A technical question about panning

[mkemd21]

I take panning shots on a regular basis. It seems to me that panning shots with shorter focal length create a more blurred background than shots with longer focal length. I look at my shots taken with a 400mm and compare with shots taken at 14mm, both with the same shutter speed of 1/20, the background of the 14mm shots are filled with streaked lines while I can still make out the background of the 400mm shots.

Let's say I use a longer lens. If a subject is 100 ft away and during panning the subject moves from the left edge of the frame to the middle of the frame, the angle of movement of my camera will be x degrees. Now I use a shorter lens and to get the same perspective I move closer and I am 50 ft away from the subject. For the same movement, the angle of movement of my camera is 2X degrees.

It seems to me the larger angle movement of my camera with a shorter lens will yield more blur. On the other hand, I believe same amount of movement with a longer lens will also create more blur. So, does a short lens yield more blurred background during panning? Thanks.

 

[Desmond]

How about posting some samples?

 

[mkemd21]

The first picture was shot with a 14-24 at 19mm. SS was 1/20.

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The second picture was shot with a 400mm lens, also at 1/20. Others looking at this picture thought it was shot at 1/125 or faster.

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If my theory is correct, I will make adjustments in future shots when using a long lens.

 

[Desmond]

I think they are two very different scenes so it is difficult to say whether one had a more blurred background than the other.
Perhaps in the closer shot with the wide angle you had to move more to pan the subject going past which would mean a greater arc in the background [think how fast you would have had to turn to follow him if he was only inches away from your camera, and how much the background would move in that time].
In the long shot it's hard to tell what is the background and what is perhaps grass in front of the subject. You would have also had to move less to pan the subject at a distance [think of someone doing that speed on the horizon] which would mean less movement of the background.
Hopefully that's the answer, either way I like the first image and think the added blur is mostly due to the difficulty of panning something right in front of you compared to a distant object.
Looking at it again in the first image it is not a 'side on' shot, he is slightly coming toward you which would also make things not look quite right.

 

[mkemd21]

I've come to the same theory that wider shot requires more camera movement. I probably need to make some adjustments going forward for longer shots, perhaps with slower SS.

It's hard to make out the background in the second shot. It's actually a cornfield. However, if you look at the foreground in front of the cyclist, you can see the gravel and the snow. It's this part of the picture that tells me the panning effect is not as smooth as I like.