canon lenses

[reemas]

three questions for someone who knows a little about photography(apertures, shutters, etc...) but NOTHING about SLR's and LENSES....

1.) what does it mean to be an SLR camera? i know that the acronym stands for, but what does that mean?

2.) i want to start with a canon rebel xt, but what are all those numbers on the lenses: 28-70mm / 3.5 ????

3.) what are ai servos for? i know what the servos in my model aircraft do, but in a camera, or on a lens?

[CyberDyneSystems]

1) Single Lens Reflex means that you see in the viewfinder through the lens,. exactly what the film will expose. The reflex has to do with the fact that to accomplish this we need a mirror/prism assembly that will get up our of the way when the shutter opens.

2) mm = focal lenght,. f/3.5 is the f/stop or aperture value. The lower the number,. the larger the aperture opening relative to focal length.

3) "AI servo" means that the camera will contnously update the autofocus as long as the focus button is pressed.

[reemas]

with f 3.5 and other aperture values, how does that compare? is a lower or higher number better?? or does it depened? and for higher f-stops, like f80, do you need a special lens?

[CyberDyneSystems]

The lower number is "better" it means more glass and more expensive most of the time.

This number is the largest aperture setting you can achieve with the lens,. these lenses however have adjustable aperutres and thus can be "stopped down" further.

I doubt there are any lenses that stop down to f/80,. but f/22 - f/32 is not unusual.

[reemas]

thanks for all the replies. this info is difficult for me to find without a forum.

so the lens that comes with the canon rebel xt is a "EF-S 18-55mm f3.5-5.6 Lens"
That means its range is probably something like 2.0 - 8.0 ? and how much can it zoom? 3x?

sorry for the very beginner questions...

[PacAce]

thanks for all the replies. this info is difficult for me to find without a forum.

so the lens that comes with the canon rebel xt is a "EF-S 18-55mm f3.5-5.6 Lens"
That means its range is probably something like 2.0 - 8.0 ? and how much can it zoom? 3x?

sorry for the very beginner questions...
For the EF-S 18-55 f/3.5-5.6, the maximum aperture is either f/3.5 at the 18mm range or f/5.6 at the 55mm end. The aperture is adjustable from the maximum wide open values given above to round f/22 or f/32.

The zooming range of the 18-55mm is 55/18 = 3X. It doesn't seem like much but the point with the SLR cameras is that you can interchange lenses to your hearts content (as long as you have the money to buy those lenses, that is :mrgreen: )

[reemas]

is that lens "good" and what makes certain lenses better? I hear that its not a great lens but for the price its worth getting.

i'm not sure if i should get it in the beginning or save the money towards a better lens.

any input on this?

[Andy_T]

Reemas,

the kit lens is ok for the price. Take a look at this review (http://www.photo.net/equipment/canon/efs18-55/).
It helps to remember that the 2 lenses it is compared to (20-35 and 28-105) cost at least 3 times as much.

Also ... bear in mind that all Canon pro-sumer cameras (DRebel, DRebel XT, 20D) have something called the 1.6 crop factor (read up on the concept here (http://www.luminous-landscape.com/tutorials/understanding-series/dslr-mag.shtml).) that will make this 18-55 lens 'behave' like a 28-90 lens on a film body.

Bottom line ... good if you want to get close to distant things, but bad if you want wide angle (e.g. for landscape/scenery shots). The 18-55 lens is the only cheap way to get a wide angle lens on the 20D. So even if you upgrade to a sharper/faster/longer lens later, it will be the only 'cost' option in the wide angle area.

I'd advise you to get it, try it out and see what you would like to have in your second lens.

Also, take a look at the member recommended lens section (http://photography-on-the.net/forum/showthread.php?t=56752). Bear in mind that the lenses featured in 'recommended starter lenses' are (apart from the 17-40/4.0L best used in addition to the 18-55 kit lens, as you use the wide angle.

Finally... take a look at these threads ... similar problems there and lots of basic information.
http://photography-on-the.net/forum/showthread.php?t=59848
http://photography-on-the.net/forum/showthread.php?t=58028

Best regards,
Andy

P.S: And ... of course ... WELCOME TO THE FORUM :lol:

[reemas]

wow thanks for the excellent replies!! andy im going to check that ou again, (i breifly read it once.) i'll post back with more questions shortly.

but whats the difference between EF lenses and EF-S lenses?

[rfreschner]

but whats the difference between EF lenses and EF-S lenses?

EF-S can only be used on the 20D and Digital Rebel cameras. They are specifically made for those models with the 1.6 crop factor.

[reemas]

if the lens has a max aperture of 3.5 such as canon's rebel KIT lens. does that mean 3.5 is the MAXIMUM aperture. or is it possible to set it to 2.8 through the camera??

(sorry this is probably an obvious question, but I heard conflicting numbers.)

[CyberDyneSystems]

Max is 3.5 so you can set it anywhere from f/3.5 - f/22 or whatever its smallest setting is.

You can't go larger (smaller f/##)