Exposure with filter question

[linuxpng]

I know with a red 25 filter you are supposed to increase exposure by 3 stops to compensate for the filter. I've also heard if you squint you should increase exposure from the meter by 2 stops. My question is if you are taking a picture with that red filter in a sunny situation do you really go 5 stops beyond the meter?

It does seem to work that way for the yellow 8. I usually do 2 stops for the squint and 1 for the filter, but 5 seems like an awful lot. Thanks ahead of time.

Steve

[Alan Davenport]

I've never heard of the Squint Rule before. It might come in handy if you don't have a meter and are starting with Sunny 16, but meters don't squint so there's no adjustment required.

The important thing is for the photographer to (1) know what is being metered, and (2) decide how that is to appear in the photograph. Then set the exposure accordingly, taking into account any filter factors.

[linuxpng]

Well, I'm pretty new to large format and always trusted my TTL metering in 35mm. I was taking a class at my local community college and the teacher had mentioned using the squint rule. I think the thought behind it is that the meter, in bright light, wasn't supposed to know if the scene was all brightly lit or not and you'd underexpose other areas of the scene.

I honestly have no idea whether or not it makes a difference that I am not using a spot meter, I honestly didn't have the money for one so I got a used analog Luna Pro on ebay.

Maybe if I give my example where it worked out ok it might clarify what I am asking (I have no idea, since I am pretty new, if I am just speaking gibberish). I was photographing a white church that had bushes etc around it. So with my meter it registered an f22 at 1/30 at ISO 100. I ultimately made the picture at f22 1/8 (which I guess I only did 2 stops) with a yellow 8 filter.

So I guess that being the case, I would go to f/22 at 1/2 sec ISO 100 with a red 25 filter?

[Ralph Barker]

The compensation markings on filters can be confusing, as some use factors, while others give f-stops. A #8 Yellow should have a factor of 2, or 1 stop, while a 25 Red usually has a factor of 5, or 2.25 stops.

Thus, working from a reading of 1/30 @ f22, the #8 Yellow would be 1/16 @ f22, and the #25 red would be 1/8 @ f22 opened a smidgen.

It's also a good idea to do a little personal testing of the filters to confirm the amount of compensation required.

[linuxpng]

I think I am asking two questions together. If you use a regular meter and meter a white object would you compensate anything from the default reading?


If so, you would add that to whatever you needed for your filters as well?

I'm sorry to be so thick, just trying to get my head around what my 35mm has been doing for me already.

[Kirk Gittings]

I've also heard if you squint you should increase exposure from the meter by 2 stops.

Man. This is a classic. Gotta love some of those college professors (I can say that because I am one).

the meter, in bright light, wasn't supposed to know if the scene was all brightly lit or not

A meter is designed for precisely measuring light levels. If it doesn't measure how brightly lit the scene is, Why would we need one? What you need to learn is how to interpret the information that your meter gives you. The contrast level of a scene can be read with a Luna Pro by taking a reading in the sunlight and one in the shadow average the two for a basic exposure and add the filter eexposure to that. There is of course much more to be said on this subject. Try some books like Ansel Adams the Camera and the Negative and Steve Simmons Using the View Camera.

Good Luck!

[Ralph Barker]

The exposure adjustment for the filter is to compensate for the overall reduction in light caused by the filter. That adjustment is applied to whatever your "base" exposure is, based on whatever approach one uses to determine that. But, if you meter a white area, you'd probably want to open up 2-3 stops from that reading to reach a "middle gray" reading to use as the base exposure.

[linuxpng]

That's kind of what I was thinking, but 4 or 5 stops from base meter sounded pretty high. I guess film is sorta cheap I should just try it out. Thanks everyone for the advice.. I will definitely do some more reading in the books Kirk recommended.

[Anupam]

I think I am asking two questions together. If you use a regular meter and meter a white object would you compensate anything from the default reading?.

If you meter a white object (I am assuming you are spot metering here) and just use the recommended exposure your white object will turn up middle grey on film. To get it back up to white you will need to overexpose by a couple of stops.

I suppose this is what the "squint" rule is trying to get at - but it is one confusing way to learn a concept.

-A

[Alan Davenport]

I was photographing a white church that had bushes etc around it. So with my meter it registered an f22 at 1/30 at ISO 100. I ultimately made the picture at f22 1/8 (which I guess I only did 2 stops) with a yellow 8 filter.

So I guess that being the case, I would go to f/22 at 1/2 sec ISO 100 with a red 25 filter?

Again it depends on what the meter was metering. Remember that the meter is really stupid -- all it knows to tell you, is how much exposure it will take to make whatever was metered become middle gray in the photo. If you meter the white side of the church, the meter will tell you how to make it gray. If you meter the dark shadows under the bushes, the meter reading will tell you how much exposure you need to render those shadows as middle gray. The meter wants to make everything an 18% middle gray because someone once figured out that an average landscape reflects 18% of the light, and so that's what they design lightmeters around.

I'll assume you metered the white wall as 1/30 @ f/22. The #8 filter costs you 2 stops, so you need 1/8 @ f/22 to make the wall gray. But the wall is white, so you'd want to add 2 more stops exposure to make the wall come out white, and you end up at 1/2 sec @ f/22.

Since the red filter costs an additional stop, the exposure would be something near 1 second @ f/22, if you metered only the white wall, and if you wanted it to render as bright white in the final image. If the meter reading included a significant area of the plants, then your exposure of 1/2 sec @ f/22 sounds good from here.

Of course, metering the highlights (bright parts) of the scene is a good method for transparency films, but it's better to meter the shadows with negatives... in that case you give less exposure than the meter indicates. Like they said, you're gonna have to burn some film while you get the hang of this.