the exposure triangle

[Donald]

Kind of . .is this done for creative control or to tweak DOF i assume the latter im trying to get my head around this because on my shoot i used a s/speed of 1/250 and someone suggested i lower that to 1/160 to let more ambient light in there has to be some kinda table i can consult im afraid my mind has a mental block when numbers come up but im determined to understand this is it like driving i can do 30 mph in 1st gear but i can also do the same speed in all the gears obviously i labor the engine in the lower gears ? so to compensate i change gears but im still doing 30 mph does that make sense ??

BINGO! Got it. I'm going to save that because it's as good a way of explaining it as I've seen.

One way I think about it when I'm out there is:

1. Okay, I want to be at ISO100.
2. What aperture do I want for this shot (and that is about DoF)?
3. Okay, with those two set, what shutter speed does the camera tell me I need? Is that going to be okay, or do I need to adjust one of the other two variables in order to be able to get a different shutter speed?

Now, to go back to your example above. If someone told you to move from 1/250th to 1/160th to get more ambient light (without changing aperture or ISO setting), then that is right. You're slowing down the shutter but still goign with teh same aperture value. So, more light is going to get in. That will give a brighter photograph. But that then is where the Histogram comes in to play, because if you keep doing that, then at some point (1/160th, 1/125th, 1/90th) you're going to be over-exposed. The histogram and the 'blinkies' (have you got tot hem yet?) are there to help you with that management of the exposure.

[Colin Southern]

Hi Colin

I seem to remember asking that same question . .and the answer was to use manual when the shot wasnt possible using AV this was demonstrated a couple of times and the exposure light was forever blinking in camera as i understand it . . once you select the right ISO for whatever your shooting (hand or tripod ) and you dial in the aperture to control DOF . .then all thats left is to is to regulate the shutter speed to ensure correct exposure ? what i cant seem to grasp is obtaining the same shot using different apertures etc . is it all about balancing things out to get the shot but how do you decide on the correct balance ?

Hi Mike,

Personally, I only ever use manual exposure either in the studio (where the lighting is totally controlled), or outside when I want consistent exposures for some reason (eg shooting a panorama) (I do use bulb mode a lot, but that's slightly different, as noted below). Ultimately though, setting the exposure manually by manipulating the shutterspeed & ISO (for a given aperture) to ensure that the exposure indicator is centred is technically no different to just being in Av mode; either way you'll end up with the same exposure - the only difference is that the camera will work out what that shutterspeed needs to be instantly, whereas it takes us humans a few more seconds.

Not sure what you mean by "exposure light" blinking - if you mean the aperture / shutterspeed blinking because the shutterspeed needed to be greater than 30 seconds for less than 1/8000th of a second (or the equivalent min/max for aperture) then "yes" - that would be another reason to take control manually (I say "yes" because in that situation you'd need to use bulb mode because manual mode won't let you select a shutterspeed outside of these parameters).

So not saying that doing it manually is wrong -- just saying there's no advantage to it a lot of the time. Bit like owning a dog and barking yourself!

[Colin Southern]

Kind of . .is this done for creative control or to tweak DOF i assume the latter im trying to get my head around this because on my shoot i used a s/speed of 1/250 and someone suggested i lower that to 1/160 to let more ambient light in there has to be some kinda table i can consult im afraid my mind has a mental block when numbers come up but im determined to understand this is it like driving i can do 30 mph in 1st gear but i can also do the same speed in all the gears obviously i labor the engine in the lower gears ? so to compensate i change gears but im still doing 30 mph does that make sense ??

Hi Mike,

It really depends on what you want to achieve. If you want to tweak DoF then you do that by changing the aperture; in manual exposure mode you need to make a corresponding change to the shutterspeed, but in Av mode the camera will make the change automatically for you. If on the other hand you're wanting to increase the exposure then in manual exposure mode either opening up the aperture or decreasing the shutterspeed will accomplish that - whereas in Av mode (or Tv mode) (say for example if the camera wasn't metering the scene to your satisfaction) then you'd just dial in some exposure compensation and the camera will vary the exposure for you.

[mishlove]

Wow...all this, most interesting.....but way beyond me, maybe one day I may even retain some of this, or even use it, right now I go out weekly, shoot what I see whilst playing minimally with the setting, and love every minute of it.....

[Lucille]

Hi Mark, You need to multiply this by the crop-factor as well...

Thanks, Colin. I didn't know about the crop factor. That explains a lot.

[mike the bike]

Thanks Donald and Colin im just reading all this and it will take me some time to digest but i believe im getting there now . I think its just a case of setting a given aperture and iso then adjusting the shutter speed to obtain the correct exposure . . using the cameras metering system i read of many pros who swear by AV and some by Manual personally i use AV a lot but i do want to understand how to use manual and ultimately how to exploit it ( i also use bulb and im ok with that . . for now ! ) with regardsd to mishlove dont worry it will all become apparent eventually youve gotta keep at it im still learning and it is overwhelming at first i suggest you search these forums for a topic that you need help with read and read again then post questions the people on here are VERY helpful as you can see . .

Ps
oh yes mate i look at the "blinkies" all the time and the histogram and ive started to ettr !!i can do it but as of yet i cant understand WHY i do it ??

[mike the bike]

Yes colin i think that was what i was doing . .i set the ISO and the aperture and i had to adjust my shutter speed to retain those values for the shot i wanted i assume now i can apply the same logic to any ISO or Aperture setting ??? er.. dont even think of mentioning focal length crop factor or warp capability im goin into bloody meltdown as it is . .(LOL)

even though im in Manual im still reliant on the camera "working out" the correct exposure for the given choice of values ( the "needle") RIGHT ??

[Colin Southern]

Thanks, Colin. I didn't know about the crop factor. That explains a lot.

Hi Lucille,

You're welcome. Just keep in mind though that the "1/Focal Length x CF rule" is really just a rough guide - it's certainly possible to get camera shake at higher shutterspeeds, and it's certainly possible to get sharp shots below this speed (especially if using IS). Personaly, I just use it as an indication of "how close I am to the danger zone", and shoot accordingly.

[Colin Southern]

Yes colin i think that was what i was doing . .i set the ISO and the aperture and i had to adjust my shutter speed to retain those values for the shot i wanted i assume now i can apply the same logic to any ISO or Aperture setting ??? er.. dont even think of mentioning focal length crop factor or warp capability im goin into bloody meltdown as it is . .(LOL)

even though im in Manual im still reliant on the camera "working out" the correct exposure for the given choice of values ( the "needle") RIGHT ??

Hi Mike,

I think you're on to it. In essence it's a case of either adjusting the exposure manually until the "needle is in the middle" or letting the camera "adjust it for you" - there's really no difference to the shot taken. If, say, you wanted to over-expose the shot by 2 stops (perhaps because the camera was mis-evaluating the scene) then you could either twiddle the knobs so that the meter read 2 stops over, or dial in 2 stops of exposure compensation (ie meter in same place) -- either way - again - same result.

What IS far more versatile is using manual mode in association with spot-metering, but that's a lesson for another day (as there's a bit more to it than meets the eye, but it's immensly powerful when you understand it).

[mike the bike]

Hi Colin .

Ive been thinking bout this all day thats how i get my head around things and being out on the bike kinda clears my head !!. Im assuming that at the set up stage you decide what ISO you need (depending on the conditions 100 for sunny days . . 400 for slightly overcast . . 800 + for grey overcast stuff etc . ) and then you decide on the aperture portraits less DOF landscapes = more DOF . . ok so now those values are locked into the camera all thats left is to adjust the shutter speed (taking into account what you said bout EV . ) and the metering system will correctly expose the shot according to the parameters you have set right ? the shot i took of Marina i used TV and a shutter speed of 1/250 which is the right speed for the lens i was using if id gone down to 1/60 would i have induced camera shake ? i was hand holding with a high ISO as i understand it its a matter of balancing these 3 parameters to obtain the shot you want a constant trade off . . and using my "driving" analogy i was trying to work out where the constant was . ? MPH = ISO ? gears = shutter speed ? i came up with this analogy so i could make sense of all this but now (at the risk of sounding stupid . ) i need someone to turn on the lightbulb for me using this analogy sorry to be going on but i know you guys will help me sort this and i thank you

[Colin Southern]

Hi Mike,

Last time I rode a motor bike for any serious distance was back in my farming days and it used to clear my mind too (well numb it anyway) ... it was a few degrees below zero (degC) and I had to practically peel my fingers off the handlebars one by one, being careful not to snap them! You might think that wearing gloves would be the obvious answer ... and you'd be right. Don't know why I didn't think of it! Never mind - the cows have a couple of ways of warming us up in the shed, unfortunately

With regards to exposure et al - yeah - basically. You'll always have a set of competing compromises -- if the shutterspeed is too slow you may get camera shake and/or subject motion; if the aperture is too big you may get insufficient DoF, and if the ISO is too high you'll limit your dynamic range that the camera can cleanly capture. Sometimes it's not hard to strike a comfortable compromise (in fact a lot of the time it isn't hard), but at other times, you'll have things right on the very edge (and may still not get things right) (such are the limits of the technology).

Most of the time you'll want to be in Av mode, because most of the time you'll want control over DoF, and (of course) we do that with the aperture). With that variable "locked in" the next thing that's likely to damage our image will be shutterspeed related; for general shooting I'll consider the shutterspeed in relation to focal length and things like IS availablity / Tripod availability. If (for example) it's a hand held shot at dusk and I'm down to 1/8th @ 200mm (even with IS) then I'll be "upping the ISO" (considerably).

I should point out that none of this really affect manual -v- automatic exposure selection - it's really only a choice between you selecting all 3 variables, or selecting 2 and letting the camera take care of the remaining one. If you've using an incident light meter - and shooting a black cat on a black rug - then you probably will want to be in manual mode (auto mode can too it too, but you'll need exposure compensation), but most of the time Av mode will accound for changes in lighting a lot faster than we humans can.

[Dave Humphries]

Im assuming that at the set up stage you decide what ISO you need (depending on the conditions 100 for sunny days . . 400 for slightly overcast . . 800 + for grey overcast stuff etc . ) and then you decide on the aperture portraits less DOF landscapes = more DOF . . ok so now those values are locked into the camera all thats left is to adjust the shutter speed (taking into account what you said bout EV . ) and the metering system will correctly expose the shot according to the parameters you have set right ? the shot i took of Marina i used TV and a shutter speed of 1/250 which is the right speed for the lens i was using if id gone down to 1/60 would i have induced camera shake ? i was hand holding with a high ISO as i understand it its a matter of balancing these 3 parameters to obtain the shot you want a constant trade off . . and using my "driving" analogy i was trying to work out where the constant was . ? MPH = ISO ? gears = shutter speed ? i came up with this analogy so i could make sense of all this but now (at the risk of sounding stupid . ) i need someone to turn on the lightbulb for me using this analogy sorry to be going on but i know you guys will help me sort this and i thank you

Hi Mike,

You're getting there with your decision making on selection of iso, shutter speed and aperture, so I do wonder why you still need an analogy? Is it because the light bulb hasn't got come on for the interaction between the three? There are two levels to that; numeric and conceptually. I'll look at conceptually ...

OK; I just thought how to make the driving analogy work;

• gear selected = aperture
• engine rpm = shutter speed
• throttle twist = iso ('twist' because you're a biker, car drivers should think 'pedal depression')
• road incline = scene light level
• speed = exposure - we're aiming for say, 30 mph as being "correct" (the number is irrelevant)

On the level, we can do 30 mph as;
4,000 rpm in 1st gear,
3,000 rpm in 2nd,
2,000 rpm in 3rd,
1,000 rpm in 4th,
500 rpm in 5th (with camera shake!)

If we meet an uphill incline (less light), we need more throttle (iso) to maintain correct speed (exposure)
If we coast down an incline, we need less throttle, or we'll over expose

That works quite well I think
Except I wouldn't want to drive a car/bike with those ratios!

We can;
think of engine rpm as 1/4000s, etc.
think of gear as half aperature; 1st = f/2, 2nd = f/4 upto 5th = f/10
think of throttle twist in say tenths of a degree for iso
think of uphill as cloudy days and downhill as sunny days
OK, don't read too much into the numbers, they certainly don't equate to each other mathematically, but they sorta go in the right directions relatively speaking.

Does that help?

EDIT: It just occurred to me that this also deals with the manual vs Av (aperture priority) shooting decision.
Shooting manual would equate to driving at the correct speed by using the tachometer reading and relying on knowledge that at a given gear and rpm, 30mph will result.
Shooting semi-auto (Av), you select the gear and use the speedometer to tell you when 30 mph is achieved, you really don't need to know the rpm (or shutter speed) within limits.

Cheers,

[mike the bike]

Bloody Hell Dave !!
Thank you for obviously taking time out to mull all this over just to help me out Im gonna have to read this through very carefully and ingest . the main reason i took the course was to help me to demistify Manual . .i had no idea owning a super doooper camera why anyone would wanna use it at all , why bother when its all done for you ? and if thats the case then why bother with SLRs at all . . i rest my case on that point ! i WANT creative control . .i WANT to do things for myself I WANT to be able to understand HOW something is achieved and apply that process to other shots in this day and age automation is everywhere cars bikes ets so much "input" from humans is slowly (and insidiously . .) being factored out of the equation i heard the other day of a camera that takes a shot without the need for focus ( that is taken care of post shot . .) now i have to admit i like all my "Gadgets" but im the master . . .they exist to enhance my life not control it WAKE UP AINT YOU SEEN THE TERMINATOR MOVIES ?? (are you listening spotty yooofs with the latest all singing all dancing mobile fones . .) i just dont feel comfortable having technology making all my desicions all the time . if that were the case then how can anyone rightly say that they took the shot ? NAH the CAMERA took the shot you just pressed the button (HA . . "and the monkey flips the switch" come on movie buffs . .which film delivered that immortal line then ? )
Im labouring the point to put it succinctly i just want to harness/exploit all my cameras potential and yep AV has its place . .and some automation is ok but i want the choice to override for the sake of being the driver and not just the operator . .

Sorry i wont bring my soap box next time and i hope i aint offended anyone please take all the above with a VERY large pinch of salt my tongue was very firmly in my cheek !!

[mike the bike]

Thanks Colin
With regards to "competing Compromises" that seems to be the crux of it all . but surely you are kinda limited in so far as the conditions at the time so in a way there can only be a small degree of choice ?IE: in regards to the ISO now i understand this its fairly straightforward and there are times ive deliberately used high ISO for artistic purposes . . (my avatar pic is a case in point ) so i get that completely . . now the reason i switched from a P&S compact was to have more control over the flash and to blur the backgrounds out. So i bought a Canon 400 D and for awhile i stayed on Automatic . realising id just substituted one camera for a heavier one i decided to explore the other options enter my 55/250 telephoto lens which cost me £200 second hand . now i switched to AV and began utilising DOF which was what i wanted i went out and shot at all the F stops using some fencing so i could see the effect in post . . and voraciously consumed magazine articles pertaining to DOF . job done i can now do that and its a valid technique every photographer should learn if they want their shots to stand out from the norm . . Now i want to get into being creative with shutter speed so i now switch to TV and begin shooting fast moving objects Bikes Cars etc . little bit tricky in so far as you have to learn how to pan and select the right shutter speed . . Small aperture = more light . . Large aperture = less light . So this is where i am at the moment i have shot some nice action shots and its getting there and to me thats half the fun . .if it was easy then there is no sense of accomplishment with TV and Manual there are soooo many things to equate (im not great with numbers) and sometimes it has to be said my brain just goes into meltdown . Now on the course i was shown how to do various things i mimmicked a lot but also saw how things were done and yep i took it all on board and i saw how things were achieved but i dont understand it enough to explain it to someone else . . for me all these nunbers just complicate the issue and i am trying to overcome this mental block and everyones posts shed more light as i read and ingest . i guess one way would be to go spend the day on Oxford St just shooting people using different settings to see how things work . .or not . (making mistakes teaches us more about what we do wrong as opposed to being told how to do things right )

Or i could just pay Dave to show me ?

[Colin Southern]

Hi Mike,

It's certainly good to play around with these things, but having just said that, I doubt you'll use Tv mode much (I don't know anyone who does to be honest), as you lose control of the aperture - whereas in Av mode you have control of the aperture (DoF is usually the biggest issue), and you can guarantee a minimum shutterspeed for that aperture by setting the ISO (plus, there are far fewer stops of aperture than there are shutterspeed - so it's pretty easy to run out of aperture adjustment if you're not keeping a close eye on changing conditions.

but surely you are kinda limited in so far as the conditions at the time so in a way there can only be a small degree of choice ?

It really depends on the shoot. If you're trying to shoot indoor sports with an F5.6 lens then you probably won't have a lot of wiggle room, whereas low light landscape with a tripod you often have anything from F11 to F32, 30 sec + and ISO 50 to "lots" to play with, but having said that, it still usually comes down to a bit of a "sanity check" where certain combinations are more convenient (say using F11 and ISO 400 for a 4 minute exposure rather than F32 and ISO 100 for a 2 hour exposure) (especially when you're standing in water during winter!) (keeping in mind that the light is often changing in this time also).

[mike the bike]

AAAH there it is . .combinations ! the 3 variables ISO . S/Speed & Aperture as i see it these are the main ingredients for our mix now . . is there a baseline ? a starting point for a given set of conditions ? a point we can go from base camp to where we make the final ascent to the summit i guess exmples in hypothesis are needed now to bring this discussion to its conclusion starting really simple with the basics .
EG:
bright sunny day/handheld shot/subject 100mm away (subject could be anything; person birdtable structure etc . )
to make this shot i would use : ISO 100 (to ensure the optimum clarity)
One Shot Focus + Evaluative Metering
Auto W/B (im shooting in RAW so can change in PP if needed )
AV so i get to choose the Aperture and the camers decides on the shutter speed
Compose half depress the shutter and take the shot . . bingo a nice clean image good DOF .
everything in focus perfect .

That is the starting point fairly basic nothing to complicated now . next scenario

Cloudy day slightly overcast same focal length same subject . .
i would use :
ISO 200/400 this is to ensure a faster shutter speed now because the conditions are less than perfect i have to take some other things into consideration now i have to make desicions and changes within the camera to ensure i get a good shot now i have to understand how to swap things around to juggle and to compensate the 3 variables to make them "line up" to make my shot the ISO determines clarity whilst keeping degredation to a minimum (noise) this in turn dictates what my aperture will do which in turn affects my shutter speed . .

It is here at this juncture that my skills begin to crumble is there a baseline i can start at to practice learning how these variables interact does anyone have any suggestions that i can take into the field ?

[Colin Southern]

Hi Mike,

In both scenarios I'd dial in the aperture I wanted, and then meter the scene to see what shutter speed the camera offered me, and go from there (primarily with regard to the focal length and IS availability).

If its too low then ... Bump up the ISO.

[mike the bike]

Cool . then if AV couldnt meter (for whatever reason) i could then go to manual ? i often read of people reading the scene in AV or TV then switching to manual to achieve the desired shot
If the camera

[Colin Southern]

Cool . then if AV couldnt meter (for whatever reason) i could then go to manual ?

Sorta / Kinda. In that scenario you'd have to work out the exposure some other way though (or guess), because the metering that gives you your shutterspeed (aperture) in Av (Tv) mode is the same metering that gives you your exposure indication in the viewvinder.

i often read of people reading the scene in AV or TV then switching to manual to achieve the desired shot

Yes. There's nothing "wrong" with doing that (and there can be valid reasons for doing it - like when spot-metering), but most of the time there's just no point in doing it, as you achieve the same result - so it's just extra work for no reward.

[Dave Humphries]

now i have to make desicions and changes within the camera to ensure i get a good shot now i have to understand how to swap things around to juggle and to compensate the 3 variables to make them "line up" to make my shot the ISO determines clarity whilst keeping degredation to a minimum (noise) this in turn dictates what my aperture will do which in turn affects my shutter speed . .

It is here at this juncture that my skills begin to crumble is there a baseline i can start at to practice learning how these variables interact does anyone have any suggestions that i can take into the field ?

Have you read the Tutorial Mike?

Thinking in whole stops, whatever the light and settings;
ISO doubles or halves
Shutter speed doubles or halves
Aperture is peculiar; the one stop list of values is 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32 - you can see how alternate numbers double.

Small aperture = more light . . Large aperture = less light

You do have to be careful describing apertures though, or people may 'correct' you even if you actually know what you mean

If you describe the iris as "wider" and "narrower", or the f number as being "higher" or "lower", it is unambiguous and better than just saying "larger" or "smaller" when describing expected DoF or effect on exposure.

Cheers,