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Old Feb 14, 2006, 4:13 PM   #11
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BowerR64 wrote:
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Thats what happens, the same settings have different shutter speeds.
You don't have the same settings. You're using a + 1.5EV setting for exposure compensation with one camera, and a +0.6 EV setting with the other. So, the one with a higher amount is going to be exposed brighter. The left photo is also using a larger aperture.

The camera's autoexposure algorithms are probably going to use different aperture/shutter speed combinations, too for identical exposure, even if you did have the exposure compensation settings the same.

A number of aperture/shutter speed combinations will give identical exposure for the same ISO speed (and you do have a slight difference in ISO speed to contend with, too).

But, Exposure compensation is only designed to let you expose a scene brighter or darker than the camera's autoexposure would. A +EV setting will cause a camera to use a larger aperture (smaller f/stop number) and/or slower shutter speed than it normally would (either one will expose brighter).


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Old Feb 14, 2006, 4:20 PM   #12
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Yeah i know they are not set the same, but these are the 2 that i think look close and i posted the results for thsoe 2 so that you could see what settings they have. Do they look similar as far as the exposure? or are they way off?



here is my lighting, 2 of these bulbs in 2 clamp lights one on each side about 1 meter or so away.



remember im just learning and any input helps, its so interesting i love it! :G
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Old Feb 14, 2006, 4:27 PM   #13
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BowerR64 wrote:
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Yeah i know they are not set the same, but these are the 2 that i think look close and i posted the results for thsoe 2 so that you could see what settings they have. Do they look similar as far as the exposure?
No. The one on the left is exposed brighter (as you would expect since you used a +1.5 EV setting with it, and a +0.6 EV setting with the photo on the right).

The white background will fool the metering. So, you sometimes need to do that. The one on the left has the better exposure from what I can see in these small photos.

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Old Feb 14, 2006, 4:28 PM   #14
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These 2 are the same, and the fuji A120 seems a little over exposed, i just asume because the ISO is 200? i thought the higher the ISO the more sensative to light the sensor is? so i figured it would need a lower ev compisation then the one with iso 160?

am i not thinking this correctly? i think im missing alot but im just trying to figure it out. Thats why im asking



JimC wrote:
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BowerR64 wrote:
Quote:
Thats what happens, the same settings have different shutter speeds.
You don't have the same settings. You're using a + 1.5EV setting for exposure compensation with one camera, and a +0.6 EV setting with the other. So, the one with a higher amount is going to be exposed brighter. The left photo is also using a larger aperture.

The camera's autoexposure algorithms are probably going to use different aperture/shutter speed combinations, too for identical exposure, even if you did have the exposure compensation settings the same.

A number of aperture/shutter speed combinations will give identical exposure for the same ISO speed (and you do have a slight difference in ISO speed to contend with, too).

But, Exposure compensation is only designed to let you expose a scene brighter or darker than the camera's autoexposure would. A +EV setting will cause a camera to use a larger aperture (smaller f/stop number) and/or slower shutter speed than it normally would (either one will expose brighter).

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Old Feb 14, 2006, 4:35 PM   #15
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Thats what happens, the same settings have different shutter speeds.
Just because you have the same amount set for exposure oompensation, doesn't mean the aperture is the same. The image on the right is using a larger aperture. So, it can use a faster shutter speed for the same exposure. A smaller aperture (higher f/stop number will use a slower shutter speed for the same exposure.

A number of aperture/shutter speed combinations will result in the same exposure. You need a model that gives you more control if you want to set those kinds of things.

You open the aperture iris larger, it can expose the sensor faster. If you have it set to a smaller opening, you need to keep the shutter open longer before the same amount of light gets in.

You will also have slight differences in the way a camera meters a scene, as well as the amount of contrast, sharpening and saturation you have from the camera's processing.

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Old Feb 14, 2006, 4:38 PM   #16
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So what can i do to get the same exposure on these 2 cameras? or is it not possible?



the only adjustments i can make are the + or - ev compinsation. Is there a formula based on what we know from these 2 cameras to get the same exposure? :?


Can i some how trick one camera to do the same thing as the other one not tricked? or somthing?
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Old Feb 14, 2006, 4:42 PM   #17
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You're getting roughly the same exposure with the same settings. There might be a third stop difference between them that you could compensate for (the image on the right could use a slight boost).

You have no control over aperture or shutter speed if you want to shoot at a specific value unless you have aperture priority, shutter priority or full manual modes.

Exposure compensation is only designed to let your expose brighter or darker than the camera normally would.

They are two different cameras. Each one is gong to behave differently. Do you have other metering modes? Use spot if you want to meter on the guitar versus taking the entire scene into consideration.

You could also play with white balance (I see incadescent set on one in the EXIF), as well as any contrast, saturation, and sharpening settings. I'd need to look up your models to see what adjustments you have available.

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Old Feb 14, 2006, 4:51 PM   #18
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Thats all i can change, the BG color and the ev compinsation. I dont think i can change anything else.

I thought this would be easy, but its not what i thought.
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Old Feb 14, 2006, 8:19 PM   #19
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This dial isn't on my flash, but on a light meter; but the old flashes had something similar.
Anyway, I think I see now what you're trying to do.

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They are 2 cheap P&S cameras that i have, one is a fuji MX1200 1.3mp it has a fixed iso of 160 but has the same ev settings as the finepix A120 -2.1 to +1.5 in 0.3 increments.

I wanted to compare the images with the same settings but since one has a 200 fixed ISO (A120) and the other is 160 they dont come out the same. If i set the ev on them both to +0.9 the one with the 200 iso is a little over exposed compaired to the 160 if this makes any sence?
Okay, I see now what you are trying to do, but I think you may be lacking a bit of fundamental understanding of what light meters and digital sensors are designed to do. I don't mean to be patronizing, but just to be sure we're on the same page:

First of all, light meters are color blind. They don't register color, only intensity of light. So we're talking black and white.

Second, unlike the human brain-eye, they're not able to subjectively adjust for differences in brightness; fundamentally they're designed to reproduce everything as middle gray (18% reflectance, or zone 5 on a 10-zone scale). What this means in practice is this: if you fill the viewfinder with gray card, the camer's meter thinks it is looking at a gray card and calculates a certain exposure to produce gray. Now, if you fill the viewfinder with a sheet of white paper, the camera still thinks it's looking at middle gray--only a very brightly illuminated middle gray--so it reduces the exposure by several steps so that a middle gray is reproduced. Contrarily, if you fill the viewfinder with a piece of black paper, the camera once again thinks it's looking at middle gray--only a very darkly illuminated middle gray--so it increases the exposure several steps until a middle gray is reproduced.

The only thing ISO has to do with this is relative, namely, the baseline for the meter. If ISO is set for 100, the camera's meter assumes that the "film" (sensor) is very insensitive to light, so it has to give lots of exposure to that black piece of paper to bring it up to middle gray tone. If the ISO is set for 800, however, that's three stops difference in sensitivity (100 to 200=1, 200 to 400 = 2; 400 to 800 = 3), so the meter thinks it can get away with giving three stops less exposure and still produce that middle gray. --And with digital cameras, that's what happens. Changing the sensor's ISO setting is like changing to a different speed of film. So no matter what the ISO is set for on a digital camera, the camera always tries to produce middle gray, and assuming a uniform subject with AUTO exposure mode, it should always produce middle gray if exposure compensation is set for zero.

Once again: if you are using an automatic exposure mode, it doesn't matter what the ISO on the two cameras is set for; in theory, both shots should come out the same if no exposure compensation (EC) is applied.

I don't have time now to do the math on the fractional fstops and shutter speeds in your two photographs' exifs, but you could figure out the EVs from those figures to see what each camera's meter was calculating.

To do a more accurate test, try using an 18% gray card as your target. Set it close enough that it fills the viewfinder of each camera; it doesn't have to be in focus, just no shadows. Set EC for 0 and use any automatic exposure mode on the camera (AUTO, PROGRAM, Aperture priority, or Shutter priority). If the two cameras' meters are accurately calibrated, the two exposures should come out with the same middle gray.

Unfortunately, aside from the normal fluctuation or calibration difference between the two light meters, when shooting a real life subject problems will occur if the meters of the two camera are designed to meter differently, for example, if one used a matrix or averaging meter while the other one was center-weighted. In this case, the composition of the scene (light/dark background, etc) could cause a varying degree of difference in the way the two cameras metered the light on the scene, resulting in the differences in exposure you see.

So with the real-life scene you're using, what I would do is this: set both cameras for 0 exposure compensation, be sure they're mounted on a tripod from the identical position, and start from there (again, using an AUTO mode). If one is brighter than it should be, then lower its exposure compensation a bit.

I think the main place your desired "formula" comes in is when using manual exposure. Just remember that 1 EV step is the same as one step of f-stop or shutter speed, and also equal to 1 step of exposure compensation and also one step in ISO value (50-100-200-400-800-1600-3200). These all have reciprocal effects on exposure.

LATER EDIT: I'm beginning to see where the misapprehension lies. I don't have time right now, but I think the whole problem with the idea of using EC with different ISOs is based on the film metaphor; if you were using the same film type in two different cameras, but with the two cameras set for different ISOs (160 versus 200), then you could use 1/3 stop EC to correct the exposure, but we're not using film here; in the case of digital, changing the ISO is equivalent to physically changing film types. More later.

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Old Feb 14, 2006, 11:26 PM   #20
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I took these, both are full auto. You can see the old one using the 160 ISO is just weak and needs a boost in exposure and the BG needs tweaked. The A120 is ok but manual mode with the ev tweaked IMO looks better. But you can see how the light sensor are not set to good, and thats why they are cheap models.


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