f Stops - Camera versus Lens

[Outback-Charlie]

I am sure this is very basic stuff but has me puzzled. The lens has an f stop rating of f4 - 5.6 yet the camera will allow the use of an f stop range of f4 through to f22 ie way outside of the range nominated for the lens. I am using a Canon 40D with a Canon kit lens 17 - 85mm lens and a 70 - 300mm lens and both lenses are f4 - f5.6. With these lenses, what is the effect of using camera aperture settings greater than f5.6 on the quality of the shot being taken?

[Mr Darcy]

Hi Charlie and welcome.
The f rating on a lens is simply the WIDEST aperture it will work at.
If there is a range stated, it means that the lens has different widest apertures at different zoom settings.
Usually, the smaller (f4) number is appropriate at the widest zoom setting, and the larger(f5.6) number at the long end.

Put simply, the wider the aperture, the better the lens handles low light. Of course, if the scene is very bright, you want to reduce the aperture (stop down) to a larger number. All lenses will operate over a range of apertures, but only the widest is publicised as this is an indicator of quality.

Now it gets tricky. The wider the aperture is the better it handles low light, but also the narrower the depth of Field
This means, you may get an eye in focus, but the nose will be out of focus. This may be a good thing, or a bad thing depending on what you are trying to achieve. The best thing to do is to play with the lens at different settings (Put the camera in A-priority mode - not Auto!) and see the different effects for yourself.

No time to go into more detail but I Hope this helps.

[surenj]

Hi Ouback Charlie and welcome to the forum.

Greg has already answered your question but the best way to learn would be to put your camera on a tripod and focus on a close subject with a busy background. Then change the f stop and examine the results. Post them up if you will and I am sure you will learn heaps more from the ensuing discussion. BTW the 17 -85 lens is quite sharp at f8 [so are most lenses]. If you are doing any portraits, I would try to be around 35 and higher with this lens; it causes massive distortion of the faces... This becomes .

[Outback-Charlie]

Thank you Mr Darcy.

I can see my question was not clearly stated. The smalest aperture rating for my lenses is f5.6 yet the camera setting allow you to select aperture settings as small as f22. How does this work if the lens aperture only closes to f5.6? Is (1) the camera compensating for the lens and restricting the amount of light? and (2) is there any impact on the quality of the shot if you ask the camera to use an aperture setting, say f16, where this is below what the lens is rated at (f5.6)?

[Killakoala]

F5.6 is the lens's largest aperture. The smallest is F22. The smaller the number the larger the hole in your lens.

So when your lens says it's F4 - 5.6 that means that at a certain zoom length, that is the widest the aperture hole will be and allow the maximum amount of light in.

The lens OPENS to F5.6 and CLOSES to F22.

The effect of aperture on the final image is related to the 'depth of field.' (DOF) A wide aperture will have a narrow DOF and a narrow aperture will have a wide DOF.

It is a bit backwards I know but after a while it will become second nature to you when you see what the effect on your images is.

Is that more helpful?

[Outback-Charlie]

Thank you Surenj & Steve. And Surenj I will definitely try some portrait shots below and above 35mm at f8 and see what the differences are. Thank you for that tip. I have been using my 40D and lenses for approx 18 months and joined a camera club 8 months ago.

I do understand how the lens operates and the effect on DOF. My problem is that I am not stating the question clearly. There is a lens (in fact two of them) and a camera body. The controls in the camera body allow the f stop to be used in the range f4 to f22 yet the lens only operates f4 to f5.6. If you set the controls in the camera body to f22 the camera will take the shot even though the lens is only rated to f5.6. How does this work?

[whitey]

No you are getting the question correct, the answers are correct too.

The Maximum Apeture for that lens is between 4 and 5.6 by focal length maximum apeture is:
17-25mm = f/4.0
26-37mm = f/4.5
38-46mm = f/5.0
47-85mm = f/5.6

The Minimum Aperture for the lens is F32

The camera body is just controlling the apeture in the lens. There is normally an Apeture ring on the lens as well that can be used to control the apeture. I am not familiar with Canon lenses, this may be similar to the Nikon G lenses where they have removed the apeture ring and all apeture control is through the camera body.

The mechanics in a Nikon camera is that there is a little lever in the mount of the lens that is mechanically moved by the camera body to close and open the apeture. When the lens is off the camera you can hold up the lens and move the apeture lever with your finger and see the lens blades moving. (not sure whether this is recommended though)

[Outback-Charlie]

Thank you Whitey. The light bulb just switched on! I now understand the "maximum" apertures at the different focal lengths and the minimum aperture. Thank you all for your responses and I now understand.

[Mr Darcy]

And thank you Whitey.
I was part way through a more detailed answer with photos when I realised you had nailed it.

Charlie,
You need to be more specific with your location.
I suspect some one may well have jumped in a car to show you in person if you had a more specific location in your profile ( I know I would have - anything to break the monotony of a wet weekend!)
Sydney is not specific enough. If you are actually in the city, then use Sydney CBD, or if not, use either the suburb or a well known locality (e.g Blue Mountains, Eastern Suburbs, The Shire)if you are paranoid. Hint: We are NOT out to get you, though it may feel like that at times

[surenj]

camera club 8 months ago

I hope you mean photography club...

We are NOT out to get you

Watch out for the mods though...

[Outback-Charlie]

Geez! You fellows really are picking on me! That's okay. I really appreciate your help and I am old enough (and big enough) to give a bit back if I think you deserve it. Digital photography has been a constant learning experience for me albeit sometimes frustrating and I am in it for the long haul. Since joining the photography club (yeah Surenj it is a photography club not a camera club!) I have been impressed by the number of people who want to help and share information and just provide good old encouragement to those trying to come to grips with the art and technology as it is a blending of art and technology. I think my old film Nikon SLR was more about art than technology.

Mr Darcy, I have changed my location to be more specific. Not sure why it has to be more specific but I hope this helps with the wet weekend blues.

Regardless of the fact that you want to be cranky old blokes and pick on me, I do appreciate your help.

[shakey]

Mr Darcy, I have changed my location to be more specific. Not sure why it has to be more specific but I hope this helps with the wet weekend blues.

Regardless of the fact that you want to be cranky old blokes and pick on me, I do appreciate your help.

Actually they are being nice to suggest to you to make your location more specific....because if you don't.... there is a REALLY cranky old bloke who turns up...breaths some fire and brimstone..... and tells you to read the FAQ. You are then on a yellow card....and that's if he's having a good day.


You've got some great answers there. The other thing to say is that the lower the aperture number that a lens has is that, in general, the better quality lens it is, and has the ability to shoot in lower light and to isolate the subject from the backgound at the lower aperture numbers.

Again, in general, prime lens have lower aperture numbers than zooms. You can get 50 mm primes with aperture numbers of 1.4 or 1.8 relatively cheaply and they are the bees knees for understanding depth of field.

[Wink]

Hi Charlie.

Have a look at this video (and the others) at... http://www1.canon.com.au/worldofeos/learn/getting-started/Definitions-of-aperture-iso-shutter-speed.aspx

[gstark]

Geez! You fellows really are picking on me! That's okay. I really appreciate your help and I am old enough (and big enough) to give a bit back if I think you deserve it.

Good.

Just watch out for that gstark character. He's a real PITA, know-it-all, and general dogsbody and dishwasher. He makes Grumpy look like Happy, and makes Doc turn Dopey.

Digital photography has been a constant learning experience for me albeit sometimes frustrating and I am in it for the long haul.

That's good to hear. There is a lot to learn, and there are many here who are supremely qualified to offer you advice and suggestions. It's always up to you to choose to accept them, or not, as you please. Nobody here will get too upset if you choose to not accept the advice offered, just as long as you listen and consider it.

So as long as you listen and ask good questions, such as you have done here, and also post some images for critique, you will truly be amazed at how quickly your skills will progress.

You've already had some good answers, but I think it's probably not a bad idea to summarise and recap. First of all, the mention by Greg of your location (and I note that you've heeded it) is important for exactly the points he mentioned. One of the best cameras to learn on is the Nikon D40/D60/D90 series, simply because of the brilliant UI they present to their owners. If need be, someone with one of these bodies in the northwest may be able to meet with you to help show you this, and help you with the comprehension.

In terms of the question you've asked here, those cameras gives a brilliant graphical display of exactly how the aperture works, with the relationship of the lower numerical values (f/5.6, f/4, f/2 etc) to a larger physical aperture opening - the hole through which you will be shooting - as compared with the higher numerical values (f/16, f/22, f/32) and the smaller or narrower hole through which you will be shooting.

At first that seems counter-intuitive, but it really doesn't take a long time to learn, and as I said, those cameras present this graphically in a manner that's easy to see and comprehend.

Now, all of that relates to how the camera and lens work in order to make an image. Your question asked about the value as it pertained to your lenses, and in that regard - as has been correctly stated - this is simply telling you the maximum amount that your lens's aperture can be opened, and it also tells you just how (optically) fast your lens is.

As we have seen, a lower number means a larger hole, and that means that the lens can allow more light to pass through at its maximum aperture. So, an lens with f/5.6 will have a smaller hole than one with f/4, and as such, the f/4 lens will be faster (lets more light through at its maximum aperture) thant the f/5.6.

Take that to the next level, and of course you will observe that a lens with an f/2 maximum aperture will have an even larger opening, and thus will be faster again, letting still more light pass through.

F/1.4 is faster again, of course, but by now you understood that, right?

Now, and not wanting to confuse you, but we need to consider a couple of physical aspects here. As we have seen, a faster lens dictates a larger hole, but to make a larger hole ... means that we probably need to make a larger lens into which that larger hole must fit. You cannot, for instance, have the hole being larger than the lens, can you? That you just be stupid. Which probably means that someone like Kia are working on this as we speak.

So, a faster lens will be bigger, and heavier too.

Yep, they cost more as well.

Not sure why it has to be more specific but I hope this helps with the wet weekend blues.

It's actually a rule, but that point aside, when you know somebody lives nearby, it's really easy to offer some assistance. A few weeks ago I met with a couple of members from the inner west when one of them was having issues with a brand new lens. We were able to confirm the problem in a very positive manner, and the lens is now back in HKG, making its excuses before its maker.

I am proud to say that people from this forum get together quite frequently - check the calendar (and link) on the portal page for next weekend's 2x2 activity; you will be more than welcome to come along to what will be a great day. Stubbsy organises these events better than anyone, and you will learn more than you believe can be learned on just one short day.

Regardless of the fact that you want to be cranky old blokes and pick on me, I do appreciate your help.

Not them. just that cranky old fart, gstark.

OBTW, welcome.