Right, I understand all of that, but what about the broad statement of larger formats (and longer lenses) having inherently more bellows extension compensation factors? Shouldn't a 150mm lens on 4x5, 300mm lens on 8x10, and a 450mm lens on 11x14, all focused to the same magnification ratio, all have the same FoV and bellows compensation amount?
At the same stop, yeah they should, with error due to those focal lengths not being exactly, perfectly equivalent. In reality, though, if you were to set up the same frame of the same subject with those three cameras and lenses, you would not be using the same magnifications nor the same stops.Originally Posted by Corran
-Chris
Ken and C.D., thanks for those clarifications on the magnification calculations.
Well, yes I suppose given DOF considerations you'd likely be at a smaller stop, and 11x14 isn't the same ratio as 4x5/8x10 (so substitute a 600mm lens on a 16x20 camera for the third camera), but that's not really the point - Would they or would they not have the same "bellows extension factor" when focused on the same object, say, 15 feet in front of them, and would they not also have the same magnification amount?
They would not have the same magnification amount if you wanted the same frame on all three cameras. Remember that we're generally more concerned with making a pleasing picture than getting a particular amount of magnification. Say you're making a picture of a baseball, which is about 3 inches in diameter, and you want to roughly fill the frame with it. The 4x5 will be at about 1:1 magnification to accomplish that. The 8x10 will need double that magnification, or 2:1, to get a 6 inch baseball on film. The 11x14, meanwhile, will need about 1.5 times what the 8x10 needs or something like 3:1 to give you a 9 inch baseball on that big sheet of film. If you want to go with a 16x20, that would need double what the 8x10 needs, so 4:1 magnification to put a 12 inch baseball on film.
-Chris
i was maybe 3-4 feet from my subjects ... maybe 5" tops ( i was shooting 7x11 11x14 might be a little closer )
So thinking about all this... a 600mm on 11x14 placed roughly two meters from the subject gives you a head and shoulders. That actually sounds like the PERFECT focal length. A few more steps back and you'll have waist up. Further back than that and it will start feeling weird. So substitute a 360mm and you will get your full body without getting too far away from the subject.
Just as on 35mm where I use 35mm and 85mm for portraits, and on 4x5 where I use 135mm and 210mm for portraits, it seems 360mm and 600mm are the similar choices on 11x14. So, why would I want a 450mm for portraits? Seems like a 'tween lens for that use?
Ah, now we're getting somewhere. That makes perfect sense. I will have to reflect some on the connection between framing and magnification ratio, and the resulting image vs. film size.
I think my original idea was correct, that any lens at a 1:1 magnification ratio would have a 2-stop compensation, whether a 100mm or 1000mm, but I did not consider the difference in framing for a given format.
Sorry to somewhat derail the thread John.
That's exactly the key. Larger film needs larger magnification ratios. For distant subjects this means longer lenses. For close subjects it can mean very, very long bellows along with long lenses. I thought it odd when Weston wrote in his daybooks about shooting the peppers and having exposures hours long and that sometimes cars going by would ruin the exposure by vibration. Then it dawned on me, those peppers on 8x10 film were somewhere between 1:1 and 2:1. Then you consider slow film, deep stops, and in some cases probably dwindling light at the end of the day.
-Chris
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