Focal Length

Even tho I have tried to understand focal length I am still struggling! I have had a look at a few 'definitions', but can't get my head around this particular aspect of photography.
I guess my first question is how do you choose a particular focal length in the first place? And, where on the camera does it tell you the focal length setting? I own a Fujifinepix 6500fd - but don't know where to find this information - even after reading the manual cover to cover.
This knowledge would really help me with the personal projects!

Just had another look at my camera - and found the information I was looking for ... now I'm trying to hide my red face! I think my previous camera is what threw me since the 'zoom' was just a button, not a manual zoom - I've ignored the 'numbers' up until now ... oh well - at least this really shows you all what a complete beginner I am ............ LOL!

There is no need to be embarrased, that's what makes photography so great, there is always something to learn and no matter how much you know there is always more to learn.

The following video may help, the guy is a little nuts but it's worth watching.

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Paul

Paul,
Thankyou for your kind words! And for the link to the video ..... LOL - what a character! Very helpful illustration, and fun to watch as well! I'm still trying to put it all together .... so - does this mean that the focal length determines the aperture width? Can that be varied? If so, is that done to achieve certain effects? Please bear with me! I have only just begun to understand aperture widths and shutter speeds and 'metering' ... and still make a mess of it all very frequently (my 'trashcan' becomes full of discarded images!).

I'm not an expert on lenses so maybe someone else can give more info but the answer to your question is yes and no. If the lens starts at 3.5 at it's biggest opening, when you zoom in on a subject the value increases, this is what I'm not sure about as to why. It's something to do with the lens design.

Most of my lenses are pro lenses and are 2.8 all the way through so on my 70-200mm I set my aperture to 2.8 but when I zoom in the aperture stays at 2.8. These lenses are commonly referred to as fast lenses and are great in low light conditions such as indoors as 2.8 will let in a lot more light than say 5.6, 8, 11 etc.. and this is why they cost so much

You are right regarding the effects and in this case the effect will be Depth Of Field. DOF at 2.8 for example is quite narrow, so when you have focused on the subject, what the lens sees in front and behind is then blurred and how much depends on your focal length. The reason it is blurred is because the big opening of 2.8 will send a splash of light to the cameras sensor but because it's a splash of light it's not able to capture the detail in front and behind the subject hence the blurring.

To capture more detail in front and behind the subject, you'll need to increase the aperture size. As the numbers increase, the hole gets smaller so light is more gradually allowed on the censor so it captures more detail. This is why around f18 is used commonly used by landscape photographers as the detail is captured from right in front of the camera right into the distance with no blurring.

That's a quick overview but pictures especially videos speak louder than words. Here is another video I've found on youtube for you:



You'd be amazed of the video resource that's available on youtube and it's worth looking on there for any photography tutorials.

Hope this helps.

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Paul

Paul,
I do understand how to achieve the depth of field I want using larger/smaller aperture sizes ... but where I am still 'stumped' is if someone were to give me a focal length to work with (as in the 'personal projects' .... I just can't wrap my head around it! If I choose a particular focal length, then does that automatically influence all the other settings??? ..... aaaaggggghhhh!! (Lenita tears hair out at this point!!!)

It all depends on what shooting mode you have selected regarding the influence in the change of shutter speed, aperture etc.

Manual: You will have full control over all settings to get the correct exposure - changing the shutter speed will not influence the settings of the aperture, they all need to be manually set depending on your meter readings.
Aperture Priority: You control the desired aperture but the camera chooses the shutter speed depending on meter readings.
Shutter Priority: You control the desired shutter speed but the camera chooses the aperture speed depending on meter readings.
Program/Auto: The camera does all the choosing for you based on the meter readings.

I generally always shoot in manual as it offers full control over the exposure.

If you do have a zoom lens that does change the aperture size as you zoom in, the influence on shutter speed will depend on the shooting mode you are in.

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Paul

Paul,

Thankyou for taking the time to answer my questions

I use manual most of the time - and 'program' when I'm in a 'point and shoot' situation (on holidays - just want a 'quick shot', for example).

My camera will zoom from 28mm to 300mm. If I use the automatic settings, I can see that the camera chooses a wider aperture as I zoom in ... but, when in manual mode, do I need to do this? Is this simply to allow more light into the camera in order to prevent camera 'shake'? If I choose a smaller aperture setting than what the camera wants to do automatically (if I want a larger depth of field, for instance), and have zoomed in to the scene, will that then have an adverse effect on my photo???? This is my dilemma! And I haven't been able to work out the answer either in practice or by reading about it!
I'm sorry to be so persistent and 'pestiferous'!

It's probably a narrower aperture as you zoom in (larger f number).
This isn't the camera choosing the aperture as much as a physical limitation of the lens, the aperture can't remain as large when zoomed in, there isn't the room inside the lens for this to happen.
You don't need to do anything about this, just zoom and shoot even in Manual mode, if autoISO is on then you will get a correct exposure until you run out of light. If you do get an underexposed result then that will be the time for you to do something about it by either slowing the shutter speed, or upping the ISO if it's not on auto already.

As Paul said, zoom lenses with constant aperture are almost always in the pro sector, this is probably so that said pro photographer knows his/her aperture will not change with focal length, this presents a more difficult design, probably higher quality components and a hefty price tag.
This is not a limitation of P&S, both of my Nikon SLR lenses do this as do most zoom lenses.
Bottom line is, set the focal length and press the button.

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