Auto Function in RAW

[nathan_rigg]

On a bright sunny day I have been taking shots in the range F11 to F16. I had understood this to be correct given

the conditions and had read something about the 'sunny 16 rule'. However when I come to view the RAW file and I

hit the auto exposure function the exposure is often changed.

 

A couple of questions: -

 

How can I tell if the exposure is 'correct'?

 

How does the auto function work i.e. am I gettingb the optimum exposure by slecting this?

 

Why is it, when I then open the shot in PS and then use the auto levels function it again chages the exposure?

shouldn't it have got it right when I did this RAW?

 

Any other tips on how I can get the exposue right exposure 'in camera'. It would really be useful if there was som

guidance around what fstop to use (generally speaking) in differing lighting conditions i.e. similar to the 'sunny 16'

 

Thanks

 

Nathan

[remco-jan.woldhuis]

The technically best exposure result in a histogram that stretches from "left to right", without clipping on the black and

white side of the histogram.

 

Most camera's are a bit conservative on the high light side, to avoid blown out whites, so they tend to underexpose a bit.

this may explain why auto-exposure changes the exposure.

 

I would avoid using the auto-exposure function and use the manual levels function. Only you (the photographer) knows how

the image should look like.

[ronald_moravec1]

Auto most anything is a photography crutch and rarely works 100%

 

I don`t know where auto exposure is in camera raw, but it will probably try to make every pic middle grey or middle toned. If you have a pic of a snow field or a black cat, that is definately not what you want.

 

Even if you hand level, be aware that the end points perhaps are not supposed to be pure white or pure black. Auto levels does just that and it will be wrong sometimes if the picture is not "average.".

[ellis_vener_photography]

"The technically best exposure result in a histogram that stretches from "left to right", without clipping on the black and white side of the histogram. "

 

That is incorrect. The shape of the histogram is purely dependent on the subject matter.

 

"On a bright sunny day I have been taking shots in the range F11 to F16"

 

The "sunny 16" rule is based primarily the sensitivity of film or the ISo setting on a digital camera. While it is a good rule of thumb in general with average subjects in bright sunlight on clear days, is a dumb rule as it has no awareness of what you are photographing. it also presumes that you will be setting the shutter speed to approximate the ISO value: f/16 @ 1/200 @ ISO 200 as an example.

 

But for arguments sake let's say that indeed the optimum exposure for an average subject with an average range of reflective qualities is f/16 @ 1/200 @ ISO 200. You'd get the same exposure if you set the camera to f/22@1/100, f/11 @ 1/400, f/8@1/800, f/5.6@1/1600, etc.

 

"If you have a pic of a snow field or a black cat, that is definately not what you want. "

 

Ronald is absolutely right about this. You have to take into account the tonal values of the subject as well as the illumination. Auto anything can be fooled, you have to use your judgement as well.

[KenPapai]

How many books do you own? You owe yourself this one Nathan:

 

"Real World Camera Raw with Adobe Photoshop CS3" by Fraser and Schewe. The CS4 version for ACR 5 is apparently due in a month or so.

[mendel_leisk]

Nathan, what's your camera and what exposure mode are you using? Is it one of the auto exposure modes? Or?

 

Aperture (f11, f16) is just *half* the equation, shutter speed being the other half. Plus "ISO", essentially the "speed" of the camera.