Basic Question (I feel kinda stupid asking it)

[seamus_kiel]

Hi all,

 

This forum is such a life saver.

 

I'm just trying to get my mind around a certain concept. Here goes:

 

I proof an exposure via polaroid with my 4x5 camera. Meter reading says F 16 @

4seconds. On the proof the image is too light. I shut down to F22 and the exposure looks

good.

 

Now, here's the tricky part for me: In shooting in with the actual film to I continue to shoot

F 22 @ 4 seconds. *Or* because this is a negative as opposed a positive (as the polaroid is)

do I go the *opposite* direction and shoot F 11 @ 4seconds.

 

I'm just a bit corn-fused.

 

Thanks for any explainations that can help this make sense to me :)

[oskar_ojala]

I don't shoot polaroids, but the basic idea is that if the polaroid's sensitivity (ie. ISO) is the same as the film's that you want the final image on (eg. both have an ISO rating of 100), then you expose the film with exactly the same settings as the polaroid.

[jbq]

Use the same exposure on film as you do on polaroid.

[carl smith]

You need to expose the polaroid correctly to know what the overall exposure should be for your film. If your polaroid is ISO 100 and you get f22 for 4 seconds, then you can adjust exposure for whatever speed color negative or slide film you want to.

 

It doesn't matter if you use negative or positive film, they all have a rated speed they need to be used at. Assuming you are shooting ISO 100 film then use the same exposure as the polaroid. If your film is a different ISO you'd need to adjust. For example, based on the f22@4 seconds on ISO 100, if you were shooting ISO 50 film for your final shot, you could do f22@ 8 seconds, or f16 at 4 seconds.

[robert_cardon]

Myabe I'm wrong, but I always thought polaroid development was a function of time and temperature; good or bad results can be attributable to development variables as much as exposure. Thus I question the validity of trying to base film exposure on polaroid results, even if the ISOs are the same. Especially with a film like Velvia.

 

But than again, I'm no expert. In fact, there are times I've gotten really pretty polaroids, which were a lot better than the prints I made of the same shot off film negs. Could be that I don't know how to print, or there are some aspects of polaroid film giving it a special look you won't get with anything else.

 

RJ

[wyverndude]

Now that you've gotten the <I>useful</I> answers... here's something you sort of asked that wasn't really addressed -and isn't really necessary- but may be ... 'enlightening' :) :

<P>

Yes, if you "go in the same direction", since you are now exposing a negative, yes, it WILL be <I>lighter</i> than your original exposure, which is opposite the "direction" you wanted to go, because it is a negative... but that's on the negative.

<P>

Remember that you're exposing for the finished print -a positive. So when you lighten your negative, you're darkening (what you wanted to do) the finished print that you'll get from that negative.

[stephen_benskin]

You will need to test for yourself. Don't forget that Polaroid is a very different material and at 4 seconds will probably have different reciprocity characteristics. Also, you are viewing a positive to determine a negative. Exposure based on a positive is determined more from the reproduction of highlights, while the negative is determined by the shadows. The lighting conditions under which you judge the positive also contributes to how it is perceived. Once again, if you want to go the Polaroid route, test to determine how you interpret the relationship.

[david_brown1]

If you are talking about Polaroid type 55, the speed of the negative is about 1/2 the speed of the print (I expose the print at ISO 50, and the negative at ISO 25) So, for the negative, go with f11 @ 4s.

[harry_akiyoshi]

Which polaroid film are you shooting? Most color polaroid film has horrible reciprocity characteristics beyond about 1/15 or 1/4 of a second.

 

At any rate, barring reciprocity error, an exposure that looks correct on 100 ISO polaroid stock will usually still look correct on 100 ISO film. They're not identical, and it takes some practice to figure out exactly how to interpret a polaroid for proofing purposes, but generally, if a polaroid is too dark (not enough exposure), then the negative will be too light (also not enough exposure).

[david choo]

Make sure the polaroid speed is the same as the film speed. :D As for the going up or down in direction, go the same direction you went with the polaroid.

[andrew_oneill]

Which Polaroid are you using? Are you using colour or B/W?

[greg_miller8]

If you are shooting slide file, why not use the Polaroid to check basic exposure. Then check for how many stops brighter your highlights are compared to midtones to be sure that you don;t blow out the highlights. The adjust as necessary.