Ok Im pretty new to this SLR stuff but one of the main things that got me interested are the pictures you see with a small DoF so that the subject is focused and the background is fuzzy.

Now Ive done a fair bit of reading on this and everything says to a) use a larger aperture (lower f.number) and b) get as close to the subject as possible either physically or by increasing focal length to achieve the same thing. An example of lowering f.number to achieve this (scroll down half way):

Understanding Depth of Field in Photography (http://www.cambridgeincolour.com/tutorials/depth-of-field.htm)

Sounds easy but as a noob Ive been using Tv mode (shutter priority) on my 350D so the aperture is set automatically. Here is one example from my Windsor Horse Show Pics:

IMG_0523 pictures from friends & fun photos on webshots (http://good-times.webshots.com/photo/2204929530068928777sjyUpj)

F6.3 1/250 @ 122mm

The horse is perfectly in focus but the background (Id estimate the white fence was another 30 ft behind the horse then more for the tent and signage) but the signs and gazebo's, whilst blurry are not as out of focus as Id like. I appreciate that DoF is gradual and that focus is not lost immediately but over a distance. However when I compare to SBradleys bike pic (borrowed from the MotoGP advice thread) the track and background is fuzzy:

http://www.motorbikestoday.com/news/Images//sbk_08_monza_3_lge.jpg

Is it just that the background in that pic is actually further away than I think or am I doing something wrong i.e should maybe use manual mode and set f.number as low as possible?

Cheers,
Simon

As you've already found out, as well as increasing focal length, you can reduce the depth of field by increasing the size of the aperture.

Therefore, rather than using the Tv mode, try using the aperture priority mode (Av, I think). This way, you can keep the aperture fully open and the camera will sort out the shutter speed automatically.

DaveD, you've hit the nail on the head.

Hmmm an obvious answer now you've said it :lol:

So you think that if I took an identical pic of that horse at F4 instead of F6.3 then the background would be a lot fuzzier (nice techical term there)?

Im gonna get a nifty fifty next so that should allow me a big more experimentation I feel.

Simon

As above, just turn the dial to Av (aperture priority) and open up the aperture (smaller number).

Alternatively, turn to P (programm shift) and set it to the largest (numerically smallest) aperture possible. IIRC, the camera won't let you open the aperture higher than the max possible shutter speed in this setting.

However, you'll be limited by the maximum aperture of your lenses as to the minumim depth of field you can achieve

This is the 50mm @ F2.3 (almost wide open)

http://i138.photobucket.com/albums/q243/rotdog/fullimage2-1.jpg

Very pronounced focus fall off (but crap bokeh - out of focus area - as its only a 5 blade aperture)

and this is the 100-400 @ 400mm wide open (F5.6)

http://img.photobucket.com/albums/0803/Diablo/image1for-web.jpg

Less prononounced fall off but nicer bokeh. (ignore the composition - was a test pic for Andy after I bought the lens)

Bear in mind, however, that lenses generally perform at their best stopped down from maximum aperture.

Subject to background distance also plays a part, together with focal length and aperture, much more so at longer focal lengths

Or you could "cheat"

Hope you don't mind me borrowing your pic for this (very) quick edit:

from this

http://i138.photobucket.com/albums/q243/rotdog/horseoriginal.jpg

to this

http://i138.photobucket.com/albums/q243/rotdog/horse.jpg

or a bit more extreme

http://i138.photobucket.com/albums/q243/rotdog/horse2.jpg

As well as focal length and aperture, the camera to subject distance plays the greatest part in giving depth of field. Tie those in with the distance from the subject to the background and an infinate number of possiblities arise.

The closer the subject (or point of focus) is to the camera then the less DoF (or more blurred the background will be).

This is why on closeup portraits and a telephoto lens, even with f5.6, the eyes are sharp but the ears are out of focus and the background is a total blur; but a landscape on a long lens focused a lot further away will have a much greater area of sharpness.

This also ties in with the hyperfocal distance, which is point you should focus on to give maximum depth of field.

Gareth

I wasn't going to confuse him with that 1 Gareth :D

The closer the subject (or point of focus) is to the camera then the less DoF (or more blurred the background will be).

Gareth

Is that strictly true in an absolute sense, or does the dof reduction arise because the the respective ratios of the difference between the distance from camera to subject compared to camera to background are different with near subjects compared to far subjects :wonder:

ie, if your subject is closer and its background is also closer, would the background blur not be the same?

Its true in an absolute sense - DoF decreases the closer the subject is to camera - thats why macro photography requires f8/f11/f16/f22 to get anything sharp :D

However it is also true that if the background is further away, while you are focusing on a close subject it will become more blurred, but even close backgrounds will benefit.

The problem with answering the original question is that Depth of Field is normally used to work out what is going to be sharp, rather than how out of focus the background will be, so while the two are related, its difficult to determine.

A small DoF combined with a large subject to background distance will give you the maximum "background blur". Thats why when I shoot rugby/football on a 400mm f2.8 wide open with the subject large in the frame, the background is just a range of abstract tones and colours. However, if I've shot a goal at the far end of the pitch at the same exposure settings, say 1/1000@f2.8, then I'll get a mass of print sales from all the people in the crowd celebrating :D :D

Edit - I've just noticed that the file was shot at f6.3 at 122mm, in that case the DoF at those settings and camera/subject distance, then the background is as I would expect it to be - if you had shot it on a 300mm by going back a bit (I guess you were in the crowd, however) then the background would have been noticable softer.

Gareth

Its true in an absolute sense - DoF decreases the closer the subject is to camera - thats why macro photography requires f8/f11/f16/f22 to get anything sharp :D

However it is also true that if the background is further away, while you are focusing on a close subject it will become more blurred, but even close backgrounds will benefit.

Duh..of course :o

Cheers :thumb:

As a starting point I just remember that when I look through the viewfinder, the image I see is the depth of field with the lens wide open (largest aperture). If the background isn't blurred enough for you then, as has already been said move closer to the subject or increase the focal length. If it's too blurred then pick a smaller aperture.

DOF & FOV Calculator/Graph Builder on Java (http://www.zknives.com/dp/dofcalc.shtml)

Have a play and change all the numbers or to see what happens, set all the numbers and then adjust one in increments to see what effect there is.

Thanks for all the replies - glad I asked now :)

Played around in the garden when I got home last night and put it all into practice and was very happy with the results even just using a lens box on top of a small table.

Cheers,
Simon

Edit - I've just noticed that the file was shot at f6.3 at 122mm, in that case the DoF at those settings and camera/subject distance, then the background is as I would expect it to be - if you had shot it on a 300mm by going back a bit (I guess you were in the crowd, however) then the background would have been noticable softer.

Gareth

Hmmm really? Everything Ive read states that focal length doesnt make any difference if the subject appears as the same size. An extract from the article on my original post:

Note that I did not mention focal length as influencing depth of field. Even though telephoto lenses appear to create a much shallower depth of field, this is mainly because they are often used to make the subject appear bigger when one is unable to get closer. If the subject occupies the same fraction of the viewfinder (constant magnification) for both a wide angle and a telephoto lens, the total depth of field is virtually* constant with focal length! This would of course require you to either get much closer with a wide angle lens or much further with a telephoto lens, as demonstrated in the following depth of field chart:

Obviously increasing focal length would increase the subject size if your standing at the same distance away. But moving backwards would surely negate this and tbh I couldnt use anymore from where I was otherwise the horse wouldnt all fit in :)

Simon

In order to keep the subject the same size in the frame when using a longer lens, say a 300mm instead of a 100mm, then you would have to go further back, as soon as you change your focal length and camera to subject distance, the DoF changes accordingly, and the relationships between subject and background change considerably because of the reduced DoF of the longer lens.

Is complicated to explain, and does seem to contradict on occassions, but experiment and you'll see what I mean. Take a full length portrait of someone stood in the street at 100mm, then change the focal length to 300mm and keep going backwards until the subject occupies the same position in the frame. Keep the exposure settings the same and take the same shot - see the difference in the background.

Gareth

Yeah sounds like your right. As you say a lot of differing info out there - I was reading this test:

DOF2 (http://www.luminous-landscape.com/tutorials/dof2.shtml)

And tbh when I look at the 400mm pic the background looks far more fuzzy than at 200mm with same size subject.

Your right in that its all subjective and its better to try it all yourself and see what works for you. But at least after starting this thread I actually understand the theory behind it all :)

Simon