Messages

991

EOS Bodies / Re: Why is everyone calling the mk3 sensor the same as mk2?

« on: July 18, 2012, 06:36:51 PM »

I too used to look for reasons to believe that DxOMark was doing honest, but, flawed testing. The more I delved into their site and their data the more I came to believe they are just Nikon Marketing Shills.

As for your comments on the superior noise capabilities of Sony sensors and the D800. The 5D MkIII has more accurate ISO, better SNR 18% scores (screen), better Tonal Range (screen), and equal Color Sensitivity (screen). All of these are components of Dynamic Range, and the D800s Dynamic Range is a straight line just like all the other measurements. Yet, the 5D Mk IIIs Dynamic Range gently levels at around 11 EV (screen), just like every other Canon camera using the CR2 file format.

It is my contention that it is NOT that Canon has not improved the Dynamic Range performance since they implemented the CR2 file format, but, that DxOMark is unable to decode the portion of the CR2 file that contains that additional Dynamic Range information. It is further my contention that the ‘pattern noise / banding’ that began when Canon dSLRs started using the CR2 file format, is actually where that additional data is stored / encrypted.

First off, I do not believe that banding and FPN is restricted to the CR2 format...look at some CRW's and you'll see similar problems in older sensors, just to a lesser degree (which is not surprising, given that older cameras had much larger pixel pitches and QE that is only marginally worse than what Canon offers today.) FPN and banding is not even relegated to Canon...its a problem inherent in most digital sensor designs except Exmor!

The reason Canon levels off at low ISO is because their read noise jumps! At ISO 800+, Canon read noise is about the same as Nikons...3 to 4 electrons worth or so per pixel. At ISO 100, Nikon's, thanks to its Sony Exmor sensors, is STILL around 3 to 4 electrons...but Canon's spikes. At ISO 400, Canon's read ISO on the 5D III is @10 e-, at ISO 200 it is @18 e-, and at ISO 100 it is @33 e-. Even if you factor in the bias offset properly, with 33 electrons worth of read noise, your bias adjustment is going to be very small or zero (so that extra 2048 levels worth that Canon reserves as a bias offset is REQUIRED to raise the black point above the noise floor...and even then, its obviously not enough as electronic noise, including pattern noise forms, still exhibit at ISO 100, 200, and 400.) The reason Canon sensors develop a "shoulder" at the low ISO end of the DR scale is because of that read noise curve.

I'm not a Nikon fanboy, I don't care much for their ergonomics nor their menu system. I do not own any Nikon gear, my entire kit is Canon. I don't care much for DXO, to a certain degree they definitely do pander to Nikon, which isn't surprising as Nikon is one of their major sources of funding. The DR curves, though, are not fake or some scam perpetrated by DXO (although I do believe their Print DR results and anything based on them IS a scam). There are a variety of other, independent sources that produce roughly the same DR curves for Canon sensors as well. Read noise is not a joke, and it is, most definitely, a DR killer at low ISO. Once you start using higher ISO settings, the physical nature of light kicks in and produces noise on a level far beyond what the electronics themselves can produce, which is why pretty much all cameras, regardless of brand, perform about the same at ISO 800+. Its not that Canon has done anything particularly special there...they don't have to to be competitive at high ISO.

Seriously!!! do you honestly believe that almost every single Canon digital camera using the CR2 file format has almost the exact same maximum Dynamic Range (as tested by DxOMark - screen).

Every single Canon camera that DxOMark has tested except the PowerShot G9 and G10 have the same maximum Dynamic Range (screen) of around 11 EV. Canon can produce a 1/1.7” sensor with 11 EV (PowerShot S90 and G11 and above), but, they can’t produce a full frame sensor with more Dynamic Range than that?
That the Canon Digital Rebel (D300) and the Canon 5D Mk III have the same maximum Dynamic Range?
That it’s all related to sensor tech and has nothing to do with the CR2 file format?
So, Canon was able to increase the Dynamic Range of the 1/1.7” sensor used in the G9 and G10, but, they couldn’t increase the Dynamic Range of their APS-C or full frame sensors since 2003?
Give me a break!!

Seriously!!!, all these Canon cameras have basically the same maximum DxOMark Dynamic Range 'measurement' (screen 10.9 EV +/- .1 EV < that's point one).
1000D
10D
1100D
1D Mk II
1D Mk IIN
1D Mk III
1D Mk IV
...

Yeah, it has everything to do with Canon's sensor tech and nothing to do with the CR2 file format. NOT!

So long as Canon does not address their low ISO read noise problems, every single Canon camera that uses sensors manufactured by Canon will have roughly the same low ISO DR problem as well. The problem scales across sensor sizes as well, as the smaller your pixel well is (barring any additional mitigating factors like a backlit design) the lower your SNR, and therefor even if you have a lower read noise, on a relative scale its about the same for every Canon sensor produced in the last 4-5 years. The 7D has lower read noise than the 5D II or III, however it has about the same DR curve. Its a denser sensor though, with a considerably lower pixel saturation point. The ratio of read noise between the 7D and 5D III is 8.6/33.1, or around 0.26. The ratio of pixel saturation point between the 7D and 5D III is 0.29. The read noise to saturation ratio for the 7D is 20178/8.6 or 2346, and for the 5D III is 67531/33.1, or 2040 (which partly explains why it edges out the 5D III DR at ISO 100). Similar ratios all around. Canon designs their sensors in a certain way, and they have not been particularly innovative over the last four years or so when it comes to their sensor design (perhaps too confident in their own superiority?? Now caught off guard by the innovation of their competitors??) The fact that the relative results between these two cameras are roughly the same despite being generations apart and different models is not surprising!

And, frankly, Canon needs a kick in the ass to get their own engine of innovation back into gear so they can claw themselves into the modern era of digital camera design.

992

EOS Bodies / Re: Mark III price dropping

« on: July 18, 2012, 06:09:13 PM »

I just ordered a MK3 body for 3,099 on evil bay. USA retail, non-grey market.

Its really too bad your supporting evil bay by buying something they will get at least a 10% fee out of on the seller side, if not more when you factor in the PayPal fees as well. :\ (I really despise ebay these days...moneygrubbing greedmonsters...meh.)

Oh well, Too bad canon didn't turn out a product that I feel is worth the extra 500$ Retail.

Well, at least Canon would put that extra $500 to GOOD use! More money to fund better R&D, so that the next sensor they release IS as good as an Exmor, maybe? ;P All eBay will do with it is hire more moneygrubbing greedmonsters to figure out how to stick it to their sellers to and even greater degree! Yay...funding ebay greed...fun....

993

EOS Bodies / Re: Mark III price dropping

« on: July 18, 2012, 01:48:21 PM »

I just ordered a MK3 body for 3,099 on evil bay. USA retail, non-grey market.

Its really too bad your supporting evil bay by buying something they will get at least a 10% fee out of on the seller side, if not more when you factor in the PayPal fees as well. :\ (I really despise ebay these days...moneygrubbing greedmonsters...meh.)

994

EOS Bodies / Re: Why is everyone calling the mk3 sensor the same as mk2?

« on: July 18, 2012, 01:44:56 PM »

Because DxOMark rated them basically the same.
If you believe, like I do, that DxOMark either can't fully decode the CR2 file and are probably just Nikon marketing shllls, then you can actually believe your own eyes.
Which according to a post I read today is a dangerous thing.

DXOMark is more than just a Nikon marketing shill. While I am not sure they are properly taking into account Canon's Bias Offset in their tests of Canon sensors (modern bias offsets in Canon DSLR's range from 1024-2048, which would mean their total DR potentially ranges from -1024/-2048 to MaxSaturation, which would affect DR calculations), DXOMark is indeed correct that Canon sensors have higher read noise levels at low ISO. Canon is still in the realm of 20-35 electrons worth of read noise at ISO 100. Sony Exmor sensors have a read noise lower than 4 electrons at ISO 100. That is a significant difference, and a very meaningful difference that ultimately results in the unsightly patterned forms of electronic noise to creep into photos (sometimes right up into the midtones...a travesty!)

The problem with DXOMark is their final results are ultimately based on their "Print DR" tests and a few other test cases wherein they grant "bonus points" if a camera beats certain thresholds in their per-test scores. The use of bonus points completely invalidates the objectivity of a test, regardless of whether bonus points are awarded the same across brands. Bonus points do not reflect actual hardware capabilities...they reflect the subjectivity of the reviewers who design the tests. The D800 is touted, by DXO, as being capable of 14.4 stops of DR, however those results are based on a non-objective test that assumes a very specific approach to downscaling that ignores the physical limitations of hardware and assumes the ability to dither in a manner that *might* improve DR, or the realities of the tools actual photographers use in the real world to process their photos.

The D800 is actually capable of around 13.2 stops of DR at a hardware level (based on the "Screen DR" tests, which ARE objective measurements of the hardware itself, although there may still be "bonus points" awarded at certain thresholds.) Regardless of whether DXO is actually taking Canon's Bias Offset into account correctly or not, 2048 levels are not going to improve Canon's DR results from just under 11 stops to 13.2 stops given how bad their read noise is. Canon sensors do indeed have very high (unacceptably high, IMO) read noise relative to Sony Exmor sensors, and that deficit does indeed have a very real affect on Canon's sensors ability to perform at low ISO. So, while I don't really believe DXOMarks tests and final results are appropriately objective (bonus points are an unwarranted aspect of pure subjectivity that don't belong), I also do not believe it is fair to call them raging Nikon brown-nosers. Its simply that their tests are not as objective as they should be, and allow an undue skew to creep into their results that are making some sensors appear better than they really are, and possibly allow other sensors to appear unduly worse than they really are.

995

EOS Bodies / Re: 7D Firmware officially announced

« on: June 29, 2012, 12:13:09 AM »

I am not excited. It's a long list but most items don't really do much for me - or most other 7D users.

Don't presume you are the supreme exemplar of all 7D users. Personally, as a 7D user, I find many of the new features to be very welcome. They are free, and they give new live to a my camera, rather than requiring that I buy a new 7D II THIS YEAR...something I don't have the funds to do. I believe the majority of 7D users are more like myself than you...welcoming FREE IMPROVEMENTS. The vocality here is a minority.

* Buffer size ... fine. Hardly ever take more than 5-10 shots in fast series anyway. I know, for sports shooters it is different. But I bet, 95%+ of all 7D users are not going to use 23 (25) RAW buffer more often than I do.

A deeper buffer is always a good thing. Its not about the number of continuous unbroken shots...its about how many full-framerate shots you can keep taking, even if they are in short bursts like 3-5 or 7-10 frames, before the camera has to start slowing down. Right now, with my bird photography, even though I usually only take 2-4 shot bursts for perching, wading, or standing birds and up to around 8-10 for BIF, its NOT infrequent that I find the opportunity to take multiple bursts one after the other, before the buffer is empty. A deeper buffer is VERY WELCOME...especially when paired with a higher speed CF card. I already get around 24-25 shots...this firmware update adds 7 more...which would mean I can get around 31-32 now. ABSOLUTELY NOT COMPLAINING ABOUT THAT!!

* Auto-ISO ... upper ISO limit. Good. But still miles away from fully functioning Auto-ISO (as seen in the Nikon D800, D4). This impementation is still a lot inferior to Nikon's D7000

This is also a welcome feature. There are times when I would prefer to shoot at ISO 6400 and expose properly despite the noise, than shoot at ISO 3200 and have to boost in post. Noise is bad either way, however an extra stop is an extra stop, and from a shutter speed standpoint a single stop can be the difference between getting the shot and not. Again, most definitely welcome feature.

As for Nikon's functionality, the only thing the 7D is lacking vs. the D7000 is the minimum shutter speed option. The minimum shutter speed exists in Canon's direct competition to the D800 and D4, the 5D III and 1D X. There are some additional options on those cameras as they have corresponding camera HARDWARE to support them, such. This is just a firmware (software) update to an old camera, its not adding new hardware, so we can't expect additional Auto ISO features that require hardware counterparts. Competitively, Canon is pretty level here, and at least they are offering this enhancement to an existing and increasingly old camera body...FOR FREE.

* faster scrolling in zoomed playback ... fine. No big deal. Why not from the very start?

When your out in the field and you need to chimp quickly, better firmware performance is always a bonus. I like my birds eyes to be sharp, but good shots are always happening around you when birds are flitting about. Spending a lot of time zooming and panning to determine if a shot is a keeper or not is also a valuable thing. Better yet if performance is improved for those short video clips that are necessary to really capture what your subject is doing when a still doesn't do it justice.

Stop complaining. If you want what Nikon has to offer, ditch Canon and move to Nikon. Bitching and moaning about Canon when they DO GIVE YOU FREE S___ ain't going to make them your friend. It won't change the past either. Going forward Canon offers competitive features like in-camera retouching and better bracketing, as well as things like in-camera multiexposure or even things Nikon cameras can't always do...such as continuous shooting at a lower rate once the buffer is full (this is an area where Canon excels, but one where Nikon is hit and miss, miss more often than not). So if you stick with the brand, you won't be disappointed. But I don't think thats going to satisfy you...the only thing that will really satisfy you, based on your comments, is a Nikon camera. SO GO GET ONE ALREADY!

996

EOS Bodies / Re: 7D Firmware officially announced

« on: June 28, 2012, 11:47:22 PM »

* metering linked to active AF-field in Spot metering?

Canon's iFCL color metering always factors in the active AF points. FOCUS, COLOR and LUMINANCE metering. Its weighted, and exactly what weighting it gets depends on your metering mode, but this has been around since the 7D was released (and is available in all other bodies that use iFCL metering, including the 5D III.)

Here are Canon's explanations:

iFCL Metering with 63 zone dual-layer metering sensor that utilizes AF and color information for optimizing exposure and image quality

The EOS 7D features a 63 zone dual-layer sensor designed to complement the 19-point AF system. By taking into account the color and luminosity surrounding chosen AF points, this system delivers high levels of accuracy for better results even in difficult lighting situations. Since the metering sensor has a color measurement function, exposure errors and focus errors caused by different light sources are minimized; the EOS 7D gives stable exposure from shot to shot in situations where light changes, such as in a theater or concert hall. This makes the EOS 7D ideal for scenes with extreme difference in brightness such as brightly lit scenes or backlit scenes; the camera balances exposure of the main subject at the background, and exposures are not overly influenced by bright areas in the shot.

And:

Metering algorithm

To work with the iFCL metering sensor, the EOS 7D also features a specific metering algorithm. The EOS 7D always measures focus with all AF points regardless of the selected AF mode. During the exposure reading the EOS 7D looks to see which points, in addition to the selected point, have achieved or almost achieved focus. This information lets the camera know which part of the image is the subject. It then takes metering readings from the zones corresponding to the AF points that have achieved (or almost achieved) focus and combines them with readings from all the other zones. This allows for consistent shot-to-shot exposure, even in complex situations – for example, where there are reflections from a model’s glasses.

997

EOS Bodies / Re: The Last Flagship DSLRs

« on: June 11, 2012, 07:30:12 PM »

Shutterless cameras will have inherent reduced cost and increased reliability.

With good firmware the shutter speed range will be dramatically extended

With the digital sensors of DSLR's, there isn't any reason you couldn't drop the shutter. I wouldn't consider that a unique factor to the mirrorless market.

998

EOS Bodies / Re: Different tools for different trades

« on: June 11, 2012, 07:28:35 PM »

Couldn't agree with all that more! The value of a cropped sensor can't be forgotten when it comes to shooting distant action or small subjects in motion...and in that respect, the 7D is king!

There is a HUGE cost to getting the same kind of reach with FF, TC's and Supertelephoto lenses, to the tune of tens of thousands of dollars. If you try to get the same reach with a 1D X, 1.4x TC and a 500mm L II supertele as you get with the 7D and the 100-400mm lens, you would be $18,000 in the hole...and that only gets you 60mm more and some extra sharpness (which, granted, is nice...but oh so unbelievably costly!) The 7D+100-400 is about $2700-$3000 at current prices.

or better still a 1D4 @f/8 significantly outreaches the 7D

Try a 1D4 with 600 + 2x for starters .....

Sure, but I think you missed my point...your spending over $18,000 for that 1D IV, 600 f/4, and a 2x TC. If you need 1560mm, then your probably in a position where such cost is easily budgeted...but on the flip side, you could get 1920mm out of the same lens and TC if you used a 7D instead of a 1D IV. All things being equal, for birds/bif, I'd still take the 7D (or, preferably, a 7D II with much-improved APS-C sensor with slightly more MP, higher max ISO, and less noise overall.)

999

EOS Bodies / Re: Different tools for different trades

« on: June 11, 2012, 04:45:44 PM »

I probably use my 5DII closer to 90% of the time.  But, that ~10% is shooting birds/wildlife, and for that the 5DII is just not up to snuff.  I'll be keeping my 7D even after swapping the 5DII for a 1D X (in fact, keeping it until there's a 7DII).

Do you really need 7D if you have 1DX?  1DX has better FPS and AF system.  You can simply use 1.4x or 2x TC for 1DX, right?

I use my 7D mainly (almost exclusively, now) with the 100-400mm.  Since, unilke previous 1-series bodies, the 1D X cannot AF at f/8, a 1.4x TC with the 100-400mm is out.  The 500mm f/4L IS II is next on the list after the 1D X...but at that point with a 1.4x, that's getting me 700mm vs. 640mm equivalent with the 7D @ 400mm - and I'm already cropping the 7D image.  When you're shooting small birds, there's no such thing as too long a lens.  If there were a m4/3 camera with good enough IQ and response rate, and a compatible 400mm lens, I'd consider it.

Couldn't agree with all that more! The value of a cropped sensor can't be forgotten when it comes to shooting distant action or small subjects in motion...and in that respect, the 7D is king!

There is a HUGE cost to getting the same kind of reach with FF, TC's and Supertelephoto lenses, to the tune of tens of thousands of dollars. If you try to get the same reach with a 1D X, 1.4x TC and a 500mm L II supertele as you get with the 7D and the 100-400mm lens, you would be $18,000 in the hole...and that only gets you 60mm more and some extra sharpness (which, granted, is nice...but oh so unbelievably costly!) The 7D+100-400 is about $2700-$3000 at current prices.

1000

EOS Bodies / Re: The Last Flagship DSLRs

« on: June 11, 2012, 03:31:30 PM »

I think this is rather naive, as most of the "End of the DSLR era" commentators are. There is a hell of a lot more to a camera than "a lens that focuses light on a sensor". Of significant note is the ability to preview what your going to be taking a photograph of, and focusing the subject(s). Both of those areas are currently areas where DSLR designs are supremely strong, and mirrorless designs are rather weak. I think it will take a good couple of generations...at least...before mirrorless starts to intrude into the territories that DSLR designs currently cover to near perfection (thanks to the fact that they are ancient, established, and well-proven designs.)

I've tried out a few mirrorless cameras, both with and without optional OVF's. One thing I can say with GUSTO is that EVF's are terrible, for a couple reasons. One, being electronic, they have to transfer information from the sensor to a small screen, which has its own inherent limitations. Despite fairly high refresh rates on the EVF screens, transferring information from the camera's sensor and processing it such that it can be displayed on the EVF takes time, often limiting your frame rate. Even at a frame rate of 30-60fps, EVF's are not immediate-mode devices...there is still a certain amount of lag. Add to that the resolution of EVF's, which is actually rather low, and often involves cycling the full set of pixels between red, green, and blue channels, results in far less than ideal results. For mirrorless cameras that have an attachable OVF, you have parallax issues, AF point selection and AF confirmation issues, etc. At the moment, and for the foreseeable future, mirrorless cameras have a very inferior viewfinder story. As I shoot action most of the time, I'll take a true optical viewfinder that shows me exactly what the lens is projecting in real-time and in full detail every time. No contest there, not yet anyway.

The other area where mirrorless lag DSLRs and need more proving is AF system. SLR designs employ a dedicated, high speed, extremely low-light sensitive sensor capable of nearly instantly detecting phase shift and adjusting lens focus in one step. Even with the advent of FPPD-AF (focal-plane phase-detection AF) built into sensors like Nikon 1 mirrorless or Canon's new 650D hybrid AF sensor, they need a LOT of proving and perfection before they could become an acceptable replacement to the proven track record of dedicated phase shift detection AF sensors. Currently, a mirror assembly is required for a dedicated PS AF unit to function, so I don't see DSLR designs going away any time soon, even as the necessary major strides in FPPD-AF designs and capabilities make leaps and bounds over current first generation ones. Again, as someone who shoots action, I'll take a DSLR mirrored design with optical viewfinder and dedicated AF sensor any day.

Finally, there is the issue of ergonomics. Mirrorless is, as I see it any way, very much a fad. Its part of a larger fad, the fad of miniaturization. There are definitely certain benefits to that...cost and weight being a couple notable ones. However tiny cameras have their definite drawbacks as well. One of the most significant that I believe will prevent many current and long-term DSLR users from switching will be ergonomics. Modern DSLR camera bodies are nearing the pinnacle of ergonomic design. Particularly Canon, I think hand fit and form, button placement, and balance are all reaching a pinnacle, where further significant improvement will be difficult to find since there are few improvements left to be made. The small form factor of mirrorless cameras does not work well with the way I use cameras, and the disproportionate size of longer lenses makes for some odd ergonomics that hinder using current generation mirrorless cameras for what I shoot....birds, BIF, and wildlife. It may be that Canon releases a mirrorless FPPD-AF camera design that uses EF mount lenses in a standard DSLR-sized body...in which case mirrorless would definitely become a more appealing option. But I don't see such a thing in the near future...it doesn't fit with the fad.

Finally, I've said this before, and I'll probably say it again many times. New options don't mean the elimination of old options. New options simply mark further diversification of markets. Film is not dead, and while it may not be as front and center as it was a decade ago, it is still used by a not-insignificant number of consumers. Film, both stills and movie film, is the single largest consumer of silver today, and use of silver in film doesn't seem to have slowed much at all despite the larger digital market today. Similar to film, digital SLR camera designs will never cease, and will probably maintain a larger significant use by consumers than film does today. Mirrorless is just a new option, that will appeal to certain users over and above DSLRs for a variety of reasons. It'll certainly gain market share, and in a decade it may indeed have the larger share (as the average consumer who just wants a good camera is more likely to buy a smaller, easier to handler mirrorless than an entry-level DSLR.) I don't believe the DSLR design will disappear from the market alltogether, not in the next couple of decades at least, and while it may take second place to mirrorless in the future, it will remain a significant option for the long term.

1001

EOS Bodies / Re: Different tools for different trades

« on: June 11, 2012, 02:53:33 PM »

I just sold my 7D because I see the rumor Canon is going to have HIGH MP low price FF.

You made a decision like that based on a rumor?      I hope that you sold it because you no longer use/need it - CR rumors, especially for things like a high MP / low price FF body (an oxymoron for Canon, I think), are not a good guide for buying/selling decisions...

I think you just got trolled... 

1002

EOS Bodies - For Stills / Re: Canon EOS Rebel T4i First Impression Review

« on: June 11, 2012, 02:51:31 PM »

Well, the first thing I have to say is that camera review site, digitalcamerainfo.com, is a very annoying site. The navigation sucks, and having full-page ad interruptions every time you change to a different page is excessively intrusive and annoying....WOW... 

If I can get through the my extreme annoyance, I might have something to say in the near future....but wow...

1003

EOS Bodies / Re: *UPDATE* Canon Rebel T4i/650D on June 8 [CR3]

« on: June 10, 2012, 01:35:57 PM »

No reason the AF system couldn't dynamically reconfigure the available AF points and point spread by lens with such knowledge.

Except the camera wouldn't know about all the lens.

Even DxO software cant cope with large whites (which is a major reason one might buy DxO) - so it would be a logistical nightmare trying to maintain the firmware as new lens come to market several years down the line.

That wouldn't be the case if the necessary information comes from the lens itself. If lenses are equipped with microchips that fully describe the optical characteristics, then the AF system wouldn't need firmware updates.

1004

EOS Bodies / Re: *UPDATE* Canon Rebel T4i/650D on June 8 [CR3]

« on: June 10, 2012, 12:20:17 AM »

@Jrista:
Any possible answer as to whether those partially masked off pixels used for PD-AF could be spread further out of the center of the frame? Could they not also be placed near the very border of the sensor?

If yes ... why did Canon limit FPPD-AF to such a narrow area in the center? Processing power of the AF-CPU? Or Canon "marketing differentiation" ... so they can offer "new, improved 30% sensor coverage" in a  70D then 50% in a 7D II and eventually 90% in the 1D X Mk. II? And another 3 years later they unlock another 10% via a firmware update?   

I would assume PD pixels will have the same kind of spread limitations as a dedicated AF sensor. For one, the farther out to the edge of the frame you go, the less accurate you can assume the incoming image is. You may have a superbly stellar lens that has very little in the way of corner softness, edge CA, or other types of aberration. As you near the edge of the frame, you experience vignetting as well, even on the best of lenses, by as little as a stop or as much as 3 1/2 to 4 stops. Phase detection requires a certain amount of light, and has to make a certain amount of assumptions about the characteristics of the light its using to judge focus. The peripheral regions of a lens' image circle are less viable for AF purposes, as your largely stuck with the lowest common denominator when making assumptions about IQ in those regions.

Additionally, because those pixels are partially masked off, they are still working with less light, just like an AF sensor. The average AF "point" involves sensitive CMOS strips of pixels, arrayed in a very specific way, that receives light from a specially built lens that is part of the AF unit (usually under the mirror). That special lens splits light by as many AF points x2 for strips, x4 for cross, and x8 for double cross (the latter only exist on Canon's 61pt AF system). It may be that standard AF sensors have generally less light to work with than FPPD-AF systems, I can't be sure...it would depend on how much of the pixel has to be masked off, and whether there is anything else special about those particular pixels that may restrict light more. It may also be that PD pixels generally have more light to work with.

I would generally expect that AF point spread with FPPD-AF would be similar to dedicated AF sensors, with possibly less restriction if they are not as light-limited. Even if they are less light-limited, that would only mean you could have more f/8 sensitive AF points in a similar spread as a dedicated AF sensor, as you still have vignetting and aberrations to deal with in the periphery. The new 61pt AF system from Canon has a point spread that covers 53% of the frame. That seemed to be quite a feat, and they had to drop f/8 AF support to achieve that (which really confuses me, as you generally only do f/8 AF with the center point(s), which wouldn't be subject to the vignetting and aberrations near the periphery of the point spread area). FPPD-AF, if it is more light sensitive, might reach 60%. I wouldn't expect anything extreme though...fully-effective full-frame point spread might not be something we see right away.


To speculate more, I don't see why it couldn't be possible to utilize lens profiles of chipped Canon lenses to dynamically tune the AF system. If you could tie in lens profiles into the AF system, it would know what amount of vignetting and what types of optical aberrations (and to what degree) it has to deal with. If you are using a top-shelf lens like the EF 600mm f/4 L II, your probably working with near-perfection and minimal vignetting. On the other hand, if you are working with a kit EF-S 18-55mm, you probably have a moderate amount of vignetting and some pretty major CA in the periphery. No reason the AF system couldn't dynamically reconfigure the available AF points and point spread by lens with such knowledge.

1005

EOS Bodies / Re: *UPDATE* Canon Rebel T4i/650D on June 8 [CR3]

« on: June 08, 2012, 08:55:05 PM »

Um, what slightly lower pixel count? As far as I understand, its still 18mp, 5184x3456, which is exactly the same as my 7D, a total image pixel count of 17.9. I believe the sensor pixel count is exactly the same as its always been, from the 7D through the 600D.

Apologies for attributing that statement to you.  Both sensors have the same count for effective pixels (17.9 MP, or 'Approximately 18.0' as Canon states it).  But the total pixel count differs - approximately 18.5 MP for the T4i, approximately 18.7 MP for the predecessor.

Ah, gocha. Its entirely possible they are excluding the PD pixels. I guess that would mean there are about 200,000 of them.