December 18, 2014, 05:43:46 PM

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Messages - Lee Jay

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16
EOS Bodies / Re: High Megapixel Camera Coming in 2015 [CR3]
« on: December 17, 2014, 11:01:22 AM »
I bet on it being a Canon sensor.  My guess is it will have the 5DIII AF System, and probably less than 4 fps.

I think I speak for everyone when I say that I hope it has no less then 14 stops of noise free DR...so the DR fights can stop  ;)

Yes, I agree.  The best application for extremely good base ISO DR is to make those that think that is an important parameter shut up.

17
EOS Bodies / Re: High Megapixel Camera Coming in 2015 [CR3]
« on: December 17, 2014, 10:17:50 AM »
1. No mirror = no vibrations = better use of high res.

This is total baloney.  DSLRs have mirror lock up for when that's required, plus shutter actuation does cause vibration in any camera with a shutter.

18
EOS Bodies / Re: High Megapixel Camera Coming in 2015 [CR3]
« on: December 17, 2014, 10:11:56 AM »
Admin - have you excluded the possibility that this is a 23-25 mp DPAF sensor?  I believe we were previously led to believe that Canon was launching a high MP APSC sensor (which later turned out to be a 40 million photosite 70D which takes 20 megapixel pictures).  Just checking to see if that's the same thing here.  If it's a 5D model, the line Canon is known for video, I could absolutely see this being the case.

No, it will be "pure" (no DPAF) high res sensor body. Possibly build around Sony sensor (not sure).
From technical point of view it would be better to put that sensor into mirrorless body, but I don't think they are going to do it.
Could you explain why the sensor would be better in a MILC, rather than a dSLR (from a technical point of view)?

He's probably thinking mirror slap, which is a non-issue except in very extreme situations (it matters when I have my camera mounted to my 2,800mm telescope).

19
EOS Bodies / Re: High Megapixel Camera Coming in 2015 [CR3]
« on: December 17, 2014, 09:40:50 AM »
When does diffraction kick in on a 50mp 35mm sensor?! How would this be good for landscapes or studio shots where you stop down? Wouldn't scaling up a lower mp shot probably look the same?

Diffraction is always present.  So I don't know what "kicks in" means.

These would be about 4 micron pixels.  Here's a chart for how diffraction affects MTF.


20
EOS Bodies / Re: High Megapixel Camera Coming in 2015 [CR3]
« on: December 17, 2014, 09:28:48 AM »
It would interest me if it has the following:

A 5DIV like body and price.
At least two, preferably three high-speed modes (pixel binning full-frame [quarter pixels], 1.4-crop [half pixels], 2.0-crop [quarter pixels]).  I'm happy with 4fps at full-res, but I'd like 6+ in the other modes.
Dual pixel technology.

And, as a bonus, I'd really, really like a built-in flash.

If you just took a 7D Mark II, same pixels, same body, same everything, and scaled up the sensor, it would be just over 50MP.  That would be pretty good for me.

Lee Jay

21
Pricewatch Deals / Re: Deal: Canon EOS Rebel SL1 w/18-55 IS STM $323
« on: December 16, 2014, 06:35:00 PM »
You want a really great deal?

My pocket camera for the last few years has been the Elph 500 HS.  24-105 range, f/2 at the wide end, great BSI sensor, great in-camera processing, sharp lens, touch screen, 1080p video, 120fps and 240fps video options, capable of 3-4fps in regular burst mode and 10fps in small burst, all in an extremely small size with rounded corners and beveled edges - very comfortable in my pocket.

Currently on sale refurbished at Canon for $63 with free shipping.

I bought two - a spare for me and one for my 6-year-old daughter.

22
EOS Bodies / Re: Focus problems with the Canon 7DII?
« on: December 15, 2014, 09:09:08 PM »
I know the difference between precision and accuracy.  I'm a data acquision engineer.  I'm less confident that Canon marketing knows the difference so I don't know what they are actually specifying.

I know the f/2.8 points will be better on f/2.8 or faster lenses.  What I'm less clear about is by how much when newer focus points are used and when more focus points are used.  Do the f/5.6 points use smaller pixels than the center point?  They aren't as sensitive in low light.  If they have smaller pixels, are they, say 1/6 DOF points?  How many standard deviations?  Is that for each point or for both of a cross point?  What happens when multiple points have the subject?  Do errors average out in the usual way (square root of the number of points) or in some other way?

Since we don't know the answers I'd like to see some actual testing on this camera with fast lenses before I accept the claim that it isn't designed to focus well with fast primes.  The AF guide says all 65 points are usable in cross mode with, say, a 35/1.4L.  Presumably Canon wouldn't spec that if they didn't work with that lens with an acceptable level of keepers.

Apologies – reading back, I jumped into the middle of the discussion instead of beginning at the beginning.

I'd say that if Westfall is confused about accuracy vs. precision, it's a good bet marketing is more so, and that's not allowing for translation from Japanese technical documentation.

Looking back at the main point, I'd have to say that while I do notice a very slightly higher hit rate with Group A/B/D lenses using the f/2.8 point(s), the hit rate with f/2.8 and faster lenses using f/5.6 points is really quite good.  The difference is pretty subtle, and I haven't tried to quantify it, just anecdotal based on thousands of shots.  I think the inter-lens difference (e.g. 40/2.8 vs 24-70/2.8 II) is as great or greater than the intra-lens difference with f/2.8 vs. f/5.6 crosses.

This has been my experience too, but that's on my cameras, which are a 20D and a 5D.  I'm pretty interested in how a modern focusing sensor like that in the 7DII does in the same sort of testing.

23
EOS Bodies / Re: Focus problems with the Canon 7DII?
« on: December 15, 2014, 09:04:10 AM »
There's a spec on the accuracy of a focus point.  It used to be 1/3 of the DOF.  So, if a point is good to 1/3 of the DOF at f/5.6, it should be good to 1 DOF at f/1.8.

Sorry, but that's two wrongs for the price of one. 

In fact, the spec is that the high-precision AF points (generally the f/2.8 ones) are precise within 1/3 the DoF at the lens' max aperture (whatever lens is attached), whereas the standard precision AF points (generally the f/5.6 ones) are precise within 1 DoF of the attached lens at max aperture.

It's also important to distinguish precision from accuracy.  Canon specifies the former (as described above), but apparently not the latter (I've had an email exchange with Chuck Westfall on this).  Accuracy is determined by the 'baseline' of the AF point, and the wider baseline of an f/2.8 line (easy to see on an image of an actual AF sensor) makes it more accurate than an f/5.6 line.

I'd be wary of anything Chuck Westfall says technically, since he once claimed that purple fringing was caused by birefringence of the stuff in front of the sensor (I forget if it was the microlenses, the AA filter or the IR filter).  Regardless, that isn't the cause of purple fringing, axial CA in the lens is.

Since neither the baseline nor the pixel density of the sensor changes with lens wide open f-stop, I don't understand how a single line sensor could be more accurate on a lens that's faster than its baseline than on one that is equal to its baseline, but that's what it would have to be if what you wrote above is correct.  It's seeing f/2.8 even on an f/1.4 lens but the DOF is half on the later so to retain 1/3 DOF performance, it would have to be twice as good on an f/1.4 lens as it is on an f/2.8 lens.

The point regarding Westfall was that I asked him if Canon specified AF accuracy in addition to AF precision, and he was not aware of such a specification (which presumably, he could find if there was one).

In our exchange, Westfall confused precision and accuracy, and it appears you are doing the same.  Precision is not the same as accuracy.  Precision is repeatability, how tightly a series of repeated measurements cluster together.  Accuracy is how close the average of a repeated series of measurements, or even a single measurement for that matter, is to the true value.



An f/2.8 AF point has a physically wider separation between the halves of the AF line, easy to see (the sets of five diagonal lines are the f/2.8 crosses):



That wider separation requires a faster lens to deliver a wide enough light cone, and that wider baseline makes the line more accurate than the narrower baseline of an f/5.6 point.  So, an f/2.8 AF point used with an f/2.8 or faster lens will be more accurate than an f/5.6 AF point used with the same lens.  That was the point that I believe GraFax was making.  In general, those f/2.8 points are also high-precision points, meaning a steeper distribution curve (but while Canon specifies 1/3 of the depth of focus, they don't provide a full description of the precision, e.g. xx% of shots will fall within that depth of focus, because I'm sure it's not 100%). 

Because the precision of the system is specified in terms of depth of focus, whether or not you notice any differences depends a lot on your typical subject distance.  As subject distance increases, DoF increases but depth of focus doesn't change significantly.  So, you gain apparent precision as your subject distance increases.

I know the difference between precision and accuracy.  I'm a data acquision engineer.  I'm less confident that Canon marketing knows the difference so I don't know what they are actually specifying.

I know the f/2.8 points will be better on f/2.8 or faster lenses.  What I'm less clear about is by how much when newer focus points are used and when more focus points are used.  Do the f/5.6 points use smaller pixels than the center point?  They aren't as sensitive in low light.  If they have smaller pixels, are they, say 1/6 DOF points?  How many standard deviations?  Is that for each point or for both of a cross point?  What happens when multiple points have the subject?  Do errors average out in the usual way (square root of the number of points) or in some other way?

Since we don't know the answers I'd like to see some actual testing on this camera with fast lenses before I accept the claim that it isn't designed to focus well with fast primes.  The AF guide says all 65 points are usable in cross mode with, say, a 35/1.4L.  Presumably Canon wouldn't spec that if they didn't work with that lens with an acceptable level of keepers.

24
EOS Bodies / Re: Focus problems with the Canon 7DII?
« on: December 14, 2014, 11:01:06 PM »
There's a spec on the accuracy of a focus point.  It used to be 1/3 of the DOF.  So, if a point is good to 1/3 of the DOF at f/5.6, it should be good to 1 DOF at f/1.8.

Sorry, but that's two wrongs for the price of one. 

In fact, the spec is that the high-precision AF points (generally the f/2.8 ones) are precise within 1/3 the DoF at the lens' max aperture (whatever lens is attached), whereas the standard precision AF points (generally the f/5.6 ones) are precise within 1 DoF of the attached lens at max aperture.

It's also important to distinguish precision from accuracy.  Canon specifies the former (as described above), but apparently not the latter (I've had an email exchange with Chuck Westfall on this).  Accuracy is determined by the 'baseline' of the AF point, and the wider baseline of an f/2.8 line (easy to see on an image of an actual AF sensor) makes it more accurate than an f/5.6 line.

I'd be wary of anything Chuck Westfall says technically, since he once claimed that purple fringing was caused by birefringence of the stuff in front of the sensor (I forget if it was the microlenses, the AA filter or the IR filter).  Regardless, that isn't the cause of purple fringing, axial CA in the lens is.

Since neither the baseline nor the pixel density of the sensor changes with lens wide open f-stop, I don't understand how a single line sensor could be more accurate on a lens that's faster than its baseline than on one that is equal to its baseline, but that's what it would have to be if what you wrote above is correct.  It's seeing f/2.8 even on an f/1.4 lens but the DOF is half on the later so to retain 1/3 DOF performance, it would have to be twice as good on an f/1.4 lens as it is on an f/2.8 lens.

25
EOS Bodies / Re: Focus problems with the Canon 7DII?
« on: December 14, 2014, 10:53:42 PM »
The centre point is double cross for lenses with a maximum of f2.8 or faster otherwise it is single cross. The rest are cross type for lenses f5.6 or faster otherwise they are single dimension: horizontal or vertical sensitive. Not both at the same time.

I think only the four immediately adjacent to the center point work at all at f/8 - the two side ones are vertical, the top and bottom are horizontal.  All the others are unavailable for slower than f/5.6 lenses.

Some of the points farther from the center are not usable for certain lenses.  I assume this is a field flatness or perhaps aberration (spherical or CA) limit for those lenses, but it doesn't say.

26
EOS Bodies / Re: Focus problems with the Canon 7DII?
« on: December 14, 2014, 08:40:28 PM »
I think he's saying the 2.8 point is more precise than the 5.6 points not that they won't work. And I believe reading the manual on my 5d3 the center point is more precise for 2.8 and faster lenses. I'm not a expert at this topic but that's how I understand it. Not that it won't work but that it's more precise. How much more precise IDK

There's a spec on the accuracy of a focus point.  It used to be 1/3 of the DOF.  So, if a point is good to 1/3 of the DOF at f/5.6, it should be good to 1 DOF at f/1.8.

Now, we don't know if that's 1 standard deviation or more, and we don't know if the spec on the 7D2's focus points are 1/3 of the DOF or something else.  That's why I wanted evidence.  I suspect that the spec is tighter now than it was when 1/3 of the DOF was the standard but I don't know that either.

With 1/3 DOF f/5.6 points I get around 80% in-focus images at f/1.4.  If the 7D2 can do that well, I'll be happy.  Since that spec is 10 years old, I suspect it will do better and that the reason it only has one f/2.8 point is that it doesn't really need the high precision points to get a good percentage of in-focus images with f/2.8 lenses like the 300/2.8 and 400/2.8.  It's also probable that having multiple focus points all working on one subject will further tighten the performance since errors will tend to average out.  And with all of the 7D2's focus points being cross points, you have at least two on every subject.

This is why I want to see some testing on faster lenses using other than the center point.

27
EOS Bodies / Re: Focus problems with the Canon 7DII?
« on: December 14, 2014, 08:33:23 PM »
I mainly bring it up because I see a lot of folks struggling to get good focus with the 7D2 in multi point zone AF modes with fast lenses. Not a great approach IMO for getting good critical focus wide open.

Prove it.

I've used f/5.6 points with f/1.4 lenses and done quite well for years.  I used them like that at my last wedding (in horribly dark conditions - f/1.4, ISO 1600, 1/30th or so) and got tons of in-focus shots.

If what you're saying is true, the f/2.8 points on the 1DX and 5DIII are just short of useless on f/1.4 and f/1.2 primes.  In reality, they work just fine, and the f/5.6 points of the 7DII should work just fine with f/2.8 lenses and faster as well.
I don't take orders or direction from you. If you don't accept there are differences in AF point sensitivity that is you prerogative. Don't expect any further response from me to your posts.

No evidence = no reason to believe you are right.

28
EOS Bodies / Re: Focus problems with the Canon 7DII?
« on: December 14, 2014, 07:29:41 PM »
I mainly bring it up because I see a lot of folks struggling to get good focus with the 7D2 in multi point zone AF modes with fast lenses. Not a great approach IMO for getting good critical focus wide open.

Prove it.

I've used f/5.6 points with f/1.4 lenses and done quite well for years.  I used them like that at my last wedding (in horribly dark conditions - f/1.4, ISO 1600, 1/30th or so) and got tons of in-focus shots.

If what you're saying is true, the f/2.8 points on the 1DX and 5DIII are just short of useless on f/1.4 and f/1.2 primes.  In reality, they work just fine, and the f/5.6 points of the 7DII should work just fine with f/2.8 lenses and faster as well.

29
EOS Bodies / Re: Focus problems with the Canon 7DII?
« on: December 14, 2014, 03:32:46 PM »
I didn't design it, I'm just pointing out the spec. The 300/400 2.8 are also used with teleconverters when reach limited and for sports are often used natively on full frame 1DX's which are optimized for fast lenses and have many more f2.8 AF points.

Many more?  5 (of 61) instead of 1.  In other words, not many.  All the f/5.6 points (of which 41 of 61 are cross type on the 1DX but all 65 are on the 7DII) will AF on f/2.8 lenses.

Quote
As an engineer, I look for the "tells" that other engineers leave behind in order to understand their design intent. In this case I think the intent is pretty clear. Others may see it differently. Canon, as usual, isn't saying much.

As an engineer and scientist, I'm often annoyed at how much stuff people will make up and believe in despite having little or no real information or evidence.

30
EOS Bodies / Re: Focus problems with the Canon 7DII?
« on: December 14, 2014, 02:58:59 PM »
Long lenses with/without tele-converters typically have maximum apertures of  f5.6 to f8. Clearly they did not intend for the 7D2 to be uses with fast primes.

You mean like the two standard sports lenses, the 300/2.8 and 400/2.8?

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