The Fast Glass TRAP - Don't Make This Mistake!

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Steve

Steve

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Think your F/2.8 lens is always the best choice for wildlife photography? Think again.

In my latest video, I’m uncovering common mistakes many photographers make when reaching for that fast glass. Wait until we get into Depth of Field and ISO - it's shocking how most photographers get this 100% WRONG - and how much it hurts them in the field!

You won't want to miss this one — it will change the way you think about fast glass. Watch now and see if you can spot the hidden trap!

 
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Steve, thanks for the great video. I will watch it again to confirm, but I think it supports two things I have learned over the years about controlling backgrounds and depth of field, etc: Getting closer to your subject by walking or by using a longer focal length lens is more important than its widest f stop, other things the same. When I bought my Z9, I skipped the 70-200mm f2.8 and got the 100-400mm instead. For my kind of nature photography, the longer focal length of the 100-400mm was more important than the f2.8 on the 70-200mm. If Nikon or Tamron offered a 70-200mm f4 Z mount lens, I might just buy it.
 
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Excellent video with very cogent observations. I think one consideration are the potential advantages that a faster lens affords for autofocus. The Canon AF system utilizes this advantage by opening the lens up while AFing, stopping down to the desired aperture when the shutter is pressed. Thus, a f/2.8 lens may AF better in situations of marginal light than a f/6.3. I'm not certain whether Nikon or Sony use similar AF strategies.

I can say that with my long experience shooting Canon gear and primes that this distinction was observable in the days of DSLR's particularly with cross type AF sensors. Whether it is as important with MILC, off the chip PD/CD AF is a legitimate question.
 
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ajrmd said:
Excellent video with very cogent observations. I think one consideration are the potential advantages that a faster lens affords for autofocus. The Canon AF system utilizes this advantage by opening the lens up while AFing, stopping down to the desired aperture when the shutter is pressed. Thus, a f/2.8 lens may AF better in situations of marginal light than a f/6.3. I'm not certain whether Nikon or Sony use similar AF strategies.

I can say that with my long experience shooting Canon gear and primes that this distinction was observable in the days of DSLR's particularly with cross type AF sensors. Whether it is as important with MILC, off the chip PD/CD AF is a legitimate question.
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I've had a few comments about AF. I know with Sony and Nikon mirrorless, they don't seem to care all that much about maximum apertures for AF -accuracy is surprisingly good, even with slower glass. As for speed, it really depends on the the lenses you're comparing. A 600PF is a pretty fast-focuser, but the 180-600, not so much.
 
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ajrmd said:
Excellent video with very cogent observations. I think one consideration are the potential advantages that a faster lens affords for autofocus. The Canon AF system utilizes this advantage by opening the lens up while AFing, stopping down to the desired aperture when the shutter is pressed. Thus, a f/2.8 lens may AF better in situations of marginal light than a f/6.3. I'm not certain whether Nikon or Sony use similar AF strategies.

I can say that with my long experience shooting Canon gear and primes that this distinction was observable in the days of DSLR's particularly with cross type AF sensors. Whether it is as important with MILC, off the chip PD/CD AF is a legitimate question.
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Hard to say, but remember the premise here is working distance remains the same between say the 70-200mm f/2.8 and 600mm f/6.3 and subsequent cropping will be used to deliver appropriate subject size from the shorter lens. So from an AF perspective there's more light but the AF system is trying to track a much smaller target with fewer pixels on the subject when shooting with the shorter focal length glass.

Whether the additional light with the shorter focal length lens helps more than the additional pixels on subject with the longer focal length lens is hard to guess but personally I'd suspect the longer lens with the larger subject in frame would have an AF acquisition and tracking advantage in most situations. One clue to this is how adding a TC can often help with subject acquisition when the subject is small in the frame with the bare lens even though the TC costs light. At least that's my experience with mirrorless cameras that don't have strict aperture limits to AF performance.
 
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well done video

wish I had seen this before I purchased multiple 400 f2.8s and wondered why I wasn't happy with them!

this video, the one about cropping increasing noise, and the one about changing busy backgrounds in 3 seconds have been the 3 most impactful videos I've seen
 
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I really enjoyed this video! Lots of good info, and with the "photography math" behind it to explain the final results that are achieved.

This is definitely good advice to keep in mind when selecting lenses for a photo trip.

I can't think of too many occasions in the past where I could have gotten 3x closer on a shot to be able to take advatage of that 2.8 glass over using my 600mm.
 
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I never knew WHY.....but I never bought into the "I need a 2.8 to shoot in low light" rationale. Mostly because those times of super low light were usually only a fraction of the time I spent shooting. For wildlife I've always used a mid-range zoom and an f4 500 or 600 prime. In low light I shoot wide open and work the shutter speed down as far as I can......ISO floats. In post processing if the ISO is so high it kills the image, I learn from it and then trash the image.

Thanks for explaining the WHY !!!!
 
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Great info Steve and timely for me. I'm heading to Kenya soon and was considering renting a 300 2.8 with 1.4tc instead of using my Sigma 500 5.6, but assuming the same distance am I correct that there's less than one stop difference in noise and depth of field?

Thanks for all you do!
Bob
 
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Bobg657 said:
Great info Steve and timely for me. I'm heading to Kenya soon and was considering renting a 300 2.8 with 1.4tc instead of using my Sigma 500 5.6, but assuming the same distance am I correct that there's less than one stop difference in noise and depth of field?

Thanks for all you do!
Bob
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Yeah, it's like a third of a stop or so for comparative output ISO and less than a stop of DoF for sure.

However...

There are going to be times when a 300 2.8 is perfect and you'll enjoy all those 2.8 benefits - same applies when you have the TC on it. You could also add a 2X TC to the mix and have 600 F/5.6.
 
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Steve said:
I've had a few comments about AF. I know with Sony and Nikon mirrorless, they don't seem to care all that much about maximum apertures for AF -accuracy is surprisingly good, even with slower glass. As for speed, it really depends on the the lenses you're comparing. A 600PF is a pretty fast-focuser, but the 180-600, not so much.
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That's true and unlike most DSLR's which had f/8 limitations (actually there were preferential focusing abilities for faster lenses with added use of cross sensors), the MILC's don't. Nonetheless, it is an interesting question whether faster lenses, if they take advantage of the Canon like autofocus algorithm, focus better. Again, when I owned Canon gear, I found my 500 f/4 and 600 f/4 to focus more consistently on my R3/R5 than the 100-500 f/7.1. It wasn't that the later lens was a slouch, quite the contrary, but the primes af'ed more consistently and accurately. Unfortunately, we are unable to test a Nikon lens on a Canon camera though it would be interesting to see if there would be a difference between say the 600 f/4 and 600 f/6.3. I guess this is largely a futile exercise because the MILC's focus so well period.
 
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I experienced this empirically when I started my progression into longer lenses. Steve's analysis explains in detail why I was seeing what I was seeking and gives it greater scientific clarity.

I started with the 70-200, added the 400mm f4.5 and later the 600 pf and 800 pf.

I realized the shorter lens could gain a little if you were close to its maximum but when you get to 400 the native 400 does better.

Similarly when I used the 400 I could get good images in the 500-600 ranges but I was not able to be effective for tonger stuff.

In the end the key is to keep the field work easy and simple. Generally when shooting with two bodies I can't easily handle more than two lenses at the same time. So I find combinations that work together for a particular shoot. I find the 400mm works well with the 800 because I can affectively cover the range in between with the 400. While I might do better than the 400 at 600 if I used the 600 pf the difference is not significant enough and the 400 gives me greater range.

Similarly if things were closer and I did not need the 800 then the combination of the 70-200 and 400mm works better for that session.

In the end I chose to let the 600 go because it had too narrow a range of effectiveness when I already had the 800mm.
 
I enjoyed the video. Well done. It's one I plan to rewatch to make sure I got the math part. We've been discussing in other threads the impact of cropping on depth of field and this adds another twist to that with the focal lengths being different. So many moving parts to it.
 
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Very good video. It backs up my thoughts on noise and background. I shoot a great deal of sports and I have the 24-70 f2.8 S and the 70-200 f2.8 S that I use for basketball. 24-70 mostly for near end from the baseline and 70-200 for far end from baseline. I shoot wide open most of the time and need a shutter speed of 1/800th of a second or faster which puts me any where from 3200 to 6400 ISO. Many times I will go to DX mode to fill the frame better and that will take my ISO higher.

So in this instance I am wondering how shooting in DX mode versus cropping impacts the image as related to the video? I have often times shot with my 300 pf f4 lens and the output seems equal. However, the AF speed on the 70-200 seems faster.
 
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Chappy said:
Very good video. It backs up my thoughts on noise and background. I shoot a great deal of sports and I have the 24-70 f2.8 S and the 70-200 f2.8 S that I use for basketball. 24-70 mostly for near end from the baseline and 70-200 for far end from baseline. I shoot wide open most of the time and need a shutter speed of 1/800th of a second or faster which puts me any where from 3200 to 6400 ISO. Many times I will go to DX mode to fill the frame better and that will take my ISO higher.

So in this instance I am wondering how shooting in DX mode versus cropping impacts the image as related to the video? I have often times shot with my 300 pf f4 lens and the output seems equal. However, the AF speed on the 70-200 seems faster.
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Thanks!

A DX crop is the same if it's with the crop tool or in-camera. So, same impacts :)
 
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Thanks for the video Steve. I have Sigma 70-200 and Sigma 120-300 2.8 lenses. I also have Canon 70-200 f4 and Canon 100-400 Mk II. All of them take Sigma 1.4 and 2 X converters. Unless I venture into rain forrest or dense local forrest situations I use the Canon lenses. Maybe if my eyesight was better and I could afford it I would use primes. Then again who would be able to tell the difference? As for AF I am too slow myself for any differences to be of any concern.
 
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