Depth of field ?

bill m

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24 Oct 2003 - 7:31 AM

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I recently saw a couple of chaffinches perching obligingly on a dry stone wall in Dorset. The opportunity was too good to miss, and I tried to think quickly. I already had the 100 - 300 mm zoom attached, and my thought processes were: they might move, so I'll go for the fastest shutter speed I can the easy way to arrive at that without too much trial and error, I thought, is to set my widest aperture on the Av setting, which I did. With zoom at full stretch, I snapped. On receiving my photo back, I can now see what has happened: one of the birds looks lovely, and is perfectly in focus; the other, no more than a few inches away along the wall, is very out of focus. Is this a depth of field question? If so, how could I have avoided it, while still retaining a fast shutter speed ? Or should I have taken the risk that they wouldn't move, and gone for a smaller aperture and slower shutter speed ? Thoughts as to how others manage to "think on their feet" in these opportunistic situations would be welcome to this relative beginner.

Pete (ePHOTOzine Staff)

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24 Oct 2003 - 8:13 AM

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If you reduce the aperture to ensure greater depth of field the shutter speed will become slower so it's a balance between camera shake/subject movement and front to back subject sharpness. Ways round this are to use faster film to allow a smaller aperture without affecting the shutter speed or stand further away or use a wider angle lens (depth of field increase)In both the latter options you then need to enlarge the picture by cropping at the printing stage.

SteveCharles

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24 Oct 2003 - 8:24 AM

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BTW, I didn't mean to repeat Pete & Barrie, they just type faster!

railton

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24 Oct 2003 - 8:38 AM

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As well as all that bracket wildly Bill [ Hicock ] and shoot lots of frames. That is how the wildlife pro's ensure they get the paying shot.

bramo

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24 Oct 2003 - 9:30 AM

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Question for Barry.

I'm a bit of a rank amatuer, but a recent trip to Africa has given me the Wildlife buzz.

Up until now all of my photos were taken using a Canon Elph APS camera. Only after my trip did I find this camera 'wanting'. Do you find 400mmm to be enough zoom for most of you wildlife stuff? I've now got an SLR (Pentax) and I'm trying to figure out which zoom lens to get.

I can get a 80-320 Pentax SMC lens for a good price. I'm currently weighing that against a Sigma 135-400 (300 squids on the online shop here). I am concerned that I may miss the extra bit of zoom if I get the Pentax lens.

Main uses will be for Wildlife and cricket. I know neither of them are particularly fast lenses, but I'm not spending more than 300 pounds...

User_Removed

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24 Oct 2003 - 10:54 AM

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Hi James (Bramo)

First of all - I'd love to go to Africa and have never been so I am very jealous!

For most of the 'big' wildlife stuff I shoot, the 400mm end of my 100-400 zoom has been more than adequate. In fact, when I was in the Everglades a couple of years back, the birds were just too close (in Florida, the birds just throw themselves at the camera - no real naturalists skill involved).

The beauty of the zoom is flexibility although there is some trade off in the maximum aperture which can affect focussing speed and viewfinder brightness but the quality these days is so good that for all practical purposes, the image quality is as good as that with a prime lens (and a lot cheaper on the whole).

Referring back to Depth of Field, you just need to remember that if you focus on the same point with a varity of lenses at the same aperture, then the depth of field will generally decrease as the focal length increases.

Barrie

Bucks

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29 Oct 2003 - 12:51 PM

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Sensia as good as Provia- very little between then, - as good as Velvia- no, but I want the extra stop. Once you take price and handiness into the equation there is no contest.
That lens does sound good value, but check around the other main shops in town before buying. If any shop has a sigma 70-300 apo for a similar price give it serious consideration too. (try them on the camera, the Sigma may hunt and chuck a bit (mine does!) and focus slower than the pentax, burt it may be sharper and better handling, which is always personal preference).
A mirror lens is a type of telephoto with a fixed focal length usually 500mm, and fixed aperture usually F8. the mirrors fold the focal length in three, so the lenses are very small for their focal length. They are usually lighter and cheaper than normal lenses, but you have no aperture control, so no control over depth of field. There are usually a few second hand ones available around town.