Couple 'O' Stuipid Questions

PhilGarber · Sep 16, 2008

Hey all,

That's it! I have gone ignorant for far too long!:x Please forgive my utter noobishness..At what 'mm' does an average lens become a wide-angle lens, a macro lens, a telephoto lens, ect? Also, what's an 'F-stop'? aperture..right? What does 'f6' f8' (ect,) mean? What does iTTL mean???

Gosh, I'm a friggin' Dumb#@% :grumpy:

Phil,

tirediron · Sep 16, 2008

In terms of focal lengths, (using a 'full-frame' 35mm size for reference) 50mm (~35mm in APS-C) is considered 'normal' and anything below that is wide-angle, above that telephoto.

You're correct, 'f stop' is the aperture, or the internal, optical diameter (Not necessarily related in any way to the physical size of the lens). Depending on who you ask, the 'f' stands for 'focal' or 'factor'. The actual number is a ratio of the aforementioned diameter expressed against the focal length.

Macro doesn't relate to a specific focal length, but rather to a lens which will focus closely enough on the subject to produce a full-size image on the sensor (1:1), that is, if the bug is 5mm long, it will take up 5mm on the sensor.

iTTL is simply Nikon's lat

tsaraleksi · Sep 16, 2008

In 35mm terms, a wide angle lens is usually something that is 35mm or shorter. If you are working with a 1.5 or 1.6 crop sensor, you're looking at 24mm and shorter. Wide angle lenses are usually in the 16/7/8 range. That said, a 'normal' zoom lens will try and start out wide. A 1.6x 'normal' lens is going to start at 17 or 18 and go to 50 (or a bit longer).

Telephoto usually means anything about 80mm or longer. Super telephoto is generally considered to start at 300.

Macro can be any length, what defines a macro lens is an ability to focus far closer than a normal lens, which lets you photograph smaller objects. Some common lengths for macro lenses are 50, 100, 150, and 180.

An f/stop is the setting on a lens that determines how much light the lens will let through. The lower the number, the more light that can come in. The fastest lens in production is the brand new Leica 50mm f/0.95, for SLRs the fastest are the Canon 50 and 85 f/1.2L. The smaller the number, the shallower the depth of field in an image, which can either be a problem or help to isolate a subject (think of a picture of a baseball player with the crowd nothing but a blur behind him).

F stops go like so-- 1.0, 1.4, 2.0, 2.8, 4, 5.6, 8, etc. Each time you move by a stop, the amount of light coming through the lens will either double or halve.

The fastest zoom lenses are usually around f/2.8, but inexpensive lenses are probalby going to fall into the 3.5-5.6 range.

iTTL is a term for a kind of flash measurement-- modern electronic flashes are set up to meter the amount of light that they need to properly illuminate their subject, and iTTL is one form of that system.

PhilGarber · Sep 16, 2008

Thanks Tirediron!

So like, what would a 18-55mm lens be considered? (The XT kit lens)

PhilGarber · Sep 16, 2008

Thanks Tsaral! Welcome to The Photo Forum, btw!

Helen B · Sep 16, 2008

'Telephoto' has two meanings: one is the loose, common 'longer than a normal lens' meaning and the other is slightly more specific, and refers to the optical design:

A telephoto design is often defined as being a lens that is shorter than its focal length when mounted to the camera. A 200 mm telephoto sticks out less than 200 mm from the image plane (the sensor or film). In technical terms the front vertex (the front of the front element) is behind the rear (or second) nodal point (the rear nodal point of a 200 mm lens is 200 mm from the image plane). There is another slightly different but similar meaning, but I'll stop there to avoid further complication.

The reverse design is an 'inverted telephoto' or 'retrofocus' lens - typically used for wide angle lenses for SLRs. The rear vertex (the back of the back element) is in front of the rear nodal point (ie all optical parts of the lens are further from the image plane than the focal length).

Best,
Helen

Bifurcator · Sep 16, 2008

PhilGarber said:
Gosh, I'm a friggin' Dumb#@%

Phil,

Ignorance and "dumbness" are not related IMO. But the best cure for this "dumbness" as you put it is wikipedia!

For example if I type in "F-Stop wiki" into my google search engine I get:
http://en.wikipedia.org/wiki/F-number

If I type in "Wide angle lens wiki" I get:
http://en.wikipedia.org/wiki/Wide-angle Which says "...a lens of focal length 35 mm or less is considered wide-angle."

etc. etc. Wiki ROCKS for this kinda stuff!

Helen B · Sep 16, 2008

Don't bother reading the Wikipedia entry on 'telephoto', however. It is full of pseudo-technical BS.

Best,
Helen

Bifurcator · Sep 17, 2008

LOL... go in and correct it. I do that ALLOT for render-centric and CG shader entries.

Moglex · Sep 17, 2008

Bifurcator said:
Ignorance and "dumbness" are not related IMO. But the best cure for this "dumbness" as you put it is wikipedia!

Rather the other way around, surely?

Ignorance is lack of knowledge which can often be remedied by the use of something such as Wikipedia.

'Dumbness' is generally defined as stupidity or lack of intellect. Sadly, neither of these conditions can be remedied by even the best of encyclopaediae.

Mike_E · Sep 17, 2008

Yes, Yes and more yes.

Wide angle lens is really in it's simplest form a lens with a greater angle of view than a normal lens and as stated that happens around 35mm on an full frame camera.

Here is a nice calculator for this, DOF and various...
http://www.tawbaware.com/maxlyons/calc.htm

PhilGarber · Sep 17, 2008

Thanks guys! ill remember that!

Warren_G · Sep 18, 2008

Helen B said:
Don't bother reading the Wikipedia entry on 'telephoto', however. It is full of pseudo-technical BS.

Psuedo technical? You mean like "inverted telephoto" or "retrofocus" or "The rear vertex is in front of the rear nodal point"?

Helen B · Sep 18, 2008

Warren_G said:
Psuedo technical? You mean like "inverted telephoto" or "retrofocus" or "The rear vertex is in front of the rear nodal point"?

Those appear to be referring to my post rather than the Wikipedia article on 'telephoto' as neither nodal point nor vertex are mentioned in the Wikipedia article. Are you suggesting that my post is no more than pseudo-technical BS? I'm gutted! I rather like the out-of-the-blue reference to the front and rear vertex mixed in with the non-technical explanation, and appreciate it that someone else has seen the humour.

Thanks,
Helen

Warren_G · Sep 18, 2008

Sorry, it just struck me as funny first thing this morning before my coffee. At least I have my priorities right: first check TPF, then get a cup of coffee.