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How many stops are between ISO400 and ISO50

G

Guest

I need a little help, and time is of the essence. Essentially I’m trying to cheat.

I’m asking if anyone would be kind enough to point me in the right direction of information about, or could even downright tell me, how many stops are between ISO400 and ISO50? I'm kinda needing to know in order to purchase the proper neutral density filter....

Backstory:
I suspect the fog will be heavy over the local snow covered water fall this weekend judging by the weather reports, and I wish to take some B&W pics. There’s only one custom photographer in this one horse town I live in, any competition is down the road aways towards the metropolis, and his rates are exorbitant. I heard tell of a special Kodak T400CN B&W C-41 process film, like what I could get developed at a little family run minilab I love to support, so I bought me some. Now I need to use it, and here’s my problem- I need to use a long exposure time, like several seconds to blur the quite rapidly moving waterfall, and this film is 400 speed. I looked online, (you know, SFTW?) and the links I found didn’t get me very far. I used ISO200 last weekend when the falls were iced over, and found that film speed to be WAY too fast. When I forced the ISO speed just to meter, I found that ISO50 was just right, and I’m expecting very similar weather conditions this weekend.

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" target="_blank">JC</a>
 
G

Guest

It's 1/3 of a stop. A full stop would be 400 to 800; the intermediate v= alues are 500 and 640. Hardly worth a compensating filter. And if your camera h= as through-the-lens metering, it will automatically compensate for the filte= r's presence. But you'll still need an ND filter if the day is sunny, and just possibl= y in an overcast, so you can get the long exposure time. You might also try a Pol= aroid filter, which is usually good for 1-1/2 to 2 stops. It's neutral, but wil= l have other effects (which I can't predict in your situation); you might or mig= ht not like them, but it would be interesting to try, Also, be sure to bracket your exposures -- but only upward. Meters will = try to average the measured area out to 18% gray, and you want the snow to be wh= ite, I presume. With my Dimage 7i, I give snow +0.7 to +1.3 stops. Lastly, remember to shoot your distant shots first, and then move in for=

close-ups. That ensures that any footprints you leave in the snow when y= ou move close in won't show up when you're shooting from afar.

Ivan Berger oldmaven@comcast.net
 
G

Guest

ISO 050 to ISO 100 is 1 stop, ISO 100 to ISO 200 is another stop and ISO 200 to ISO 400 is another stop. I count 3 stops.
 
G

Guest

Thanks folks, I appreciate the info. I thought 1/3 of a stop sounded goofy... but my GF, who worked for a custom photographer for a dozen years (and whose old studio Maxxum 9000 she owns and I use) told her it was a half stop between film speeds, and it'd be a stop and a half what I'm looking for.

I'm a bit of a newbie here, and I'm sorry for my first post to be a hurry hurry question, usually I like to establish a presence on a board, but this place looks pretty new. Thanks again!
 
G

Guest

A stop and 1/2 up from ISO 050 would be ISO 150. Some camera's won't support odd ISO's like that, so you may have to goto ISO 100 and open up another 1/2 stop on your apeture or shutter speed.

Enjoy!
 
G

Guest

JCD, at the risk of confusing you still further, the accepted ISO standard for describing film sensitivity (speed) *does* increment in 1/3 stops, like this:

6 8 10 12 16 20 25 32 40 50 64 80 100 125 160 200 250 320 400 500 640 . . .

and so forth. As you can see, the measurement doubles itself with 'every third' number in the series. The other widely accepted standard, 'DIN', also increments in 1/3 stops, but uses a logarithmic scale. Since DIN is more commonly employed outside the USA/Canada, perhaps I should defer to one of our European members to elaborate about its logic and derivation. ;-)
 
G

Guest

Wow, I really like it here. I’ve been following another photography bulletin board, and ya’ll folks here are pretty nice. Ivan, Garry, and Alywn- thanks for your solid technical advice. What I meant by “1/3 stop sounded goofy†was to say in my particular application it didn’t jive with what I knew.

And, for the record, I went out this evening and bought a Kodak technical reference book, chock full of charts, reference, and calculator wheels.

I hope I don’t get blasted too hard for this, but I wanted to share the fun! I've coded a coupla JavaScript quizzes, they’re great fun methinks.
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Thanks again!
 
G

Guest

It sounded goofy because it was -- I'd misread the original question, so = of course my answer made no sense.
 
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