Question about proper exposure with a manual lens

[KmH]

A Stop

A stop of exposure is a fundamental photography concept.
A 'stop' is a doubling (2x) or a halving (0.5x) of the amount of light that reaches the recording media, be it film or an electronic sensor.
Since exposure is a triad of adjustments (shutter speed, ISO, lens aperture) you can change 1, 2 or all 3 of the triad settings.

If you want 1 more stop of exposure (brighter) you can adjust just one of the 3 by 1 more stop.
Or, you can change 2 of the 3 by 1/2 more stop each for a net gain of 1 stop of exposure.
Or, you can adjust all 3 by 1/3 more stop for a net gain of 1 stop of exposure.

You can also change the triad of settings and have no change in the exposure.
If you change 1 of the 3 settings by 1 stop more exposure and change a 2nd setting by 1 stop less exposure the net change is zero.

Suppose you subtracted a stop of shutter speed to help stop subject motion, you could add a stop of lens aperture to keep the exposure the same. However, adding a stop of aperture will also affect the total DoF by a small amount. So, if you don't want the DoF to change you would add a stop of ISO instead, however, adding a stop of ISO will increase by some amount the image noise in the photo.

Note: DSLR cameras are set by default to adjust the exposure settings in 1/3 stop increments.
Most DSLR cameras let you change that to 1/2 stop or 1 stop increments.
However, the advantage of 1/3 stop step increments is more precise control of exposure.

 

[gsgary]

I just tested something...looking at the same subject with the same focus and making no changes at all, set to aperture priority and the camera selected 40 as the shutter speed and I took a picture. It was slightly underexposed but definitely right in the ballpark.

Immediately after I switched to manual, the camera was set to 250 shutter speed and indicated that it was exposed correctly (of course it was very dark).

When you tested it in Aperture priority was the compensation set to zero, you could have easily taken a reading from a different position, it needs to be on a tripod so it meters off the same spot

 

[petrochemist]

Cameras generally do not meter down to the low light levels used for night skies.
Even if the did they would try to make the image average to 18% grey - not what you want!

It's usually best to put the camera in manual mode & set the shutter speed yourself. Anything longer than about 30 seconds (with your camera & lens) will start to show movement of the stars due to the earth's rotation. The '500 rule' gives the maximum to avoid star movement.

The quality of your skies (basically light pollution) will often have a significant effect on how many stars you can see - round here (semi rural England) 'sky glow' is a significant nuance for astronomy.

 

[Novelectro]

I just tested something...looking at the same subject with the same focus and making no changes at all, set to aperture priority and the camera selected 40 as the shutter speed and I took a picture. It was slightly underexposed but definitely right in the ballpark.

Immediately after I switched to manual, the camera was set to 250 shutter speed and indicated that it was exposed correctly (of course it was very dark).

When you tested it in Aperture priority was the compensation set to zero, you could have easily taken a reading from a different position, it needs to be on a tripod so it meters off the same spot

This was in the exact same spot, aiming at the exact same place, where aperture priority was indicating that "40" appropriate and then immediately switching over to manual, which thought that 250 should be dead centered on the meter.

 

[Novelectro]

Cameras generally do not meter down to the low light levels used for night skies.
Even if the did they would try to make the image average to 18% grey - not what you want!

It's usually best to put the camera in manual mode & set the shutter speed yourself. Anything longer than about 30 seconds (with your camera & lens) will start to show movement of the stars due to the earth's rotation. The '500 rule' gives the maximum to avoid star movement.

The quality of your skies (basically light pollution) will often have a significant effect on how many stars you can see - round here (semi rural England) 'sky glow' is a significant nuance for astronomy.

I'm not even attempting to take night sky photos yet. I'm just sitting on my couch aiming at furniture and the meter is dead center when it's way way way underexposed, and when I just try to expose it properly through trial and error, I have to go up to +3 until my histogram is telling me that I am in the right spot.

 

[gsgary]

I just tested something...looking at the same subject with the same focus and making no changes at all, set to aperture priority and the camera selected 40 as the shutter speed and I took a picture. It was slightly underexposed but definitely right in the ballpark.

Immediately after I switched to manual, the camera was set to 250 shutter speed and indicated that it was exposed correctly (of course it was very dark).

When you tested it in Aperture priority was the compensation set to zero, you could have easily taken a reading from a different position, it needs to be on a tripod so it meters off the same spot

This was in the exact same spot, aiming at the exact same place, where aperture priority was indicating that "40" appropriate and then immediately switching over to manual, which thought that 250 should be dead centered on the meter.

In your post you said you were using +3 compensation this would account for the difference

Sent from my SM-G903F using Tapatalk

 

[Novelectro]

That lens does not communicate electronically with the camera, and metering must be done stopped down. If you can't do stopped-down metering with your camera, then you have some arithmetic to do. Meter at f:2, which is wide open, then adjust your reading for what you want to set your aperture to. If you want f:8, for example, then whatever it meters for your shutter speed when it's wide open, you need to lengthen by 4 stops, since f:8 is four stops under f:2.

I think you're right that the only way of dealing with this is via math/formula. It doesn't seem like this is something that can be "fixed". When you say that I should meter from f2 to know how to meter when I'm stopped down - I am somewhat confused. I don't get correctly metered at f2 either. I'm "guessing" as to where my shutter speed should be whether the lens is wide open or not.

 

[wfooshee]

Stopped-down metering means that you have the aperture set where you want it for the picture, and you'll see that the viewfinder is darker than it usually is. I'm not a Canon user, but my brother is, and he's telling me that the camera will show 00 as the aperture rather than the actual setting, because it's getting no information from the lens. Set the aperture on the lens (with the aperture ring, not the camera dial - the camera cannot control the lens's aperture) to its largest aperture (smallest number) to compose and focus, because that's where you get the brightest viewfinder. Then set the aperture on the lens that you want to use and then meter the scene. You'll see the viewfinder darken as you turn the aperture ring on the lens. You should be able to meter in Av or M modes, but you may not be able to use evaluative mode on the meter; just spot or center-weighted.

The term "stopped-down metering" is opposed to auto-aperture metering, which is how we're all used to using the camera. The lens stays wide open, no matter what the aperture is set to, until the shutter is triggered, and at that point the lens automatically stops down to the selected aperture to take the picture. The meter knows this will happen and compensates automatically. It knows that the lens wide open might be f:2 or f:5.6, whatever it happens to be, and when you have the camera set for say, f:11, the camera reads the light through the wide open lens and computes what it will need to be when the lens stops down. By the way, this automatic aperture capability, where the camera meters wide open and the viewfinder operates wide open, and the lens stops down just for the instant when the shutter fires, is what the term "AUTO" means when you see it on a lens. That tells you that the lens is capable of automatically stopping down to the selected aperture for the shutter to fire, but remains wide open for metering and viewing. We take that for granted, but it has not always been the case! With your lens, it's not the case.

You set the aperture ring to maximum aperture to focus and compose, then set it to the desired aperture for metering and shooting. Use a metering mode other than evaluative.

 

[Novelectro]

Thanks for explaining that, wfooshee. I think that the other problem though is that I can't really see anything at f2 anyway (when metered at what is supposedly a perfectly exposed picture). I still don't really get it, even if the lens can't electronically communicate with the camera, it seems like the camera should still understand roughly where the meter should be.

 

[Vtec44]

What about shooting with live view or a using a light meter?

 

[Novelectro]

What about shooting with live view or a using a light meter?

I am shooting with live view. Going to mess around with some light meter apps.

 

[gsgary]

What about shooting with live view or a using a light meter?

I am shooting with live view. Going to mess around with some light meter apps.

Do you know how to use a lightmeter

Sent from my SM-G903F using Tapatalk

 

[Novelectro]

What about shooting with live view or a using a light meter?

I am shooting with live view. Going to mess around with some light meter apps.

Do you know how to use a lightmeter

Sent from my SM-G903F using Tapatalk

No I don't. The one I downloaded "myLightMeter" looks relatively self explanatory?

 

[Novelectro]

So I realized today that I don't have this issue with taking photos through the viewfinder. The metering seems to be roughly where it's supposed to be. The problem only exists when shooting in live view.

So at least Ive made some progress. Any ideas as to why the live view metering is acting so differently? I think it's something that I can live with, but I like to take a lot of shots from really low angles - it's nice to be able to compose my shots from the live view screen since I can angle it up when the camera is only a few inches off the ground.

Appreciate everyone's contributions btw.

 

[john.margetts]

Your camera probably came with a soft rubber 'plate' to go over
the viewfinder. This stops the meter responding to light entering the camera through the viewfinder when your eye is not blocking it. Try it.