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Messages - epsiloneri

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Lenses / Re: Delivery of the Canon 1.4X III HAS STARTED
« on: January 06, 2011, 05:57:34 AM »
Extenders enlarge the flaws of any lens, but the 200mm f2.0 is THE perfect lens, so no surprise that we cant see a big difference, but i bet that on for example the new 70-200, the improvement will be more obvious.

This sounds backwards to me. Surely extenders are not able to correct lens flaws? For a "perfect" lens I would expect it to be easier to differentiate between the II and III extenders, as any flaws added by the extenders would be more visible. On a less perfect lens, however, any extender flaws might be masked by the magnified lens flaws.

EOS Bodies / Re: 5D Mark III [CR1]
« on: December 27, 2010, 05:10:29 AM »
I'm also looking forward to see if the dynamic range is improved. I'd trade 6-figure ISO for more DR any day of the week.

I totally agree. I find the biggest problem for the image quality from a 5D2 to be its low-iso pattern noise (banding) that severely limits the dynamic range. 50D also has this problem (it's from the same generation). The 7D is way better in this respect, and I expect a 5D3 to be as well. See http://photography-on-the.net/forum/showthread.php?t=750731 for a detailed discussion.

Unfortunately, these rumoured specs do not look very credible... at all. I'm expecting a 5D3 no earlier than by the end of 2011. Hopefully together with a 24-70/2.8L IS  :P

EOS Bodies / Re: Finding the optimal Micro Adjustment
« on: December 26, 2010, 06:16:37 PM »
There are several parameters that can affect the focus, and specifically the autofocus, of a lens. A few I can think of:

* Focal length of lens (for zoom lenses)
* Distance to focus target
* Aperture of lens
* Shape of focus target
* Colours (spectrum) of focus target
* Relative (3D) velocity to focus target
* Temperature of lens
* Temperature, humidity and pressure of air

As testing for MA is a bit time consuming, I have only really checked the first two parameters, and not very thoroughly. For one lens (and two camera bodies), I found that changing the distance to the target from 25x to 40x the focal length did not affect how the AF behaved as a function of MA. The set focal length on zoom lenses, however, did change the optimal MA. The contrast as a function of MA does not qualitatively look different from the prime lenses, but it changes with set focal length. I give an example in the attached figure, which shows the contrast as a function of MA for the EF 24-105/4L lens on 7D, set at 24mm (green) and at 105mm (blue).

EOS Bodies / Finding the optimal Micro Adjustment
« on: December 22, 2010, 05:11:48 PM »
Is focus micro adjustment a must-have feature? The absence of the feature in the recent 60D has sparked some debate. Triggered by a recent problematic lens, I've been interested in measuring the focus performance of my lenses and the possibility to micro adjust (MA) focus offsets of the auto focus (AF). The usefulness of the MA feature is dependent on the ability to accurately (and consistently) establish any potential focus offset, otherwise there is not much point in tweaking the MA. E.g., if the variance of the AF is greater than the MA, then there is very little benefit with MA.

I've experimented a bit with various methods, and the trouble I have with most of them is that they require visual inspection of images very similar to each other, which I found hard to do. Instead, I opted for the quantitative approach of measuring the contrast in an image as a proxy for its sharpness, with the assumption that more out-of-focus images will be less contrasty. That is the way "live view AF" works, which I've found to give very accurate and consistent results in good light (albeit a bit slow).

To obtain consistent results, I used a focus target properly aligned with the camera. I think any contrasty image in principle can be used as a focus target, I used one I found from Keith Cooper's MA page (below is a crop of the full image)

I found it good because it provides contrast structures on many angular scales. I displayed that image on my computer TFT screen and used the screen as a focus target. To align the the camera with the screen I taped a CD flat onto the screen, to use it as a mirror, and then checked that the center of the camera lens was seen centered in the viewfinder of the camera. This ensures that the focus target is orthogonal to the optical axis, which is again orthogonal to the image plane; that is, the focus target and the image plane are parallel. During the test shots I naturally removed the CD.

The camera was placed at a distance 25 times the focal length (i.e. at 2.5 meter for a 100mm focal length lens). I also once tried at 40 times the focal length and got consistent results, albeit with more scatter.

I took a reference image using live view contrast AF, and then obtained 4 images per MA setting using phase AF, and varied MA from -20 to +20 in steps of 5, i.e. 1+36 images in total per lens (camera, and focal length combination). I de-focused twice to infinity and twice to the near limit per MA setting, before AF.

To quantify the contrast of an image, I looked at the subimage of the focus target only (it doesn't cover the whole field) and computed the standard deviation of the intensity distribution (that is, of the grayscale image; I used MATLAB to do this, you can probably do it less conveniently in photoshop. There is also the free MATLAB clone octave if you're GNU inclined). The same procedure was repeated for both a 7D and a 5D2.

An attached figure shows an example of contrast measurements as a function of MA for a Canon EF 100/2.8 USM macro lens mounted on a 5D2. The error bars are derived from the 4 measurements per MA. A parabola is fit to the 5 best points, and in this case the optimal MA was found to be 8.9 +/- 1.2. I repeated this measurement for a number of lenses, here are the results:

Lens                                                         7D                        5D2
Canon EF 14/2.8L II                             -4.3 +/- 1.0         2.9 +/- 1.0
Canon EF 15/2.8 fisheye                     10.3 +/- 0.7           19 +/- 3
Canon EF 24/1.4L II                           -11.8 +/- 0.6        -6.7 +/- 0.8
Sigma EX 50/1.4 HSM                            3.2 +/- 0.5        13.8 +/- 0.7
Canon EF 85/1.8 USM                         -19.2 +/- 2.8        -7.2 +/- 1.2
Canon EF 100/2.0 USM                       -14.3 +/- 0.5         0.4 +/- 0.8
Canon EF 100/2.8 USM macro             -0.8 +/- 0.5          8.9 +/- 1.2

Canon EF-S 10-22/3.5-4.5 USM IS @ 10mm -11.0 +/- 0.4
Canon EF-S 10-22/3.5-4.5 USM IS @ 22mm -10.5 +/- 0.5

Canon EF-S 17-55/2.8 USM IS @ 17mm         2.9 +/- 0.5
Canon EF-S 17-55/2.8 USM IS @ 55mm      -11.9 +/- 0.5

Canon EF 24-105/4.0L USM IS @ 24mm      -1.0 +/- 0.4       6.1 +/- 0.7
Canon EF 24-105/4.0L USM IS @ 105mm    -7.4 +/- 0.5       0.5 +/- 0.9

Canon EF 70-200/2.8L USM IS @ 70mm       1.2 +/- 0.5      -2.7 +/- 1.2
Canon EF 70-200/2.8L USM IS @ 200mm    -2.6 +/- 1.8       8.2 +/- 1.5

There appear to be a fair range of optimal MA, more than I would have guessed. I will have to verify that these results hold up in the field, but that will take a while.

One question I was interested in is whether there is a constant MA offset between the 7D and 5D2. Looking at the primes only, I plot the 7D MAs versus the 5D2 MAs in the figure attached. There appear to be a clear linear correlation; I find the best fit to be that MA_5D2 = MA_7D + 9.7, with an error in the mean of 1.3 and a scatter of 3.2. The 7D seems more well centered, despite the 5D2 having been recently sent to CPS for recalibration.

The zoom lenses show a more complicated behaviour, with MA changing with focal length.

In summary, I think measuring the contrast in an image as a function of micro adjustment, with the aim to find an optimal adjustment, is an attractive alternative to visual inspection. I realise this method is not for everyone, as it involves more image analysis and data manipulation than most photographers are probably comfortable with (or used to).

EOS Bodies / Re: The 60D Needs AF Microadjustment
« on: December 15, 2010, 05:40:34 PM »
Thanks for your reply!

From a pragmatic standpoint, it's irrelevant - I will just continue to do an AFMA for each body+lens combo I have...

Except that it would simplify things a lot if it worked that way... you wouldn't have to measure each lens/body combination. Too bad it doesn't!

The other issue with that method (and with focusing on any image as a target) is the alignment of the target with the camera's sensor.  Ideally, you want the target to be completely flat and perfectly parallel to the sensor.  That's really a main function of the LensAlign tool - the sighting gates that allow you to align the target to the camera.  If not for that, I could just prop a ruler against a wall and have saved a few bucks. 

Actually, I have figured out a very simple way of achieving perfect alignment. Just take a flat mirror and fix it flat against the screen. Then make sure you see the reflection of the camera centered through the viewfinder, where you want it to be centered on the screen. This will ensure that the screen is perpendicular to the optical axis. I don't have a convenient flat mirror at home, so I use a CD that I tape onto the screen (it's reflective and flat enough). I haven't actually started to measure MAs yet, just wanted to poll your experience before I do.

I have found that live view manual focus works very well for me (on the 7D), I don't seem to have the problems you do. Best focus seems well defined, though I sometimes find that the focus ring could be more precise. Very seldom do I find the focus even slightly off in manually focused images. Much more common is slight motion blur (even with tripod). Contrast AF using live view usually also works as well (on well-lit objects). Both methods are always as accurate or better than AF-sensor AF (albeit much slower).

Non-integer up-scaling likely removes some contrast in the image, but the optimal focus probably still produces the sharpest image, even in the up-scaled version. Usually I find even the best resolution to be quite coarser than the pixel resolution of the sensor. This may in part be due to the anti-aliasing filter on the sensor.

If you AF on a point then switch to 10x Live View and see if it's sharp, that's static viewing; if you then rack the focus to check if the AF hit the spot, how do you know you're ending up at the same point? 

Hmmm, I don't think I understand... I imagine the procedure as follows:

1) AF focus on a target, say a properly aligned focus target. The camera registers what it thinks is the best focus.
2) Without moving the camera or the focus tagert, go to 10x live view and manually focus to what you think is the best focus, push a button or something for the camera to register what your preferred focus is.
3) The camera makes use of info from 1 and 2 to compute MA.

No need to go back to what the AF thought best... or am I misunderstanding? This procedure of course assumes that you are better than the AF at focusing (under static conditions), but in my case I've found that to always be the case. Alternatively, one could let the camera itself compare the AF between the AF sensors and the live view contrast AF, and compute MA under the assumption that live view AF is more accurate. That would be even simpler, and according to my experience, live view contrast AF is nearly always accurate (but slower). Contrast AF is not affected by front/back focus issues, since it uses the actual detected image for AF, so it would be perfect to correct for AF sensor MA. I can imagine setting up the camera on a tripod and align it to a focus target, select "calibrate AF" from a camera menu, and then let the camera automatically cycle through 10 AF measurement cycles (say), computing the best MA. Why not, Canon?

EOS Bodies / Re: 1Ds Mklll - and what comes next?
« on: December 15, 2010, 04:39:33 PM »
I think medium format cameras are becoming dinosaurs.

I know you asked for macfly's opinion, I'd just like to comment on this. I think medium format cameras will always find their audience, and as the sensors become better and cheaper, even more so than today! The number of pixels is not everything, cramming 50 mp into FF will not make it MF equivalent. The MF main advantage is not in their number of pixels, but in their larger sensor areas that are easier to produce excellent lenses for. I envision that in a not too distant future the sensor will be an insignificant cost of a camera, while lens prices will dominate the budget. In such a situation it is much cheaper to produce a MF camera with lens than a FF camera with lens that produces an equivalent quality picture. Today that's not the case, as MF sensors are very pricey. It's the same reason you need a really outstanding lens to produce as nice images on an APS-C as a mediocre lens is able on a FF, only amplified in the MF case.

EOS Bodies / Re: The 60D Needs AF Microadjustment
« on: December 15, 2010, 02:25:33 PM »
Ok, so I have a few questions for neuroanatomist:

1) You now have a 5D2 in addition to your 7D. Have you retested your lenses with you new body? Do you find a constant offset from your adjustments for 7D? In principle I think you should be able to, and that would mean it would be sufficient to only measure one lens, say a sensitive one like your 85/1.2L, and then apply the difference between the MA for that lens and 7D and MA for 5D2 to all other lenses to have the calibration to 5D2 without having to remeasure all lenses. I don't know if this works in practice, however, as it assumes the MA scale is linear which it may not be (I don't know). It would therefore be interesting to read your experience!

2) Have you tried to use an interference image on a computer screen as a focus target instead of the LenAlign Pro? I mean as detailed in this post by Keith Cooper.

3) Have you attempted to check whether there is a distance dependence to the optimal MA for your lenses? I've seen recommended distances for measurements to be 25-50 times the focal length, but I'm curious how well the adjustment works for other distances as well.

Something that would simplify MA would be to have a "calibration wizard" where you 1) autofocused on a target and 2) set the optimal focus manually (using live view). The camera should then be able to compute the corresponding MA itself. (This could even be generalised to MA as a function of distance.) This would ideally decrease the time required for a lens calibration to a few minutes instead of an hour.

Another thing I would love to see is focus bracketing. It was available on my Canon G2, but I haven't seen it since.

In mjardeen's defense, the OP contradicts itself.  He does put out the suggestion of the 16-35, but also says he want's something wider than his 15-85.

I don't find it contradicting to compare the IQ of two lenses of different focal length ranges. MTF, colour aberration, and vignetting, are all examples of things you can compare. You can even compare the IQ of a 14mm/2.8 lens to a 400mm/2.8, even if there of course are very few situations where you can substitute one for the other.

Everything I've read says the Tokina 11-16mm f2.8 is the best APS-C ultra-wide lens out there.

"Best" in some areas, but not all. Looking at the review you linked to, the Canon seems obviously sharper in the corners already from f/3.5, while the Tokina becomes similarly sharp only at f/5.6 (and is very soft at f/2.8 ). The MM of the Tokina is very low, and the chromatic aberrations not very well controlled. I agree that the light gathering power and lower price makes the Tokina a very attractive option, but not best in all areas.

Lenses / Re: 24-70 mm f/2.8
« on: December 12, 2010, 08:17:01 PM »
I know this is also probably not what you want to hear, but I don't think either is a very good match for your 7D. It of course depends on what you are looking for in a new lens, but if it is light gathering power, I would suggest the EF-S 17-55/2.8 IS instead. Both lighter and cheaper than the EF 24-70/2.8L, but just as good, if not better, IQ. Also a more useful focal range, IMHO. 24mm is not really wide enough on APS-C (try it on your current lens). No weather sealing though, if that's a big deal for you.

I don't know how the EF-S 10-22mm compares to the EF 16-35L on APS-C in the focal range where they overlap, but overall, the 10-22mm is very well regarded and I don't think you would disappointed by it. There are plenty of professional online reviews you can consult if you're uncertain.

If you're anyway planning to stay with APS-C for some time, I think it's a bad idea to insist on FF lenses and not take advantage of the EF-S format at the wide end (lighter, cheaper). My advice is to sell your EF-S lenses when/if you make the APS-C to FF switch. You will not lose that much money, and the money will be well spent. There is no current Canon FF lens on the APS-C able to compete with the EF-S 10-22mm at the wide end.

EOS Bodies / Re: Canon EOS 7D Mark II - sensor
« on: December 04, 2010, 03:12:50 AM »
if I wanted to shrink my 300 F4's length, I'd shoot it on my film rebel.

Ha! Ha! I think we are all getting spoiled by the extra reach of the 1.6 crop. I'm certainly not interested in going backward either.

I don't get this. The way things are going, in the future the price of a camera will be set by its optics, not its sensor. If you're anyway using a FF lens, why not let the sensor cover the whole available field? Your "crop" camera will be equivalent to cropping the image of the FF (hence the name "crop" camera). Is it the larger magnification of the view finder on crop cameras you will miss? Concern about many pixels taking space while going unused? Perhaps Canon could do like Nikon and have an "APS-C" mode with in-camera cropping.

Edit: Here's and idea. What would you think of a 3.2x crop camera then? You'd have twice the reach compared  to 1.6x!

EOS Bodies / Re: Changes to dials on Canon 5D and 7D
« on: December 01, 2010, 06:34:09 PM »
I think it's a nice addition; it happens to me from time to time that the dial moves accidentally, resulting in a lost shot. I wouldn't spend $100 on it, however. For some professionals it could perhaps be worth it.

Lenses / Re: 24 - 70 f/2.8 L : When Is The New Version Expected?
« on: November 29, 2010, 12:25:25 PM »
I also tested both 17-55 2.8 IS and the 24-70 2.8 on my 50D. 3 people looked at the photos and the 17-55 produced a ted better photos. So until Canon does not come with a better lens for FF I will not switch to FF

But how do you know the 24-70/2.8 does not produce better photos on a FF than the 17-55/2.8 on the 50D?

Lenses / Re: 24-840mm zoom
« on: November 23, 2010, 03:01:03 AM »
I want a Canon 10-5000mm F1.2 L IS USM

In principle, you could build such a lens. Unfortunately it would have to be >4m in diameter.

The longest lens I've used was a 123000mm f/15 IS prime :P It wasn't either very portable, though (and didn't have an EF mount). The longest lens I've connected to an EF camera was an 11000mm f/11 prime. Biggest IQ limitation was the atmosphere. I probably don't have to add that those lenses dwarf even an EOS 1Ds mkIII.

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