RX10iv Focusing (Good News)

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Horacecoker Senior Member • Posts: 1,947
RX10iv Focusing (Good News)

Right here goes folks, it's hold my hand up time.

First thing is my statement that the focusing on RX10iv will be exactly the sames as the focusing on the RX10iii in AF-S mode. According to Imaging Resource performance figures that statement is false. And I believe their figures because out in the real world where there's plenty of contrast, it is blindingly fast! I only wish I hadn't part-exchanged my iii then perhaps I could appreciate the difference.

Thank you to the poster who posted the link to the performance figures on Imaging Resource. When I first looked at them I couldn't make head nor tail of um but having plenty of time today I gave them another squint and finally sussed them out. The text explaining the figures we are interested in isn't the best that's why I failed to see the significance of them on a first glance.

Oh, and this is going to be complicated but keep with me.

These are the important figures from the RX10iii first.


As can be seen by the title 'Shutter Response (Lag Time)' it's not very clear that what they are really talking about is focus acquisition time. I only realised this by looking further down the chart and finding this

RX10iii Prefocused

It makes sense now, you simply take the 0,024 off the first two figures and you get the actual time it took the camera to focus from scratch.

If you are with me so far, let's compare those figures to the RX10iv


RX10iv Prefocused

As can be seen it's a lot faster but how much?

I think averaging out the wide angle and tele times then deducting the prefocused time will keep it simple (he says)

RX10iii 0.196 + 0.218 / 2 = 0.207 - 0.024 = 0.183

RX10iv 0.034 + 0.036 / 2 = 0,035 - 0.009 = 0.026

0.183 / 0,026 = 7.038

So according to those figures the RX10iv focuses 7 times faster than the RX10iii.

At this point I had two problems to overcome! Because Imaging Resource don't say anything to the contrary I've got to assume that the tests for both cameras were carried out on AF-S. If I assume that, does that mean to get this whopping speed increase, is the RX10iv actually using PDAF in AF-S when I've been saying all along it doesn't? After about 20 minutes of deep thought, It occurred to me that there could be another explanation. Could it be possible that the newly developed Bionz X processor (borrowed from the a9) is responsible. A clue for me to come to this assumption is that the prefocused time of the RX10iv had also decreased quite dramatically and that can't have anything to do with PDAF.

After another bout of deep thought I had a brainwave. Compare the RX100iv to the RX100v. As I'm sure you all know the RX100v as the same processor as the RX100iv. So by my reckoning if the RX100v focuses 7 times faster than the RX100iv it can only be due to PDAF but if the times are similar that means it's the new processor in the RX10iv that is responsible for the much faster times of the RX10iv over the iii.

If anybody is still with me I warned you it was complicated.

Anyway without screen printing all the charts for the RX100 cameras here are the results

RX100iv 0.156 + 0.228 / 2 = 0.192 - 0.010 = 0.182

RX100v 0.186 + 0.210 / 2 = 0.198 - 0,009 = 0.189

So no speed increase there, surprisingly the R100v is ever so slightly slower at focusing than the RX100iv so obvious PDAF has no bearing on any of these tests. It also proves that all cameras were set to AF-S and the massive increase in speed for the RX10iv on AF-S is due to the processor borrowed from the A9.

This is all good news but it still leaves my firm belief that PDAF does not operate in AF-S intact.

Now, the other thing I got wrong was stating that the RX10iv only uses PDAF in wide area when set to AF-A. I found out today outside in the real world that it also works in Expand Flexible Spot. The fact that it's more subtle and the little green boxes don't dance, fooled me previously.

Both of today's findings paint a very different picture on the advancement of the RX10iv over the iii. The fact that it focuses 7 times faster on AF-S without even using PDAF is a revelation. Also now the AF-A position on the switch is good, very very, good! Most folk can leave it on that and never touch it. The camera seems to be very clever and can work out when to bring AF-C into play thus applying PDAF.

Obviously, I apologise to all concerned if my previous ramblings have caused any misgivings, especially to our American friends who have the camera on order. Tbcass was right, I should have kept my trap shut (he didn't actually use those words) till I'd thoroughly tested the camera. I blame that out of focus branch in my back garden for all this unnecessary upset!

To anybody out there who is thinking of buying or upgrading to the RX10iv, do so with my blessing, you won't be disappointed.


 Horacecoker's gear list:Horacecoker's gear list
Sony RX100 III Sony RX10 IV Sony Alpha a7R III Sony FE 55mm F1.8 Sony FE 28mm F2
Sony a9 Sony RX100
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