There's a few question that im interested in knowing hopefully all the sifu can help out.
For a lens normally it will says 18-55mm F3.5/f4.5.
1) How to see how much the lens can zoom? Any calculation?
2) What is the F value for? Aperture?
3) The 18-55mm represents what? Focal length?

Thanks all

1) zoom = 55/18 = 3.055X
2) apperture = F3.5 at 18mm (28.8mm for APS-C), F4.5 at 55mm (88mm for APS-C)
3) 18-55 = capability of zoom at full frame 35mm format, if translated to APS-C format it will be 28.8-88mm

APS-C = common size of non full frame CCD for DSLR

only apply to 1.6x crop APS-C sensor.

Some sensor like Olympus is 2x crop. Some are full frame

1) Maximum focal length divide by minimum focal length.

Example 1 (18-55mm lens): 55/18 = 3.05X zoom
Example 2 (55-200mm lens): 200/55 = 3.63X zoom
Example 3 (18-200mm lens): 200/18 = 11.11X zoom

2) In layman's term, aperture is something like iris. Bigger the aperture, more light comes in, the brighter the picture. Other effect is shallow depth of field (sharp on focus, other part just blur)

3) It represents focal length in 35mm format. To get actual focal length, multiply with crop factor (which depends on camera sensor size)

and u might be asking why there are f3.5/f4.5,

becoz for entry level lens, the aperture is not constant,

for example, the 18-55mm f/3.5-5.6 kitlens for nikon d40,

the maximum aperture on 18mm is f3.5, but as u zoom in, to 35mm let's say, the maximum aperture will drop, to around f4.x (i forgot edy), and when u r in 55mm, the maximum aperture will be f5.6.

of coz, the bigger the aperture (the smaller the f-number) the better it is, because on 18mm, u still can set the aperture from f3.6(maximum aperture) to f22(minimum aperture).

while on 55mm, the aperture range is from 5.5 to 36 (IIANM).

usually, ppl seldom look for the minimum aperture(the biggest f-number), because when u are in minimum aperture, the image will turn out soft, thus, normally we wont be using that, even in shooting landscape.

Thanks... Nice nice replies from you guys.

focal length does not change even in crop frame sensors... only angle of view changes. 50mm remains 50mm.

awwhh man
what r u guys talking?
very the noobness
bwahahaha

interested to know but make it more easy sentences for layman like me

how to use focal length n aperture to estimate subject distance and depth of field range?

dun play play, the smaller the f-number, the better killer portrait shots you have

ermm.... hard to explain already worrr... a pns camera can't really play with aperture settings. it's usually set to f2.8 (canons taht is)

just know that, the lower the f number for exmaple f1.8, u focus on a small area and the rest all blur out...
layman's terms : those nice nice picture where the gal's face is a sharp and pretty, but the background all blur blur....

bokeh and shallow depth of field same or not??

in a way, yes.

bokeh means the out of focus effect

the more shallow the DOF is, the more obvious the bokeh is

So the higher the aperture the better?

It's better to use higher aperture to shoot potraits where you wanna focus on that person and blurs the background. For landscape shots, you'll need lower aperture to make sure everything is in focus.

I think the lower the valur more geng...

I was told that nowaday the most geng one are from Canon. Something like EF50 f1.2 L and EF85 f1.2 L, which both can gather the most avaiable lights. At this moment, Nikon are kind of stuck at f1.4 only...

Come on Nikon, do come up with something like f1.0 and beat the Canon!

Then Canon pula come out more geng lenses like f0.8... and then Nikon f0.7, then 0.5, 0.4, 0.3, 0.2, 0.1, and finally 0.0, which is basically a black hole to suck light at no limit....

Canon 50mm f1.0

Just imagine if one day our avaiable ligth in indoor like inside the room suddenly darken for split second because someone was using his f0.0 lense to take picture....

I think it is wrong to say the phrases like "lower aperture is better" or "higher aperture is better".

It all depends on situation.

It's good to know know when lower aperture will produce better image, and when higher aperture is more superior.

If you're taking portrait shots (clear, sharp face, blur out backgrounds), then use high aperture (means low f-stop values like f4.0 or f5.6 for most lenses). If your lens permits you to go higher, then go ahead (like f1.0 or something )

If you're taking landscapes, you want the whole picture to be sharp and clear (well, theoretically), use lower aperture (means high f-stop values somewhere around f10 or f11 or something).

In what situation do we go until f20++ ... this... I need to ask my si-fu here in the forum. How ah?

http://www.canon.com/camera-museum/camera/...5/s_50_095.html
50mm @ f0.95... now try to beat that !

well it's S-mount though

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Added on January 25, 2008, 10:24 pm
f20+ when taking macro

you will want to capture the superb details

not really.....f20 can cause serious distortions. no lens at either extremes are good.. .
hence ppl say sweet spot for any lens is 2 stops above the rated i.e. if it's a f1.8 lens, shooting at f3.8 is it's 'sweet spot'.

then again depends on what u wanna shoot la..

f20 is still too distorted! (try squinting ur eyes)

so its the larger the value difference of the minimum aperture and maximum aperture the better?

bro... i suggest go read up...

just to make things simple for u ..... if there's an aperture range (i.e. f range) say from 3.5 - 5.6 means at the widest possible of the lens (say 18mm) it is f3.5. and if it's at the longest, or zoomed out the max, say (200mm) it is f5.6.

meaning it's not able to keep a constnat f size all through the zoom range. this is because it's not cheap or not physically possible to make constant f size all through the zoom range (e.g. 18-200)

if u still dont' get it. ask urself why the 70-200 f2.8 is sooooo expensive and how come the 70-300G (f 3.5 - 6.3) is soooo cheap....

the ratio which ure talking about syyang85, is not important lah! don't bother.....

i don't want a 50mm with a front lens element as big as an Astro dish