I know I could just go outside and try some stuff, but I am more interested in the technical aspect of the answer...

Distance/lens/DoF and how they affect each other.

Let's say I use a 70-200 lens and want to have the background very blurred, but have about close to 3 feet of my subject in focus..
Does it make a difference which distance I am from my main subject?
If I shoot at F:2.8, will is affect the area in focus if I'm shooting at 70 or if I'm shooting at 200? For the same subject size in the photo, meaning if I'm close or if I'm far out and zooming more...
With that in mind, will distance affect also the background blur as well?

Same question goes with the 24-70..
If I want to shoot at 2.8, will distance affect my DoF if I'm close or far to the subject, hence shooting at 24 or at 70...?

Hope you can understand what I am trying to ask...

Thanks in advance!

it does.
and this website has some very explanatory images on its page http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

in theory, larger aperture = smaller dof.
longer lens = smaller depth of field. (larger focal length)
shorter distance = smaller depth of field. (smaller focal distance)

ofcourse keeping all the other parameters equal.

yes makes a large difference



as punisher said

if you using a 200mm lens 50m/yrds away
your dof will be similar to 100mm lens 25m/yrds away
althought the photo will look totally different

1stop in aperture is proportional to doubling or halfing ur distance to the subject - make sense? cant thing how to word it correctly (just woke up and still dopey)

hope every1 is having a good easter

I understand how DoF is affected by the aperture...
What I have a hard time to visualize, is for the same aperture (let'S say 2.8) how distance is affecting the background blur...
I am reading the tutorial now but it is still quite confusing for me...

Let's make a practical example...
Which background will have more blur in the case of a horse in a field.
Shooting at 200 mm at a further distance?
Shooting at 70mm at a closer distance.
In both cases I want the horse to fill the image, so the distance between me and the horse is what is changing, along with the lens...

Ok.. I read many links and info pages about what I want to know, and I still don't understand...

Let's say in more practical ways....
In May I will go take pictures of a Dressage Clinic... a Master of Equitation from Europe comes here and teaches people on their horse for 200 $ and hour...
Last Fall I took photos, but it was inside an indoor arena, so I was mostly standing in the middle of the ring and shooting with 50 mm or 24-70.
Now being in May, I have a choice... I either use the 24-70 and shoot from inside the ring (which will probably be around 20m x 80m) or rent a 70-200 and shoot from outside.
If I use the 24-70, I'll have to be closer to the horses, if I use the 70-200, I will be further away.
Both lenses are 2.8 max aperture.
Let's suppose I shoot at 2.8 on both, will the background blur be affected by the distance from the focal point and the background?

Thanks in advance for explaining in a very simple way

basically these 2 will give u very similar DoF
200mm focal length with subject distance 50m
100mm focal length at a distance of 25m
focal length and distance are inversly proportional
however the bokeh and background will be very different, generally the longer focal length will be more pleasing as the background will be less busy

here is a calulator: http://www.dofmaster.com/dofjs.html

ok I used your link and yes, with the distance taken in consideration and the focal lenght, there isn't much difference...
I understood that part
But you say the bokeh will be nicer with the 70-200 right? I couldn't find that part in the link (or just couldn't understand the terms)...
Thank you!!!!

that is just from experience, because there wont be a large difference in the distance to the back ground so the longer focal length will look better / less distractions
and then for the different in background veiw: http://photo.tutsplus.com/tutorials/photography-fundamentals/exploring-how-focal-length-affects-images/

This post was edited by jayandnix on Apr 15 2012 12:10pm

I love this link!!!! Now I see it very well!!!
Thank you so very much!!!!

my pleasure glad i could help