Newbie Lens/Focal Length Question

Hello,

Please correct me where I am wrong.

I understand that the focal length of the lens can be varied and in
doing so you change the "zoom" of the lens.

I understand that 50mm sees things pretty much as I see it. I have a
1.6x crop so to see things through the camera as I see it, I 'd shoot
at 50/1.6= ~30mm.

If I wanted 10x zoom, would I be looking for an effective focal length
of 500mm?

Thanks

I understand that the focal length of the lens can be varied and in
doing so you change the "zoom" of the lens.

Prime lenses are fixed in FL and zoom lenses allow a range of FLs.

I understand that 50mm sees things pretty much as I see it. I have a
1.6x crop so to see things through the camera as I see it, I 'd shoot
at 50/1.6= ~30mm.

50 mm is a "normal lens" meaning the field of view is about what we see.
Yes, 30 mm is close to normal with your camera.

If I wanted 10x zoom, would I be looking for an effective focal length
of 500mm?

(10 x normal)/1.6 = 300 mm (if I understand you correctly).

I understand that the focal length of the lens can be varied and in
doing so you change the "zoom" of the lens.

Prime lenses are fixed in FL and zoom lenses allow a range of FLs.

I understand that 50mm sees things pretty much as I see it. I have a
1.6x crop so to see things through the camera as I see it, I 'd shoot
at 50/1.6= ~30mm.

50 mm is a "normal lens" meaning the field of view is about what we see.
Yes, 30 mm is close to normal with your camera.

If I wanted 10x zoom, would I be looking for an effective focal length
of 500mm?

(10 x normal)/1.6 = 300 mm (if I understand you correctly).

Capt,
My understanding is that the 50mm = 1x rule is correct for 35mm film
cameras, but that for digital SLR's it more like a focal length of 35mm = 1x
due to the smaller size of the CCD.

Randy L.

"Capt Donkey Smile" wrote in message
oups.com...
Hello,

Please correct me where I am wrong.

I understand that the focal length of the lens can be varied and in
doing so you change the "zoom" of the lens.

I understand that 50mm sees things pretty much as I see it. I have a
1.6x crop so to see things through the camera as I see it, I 'd shoot
at 50/1.6= ~30mm.

If I wanted 10x zoom, would I be looking for an effective focal length
of 500mm?

Thanks

Capt,
My understanding is that the 50mm = 1x rule is correct for 35mm film
cameras, but that for digital SLR's it more like a focal length of 35mm = 1x
due to the smaller size of the CCD.

Randy L.

"Capt Donkey Smile" wrote in message
oups.com...
Hello,

Please correct me where I am wrong.

I understand that the focal length of the lens can be varied and in
doing so you change the "zoom" of the lens.

I understand that 50mm sees things pretty much as I see it. I have a
1.6x crop so to see things through the camera as I see it, I 'd shoot
at 50/1.6= ~30mm.

If I wanted 10x zoom, would I be looking for an effective focal length
of 500mm?

Thanks

"Capt Donkey Smile" wrote in message
oups.com...
Hello,

Please correct me where I am wrong.

I understand that the focal length of the lens can be varied and in
doing so you change the "zoom" of the lens.

I understand that 50mm sees things pretty much as I see it. I have a
1.6x crop so to see things through the camera as I see it, I 'd shoot
at 50/1.6= ~30mm.

If I wanted 10x zoom, would I be looking for an effective focal length
of 500mm?

Thanks

Your math (and most on here) refers to a "crop factor", i.e., trying to
reference
everything back to 35mm. IF you have no previous 35mm experience, you CAN
make things easier on yourself by thinking in terms of whatever your camera
is from
the beginning. "Normal" is the diagonal of the sensor. "Portrait" is
usually anywhere
from 1.7 x Normal to 2.4 x Normal. 4 x Normal to 6 x Normal gets used a lot
in
sports and wildlife (6 x Normal is about the beginning of the range for bird
photography).
Now, for example, on a Nikon D-70 the sensor size is 23.7mm x 15.6mm, so the
diagonal is 28.37mm, so "Normal" would be about a 28mm lens. "Portrait"
would
be 48mm to 68mm. And for sports and wildlife, one would probably use 113mm
to 170mm. If you think these numbers are a bit on the "low" side, it is
mostly due
to referencing back to 35mm...you see, the diagonal of the film would
indicate that
a "normal" 35mm lens would be about 43mm. In medium format photography (6cm
x 4.5cm, 6cm x 6cm, 6cm x 7cm, and 6cm x 9cm) and large format photography
(4in x 5in, 8in x 10in, etc) "normal" is closer to the film (or sensor)
diagonal.

Looking back at this, I HOPE this made it easier and not more confusing.

George

"Capt Donkey Smile" wrote in message
oups.com...
Hello,

Please correct me where I am wrong.

I understand that the focal length of the lens can be varied and in
doing so you change the "zoom" of the lens.

I understand that 50mm sees things pretty much as I see it. I have a
1.6x crop so to see things through the camera as I see it, I 'd shoot
at 50/1.6= ~30mm.

If I wanted 10x zoom, would I be looking for an effective focal length
of 500mm?

Thanks

Your math (and most on here) refers to a "crop factor", i.e., trying to
reference
everything back to 35mm. IF you have no previous 35mm experience, you CAN
make things easier on yourself by thinking in terms of whatever your camera
is from
the beginning. "Normal" is the diagonal of the sensor. "Portrait" is
usually anywhere
from 1.7 x Normal to 2.4 x Normal. 4 x Normal to 6 x Normal gets used a lot
in
sports and wildlife (6 x Normal is about the beginning of the range for bird
photography).
Now, for example, on a Nikon D-70 the sensor size is 23.7mm x 15.6mm, so the
diagonal is 28.37mm, so "Normal" would be about a 28mm lens. "Portrait"
would
be 48mm to 68mm. And for sports and wildlife, one would probably use 113mm
to 170mm. If you think these numbers are a bit on the "low" side, it is
mostly due
to referencing back to 35mm...you see, the diagonal of the film would
indicate that
a "normal" 35mm lens would be about 43mm. In medium format photography (6cm
x 4.5cm, 6cm x 6cm, 6cm x 7cm, and 6cm x 9cm) and large format photography
(4in x 5in, 8in x 10in, etc) "normal" is closer to the film (or sensor)
diagonal.

Looking back at this, I HOPE this made it easier and not more confusing.

George

The 50mm focal length is consider "normal" for the 35mm format. It doesn't
cover the entire field of view our eyes cover, but it does cover about what
we see in the sharper center portion of our field of view. Some lenses are
of a fixed focal length which cannot be varied. Zoom lenses allow varying
the focal length over a pre-determined range. This zoom range is determined
by the ratio of the longer focal length to the shorter focal length.
Therefore, a 10x zoom will have a range in which the longer setting is 10
times the shorter setting. A 50-500 zoom lens would have a 10X zoom range
while a 100-500 zoom lens would have a 5X zoom range. Both a 35-105 zoom
lens and a 70-210 zoom lens have a 3X zoom range.

KB


"Capt Donkey Smile" wrote in message
oups.com...
Hello,

Please correct me where I am wrong.

I understand that the focal length of the lens can be varied and in
doing so you change the "zoom" of the lens.

I understand that 50mm sees things pretty much as I see it. I have a
1.6x crop so to see things through the camera as I see it, I 'd shoot
at 50/1.6= ~30mm.

If I wanted 10x zoom, would I be looking for an effective focal length
of 500mm?

Thanks

The 50mm focal length is consider "normal" for the 35mm format. It doesn't
cover the entire field of view our eyes cover, but it does cover about what
we see in the sharper center portion of our field of view. Some lenses are
of a fixed focal length which cannot be varied. Zoom lenses allow varying
the focal length over a pre-determined range. This zoom range is determined
by the ratio of the longer focal length to the shorter focal length.
Therefore, a 10x zoom will have a range in which the longer setting is 10
times the shorter setting. A 50-500 zoom lens would have a 10X zoom range
while a 100-500 zoom lens would have a 5X zoom range. Both a 35-105 zoom
lens and a 70-210 zoom lens have a 3X zoom range.

KB


"Capt Donkey Smile" wrote in message
oups.com...
Hello,

Please correct me where I am wrong.

I understand that the focal length of the lens can be varied and in
doing so you change the "zoom" of the lens.

I understand that 50mm sees things pretty much as I see it. I have a
1.6x crop so to see things through the camera as I see it, I 'd shoot
at 50/1.6= ~30mm.

If I wanted 10x zoom, would I be looking for an effective focal length
of 500mm?

Thanks

"Capt Donkey Smile" wrote in message
oups.com...
Hello,

Please correct me where I am wrong.

I understand that the focal length of the lens can be varied and in
doing so you change the "zoom" of the lens.

Well, with a zoom lens you can change the focal length, yes. That's what
zoom lens means. Changing the focal length changes the image size in
direction proportion, e.g. 2x the focal length = 2x the image size.



I understand that 50mm sees things pretty much as I see it.

Actually, NO camera lens really "sees thing pretty much as [you] see it,"
for a lot of reasons. Your visual angle of view (assuming normal eyesight)
is much wider than the field of view of a 50mm lens, as you can easily see
for yourself. On the other hand, most of what you can see over that wide
field of view (typically about 180 degrees horizontally) you cannot see very
sharply, while the 50mm lens covers everything sharply. Also, your eye's
"film," the retina, is essentially the inside of a hemisphere whereas in a
film or digital camera the corresponding sensor is flat. So there is just no
way any conventional camera can really see as your eye sees.

The 50mm lens (on a 35mm camera) has been regarded as "normal" for decades.
That doesn't mean the camera with such a lens sees as your eye sees, only
that it produces an image that "looks about right," neither too wide nor too
narrow in angle of view. Actually the 50mm lens is a little long for
"normal" on a 35, since traditionally "normal" has meant equivalent to the
diagonal of the negative--which would be about 43mm on a 35. "Normal" lenses
for 35s have been made with all sorts of focal lengths, from 40 to 58mm at
least. There is nothing sacred or cosmically significant about 50mm.



I have a
1.6x crop so to see things through the camera as I see it, I 'd shoot
at 50/1.6= ~30mm.

Right, a 30mm lens on such a camera would give you the equivalent of 50mm on
a 35. Just don't take that focal length as being too important, as it is
not.



If I wanted 10x zoom, would I be looking for an effective focal length
of 500mm?

Depends. Most zoom lenses are somewhat wide angle at the short end, not
"normal." If you assume that you want a zoom that STARTS at around "normal"
then yes, something equivalent to 50-500mm would be the 10x zoom you'd look
for. But much more usual is a 10x zoom somewhat wider at the short end, like
38-380mm.



Thanks

N.