A55/NEX-5 video AF comparison w/ SAM/SSM lenses

Thanks for the comparison albnok.

Did you notice that the AF (contrast detect) on NEX is significantly slower in video mode? It is because in video mode it only does wide area focusing, it does not obey the selected focal point. In still mode it is quite a bit faster because it only tries in the selected area, and does not try to evaluate the focus location.

Is it the same with video mode on A55?

Cheers,

N

Edited by Micholand - 20 October 2010 at 18:12

Exhibit #5 of 5: Sony SLT-A55 with ECM-CG50 shotgun mike comparison
http://www.youtube.com/watch?v=dx7TZf_kA6M

Compared the Sony SLT-A55 with Minolta 24-50mm F4 (a screw-drive lens, sure to make a sound when focusing) and the ECM-CG50 shotgun mike in three situations;

1) using on-board mike
2) using ECM-CG50 shotgun mike
3) using ECM-CG50 shotgun mike with low cut filter on


The holder itself has rubber to form an isolation mount - this prevents vibrations from pressing the camera buttons, from reaching the mike. The iISO to ISO coldshoe adapter (it cannot work for flashes) is included in the package.

VERDICT?

We can observe certain things - for one, the average video length with the NEX-5/LA-EA1 combo with SAM lenses was 30 seconds (minus the introduction.)

The average video length with the NEX-5/LA-EA1 combo with SSM lenses was 20 seconds (minus the introduction.)

Meanwhile, the A55 videos clocked in at an average of 4 seconds (minus the introduction.)

These were all for 3 cycles, focusing close, then further, then close again. I had to adjust my shooting location to accomodate lenses that could not focus so close, like the telephoto lenses.

Contrast Detect AF, especially on the NEX-5/LA-EA1 with Sony 30mm F2.8 DT SAM Macro, was particularly loud! This was probably because the NEX-5/LA-EA1 decided to go all the way to minimum focus distance (MFD), then to infinity, then back, then to the focus point.

The camera tells the lens motor to go at full speed from MFD to infinity which causes that loud sound.

Compare this to Phase Detect AF, where the camera just tells the lens motor to go to the focus point (quite simply, because it only needs to look once to get it in approximate location.)

Contrast Detect AF also seems to be a lot faster with shorter focal lengths. The Sony Carl Zeiss Vario-Sonnar T* 24-70mm F2.8 ZA SSM in particular proved to be the fastest in both contrast detect and phase detect situations.

Contrast Detect AF also does much, much better with brighter lenses.

The NEX-3/NEX-5 has another handicap - you cannot set the AF point to be fixed on the center; it will always go into Wide Area AF whenever it records video. The A33/A55 lets you change AF points even when recording video!

My next mission - to find the Sony Alpha 580!

So I tried the Sony Alpha DSLR-A580 - the less famous cousin of the Sony Alpha SLT-A55V. Its sibling, the A560, was delayed to 2011. It has a real nice grip to it, with a nice embossed mode dial.


The firmware is interestingly, Version 1.11.

In the menu you can choose Contrast Detect AF or Phase Detect AF to be used in Focus Check Live View.

In the A550, it was called Manual Focus Check Live View. Now that the camera can focus in main-sensor Live View (which is what Manual Focus Check Live View is, really) it had to change its name.

Phase Detect requires that the mirror drop back down so it can direct light to the Phase Detect AF sensors in the bottom of the camera.

Contrast Detect just uses the main sensor Live View to focus, albeit a lot, lot slower. At least the mirror does not move.

http://www.youtube.com/v/5Of7zv5EXBY

I recorded a video to show this.

Yes, there is no autofocus in video! You cannot manually focus and get a focus confirmation either! (The A55 and its sibling, the A33, show focus confirmation because its phase detect AF sensors are still seeing the view.)

gwbuffalo: That has got me thinking - the VG-10 is numbered such, like the A100, to be the first. They might just have a higher end model coming up without the handicaps of the VG-10.

I am tempted to give my local rep a call and see if he can hook me up with a ECM-CG50 to review and bring to a loud gig to see if it can prevent clipping!

Thanks for the great work albnok

gwbuffalo wrote: But what's really needed to make the NEX series shine for audio/video work is more E-mount lenses! I think that's sure to happen because of the very existence of the VG-10 (and any follow on models).

Interesting thought there.
Could be that the video/still dual existence is also the reason to chose in-lens OSS.

New lenses are coming so let's see what they bring^^

gwbuffalo wrote: I hope you can repeat the tests with an A580, but I have been reading there is no contrast AF during video capture on that model, only manual focus. If that's true, I am sure Sony did that because of the non-proportional (full on) focus motor control on A-mount lenses.

All DSLRs have trouble with the CDAF in video mode.
Of cause you can say Sony rather removes a feature than bad implements it while the others rather bring a feature that is to improve ;o)
But really if you shoot video with CDAF on a DSLR it certainly will jump to infinity as soon as it loses track.
That alone ruins the record actually.

The A580 seems to be a really competitive camera.
Too bad it get almost no press coverage duo to the A33/A55 crush landing...

Edited by Sick - 22 October 2010 at 01:32

Thanks wyip! I've asked him how it does in smaller venues. It appears to be pretty acceptable for big concerts.

gwbuffalo: I wonder if it would be too much to ask for a Sony E 60mm F2.0 Macro, in the style of the Tamron 60mm F2.0 DiII. It would double as a portrait focal length!