Correct me if im wrong, Aperature, ISO, SS

blade_922

blade_922

Messages
244
Name
Omar
Edit My Images
Yes
Okay, had my canon DSLR 550d for a few days now. I've taken a good couple of hundred random shots, ie stars and just other objects and pieces all in manual mode.

Am i right in saying a higher ISO means more noise to the image, so its always best keeping a low ISO as possible? So really to capture more light instead of using a higher ISO, you have to balance a lower ISO and slower shutter speed but not to slow that it leaves trails and is blurry. Also keeping the aperature wider to provide more light. Should you try keep the aperature as wide as possible in the situatuon of the photo to provide more light rather than slowing down the shutter speed?

Bit confusing eh but you know what i mean, you have to balance all three to get the best possible image. But from what i have learnt

ISO low as possible to avoid noise?
Wider aperature rather than slower shutter speed to get light?


It obviously all depends on what kind of shot you want right. But just checking whats best to sacrifice out of the three (aperature, ISO and shutter speed) to minimise quality loss in all sorts of situations.
 
You've got it :)

Although also bear in mind that a lower f number gives you shallower depth of field.
 
Nawty said:
You've got it :)

Although also bear in mind that a lower f number gives you shallower depth of field.
Click to expand...

Still getting used to the technical terms, so let me get this right:
shallower depth of field
Click to expand...
means things in the distance will be more out of focus, more blurry. A lower f number means wider aperature meaning more light getting through but focus will be more on the nearer objects than the further objects?

So if i was to have a larger f number meaning less light getting through, that would mean things in the distance if i were to zoom in would be more focused than if i were to have a lower f number? :p

right/wrong?
 
Sounds like you are learning the essentials quickly and well.

Yes, wide aperture means a more shallow depth of field = blurry background. It also means that if you have a fast lens (f/1.8 etc) you can easily miss the focal point if you are shooting wide open (f/1.8 etc).

A higher ISO isn't a bad thing, it's a tool you can use to keep your shutter speed faster so as not to cause the motion blur. Yes, it can be noisy when it's higher (more grain), but there is software to remove the noise and hey, sometimes noise in a picture isn't a bad thing at all.

You're on the right track. Embrace this knowledge and keep going!
 
If shooting the stars, you have to remeber that they are in reality a moving target, and the longer the focal length the shorter shutter period to avoid trails and still show as points of light. Most astronomy shots are done with a tracking mount, and also staked exposures.
 
blade_922 said:
Still getting used to the technical terms, so let me get this right:

means things in the distance will be more out of focus, more blurry. A lower f number means wider aperature meaning more light getting through but focus will be more on the nearer objects than the further objects?

So if i was to have a larger f number meaning less light getting through, that would mean things in the distance if i were to zoom in would be more focused than if i were to have a lower f number? :p

right/wrong?
Click to expand...

:thumbs::thumbs::thumbs:
 
Thanks for the vote of confidence :D

BarryG said:
Sounds like you are learning the essentials quickly and well.

Yes, wide aperture means a more shallow depth of field = blurry background. It also means that if you have a fast lens (f/1.8 etc) you can easily miss the focal point if you are shooting wide open (f/1.8 etc).
Click to expand...

So its harder to focus on an object with a wider aperature because more light is getting in right. So keeping a narrow aperature would mean you have more chance of focusing on an object more clearly if its in the distance or even near. But if the object is nearer its easier to focus into with a wider aperature than an object in the distance with a wider aperature. right?

BarryG said:
A higher ISO isn't a bad thing, it's a tool you can use to keep your shutter speed faster so as not to cause the motion blur. Yes, it can be noisy when it's higher (more grain), but there is software to remove the noise and hey, sometimes noise in a picture isn't a bad thing at all.

You're on the right track. Embrace this knowledge and keep going!
Click to expand...

I have photoshop, to be honest, i've not used photoshop for a good few years. I take it i could remove the noise via photoshop. I did notice that when shooting in low light at times i would have to increase the ISO so as there was no motion blur. So i guess it comes in handy when required.

If shooting the stars, you have to remeber that they are in reality a moving target, and the longer the focal length the shorter shutter period to avoid trails and still show as points of light. Most astronomy shots are done with a tracking mount, and also staked exposures.
Click to expand...

Tracking mounts and stacked exposures would give a better image sometimes, ive read quite a bit about that online so i know what you mean. Thanks.
 
for a given f number, as the object gets closer the depth of field gets shallower. When you're focusing 1:1 with a macro lens the depth of field is tiny - only a mm or two.

Wen you have this limited depth of field you sometimes have to be careful to ensure that everything you want is in focus. So when it's dark you need to be aware that a low f number will give yo more light BUT you may not get everyone's face in a group in focus (kit lenses probably wont ever have this problem but at f/1.4 or f/1.8 at can). This is when bumping up the iso is important.
 
Nawty said:
for a given f number, as the object gets closer the depth of field gets shallower. When you're focusing 1:1 with a macro lens the depth of field is tiny - only a mm or two.

Wen you have this limited depth of field you sometimes have to be careful to ensure that everything you want is in focus. So when it's dark you need to be aware that a low f number will give yo more light BUT you may not get everyone's face in a group in focus (kit lenses probably wont ever have this problem but at f/1.4 or f/1.8 at can). This is when bumping up the iso is important.
Click to expand...


Yeh i get what you mean. Let me give you an example, let me know if im right. A group of 5 people are lined up 3 tall people at the back and 2 smaller people infront of them. If there is a wide aperature, i may lose focus of the 3 at the back or if i focus on them then lose focus of the 2 at the front. This could also happen with 5 people lined up side by side, i could try focus all 5 but may only get a couple or more in focus. right?

BUT

if i had a narrower aperature i have more chance of focusing all 5 people into the picture right?

Another way to put what im saying is,

Imagine a person 4ft away, another 6ft away but slightly to the right. Now with a wide aperature say f1.8 i have no chance of focusong both people in, its one or the other in focus. But say i have a narrow aperature f20 I'll be able to focus both of the people in the photo.

***LIGHT BULB FLASH***

My head just got round the depth of field while i was writing out that last line of the second example(i think) correct me if im wrong.

So depth of field is, here goes another example:

Imagine 2 people holding onto a rope just 0.25ft long, one infront of the other, so they are very close together. I try to focus both into the picture with say f1.8 and i succeed. I then give them a rope of 5ft long and keep same aperature f1.8 but only one can be in focus. Now because they are further apart, to bring both into focus, i need to increase f number?????

:thumbs::thumbsdown::thumbs::thumbsdown::thumbs::thumbsdown:

right/wrong?

I usually find giving my own examples to problems i face mean being able to understand what im doing a hell of a lot more than just reading someones example and sitting infront of the camera confused for hours. If my head can get round it on its own, then i know im heading in the right direction :p
 
Last edited:
Okay,

Another situation:

Person standing 5 feet away from the camera, against a snowy mountain backdrop. Now if i wanted to focus both the person(full body) and the mountain backdrop, im best using a narrow aperature i.e a high f number so as to bring the mountain and person into focus, right? Now to understand this a little more, would x lens over y lens bring both more into focus. Say i have a 18-55mm kit lens, 50mm 1.8 and 55-250mm lens. Now the 18-55 would mean i get more of the background in to the shot and if using the other 2 at 55mm it would be the same. Now each lens has its widest and narrowest aperature (lowest and highest f number that the lens can achieve), so in this situation would it be best to use the lens that can achieve the narrowest aperature i.e highest f number as this would give the best result of what im trying to achieve to focus on both the backdrop and person.

right or wrong?
 
From reading the thread you have a good grasp of the basics here yeah.

These sorts of lenses have '2 numbers' and im guessing on your 18-55 it will be f4-f5.6, meaning at 18mm (zoomed way out) you will be able to stop down to f4, and when you zoom in to 55mm you will be only able to go down to f5.6.

It isnt the same at the other end of the aperture scale, they will both go up to something like f22 or f32 no matterif you are at 18mm or 55mm

In your example you are thinking that you will have to get a high F number to get the person and snowy mountain in docus, It's a wise assumption but in landscapes you will mostly shoot f14 to f16, focussing 1/3 of the way into the image, that will give you enough depth of field to see clear focus from the front to the back.

If I am assuminbg your problem correct, then oyu just need to use the 18-55, zoomed out at 18mm, pick a nice Aperture to begin, say f14. depending on the weather conditions you should choose a suitable ISO, 100, 200, 400. then find the shutter speed which will give you the correct exposure for your aperture and ISO chosen.

Baring in mind that if you end up picking f14 and ISO100 - if the weather is pretty poor and overcast you may need a slightly longer shutter speed to get enough light in. Once you start going to 1/100 and lower with a person in the shot - their movement may cause blur. Combat this by taking the ISO up a peg to ISO200 and then raise your shutter speed to get back to something usable. (you may even find you have to go up to 400 or more)

Hope this helps (and wasn't incorrect)

Rich
 
Here's a practical demonstration of how aperture affects depth of field.

f16_cropped.jpg


Look at where the lens is focussed (opposite the green mark). It's at 5 metres. Now look at the figures either side of the green mark. Notice the 'infinity' focus point is opposite '16' to the left and about 2.5M is opposite it to the right. What this is telling you is when the lens is at f/16, everything between 2.5M and infinity will be in focus when the lens is nominally focussed at 5 metres.

Now look at this picture

f4_cropped.jpg


If the lens is set to f/4 and the focus is adjusted so that infinity is opposite the '4' mark, the corresponding mark on the ther side of the indicator is 10 metres. This shows that at f/4, if you want infinity to be within the depth of field, the closest an object can be and still be in focus is 10 metres.

Apologies for the ancient lens. It's an old Chinon (Dixon's special) manual everything which shows the depth of field markings.
 
Thanks for you help and confirmation of what im doing.

Much appreciated.
 
This has been something I've been meaning to do for a while. OK, so low ISO will give a slow SS. Normally, that would mean better IQ. But in very low light, long exposure, wouldn't a bit higher ISO give better IQ/lower noise? My reasoning being that the sensor would be less liable to bleed at higher ISO's. I dunno. Thoughts?
 
I've found this really useful folks. Thanks! The camera simulator is a great wee thing for playing about to see the effect of each of the settings.

Had a good play about with my camera yesterday and this morning and it's all starting to make sense. (ish)

:)
 
Carter64 said:
This has been something I've been meaning to do for a while. OK, so low ISO will give a slow SS. Normally, that would mean better IQ. But in very low light, long exposure, wouldn't a bit higher ISO give better IQ/lower noise? My reasoning being that the sensor would be less liable to bleed at higher ISO's. I dunno. Thoughts?
Click to expand...

It's all about getting your head round it. Each situation is different and will most likely always require different settings.

Mike (Carter64), firstly every situation is different. Dont just think of it in general terms, apply it to a situation. In manual mode you can choose ISO, Shutter Speed etc. So you can have LOW ISO or HIGH ISO with High SS or LOW SS.

In low light conditions, say outdoors after sunset. Its pretty dark, no moon out and pretty cloudy. Your on a bridge wanting to take a picture of the river and another bridge further down the river. Your going to shoot a long exposure, say 1 second. Because your doing a longer exposure, it will pick up more light. So you may not need to have a higher ISO. If you think its still pretty dark, you can either increase the ISO or have a wider aperature. In my opinion i THINK that increasing the width of the aperature(lower f number) would give better results than increasing the ISO. Increasing the ISO means more noise.

The best way i think to get your head round it is to think of different situations, by all means type them up and reply here with a situation and what you think you would have as the settings and also type up why you would have those settings rather than a higher or lower setting. This way, you have your reason for doing it your way, it may not be the best way, but let the people of this forum help you and tell you whats better in which situation generally. That way you know what your doing wrong in terms of not getting the best picture and at least you'll understand why its wrong to.
 
blade_922 said:
I
Mike (Carter64), firstly every situation is different. Dont just think of it in general terms, apply it to a situation. In manual mode you can choose ISO, Shutter Speed etc. So you can have LOW ISO or HIGH ISO with High SS or LOW SS.
Click to expand...
Thank you for that. Now how do I suck eggs?
 
I was thinking more along the lines of the root causes of noise in the first place, which is like signal degradation through increasing gain. Which is what happens when you set the ISO higher.

Now, say your meter says 60sec at f5.6, using 100ASA setting. We'll assume this will allow the sensor to gather the amount of light required for your correct exposure.
Likewise, 7.5secs at f5.6 using 800ASA would allow the sensor to gather the same amount of light. Now my question is (and was): The long time the shutter is open at 100ASA would increase the likelihood of interference, thus noise? Would it still be lower noise than the 800ASA?

blade_922 said:
Mind you your probably used to the feeling of something like that being in your mouth.
Click to expand...
Would you care to clarify and justify that remark?
 
I think the remark would probably be better dropped than explained. Put it down to what you'd say as a joke face to face not translating into text?

Useful thread so please keep it on track :)

My experience on high iso noise is that it is better to have a good well exposed picture than to worry about stepping up another iso notch. Under exposure and trying to brighten the image is the thing that really makes noise stand out.
 
Carter64 said:
I was thinking more along the lines of the root causes of noise in the first place, which is like signal degradation through increasing gain. Which is what happens when you set the ISO higher.

Now, say your meter says 60sec at f5.6, using 100ASA setting. We'll assume this will allow the sensor to gather the amount of light required for your correct exposure.
Likewise, 7.5secs at f5.6 using 800ASA would allow the sensor to gather the same amount of light. Now my question is (and was): The long time the shutter is open at 100ASA would increase the likelihood of interference, thus noise? Would it still be lower noise than the 800ASA?


Would you care to clarify and justify that remark?
Click to expand...

Not so. 7.5 seconds at f5.6 will gather only 12.5% of the light gathered in 60 seconds. Using an ISO setting of 800ASA will cause the camera electronics to output the same sized signal as 60s at 100ASA. What 'turning up the ISO' does in a digital camera is turn up the gain of the amplifier. However, turning up the gain increases not only the wanted signal but also the inherent noise of the sensor and of the electronic processing circuitry. Think of it as turning up the volume on a quiet recording. You also increase the 'hiss'.

A given combination of shutter speed and f-number will allow a certain amount of light through the lens, that amount is fixed before it ever hits the sensor. The ISO setting sets how much the sensor signal is amplified by the electronics in the camera.
 
Of course, yes. The thread as written is wrong, no excuses. Don't know where my head was but it wasn't connecting to my fingers. Maybe replace 'to gather' with 'use'. Or I could re-write it... :)
 
I was probably distracted by Lady GaGa's new vid while I was painting my nails. You know what 'us lot' are like. Still, better than getting drunk all day or being Glaswegian. Same thing. Oh, that was a joke that didn't translate from speech to text.
 
You must log in or register to reply here.
Back
Top