If I rate Portra 160 at 100, what ISO do I tell my lightmeter I'm using?

[b_covey]

I recently read on www.lightingmagic.com that in a studio setting one

should rate Portra 160 at 80 or 100. Fine, but when I set my ISO on

my lightmeter what ISO do I use?

[q.g._de_bakker]

If you're rating it at ISO 100, you should set your lightmeter to ISO 100 as well.

Then have it processed normally, i.e. don't, whatever you do, ask to have it pulled.

 

I do habitually expose Portra 160 as ISO 100 myself, and like the results better than when rated at 160. But it is perhaps a matter of taste.

[wayne_crider4]

The ISO that you want to shoot it at. Make sure that if your shooting at a different ISO you don't go and over or underexpose additionally on top of your setting when developing normally. You may wind up with problems in frames at developing time. I normally shoot at the rated ISO, and vary my exposure thru compensation per shot on print film WHEN it's being processed normally. In this way I can somewhat test the film. When pushing or pulling an entire roll it's a different matter.

[edsel_adams]

Setting your meter to 100 is correct.You could also take a meter reading,add 1 stop each time you shoot a frame.This would equal exposing at ISO 80.Really what you are doing is assuring some detail(negative density)in your shadow areas.Your meter wants to average the world to mid toned grey.You are telling it that grey is a bit darker by over exposing.The beauty here with Portra is that you cannot overexpose this film!You can burn out the highlights,assuring dense shadows and make excellant prints.

[ellis_vener_photography]

Wait! you are believing something you read on the

<I>internet</I>?<P>

here is the problem with that: you aren't that photographer, you

aren't using his/her equipment, and you aren't having the same

lab process your filma nd make your prints.<P>What you need to

Do is do some testing with your own equipment. Start with your

meter set at at ISO 160 and then do a bracket of exposures, at

1/3rd of a stop increments changing only the f-stop and nothing

else -- not the shutter speed, not the lens (or focal length setting

ifusing a zoom lens), notthe position of the lighting-- , and do this

over a two stop range in both directions if your camera and meter

will allow you to adjust your aperture in 1/3rd stop increments. If

not 1/3rd incrementsthen do it in 1/2 stop increments. Have your

film processed normally. <P>If the image that looks best is with

the lens set 1/3rd of a stop more open than what the meter (set

to ISO 160) indicated then set your meter to ISO 125; if 2/3rds of

a stop more open, then set your meter to ISO 100. <P>Now

here is the important part: Your film, even if you are now rating

the film at a different speed rating, should still be procesed

normally.

[ellis_vener_photography]

Wait! you are believing something you read on the

<I>internet</I>?<P>

Here is the problem with that: You aren't that photographer, you

aren't using his or her equipment, and you aren't having the

same lab process your film and make your prints that they

are.<P>What you need to do is do some testing with your own

equipment. Start with your meter set at at ISO 160 and then do a

bracket of exposures, at 1/3rd of a stop increments changing

only the f-stop and nothing else -- not the shutter speed, not the

lens (or focal length setting ifusing a zoom lens), notthe position

of the lighting-- , and do this over a two stop range in both

directions if your camera and meter will allow you to adjust your

aperture in 1/3rd stop increments. If not 1/3rd incrementsthen do

it in 1/2 stop increments. Have your film processed normally.

<P>If the image that looks best is with the lens set 1/3rd of a

stop more open than what the meter (set to ISO 160) indicated

then set your meter to ISO 125; if 2/3rds of a stop more open,

then set your meter to ISO 100. <P>Now here is the important

part: Your film, even if you are now rating the film at a different

speed rating, should still be procesed normally.

[mark_hubbard]

If you are interested in a more detailed explanation and step-by-step guidance on what Mr. Vener is suggesting, I recommend the book "John Shaw's Close-Ups in Nature," which is available from Amazon.com for $15.75. Ostensibly a book only about macro photography, Mr. Shaw shares an amazing amount of information useful to all photographers, including how and why to test your equipment and meters to insure that you are getting the exposure that is right for you.

 

If you choose to buy the book, I should warn you that it will likely fall apart within a few days or weeks at most, as the glue-back binding is as poor as I have seen. However, even as a loose-leaf book (or you could keep it in a binder) it is a treasure worth having.

 

That said, and while Ellis is correct, you are always free to dive right in and try rating your film any way you like. When I was much younger, I simply could not afford to do film tests, so rating VPS at 125 was just something I tried, liked the results, and stuck with it as long as I owned that old Rollei.

 

If you follow Ellis' advice or read the John Shaw book, you will learn a great deal about photography that 99% of camera owners simply do not know.

 

Best wishes,

 

Mark

[kevin_kolosky]

I could not agree with Ellis more. For example, what if that person on the internet had a camera that for some strange reason had faster than marked shutter speeds, or that had a meter that was off a stop, or if his/her lab did things differently than yours does. It is okay to ask for suggestions, but you need to test becasue EVERYTHING AFFECTS EVERYTHING in photography. I also agree with the statement that it is hard to overexpose color negative film. If it is overexposed even up to 3 stops you can usually get a decent print. But it is also very intollerant to underexposure, which is why alot of people rate it slower than the published ISO. I HAVE FOUND Portra 160 to be an ISO 160 film for my situation when exposed to sunlight and to strobe lights. However, when you get in a shady situation where the color spectrum loses some red light, you will find that color neg films lose alot of speed. I find that in very shady situations an ISO of 80 works well. BUT AGAIN, you should test that out on your equipment with your lab.

 

Kevin

[q.g._de_bakker]

About believing things people say on the Internet...

Wait! Are you saying, on the Internet, that one shouldn't believe what people are saying on the Internet?!

 

Rating Portra at ISO 100 is more than just a matter of people's individual preference. It is so commonly done (at least, as far as i can find out)that it must have something to do with the film itself too.

Perhaps it is simply *is* really a ISO 100 film, just like its predecessor, GPX?

But of course, we should all try and see how we like a particular film best ourselves.

[roger_michel]

i certainly second the empirical approach. what works is what works in practice, not in theory. having said that, there is no question that iso (i miss asa almost as much as aluminum film cans) ratings for some films is not accurate. for example, if you shoot a frame of the same scene with the same camera under the same lighting conditions with tri-X and hp5+, rating both at 400, you will get more shadow detail with the ilford film. tri-x is not really a 400 speed film (although it is my favorite film). you have to expose it at about 300 to get the same detail as most 400 speed mono films. my only point is that, sure you should do your own experiments to determine what speed rating/development regime works best for you. however, it is also important to understand that nominal iso ratings are just a starting point, and often are unreliable.

[richard_freedman1]

I overexpose all neg films, but know folks who don't and get fine results. Maybe because I shoot people, and skintones look better slightly overexposed. Anyway, here's my formula: I shoot a lot of Portra NC160 as well as Fuji NPC, also 160 ISO. I always shoot Polaroid, and when shooting these two neg films, I first shoot an instant shot on Fuji FP-100C instant film, metered @80 ISO. If I like the test shot, I shoot the film at the same exposure. Yes, I realise Polaroids are affected by the temperature, I just rub it when it's cold. Man, I love the latitude of neg films!