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My husband wishes that I would "unload" all of my photography stuff.
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Ian, actually, what you describe agrees surprisingly well with what I said.

Obviously my factors are going to work better when the formats are closer together and the two film speeds that you are comparing are in the middle ISO range, say 100 to 800 or so.

Moreover, as I said in the blog, "a linear relationship .. will certainly fail at ISO extremes." APX 25 is an ISO extreme... what 4x5" 400 speed APX film can we even compare it to, fairly?? So we wind up comparing it to hp5+, tmax, delta 400, etc. Then it's all apples and oranges.

Anyway, that said, let's see just how "way off mark" my estimates are. Atcually I don't think it's so bad as you imply:

APX25 ->APX100 = 2 stop increase
6x9 -> 4x5 = 1 format jump
so my simple theory is off by maybe 1 stop? Pretty good, no?

As for 400 speed 5x4 being well ahead of any 35mm film, sure but again I don't think I am that far off at all, considering the size of the jump. The ratio of the area of 5x4 and 35mm films is roughly fifteen. That is huge. So that implies something like 4-stop difference on the ISO scale, i.e. ISO 400 4x5 = approximately ISO 25 in 35mm format. Again that is placing the 35mm film right on the ragged edge of what is technically possible. Realistically, to get the very best out of the ISO 25 films in 35mm format requires some special development. So, some nonlinearity doesn't surprise me at all.

Anyway.. like I said.. simple theory based on one simple assertion about amplification of noise, just to give some ballpark ideas! The idea was to give people an idea of what a format jump really does for them, in terms of detail per grain.
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I think your factors are way off mark. From experience APX25 in a 6x9 back was equivalent to 5x4 APX100, and 400 ISO 5x4 is ahead of any 35mm film, even of 25 ISO.

Ian
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Congratulations, Scott. Can't wait to see the picts!
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When is opening night for you guys, Scott?
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I actually have a Canonet QL17, but the light seals are screwed up at the moment. Gotta get around to fixing those so I may reenter rangefinder land.
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Ash, Sidearm, do not pine for for Swedish perfection. Take one week's lunch money down to the camera store and buy a Canonet QL17 for about \$25. Yes, it was made 40 years ago, but there are millions out there, and most of them still work. You will have a pro-quality lens in a fast, practical camera body. Not as wide as a 60 on 6x6, of course, but wide enough to feel wide if you use it thoughtfully. And, competitive with any single camera-lens combination I can think of .... don't let lens lust destroy your young life, Sidearm! Go and Shoot!
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Thats a pretty nice selection. I must admit I can hardly pass up buying a used photo related book. I must have over a hundred by now. I always seem to learn a little from each one.
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Yeah, an XG-M is so easy to sneak through the checking account police as long as I don't get stupid G.A.S. happy and get four at a time.
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Well done Lori!

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