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Newbie Question
I am brand new to using a DSLR and would a quick crash course in Lenses.I purchased a Nikon D40 with the kit lens of 18-55mm f3.5-5.6G ed /AF s Dx.

When I look at this I am courious what the 18-55mm represents is this having to do with distance that is viewable thru the lens? Again I am brand new to using DSLR camera and looking to get another lens something in the line of a 55-200 or 70-300. and would like to understand what those figures represents...

Comments (14)

See here...

Http://www.dpreview.com/learn/?/Glossary/Optical/Focal_Length_01.htm.

'I reject your reality and substitute my own' -Adam Savagehttp://www.flickr.com/photos/mrnoronha/sets/..

Comment #1

The 18 and thre 55, and everywhere in between is the focal length..

Because this lens has lots of focal lengths, it's called a zoom lens.A lens with only one focal length, 50mm for example, is called a prome lens..

The lower the number, the wider the view..

In your lens, 18mm is wide angle, and 55mm is short telephoto..

For learning, go out with your camera set at 18mm, and look at something that fills the frame from top to bottom. See how much background there is..

Now back up, while changing the focal length, so the object keeps filling the frame from top to bottom..

Notice how the background changes..

BAK..

Comment #2

To compare lenses magnify focal lengths to get 35mm equivalent. Nikons have "magnification factor" of 1.5x - therefore your 18-55mm kit lens has a 35mm equivalent of 27-82.5mm. Pentax, Sony & Fuji are also 1.5x, Canon are 1.6x, Sigma 1.7x and Olympus 2.0x..

A common Olympus kit lens is their 14-42mm which when converted to 35mm equivalent (x2) is 28-84mm (Nikon was 27-82.5mm). So, it's not as wide angled as your 18-55 even though it's 14 is lower than 18 of Nikon - but it's more tele than 18-55 even though it's 42 is lower than 55 of Nikon - hope that makes sense!.

Regards......Caster..

Comment #3

Ok but that doesnt really answer the question as to what they number represents. you telling me how they get the number and what to convert it to by adding 1.5 or what ever.

What I asked is what do the numbers represent is it a focal point or a field of view when looking in the view finder? meaning if I put my eye to the viewfinder and it's at 18mm then I am seeing a feild of view of 18mm? or what ever it woudl be timesed by 1.5.

I need a simple answer for this not some long drawn out explination on how lenses work and what the times magnification is for the lenses. thanks and sorry if my reply sounds short or curt but this forum is for beginners and the answers seems to be for someone that knows something about lenses..

Comment #4

Motownmadmann wrote:.

What I asked is what do the numbers represent is it a focal point ora field of view when looking in the view finder? meaning if I put myeye to the viewfinder and it's at 18mm then I am seeing a feild ofview of 18mm?.

Nope..

I need a simple answer for this not some long drawn out explinationon how lenses work and what the times magnification is for thelenses. thanks and sorry if my reply sounds short or curt but thisforum is for beginners and the answers seems to be for someone thatknows something about lenses.

Ok, simple beginner answer: 18 and 55 are the focal lenghts of the lens assembly. There's your answer..

And the focal lenght is the distance from the middle of the equivalent lens to the focal point..

AND the equivalent lens is a lens which has the same focal lenght as the lens assembly..

So, basically, if, instead of a lens assembly you would have only one lens, the focal lenght would be the distance from the focal point to the middle of the lens..

A bit circular, isn't it? That's because the lens assembly is DEFINED by the focal lenght..

There is no way to get an answer based on these numbers WITHOUT going through an optics course..

Either you "know" what perspective a certain focal lenght lens gives you or you will learn. Until then, I suggest to visit the manufacturer's web site - or b&h's - where the field of view is also listed for most lens. It won't make much more sense, either, but at least it's more intuitive...

Comment #5

That help a little so if I have my 18-55mm and my focal point is say 10 feet away and I have the lens focused at 18mm... what does that mean..

Comment #6

Okay, I'll give you simple. You're going to use your 18mm and low numbers for panoramic views or wide angle shots. You're going to use your 55mm end for what is mild telephotic shotsthink of using maybe a 4X binoculars..

200mm and higher would be like using a 10X binoculars or. 800mm might be compared to a weak telescope..

But basically you decide what you want to take a picture of, look at th 2-1/2 inch LCD which is like a small TV screen, move the zoom IN and OUT, and stop the zoom when the scene fills this little view the amount you want it filled..

Then boublecheck that you have the camera set for the proper mode and SNAP the shot.ngk20000..

Comment #7

Motownmadmann wrote:.

That help a little so if I have my 18-55mm and my focal point is say10 feet away and I have the lens focused at 18mm... what does thatmean.

To answer PRECISELY what you asked: first, you'll need a strong mule to pack a camera at least 10 feet deep. And you'll break the lens trying to focus at 18 mm distance..

To answer what you MEANT to ask: you'll get a picture. And it means nothing. It's pretty much like asking: "I am driving to my destination with 16 inches rims and the gas is 3$ a gallon. What does it mean?"..

Comment #8

To see the effect of different focal lengths, take a look at this page.http://www.tamron.com/...es/learning_center/tools/focal-length-comparison.php.

Move the slider at the bottom to left and right, see the image change; the focal length as well as angle of view is displayed.Regards,Peter..

Comment #9

I think the answer which should be clear is that you don't "really" need to know what these numbers are based on. Just write it off as internal optical stuff, you can happily go through life without ever really understanding what is happening to the light as it passes through your lenses and focuses an image on your sensor..

What you do need to know is that a low number on a lens gives a really wide angle of view so you can fit loads in the frame. A very high number and the feld of view will be very small, a bit like looking through binoculars as someone said earlier..

What this means in practice is something you will learn as you go along. A lens which goes from 18mm starts out pretty wide, and by the time you get to 50mm it will be a lot narrower, but pretty good for "head and shoulders" type portrait shots. After using a lens like that for a bit you will get much more of a feel for what the focal lengths look like through the viewfinder and then you'll find yourself saying "Actually I need 10mm (or 100mm) for this shot" (depending on the artistic effect you want to achieve)..

Have fun...

Comment #10

Motownmadmann wrote:.

That help a little so if I have my 18-55mm and my focal point is say10 feet away and I have the lens focused at 18mm... what does thatmean.

I'm not sure if you got an answer to this. The 18mm or 55mm is the distance from the optical center of the lens to the light sensor when focused at infinity. As someone has said, the shorter focal length will give you a wider field of view and the longer focal length will give a narrower field of view. Only experience will show you what it means to you..

David..

Comment #11

Well said, and here's a link from the glossary here that may help.............http://www.dpreview.com/learn/?/Glossary/Optical/Focal_Length_01.htmRegards,Hank.

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window..

Comment #12

Thanks that link helps I see as I slide the arrow to the low end the angle of view is greater I guess you can say that it's reduces the perriferal (misspelled) vision in a way. but the link help..

Comment #13

Not sure anyone really answered your question about using 18mm portion of lens at a distance of 10 feet. Many responders here are so knowledgeable and hi-tech they have trouble backtracking to novic beginner..

The 18mm is the extreme wide angle or panoramic setting of your 18-50 lens. So, you're trying the get the most area in your image without you and the camera moving farther away..

The 10 feet tell us that you are probably not taking pix of big landscape. You're reasonably close to something like a small group of people, a garden shot, or taking a picture of the opposite wall in a 12-foot room..

There must be a reason for the 10-foot distance as most shooters would back up farther, use 40-50mm zoom and have less distortion in the final picture..

To summarize, in selecting the 18-50 zoom, just position yourself in the best location for shooter and camera, then zoom in an out until you get the desired composition in the picture..

Suggestion: Your questions indicate you might benefit greatly from a beginner photography course, or even reading the basic text for such a course. Try the library.ngk20000..

Comment #14

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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