Why did a 50 1.8 slow down my frames per second?

For the first time tonight at a basketball game, I started shooting with a new 50mm f/1.8 on my Canon 40D. I had the continuous setting on HIGH and the auto focus on AI Servo, but the camera was slowed down and wouldn't shoot at the fast rate like it should.

I switched to my 70-200 2.8 lens (that I usually shoot sports with), made no other camera adjustments and it worked at the high speed rate. Back to the 50 I went and again it would not shoot at the fast rate.

What gives? Thanks in advance. Hank

Were you shooting the 50mm wide open? If not I wonder if the aperture just couldn't keep up.

I was shooting at 1/400 at f/2.0

Strange, because only the 1D bodies have a custom function that will give focus priority in servo mode. So far as I know all other bodies will happily snap away totally OOF images in servo mode while maintaining the set speed.

I'm no expert but I'm going to say with the reputation the 50mm has with it's 'impressive' AF it will have something to do with that. Flick the 50mm to MF with the same settings and you'll probably find you'll get all that FPS back... At times things can get a little clunky when I use AI Servo and the 50mm f1.8 (In difficult conditions instead of click-click-click-click on my 18-200, the 50mm f1.8 can occasionally make it click--click--click-----click-click-click---click (random and not constant)

That's just in my experiences, and its rare that it happens, too.

My $.02, but I'm sure someone else more experienced will come along and shut me down :P

50mm f1.8 has been fairly slow focus, for me, IMHO. I think, as mentioned in the prior posts, if you switched to manual, you'll get all that frame rate back. Try the difference between AF and M and you should notice the difference there.

JeffreyG wrote in post #7174255
Strange, because only the 1D bodies have a custom function that will give focus priority in servo mode. So far as I know all other bodies will happily snap away totally OOF images in servo mode while maintaining the set speed.

Jeffrey,

I can only say that both my 20D and 50D will, at times, slow down the frame rate to aquire focus. I could be wrong, but I'm pretty sure that's what it is.

BINGO!! I flicked it to MF and it was fast like it should be. I just don't understand. The 70-200 has a high FPS rate in either auto OR manual focus.

I guess I'll have to quit being lazy and shoot MF with the nifty fifty.

ShauningtoN wrote in post #7174282
I'm no expert but I'm going to say with the reputation the 50mm has with it's 'impressive' AF it will have something to do with that. Flick the 50mm to MF with the same settings and you'll probably find you'll get all that FPS back... At times things can get a little clunky when I use AI Servo and the 50mm f1.8 (In difficult conditions instead of click-click-click-click on my 18-200, the 50mm f1.8 can occasionally make it click--click--click-----click-click-click---click (random and not constant)

That's just in my experiences, and its rare that it happens, too.

My $.02, but I'm sure someone else more experienced will come along and shut me down :P

Focus speed would seem to be the culprit, but I agree with Jeffrey, it shouldn't matter as there is no focus priority on the 40D. Just darn strange. I'll have to try this out and see if it makes any difference.

What was your ISO on each lens, you weren't getting f/2 out of the 70-200, did you bump ISO or change another setting to keep the shutter speed constant between the two lenses.

The 70-200 has a MUCH better AF system than the nifty. You might have noticed a slight difference in their price when bought them...

Hank E wrote in post #7174364
BINGO!! I flicked it to MF and it was fast like it should be. I just don't understand. The 70-200 has a high FPS rate in either auto OR manual focus.

I guess I'll have to quit being lazy and shoot MF with the nifty fifty.

Well saw this after I posted. This is the darnedest thing, it shouldn't matter in my experience. Shows what I know.

ssracer wrote in post #7174370
The 70-200 has a MUCH better AF system than the nifty. You might have noticed a slight difference in their price when bought them...

Well, only about 15:1 :: 50mm/1.8:70-200mm/f2.8 IS...

scslmd wrote in post #7174410
Well, only about 15:1 :: 50mm/1.8:70-200mm/f2.8 IS...

Well probably 16 to 17 times more expensive, but then who's counting.

Does the 50 1.4 focus faster?

Hank E wrote in post #7177553
Well probably 16 to 17 times more expensive, but then who's counting.

Does the 50 1.4 focus faster?

Yeah, the 50mm 1.4 and 85mm 1.8 have USM focus motors like your 70-200. Should be quite a bit faster for what you are trying to shoot.

ShauningtoN wrote in post #7174282
I'm no expert but I'm going to say with the reputation the 50mm has with it's 'impressive' AF it will have something to do with that. Flick the 50mm to MF with the same settings and you'll probably find you'll get all that FPS back... At times things can get a little clunky when I use AI Servo and the 50mm f1.8 (In difficult conditions instead of click-click-click-click on my 18-200, the 50mm f1.8 can occasionally make it click--click--click-----click-click-click---click (random and not constant)

That's just in my experiences, and its rare that it happens, too.

My $.02, but I'm sure someone else more experienced will come along and shut me down :P

Is this an attempt at sarcasm? or do you believe the 50/1.8II has a fast AF motor?

This motor is a slow slow sloth.