Aperture question

[UKBob]

Im not going to have time until the weekend (or next) to experiment, but could anyone provide a guestimate of how much more DOF would be gained, by changing my aperture from f11 to f13, using my 24-70L for macro work, when shooting subjects the size of erm... a hamburger or piece of fruit for example.

[GetCarter]

Only if you can tell me how much my VAT bill will be this quarter.

[UKBob]

GetCarter said:

Only if you can tell me how much my VAT bill will be this quarter.

17.5% of your turnover

[GetCarter]

excellnt... that'll be about £3 then

[V6GTO]

GetCarter said:

Only if you can tell me how much my VAT bill will be this quarter.

Zero if you get a good/bent accountant

Martin.

[doodah]

fractionally greater...

[Graham@Reading]

Depends on the focus distance.

It's not going to be much anyway. Probably not even noticable.

[doodah]

bob, you do realise that the dof is on both sides of the focal point, right?

[Ed_P]

If it's any help, there's a DoF calculator at
[url]www.cambridgeincolour.com/tutorials/depth-of-field.htm[/url].
Calculates total DoF and distance either side of focus point. Haven't used it though.

Ed ...

(Sorry, didn't format that link properly!)

Edited by Ed_P on Thursday 12th October 15:31

[le gravy noire]

DOF is a function of the aperture, focal length and focal distance.

The DOF will be greater at 24 mm with a very small aperture with a distant focal point. Shooting at 70mm @ f2.8 on the close focus limit will be thin indeed. Too many variables there chap.

Matt

[UKBob]

Graham@Reading said:

Depends on the focus distance.

It's not going to be much anyway. Probably not even noticable.

Oh dear

doodah said:

bob, you do realise that the dof is on both sides of the focal point, right?

Ed_P said:

If it's any help, there's a DoF calculator at
[url]www.cambridgeincolour.com/tutorials/depth-of-field.htm[/url].
Calculates total DoF and distance either side of focus point. Haven't used it though.

Cheers Ed. 13 must be a half stop, as it wasnt included in as an option in the calculator.

My issue is this: Warehouse express insisted 125w would be sufficient for light tent work, but I got 250w lights instead. I wanted more powerful, but they said 500w would be FAR too powerful for light tent work, even if the power was turned down. So I got the 250w bowens lights instead.

I suspect I have enough power to blow out backgrounds if I stop down from f11 to f13, but I'll be on 95% power. Meaning I dont have more power to further decrease the size of my aperture.

F11 doesnt give much DOF (I shoot at around 50mm+ usually)

Which would give me more dof. Moving in and zooming out a little. Or moving back and zooming in a little (keeping the aperture the same)?

[doodah]

you could always use multiple flashes if you need to... as long as your subject isn't moving, obviously

[fergusd]

UKBob said:

Which would give me more dof. Moving in and zooming out a little. Or moving back and zooming in a little (keeping the aperture the same)?

Move in and zoom out, the shorter the focal length the larger the DOF for a given aperture.

Or you could just lower your shutter speed to reduce the aperture, I'm guessing whetever it is you're shooting isn't moving very fast . . .

Fd

[UKBob]

Excellent, thanks.
I can move my lights a bit closer
Im sure I can stop down to f13 too
And I shall try and move in a little closer too, and zoom out a bit.

And Im quite sure I do have enough power to stop down just one more stop. And my pics are ok as they are, a little more dof will help even more. So I'm ok

[matthew_h]

Bob, do you shoot on digital? I assume you do. If so, why not try a few different arrangements and see what difference they make. Nowt like seeing the effect that changes have for yourself.

[badbeachbuggy]

Who's gonna mention ISO

[UKBob]

matthew_h said:

Bob, do you shoot on digital? I assume you do. If so, why not try a few different arrangements and see what difference they make. Nowt like seeing the effect that changes have for yourself.

Different arrangements as in what, exactly? Ive got a Canon 30d.

Because I only use my lights for light tent stuff, I dont need to move or adjust any settings. Lights are set up for exposure at f11, and will be set up for f13. Most products are the same size and I dont have enough power to blow out backgrounds (its a big tent, the background is nearly a metre away from the subject) at a smaller aperture than 13 I dont think, so there isnt much I can change... except the white card, after the gerbils have pissed and shite-ed all over it.

[UKBob]

badbeachbuggy said:

Who's gonna mention ISO

I will. 100. Sorted

[m12_nathan]

Bob - this calculator has more options for you:

www.dofmaster.com/dofjs.html

[Gemm]

UKBob said:

matthew_h said:

Bob, do you shoot on digital? I assume you do. If so, why not try a few different arrangements and see what difference they make. Nowt like seeing the effect that changes have for yourself.

Different arrangements as in what, exactly? Ive got a Canon 30d.

I think he meant you should be able to see the difference between f11 and f13 immediately if you are shooting digital, so why don't you just try it and see the results for yourself. (which I totally agree)