iso vs shutter speed

[Don_Won]

hello guys
i just recently bought myself a dslr camera (canon 500d) and ever since, ive been having more and more fun taking pictures. I'm currently at the stage where i start using manual settings instead of auto.
i've taken some pictures, with 2 entirely different settings, which (surprisingly for me) gave very similar results. 1st pic was taken with: 1/100s shutter speed, F6.3 and ISO 3200, whereas the second was 1/30s, F3.5 and iso 400. how did that happen?
also, if someone could please explain to me the basics of manual settings. like when do i use higher iso instead of a slower shutter speed? same with aperture vs shutter speed etc. all i know is that higher iso may cause noise.

like i said, im at the very beginning of my adventure with photography, and id really appreciate if someone helped me learn more about it, thanks

[eclap]

I guess you were using the kit lens. so let's say you used around 40mm zoom level. At 40 mm the difference between f6.3 and f3.5 will be negligible although still visible with to a trained eye. ISO 3200 is more grainy that ISO 400. Just try a 100% crop of both images and you'll see a lot more grain from the ISO 3200 photo. Also, at 40 mm 1/30 is often borderline for getting a sharp photo.

Now imagine using a 400mm lens, difference between f6.3 and f3.5 would be a lot bigger. Also, 1/30s would be clearly more blurry than 1/100. I'd suggest going back to presets and auto shooting until you know what you're doing.

Good luck.

[Miller]

A very basic explanation might be:

ISO - alters the "amplification" of the signal from the sensor. Increasing the ISO increases the noise of the photo and increases the shutter speed.

Changing the ISO becomes important particularly when shooting indoors in low light. Suppose your lens opens to F4 and at ISO 200 the shutter speed is only 1/30th of a second, at ISO 400 the shutter speed would be 1/60th.

You have to weigh up the choice of introducing more noise to the photo versus a slow shutter speed. Sometimes it's better to have an un-blurred photo with some noise than a noise-free photo with motion-blur.

[Glidefan]

Depends as well on what you want to do. want to take the picture of a fast mooving target? use a higher ISO to be able to crank up a faster shutter speed. That would make you a sharp photo of the moving target.
Want to grab the picture of something moving and having some motion blur for an effect?
Use a lower ISO value so that you will be able to lower the shutter speed to give you that effect.

[PCthug]

As a rule of thumb, use a shutter speed that is no slower than the focal length your shooting.
So, if your using the kit lens 18-55, and shoot at the 55 setting, then you dont want to be shooting any slower than 1/55 sec (actually 1/60 as cameras wont allow 1/55).
If its a 400mm lens, then 1/400 sec.
Any slower then you will get a blured shot (unless you use a tripod).

I recommend the oposite to eclap, and think you should keep using M mode, or at least shutter priority TV mode (Time Value) or aperture AV mode (aperture value). Thrown in at the deep end, you will either sink or swim.

The easiest thing to do is keep it in aperture mode, and then you can set the DOF (depth of field), and the camera will set the shutter speed for you. The higher the number for the aperture (f11 to f22 for instance) will mean a longer shutter speed and greater DOF (and smaller aperture). If the shutter speed gets too slow (a smaller number than the apeture size, like 1/20 sec at 55mm) then increase the iso (which will increase the shutter speed, but add more noise/grain).
By lowering the aperture number you will get a shallow DOF and a faster shutter speed.

ISO 100 will give a 'better' (clearer) picture (but slower shutter speed) than ISO 3200.

[eclap]

Pcthug - although I agree that shooting in manual is the best (all I ever use), I wouldn't bother with manual until I understand what ISO, aperture and shutter speed mean. I recommend reading up on the basics before dwelving into M mode, otherwise he'll end up with badly exposed blury nonsense...

[Finchwizard]

I generally don't even go into Manual mode that much.

I'm usually wanting to either adjust Shutter times or Aperture, so it's TV or AV for me.

I did a shoot at a Drama Production the other night, and had to shoot in 3200ISO, with the 70-200mm f/2.8 from the back of the room, and it's noisy, but you can generally hide the noise pretty well as well.

The only real time to increase ISO is if your shutter speed is too low. Otherwise keep it as low as you can at all times.

[ScoobyDooby]

Originally Posted by eclap

Pcthug - although I agree that shooting in manual is the best (all I ever use), I wouldn't bother with manual until I understand what ISO, aperture and shutter speed mean. I recommend reading up on the basics before dwelving into M mode, otherwise he'll end up with badly exposed blury nonsense...

Maybe at the start his shots will be blurry, but it will help in the long run to start working in Manual since naturally it offers the most control.
Better that than starting with the A or TV modes.. I find them totally useless. Thats what I did anyway.. read up on the manual, then started playing around

[Don_Won]

thanks for all your responses. Having read them all, and having taken some pics i start to understand the basics. I'm far from perfect of course, but at least i know what i'm talking about now

I don't use the kit lens. i have 2 lenses from my dad's old analog slr which are 28-80mm and 70-300mm, and here's another question. Someone told me that those lenses do not tranfer firectly into the dslr numbers... that the focal lengths need to be multiplied by 1.5. is it true?

[eclap]

1.6x on your canon 500d... so the 300mm will act as a 480mm on a 35mm film or full frame DSLRs (like canone eos 5d or nikon d3).

[chiefmasterjedi]

When I first got my camera I tried to shoot as much as possible in manual mode, so I could get a better understanding of how ISO, shutter speed and aperture effect exposure. Now I shoot nearly everything in aperture priority mode (AV on canon) and I lock my iso at 200. The reason for this is I normally shoot portraits of my daughter and I know what DOF I'm wanting and rather than dialing in the shutter speed and missing that important, one off shot, I just let the camera do the work. If I have strong back light or blown highlights I just adjust the exposure compensation and keep on shooting.

The only time I shoot manual now is macro and night photography. For macro I like to use 1/200 shutter speed (because I hand hold all my macro shots) F16 aperture and ISO 200. The rest of the maths is dealt with by the i-TTL flash and I'll dial in -/+ on flash compensation.
I'm no expert on the fine art of photography but I just do what I feel comfortable with. I think the mode you are shooting in depends on your subject and surroundings.

[UTHammy]

To get a better understanding of these three: ISO, Shutter (Tv) and Aperture (Av), you'll need to know that they work in unison - each affecting the other.

ISO - sensitivity of the sensor (think of ASA rating of film) The higher the ISO, the more sensitive the sensor is to light. This allows for faster shutter speeds, at the expense of more noise (due to the extra electricity being pumped to the sensor pixels)

Aperture - amount of light coming through the lens (think of your iris in your eye) The higher the number, the SMALLER the hole in the lens. The lower the number, the WIDER the hole in the lens, letting more light in. By default, when your camera is focusing, it is always wide open to get the most light. Only when the shutter fires, does the lens blades snap tighter for the exposure.
The other control that Aperture puts on your images is Depth of Field (DOF). The wider the opening, the more light gets bent by the glass, creating a shallow DOF where the subject is more infocus than the rest of the frame. A higher number (smaller opening) causes everything to be in focus as it limits the amount of light coming in through the lens.

Shutter - is just as it sounds - the amount of time the shutter is open, exposing the sensor. The faster shutter, the more it stops action - both of your subject and any camera shake that you may be imposing. The slower shutter lets more light in, allowing light to build up on the sensor - but possibly at the expense of the camera shaking at slow shutter speeds.

How they all work together, is that at any given proper exposure, if you change one setting, you'll need to change another one. Usually, you would do this for a desired effect:
- stop action: faster shutter - needs higher ISO or more aperture (lower number)
- Less DOF: low Av number, allowing more light in - needs lower ISO or faster shutter
- more DOF (scenics): high aperture number, letting less light in - needs higher ISO or longer shutter speed
- Lower noise: lower ISO - needs longer shutter or more aperture

And by changing one dramatically, one can compensate exposure by changing one or BOTH of the other two (in smaller increments)

So in your example:
1/100th, f/6.3 at ISO3200
By changing the ISO to 400, that is equal to 3 stops of light (3200 > 1600 > 800 > 400) which needs 3 stops of compensation for the other two (shutter and aperture)
1/100th to 1/30th is 1 and 2/3rds stops compensation (1/100th > 1/50th > 1/25th would be 2 full stops)
Finally, going from f/6.3 to f/3.5 is actually 1 and 2/3rds stops also (f/6.3 > f/4.5 is one stop, going to f/3.2 would be two stops)

So the second exposure was actually 1/3 stop over exposed compared to the first one - barely noticable, but what you'll see different in the two photos:
The first one will have more noise, more DOF but a faster shutter speed so less motion than the second which will be cleaner and less in focus.

Personally, I shoot Manual most of the time - except in dynamic lighting situations. And I prefer to shoot wide open with all lenses (200mm f/1.8 being my FAVORITE lens) to get only the subject in focus, allowing for faster shutter speeds also. My ISO is what I'll change the most - up to 3200 or higher if I have to to get the shot. Noise can be cleaned up pretty well (NeatImage), whereas DOF and motion blur are harder to create/fix.

Hope this helps...

Hammy.

[PCthug]

Very well explained Hammy.
What gear do you use?

[UTHammy]

PCThug,

I use Canon MarkII-N bodies (3 of them), along with mostly prime lenses: 400/2.8, 200/1.8 (2 of these beauties), 135/2, 85/1.8, 50/1.4, 20/1.8 and some zooms: 70-200/2.8, 24-70/2.8, 12-24/4 (2 of these great Tokinas), 10-17/4.

I cover mostly youth sporting events and take up to 100 terminals with me to sell back to the parents around the country.

Hammy.

[PCthug]

Great bit of kit.
I have the Canon 400d, 18-200, 10-20, 100-400L, 60mm macro.
I am hoping to buy a 5d mkII with the 24-105L in the next few days.
I shoot almost anything, but quite like portraiture at the moment.