*UPDATE* Canon Rebel T4i/650D on June 8 [CR3]
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neuroanatomist said:
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.
I think its a new sensor because the pixel masking necessary for phase-detect pixels has to be added underneath the microlensing, as the microlens is an important factor in making FPPD-AF work. That would require some degree of reengineering...even if it is relatively minor. There may also be additional activate/read wiring to read out only the phase-detect pixels for AF before activating the full sensor for an image readout.
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jrista said:
So you're really saying they had to re-engineer the sensor, but obviously managed to keep the rest without any trace of improvement? Doh. But sounds like Canon to me, they'll keep the little sensor upgrade they can do to the 70d to make the jump from the 60d/7d seem bigger.
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jrista said:
Well, the sensor surely had to be tweaked to accommodate the hybrid AF and maybe other minor enhancements.
You surely cannot just plug-in a 7D sensor in the 650D and expect it to have hybrid AF.
But the underlying sensor architecture and technology appear to be the same.
Hence, the sensor will perform the same way (more or less) as the 600D/60D/7D sensors.
Or, as I put it in another post:
It's a brand new sensor ... with the same performance as the old one
.
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Marsu42 said:
Well, I can't speak to "keep the rest without any trace of improvement". Like everyone else, I'll have to wait and see...I certainly hope its more than just some PD pixels and an extra stop of ISO. I don't know how to read Canon these days. Its been four years, about two generations, and they are just letting the competition RACE by them at near-blinding speed. They either seem to think they are undefeatable and that consumers will well and truly just buy their products regardless of how good they are; they literally can't innovate like they used to...too much process bloat and not enough patents, and they are now stuck with what they have; or they were simply caught off guard, and are working on new tech and its just not ready yet.
I am really hoping its the latter. When it comes to competition, Canon could be perpetually behind the curve if they DO have new tech in the works, but only try to compete with whats already been released. For Canon to truly compete in the future, they need to develop something that is competitive with whatever the future holds from Sony, Nikon, etc. and in multiple markets. They seem to have layered RGB CMOS patents...now if they can make a sensor with that design that has some 13+ stops of raw dynamic range, and reduce the noise floor to 2-3 electrons, and/or possibly bump the full pipeline, sensor to image processor, up to a full 16-bits...then they might be solidly competitive come next generation.
The pessimist in me says that Canon has not only dropped the ball, they deflated it, froze it, and shattered it as well...they don't really have any VIABLE patents they can actually act on, they passed up patents they could have bought in the past that might have given them a few opportunities now, and they are limited in or down right incapable of producing their own patents that are capable of rivaling what the competition has been offering for two generations of cameras now. Canon needs to catch up the the third-generation SoNikon product that will be released two-three years from now, and they don't have the technology to do it.
So, pessimistic hope....?
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Loswr
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jrista said:
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.
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neuroanatomist said:
Ah, gocha. Its entirely possible they are excluding the PD pixels. I guess that would mean there are about 200,000 of them.
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jrista said:
I get the feeling Canon just doesn't care, and until Nikon can ramp up production to really steal away market share, their attitude might not change. According to DxO, the 7D sensor is only marginally improved over an ancient 20D.
20D
Color Depth: 21.9 bits
DR: 11 Evs
ISO: 721
7D:
Color Depth: 22 bits
DR: 11.7 Evs
ISO: 854
So, aside from resolution, Canon's current APS-C flagship has a sensor that's barely improved in the over a 7-8 year old 20D. During the lifespan of both bodies, Nikon has made leaps and bounds in sensor tech, yet Canon has increased its market share. If you're a Canon exec, why would you care to spend loads of R&D improving DR when lagging behind the competition in that metric hasn't impacted sales? I'm not saying that makes that kind of attitude OK, but merely pointing out that hoping and praying for substantially improved DR may be wishful thinking unless sales take a dump.
Personally, I find the DR of Canon's sensors adequate for my uses, so I really don't care that Nikon is kicking Canon's ass in that department. If DR was that important to me, I'd be shooting Nikon, granted I could find the gear in stock somewhere
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Marsu42 said:
I'd say the vast majority of burst frame use on a camera like this is only going to be looking to cover a second or so anyway. Anyone looking to do more serious action shooting is going to be buying a higher end model.
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moreorless said:
Yes and no - while not serious, shooting your kids running around is action too, and people might be disappointed about the high fps 650d if their camera slows down to a crawl after a few shots.
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@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? :
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? :
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AvTvM said:@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.
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briansquibb
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jrista said:
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.
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briansquibb said:
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.
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