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04-17-2008, 06:22 PM   #1
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Help with focus?

Hey everyone, over the past couple days I have been trying my hand at car photography. I have had some great shots but on the shot below I was wondering how you get the car in sharp focus when using a large aperture. What I was trying here was use the large aperture to make the backround blurry while having the car in sharp focus. Well, you can be the judge on this one because to me the car doesn't appear as sharp as I was hoping. Do you think on my next shoot I should just take a bunch of shots at different apertures to see if I can do better?

Thanks for any advice.

Cory

And yes, the camry is mine.



04-17-2008, 06:44 PM   #2
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QuoteOriginally posted by Tuner571 Quote
I was wondering how you get the car in sharp focus when using a large aperture.
1) use DOF calculator to find out parameters (distance, etc)
2) PP (resize/sharpen)
3) focus stacking
4) combine 2 shots (cut just the car from one with the empty and blurry background from another)
5) you name it
04-17-2008, 06:50 PM   #3
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Thanks for tips, but after looking at the DOF calculator I'm really confused. Can someone simplify it for me?
04-17-2008, 06:55 PM   #4
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I've been struggling with the same issue for months now. My pics are almost invariably OOF.

I fail to grasp certain concepts... like why its necessary to calculate DOF etc. If the camera is set to use AF, shouldn't it be focusing properly?

Can someone please enlighten me in the simplest terms possible?

Nice Camry btw.

04-17-2008, 07:02 PM   #5
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QuoteOriginally posted by zoomzoomfan Quote
I've been struggling with the same issue for months now. My pics are almost invariably OOF.

I fail to grasp certain concepts... like why its necessary to calculate DOF etc. If the camera is set to use AF, shouldn't it be focusing properly?

Can someone please enlighten me in the simplest terms possible?

Nice Camry btw.

Thanks man, I normally do landscape photography so this is all new to me. Also, I am using a SMC-A manuel lens, but the camera was telling me I was in focus, so I know it has something to do with the aperture.
04-17-2008, 07:11 PM   #6
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QuoteOriginally posted by zoomzoomfan Quote
I fail to grasp certain concepts... like why its necessary to calculate DOF etc. If the camera is set to use AF, shouldn't it be focusing properly?
Depth of field - Wikipedia, the free encyclopedia
04-17-2008, 08:10 PM   #7
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Ok... maybe I didn't explain myself properly. I don't lack the ability to google the term DOF and find the associated Wikipedia article. I simply don't understand why its necessary to get out the sliderule when the camera's supposed to be able to figure out focus on its own.

BTW, I read that article months ago. I doubt I'll gain anything from reading it again. Thanks anyways.
04-17-2008, 08:23 PM   #8
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QuoteOriginally posted by zoomzoomfan Quote
I simply don't understand why its necessary to get out the sliderule when the camera's supposed to be able to figure out focus on its own.
focus - yes... well - "yes", because as we know AF is not perfect

BUT your camera does not know what do you want to be within DOF

04-17-2008, 08:48 PM   #9
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The point the camera focuses on, and the depth of field are two different things.

Having said that, I'm sure I'm opening myself up to corective comments from those with greater technical knowledge...

In simple terms, the camera will calculate the point the lens is focused on. The area in focus forward and aft of that point is controlled by the aperture. This is the depth of field.

Neither the K10D nor the K100D have the ability to know what the depth of field is that you want.

There are a number of ways you can check your depth of field. One is the aformentioned DOF table. Another is to use the DOF preview that the camera has. Some people use the optical methode (ie through the view finder) others use the screen method. Give it a try.

A gret way to learn about DOF is with an old lens. Back in the day, lenses had a DOF table printed on the barel. So, you could set your aperture to f8, and look at the guide on the barel. In the case of my 135 3.5, at f8, focused at 15 feet, the DOF is about 14.5 to 16 feet.

So for your car. At that angle of the car, I am going to asume the length you want to be focused is about 182" for a camery. So 15'

Looking at the guide on the lens...

@ 20' f22, I get a DOF from 16' to 27' .....not enough
@ 20' f32, I get a DOF from 15' to 30' .....plenty for the car. As long as the lens is focused to 20'

But, f32 might need a tripod. It might also not be the shapest for the lens.

@ f11 i can get a DOF from 30' to 50' (estimated) with a focus point at about 35'.

This might be sharper for the lens.

Hope this helps.

Last edited by KungPOW; 05-20-2008 at 09:26 PM.
04-17-2008, 08:51 PM   #10
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Okay, so here's what you want to do:

First, figure out how much DOF you want. How much of the car do you want to be in focus? All of it? How long is a car, about 10 feet?

Go to the DOF calculator. Choose your camera, and play with the settings until the total DOF shown on the right reflects what you want.

For instance, if shooting with the FA50mm from 20 feet away, an aperture of f/5 will give you a DOF of about 10.4 feet. (Keep in mind that all this is approximate.) From the calculator, I see that everything 3.9 feet in front of the focus point will be in focus. So try to focus about 4 feet from the front of the car. I'd try the door handle.

If your background is sufficiently far away, it should be quite blurry.

Hope that helps.
04-17-2008, 09:29 PM   #11
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Ironically, the DOF of my example photo is off...
04-18-2008, 04:49 AM   #12
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WOW, thanks for all the help guys, its much appreciated. For this shot I was using my SMC-A 70-210 manuel focus so it does have that chart on the lens barrel. Problem is I just never learned to read it. As for the shot above I was using a aperture of f/6.7 at a focal length of about 155mm, so do you think next time I should just bump the aperture a few stops.

BTW here is what I was trying to do, this is not my picture.

EXIF data shows that he was at f/5.6 at 160mm


Last edited by Tuner571; 04-18-2008 at 04:55 AM.
04-18-2008, 06:12 AM   #13
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Did you look at the EXIF on that photo? It was shot at f/5.6 with a focal length of 153mm. But the EOS 1D Mark II has an oddball 1.3x crop factor, whereas our Pentaxes have a 1.5x factor. So it's not really comparing apples to apples.
04-18-2008, 06:27 AM   #14
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Was it 153mm, I was trying to remember. Aside that, I was using it a example to show what I want to do. Do you think I can get the same result using a smaller aperture?
04-18-2008, 06:49 AM   #15
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Try using different focal lengths and position youself accordingly to frame the picture the way that you want. A longer focal length will give a higher compression facter than a wider lens at the same settings. Depth of Field and Hyperfocal Distance. The DOF calculator link on that page is awesome. Based on those settings, try it at 75mm, f/8, about 30 feet away from the front of the car.

Last edited by code4code5; 04-18-2008 at 06:56 AM.
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