October 22, 2014, 06:35:30 PM

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Messages - horshack

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1
Lenses / Re: Is FoCal worth ~$150?
« on: October 07, 2014, 11:53:34 PM »
you can also try Magic Lantern's free dot_tune module which also automatically adjusts afma. Opinions are divided abut how precise it is, but for me (using a 6d) it's working just fine.

Do you know if dot_tune will tell me if my 60D is out of whack?  I'm very much aware that the 60D does not support AFMA, but it would be nice to have it call to my attention how far out of tune it is.

Feel free to tell me to RTFM (or just try it), which I'd planned to do.

Thanks.

You can use an abridged version of the DotTune process to see if your 60D+lens is out of calibration (ie, would require AFMA if there was support for it). To do this, perform the initial steps of the DotTune process, including setting up a target, focusing on the target in Live View, and then exiting Live View and do a single viewfinder AF confirmation check and see if you get a solid green confirmation. If the confirmation waivers then your 60D+lens combo would benefit from AFMA (again, if AFMA was supported).

2
Here's one more example using this technique.   

When the Sky Rolled Back by Thousand Word Images by Dustin Abbott, on Flickr

For my taste, that part around the sun is very strange. There are some kind of halos or something like that. I see that in my case too, when I was merging several exposures in Photoshop's HDR Pro. That's the reason why now I prefer to blend exposures manually by using luminosity masks. Especially when you have straight horizon, it's quite easy to do.

And there is quite a lot of "ghost-ing" around the clouds, too.

Otherwise, it's nice image.

The area around the sun is due to the MKII's inability to natively bracket 3 stops in both directions.  I never have similar issues when shooting with my 6D, but you're right about the way to rectify it.

I initially thought there was some ghosting around the clouds, too, but that is actually the way that the clouds were.   ;D  It looks the same in single exposure files.

Adobe's merge to HDR will produce halos and posterized gradations when the exposures are more than 1EV apart. I use Magic Lantern on my 5D to achieve that. Btw even with stock Canon firmware you can bracket 3EVs in both directions - you just have to change the centered exposure accordingly. For example, meter the scene to produce your darkest exposure (ie, the brightest exposure that retains highlights). Then change your exposure to be 3EV brighter than that. Then shoot a 3-shot 3EV bracket; your darkest exposure will be the one that retains highlights, the next brighter exposure will be 3EV above that, and the brightest exposure 6EV above the base.

3
2 years behind? who behind who?

This seems much more a 5D3 variant to me, 2 years after the 5D3 is released on the market, then only this spec? The Nikon reactions are not that positive. This is not a worthy successor of the marvelous D700. Think about water sealant, fps, 1/4000 max shutterspeed, missing AF-On, max 1/200 x-sync.

As mentioned by the OP, a lot of this camera is a mix of pro but also of entry level. Thought this Nikon would really push Canon to look at further development. However, it only seems a spec that's close to the 5D3. Never the less a nice specification, but not a D700 version 2.

Features-wise, I understand your point, but I price would imply pros will value this camera less.  5D3 is a D8-something competitor (regardless of the MP count).    The 5D3 is a $3399 camera vs. the D750 at $2300. 

So I'm assuming the build quality, pop-up flash, etc. imply the D750 is for enthusiasts more than pros.  It may not be built for dyed-in-the-wool pros with tougher needs and higher expectations.

- A

The price and build may imply prosumer but Nikon wedding shooters will be looking past that and snapping up the D750. The D750 is basically a 5DM3 for Nikon shooters, albeit a few years late :) It solves the primary shortcoming of the D600/D610, which was the AF system, while giving them the lower MP they want vs the D800/D810.

4
Photography Technique / Re: Benefits of IS in fast shutter speeds
« on: September 10, 2014, 12:12:17 PM »
Chuck Westfall of Canon has stated in the past that IS helps for action photography by stabilizing the image that the AF sensors see.

5
Technical Support / Re: Any way to extend a failing shutter's life time?
« on: September 06, 2014, 04:30:53 PM »
I don't have any ideas on how to extend the life of a failing shutter but if yours is failing in a way where the two curtains are losing relative sync because of the first curtain being out of spec then shooting in Live View will help give you accurate exposures since the camera will use the electronic first curtain shutter rather than the mechanical one. The first mechanical curtain will still cycle after each photo in LV but its failing timing wont affect your exposure.

6
Reviews / Re: DxO reviews Sony A7s: king of low light photography?
« on: August 07, 2014, 05:17:39 PM »
So, on the topic of DXO and their trustworthiness, since ZigZag decided to recreate his account and ruffle feathers again. I often use SensorGen.info, which uses DXO's raw data to provide unbiased statistics of cameras. I found this to be interesting:

http://sensorgen.info/NikonD800.html
http://sensorgen.info/NikonD810.html

D800 @ ISO 100:
QE: 56%

D810 @ ISO 64:
QE: 50%


Quantum efficiency got 10% worse with the new sensor? Or does sensitivity affect QE (hence losing 6 percentage points with the lower native sensitivity)?

Quantum efficiency describes the ability of the photodiodes to convert incident photons to free charge. It IS sensitivity. At 50%, the D810 converts 50% of the incident photons to free electron charge in the potential well. That means it is, quite literally, 6% LESS sensitive than the D800.

I don't know why, doesn't seem logical to me, hence the reason it's interesting. That, and the fact that somehow, Nikon and/or Sony figured out how to nearly double the saturation point for those pixels, despite the fact that they are the exact same size as the D800? I dunno....that smells really fishy to me...capacity is primarily related to pixel area. The pixel area is identical for those two sensors (at least, as far as I now...I guess it's possible Sony moved to an even smaller process, but that isn't going to double the photodiode area by any means...)

The pixels have roughly the same capacity at ISO 100, so it makes me think that Nikon is doing something...quirky...with ISO 64.

One thing I will say, though...I find the DR numbers of the D810 more believable than the DR numbers for the D800. There is always some overhead, even if it's a fraction of a bit. Either Sensorgen.info is really referring to information in analog space (in which case were talking about electrons in a circuit, before the ADC has kicked in), or there is some amount of error in the numbers they are displaying. If they have actual electronic measurements taken directly from the sensors pixels...well that would be pretty amazing.

I wouldn't put too much stock in the exact precision of the Sensorgen-derived QE numbers; they're based on various interconnected metrics of DxO's results rather than a more direct QE measurement method. The quoted difference is 10% not 6% (on a relative basis). As for the increase of full-well capacity for the D810, there are several established techniques for achieving that, including Aptina's DR-Pix technology, which is rumored to be what Nikon uses on the D4 sensor https://www.aptina.com/products/technology/DR-Pix_WhitePaper.pdf.

7
Third Party Manufacturers / Re: DXO uh-oh?
« on: July 27, 2014, 09:52:59 PM »
The margin of error in her D3s measurements were very small; she included them for completeness, and was open about not understanding their source. The variance was small enough to be immaterial to the results.

Sorry, but your statement does not align well with hers:

I re-tested both of my D3 bodies, plus the new D3s, for this - just to make sure I produced a valid comparison. For some obscure reason - sunspots or moon phase or other strangeness - photons are behaving better today, and I achieved higher FWC results for my D3's than I have before. Because of this discrepancy, I am only going to report relative performance between the D3s and D3, instead of giving absolute measurements.

She states the discrepancy was significant enough that she would not report the absolute values.  If the source of the discrepancy could not be identified, it cannot be assumed to be a systematic error, i.e. one which would affect the measurements of the new D3s with similar magnitude and direction as it would the old D3 bodies. 

Inconsistent data, flawed assumptions...bad science.

She has a high standard for what she publishes. Her relative D3s vs D3 results still match DxO's results, and her absolute results are very close as well.

'Black box' methods...bad science.
 
I think we're done here.

Seems we couldn't come to an agreement but I appreciate the discussion.

8
Third Party Manufacturers / Re: DXO uh-oh?
« on: July 27, 2014, 09:03:26 PM »
The margin of error in her D3s measurements were very small; she included them for completeness, and was open about not understanding their source. The variance was small enough to be immaterial to the results.

As for the exact formula DxO uses for their composite scores, I have not seen them published. If you look at the scores for a cross-section of cameras and then relate them to the individual data points DxO publishes (SNR, DR, color selectivity), you can get a general idea of their weighting, but yes, the precise formula is not published. If it were I imagine we would instead be discussing how the weighting unfairly favors one camera over another, which is the natural consequence of any subjective composite score, and why DxO publishes the individual data points for those wanting to look behind the curtain.

9
Third Party Manufacturers / Re: DXO uh-oh?
« on: July 27, 2014, 07:37:47 PM »
as a multi-system user I have to agree with DXO guys, they are honest, much more so than DPR or any other unscientific review sites online.

The problem is that DXO's "science" is in dispute. How can you trust something that produces inconsistent and obviously incorrect results?

Perhaps they should submit their 'science' to the Journal of Irreproducible Results.  They may even be worthy of consideration for an IgNobel Prize.
DxO documents their sensor testing procedure here:
http://www.dxomark.com/About/In-depth-measurements/DxOMark-testing-protocols/Noise-dynamic-range

DxO results have been independently reproduced at various times. For example:
http://www.dpreview.com/forums/post/33806693
http://www.dpreview.com/forums/post/33833501

Your DxO link describes one of their Measurements, which as I've stated on multiple occasions (at least dozens, if not hundreds on these forums) I find generally well done and useful (except when they make errors and deny it, which seems to occur mainly in their lens tests).  The problems are not with their Measurements, but with their Scores.  Can you provide a link where DxO explicitly describes how their Scores are calculated from the Measurements?  No, because they don't disclose the specifics of how those Scores are calculated.  Nor do they explicitly describe the bias inherent in their Scores.
You can read about the methodology of their scores here:
http://www.dxomark.com/About/Sensor-scores

And I describe in detail their low-light score, the score which typically produces the most Canon vs Nikon controversy in online debates:
http://www.dpreview.com/forums/post/41265241

As for your 'independent reproduction,' I clicked your first link but to be honest, I stopped reading after, "For some obscure reason - sunspots or moon phase or other strangeness - photons are behaving better today, and I achieved higher FWC results for my D3's than I have before."  Sorry, but independent verification of poor pseudoscience with worse pseudoscience is even less valid than two wrongs making a right.
She wrote that as tongue 'n cheek, and it actually represents a sign of humility and willingness to be open to contrary points of view, signs of a good engineer/scientist. As for her credentials, if you follow her posts on dpreview you'll see she one of the most informed technical minds for camera sensor info. To cite a specific example, she reverse-engineered Nikon's long-exposure noise algorithm, identified serious problems with it, devised a much improved alternate algorithm which was relayed to Nikon by Thom Hogan and then later adopted by Nikon in subsequent camera designs.

10
Third Party Manufacturers / Re: DXO uh-oh?
« on: July 27, 2014, 05:41:12 PM »
as a multi-system user I have to agree with DXO guys, they are honest, much more so than DPR or any other unscientific review sites online.

The problem is that DXO's "science" is in dispute. How can you trust something that produces inconsistent and obviously incorrect results?

Perhaps they should submit their 'science' to the Journal of Irreproducible Results.  They may even be worthy of consideration for an IgNobel Prize.
DxO documents their sensor testing procedure here:
http://www.dxomark.com/About/In-depth-measurements/DxOMark-testing-protocols/Noise-dynamic-range

DxO results have been independently reproduced at various times. For example:
http://www.dpreview.com/forums/post/33806693
http://www.dpreview.com/forums/post/33833501

11
Third Party Manufacturers / Re: DXO uh-oh?
« on: July 25, 2014, 06:42:45 AM »
This really isn't a surprise. DxO and Nikon are inseparably joined at the hip. Plus, all this really means, particularly the new 14.8 stops Print DR number, is that Nikon is cooking their RAW files EVEN MORE. Nikon/Sony's biggest "cheat" is the fact that they clip to black point, instead of offsetting to black point. Nikon cameras just throw away a lot of low-level signal information. The Sony Exmor sensor gives them more room to do that, for sure, but they are still throwing away information.

Clipping the back point does not affect the DR measurements because DxO's methodology (and other testers whose independent results match DxO's) account for the clipping. Also, Nikon stopped clipping blacks starting with the Sony Exmor in the D5300 (see here: http://www.dpreview.com/forums/post/52493166).

12
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.

13
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).

14
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.

15
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

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