Yet another focus question :-(

blondie606

blondie606

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Lynne
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Hi all

Not quite sure how to explain what I'm trying to find out but here goes :

Imagine a scene with a person stood at either side , say 12ft apart with a dog running from one to the other . You are standing approx 20ft away .
How do you get the focus sharp on all 3 ?
I'm used to shooting one or several objects but very close together & manage these shots ok

Tried this today in pants light (miserable british weather) ,managed to get one & the dog or the just the dog in focus but not all 3 (unfortunately can't post a pic as it's for a project ) Was using tamron 70-300

Is it a case of standing further back then cropping ? Had the shutter at 1/800 to blur the background & f4.2 . ISO was set to 200 as I find the D80 a bit noisey but thats probably pilot error as well (did a crop on 1 shot & it does look noisey ). One of those situations I could'nt repeat today but am going back to have another go so appreciate advice please .

many thanks

Having typed this out I'm thinking I should have lowered the shutter speed & sacrificed the background blur ?

many thanks ,Lynne
 
Use a compact camera......:lol: (just joking)

Your not doing yourself any favours, low light, fast shutter speed, slow zoom lens etc.
you need to use a DOF calculator, set to (actual)focal length used on zoom lens and aperture used, you will see DOF is probably not adequate.
now change aperture in calculator until all desired objects are within the DOF range.

Have fun.....
 
If all 3 subjects are in a straight line accross the lens ( same distance from you ) then you can just focus on one of them ( moving the focus point would be best ) then take the shot. The closer you are to the subjects ( feet or zoom ) the the less DOF you have to play with. Shutter speed won't blur the background, apeture will. Shutter speed would only blur the running dog with the scene you describe.
 
Yup, I think I am right in saying your aperture number is too low, if its increased then you will have a greater DoF and should be able to get all 3 people in focus! As said above, being close to the subject, and far away from the background will create more background blur (bokeh?), and this can be amplified with a smaller aperture number. So in your situation I think its a bit of a trade off!

Possibly increase ISO a little and increase the time your shutter is open for and you will be able to get a brighter picture!

:) HTH
 
Thanks Guy's

just so I've got it clear - I need to slow the shutter speed & up the F stop ( higher number) .
Can't do much about the lens but could try the 150-500 Sigma ?

Seems so simple a solution but this morning when I was in panic mode over the light ( or lack of it) my mind just went blank .....well,more blank than usual:lol:

One of these days I may just get it right !

Confused myself again ! Faster shutter speed freezes the action (I think) & thats what I was trying to do with the dog .So if I slow the s/speed, up the Fstop I can get the 2 people in focus & have the dog clear as well rather than just a blur ? I'm used to freezing the action in bike shots which results in an oof background ,think thats what was throwing me . Off to find one of these DOF calculators as mentioned !
Sorry for being so dim , just need to hammer it home sometimes !
 
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Hi

Sounds like your priority is freezing the dog running, secondary is depth of field and lastly noise.

You will need to select the shutter speed first lets say 1/100 (3stops from 1/800) and see if thats fast enough to freeze any movement. Lets say it is fast enough in this example.

If so you could then close the aperture down to f11 (3stops+/- from f4.2) for more depth of field (this could bring the third person into focus at some sacrifice of background blur)

Assuming the exposure is ok with your figures it will remain so as we have adjusted 3stops in either direction (opened/slowed up the shutter yet closed down the aperture)

Looking at Depth Of Field Master http://www.dofmaster.com/dofjs.html, shooting at f4 at 200mm (I am guessing 200mm here and using it as an example as I couldn't see exactly where you shot the 70-300);
a) at f4 at 200mm, 20 feet from your subject your Depth of Field is only 0.47feet
b) at f11 at200mm, 20 feet from your subject your Depth of Field is still only 1.34feet

This is not a lot of DoF to have two people and a running dog within its limits I wouldn't think:thinking:

If you focus on one of the people and recompose you are also shifting the focal plane a little. Also all three subjects would need to be within depth of field for them to appear acceptably sharp - this means parallel to the sensor or focal plane.
http://www.anstendig.org/autofocus_1.png
autofocus_1.png


Lastly ISO is your other option. I didn't like using ISO in the beginning, but if you need to bump it to increase shutter speed or close the aperture down further its not a bad option particularly as you can apply noise reduction software afterwards.

An out of focus or blurred shot can't really be rescued easily if at all in post processing whereas noise reduction can have a decent effect on the final image. I use Noiseware Community Edition (freeware).


Andy
 
Hi ya

Corbystock...many thanks for the link , saved to faves for the next time I have a blank mind (should'nt be too long ):thumbs:

Andyb....most helpful info ,gonna look at downloading the noise reduction software you linked to over the weekend .Found a similar thing on PSE by accident tonight but suspect not as good as the link you sent.
Great info on the other link with the calculator ,also saved to fave's so I can sit & study it

Many thanks to everyone for all replies & advice ,much appreciated :thumbs:
 
I think the short answer is you need a lot more light.

You need a fast shutter speed to freeze the movement (1/800sec sounds fine), you need more depth of field to cover everything adequately and you also need good edge sharpness so I would say f/8 or f/11 to secure both. And you also need low ISO for best quality (and beware under exposure). All of which adds up to a lot more light!

On the depth of field thing, you don't get any more or less of it when you change focal length, assuming that the subject always stays the same size in the image - as it sounds like it would in this example. DoF only changes when the size of the subject changes, so if you fit a lens that is twice the focal length, but then move back to twice the distance, the DoF doesn't alter (at the same f/number, obviously). However, the field of view changes, so what you get in the background will look different, even if the amount of blurring is the same.

Apart from the field of view thing which may or may not be a deal breaker, I would try and get a bit closer and use a shorter lens.
 
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