Not really clear on EV steps...

AutumnJazz · Jun 10, 2008

Ok, I have a question. Let's say I have a light meter, camera in manual mode, and a filter on my lens. That filter is +1.3 stops (or whatever). I use the light meter to find the correct exposure. Can I correct for the filter by setting my camera +1.3 EV steps?

Thanks...

matt miller · Jun 10, 2008

You sure can.

Kino · Jun 11, 2008

Errr... wouldn't you subtract the EV? I mean, aren't you loosing the light rather than gaining it?

Guess it's all how you phrase it...

Open up 1.3 stops

Reduce metered amount by 1.3 EV

Lower your ASA by a factor 1.3 or about 80%

All the same thing.

Leon · Jun 11, 2008

I always find exposure compensation/ film speed adjustments etc terminology very confusing. The key thing to remember is the filter reduces the amount of light entering the camera, so you want to compensate for this by allowing more light in so, yes, setting auto exposure comp to + 1.3 would be perfect, or slowing down the film speed by 1.3 stops to force a slower speed would also work fine.

whoops - I wrote this not realising I've echoed what Kino and Matt have said - I think matt puts it best.

AutumnJazz · Jun 11, 2008

How do you calculate it as a factor of film speed (ISO/ASA)?

matt miller · Jun 11, 2008

You can lower your film speed rating by the filter factor when metering. If you're using 400 speed film, and usually meter at 400, then you can set your meter to 160 (with your 1.3 stop example) to get the proper exposure.

rwyoung · Jun 11, 2008

AutumnJazz said:
How do you calculate it as a factor of film speed (ISO/ASA)?

Powers of 2 are your friend. " ^ " means "raise to the power of" in this example.

Film Speed / (2 ^ factor) = new speed

factor = 1.3
Film Speed = 100
new speed = 100 / (2 ^ 1.3) = 40.61

But as you may have noticed, you don't have 40.61 as an option for film speed. Set to the closest value on your dial and be happy, probably 40.

You can carry around a cheap (seen them for $5) calculator, or make up some cheat sheets (Excel / OpenOffice) or remember a few "tricks" and simply count 1/3 or 1/2 stops on the dials.

Kino · Jun 11, 2008

Leon said:
I always find exposure compensation/ film speed adjustments etc terminology very confusing. The key thing to remember is the filter reduces the amount of light entering the camera, so you want to compensate for this by allowing more light in so, yes, setting auto exposure comp to + 1.3 would be perfect, or slowing down the film speed by 1.3 stops to force a slower speed would also work fine.

whoops - I wrote this not realising I've echoed what Kino and Matt have said - I think matt puts it best.

That's probably where we are differing; I am assuming a change of EV value on a hand held meter and I think (correct me if I am wrong) you are speaking of exposure compensation adjustments on a camera; right?

And, you are right, it is always confusing...

Leon · Jun 11, 2008

Kino - I assumed the OP was referring to camera auto compensation, so that is what i was referring to, but probably just clouded matters more. this kind of thing can drive me nuts! recently, fellow apugger Stoo Batchelor came round for a cup-a-tea and we were trying to work out matching his spot meter readings with a 1.3 stop auto compensation on his camera - a simple thing on the face of it, but it took us ages to work out that what he was doing was right in the first place. Bloody Nightmare

eddym · Jun 11, 2008

It's not hard at all once you learn to "think in f-stops." The first thing to learn is the film speeds, which progress in 1/3 stop increments, as follows, and starting from 25:
25 32 40 50 64 80 100 125 160 200 250 320 400 500 650 800 1000 1250 1600 etc.
The numbers are easy to remember once you notice that each third number is doubled: 25 50 100 200; 32 64 125 250; 40 80 160 320

And of course, each third film speed is a full stop faster or slower, depending on the direction you move.

Full f-stops are also a numerical progression; every other one is doubled:
f1.4 2.0 2.8 4 5.6 8 11 16 22 45 etc.

To apply compensation, all you have to know is whether you are opening up or stopping down, and how many stops.

AutumnJazz · Jun 13, 2008

eddym said:
It's not hard at all once you learn to "think in f-stops." The first thing to learn is the film speeds, which progress in 1/3 stop increments, as follows, and starting from 25:
25 32 40 50 64 80 100 125 160 200 250 320 400 500 650 800 1000 1250 1600 etc.
The numbers are easy to remember once you notice that each third number is doubled: 25 50 100 200; 32 64 125 250; 40 80 160 320

And of course, each third film speed is a full stop faster or slower, depending on the direction you move.

Full f-stops are also a numerical progression; every other one is doubled:
f1.4 2.0 2.8 4 5.6 8 11 16 22 45 etc.

To apply compensation, all you have to know is whether you are opening up or stopping down, and how many stops.

This post is exactly what I've been looking for since I started photography again. I pretty much forgot the basics. I'd been able to piece nearly everything back together except for the above.

I love you!

HarryW · Jun 13, 2008

Hello,
This is a very helpful thread and Eddy makes it very clear on the relationship of film speed and f-stops. I do however want to make sure that I am clear on this - is the original poster and the responses dealing only with a hand held meter and a non-metered camera? What I have never been clear on is if you use a filter on a TTL metered camera does the TTL metering system fully take care of the reduction in light getting to the film or are there circumstances where you would have to make additional compensation to the TTL meter reading.
Regards
Harry

John Koehrer · Jun 13, 2008

HarryW,
Yes, The meter compensates, sort of.
But. The meter doesn't have the same response to color that film does. So in theory it's not 100% accurate. The question is can the differences be seen.
Try exposing the same scene with and without the filter & process the film.
The exposures should be very close. If not you need to provide a bit of a fudge factor.

HarryW · Jun 13, 2008

John,
Thank you for this response. It's good to know and I guess that I will try this over the coming days. I should however have been more specific in my question and it relates to very dark filters in b+w photography for example a dark red (Nikon R60) to give really dark skies. I have never had much success with this filter and I don't have the filter factor for the R60 however I have seen 4-6 stated on the internet (which I assume equates to 2-3 stops). Is it best to use a handheld meter and adjust manually, or use a TTL meter and bracket when using dark filters?
Regards
Harry

John Koehrer · Jun 14, 2008

HarryW,
I've never been one to do things the easy way.
Personally I'd be inclined to the test exposure/process with each of the darker filters rather than ttl. You could use the in-camera meter and adjust for a tested compensation or use a dial in +X compensation.
Or, bracket. I would think to the side of overexposure rather than under.

Not really clear on EV steps...

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