Can someone PLEASE dumb down...

[sabrina860]

...Focal length? Ive been to tons of sites and I just dont get it! *cries*

What the heck does this mean:
"Very simply, focal length is the distance from the lens to the film, when focused on a subject at infinity."

Does this mean the distance from the lens to the subject? UGH! This is the ONLY thing im stuck on. Do i even need to know this?

And also what size filter do I use for my Nikkor 18-55mm lens? Someone told me i need a size 52mm. Why is that???

these lens specifications are so confusing!!

Help IS APPRECIATED!

[tuxcomputers]

Originally Posted by sabrina860

And also what size filter do I use for my Nikkor 18-55mm lens? Someone told me i need a size 52mm. Why is that???

Take your lens, look at it from the front, around the front edge will be a threaded ring, the diameter of that ring is 52mm.

When you look at filters you will see many different types (UV, Circ Pol, Graduated etc) and you will see different sizes for each type. The size you want is 52mm for that lens so that it screws onto the front threaded ring.

[jamesev]

Originally Posted by sabrina860

...Focal length? Ive been to tons of sites and I just dont get it! *cries*

What the heck does this mean:
"Very simply, focal length is the distance from the lens to the film, when focused on a subject at infinity."

Does this mean the distance from the lens to the subject? UGH! This is the ONLY thing im stuck on. Do i even need to know this?

And also what size filter do I use for my Nikkor 18-55mm lens? Someone told me i need a size 52mm. Why is that???

these lens specifications are so confusing!!

Help IS APPRECIATED!

Because if you are getting a screw in filter (a round one that screws onto the lens) you will see that the end of the lens has a very small lip and the glass is set a little way into the lip. Between the end of the glass and the end of the lip is a thread.
52 mm refers to the diameter of the inner end of the lens that you need to screw the filter into. Simples...

[sabrina860]

Originally Posted by tuxcomputers

Take your lens, look at it from the front, around the front edge will be a threaded ring, the diameter of that ring is 52mm.

When you look at filters you will see many different types (UV, Circ Pol, Graduated etc) and you will see different sizes for each type. The size you want is 52mm for that lens so that it screws onto the front threaded ring.

oh duhhh! Thankyou! I feel like an idiot. I didn't know it was the diameter...

Do you know anything about focal length? Do I need to know about it... and in play with the exposure triangle?

[gturner]

Focal length has nothing to do with the subject. I is the distance from the front glass on your lens to the senor. It is measured in millimeters.

14mm is short focal length (wide angle)

500mm is a long focal length (super telephoto)

A ZOOM lens is one where the focal length can change - IE 18 can change to 55mm by turning the barrel)




The FILTER goes on the front of the glass. . 52mm is the DIAMETER of the lens on the front where the filter screws into place. Different lenses have different diameters. (more expensive/ better quality have bigger sized front ends as they allow more light in)

[sabrina860]

Yes I know this now. It was just me thinking too hard. I thought somehow the 18-55mm came into play somehow to get the 52mm lens number.

[tuxcomputers]

Originally Posted by sabrina860

Do you know anything about focal length? Do I need to know about it... and in play with the exposure triangle?

All I know about focal lengths is:

1. Small focal lengths are wide angle, the smaller the wider
2. Large focal lengths is zoomed in, the larger the more zoomed.
3. 50mm on 35mm film was neither zoomed in or zoomed out, it was "normal". With the crop factor of digital cameras it is different.
4. It has nothing to do with the exposure triangle
5. I do not need to know any more than that unless I want to become a lens designer, I don't.

[sabrina860]

Originally Posted by gturner

Focal length has nothing to do with the subject. I is the distance from the front glass on your lens to the senor. It is measured in millimeters.

14mm is short focal length (wide angle)

500mm is a long focal length (super telephoto)

A ZOOM lens is one where the focal length can change - IE 18 can change to 55mm by turning the barrel)




The FILTER goes on the front of the glass. . 52mm is the DIAMETER of the lens on the front where the filter screws into place. Different lenses have different diameters. (more expensive/ better quality have bigger sized front ends as they allow more light in)

""I is the distance from the front glass on your lens to the senor.""

JESUS Why don't sites just say this?!

Thankyou for your SIMPLE detailed explanation

[sabrina860]

Originally Posted by tuxcomputers

All I know about focal lengths is:

1. Small focal lengths are wide angle, the smaller the wider
2. Large focal lengths is zoomed in, the larger the more zoomed.
3. 50mm on 35mm film was neither zoomed in or zoomed out, it was "normal". With the crop factor of digital cameras it is different.
4. It has nothing to do with the exposure triangle
5. I do not need to know any more than that unless I want to become a lens designer, I don't.

LOL... thankyou!

[tuxcomputers]

Originally Posted by sabrina860

""I is the distance from the front glass on your lens to the senor.""

Not quite, the length from the front of the glass to the sensor is wrong, my 18-55mm starts out long, shortest around 35mm then lengthens again to the 55mm mark.

If you have seen diagrams about focusing you will see the lines that come from the sides cross over the line coming from the other side and ends up on the opposite site.

Where the lines cross is the focal point, the distance from the cross point to the sensor is the focal length of the lens.