Aliasing and moire

[Alister Chapman]

I've taken a look at the MTF curves for the F3 and they are quite revealing showing that an OLPF is in use which is giving an MTF50 of around 800 LW/PH V and 950 LW/PH H. This is not quite as high as an EX1 but are quite reasonable figures. This suggests that the aliasing is largely limited to the chroma sampling of the sensor.

Tests performed with a Tokina ATX-Pro 28-70mm lens at 25P

Feeling a bit better about my F3 now :-)

[Jim Michael]

So is the artifact centered at the frequency of the resolution limit? What conclusions can be drawn regarding the symmetry (or x-y location) of the artifacts?

Thanks for posting those tests. It's good to know where the physical limits reside.

[Alister Chapman]

The chroma moire appears to occur at frequencies less than the luma extinction point, which does suggest it to be a bayer type artefact (not enough B/R pixels compared to G). It's pretty symmetrical.

I've tried to induce moire in further shots and it only appears in shots with the dark red brickwork of the original instance. Other shades of brickwork don't appear to trigger it. So.... perhaps not the problem I thought it might be at first.

[Alister Chapman]

A further update. Sony have requested the original clips with the moire, and I have provided them with these. I have not been able to reproduce the effect with any other brickwork, roof tiles or other repeating patterns other than charts. There seems to be something about the particularly dark shade of bricks with very bright mortar (cement) that the F3 doesn't like. I am very pleased with the images I'm getting from my F3 having just finished my first paying job with it. It was nothing exciting, just a corporate shoot, but the shallow DoF and reduced amount of lighting required has resulted in some really nice footage of an otherwise dull subject.

[Jim Arthurs]

Perhaps the F3 isn't as sharp and alias free as my 3 year old EX1, but it seems to fair better than the high end Sony F35, as tested here; (pages 4 and 5)

http://www.alfonsoparra.com/php/baul/F35TestEV.pdf

It would also be interesting to compare the F3 to an Alexa, which, suggested by Graeme Nattress, over-samples 1.5X compared to the F3 at 1.27X (based on the Sony stated 3.36Megapixel sensor value).

Is there any selling "new generation" camera as tack sharp as the EX1/EX3 in the prosumer market? Suddenly I'm not sure I'd want to sell my EX1... :)

Regards,

Jim Arthurs

[Andy Wilkinson]

Regarding sharpness, amazingly there is something close to the EX3 - my new Panasonic TM900 when it's in 1080p50 mode (28Mbps AVCHD). Several times now I've got to pinch myself that a camera that cost about 1/8th of the cost of my EX3 produces almost as sharp a result when viewed on my 1920x1080p monitors. Sure it's more high end consumer than prosumer but we all know those boundaries are increasingly blurred.

Just maybe, with NAB not too far away, if Panasonic announce an "upgrade" of some of their "lower end Pro, 3 chip cams" with 1080p50/60 capability at this bit rate your question might get answered (pure speculation on my part I will add). Anyway, I digress, let this thread return to the F3!

[Steve Kalle]

Originally Posted by Jim Arthurs

Perhaps the F3 isn't as sharp and alias free as my 3 year old EX1, but it seems to fair better than the high end Sony F35, as tested here; (pages 4 and 5)

http://www.alfonsoparra.com/php/baul/F35TestEV.pdf

It would also be interesting to compare the F3 to an Alexa, which, suggested by Graeme Nattress, over-samples 1.5X compared to the F3 at 1.27X (based on the Sony stated 3.36Megapixel sensor value).

Is there any selling "new generation" camera as tack sharp as the EX1/EX3 in the prosumer market? Suddenly I'm not sure I'd want to sell my EX1... :)

I'll take the very LOW noise of the F3 over the incredibly high noise of my EX3 & EX1.

[Jim Arthurs]

Originally Posted by Steve Kalle

I'll take the very LOW noise of the F3 over the incredibly high noise of my EX3 & EX1.

I've never characterized the EX1/EX3 as "incredibly high noise", but a lower noise floor would be a fair trade off over some slight aliasing, especially for the sort of green and blue screen work I do. Life is about compromises.

If the virtually silent at low ASA F3 noise floor can help retain shadow detail without noise buzzing during the process of pulling a green screen matte, I'd be a happy camper. I will test as soon as able.

Regards,

Jim Arthurs

[Alister Chapman]

The noise performance of the F3 is nothing short of incredible. I can flick in +18db of gain on the F3 and there is barely any more noise than my 0db EX1R.

As Jim says, cameras are often about trade off's... resolution for aliasing, noise for sensitivity etc.

To some extent that's why I've back tracked a little over the aliasing issue. Yes, it's there, yes, I've seen moire in shots where I don't think I should be seeing it. But every other aspect of the image is so outstanding that I am still looking for a second F3 for my 3D productions as soon as my budget will allow.

If I had a feature request for Sony right now it would be to allow the use of +24 and +36 db gain on the F3. I think the F3 would be the first camera where these ultra high gain levels might actually be useable.

Regarding the TM900... is it sharp because it's aliasing or is it sharp because it has true high resolution? I'd like to see a zone plate from that before passing judgement. The Canon DSLR's appear to be sharp because every hard edge is aliased. Actual resolution though is way down compared to most HD video cameras.