# Question on lens

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##### New Member
I am getting a 350D this weekend. But I have a few questions in regards to lens:

How do I determine the optical zoom for the lens with use on my 350D? I read that the sensor is smaller than 35mm and therefore the focal length tends to increase. What effect does it make? Sorry if I sound really ignorant but I'm totally new to such things and I need some advice.

So if I were to buy Tamron AF 28-200mm, how would the optical zoom be like? How is it calculated?

#### billpepsi

##### New Member
I am getting a 350D this weekend. But I have a few questions in regards to lens:

How do I determine the optical zoom for the lens with use on my 350D? I read that the sensor is smaller than 35mm and therefore the focal length tends to increase. What effect does it make? Sorry if I sound really ignorant but I'm totally new to such things and I need some advice.

So if I were to buy Tamron AF 28-200mm, how would the optical zoom be like? How is it calculated?

IIRC, 350D multiply factor is 1.6, hence a 200mm is equivalent 320mm (35mm)

##### New Member
I'm sorry... so 320mm is near to 10X optical zoom?

#### rebbot

##### Senior Member
28-200 is a 7.1x zoom if you want to know how many "times" it is. It is derived from dividing 200 by 28.

##### New Member
Ooh... so every lens optical zoom is derived by maximum focal length / minimum focal length?

Hey, thanks!

#### mpenza

##### Senior Member
note that the number of times of zoom doesn't really make a lot of sense in the SLR world. e.g. there are primes (fixed focal length) that could give you tighter framing than a "10x" zoom.

#### majere2sg

##### Senior Member
I'm sorry... so 320mm is near to 10X optical zoom?
Hi, you don't have to worry or concern with the optical zoom, 10X 8X all these are calculated based on the minimum zoom to the maximum zoom.. so 28-200mm is 200mm/28mm = 7.14X
Depends on ur shooting style and what u shoot.. even a 300mm prime lens which periodically has 0 optical zoom is good for animals/bird shots.

##### New Member
I'm sorry... but I don't really get it...

Is there any site that I can read to know more about lens.

So that I can know which lens to invest to suit my needs, thanks alot...

The main issue I am confused now is, what has the "mm" helps in photography?

Pardon me as I'm really new... but I would love to learn the art of photography.

#### surge

##### New Member
compacts always use the times thingy to measure there zooms cos it is easier to understand and the lens cant be changed. so you are right to say that

the times is actually the long end of the zoom over the short end

ie a 10x zoom of a cam that starts at 35mm will have long end 350mm. but a same 10xzoom that starts at 28 will give you 280.

if you using DSLR, is better you learn to understand the different angle of view based on the focal length.

there are many websites that teaches this aspect and also have pic showing the different angle of view so that you can understand them better. don get caught in the number game

##### New Member
Um, sure.. I am reading some articles from dppreview.com

Thanks for all the help here.. really appreciated...

Can't wait to get my hands on 350D this weekend~! Woohoo

#### rebbot

##### Senior Member
like all the CSers have commented, all boils down to your shooting style I would think do not waste money buying lens to later find out its not what you want.

Go down to the more reputable shops, try out various lens and see if the focal length is sufficient for your shooting style.

I dun mind helping as I had this problem earlier while transiting from P&S and prosumers but if I am available~

##### New Member
Sorry.. one more question...

what do they always mean by prosumers? and what's P & S?

#### user111

##### Senior Member
prosumer = high end PnS, ut not yet SLR. eg sony f828, canon S2IS,
PnS = point n shoot eg canon ixus, casio exislim

#### Feinwerkbau

##### Deregistered
First, you would have to understand how the focal length affects the angle of view, i.e., what mm gives you how wide, or how narrow a picture is going to end up in YOUR camera.

For a fun and easy way to see the different effects, go here and fool around with the different focal lengths:

http://www.canon.com.sg/index.cfm?fuseaction=digitalcamera&prod_type=tipsnhints#focal

Next, as you already know, whatever focal length you choose, when you mount it on your camera, just mutlipy the stated mm by 1.6x.

Then, I would seriously suggest you look for websites with titles like 'understanding the basics of photographic lenses', 'understanding modern digital photographic equipment' and so on.

The basics do not change, even if equipment does. Once you understand the basics, you can then apply that knowledge to just about any equipment developed.

Hope this helps!

CHEERS!

Thanks!

#### ortega

##### Moderator
Staff member
Sorry.. one more question...

what do they always mean by prosumers? and what's P & S?

Prosumers = "pro" consumers = Advanced consumer compact cameras
P&S = Point & Shoot = Compact cameras

#### Joel Lyn

##### New Member
somehow after reading all the focal length and maths stuff... still feel like doing physics

#### obewan

##### New Member
Joel Lyn said:
somehow after reading all the focal length and maths stuff... still feel like doing physics
Hehe... :bsmilie: Seems like photography is more than Arts. It involved Maths and Science.

#### markccm

##### Deregistered
to me photography is a technical art.

it involves both technicalities & the artistic element.