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Thread: Focal length

  1. #1
    Regular Member Spikeyİ's Avatar
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    Default Focal length

    Here's one for the experts:

    What sort of focal length and aperture do you reckon would be necessary to take a 3/4 shot of the car, compressing the depth of field to a point that just covers the length of the car?

  2. #2
    [Ex]Admin Duncan's Avatar
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    Default

    Depends how far from the car you are and your focusing distance.

    D

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    Regular Member Spikeyİ's Avatar
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    Default

    You'd need to be far enough away to fit the whole car in (suppose this distance would depend on the focal length) with a tight crop, preferably focussing on the nearest point of the car. Assuming the car length at 3/4 angle would be 4m(?) your depth of field would be 8m(?).

    Does that make sense?

  4. #4
    [Ex]Admin Duncan's Avatar
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    You'll want to focus towards the front of the car - maybe front door, but not the front of the car - as DOF extends about 1/3 in front and 2/3 behind the point of focus.

    You're on a smaller chip than 35mm so any calculations for 35mm are out the window - you'll have greater DOF for the same aperture.

    Does your lens not have DOF markings? If so, you can see how much either side of a chosen aperture you will have sharp focus. Although they're likely to be for 35mm! If it's a newer lens then it's quite possible it won't have these markings - they seemed to ditch them on newer lenses.

    At a guess, on your camera, I'd say a tight crop at 135mm, f8 is probably a good bet.

    But seeing as your digital, this is where you have an advantage if you want to get the car sharp but minimise the background being sharp. Shoot at different apertures and review on your screen and zoom in. You'll see the aperture where it starts to go soft on the car.

    To maximise the effect of the b/g going out of focus quickly, shoot onas long a lens as you can and as wide an aperture as you can get away with to keep the car sharp.

    HTH

    D

  5. #5
    Regular Member Spikeyİ's Avatar
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    Default

    Sadly, the DOF markers do seem to have disappeared ergo this question it's been a long time since I did this seriously and at one point i would have been able to calculate the DOF from a formula lol. From memory with 35mm I was thinking along the lines of 300mm at f5.6 which I think equates to about 190mm digital format? So I reckon your guess at 135mm would be a good bet. Looks like a zoom up to around 200mm would be enough to grab this shot then, hopefully will be in a position to buy one in the next couple of weeks

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    What??Uhhh????Ahhhh????

    yeh ok den,i agree wiv u all

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    [Ex]Admin Duncan's Avatar
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    Default

    Quote Originally Posted by PIMM
    yeh ok den,i agree wiv u all
    - in that case I won't get into 'Circles of Confusion' as that'll just, err, confuse! (Seriously - that is an optical term related to depth of focus!)

  8. #8
    Regular Member Spikeyİ's Avatar
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    Quote Originally Posted by PIMM
    What??Uhhh????Ahhhh????

    yeh ok den,i agree wiv u all
    LOL, trying to find out what lens i would need to take a photo of the car, so that only the car and NOT the background is clear, sharp or in focus. Does that help any?

  9. #9
    Regular Member philzi's Avatar
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    Default Why not do the work in Photoshop....

    Quote Originally Posted by Spikeyİ
    From memory with 35mm I was thinking along the lines of 300mm at f5.6 which I think equates to about 190mm digital format?
    Have you got your figure mixed up here?

    190mm on a 35mm SLR is going to be approx 300mm on a Canon D-SLR as its a 1.6 multiplier NOT divider....

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    Ex Vec-C Admin & Founder Bainie's Avatar
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    Default

    I am going to run this thread through babelfish, see if it can translate it for me ???

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