Wrong ISO speed for film, what should I do?

[WINDY.]

Hi there,
I've been shooting a lot of film recently these days. Currently using an AE1, most of the situation I shoot requires a film speed of ISO 400. I've set the ASA speed of the camera to 400 and for the first time I loaded a portra 100 daylight film. Had about 20shots so far, to realise that I've been metering at ISO400...

Will my photos all be underexposed because of this? I don't know what I should do now after realising this mistake. Should I change to ISO100 on my camera then continue shooting? I've been shooting slides so I don't know is it possible to be able to recover my exposure?

I had a lot of keepers at least and hope to be able to have them usable, any help here?

[krb]

You could finish the roll at ISO 400 and have the lab push them 2 stops, but I have no idea how they would turn out.

[D Thompson]

Originally Posted by krb

You could finish the roll at ISO 400 and have the lab push them 2 stops,

+1. I wouldn't change the ISO for this roll, just make sure the lab knows so they can process.

[Lizzy7]

Hi Windy,

I'd probably remove the film now (or carry on shooting at 400 if it's not really important stuff) and take it to the lab and let them know.

I was a bit confused, you said you were shooting portra but then you mentioned slides? Portra is a neg film and goes through C41 process. C41 pushes ok although I think we could only push one stop on the machine we had

[Photon Phil]

Well I'd hoped you'd rated 400 as 100 because the headroom is tremendous. But I think you will get something you can work with the scans from, even underexposed. Just correct your settings on cam now and keep shooting.

[sandpiper]

Originally Posted by Photon Phil

Just correct your settings on cam now and keep shooting.

Not a good idea.

Keep shooting at 400 until you finish the roll and just have it push processed as others have mentioned. Back in the days before we had 6400 ISO to play with, we would often set the exposure a stop or two underxposed for the whole roll, then pushprocess to correct it.

I certainly wouldn't recommend changing the ISO now as then you can't correct for the error

[sapearl]

Hi Windy, sorry to hear about your misfortune - that can be very frustrating.

Basically, having shot your Portra 100 film at an ASA of 400 means they will be 2-stops underexposed. A number of your shots will certainly be underexposed, but you may be pleasantly surprised by some of the results since you are shooting slide film, if you have them processed in the conventional manner.

One alternative is that you could continue to shoot everything at 400 on that roll and then tell the lab to "push process" it, explaining what you did, and that may save some of the images. Or you could just change to 400, continue to shoot at the corrected ASA, and hope for the best. Do you have plans to scan any of these slides, or were you going to project them in the (old) conventional manner? - Stu

[Wilt]

Portra 100...a color negative film, I believe. Color neg has long enjoyed a very wide latitude of exposure, acceptable results from -2EV to +3EV. Underexposure will result in somewhat muddy, less saturated shadow tones, but otherwise the prints will be pretty acceptable, without resorting to push processing. If underexposed to a greater degree than -2EV, I'd follow the recommendation for push processing.