July 24, 2014, 06:51:29 AM

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Messages - horshack

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Third Party Manufacturers / Re: Anyone own both Canon and Nikon
« on: July 08, 2014, 12:12:47 AM »
If you're not in a rush I would wait for Photokina and see if Canon comes out with a body that tickles your fancy.

If you think through what typical High ISO shooting represents then you'll reach the conclusion that there is no detail advantage for higher-density sensors in this application. Specifically, High ISO is typically used in hand-held situations for scenes that are shutter-speed limited, ie ISO is bumped to achieve the minimum shutter speed necessary to avoid motion/camera shake. Higher-density sensors require faster shutter speeds to achieve the same pixel-level sharpness as lower-density sensors - this same pixel-level sharpness is required in order for the higher-density sensor to have a detail advantage over the lower-density sensor, even for downsampling cases, otherwise you're just oversampling motion blur/camera shake. Without a faster shutter speed the higher-density image will have the same acuity as the lower-density sensor at equivalent viewing sizes (but not worse). Because the High ISO image requires a faster shutter speed, the absolute exposure (roughly ISO) will be lower on the higher-density sensor, normalizing the detail advantage over the lower-density sensor due to higher noise.

Most High ISO comparisons are done with tripod-mounted setups, which fails to account for the necessary shutter speed adjustments since a stabilized setup can achieve pixel-level sharpness at any shutter speed (at least for camera shake if not motion blur).

Reviews / Re: DxO reviews Sony A7s: king of low light photography?
« on: June 18, 2014, 03:37:49 PM »
The intent of DxO's composite low-light score is to measure the total sensitivity of the sensor, which includes noise, color noise, and dynamic range. The problem with the score is that it applies subjective thresholds to each of these elements (I describe this in more detail here: http://www.dpreview.com/forums/post/41265241). In general I agree with their premise to include color noise/selectivity in the score since reducing color performance is one method sensor designers have used to improve High ISO, and boosting the saturation in PP to match a more color-selective sensor increases noise and thus would make the IQ comparison unfairly penalize the better color perfomer. However their threshold for selectivity is arbitrary. Their threshold for dynamic range is even more arbitrary (and underweighted in the score IMO), which is why cameras like the 1DX/6D (and now even the A7s) are rated lower than they should be since High ISO DR (shadow noise) is one of the most important components for subjectively pleasing High ISO performance.

Reichmann is a bit optimistic in his appraisal of the A7s's High ISO capabilities. That said, the A7s High ISO raws posted at http://www.dpreview.com/forums/post/53852362 demonstrate what to me looks like a 1EV improvement in High ISO over the current best FF sensors (1DX/6D/D4s/Df). You can see the converted JPEGs here: http://www.dpreview.com/forums/post/53855688

Thanks horshack.  I think I have the AFMA at the best possible setting, based on multiple tests, it just isn't quite as sharp as when focusing with Live View.
The DOF increments associated with each AF tune increment are pretty thin, so if you're not getting AF results that match LV then that might suggest you haven't arrived at the optimal tune value just yet. In your testing, is every AF photo consistently not as sharp as your LV at your arrived tune value, or is it that there is shot-to-shot variability at your tune value? Do you see the problem at all focal lengths on the zoom?

Make sure when you AFMA you're using the extreme ends of the focal range (70mm and 200mm) and set the AFMA for each end appropriately. Any attempts to AFMA with the zoom in between those extremes will produce unpredictable results since the 5DM3 firmware interpolates the AF tune value between the AFMA values of the extreme ends. Additionally, I would give DotTune a shot:
DotTune: Autofocus fine tuning in under 5 minutes Small | Large

What is the potential risk with ML anyway? I believe I've read something about frying your sensor (!) when using Dual-ISO. Is that a big risk and if so, why?
No risk. ML runs on your memory card, the moment you replace the memory card, there is no ML ... use it without fear.

My understanding is that once you install it on the 5DIII you cannot undo the boot flag. This means that if you don't like it (slow boot times, or something else), you can't "reset" your cmaera to factory performance. That is a barrier to me. I'll give it a try when I see that it is completely reversible.

That was a limitation of the previous 5DM3 ML releases. It's been fixed in this release - the bootflag on the body can now be cleared.

Lenses / Re: Strange AFMA results with canon 50 f1.4
« on: February 25, 2014, 11:49:09 PM »
The 50 is one of my favorite Canon lenses but it's micro-USM motor makes it a rather finicky and imprecise focusing lens (shot-to-shot variability). I've had the most success with it by tuning at infinity - that produces good results at all distances whereas the opposite is not true (tuning at 50x and expecting it to focus well at middle to infinity distances).

EOS Bodies / Re: Patent: Microadjustment Automated
« on: January 13, 2014, 08:33:34 PM »
I don't think CDAF's lack of predetermine directionality would matter in this case. All that is necessary is for CDAF to achieve focus as a reference point. Once a reference point is attained (and CDAF CAN indeed achieve very good focus once it's done going through all its gyrations), you save the focus group position of the lens, then all you need to do is test PDAF at a distribution of AFMA settings until you zero in on the one that most closely matches the CDAF position, and ensure that setting produces repeatable results.

The PDAF cycles aren't required. Once CDAF has found the optimum contrast point, the AFMA value can be determined almost instantly by evaluating the phase differential and then applying the appropriate AFMA adjust value to bring that differential to its minimum. This is one method outlined in Canon's patent.

EOS Bodies / Re: Patent: Microadjustment Automated
« on: January 13, 2014, 12:00:33 AM »
I'd have to read through the patent to see if there are any unique elements to it but generally speaking the idea of using CDAF to auto-tune PDAF has lots of prior art online.

EOS Bodies / Re: Canon Dual-Scale Column-Parallel ADC Patent
« on: December 20, 2013, 07:29:44 PM »
Some of this patent seems to overlap what Emil Martinec came up with back in 2008:


Software & Accessories / Re: Magic Lantern and the automated Dottune
« on: December 14, 2013, 04:03:36 PM »
I use Reikan Focal.  It works and is accurate.  Dot Tune seems to have a broad tolerance for accuracy. 
There is no broad tolerance with DotTune. The midpoint of the confirmed range is the optimal AF tune value. Those who have tried both FoCal and DotTune report to me that both arrived at the same calculated AF tune value.

Software & Accessories / Re: Magic Lantern and the automated Dottune
« on: December 14, 2013, 03:59:50 PM »
Hi all,
I am having trouble discerning the progress of the automated dottune in Magic Lantern.
I have tried reading their website, but am a little confused if it is available.
If it is available (5DMk3), which version of Magic Lantern do i need to download.
If I use Magic Lantern to determine an amount of fine adjustment, will it move it to the cameras internal
memory area, or do I need to modify that value manually.
Essentially, I was wondering if I needed to be using Magic Lantern all of the time to be able to get the adjustment
during actual use of the camera/lense combo

Thanks for any info you can provide.

GlassEye :o

It's been available in the developer stream since its inception but I don't believe there's been an official ML release yet since that date. When executed it will store the AF tune value in the camera's memory automatically upon completion.

Third Party Manufacturers / Re: Review: Zeiss 15mm f/2.8 Distagon
« on: November 14, 2013, 10:53:35 AM »
I'm generally a Zeiss fan myself but the Nikon 14-24 (w/adapter) represents a much better value and is sharper across the frame when stopped down vs the Zeiss.

FF sensors have 2.25x more area than an APS-C sensor. That means than APS-C sensor must be 2.25x more efficient at converting light in order to even just match a FF sensor's performance let alone exceed it. That's just not possible when both chips benefit from the same technology improvements. It's only possible when comparing a much older FF sensor vs a contemporary APS-C sensor, such as the 5Dc vs D7100/K-3.

ok.. thatá what logic tells us.... so how do you explain the results?  :)

There are an infinite number of ways to perform invalid tests. And another infinite number of ways to misinterpret the results :)

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