I am a beginner! Lens confusion

[rosie_featherstone]

<p>I have been bought a Cannon eos 550d I am confused about the lenses.<br>

There seem to be 2 parts to the lens, one part which is a Tamron 18-270mm F/3.5-6.3, underneath that is a second part which is labelled in ft and m with numbers to infinity<br>

I have been tryog to sort out depth of field and am confused about which parts of these lens/lenses I use!<br>

Are they linked? Do I set one then focus with the other?If so which?<br>

I am trying to operate in Aperture Priority mode<br>

Sorry I am being dim but I dont know where to look </p>

<p>Rosie</p>

[damian_tinsley]

<p>Bless!<br>

OK the numbers are the distance the lens is in focus at. 5m means that stuff 5m in front of the lens will be in focus. Stuff further away or closer will be blurred. One of the rings (probably the smaller of the two furthest away from the camera body) will adjust the focus. [For all you experts out there - yes I know it's a plane focal system not a straight distance, but that won't help Rosie.]<br>

The 18 and the 270 refer to the focal length and are the values that govern the zoom range of the lens. 18mm is wide angle and the 270 is quite a respectable telephoto. One of the rings on the lens will zoom through this range.<br>

Depth of field is essentially linked to the aperture value. The higher the number the more depth of field you have. The 3.5 figure means your lens will have an effective widest aperture of 3.5 when the zoom is at 18mm and the lens will have an effective widest aperture of 6.3 when the lens is at 270mm. Some more expensive lenses maintain the f number throughout the range (and these are called constant aperture). The smallest aperture you can have on that Tamron lens is I guess (someone help out) about f32.<br>

You will get more depth of field if the aperture number is higher, but the downside to this is the lens lets less light in so the shutter speed is slower, and this makes it more likely you will have a blurry picture as a result of camera shake becaus the the shutter speed is low.<br>

Hope this helps,<br>

Happy snapping</p>

<p>Damian</p>

<p> </p>

[greg_moss4]

<p>Ring near lens is the zoom setting. It determines your focal length or field of view, (Close or far away)You may notice that it also extends the front of the lens as you dial up the telephoto settings.<br>

The ring near the front of the lens is your focus setting.<br>

Try this DOF calculator:<br>

<a href="http://www.dofmaster.com/dofjs.html">http://www.dofmaster.com/dofjs.html</a><br>

Focal length, F-stop and distance all work together to determine the DOF.</p>

[damian_tinsley]

<p>PS<br>

Aperture is set by controls on the camera, rather than on the lens. <br>

Long zoom lengths tend to accentuate the effects of any given aperture i.e. a wide-ish aperture (small f number) at 270mm (say f6.3) will appear to have less depth of field than the same f6.3 at 18mm. <br>

Take care</p>

[MarcelRomviel]

<p>You can find info about the lens here:<br /> http://www.dpreview.com/lensreviews/tamron_18-270_3p5-6p3_vc_n15/page2.asp<br /> The big ring is for the zoom, the little ring is for focusing.<br /> Only use the little focus ring when you have set the lens at manual focus.<br /> It is explained in the link.</p>

<p>You can learn more when you click at the learning tab above the page on photo.net.</p>

[markonestudios]

If your camera and/or lens came with an instruction manual, you would do well to start by reading that first...

[damian_tinsley]

<p>@ Mark</p>

<p>Speaking as an engineer I tend to look on any user manual as a last resort...</p>

<p>Happy to help out anyone who feels the same way. ;-)</p>

[rosie_featherstone]

<p>Normally I use handbooks and manuals but the Tamron lens was not supplied with one! I find that asking interested individuals usually gets me the information I need. As indeed it did this time. Part of the problem I think is that the lens wont go down far enough to be much use working with a short focal length and in a short depth of field Thank you all </p>

<p>Rosie <strong> </strong></p>

 

[phule]

<p>[[Part of the problem I think is that the lens wont go down far enough to be much use working with a short focal length and in a short depth of field]]</p>

<p>Can you explain more? What is your goal? Are you looking for shallow DoF at 18mm or wider? </p>

 

[vikram_gulati]

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