View Full Version : What's going wrong here?
Can someone explain why the front of the car and the back of the car are blurred yet the centre (where I was focusing) is sharp?!?!?!
http://www.talkphotography.co.uk/gallery/data/613/F1_IMG_6799-01.jpg
:thinking:
Oh, EXIF is:
ISO SETTING: 200
EXPOSURE TIME: 1/125s
APERTURE: 11.0
FOCAL LENGTH: 53.0mm
Camera rotation as you panned?
more likely lateral movement on the car, is it coming off a corner?
It is coming off a corner but she was pretty straight by this point.
I thought the same as Rob but it just surprises me when I see the same type of photos taken by other without this effect.
Could it be due to me being quite close?
Marianne
25-07-2006, 09:40
its one of those new bendy cars I reckon...bit like a bendy bus ;)
silkstone
25-07-2006, 09:54
I think it's because of the perspective effect when using a relatively short lens. You always get some distortion at the edges of the frame because the lens is trying to display the image in a flat plane. This is more noticeable with w/a lenses where objects at the edges appear stretched.
Although 53mm is not w/a, you'll still get more of this effect than with a longer telephoto. So as you pan, the degree of distortion towards the edges will change even if you track the centre perfectly, causing the image to appear more out-of-focus as you get further from the focus/tracking point.
That's my theory and I'm sticking to it. :)
That sounds perfectly feasable!
:)
silkstone
25-07-2006, 10:04
It does? :eek: :D
There's another thing too.... (or maybe it's just saying the same thing a different way!)
The car was getting slightly closer to you during the exposure. 1/125 is fairly slow for a shot like this. So it filled more of the frame at the end of the exposure than at the beginning - hence the ends moved relative to the middle, and appear blurred. ;)
What shutter speed would you recommend then? I wanted to maintain to movement blur in the background and wheels.
silkstone
25-07-2006, 10:52
You've done a wonderful job panning at that speed, and obviously you won't get the same effect if you shoot faster. Generally about 1/400 or faster is recommended, but that assumes a longer lens which needs the speed to overcome shake (unless you're using a tripod), never mind the moving subject.
It's all a bit of a compromise - so perhaps try something in between?
I'll have a look at my other photos that were done at different speeds to see if the effect is there or better.
Thanks for the advice all.
:)
antonroland
27-07-2006, 06:17
Hey SammyC
Please let me know what you figure out.I have seen exactly the same thing with photos I took at the Volkswagen rally a week or two back.
I take it you want the movement in the background but without the car appearing "frozen" like it was parked there right?:shrug:
I think it must be a combination of the two points silkstone raised.
Basically I think you'd need a shutter speed of 1/250th or there abouts.
antonroland
27-07-2006, 09:35
I have thought of prefocusing on a certain spot where you anticipate snapping the car with , say, f/8 or so.(mf obviously)
Only prob I see there is that if you pan then you could miss out on sharp focus maybe??One obviously wants a slow shutter,right.
I should maybe check the exif data on the shots I took that worked:thinking:
Gary Bagshawe
27-07-2006, 12:23
When I take pics of motorbike racing I use 1/250th and pan, it gives me just enough blur on the background whilst maintaining a sharp image of the bike.
I think it must be a combination of the two points silkstone raised.
Basically I think you'd need a shutter speed of 1/250th or there abouts.
I don't understand , all points of the car are moving towards you at the same speed. If the front and back are blurred surely the middle will be too.:thinking:
The back (et all) looks pretty sharp to me considering the shutter speed
My theory is its the way the centre of the car is darker and the front being over exposed is making it look worse than it is
The back (et all) looks pretty sharp to me considering the shutter speed
My theory is its the way the centre of the car is darker and the front being over exposed is making it look worse than it is
That's pretty well what I thought. The car is at an angle to the camera, so it could be as simple as the front being just enough closer to the camera to be slightly oof.
Maybe but I'd hope for a bit more DoF at f11! :)
Maybe but I'd hope for a bit more DoF at f11! :)
you cant possibly see the DOF as the movement blurs anything in focus anyway
The reason that the edges of the car are showing more blur is the relative speed of the pan across the lenth of the subject. The wider the lens the more you get this. Actually, it's more to do with the closer you stand than the width of the lens but one tends to lead to the other.
It's really hard to explain (for me anyway :lol: ) but I'll try to make some sense here.
If you imagine drawing a circle with yourself at the centre and the radius being the distance to the subject, the arc you'd get in front of you represents the pan. If your subject was following this arc you would be able to prefectly match it's speed with your pan and all would be pin sharp.
When you close into the subject, the circle will get smaller and hence the arc will be tighter. (anyone still with me here?)
When you're shooting cars on track, or any subject passing across your position at a tangent, technically only one part of the subject is actually intersecting your pan (or arc) and the closer you are (or smaller your circle) the less of the subject this is.
If you use a longer lens you end up further away, the circle gets bigger and the distance between the part of the subject intersecting the arc and the parts that aren't reduces.
The bigger the gap between the arc and parts of the subject that aren't intersecting it, the larger speed differential becomes and the more blur you get.
I need a beer now. :lol:
Forbiddenbiker
07-08-2006, 07:13
:clap: :thumbs:
Makes good sense to me.
That's what I suspected..... honest
Cheers mate!
The reason that the edges of the car are showing more blur is the relative speed of the pan across the lenth of the subject. The wider the lens the more you get this. Actually, it's more to do with the closer you stand than the width of the lens but one tends to lead to the other.
It's really hard to explain (for me anyway :lol: ) but I'll try to make some sense here.
If you imagine drawing a circle with yourself at the centre and the radius being the distance to the subject, the arc you'd get in front of you represents the pan. If your subject was following this arc you would be able to prefectly match it's speed with your pan and all would be pin sharp.
When you close into the subject, the circle will get smaller and hence the arc will be tighter. (anyone still with me here?)
When you're shooting cars on track, or any subject passing across your position at a tangent, technically only one part of the subject is actually intersecting your pan (or arc) and the closer you are (or smaller your circle) the less of the subject this is.
If you use a longer lens you end up further away, the circle gets bigger and the distance between the part of the subject intersecting the arc and the parts that aren't reduces.
The bigger the gap between the arc and parts of the subject that aren't intersecting it, the larger speed differential becomes and the more blur you get.
I need a beer now. :lol:
That theory works for close-up subjects and sounds right, but at f/11? I don't think so - what it looks like to me is motion blur: remember that even though we're (most of us) shooting digital, that these cameras still have focal-plane shutters, which occasionally do wierd things with moving subjects. I'm on a satellite link right now, but I'll go into this in greater depth when I get home next week.
That theory works for close-up subjects and sounds right, but at f/11? I don't think so - what it looks like to me is motion blur:
See I knew what was in my head would get lost in translation somewhere. :lol:
Motion blur is exaclty what I think it is, although you would get the same with a leaf shtter too. If it was anything to do with the shutter opening travelling over the chip, then the motion blur would pass from one side of the frame to the other (or top to bottom of course). You could take a shot like that one at f1, f11 or f1011 and it wouldn't have have made the slightest difference.
In this shot the car is captured before it gets to a perpendicular point and therefore the arc of the pan is still moving outward from the camera position. If you look at the car and imagine a line drawn from the camera out to the bottom of the windscreen on the far side, you can see it's a little shaper than where it intersects the front wheel and bumper.
When you are that close to a subject moving across your path at at a right angle and you pan to capture it, there is a difference of speed relative to the film/chip plane. You can only match the speed of part of the subject and will therefore always have some motion blur on the other parts.
'Tis my take on this old chesnut anyway but I've never been too hot on explaining the science in a way that makes sense. ;)
That's it... I've started bleeding from the ears - I need a lie down! :lol:
So it's more a case of rotation blur than parallel motion blur?
Forbiddenbiker
09-08-2006, 16:13
Taken from what you've said guys, I made this up...is this what you mean..?
http://myweb.tiscali.co.uk/optiflow/panarc.jpg
Is this pic loading ok...?
is this what you mean..?
Yup... you sir are a top bomber. :thumbs: :D
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