depth of field

  podlod 16:24 26 Sep 2008

Hi, I have a Nikkor Macro 70-200mm lens and although I am more than happy with the results it gives me, my depth of field seems to be somewhat limited, it there something I can do or use to improve results? thank you.

  dms_05 16:43 26 Sep 2008

Depth of Field varies with the f number you chose. The larger the f number (ie aperture) is the more the depth of field (ie f22 gives more than f4). However increasing the f number will mean using a slower shutter speed.

Depth of Field is also greater the shorter the focal length of the lens. So at 70mm you will get more depth of field than at 200mm.

They are both laws of Physics and cannot be altered. So if you want more depth of field you need to increase the f number and use a slower shuter speed. This of course is difficult as the focal length increases, so use a tripod as well.

Generally I use the rule of thunmb that I can hand hold the camera when the shutter speed is no lower than 1/n where n is the focal length. So I can handhold a 70mm focal length at 1/70 sec speed but would need to have 1/200 sec for a 200mm lens.

  Kemistri 17:17 26 Sep 2008

You forgot the third and fourth factors: distance from subject and frame size.

Newbies may find a DoF chart to be useful. click here

  bobbybowls 20:16 26 Sep 2008

you might want to have a look at click here i have picked up some very good tips.

  Stuartli 00:08 27 Sep 2008

>>So I can handhold a 70mm focal length at 1/70 sec speed but would need to have 1/200 sec for a 200mm lens.>>

Apart from the fact that a shutter speed of 1/70th of a second is a new one on me (apart from an automatic equivalent), you would certainly need to use an even faster shutter speed than 1/200th of a second using a lens at that focal length to obtain a similar shake-free result.

There are two points to be considered in this case - depth of field and depth of focus.

Many people are confused by the similarity.

  dms_05 09:45 27 Sep 2008

Of course it's more complicated than my original general view. Depth of Field depends upon what you can tolerate as the maximum circle of confusion. If you have a digital camera with a relatively low number of pixels then you have (by definition) a larger minimum for the CoC and therefore a better depth of field. I also understand some sophisticated digital cameras allow you to select a depth of field after the image has been taken, but I have no experience of these.

Stuarti - my 1/n concept has helped me understand the general magnitude of the shutter speed I need. I can hold a 21mm lens at well below 1/20 sec and obtain good results, equally I can (with a suitable stance) hand hold a 200mm lens at 1/200 sec. However where possible I use a support at all speeds. And I round the 1/n to the nearest speed but my Nikon DSLR seems able to deliver almost any fraction of a speed without a problem - I noted it recently used a shutter speed of 1/372 sec.

Finally if you are using a digital camera the size of the imaging chip effects the equivalent 35mm film size comments. In my case a 50mm focal length lens is equivalent to approx 75mm on my DSLR.

  Stuartli 10:54 27 Sep 2008

My six-year-old Minolta digital camera can produce a shutter speed appropriate to the requirements of any particular aperture and lighting conditions i.e. the shutter speed can be, for instance, 1/239.2 of a second (the information is available via the EXF facility in, amongst others, Irfanview).

You are, of course, quite right about the 1.5 times magnification using standard film lenses; this is, of course, why digital camera manufacturers normally state, for example, that a particular 3x zoom lens model is equivalent "to a 35-105mm standard lens".

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