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Author Topic: focus on wideangle lenses  (Read 7891 times)

willie45

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focus on wideangle lenses
« on: June 07, 2006, 05:35:28 PM »

Hi

I have fairly recently started getting serious about photography and have bought a Canon 20D with 2 Tamron zoom lenses of 17-35mm and 28-75mm respectively.
I have noticed that when shooting landscapes and going for the hyperfocal distance at 17mm that the leaves on further away trees seem to be out of focus and blurred. They are almost merged into each other like a painting. I wonder if this is a fault with my lens or my technique or whether this is just the way wide angle lenses record leaves.

I realise this might well be a silly question and if it is I hope you will forgive me but I would welcome all answers or assistance with this issue.

Thanks

Willie
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DarkPenguin

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« Reply #1 on: June 07, 2006, 06:13:30 PM »

Kind of need an example to know what you are talking about.  What is your fstop?
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Tim Gray

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« Reply #2 on: June 07, 2006, 06:37:27 PM »

Aperture is a good starting point, - here's a tutorial that explains what's going on and why shooting at f 22 detracts from the sharpness of an image given your pixel pitch.

http://www.cambridgeincolour.com/tutorials...hotography.htm#
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willie45

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« Reply #3 on: June 08, 2006, 07:22:40 PM »

Thanks for the replies. I was shooting at f16 on this occasion in an attempt to render the  scene sharp with maximum depth of field. The main areas of concern were leaves on the trees in the background. Having read the tutorial on diffraction and trawled around a few sites I am inclined to believe my problem might be caused by this and the use of hyperfocal distance in the shots. I was amazed by the difference in the example picture! Is this a problem only on digital cameras or are film slrs prone to it too? I was a little concerned that my hard earned Canon 20D would cause me such problems. Maybe I am expecting too much.

Anyway, I will try a different method of trying to ensure max dof mentioned in some of these and compare results at a larger aperture.

Thanks again

Willie
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dlashier

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« Reply #4 on: June 08, 2006, 07:43:35 PM »

> I was shooting at f16 on this occasion in an attempt to render the scene sharp with maximum depth of field.

A very wide-angles the DOF is so great that I rarely find need to go beyond f8 or f11, even when including close foreground. Just remember that your hyperfocal point is very close! If a critical shot I'll usually bracket a couple shots on focus point.

- DL
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benInMA

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« Reply #5 on: June 09, 2006, 12:21:24 PM »

Bleck... I just ruined one of my shots last night because I didn't get the hyperfocal calculation right.   (I can probably go back and take it again)

Without carrying around a computer/PDA to calculate it any recommendations on the best way to figure it out in the field?

In my case I was shooting a 28mm shot (35mm format) that had a bunch of plants & a log in the foreground, at f/8.

If I had set the focus to 10ft I would have gotten everything from 5ft to infinity in focus... but I screwed up and set the focus more like 4-5ft and got exactly the same problem as the original poster.

I know better but it's still easy to screw it up.

Would a print out of the hyperfocal distance & near focus distance for each aperture with my lenses be a good idea?

I do have a small PDA I could stick in my bag but it's one more thing to charge up and PITA IMO.

I suppose I would have done better at f/16-f/22 but the diffraction effects are definitely there.
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fike

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« Reply #6 on: June 09, 2006, 02:09:01 PM »

I did some experimenting with hyperfocal calculators for my Canon Pro1 which has a small sensor (4x crop factor).  I am not an expert on this, but the hyperfocal calculation is dependent upon your tolerance for fuzzy focus.  As you probably know, a photo that is printed at 4x6 has a much lower need for sharpness (larger acceptible circle of confusion) than a photo printed at 13x19.  This has to do with the circle of confusion that was discussed above.  With crop sensors like the 1.6x in the 20d and the 4x in a pro 1, you are in effect multiplying the focus (or fuzziness).

Put another way, the projection of fuziness from the lens remains the same, but the smaller sensor magnifies the fusiness.

--so--

printing a 4x6 photo taken with a 1.6x crop factor camera will have the aparent sharpness properties of a 5.6"x 9.6" print.  

What I am surmising is that the hyperfocal calculators are using a circle of confusion number that is appropriate for a full frame sensor at a smaller print size.  If you plan on printing larger prints with a crop factor, you will need to factor in a much smaller circle of confusion.

I am still formulating this understanding in my mind, but I think I have this right.  Does anyone have any clarifications on my hypothesis.
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benInMA

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« Reply #7 on: June 09, 2006, 04:08:52 PM »

You're right.

If you look on the web you can find calculators with all the values plugged in for whatever digital camera you want.

In my case I was just lamenting not having the information with me out in the woods.

I may have just needed a tilt/shift lens to get that shot anyway though, wide angle shots with the camera 12" off the ground are pretty demanding in terms of getting full depth of field.
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dlashier

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« Reply #8 on: June 09, 2006, 05:44:52 PM »

Quote
If I had set the focus to 10ft I would have gotten everything from 5ft to infinity in focus... but I screwed up and set the focus more like 4-5ft and got exactly the same problem as the original poster.

10 ft. is a good rule of thumb. Most of my WA shots are in the 17mm to 25mm range. I don't calculate hyperfocal but typically just lock focus on the ground about 10 feet away, then recompose and shoot, sometimes bracketing focused about 20 feet and 6 feet (lock on my feet). Even calculating hyperfocal is not foolproof because of all the other factors that enter including the relative presence and importance of foreground and distance detail.

- DL
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manrico Scremin

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« Reply #9 on: June 15, 2006, 12:11:56 PM »

Are you sure it was a depth of field / hyperfocal issue?  The leaves definitely won't be sharp if there was any kind of breeze and a slower shutter speed.
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jimhuber

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« Reply #10 on: June 16, 2006, 02:32:10 PM »

That was my first thought, too: leaves blurring due to slow shutter speed and a breeze rather than out of focus. At 17mm I rarely have to go past f/11 to get the DoF I need, and usually f/8 will do.

My field solution for hyperfocal distance is a printed spreadsheet for various focal lengths and apertures. It includes full frame (5D), 1.6x reduced frame (Rebel XT/350D), Sony DSC-F828 and the Canon PowerShot S70 point-and-shoot. Here's the URL:

hyperfocal_distance.xls
« Last Edit: June 16, 2006, 04:17:18 PM by jimhuber »
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Gregory

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« Reply #11 on: June 16, 2006, 08:18:58 PM »

Quote
My field solution for hyperfocal distance is a printed spreadsheet for various focal lengths and apertures.
[a href=\"index.php?act=findpost&pid=68329\"][{POST_SNAPBACK}][/a]
hi.

how do you use it?
are the measurements in metres or feet?
« Last Edit: June 16, 2006, 08:19:47 PM by Gregory »
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jimhuber

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« Reply #12 on: June 17, 2006, 11:53:24 AM »

Oh, the details are in the header and footer, which you won't see without going to page setup or printing it. The distances are the closest point in focus, in feet, so the lens should be focused at twice that distance.

Although the numbers are precise, it's not "black and white" as mentioned, but really a continuum from sharply in focus to blurred.
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TTHU

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« Reply #13 on: August 13, 2006, 07:53:03 AM »

Quote
Oh, the details are in the header and footer, which you won't see without going to page setup or printing it. The distances are the closest point in focus, in feet, so the lens should be focused at twice that distance.

Although the numbers are precise, it's not "black and white" as mentioned, but really a continuum from sharply in focus to blurred.
[a href=\"index.php?act=findpost&pid=68397\"][{POST_SNAPBACK}][/a]
I usually use the best aperture of each lens, and after that, I use hyperfocal point for focusing.
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