Beginner Aperture calculations

Thatchapthere

Thatchapthere

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Hey, guys!

Sorry if this is going over old ground for some, however I'm in a bit confuzzlement re exact aperture. I understand the rudimentary stuff; low F number for shallow DOF and vice-versa - plenty of reading done in this regard.

At the moment however, I feel I'm just guessing the aperture for max focus. I'll say, ''if thats quite close then I'll need to use a low F number'', following that rule along the F number/distance range. Tho as mentioned I feel its just guess work at the moment based on the principle I'm following.

Should I be using one of them DOF calculator thingy-ma-bobs and learn from that?
 
Choosing aperture will depend on light available and what look you are trying to achieve i.e. shallow depth of field, or 'everything' in focus. You can use calculators but I find I'm not the best at judging subject distances and interpreting what, for example 0.56m DOF is going look like overall with my final image and so don't find DOF calculators useful half the time (some do though, and if you do they are a great tool). Experience plays a large part, also some cameras have preview buttons so that you can see the effect of aperture, and sometimes just reviewing the image can tell you if DOF is too large/too small and so you can re-shoot. Clearly it's best if you can get it right first time, but the beauty with digital is that you can take as many pics as you like. I personally find taking a shot, reviewing the image and adjusting the aperture accordingly much faster than judging distance, and then inputting the relevant details into the calculator (I'll probably get flamed for this ;)). With experience you need to do this last bit less and less as you instinctively know what aperture to use.
 
Think of f numbers as a fraction of 1. Thus, f/11 = 1/11th of a circle. F/2.8 (ok round up to 3) = 1/3rd of a circle. Which is the bigger slice? That is the wider aperture.
Don't over think which aperture to use. If you want all or most of the scene in focus, start with f/8 or f/11 and go from there. If a small aperture reduces your shutter speed such that you get camera shake, you have the choice - up the iSO OR widen the aperture.

Aperture has no effect on focus. You need to use the autofocus capability to focus accurately on the subject in the image. If there is 'no' subject, just a landscape, then focus on something 1/3 way in the pic.

Learn about the exposure triangle. It will speed up your knowledge.
 
Thatchapthere said:
Hey, guys!

Sorry if this is going over old ground for some, however I'm in a bit confuzzlement re exact aperture. I understand the rudimentary stuff; low F number for shallow DOF and vice-versa - plenty of reading done in this regard.

At the moment however, I feel I'm just guessing the aperture for max focus. I'll say, ''if thats quite close then I'll need to use a low F number'', following that rule along the F number/distance range. Tho as mentioned I feel its just guess work at the moment based on the principle I'm following.

Should I be using one of them DOF calculator thingy-ma-bobs and learn from that?
Click to expand...

Just go out and shoot. The more you take, the more you will realise what is going on.
It all falls into place eventually.

Don't let it get in the way of the enjoyment.
 
kendo1 said:
Just go out and shoot. The more you take, the more you will realise what is going on.
It all falls into place eventually.

Don't let it get in the way of the enjoyment.
Click to expand...

That

Ive been taking photos for something like 35 years , I have never used a Dof calculator
 
big soft moose said:
That

Ive been taking photos for something like 35 years , I have never used a Dof calculator
Click to expand...

I've only been doing it 30, but I've never used one either...

And clearly I spent most of that time with manual only cameras, but I never heard the phrase 'exposure triangle' until a few years ago, and apparently it's impossible to shoot manually without learning that first
 
Phil V said:
I've only been doing it 30, but I've never used one either...And clearly I spent most of that time with manual only cameras
Click to expand...

We did have rather handy DoF markings on old manual lenses though. And quite often rather quaint DoF 'stop-down' preview button.
Useful if you wanted to put your DoF where you wanted it and focus ahead or behind your subject, rather than on it( them?) and get 1/3 in front 2/3 behind.

Phil V said:
, but I never heard the phrase 'exposure triangle' until a few years ago, and apparently it's impossible to shoot manually without learning that first
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But, Phil! You HAVE to, you just must! its like, like, well, Forty-TWO!;)
 
Teflon-Mike said:
We did have rather handy DoF markings on old manual lenses though. And quite often rather quaint DoF 'stop-down' preview button.
Useful if you wanted to put your DoF where you wanted it and focus ahead or behind your subject, rather than on it( them?) and get 1/3 in front 2/3 behind...
Click to expand...
You're right the lenses were marked up, but DoF preview buttons were as useful then as they are now (actually improved with EVF's).
 
DOF vs distance and aperture (when shallow):
If you change the distance by 2 (2x or 1/2) you have to adjust the aperture by four stops in order to keep the same DOF.

changes of 2 (2x or 1/2)
Aperture- DOF also changes by 2
FL- DOF changes by ~4 (4x,1/4)
Distance- DOF changes by ~4

FL & Distance affect in opposite directions... if you increase FL & Distance together to keep the same subject framing the DOF will remain ~ the same.

I also use a rough guide of 1+1=2. 100mm(1) at 10ft(1) gives a 2ft DOF (f/16 w/1.5DX, f/11 w/FF). From there I can quickly swag a rough estimate of the DOF... no need to be exact, just an idea of "enough or not."

DOF preview is about useless, as is reviewing an image on the LCD.
If it's a situation you work in frequently, eventually you "just know" because you've used those settings in that situation numerous times already.
 
I thought cows week wasn't till august :p
 
Phil V said:
I've only been doing it 30, but I've never used one either...

And clearly I spent most of that time with manual only cameras, but I never heard the phrase 'exposure triangle' until a few years ago, and apparently it's impossible to shoot manually without learning that first
Click to expand...
Last century in the days of film it wasn't so much of a triangle because ISO wasn't something you could adjust per shot. It was written on the film packet plus whatever adjustment your development of that roll chose.

Weird that these young kids call it a "triangle" because it isn't. It's much simpler mathematically than a triangle, it's just a three variable compound. Maybe they don't teach the kids maths in school anymore :)
 
sk66 said:
Hasn't really changed... variable ISO is much like pushing/pulling film.
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No it's not.
Pushing or pulling film had to be done for a whole roll and affected the development requirement.
 
Its good you are doing your research to get a better understanding so you can make a decision based on what you want for your chosen picture.
But sometimes you just need to keep it simple with a rule of thumb.
- f2.8 when struggling with low light or want shallow dof.
- f8 when after a 'normal' portrait of 1-2 people
- f11 for groups of people or landscapes.

You can get a lot more complex with hyperfocal distances, diffraction, and calculators for your specific camera and lens combination and the distances you will be taking your shots at. However, since this is the beginners section, I'd recommend
1 - the above as a rule of thumb
2 - take another photo on either side of your choice (if possible. i.e. if f8 is basis then take the same shot at f4 and f11)
3 - then look at the pictures you take afterwards and think about if it could have been improved to your tastes by varying those parameters.

If you do this a few times, you should soon develop your own preferences and learn to work within the limitations of your camera equipment.
 
chris malcolm said:
it's just a three variable compound. Maybe they don't teach the kids maths in school anymore :)
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Sorry to hijack but could you expand on that a little, the triangle thing sort of makes sense but I would definitely appreciate another way of looking at it
 
I wouldn't like to put words into anyone else's mouth, but if you'd asked me to explain exposure in terms of three variables mathematical-fashion, I'd have taken the analogy of volume. The volume of a box is calculated by multiplying the length, width and height together - three variables which we can call L W and H, so that the volume V = LWH.

Think of correct exposure as being a quantity which is calculated from three variables, in this case aperture, time and sensitivity. Just as you can "fix" the volume of a box that you want and adjust the other variables to suit so that the volume remains the same, so with exposure. Want to double the time? Then reduce the aperture and/or sensitivity to suit.

It's just an equation of the form V = LWH where if you want to change L, W or H and keep V the same, you just slot in the numbers.

Having put in two equations (even though they are the same) I have just lost nearly all my readers (according to conventional advice to authors) :D
 
Actually "exposure" is three variables, but ISO is not one of them. It is light, SS, and aperture... that is truly what controls how much light/data is collected (the exposure) just as it always was.

But since we now have "variable ISO" we have started thinking in terms of the "exposure triangle"/metering and largely ignore any thoughts of controlling/choosing the light (adding/reducing). The problem with this is that ISO isn't actually changing the sensor's sensitivity/reactivity to light as it was with film. ISO is amplification of the signal *after* the exposure.
 
That sort of makes sense, but how do we adjust the sensitivity if it is not the ISO setting doing this

Would this be exposure comp?
 
buy a 50mm 1.2 and play ....

(or more realistic) get a 50mm 1.8 which is typically cheap as chips and have a play with that and see what results you can achieve changing the f number.
 
Petejones said:
That sort of makes sense, but how do we adjust the sensitivity if it is not the ISO setting doing this

Would this be exposure comp?
Click to expand...
I think the point is that you don't adjust the sensitivity, as it's a physical attribute of the sensor, so it's done in software. However, that's overly technical and we generally refer to the ISO being adjusted in camera as if it's a physical change - it's not, but knowing that doesn't really help any.
 
Petejones said:
That sort of makes sense, but how do we adjust the sensitivity if it is not the ISO setting doing this

Would this be exposure comp?
Click to expand...

No, exposure compensation is a manual override of settings suggested by the camera's metering system when it thinks it's right, but is not.

Try the water/bucket analogy. Correct exposure is when the bucket is filled to the top.
- shutter speed is how long you leave the tap on
- lens aperture (f/number) is the flow - how hard you turn on the tap
- ISO is the size of the bucket
and then:
- water pressure is the brightness of the light

Steven is right, strictly speaking, but that's not how we work and it's not helpful when talking about the camera's three exposure controls.
 
HoppyUK said:
No, exposure compensation is a manual override of settings suggested by the camera's metering system when it thinks it's right, but is not.

Try the water/bucket analogy. Correct exposure is when the bucket is filled to the top.
- shutter speed is how long you leave the tap on
- lens aperture (f/number) is the flow - how hard you turn on the tap
- ISO is the size of the bucket
and then:
- water pressure is the brightness of the light
...
Click to expand...

My favourite part of this analogy is when we start looking at the size of the buckets as the things that capture light (and think of light as a physical object), with low ISO we have really big buckets so it's easy to see how much light they each get filled with giving accurate colour representation, once the bucket is full that's 'white' and no matter how much extra light you try to get in, it'll hold no more - so an overexposed pixel can never be manipulated in post to give up detail. A tiny amount of light falling into the bucket is very hard to measure and trying to amplify the tiny signal just produces noise because we don't have a measurable amount of information - so we can attempt to pull detail from shadows, but we only get limited success before there's more rubbish than actual data.
Of course at higher ISO's we're stretching a small amount of information in each bucket, and the more we try to glean from it, the more the software's guessing just turns to rubbish.

Of course in reality - sensor technology is much more complicated than this but it's easy to understand and is near enough the truth that it works.
 
sk66 said:
Actually "exposure" is three variables, but ISO is not one of them. It is light, SS, and aperture... that is truly what controls how much light/data is collected (the exposure) just as it always was.

But since we now have "variable ISO" we have started thinking in terms of the "exposure triangle"/metering and largely ignore any thoughts of controlling/choosing the light (adding/reducing).
Click to expand...

I disagree. The exposure triangle is not a new concept. I was taught this back in the days of film on the Tri-Service All Arms Photographic Course at RAF Cosford back in the early 80s.

This still hold true today speed, aperture and ISO are intrinsically linked the control of all three effect the final output. If you want to start ignoring ISO then you may as well just use the 'P mode' and stop thinking altogether.
 
Okey dokey, my brain is hurting a little now so I'll read this a few times over the next week to try and make some more sense out of it
 
Blank_Canvas said:
I disagree. The exposure triangle is not a new concept. I was taught this back in the days of film on the Tri-Service All Arms Photographic Course at RAF Cosford back in the early 80s.

This still hold true today speed, aperture and ISO are intrinsically linked the control of all three effect the final output. If you want to start ignoring ISO then you may as well just use the 'P mode' and stop thinking altogether.
Click to expand...
ISO was always part of the equation... But it was fixed; you chose a roll and what was left was aperture/SS/light. That's where the "sunny 16 rule" came from. The same is true, perhaps more-so, today.

The difference between a sensor and film is that different ISO films had different sensitivities to light and sensors do not. In fact, we are getting very close to having "ISO-less"/"ISO neutral" sensors where you can recover underexposure in post equally as well as having used a higher ISO. The IQ of a sensor/image is entirely dependent on saturation in every aspect; i.e. aperture/SS/light determine noise(SNR)/DR/color/etc... ISO really only determines how bright it is (but digital ISO can add extra noise/errors).
 
HoppyUK said:
No, exposure compensation is a manual override of settings suggested by the camera's metering system when it thinks it's right, but is not.

Try the water/bucket analogy. Correct exposure is when the bucket is filled to the top.
- shutter speed is how long you leave the tap on
- lens aperture (f/number) is the flow - how hard you turn on the tap
- ISO is the size of the bucket
and then:
- water pressure is the brightness of the light

Steven is right, strictly speaking, but that's not how we work and it's not helpful when talking about the camera's three exposure controls.
Click to expand...

I've thought of something else for ISO, to please Steven :D

Raising ISO doesn't reduce the size of the bucket, it adds washing up liquid so the bubbles fill to the top. The bucket is still full, just not full of plain water, but water and other imprurities, ie noise etc.
 
sk66 said:
ISO was always part of the equation... But it was fixed; you chose a roll and what was left was aperture/SS/light
Click to expand...

ISO is still fixed today if you choose it and don't use Auto ISO.

I personally don't use Auto ISO which you are referring to, preferring to be in control of the the Aperture, Speed and ISO. It's just continuum of what I've been doing for 35 years. I do use Speed and Aperture modes but I want to be able to control the amount of noise produced (grain in emulsion days) that's why I choose not to use Auto ISO.

For me, In film days changes of light and ISO were not an issue due to the amount of film we got through. If necessary changing film mid-roll (or film backs) and changing the ISO accordingly due to rapid changes of light. No other option back then. That said I'm glad technology has evolved and it's just a flick of a dial or wheel. It's just that I am fully aware of the three primary controls and the effect of inter-operation on the final output of the image pre-processing and like to remain in control. It's all down to personal preferences if people want to shoot in Programme Mode / Auto ISO then crack on and stay within your comfort / Knowledge zone if it works for you.
 
Blank_Canvas said:
ISO is still fixed today if you choose it and don't use Auto ISO.
Click to expand...
I use auto ISO all the time...because w/in a certain range the penalties of using a higher ISO are not significantly worse/different than recovering in post (camera/software dependent). And it's also nice to be able to see/evaluate your images at the time. But it's also true that sometimes you may be better off underexposing and recovering in post, at least you get to decide where/how the noise/etc is added. And sometimes, underexposing and recovering in post can generate slightly "better" results than using a higher ISO; especially compared to digital ISO ranges (but not generally worth the hassles IMO).

I like the bucket analogy... I've taken it even farther and used cups vs buckets to help explain the differences between lower resolution/larger pixel sensors vs higher resolution/smaller pixel sensors.

And there's another aspect that plays into this... you can use a higher ISO in order to enable an even higher SS or smaller aperture when the light is stronger w/o the same associated penalties (less significant impact). That's because in low light it's like trying to capture a light sprinkle of rain in your cups/buckets. But in strong light it's like trying to capture a heavy downpour... even if you catch less of it, the cups/buckets will be more evenly filled. And that's what makes a lot of the online "high ISO tests" rather useless... they vary camera settings (Ap/SS) and not the light levels.
 
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