Aperture priority combined with Auto ISO and Zoom lens seems odd

[ajax]

Could use some help from more knowledgeable photographers.

To get started I bought a camera equipment bundle which included a DSLR camera with 2 zoom lens. When using the longer zoom lens with camera set to aperture priority and automatic ISO it seems odd, to me, that the camera chooses what, I'm thinking, are high values for both ISO and shutter speed. The automatically selected values are most extreme with maximum zoom. For example, with aperture set to f22 and lens at 300mm in what I'd call normal daylight the camera chooses ISO 800 and shutter speed 500. Both values seem, to me, to be extreme. Why doesn't the camera opt for lower values for both.

I have recognized when moderating the amount of zoom these values seem to come back into a somewhat more normal range. For example, the same shot as above with lens at 75mm the camera changes to ISO 400 and shutter speed 160. That still seems like pretty fast shutter speed and relatively high ISO. When I set the ISO at 200, rather than Auto, the shutter speed goes to 80. Then bringing the ISO down to 100 causes shutter speed to change to 40. Why doesn't the camera opt for the later when ISO is set to Auto?

Is it possible that I've unknowingly changed some other setting that causes this behavior? Or am I simply failing to understand why the camera is doing what most photographers would want?

[Manfred M]

When it comes to the type of automation you are asking about, the camera manufacturer has designed the algorithms in a way that are likely to improve the likelihood of getting a usable picture. I'm really not sure what you mean by "normal range", as I have used shutter speeds that can be measured in minutes right down to 1/8000th sec, depending on what I was shooting. Likewise, my ISO setting can vary from IS0 64 right up to ISO 128000, depending on what I can shooting

The longer the focal length, the more likely you will end up with an image that has camera movement (i.e. camera shake), so the camera will try to assign a shutter speed, that will work in conjunction with the ISO to balance out those two factors. If you have set the camera to auto ISO, it can play with two variables to try to get settings that will get you an acceptable image. If you select both Aperture Priority AND set the ISO, the camera can only adjust a single variable, the shutter speed.

If you are shooting with a long focal length; let's assume a full-frame equivalent of 200mm and you have fixed the ISO, then to get a proper exposure, the camera will choose a shutter speed that give you a correct exposure. If you are shooting a relatively static scene and have the camera mounted on a sturdy tripod, then 1/40th sec is definitely going to work. If you are trying to hand-hold the camera, even with image stabilization, there is a good chance that your image will be soft due to camera shake.

[Stagecoach]

Could use some help from more knowledgeable photographers.

Hopefully.

To get started I bought a camera equipment bundle which included a DSLR camera with 2 zoom lens. When using the longer zoom lens with camera set to aperture priority and automatic ISO it seems odd, to me, that the camera chooses what, I'm thinking, are high values for both ISO and shutter speed. The automatically selected values are most extreme with maximum zoom. For example, with aperture set to f22 and lens at 300mm in what I'd call normal daylight the camera chooses ISO 800 and shutter speed 500. Both values seem, to me, to be extreme. Why doesn't the camera opt for lower values for both.

You do not say what camera and lenses you have.

For many cameras the 'Auto ISO' function allows you the user to input a 'maximum ISO' allowable and a 'minimum Shutter Speed' allowable. Does yours have that function and are you using it?

I have recognized when moderating the amount of zoom these values seem to come back into a somewhat more normal range. For example, the same shot as above with lens at 75mm the camera changes to ISO 400 and shutter speed 160.

The camera will adjust settings (those that are not fixed by the user) to maintain what it thinks is correct exposure and this is controlled by the metering system that 'measures' what it sees within the framing of the shot. Changing zoom will change what is in the framing and hence what is measured.

I am not aware of any camera when in Aperture Priority that uses Focal Length in 'weighting' the balance chosen between ISO and Speed, but may be wrong.

Is it possible that I've unknowingly changed some other setting that causes this behavior? Or am I simply failing to understand why the camera is doing what most photographers would want?

I would check and become familiar with your 'Auto ISO' function user settings if your camera has them.

[xpatUSA]

Could use some help from more knowledgeable photographers.

To get started I bought a camera equipment bundle which included a DSLR camera with 2 zoom lens. When using the longer zoom lens with camera set to aperture priority and automatic ISO it seems odd, to me, that the camera chooses what, I'm thinking, are high values for both ISO and shutter speed. The automatically selected values are most extreme with maximum zoom. For example, with aperture set to f22 and lens at 300mm in what I'd call normal daylight the camera chooses ISO 800 and shutter speed 500. Both values seem, to me, to be extreme.

Earlier I posted something unhelpful, just now deleted it.

The exposure the camera chose (1/500 sec for f/22) does not match "normal daylight"; see https://en.wikipedia.org/wiki/Exposure_value where I'd say normal daylight is about 14 EV. But f/22 and 1/500 sec work out to almost 18 EV causing your image to be 4 EV under-exposed! I don't know your camera so I can't offer why it did that but you are quite right in thinking there's something wrong - badly wrong, IMHO.

... Or am I simply failing to understand why the camera is doing what most photographers would want?

Not sure that "most photographers" would want that kind of behavior, to be honest. But I rarely use Auto-anything, so others here can help solve the riddle better than I.

Good luck with it!

[dje]

Following on from Grahame's post, my experience with Aperture Priority and Auto ISO is that the camera will select the lowest ISO consistent with achieving a certain minimum shutter speed. In some cameras, the minimum SS can be selected, in others it's fixed eg 1/60sec. You need to check your settings.

Also bear in mind that when you zoom in, with the less expensive lenses, the largest aperture allowable for the lens gets smaller.If you have initially set an aperture that is achieveable at the wide end, but that is not achievable at the long end, the aperture setting will be automatically changed by the camera to the maximum achievable for that lens at that focal length.

Dave

[Stagecoach]

Earlier I posted something unhelpful, just now deleted it.

The exposure the camera chose (1/500 sec for f/22) does not match "normal daylight"; see https://en.wikipedia.org/wiki/Exposure_value where I'd say normal daylight is about 14 EV. But f/22 and 1/500 sec work out to almost 18 EV causing your image to be 4 EV under-exposed! I don't know your camera so I can't offer why it did that but you are quite right in thinking there's something wrong - badly wrong, IMHO.

I'm confused now as two different calculators tell me its 14.67/15 EV as per sunny 16. What am I missing, f/22, 1/500s and ISO 800, no doubt something obvious?

[pschlute]

Is it possible that I've unknowingly changed some other setting that causes this behavior? Or am I simply failing to understand why the camera is doing what most photographers would want?

Manfred has given you the explanation. The camera is aiming to keep the shutter speed up as you zoom in in order to prevent shake. The old rule on film was always to use a shutter speed the reciprocal of the FL. So a 300 mm lens hand-held = minimum shutter speed 1/300. Today with lens/camera stabilisation or if you are on a tripod you can get away with more leeway.

I rarely use Auto ISO.

[Stagecoach]

Manfred has given you the explanation. The camera is aiming to keep the shutter speed up as you zoom in in order to prevent shake

I had not been aware that is a function available on some DSLRs, interesting.

I see it's available with some Sony cameras

[MrB]

If your camera has an APS-C size sensor, then a 300mm focal length has the equivalent field of view of a 450mm lens on a full-frame sensor camera. So, in an auto mode, the camera will attempt to set a shutter speed close to 1/450 of a second to minimise blur from camera movement. It selected 1/500s which is pretty close to 1/450s. However, that is a very short exposure time, so it will reduce the amount of light reaching the sensor which would darken the image. Therefore the camera has raised the ISO to 800, effectively to brighten the final image back to an acceptable level.

Is there some good reason for you selecting f/22 - a very small aperture. Increasing the aperture should cause the camera to choose a lower ISO value, e.g f/11 should give ISO 200.

Philip

[pschlute]

I'm confused now as two different calculators tell me its 14.67/15 EV as per sunny 16. What am I missing, f/22, 1/500s and ISO 800, no doubt something obvious?

I don't think you are missing anything. f22 vs f16 is 1 stop underexposure. 1/500 vs 1/800 is approx 0.75 stop overexposure. Pretty much "sunny 16" adjusted for f22

[pschlute]

I had not been aware that is a function available on some DSLRs, interesting.

I see it's available with some Sony cameras

I think it is is a pretty standard programming parameter. Most cameras allow you to tweak it further by choosing a "sports" mode or change a setting that keeps the shutter speed up at the expense of ISO. This only applies when you are allowing the camera to choose two of your exposure triangle variables (one of which must obviously be shutter speed).

[pschlute]

Is there some good reason for you selecting f/22 - a very small aperture. Increasing the aperture should cause the camera to choose a lower ISO value, e.g f/11 should give ISO 200.

Philip

Good point, shooting at f22 can also lead to diffraction, causing your image to suffer in overall sharpness.

[Stagecoach]

I think it is is a pretty standard programming parameter. Most cameras allow you to tweak it further by choosing a "sports" mode or change a setting that keeps the shutter speed up at the expense of ISO. This only applies when you are allowing the camera to choose two of your exposure triangle variables (one of which must obviously be shutter speed).

I picked it up from here when doing a quick search ....................... STD (Standard)

ISO AUTO Min. SS
If you select [ISO AUTO] when the shooting mode is P (Program Auto) or A (Aperture Priority), you can set the shutter speed at which the ISO sensitivity starts changing.
This function is effective for shooting moving subjects. You can minimize subject blurring while also preventing camera shake.

MENU → (Camera Settings1) → [ISO AUTO Min. SS] → desired setting.
Menu item details
FASTER (Faster)/FAST (Fast):
The ISO sensitivity will start to change at shutter speeds faster than [Standard], so you can prevent camera shake and subject blurring.
STD (Standard):
The camera automatically sets the shutter speed based on the focal length of the lens.
SLOW (Slow)/SLOWER (Slower):
The ISO sensitivity will start to change at shutter speeds slower than [Standard], so you can shoot images with less noise.

[pschlute]

I picked it up from here when doing a quick search .....

Exactly the reason why I never mess with those kind of settings and very rarely use auto ISO, prefering to use fixed ISO and Av or Tv mode or Manual mode.

If I relied on a setting hidden within the darkest corners of the menu, how would I ever remember what I had last set it to when picking the camera up ?

[dje]

I picked it up from here when doing a quick search ....................... STD (Standard)

ISO AUTO Min. SS
If you select [ISO AUTO] when the shooting mode is P (Program Auto) or A (Aperture Priority), you can set the shutter speed at which the ISO sensitivity starts changing.
This function is effective for shooting moving subjects. You can minimize subject blurring while also preventing camera shake.

MENU → (Camera Settings1) → [ISO AUTO Min. SS] → desired setting.
Menu item details
FASTER (Faster)/FAST (Fast):
The ISO sensitivity will start to change at shutter speeds faster than [Standard], so you can prevent camera shake and subject blurring.
STD (Standard):
The camera automatically sets the shutter speed based on the focal length of the lens.
SLOW (Slow)/SLOWER (Slower):
The ISO sensitivity will start to change at shutter speeds slower than [Standard], so you can shoot images with less noise.

Which Sony camera Grahame? It's not available on my a6000 or on my Nikon D610.
Dave

Edit: Correction to underlined statement above added in post 51.

[Stagecoach]

I don't think you are missing anything. f22 vs f16 is 1 stop underexposure. 1/500 vs 1/800 is approx 0.75 stop overexposure. Pretty much "sunny 16" adjusted for f22

That's as I thought, but could not understand why Ted considered there was something "badly wrong" with the settings as given.

[Stagecoach]

Which Sony camera Grahame? It's not available on my a6000 or on my Nikon D610.
Dave

It's the Sony ILCE-9, here's the link Dave https://helpguide.sony.net/ilc/1650/...001477988.html

Whilst it's obvious to most of us that faster shutter speeds are better for longer FLs I had not heard of cameras using that variable logic in their 'Auto ISO' systems.

[dje]

It's the Sony ILCE-9, here's the link Dave https://helpguide.sony.net/ilc/1650/...001477988.html

Whilst it's obvious to most of us that faster shutter speeds are better for longer FLs I had not heard of cameras using that variable logic in their 'Auto ISO' systems.

Thanks Grahame

I wasn't aware of this feature either. It sounds to me like it might only be available in recent high end cameras?

Dave

[Stagecoach]

Thanks Grahame

I wasn't aware of this feature either. It sounds to me like it might only be available in recent high end cameras?

Dave

Maybe just mirror-less, but we still don't know what camera David has and whether this is applicable to his situation as described.

[Manfred M]

The old rule on film was always to use a shutter speed the reciprocal of the FL. So a 300 mm lens hand-held = minimum shutter speed 1/300. Today with lens/camera stabilisation or if you are on a tripod you can get away with more leeway.

That rule applied to viewing an 8" x 10" (~ A4 size) print held 30cm / 12" away. Larger size prints required higher shutter speeds.

I rarely use Auto ISO.

That is something I generally do as well, but have found that Auto-ISO works well when shooting conditions have highly variable lighting conditions. When shooting at outdoor events where the action moves from full sunshine to full shadow, Auto-ISO works well.

As a rule I try to shoot with as low an ISO as I can (just like in the film days), to maximize image quality (noise, colour bit depth and dynamic range).