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FORUMS Photography Talk by Genre General Photography Talk 
Thread started 19 Jan 2007 (Friday) 05:25
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Focus Issues

 
zasboy
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Jan 19, 2007 05:25 |  #1

Hi. I'm pretty new to photography and have lots to learn. One issue I usually stumble upon is focus. Even though I think I have the camera settings correct, when I reviewed the photos, it doesn't look sharp or focus at all.

Here are some example photos from my school open gym. Lighting was poor and had to use some 'extreme' camera settings. Only edits I did was using auto settings in CS2 Camera RAW. No crop, but resized though.

1) Face doesn't look sharp

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2) Face does look somewhat sharp but can be better?
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Here are the equipments I used:
- Canon Rebel XTi w/grip
- Canon 50mm f/1.8

Here are the settings I used:
- Manual Exposure
- Shutter : 1/250th
- Aperature: f/1.8
- ISO: 1600
- AI Servo AF
- Manual Focus Point: Center Focus

The issue I'm having is that even though I have the center focus point on the player's face, I can't seem to get a sharp photo. I'm pretty sure it has to do something with DOF(depth of field) but I don't know much about this. From what I know(hopefully this is correct) that a large fstop such as f/1.8 would produce a shallow DOF which mean objects would appear sharp if they are closer to the camera and anything beyond a certain distance will be blurry. A small fstop such as f/22 would produce deep DOF which mean everything from a short to long distance would be sharp. I'm hoping this is correct. Please correct me.

I also know that some lenses has a sweetspot at some aperture. I think on the Canon 50mm f/1.8, the sweetspot is around f/2.8 but I wished I could use that. I could try to slow down the shutter to 1/200th and raise the aperture by one stop but not sure if the shutter speed would be fast enough to "freeze" the shot.

Or my last idea is that I pushed my equipments to their limits and it's the best quality I can get. Even that's the case, I still want to get some opinions on DOF and how that effects focus. I think that is my problem that I don't understand how DOF works. I also heard something about focusing 1/3 on the subject? Maybe that could help?

And finally, any tips, advices, suggestions or comments for a new photographer would be grateful too :)

-Thanks



  
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pmburden
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Jan 19, 2007 05:45 |  #2

I think you've almost got it

The size of the aperture does determine the depth of field or area that appears sharp (1.8 shallow and 22 deep) as you say. However I think your slightly confused over the distance from the camera. The area that will be in focus is determined by the distance the lens is focussed at and the depth of field either side of that focus point - not how far the subject is from the camera per-say. Although the closer the subject is, the smaller the depth of field is possible.

Hopefully that's helped a little.


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Box ­ Brownie
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Jan 19, 2007 06:08 |  #3

Hi

I see that you used Camera RAW defaults, well AFAIK the sharpening level at default is fairly gentle.

Can I suggest you try again using it set to zero and when you have brought the image into CS2 and resized it to the final size like above then use Smart Sharpen ~ the settings I use with my 350D (XT) is 52% and 0.9 Granted I will have done other steps in the PPing to suit the particular image but that final sharpening at the usage size nails the image for me.

Oh, and yes depending on how far away from the subject you were the aperture of f1.8 could result in one eye being in focus and the other eye being out if the subject is 3/4 on to the camera ~ worst case scenario if you were rather too close. I suggest you try some experimenst to understand & see what I am describing ;)

HTH :)


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zasboy
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Jan 19, 2007 20:10 |  #4

Yeah, I figure out that I was pushing my equipments to their limits and it's the best I could do from the camera point view. Of course, I could of gotten better shots if I played around with the settings but my priority was maintaining a shutter speed of 1/250s and to obtain that, I had to use ISO 1600 and fstop of 1.8. So I couldn't do much.

One idea that was proposed was to underexposed the shot. Maintain the shutter speed at 1/250s and ISO at 1600 but use an fstop of 2.8. Then using Camera RAW, increase the exposure. The result would be better DOF and higher chance of getting sharper photos but at the cost of image quality(contrast and noise level will suffer). I will try this at the upcoming open gym.

I did some edits on the photos using noise reduction and unsharp mask. Feel free to take a look at them in my gallery: Click Me (external link)




  
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Box ­ Brownie
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Jan 20, 2007 05:27 |  #5

zasboy wrote in post #2568733 (external link)
One idea that was proposed was to underexposed the shot. Maintain the shutter speed at 1/250s and ISO at 1600 but use an fstop of 2.8. Then using Camera RAW, increase the exposure. The result would be better DOF and higher chance of getting sharper photos but at the cost of image quality(contrast and noise level will suffer). I will try this at the upcoming open gym

Hi

Using camera RAW will give you some chances of rescuing an under or overexposed image i.e. getting some imformation/detail out of the shadows and highlights. But the one thing it will not help is DoF, the DoF is is an optical function as result of the aperture used and the distance from the subject.

I have seen examples of PPing that have improved the focus of an OOF shot but have never seen them (yet) applied to DoF improvements.

Had a quick look at the gallery and yes the PPing has given them the expected crispness. I still use USM but find Smart Sharpen less aggressive and keeps the edge definition better IMHO. ;)

HTH :)


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René ­ Damkot
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Jan 20, 2007 06:36 |  #6

The focus on #1 is probabely on the arm.
The actual AF erea is quite a bit larger then the red rectangle in the VF (this is a 10D):

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zasboy
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Jan 20, 2007 19:33 |  #7

Great information. I was using f/1.8 and was getting good exposure. I was thinking of using f/2.8 and getting underexposed photos. I want to get a deeper DOF and see if that will help with focus. It will be an experiment and good see what would happen. I'm hoping that I can still save the photo using Camera RAW.

I'll look into using Smart Sharpen. I'm still experimenting with different filters. In my workflow, I would crop the picture if needed, then noise reduction and finally unsharp mask. Not sure if this is producing good results but I'm still learning and trying other methods. The photos above in my original post are straight out from RAW with no noise reduction or USM. The photos in my gallery has those filters applied.




  
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Focus Issues
FORUMS Photography Talk by Genre General Photography Talk 
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