AF speed

[Stan4444]

I am considering a 70-200mm for my A7R4. If cost were no object this is a no brainer...the Sony 70-200mm GMII. However price and size/weight matter to me. Unfortunately fast autofcous also matters. The reviews I have read indicate that the Sony autofocus significantly outperforms the Tamron 70-180mm (in terms of % keepers) for the old running at the camera tests. Unfortunately for me, this comparison is always done on A1 camera which makes a lot of sense as it can clearly compare the lens focus speeds with its 120 focus calculations per sec. My question is; with the much slower updating A7R4, at 20 per sec, would I still see this dramatic difference in keepers. That is, does the camera focus update speed now become the gating item when using an A7R4. Has anyone done a comparison using an A7R4?

 

[MILC man]

we don't have any idea what you are shooting, so there is no way to predict keeper rate differences.

are you in a position to rent first?

 

[Stan4444]

For purposes of this question, I'll stay with a person jogging toward the camera as what I am shooting. The question however is really a more general question. I believe the reviews show that the Tamron lens doesn't move as fast as the Sony. The question is: does the slow lens movement actually matter if the focus calculation updates arrives 6 times slower with the A7R4. (20 vs 120 per sec). Am I going to get a keeper rate that is now dominated by the camera focus update rate rather than the lens movement speed ?

 

[TomV1]

Dustin Abbott does a nice review of the lens here:

https://dustinabbott.net/2020/04/tamron-70-180mm-f2-8-vxd-a056-review/

 

[River Photography]

For purposes of this question, I'll stay with a person jogging toward the camera as what I am shooting. The question however is really a more general question. I believe the reviews show that the Tamron lens doesn't move as fast as the Sony. The question is: does the slow lens movement actually matter if the focus calculation updates arrives 6 times slower with the A7R4. (20 vs 120 per sec). Am I going to get a keeper rate that is now dominated by the camera focus update rate rather than the lens movement speed ?

my dog running towards my a74 and the tamron 70 180 is a walk in the park.

Rp

 

[Michael Fritzen]

Hi,

I think you've answered your question in part yourself. There are limits certainly on both ends: when the cam's AF speed is held back by the speed the lens could execute the adjustment commands, no gain of the ultra fast cam. Same applies to the inverse situation, when the cam's AF is the bottle neck.

A secondary question which is linked to your demands and needs is how many shots in a burst of an upcoming jogger do you want in perfect focus? Generally speaking the approach of shooting in short bursts is usually rising the odds to get at least one shot in focus (and ideally in a nice looking moment of the cycle of the move). So it's also about having shots to select from.

Still generally speaking, photographing a jogger or an upcoming jogger is not among the most challenging situations for modern gear. The right setup of the cam's AF AND of the lens, depending on the subject, its speed of approach, but also the vantage point (cluttered BG or clean?), elements or other people in the frame which could draw the focus tracking...

 

[Stan4444]

Michael, Thanks, your first paragraph articulated the issue much more clearly than I did and the last 2 paragraphs pointed out some important considerations. The question however is still not answered.... does the bottleneck move to camera from the lens when the camera goes from A1 to A7R4? If it does then spending a lot of money on a lens in anticipation of better AF is not a good idea. Or put another way, do you need an A1 or A9 to see the advantage in AF of the faster, more expensive lens. And yes, I have ignored an important question.... is the A7R4 / Tamron combo good enough for my applications.

 

[Michael Fritzen]

Hi,

well, I got a beer, prepared some popcorn and now I'm waiting relaxed sitting in an armchair for someone coming around the corner with the definte answer to this question.

But back to more serious discussion I think it will be hard to point out where exactly the limitations will happen on either camera or lens side. Cam's AF performance may benefit from the "latest and best" on the lens side - or better, the combo's performance may benefit. At least from theory side and from some type of (scientific) metering. However if the photographer benefits, well this is another story. Probably though, cam and lens of the same brand should "communicate better" - at least the marketing departments want us to believe. OTOH suboptimal (or bad) communication with 3rd party lenses were well known issues in the past but I'm not aware of issues in current lens generation.

And then we come to the question if a "bottle neck" existing in theory but apllying perhaps to extreme situations and demands only, matter to "real photography" in the real world - or are they just another attempt to point out to us consumers "important differentiation factors" origined by smart brains in the marketing department.

--
Cheers,
Michael Fritzen

 

[QuietOC]

I've used the 70-180 VXD on my A7RIV. The VXD motor is fast. It did fine for motorsports. But the slower 70-300 RXD does well for me for that too.

I sold the 70-180 as I generally need more focal length.