Alpha 550 review is now on line

[David Kilpatrick]

When I say focus accuracy, I mean accuracy and not low light sensitivity or speed. The A550 has much the same type of AF module as the A100,200,300,350 etc. I don't think it is any faster than the A200 generation (which speeded up the motor relative to the A100) or any more sensitive, and if anything it hunts more with very dark or difficult subjects.

However, that is a result of greater accuracy. Sony long ago asked whether people wanted speed (i.e. rapid lock on - even if not precise) or accuracy. The Alpha 700 is very fast but frankly not all that accurate - it confirms focus far too readily. The A550 is more picky and so far has given very accurate focus, but not always as easily. I have had to try a few times with some subjects I would expect the A350 to have locked on faster.

I guess it is just a further fine-tuning of AF algorithms - possibly optimised for SAM lenses though I did most of my tests with the CZ 16-80mm. I have also done a shoot using the 70-300mm SSM on the A550 and find it surprisingly accurate in agreeing, precisely, with what I was intending to focus on.

So - no claims for improved low light, or lack of hunting, or AF speed in terms of the motor fitted (the camera's overall response is faster - the shutter for example just seems to respond quicker, including first pressure). The main improvement is the final result in terms of accurate focus once confirmed.

David

[bakubo]

However, that is a result of greater accuracy. Sony long ago asked whether people wanted speed (i.e. rapid lock on - even if not precise) or accuracy. The Alpha 700 is very fast but frankly not all that accurate - it confirms focus far too readily. The A550 is more picky and so far has given very accurate focus, but not always as easily. I have had to try a few times with some subjects I would expect the A350 to have locked on faster.

Yes, I remember the survey from a few years ago where Sony (or maybe it was KM) asked about which was preferable, speed or accuracy. I answered accuracy. Of course, we all want both! What are your thoughts about the A700 slow and fast AF settings? I had assumed that the slow was more accurate, maybe the phase detection AF would tell the camera how many screw turns and then rather than be done (like maybe fast does), it would then check again, and adjust. Purely an assumption. I generally kept mine on slow, but there was a recent thread on dpreview about this and no one, including me, has ever really been able to see that slow is more accurate or that it is really any slower. What do you say?

[David Kilpatrick]

Slow is more accurate with certain lenses, I believe, and more compatible with Minolta AF HS lenses in particular. I don't think you would ever see a benefit with a Tamron based lens - even the Sony revisions are slow on the fast setting. Also, I have never actually checked to see if this setting alters SSM behaviour. If it does, then using Slow AF with a teleconverter on an SSM lens might solve the overshoot problem (SSM lenses used with a teleconverter focus too fast the system to acquire a reading). Will have to look at this.

David

[Greg Beetham]

Just a little side note: The focus motor is not like an ordinary electric motor that has to spool up and spool down, it's a stepper motor that has fine sequence magnetic locksteps (very high torque), the number of steps it takes to do a revolution is a known quantity, so the AF module calculates how many steps it needs to actuate on the motor to achieve focus in the lens based on it's current focus position and the focus position it needs to move it to.
Greg

[bakubo]

Although I have a few Minolta lenses about the only thing I use on the A700 is the Sony versions of the 18-250mm and 11-18mm so I can't speak to how the slow/fast setting works on other lenses. It would be good to know though.

[alexramos7]

Would a on-lens micro-motor be more accuracy and faster than on-camera screw-motor for contrast AF?

I think Sony could be changing its lenses for a future contrast AF LV system.
The micro-motor seems precise with fine and short movements than screw-motor and these would be useful for contrast AF.

[David Kilpatrick]

I think it's essential for contrast detection AF and that is the main reasin they have taken this route. SSM, not SAM, is needed for video - it's vital to keep operating sounds to a minimum volume level, and SAM is louder than SSM.

David

[alexramos7]

I think it's essential for contrast detection AF and that is the main reasin they have taken this route. SSM, not SAM, is needed for video - it's vital to keep operating sounds to a minimum volume level, and SAM is louder than SSM.

David

Surely we can hear louder both motor system (SAM and screw-motor), but an off-camera motor like SAM maybe is less noisy for video than an on-camera motor.

Sony must be changing soon the AF driver of many lenses to SAM and we could be seeing new 18-250mm, CZ 16-80mm and SWA zoom SAM

[alphaPDX]

Yet another example of how implementing video is diverting resources from still-photo shooting. It's sad, but "everyone" is doing this so no real way to prevail on this one.

Maybe for us lo-tech folks Sony should bring out a DNG-only, MD mount camera - hopefully with TTL metering Plan 'B' is to make the firmware open-source for their early models.. wouldn't that be cool?

sometimes even I can't tell when I'm kidding..

[bakubo]

I didn't see a post about this already, but David has a new article up titled Alpha 550: sky noise, exposure and Auto ISO:

http://www.photoclubalpha.com/2009/11/2 ... -auto-iso/

[agorabasta]

David's writeup on sky noise and other issues deals with three separate matters, actually.

1. A hard fact. A550 could expose its sensor 1-2 stops more. And up to 2 bits of already limited 12bit raw are simply unused.
2. A conjecture. The A550 cameras may be doing strange tricks juggling analog and digital gain factors in their processing.
3. A conjecture. The A550 may outright incorrectly report the equivalent ISO when set at auto-ISO.

[bfitzgerald]

Lots of questions, not many answers!

Not sure I see the sky noise issue as a serious one, but hey I don't do stock photography.
Maybe the cameras underexpose, certainly the last batch did..and by some margin (at times)

[Greg Beetham]

You can get some noise in the sky with an A100, on occasion, (I know, I own one), as long as it's fine and reasonably unobstusive, not a contrasty looking grain I don't mind all that much, if you look at the real sky it's got a zillion fine light coloured specks in it anyway, so a fine specked sky in an image, (visible at 100%) looks pretty natural to my eye.
What looks really odd is a sky that has a painted look, like a blue plastic sheet that's faded at the bottom, THAT looks odd to me.

The other thing I don't really get is this obsession with high ISO, I realize there are some people who want low light performance and that's fine, so why not bring out a low light model, (the A550 looks like it's heading in that direction anyway) preferably with Video in it as well, (therby killing two birds with one stone) that's aimed at low light sports shooters, then the majority won't have to suffer the compromises.
We also want a normal model, (all who agree say eye), that starts out at ISO25 for the rest of us....who prefer to shoot reasonably well lit subjects, daylight or flash...whatever.
Greg

[alphaomega]

I basically agree with Greg Beetham that Sony should plan to have two strands of cameras. One for low ISO high quality starting at ISO100 and one for higher ISO capability but acceptable low ISO performance perhaps starting at ISO200.
To return specifically to the A550, I fancied the camera until David K. and others got into the nitty gritty of what this DSLR can and cannot do. At present I will keep my wallet in my pocket, but if Sony issued a firmware upgrade resolving the intermittent quality issues with low ISO images and added intermediate ISO settings as well as Program shift I guess I would buy a copy. I cannot see why these changes could not be made through firmware updates. MLU and DOF are issues that cannot now be resolved on this model.
I was amazed at David K's contention

Experienced Alpha 900 users set ISO 320 manually because the sensor is at its optimum at roughly ISO 160 (DxO tests bear this out). The standard ISO 200 setting can produce more noise than ISO 320 because two different digital stages are used to produce the gain.

I wondered if the same applies to my A700? I often actually use ISO250 or 320 in preference to ISO200 to get that little extra shutter speed and been very satisfied with the results.

[bfitzgerald]

Cannot say I have ever noticed any "blue sky issues" on the 5d or the A200, though I admit I am far more likely to shoot scenics on film now, so I guess I got over grain a long time ago. Well even on that, nothing a bit of multi pass scanning cannot solve!

I don't think it's ideal to have a "2 tier" situation with DSLR's, after all they are meant to be flexible by their very nature. Having to buy 2 to get decent performance both ends would be off putting. I don't think the high ISO thing is "overplayed" or an obsession. Maybe to some, sure I use high ISO, and see it as one of the strong points for digital..and I use high ISO more often than most I imagine. However..do I seek an ISO 12800? Nope that's more than anyone would ever likely need. 3200 is fine, 6400 at a push, I see no need to go higher than this.

I suspect ISO 12800 has a lot more to do with "big sticker on the box" than users really needing it, same for 7fps..headline figure..for impact mostly. I would not be certain that MLU cannot be added via firmware..we don't know for sure, but looking at what's been going on, it's mostly about Sony taking stuff off, not because they cannot do it, but because they don't want to!