F stop query on something I saw on youtube video

Carlh

Carlh

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Carl
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Hi,

Its just a query Id like an explanation for.

Normally, if Im shooting something up fair close (a few feet) and I want to get the object in nice and sharp and the background pretty blurred out, I would open the aperture as much as I can (in a 50mm, f1.8) lets in loads of light, shutterspeed nice and high and lots of bokeh in the background and still have a sharp subject.

All fine and dandy.

Now, ive got a conflict which to me doesnt sit right, from information on the video. There's this guy photographing a spiders web.

He's 2 or 3 foot away from it and sets his camera to F16.
His ISO is set to 400 and the image looks great, the spiders web is in focus, the background has a lovely soft bokeh.

So - did he use F16 because he wants the whole web in-focus and the natural foilage behind the web, bokeh'd because the focus was on something so close that ran in many different directions (the web). I honestly though the background would have come out in the image but its all blurred lovely (no pp)?
 
Macro photography lenses have a very very shallow dof - I regularly shoot on anywhere from f6.3 to f16 - to get images like this shot on f7.1 but the Bg is out of focus, like shooting wide open


4 spot chaser 2 by Les Moxon Photography, on Flickr


Les :thumbs:
 
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Not sure why he'd want to use f/16. You don't need much DoF with a spider's web, assuming it is photographed flat and square to the camera. Maybe it wasn't, but high f/numbers like that are not good for best sharpness (diffraction).

On the other hand, DoF is so shallow when you get close that even with a high f/number the background will be blurred. The trick for really out of focus backgrounds is to move as close as you can to the subject, and put as much distance between the subject and background as possible.
 
Gazamonk said:
A lot of people are often surprised by just how shallow DoF is even at large f numbers. Try one of these for fun.

http://www.dofmaster.com/dofjs.html
Click to expand...

DOF is affected at least 2x as much by working distance than it is by aperture selection. And can be fairly easily swagged.

A quick example: a 100mm lens with a 10ft subject distance will have a DOF of ~ 2ft at f/16 on a crop body (f/11 FF).

At 5 ft (1/2 the distance) the DOF is 1/4 of what it was. ~1/2 ft.
But if you halve the aperture (f/8)instead the DOF is 1/2 of what it was. ~1ft
It works the other way as well.

Changing focal length has the same effect as changing working distance...double the focal length = 1/4 DOF.

(***these estimates only work well when working short of hyperfocal distance)
 
I guess your eyes missed the word 'fun' :shrug: it was at the end of the sentence so was probably out of focus since I wrote it at f8. :lol:

It was only meant to give an indication of how shallow DoF can be at short subject distances.
 
Carlh said:
Hi,

Its just a query Id like an explanation for.

Normally, if Im shooting something up fair close (a few feet) and I want to get the object in nice and sharp and the background pretty blurred out, I would open the aperture as much as I can (in a 50mm, f1.8) lets in loads of light, shutterspeed nice and high and lots of bokeh in the background and still have a sharp subject.

All fine and dandy.

Now, ive got a conflict which to me doesnt sit right, from information on the video. There's this guy photographing a spiders web.

He's 2 or 3 foot away from it and sets his camera to F16.
His ISO is set to 400 and the image looks great, the spiders web is in focus, the background has a lovely soft bokeh.

So - did he use F16 because he wants the whole web in-focus and the natural foilage behind the web, bokeh'd because the focus was on something so close that ran in many different directions (the web). I honestly though the background would have come out in the image but its all blurred lovely (no pp)?
Click to expand...

It depends on the lens he is using.

If he was using something like the Canon 180mm Macro lens then he wouldn't have to be so near to get a close up shot as he would if he was using the Canon 50mm f1.8 lens with tubes.

I use my 70-300mm L IS USM lens with Kenko extension tubes to allow me get good close up shots of bees, butterflies etc without disturbing them but also use flash and a small aperture (f11-f32) to make sure that I get a good sharp picture since the DOF is extremely small:


And as you can see this also gives excellent bokeh on the B/G.
 
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