Newbie lens doubts


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shas3n

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Jun 4, 2003
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#1
Hi,
i just have a compact cam that does not even have a lens thread..:cry: but someday i hope to upgrade to an SLR and was having doubts about all the lenses you pros seem to speak of.
here are my doubts
1. What is the significance of the focul length of the lens?
2. If 28-80mm or 35-105 or 50-150 (not sure of numbers) all give 3x zoom.. then why do we need all the 3 lenses?
3. If we do need such lenses what to use when?

Please enlighten me. Even giving links is enough.
thanks in advance
Shastri
 

shas3n

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#4
thanks kex...that is an encyclopedia:thumbsup: :thumbsup: . Will be busy with it for atleast a few days i guess.
thanks
 

majere2sg

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Mar 31, 2003
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#5
Originally posted by shas3n
Hi,
i just have a compact cam that does not even have a lens thread..:cry: but someday i hope to upgrade to an SLR and was having doubts about all the lenses you pros seem to speak of.
here are my doubts
1. What is the significance of the focul length of the lens?
2. If 28-80mm or 35-105 or 50-150 (not sure of numbers) all give 3x zoom.. then why do we need all the 3 lenses?
3. If we do need such lenses what to use when?

Please enlighten me. Even giving links is enough.
thanks in advance
Shastri
for 28-80mm, you can use it as a wide angle lens at 28mm.
for 50-150mm, you can use it as telephoto lens at 150mm ?
although the zoom is the same at 3x but the image size is different for all the 3 lens at the widest and telephoto end.
 

Tweek

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Jan 17, 2002
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#6
Originally posted by majere2sg
but the image size is different for all the 3 lens at the widest and telephoto end.
image size is the same, all of the 35mm frame size. ;)

subject size also can be the same, if you alter the distance to make up for it.

I guess the most accurate way to put it, is that the angle of view is different.
 

Aug 19, 2003
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#7
majere2sg is right about how photographers usually use their lenses... they all give 3x zoom, but the composition may be different for all the lens.

i've been reading michael langford's 35mm handbook recently and this is what i've gathered... hope it will be short but comprehensive enough for you to understand?

1. Focal Length Range
The bigger the focal length, the further you're able to capture. Hence, if you compare 35mm with one that can reach 300mm, you realize the 300mm lens can reach a farther distance to capture your subject.


2. Angle of View
Larger focal lengths give smaller angles of view. Hence for the standard 50mm, your angle of view for your lens would be 45degrees. Everthing that falls within 45degrees would be captured. For 300mm, the angle of view will be narrowed down to 15degrees or so. So you cannot capture a wider angle at 300mm.

For fisheye lens, you can capture everything with 180degrees of where your lens is pointing. You can even capture your feet if you're not careful of your pose while shooting with your camera :)


3. Perpective and Field of Depth
Wider lens will give more depth of field as compared to telephoto lens of the same aperture. Hence, using a wide-angled lens (e.g. 21mm) closer to foreground elements in your composition will exaggerate their size relative to background elements, hence giving a strong depth of field.
A telephoto lens will give you the opposite effect. Your foreground elements in your composition will look closer to your background elements and the entire image looks slightly flatter.

Final Tips:
When you change to a differect lens focal length, you will alter image magnification. Details of your subjects become enlarged. Hence, subjects from a 300mm lens will appear 10 times larger than subjects used on a 28mm lens.

In cramped conditions, eg in a room, use a wider angled lens (28mm - 35mm) and you will be able to include most of the room into your shot.

If the subject is far away, use a zoom or telephoto lens to shoot i.e. 135mm - 600mm, depending on how far and how large you want your subject to appear in your picture frame.

Hope this helps... and not too lor-sor :)
 

frisky

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Oct 13, 2002
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#8
Of course, all these assumes that the lens in question are all used for a 35mm SLR (flim or full frame Digital). If it is used on flim or digital CCD that are not 36x24mm, then there is another layer of complications.
 

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