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 Post subject: Depth of field
PostPosted: Sun Feb 07, 2010 5:12 pm 
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Joined: Wed Sep 02, 2009 8:04 am
Posts: 260
Location: Hampshire, UK
Sorry if I have posted this in the wrong area, I have a DSLR and it made sense to put it here...

There is tonnes of stuff on the web about depth of field and frankly some of the sites confuse me.

I understand that assuming no other settings are changed, f5.6 gives you less of a DOF than F11, so I have got that.

What I can not figure out is I have an 18-200mm lens, assuming again no other settings are changed, do I get a larger DOF at 18mm or standing back from the subject and zooming to 200mm so the photos is in effect exactly the same, just one close up and one from a distance zoomed in.

Any help greatly appreciated.

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 Post subject:
PostPosted: Sun Feb 07, 2010 6:24 pm 
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Joined: Sun Feb 15, 2009 12:59 pm
Posts: 6009
Location: The Netherlands
DOF is a factor of how close you are to the subject, the focal length, and the aperture. Just try it all, no need to ask us. Experiment! :)

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 Post subject:
PostPosted: Sun Feb 07, 2010 6:39 pm 
Hi AL,

There are a number of DOF-calculators on the web and even some nifty charts that makes it a lot easier to "see" the DOF-range at any given setting...aperture, distance, focal settings etc.

Any search-engine will give you some useful links.

As for your question - with:
- same distance to subject
- same aperture

you get a wider DOF @ 18mm than @200mm.

Cheers :-)


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 Post subject:
PostPosted: Sun Feb 07, 2010 6:52 pm 
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Joined: Wed Sep 02, 2009 8:04 am
Posts: 260
Location: Hampshire, UK
Thank you LahLahSr will look into that and you have answered my question.

Yes, will have a play and see...

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 Post subject:
PostPosted: Sat Feb 27, 2010 8:50 pm 
I recomend you watched this if you haven't already:

http://www.dslrtips.com/workshops/How_t ... ield.shtml


With your 18-200mm lens:

First of all, a larger DOF means more of the background is in focus while a shallower DOF means less of the background is in focus.

Some zoom lenses have a minimum aperture range that changes depending on how much you zoom in. Generally the biggest aperture is given when the lens is zoomed out. This will give you a shallow depth of field

You particular lens has a minimum aperture range of 3.5 to 5.6.

This means the minimum aperture you'll be able to get is 3.5 when the lens is fully zoomed out at 18mm. If however you want to zoom in the minimum aperture will go down to 5.6.

If you want a larger DOF you will be able to use a small aperture such as F8 through all the range of your lens. So it doesn't matter if you zoom in or out. (in terms of DOF).

But if you want a shallow DOF then the best result will be achieved when zooming the lens out as this will enable you to use the bigger 3.5 aperture.

Other lenses like the 70-200 have constant minimum aperture. But this makes them more expensive.

I think you might of been confused by some photographers who use telephoto lens and stand back. They do this to avoid distortion that occurs at shorter focal lengths; not to achieve a larger DOF.


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 Post subject:
PostPosted: Sun Feb 28, 2010 7:29 am 
agun wrote:
But if you want a shallow DOF then the best result will be achieved when zooming the lens out as this will enable you to use the bigger 3.5 aperture.


You're right about having larger aperture @18mm with this lens, but generally, if you use 18mm f/5.6 vs. 200mm f/5.6 and move to produce the same picture, you'll have shallower DOF in 200mm.

Another thing AL, DOF is also affected by the distance from you to the object. So, if you use 100mm and stand 2m from the object you'll have a shallower DOF than standing 20m from the same object with the same settings (of course, in this case the picture will come out different).


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 Post subject:
PostPosted: Sun Feb 28, 2010 12:03 pm 
found the guy on these vids helped me understand alot

http://www.youtube.com/user/bridgeoverwater627#p/u/8/Xk-JQ4K7fBw


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 Post subject:
PostPosted: Sun Feb 28, 2010 5:36 pm 
Haha that guy seems to think a lot of himself from the videos I've seen of him. But he does give some good advice.


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 Post subject:
PostPosted: Sun Feb 28, 2010 7:29 pm 
lol


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 Post subject:
PostPosted: Sun Feb 28, 2010 7:58 pm 
wow, amazing how little views he gets.. he's the only guy on youtube i noticed so far that explains things the same way i would. i knew pretty much everything he was going to say and he said it exactly as i picture it.


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