DoF issues with Motorsport

<p>Recently, I have been trying my hand at some motorsport photography for fun, but there's obviously something I'm not understanding here.</p>

<p>In this shot the driver is clearly in focus but the front of the car isn't:<br>

<img src="http://www.litherland.me/images/JBB1.jpg" alt="" width="600" height="400" /><br>

Closer<br>

<img src="http://www.litherland.me/images/JBB2.jpg" alt="" width="600" height="400" /></p>

<p>Here's the EXIF data:</p>

<p><img src="http://www.litherland.me/images/EXIF1.png" alt="" width="256" height="275" /></p>

<p>Now I figure that I was about 240ft away and I calculate the DoF to be about 51ft for f10, 400mm on a 1D Mk III<br>

<img src="http://www.litherland.me/images/DoF.PNG" alt="" width="640" height="960" /></p>

<p>There's no way that there's a DoF of >50ft in that shot, even allowing for vagaries of CoC and some miscalculation of distance.<br>

What am I missing?<br>

Thanks</p>

<p>Mark</p>

<p> </p>

<p>Your shutter speed looks low to me. The front of the car may be bobbing and moving faster (up and down) than the cockpit. I'd bump the ISO up to 800, keep aperture where you have it and raise SS. I would also focus on the front of the car, not the windscreen. (Can you show us the AF point? DPP will reveal it).</p>

<p>To check if it's car movement, blow up the curb to the car's left to see if it's sharp.</p>

<p>I think David's point is well taken. When shooting on-coming cars (or cars moving away) you have a combination of standard DOF challenges and car movement. In those shots where I'm looking for crispness on the track I work in shutter priority, shooting at as high a speed as possible. Your exif data shows you were in shutter priority, but a 400mm lens at that distance using 1/200 shutter speed is pushing your luck on car movement. Its obviously not a bright and sunny day, so you're going to have to compromise somewhere. There's a certain amount of luck involved in shooting motorsport, and some days you forego crispness for the opportunity to shoot action.</p>

<p>Agreed the shutter speed is low, I was set up for the panning shots that I took a few seconds after this. They were fine.<br>

But it's possible that you have a point about the front of the car bobbing more than the windscreen. It's not camera shake, otherwise the driver and windscreen wouldn't be so clear. <br>

I need to go out an experiment some more to identify the DoF better. I'll start at 1/1000s and go from there.</p>

<p>It does actually look like there could be 50' of focus in the photo; but it starts near the driver and extends behind the car for the most part. Seems to me part of the solution might be pre-focusing (manually) and capturing cars (in a given spot) as they pass a certain trigger point.</p>

<p>Maury - that's a good point about pre-focusing and working on a given spot. It does work well if you've set it up properly.</p>

Thanks All.

 

Maury, I think you have a point about the DoF lagging the car and maybe there is 50' there. I'm loathed to go back to the 'Pre-focus and

wait until the car gets there' method though. If we have sorted the DoF puzzle, then I need to nail the AI Servo settings for Motorsport. I

usually just use the centre point for AF but it's probably a good time now to widen the options out and see how the camera works with 19

points on the 1D3 and the 61 points of my 5D3.

 

Also, probably a good time to go through the AI CFn settings of both cameras.

 

Closest track day is Cadwell on Sunday. Might be a good chance to experiment and see what works.

 

Cheers

 

 

Mark

<p>Mark, you don't want to use all of the 5D3's 61-points in AI Servo mode. It'll grab points all over the car. Use single-point or single-point expanded and put the point on the exact point that you want to be the center of focus. I haven't pulled out my manual, but there's an AF mode that favors fast closing subjects. In the position you were in here, you want that.</p>

<p>I do a lot of bird in flight photography and the birding guys that have shot both the 1D3 and the 5D3 say that the 5D3's AF system is superior, if that helps. Forget MF pre-focus, since these cameras will keep up in AI Servo mode.</p>

<p>I will echo David's comment about using a single point. Most of the time I'm using center-point focus and AI to let the camera manage the need to constantly and quickly adjust focus as the car approaches. Otherwise a slight movement of the camera can cause some other AF point to control the shot. </p>

<p>However, I still use pre-focus occasionally if I'm standing in one spot and shooting cars coming through that position. If it's on the racing line then you'll consistently get cars at that point, and you don't need to fuss with anything else. Perhaps that's old-school, but I've been using it for a long time and it still works with DSLRs.</p>

<p>I agree with David Stephens on both counts:</p>

<ul>

<li>on single point (or expanded) AF. I don't shoot cars, but I do shoot football (Soccer) and (Field) Hockey, with 5D's and 1 Series cameras.</li>

<li>also - IMO the front of the car is moving <strong><em>horizontally</em></strong> at a faster speed than it is moving horizontally centre of the car.</li>

</ul>

<p>I enlarged a section of the front fender and also a section at the windshield.<br />Even from the low resolution upload, one can see a longer trailing line of movement blur, on the white paint line near the fender, than at the windshield.</p>

<p>WW</p>

<p>I want to make it clear that I believe in and use pre-focus, but in AF mode. If a subject is approaching, I grab a pre-focus at around the distance that I expect to shoot my subject, then I grab the subject with AF as it comes into the area and let AI Servo mode fine tune the focus, allowing me to shoot bursts of multiple shots that are in focus.</p>

<p>With MF, you can't shoot a burst with a subject moving toward or away from you. Also, it's very hard to MF super-telephoto lenses. Believe me, I tried it a bunch, thinking that I had focus while I was in the field, but seeing softness back home on the computer. The new AF systems are amazing, once you figure out all their ins and outs.</p>

<blockquote>

<p>Even from the low resolution upload, one can see a longer trailing line of movement blur, on the white paint line near the fender, than at the windshield.</p>

</blockquote>

<p>Also, the edge of the track in the lower left foreground appears to be just as sharp as the edge of the track behind the car - definitely not a DOF issue.</p>

<p>You should be able to shoot at or close to f2.8 and still have very good dof distance, I imagine. I agree the SS is too slow.<br>

Also, the cropped image exif data shown here indicates that you have cropped out more than 1/2 the pixel data. 1/4 should be the Max.<br>

Looks like an overcast day - increase your ISO too.<br>

Might be good to focus on the contrasting area on the hood as you get more sharp distance beyond the focusing point than in front of it.</p>