Alan Roberts is respected by all who read his findings when he assesses various cameras for the BBC but recently people have begun to question his findings especially with the Sony PMW-F3. I take you back to his conclusion on the Canon XF305 last year when he concluded…
This camera performs well at HD, for such a small- image format. Resolution is very well maintained and is refreshingly alias-free. Detail controls work well, and the factory settings are good. Noise levels are typical for 1”/3 sensors, but sensitivity is unusually good. Operating the camera at significantly lower gain will reduce the noise level without sacrificing significant sensitivity.
The integral lens has a maximum aperture of F/1.6, unusually large for a small camera, and there was mo perceptible loss of resolution through iris diffraction until the lens was stopped down to F/8, at which point significant resolution was being lost. Again, this is unusual for such a small image size. Thus, the camera has a useful aperture range from F/1.6 to about F/6.8. This, together with the 3-stage neutral density filters (each providing a further 2-stops of control), means that the camera has a much better exposure control range than is normal in a small camera.
I don’t doubt the conclusion and for Mr Roberts it’s a glowing report on the Canon XF305 but now I will show you his conclusion on the Panasonic AF101…
This camera does not perform particularly well at HD. Clean resolution is limited to about 1210×680 by the presence of high-amplitude spatial aliasing. This is a little disappointing from a camera with a large-format sensor, and indicates that optical low-pass filtering is either absent or inadequate, and that the scaling from the resolution of the sensor down to 1920×1080 has not been done in the best way.
Noise levels are rather high, even though the pixel size is that of a conventional 3 sensor 1⁄2” camera. Sensitivity is also similar to that of a 1⁄2” camera.
If this camera is to be used for HDTV shooting, then it should be clearly understood that it’s only advantage over smaller-format cameras is the smaller depth of field. However, to achieve a smaller depth of field in this camera, relative to, say, a 1⁄2” camera, then the lens must be opened by at least 1.5 stops; using an F/2.8 lens on this camera, wide open, will give the same depth of field as on a 1⁄2” camera with a lens opened to F/1.6. This camera will not necessarily always deliver short depth of field, large aperture lenses must be used to achieve that.
This conclusion is far from satisfactory in my opinion as the camera performs fantastic in HD and there is no noise in the picture even at 9dBs, did Mr Roberts tweak the camera as we all know out of the box this camera needs 2 settings changed to remarkably reduce the noise. The BBC have conditionally approved this camera for HD production.
The last assessment is the most controversial I have had a play with the Sony F3 and it excels in low light and has the cleanest picture I have seen in a long time, surprisingly and this is where I take issue with Mr Roberts we don’t get a conclusion so we are not savvy to Mr Roberts final thoughts on the F3. Alister Chapman who in my opinion is far better versed to write about the Sony F3 is also puzzled with Alan Roberts comments and lack of conclusion…
Alister “In the report Alan observes the aliasing that I have seen from the camera, in particular the high frequency moire, so no surprise there. But he also measures the noise at -48.5db. Now I don’t have the ability to measure noise as Alan does and I normally respect his results, but this noise figure does not make sense, nor does his comment that the camera has similar sensitivity to most 3 chip cameras. To my eyes, the F3 is more sensitive than any 3 chip camera I’ve used and it’s a lot less noisy. The implication of the test is that the F3 is noisier than the PMW-350. Well that’s not what my eyes tell me. Take a look at the noise graph Alan has prepared. The hump in the noise figure curves at 0db also appears to be dismissed as insignificant, yet it means a greater than 4db difference between what the curve implies the noise figure should be and the measured noise figure. It really doesn’t seem to fit and is very strange. Video amplifiers and processing are normally pretty linear with gain giving a consistent increase/decrease in noise that follows the gain curve. If you read off the noise figures from the graph, the F3 appears to have less noise at +6db gain (-49.5db) than at 0db (-48.5db). So id we are to believe Alan’s test then we should be using +6db gain or -3db gain (-53.5db) but not 0db, sorry but that just does not add up and to dismiss the 0db noise bump as “not significant” is something I don’t really understand as too me it is significant. Either there is something very strange going on with the F3 at 0db, or there is something up with the test. I suspect the later, perhaps the individual camera had some odd settings, as my F3 is quieter (visually) at 0db than +6db. I would need to check it out on a scope back at home to verify this.
There are also assumptions made about the pixel size and sensor pixel count that are quite wrong. Alan suggests the sensor to be a 12 Mega Pixel sensor, this suggestion is based on Alan’s opinion that the F3 has similar sensitivity to a 2/3″ 3 chip camera, so therefore the pixel size must be similar and the bigger sensor means that it must have 12 MP, yet Sony have published that it is 3.3 mega Pixels (same sensor as FS100). 3.3MP equates to roughly 2422 x 1362 pixels, for a bayer sensor this is a little under the optimum for 1920 x1080 (IMHO) and may explain the aliasing as Sony are probably trying to squeeze every last bit of resolution out of the sensor.
Alans assessment of his zone plate results also concludes that the R, G and B resolutions are the same and that the sensor resolution must be much higher than 2200 x 1240. Well I would not call 2422 x 1362 “much” higher and if this is a bayer sensor (neither admitted or denied by Sony) then the G resolution should be higher than the R and B. So could this be a case of conventional conclusions about an unconventional sensor, or have Sony managed to completely wrong foot Mr Roberts?
An interesting finding was that detail at zero, frequency at +99 and aperture at +20 gives the least aliasing. This is quite different from my own findings and will need further exploration.
The F3 assessment is also missing the usual customary round up from Alan where he suggests whether the camera is suitable for HD broadcast or not. I’m really glad I got my F3 before reading the report as I have seen with my own eyes the beautiful clean images the F3 produces. I strongly recommend anyone considering the F3, but put off buy this report to take a look at the pictures for themselves before making any decisions.” www.xdcam-user.com
HDW : Personally I think the BBC should be taking their camera advice from at least two independent sources and not from insiders or in Mr Roberts case a retired employee of the BBC. As an independent producer and someone who reviews camcorders I firmly believe to get bogged down in techno speak can be detrimental to the camera and more often than not can confuse a lot of people who are only interested in one thing…does it produce a good clean picture.
I am very much with Alister on this one the F3 is the cleanest, best picture at this price point you will see and I can assure you beats all the older APPROVED HD camcorders by a mile, the other reason for my request for two independent assessors is the need for comparison, sometimes the camera you receive is not up to scratch so two conflicting reports would highlight this.
I think the BBC need to take a good hard look at themselves in one hand they are allowing the use of Canon 5DMk11 DSLR for “Extreme SDoF work” and using Sony EX-3s without a Nanoflash for full HD programming yet they “conditionally approve” the Panasonic AF101 and talk about the Sony F3 as if it was no better than a 2/3″ P2 camcorder…nonsense.
UPDATE : Alan Roberts reply’s as a moderator on DV Doctor forum after taking flack about his AF101 report…
“I apologise for my outburst last week. It was unduly vitriolic.
Here’s the background.
For 11 years, I have been here, posting answers and solutions to problems, providing the science and psychophysics behind the science. Thousands of times. Many times, I have given the same explanation, largely because people seem unaware of the rather splendid search facilities here. Never mind.
Some of the questions have been interesting, some banal, needing only common sense for an answer. I’ve been happy answering them though, because it’s always a pleasure seeing the dawning of understanding. Other forums seem not to work this way, being largely platforms for vested interests to shout at each other. That’s why I stay here.
But, in the last couple of years or so, things have been changing. Now, the questions are more along the lines of ‘you’ve got it wrong because…’, and some of the posters and postings are clearly biased for/against individual cameras and/or manufacturers.
I have always been totally neutral on such things, I measure and report. My neutrality has often been questioned; I’ve been accused of being in the pay of both Sony and Panasonic, so I suppose my neutrality is still observable. It will always remain so.
The recent furore over the AF101 has been the last straw. I got so angry with the continued blether about it that the fuse finally blew. So, here’s my statement for the future:
I WILL NO LONGER READ, OR REPLY TO, ANY COMMENTS ON ANY CAMERA, FOR ANY REASON.
If you want to talk rubbish about cameras, get on with it, I won’t comment either way.”
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