Lens and Aperture

Mclovin101

Mclovin101

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Richard
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Hi All

Im gonna be really silly now but can someone explain to me what these numbers mean on my lens

I have read alot about it and still cant get my head around it

1st lens is a Canon EF-S 18-55mm (non IS) - Aperture f/5.6-3.5.

2nd lens is EF 75-300mm III - Aperture f/5.6-4.

Please go easy on me :suspect::suspect:
 
Im gonna be really silly now
Click to expand...
It's only silly to say this in the basics forum! :)

This is how I'd explain the numbers:

Every lens that you will use on your camera will have two pieces of information that tell you about what it does and how you can use it.

The first is the focal length which is measured in millimetres (it's the distance between the sensor inside the body of the camera and the hole at the front of the lens called the aperture).
So lets say you wanted to take a picture of a bird in the distance, you're going to need something like 300mm. Taking a portrait picture might be done at 55mm and a landscape shot might be taken at 18mm. Notice how your lenses will cover these! This is also known as 'zoom' in it's simplest form, the bigger the number in millimetres, the more powerful the zoom. The actual millimetre measurements are relatively meaningless as a number but you'll soon get a feel for what 'focal length' you'll need for a photograph.

The other number is the aperture (also known as the f-stop or f-number). The aperture is made up of little blades that can open and close depending on your camera setting. The first thing to note about aperture is that bigger the aperture, the smaller the number that is used to describe it.

Let's take this lens that has an aperture of 2 (small number, very big hole!).

This lens on the other hand has an aperture of F4 (not so big).

This number represents the maximum size (or minimum f-stop number) that the aoperture will open up to. The reason we show the max aperture on lenses is the generally speaking the bigger the better. A bigger aperture means you can let more light in, and also means you can be creative with something called depth of field.


To get those nice sharp images there are two important factors; focus and shutter speed.

Focusing your lens on the subject is something that shouldn't be taken for granted. Choose the spot that you want to focus on, such as the eye, then make the camera do this (using single point focus, feel free to ask if you want this explained!). Make sure you focus right before taking the picture as any movement of you or the subject back & forward will put it back into the blurry zone of doom.

Shutter speed should be high enough to avoid subject blur (caused by a fast moving subject such as a dog/child/bird) and also camera shake, caused by the whole camera and lens moving.

Your minimum shutter speed should be higher at 300mm than 18mm requires, so a good rule of thumb is take the focal length, then turn it into a fraction:
Approx 300mm focal length requires approx 1/300 of a second.
Approx 18mm will require a minimum of 1/20 of a second (rounded up).

This should help get sharper pictures and make sense of the numbers. And yes, any of your lenses will help you get sharp pictures using the info above.

I'll stop here as I don't know if I'm rambling pointlessly...!

EDIT: I'd like to add that the info above has been simplified for the purpose of explaning basic principles, there's no use in baffling people with field of view, cropped sensor factors and chromatic aberrations yet!
 
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Digital_Clarity said:
It's only silly to say this in the basics forum! :)

This is how I'd explain the numbers:

Every lens that you will use on your camera will have two pieces of information that tell you about what it does and how you can use it.

The first is the focal length which is measured in millimetres (it's the distance between the sensor inside the body of the camera and the hole at the front of the lens called the aperture).
So lets say you wanted to take a picture of a bird in the distance, you're going to need something like 300mm. Taking a portrait picture might be done at 55mm and a landscape shot might be taken at 18mm. Notice how your lenses will cover these! This is also known as 'zoom' in it's simplest form, the bigger the number in millimetres, the more powerful the zoom. The actual millimetre measurements are relatively meaningless as a number but you'll soon get a feel for what 'focal length' you'll need for a photograph.

The other number is the aperture (also known as the f-stop or f-number). The aperture is made up of little blades that can open and close depending on your camera setting. The first thing to note about aperture is that bigger the aperture, the smaller the number that is used to describe it.

Let's take this lens that has an aperture of 2 (small number, very big hole!).

This lens on the other hand has an aperture of F4 (not so big).

This number represents the maximum size (or minimum f-stop number) that the aoperture will open up to. The reason we show the max aperture on lenses is the generally speaking the bigger the better. A bigger aperture means you can let more light in, and also means you can be creative with something called depth of field.


To get those nice sharp images there are two important factors; focus and shutter speed.

Focusing your lens on the subject is something that shouldn't be taken for granted. Choose the spot that you want to focus on, such as the eye, then make the camera do this (using single point focus, feel free to ask if you want this explained!). Make sure you focus right before taking the picture as any movement of you or the subject back & forward will put it back into the blurry zone of doom.

Shutter speed should be high enough to avoid subject blur (caused by a fast moving subject such as a dog/child/bird) and also camera shake, caused by the whole camera and lens moving.

Your minimum shutter speed should be higher at 300mm than 18mm requires, so a good rule of thumb is take the focal length, then turn it into a fraction:
Approx 300mm focal length requires approx 1/300 of a second.
Approx 18mm will require a minimum of 1/20 of a second (rounded up).

This should help get sharper pictures and make sense of the numbers. And yes, any of your lenses will help you get sharp pictures using the info above.

I'll stop here as I don't know if I'm rambling pointlessly...!
Click to expand...


not my thread but that was very helpful for me too...:thumbs:
 
Whilst very comprehensive, Dave just missed one thing, to tell you actually what your numbers mean.

The first lens Canon EF-S 18-55mm (non IS) - Aperture f/5.6-3.5.
This means it has a focal range from 18mm to 55mm. The other numbers as you know are the aperture. With this lens youve written it wrong, the 3.5 should be first.
These numebrs mean the maximum aperture range for the lens is f/3.5 to 5.6. Beacuse your lens is a cheaper budget zoom, the aperture actually changes as you zoom. At 18mm the maxiumum aperture (the biggest the hole will go) will be f/3.5. As you zoom, the hole will get smaller, so at 55mm the hole will now be f/5.6.

Your other lens EF 75-300mm III - Aperture f/5.6-4.
Again the numbers are th wrong way, it should be 4-5.6. Again this means the aperture changes as you zoom. At 75mm the maximum aperture will be f/4 and at 300mm the max aperture will be f/5.6

And yes both those lenses are cabable of sharp shots, although of course they wont compare to much more expensive lenses in some cases.
 
Digital_Clarity said:
It's only silly to say this in the basics forum! :)

This is how I'd explain the numbers:

Every lens that you will use on your camera will have two pieces of information that tell you about what it does and how you can use it.

The first is the focal length which is measured in millimetres (it's the distance between the sensor inside the body of the camera and the hole at the front of the lens called the aperture).
So lets say you wanted to take a picture of a bird in the distance, you're going to need something like 300mm. Taking a portrait picture might be done at 55mm and a landscape shot might be taken at 18mm. Notice how your lenses will cover these! This is also known as 'zoom' in it's simplest form, the bigger the number in millimetres, the more powerful the zoom. The actual millimetre measurements are relatively meaningless as a number but you'll soon get a feel for what 'focal length' you'll need for a photograph.

The other number is the aperture (also known as the f-stop or f-number). The aperture is made up of little blades that can open and close depending on your camera setting. The first thing to note about aperture is that bigger the aperture, the smaller the number that is used to describe it.

Let's take this lens that has an aperture of 2 (small number, very big hole!).

This lens on the other hand has an aperture of F4 (not so big).

This number represents the maximum size (or minimum f-stop number) that the aoperture will open up to. The reason we show the max aperture on lenses is the generally speaking the bigger the better. A bigger aperture means you can let more light in, and also means you can be creative with something called depth of field.


To get those nice sharp images there are two important factors; focus and shutter speed.

Focusing your lens on the subject is something that shouldn't be taken for granted. Choose the spot that you want to focus on, such as the eye, then make the camera do this (using single point focus, feel free to ask if you want this explained!). Make sure you focus right before taking the picture as any movement of you or the subject back & forward will put it back into the blurry zone of doom.

Shutter speed should be high enough to avoid subject blur (caused by a fast moving subject such as a dog/child/bird) and also camera shake, caused by the whole camera and lens moving.

Your minimum shutter speed should be higher at 300mm than 18mm requires, so a good rule of thumb is take the focal length, then turn it into a fraction:
Approx 300mm focal length requires approx 1/300 of a second.
Approx 18mm will require a minimum of 1/20 of a second (rounded up).

This should help get sharper pictures and make sense of the numbers. And yes, any of your lenses will help you get sharp pictures using the info above.

I'll stop here as I don't know if I'm rambling pointlessly...!

EDIT: I'd like to add that the info above has been simplified for the purpose of explaning basic principles, there's no use in baffling people with field of view, cropped sensor factors and chromatic aberrations yet!
Click to expand...

Keep going my freind i found that really helpful thank you.

It will just be putting things to the test now so.
 
TCR4x4 said:
Whilst very comprehensive, Dave just missed one thing, to tell you actually what your numbers mean.

The first lens Canon EF-S 18-55mm (non IS) - Aperture f/5.6-3.5.
This means it has a focal range from 18mm to 55mm. The other numbers as you know are the aperture. With this lens youve written it wrong, the 3.5 should be first.
These numebrs mean the maximum aperture range for the lens is f/3.5 to 5.6. Beacuse your lens is a cheaper budget zoom, the aperture actually changes as you zoom. At 18mm the maxiumum aperture (the biggest the hole will go) will be f/3.5. As you zoom, the hole will get smaller, so at 55mm the hole will now be f/5.6.

Your other lens EF 75-300mm III - Aperture f/5.6-4.
Again the numbers are th wrong way, it should be 4-5.6. Again this means the aperture changes as you zoom. At 75mm the maximum aperture will be f/4 and at 300mm the max aperture will be f/5.6

And yes both those lenses are cabable of sharp shots, although of course they wont compare to much more expensive lenses in some cases.
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So i assume the high u go the more you can change and play about with the aperture i mean the high price ones.

These are how the numbers are on my lens so

But thank you for you help

Its slowly sinking all in lol
 
Generally the more expensive lenses have constant F number throughout the zoom range (typically f/4 or f/2.8), this means that A) you don't have to change exposure settings as you zoom and B) you will typically have a faster lens you can use in lower light (i.e. a low f number).
 
Nawty said:
Generally the more expensive lenses have constant F number throughout the zoom range (typically f/4 or f/2.8), this means that A) you don't have to change exposure settings as you zoom and B) you will typically have a faster lens you can use in lower light (i.e. a low f number).
Click to expand...

But i bet you pay quite a bit for those or are they a ok price??
 
Mclovin101 said:
But i bet you pay quite a bit for those or are they a ok price??
Click to expand...


Depends really. The canon 70-200mm f/4 is reasonable, but then the 70-200mm f/2.8 is more of a bank loan job.
The best value for money fixed aperture lens has to be the 50mm f/1.8 at under £100. A super sharp lens for very little money.

Fixed aperture lenses are usually the more professional ones, so do command a slightly higher price, but the control over your aperture, build quality and design are worth the extra IMO.
I haven't bought a non fixed aperture lens in a long time.
 
You do pay a premium for a fast and fixed aperture lens.

Whether or not they are an 'ok' price is quite subjective.

Typically these lenses are better built, better optics, better focus motors, they may also be weatherproof.
 
thanks lads i to learnt a lot there.
so when we look for better lenses, we are looking for focal length and an F without an increased number next to it.
 
The f in the front of the aperture number denotes the fact that the size of the aperture actually relates to the focal length of the lens.

If we take a 50mm 'standard' lens as an example with a maximium aperture of f/2, if you measured the width of the open aperture at f/2 you'd find it would be 25mm which divides into the focal length twice hence it's an f/2 lens. If the maximum aperture diameter was 50mm then you'd have an f1 lens. Canon did actually make an f/1 lens for a while and if you can still find one it will cost you a bomb. We refer to lenses with a big maximum aperture in relation to the focal length as 'fast' lenses because they'll always enable faster shutter speeds (or lower ISOs) in any given situation, but they're particularly prized for their abilty in low light situations for those who have to operate in all conditions.

As lenses get longer it gets more and more expensive to manufacture the glass as the lens elements have to get proportionally bigger for a fast maximum aperture, and the lenses start to get increasingly heavy, which is why, using the 500mm lens as an example, you don't see any larger than f/4 - partly down to manufacturing cost, and partly down to hugely increased weight, but f/4 is still considered 'fast' for a lens of that focal length. With shorter lenses f/4 would be considered a pretty moderate max aperture.
 
PREM said:
thanks lads i to learnt a lot there.
so when we look for better lenses, we are looking for focal length and an F without an increased number next to it.
Click to expand...

Good quality lenses come in all sorts of focal lengths, from wide to long telephoto, so the focal length can't be used as a guide to whether a lens is good or not.

However, the maximum aperture of a lens might be a better guide. If a prime lens has a wide maximum aperture (small number), generally speaking it can be considered as a good lens. If a zoom lens has a constant maximum aperture it too will generally be of a better quality. In both cases, the price will also be higher than lenses of similar focal lengths, but with more restrictive apertures.

There are some exceptions to this, but it should serve as a useful guide.
 
PREM said:
thanks lads i to learnt a lot there.
so when we look for better lenses, we are looking for focal length and an F without an increased number next to it.
Click to expand...

Kinda....the focal length isn't really an indicator of quality although some of the longer reach/longer focal length lenses do cost a fair bit more and are superb lenses...many thousands more infact.

Generally aperture is a better indicator of quality, the smaller number the wider the aperture. For zooms this will be probably f2.8, and primes typically begin at f1.2 or f1.4.

You can buy zoom lenses with a focal range of 70-300mm at f5.6 for around £400, and a 70-200mm at f2.8 for £1700

You can buy prime lenses at 85mm f1.8 for around £300 and a 85mm f1.2 for £1800.
 
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TCR4x4 said:
Depends really. The canon 70-200mm f/4 is reasonable, but then the 70-200mm f/2.8 is more of a bank loan job.
The best value for money fixed aperture lens has to be the 50mm f/1.8 at under £100. A super sharp lens for very little money.Fixed aperture lenses are usually the more professional ones, so do command a slightly higher price, but the control over your aperture, build quality and design are worth the extra IMO.
I haven't bought a non fixed aperture lens in a long time.
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If i just google this will it bring it up. Wouldnt mind looking at this

Thanks for everyones input. Made a nice read this morning when i got into work.

I had a play around last night just focusing on a certain thing and changing the aperture to suit which lens i had on. I found i got no camera blur if i was using a tripod but when free handing it (so to speak ) if the object didnt have a good Back ground light i was getting blur. Is the general saying the more light the better?????
 
If i just google this will it bring it up. Wouldnt mind looking at this
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Not sure if this is the cheapest but I've bought from Park Cameras before:

http://www.parkcameras.com/72/Canon-EF-50mm-f-1-8-II.html

I had a play around last night just focusing on a certain thing and changing the aperture to suit which lens i had on. I found i got no camera blur if i was using a tripod but when free handing it (so to speak ) if the object didnt have a good Back ground light i was getting blur. Is the general saying the more light the better?????
Click to expand...
Generally speaking, you'll find what is the minimum light you'll need to get your photos and in most cases more light is better. If you want to take a picture that is exposed well (not too bright, not too dark) where the light is low, you can increase the ISO (sensitivity to light) and make the aperture as wide as possible but if you're in an 'auto' mode where the shutter speed is chosen for you, it will sometimes be so low that the picture will be blurred.
 
Digital_Clarity said:
Not sure if this is the cheapest but I've bought from Park Cameras before:

http://www.parkcameras.com/72/Canon-EF-50mm-f-1-8-II.html





Generally speaking, you'll find what is the minimum light you'll need to get your photos and in most cases more light is better. If you want to take a picture that is exposed well (not too bright, not too dark) where the light is low, you can increase the ISO (sensitivity to light) and make the aperture as wide as possible but if you're in an 'auto' mode where the shutter speed is chosen for you, it will sometimes be so low that the picture will be blurred.
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Do they call this the nifty fifty???



Yeah the ISO was at the highest and had the smallest F number (largest opening) is that correct. And it was still blur if i was freehanding it. Maybe i dont have a steady hand lol. But if i moved the object into a better lit area it was spot on and u could certainly know the differece

More practise is needed i think
 
Do they call this the nifty fifty???
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Yes, aka plastic fantastic.
Yeah the ISO was at the highest and had the smallest F number (largest opening) is that correct. And it was still blur if i was freehanding it. Maybe i dont have a steady hand lol.

More practise is needed i think
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Not neccessarily, a steady hand will only do so much. Have a read about the shutter speeds again (at the end of my post from earlier) and you'll get an idea for what you can do with a steady hand.

If your shutter speeds are coming out at anywhere slower than 1/20 of a second then you're going into tripod territory :)
 
Ok i will have a look. Am i correct in saying that when in AV mode on a canon i can only change the aperture and in TV mode it will only allow me to change the shutter speed. If i go into M mode and try and change both i get just a dark photo :S. Again this is in a low light room.
 
Ok i will have a look. Am i correct in saying that when in AV mode on a canon i can only change the aperture and in TV mode it will only allow me to change the shutter speed. If i go into M mode and try and change both i get just a dark photo :S. Again this is in a low light room.
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That's right, Av means you choose the aperture, Tv means you choose the shutter. On both Av and Tv you can change the ISO. Set the ISO higher when it's dark (try all the way to 1600 or 3200 to start with), this will mean your shutter speed will be quicker therefore stopping the blur.

Changing the ISO to a high figure means that we can use faster shutter speeds and take photos in dark areas but there's no free lunch here. The higher the ISO the more grainy the image will be.

Best way to decide what ISO to use in a dark room is to eyeball it and make a guess (lets say ISO 800). Point your camera at the subject and take a photo. If the shutter speed was too low and the picure is blurred, try the next ISO up (1600). Keep going until you find an ISO that keeps your shutter speed nice and quick (let's say 1/60 of a second with your 18-55mm).

With practise you'll know what ISO to set without so much of the trial and error used above.
 
Mclovin101 said:
If i just google this will it bring it up. Wouldnt mind looking at this

Thanks for everyones input. Made a nice read this morning when i got into work.

I had a play around last night just focusing on a certain thing and changing the aperture to suit which lens i had on. I found i got no camera blur if i was using a tripod but when free handing it (so to speak ) if the object didnt have a good Back ground light i was getting blur. Is the general saying the more light the better?????
Click to expand...

It depends what was blurred.

In theory using hand or tripod properly will not affect the blur / depth of field so the images should be identical at the same aperture, at the same focal length, at the same distance to the object in focus - all things being equal.

If you had poor light and were shooting in poor light, I'm guessing the shutter speed was slowing down to compensate for exposure in Av mode, or you were Manual-ly slowing it to balance the exposure meter. This would create the effect of blur, but would be actually camera shake as opposed to out of focus areas or shallow depth of field. Bright light would have the opposite effect and increase shutter speed eliminating potential camera shake.

Probably the best way to test the out of focus areas is initially to zoom in, get as close as you can to the main subject and open up the aperture (smallest f number f4,f5.6 as opposed to f16,f22) the lens can achieve.

Andy
 
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1600 is the highest on my 1000D so but yeah i get what your saying.

Thank you very much for your help and time

Put all this into practise now. Also looking for a nifty fifty they seem rare atm which means to me they must be worth the money lol
 
AndyB1976 said:
It depends what was blurred.

In theory using hand or tripod properly will not affect the blur / depth of field so the images should be identical at the same aperture, at the same focal length, at the same distance to the object in focus - all things being equal.

If you had poor light and were shooting in poor light, I'm guessing the shutter speed was slowing down to compensate for exposure in Av mode, or you were Manual-ly slowing it to balance the exposure meter. This would create the effect of blur, but would be actually camera shake as opposed to out of focus areas or shallow depth of field. Bright light would have the opposite effect and increase shutter speed eliminating potential camera shake.

Probably the best way to test the out of focus areas is initially to zoom in, get as close as you can to the main subject and open up the aperture (smallest f number f4,f5.6 as opposed to f16,f22) the lens can achieve.

Andy
Click to expand...

Thank you Andy i will try this aswell. If i get another blur pic i will upload to show you as i delete them after ive taken them
 
Mclovin101 said:
1600 is the highest on my 1000D so but yeah i get what your saying.

Thank you very much for your help and time

Put all this into practise now. Also looking for a nifty fifty they seem rare atm which means to me they must be worth the money lol
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http://www.amazon.co.uk/Canon-EF-50-1-8-Lens/dp/B00005K47X/ref=sr_1_1?ie=UTF8&qid=1294306812&sr=8-1

£85 from Amazon, next day delivery for £10.

There is also a forum trader in the sales section, who is highly recommended on price and service, Kerso. I've not used Ian yet, but haven't heard a bad report yet!
 
Mclovin101 said:
Thank you i will have a look and see if i can track him down
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http://www.talkphotography.co.uk/forums/showthread.php?t=185895

There you go , i got my nifty off him a while ago a cracking lens for the money.


This is my god daughter taken with this lens

IMG_0469.jpg
 
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TCR4x4 said:
Buy a bigger kit bag too... You're gonna need it when the bug sets in :lol:
Click to expand...

Ive just brought a Slingshot 200aw off here so i hope it will be bigger enough :lol::lol:

The bug is already setting in. I play paintball alot but im thinking i may have to tone that down abit to buy the bits i want

Def looking at a Nifty lens next. I want to get my head around the aperture 1st as i was playing last nite and was getting some really good snaps
 
love that pic, i think B/W shots really capture the mood...

just bought from the forum a used Nikon 50mm f1.8 as herd so many good things and seen great pics taken with nifty 50's, trouble is i havent bought a body yet lol
 
Mclovin101 said:
Ive just brought a Slingshot 200aw off here so i hope it will be bigger enough :lol::lol:

The bug is already setting in. I play paintball alot but im thinking i may have to tone that down abit to buy the bits i want

Def looking at a Nifty lens next. I want to get my head around the aperture 1st as i was playing last nite and was getting some really good snaps
Click to expand...

The nifty is a great lens to have early in a collection IMO for aperture and price. It gives you some more control over the image and takes another step away from the point n shoot look, some more creativity shall we say. Its not the best built lens and some say its a tight angle on a crop camera.

The problem is....it gets a addictive when you have more control over the image.

Then you think...hmmm what about a flash gun, what about a nice macro, what about a ultra wide angle..then what about a better lens in the range you already have covered...then hmmm my ISO looks a bit noisey - what about full frame and on and on :lol::bonk:
 
So very true , my flash gun is stuck in customs :bang:

Then you think...hmmm what about a flash gun, what about a nice macro, what about a ultra wide angle..then what about a better lens in the range you already have covered...then hmmm my ISO looks a bit noisey - what about full frame and on and on :lol::bonk:[/QUOTE]
 
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