Why take exposure readings at wide open aperture?

[Dieter01]

In all the books I have read on photography the author uses the smallest apperture (wide open) when measuring light. If that is not the desired aperture you step down aperture and step up shutter speed, and then take the picture. Like this example (in manual mode):

1. Take an exposure reading: f/2.8 | 1/30
2. You were however looking to use f/8 for optimum quality and fitting DoF
3. Step down camera to f/8 (=3 stops). Step up again to 1/4 sec (=3 stops)


But why go through all this math and step up / step down stuff? Why not just take your meter reading at f/8 and get it right then and there? I understand if it means shutter speed will be "bulb", but otherwise I don't get it.

What makes it better to take reading at wide open?

 

[mysteryscribe]

I personally always decide what I want.

1...stop action
2...show action
3...short dof
l4...ong depth of field.

Then i set whatever I want frist ie stop action... 250 shutter speed then match what fstop i need to be a good exposure

or short depth of field f2,8 then find the right shutter speed.

thats how i do it

 

[Dieter01]

The thing I can't understand though is why these books do the exposure reading at f/2.8 even when they know before the result comes out that they are going to step it down to f/8 afterwards. Not sure if I am making any sense here, but what I don't understand is why they don't make that meter reading at f/8 instead. Is there a reason?

 

[mysteryscribe]

If I have a good meter in the camera I do it just like i said set one then work the other to it... Review the results and then make any adjustments.

You do view the subject with a wide open lens most of the time because the camera only stops dawn when you depress the shutter. Otherwise it is wide open.

Maybe they mean you are viewing wide open while you meter. Not that you meter at 2.8 first.

 

[Dieter01]

Maybe they mean you are viewing wide open while you meter. Not that you meter at 2.8 first.

I think a lot of text can be interpreted this way, but not the books I am refering to. Well, i guess there was no reference, but Bryan Peterson in "Understanding Exposure" and Lee Frost in "Night and low Light Photography" were two. I am trying to find out if the reason why they consistantly use this method is to teach the reader what the f/stops are (learning to count up and down, seeing why several combinations allow the same amount of light to reach the film), or if its simply better for some reason. More accurate perhaps...

I don't think it has to do with stopping down the lens prior to taking the shot / using a DoF preview.

 

[mysteryscribe]

Then darned if I know.

I personally have never done it that way. When I was teaching, I used to just get a hand held meter and pass it around the room. It was more effective than drawing pictures on the board.

After they saw the combinations we discussed what each one did. Thats the only think I ever used as a tool for exposure. To me camera meters are just there to set the camera. You either understand the controls functions before then or you learn them as you go along.

 

[mysteryscribe]

Then darned if I know.

I personally have never done it that way. When I was teaching, I used to just get a hand held meter and pass it around the room. It was more effective than drawing pictures on the board.

After they saw the combinations we discussed what each one did. Thats the only think I ever used as a tool for exposure. To me camera meters are just there to set the camera. You either understand the controls functions before then or you learn them as you go along.

 

[fightheheathens]

odd. my best guess would be that when you stop down, its harder to see through the view finder because less light gets in. But that would only be the case if for some really odd reason your camera's F stop has no spring action or what not allowing it to close when you release the shutter? understand?

 

[newrmdmike]

well . . . consider the masters, they ask you what film you have. tell you, rerate it at this iso, f/5.6 at a 30th. they never even looked through it. after that many years of shooting for a profession it isn't any math at all for a master to meter everything at f/2.8. its just easier for them, why bother turning the dial on a meter when your on your way to becoming one yourself.

 

[mysteryscribe]

I don't get that last bit. I might be just dense, but with a camera meter, I personally never saw one that would give you all the possible combinations in the view finger. usually you set one and then the other is displayed depending on the camera.

Okay so we have aperture priority and we set it at 2.8 and it give us shutter speed at 100. But what we really want is the shutter speed for f8 so now we reset both the shutter speed and the aperture. while we are doing this the girl in the bikini puts her top back on. That just makes no sense to me.

Of course I'm just a hack but it still makes no sense. And with a hand held meter, which is what I mostly use, you have all the combinations at a glance.

Okay one possibility is the one for night and exposure. Okay this might work out for night. You want to use f16 but your meter doesnt have enough time on it for that long an exposure, so you read it at f2,8 then figure the time for f22 or whatever. Now that happens to me on the paper negs now and then. I have exposures of 10 minutes or longer and there is no time like that on the meter but I can get 2.8 at one minute say and figure the correct exposure time...

 

[fmw]

I don't know which camera you are using but I'll explain. Since it is better to view your subject at maximum aperture (brighter viewfinder) the diaphragm is indexed to maximum aperture so that it closes when you press the shutter release just before making the exposure. The meter is indexed in the same manner. No matter where you set the aperture, the meter reads through the wide open aperture. Since it is indexed to the maximum aperture, it can calculate based on where you set the aperture ring.

 

[mysteryscribe]

this was the original post:
In all the books I have read on photography the author uses the smallest apperture (wide open) when measuring light. If that is not the desired aperture you step down aperture and step up shutter speed, and then take the picture. Like this example (in manual mode):

1. Take an exposure reading: f/2.8 | 1/30
2. You were however looking to use f/8 for optimum quality and fitting DoF
3. Step down camera to f/8 (=3 stops). Step up again to 1/4 sec (=3 stops)

What you are saying is pretty much what everyone is saying. You still set one first and match it since you reasonably know what you want. You DONT set the aperture before hand at 2.8 then make all the foolish up and down moves we were all discussing. Nothing has changed some 'expert' just explained it in different terms so the photographers reading his expert advice "wouldn't be confused" by reality. That makes perfect sense.

By the way all meter measure light nothing more. The just express how many lux (I think that is the term) there are in the available light. well normal meters anyway. It's up to you to decide how you use the light.