an image of an object that is, say 2 inches wide but appears 4 inches wide on the negative as a magnification of 2x or 2:1. The formula for bellows factor using magnification (as opposed to the formula that determines bellows factor from focal length and subject distance or from focal length and bellows extension) is--

SNIP
Here's where I think we were talking past each other. Linear multiplication is the way to figure out subject sizes. If you have a head on a 4x5 negative that is 3" across and you want to know what size print you need to make that head 30" across, then the linear multiplication of 10 will give you the right answer, a 40x50 inch print. However, if you want to know what that print will *look* like as far as grain, focus errors, lens problems, and anything else that you'll see better at higher magnifications, you need to square the linear result to get the actual enlargement factor of the negative, which is a 100 times in this case. The reason that I brought this up is that the poster was wondering if this could be done with a 4x5 negative and another poster responded that it's only a 10x enlargement, so it should work. The question of which format to use for a desired print size isn't one about subject magnification, it's about negative enlargement. The danger is that the original poster could look at a 4x5 neg with an 8x loupe and say to himself "That looks pretty damn good, this'll have no trouble holding together at 10x" and then be more than a little disappointed in the final result at 40x50.

, obviously the relation between magnification and exposure is not linear, but in the context of photography, the value for magnification by convention is always expressed in linear terms, and the inverse square relation is built into the formula.

The value of subject magnification is always expressed linearly, as it should be. But in order to figure out what format to use for a given viewing distance, you'll need to square that linear result to get an idea of magnification effects. As a long time lab flunkie and lab order taker, I try to head off problems BEFORE things get printed I'm sure David is familiar with these issues, but I want to make sure everyone else knows how to calculate grain differences for a given viewing distance and to pick the appropriate format for whatever they want to do.

Isaac

 

[rbarker]

Not to belabor the point, but I think my comparison of an 11x14 from a 35mm neg being approximately equivalent to a 40x50 print from a 4x5 negative still works in either context (linear or area), and may be easier for the average person to grasp.