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Author Topic: A7r first impression  (Read 14612 times)
CptZar
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« Reply #100 on: December 10, 2013, 11:08:08 PM »
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Not only does the A7r appear to have lower DR than the D800 at ISO 200 (which in itself is not necessarily a deal-breaker),



Lloyd Chambers doesn't find such behavior in his ISO series. He writes the A7r is on par with the D800. ISO 100 and 200 are hard to distinguish. He calls it a state of the art performance.
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aaykay
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« Reply #101 on: December 11, 2013, 02:17:15 AM »
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Of course I don't prefer unnecessary bulk and weight. I'm not silly. Wink  If I didn't already use a couple of Nikon bodies and a few Nikkor lenses, I'd probably consider the A7r, with Metabones adapter to suit my Canon lenses, a worthwhile upgrade.

Even if the camera wasn't lighter and less bulky, the higher resolution and better DR at low ISOs would make it a worthwhile upgrade to replace any current Canon DSLR, provided the adapter provides full functionality.

However, in my situation, the only advantage I can see is a 400 gm reduction in weight which is offset by the disadvantage of an electronic viewfinder (I don't like them), and a lower DR at the frequently used ISO of 200. I also doubt that there's an adapter that provides full functionality with Nikkor lenses, but I could be wrong.

Agreed, that in your particular situation, where you want to use the A7r with your existing gear, it does not make sense. 

However, from a clean slate perspective, I would have absolutely no trouble in eschewing the big/bulky  DSLR stuff and going with an A7r and the relatively petite lenses that come natively with the mount.
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Ray
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« Reply #102 on: December 11, 2013, 08:33:33 AM »
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Lloyd Chambers doesn't find such behavior in his ISO series. He writes the A7r is on par with the D800. ISO 100 and 200 are hard to distinguish. He calls it a state of the art performance.

I'm not a subscriber to Lloyd's site. Could you be a bit clearer. Do you mean that Lloyd has compared the  DR of the A7r with that of the D800 at ISO 200 and found no difference? There should be no noticeable image quality differences between the two cameras at all other ISOs.

At all ISOs, including ISO 200,  the Color Sensitivity, SNR at 18%, and Tonal Range should be approximately the same for both cameras. It's the DR at ISO 200 which is the anomaly.
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Manoli
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« Reply #103 on: December 11, 2013, 08:51:04 AM »
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I'm not a subscriber to Lloyd's site. Could you be a bit clearer. Do you mean that Lloyd has compared the  DR of the A7r with that of the D800 at ISO 200 and found no difference? There should be no noticeable image quality differences between the two cameras at all other ISOs.

At all ISOs, including ISO 200,  the Color Sensitivity, SNR at 18%, and Tonal Range should be approximately the same for both cameras. It's the DR at ISO 200 which is the anomaly.

If you consider what Iliah says in this thread,  http://www.luminous-landscape.com/forum/index.php?topic=84842.msg687161#msg687161 ,  I would think there would be a difference throughout ( not least due to 13-bit v true 14-bit). Whether or not we would 'see' that difference in print is another question ..
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BJL
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« Reply #104 on: December 11, 2013, 09:15:31 AM »
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I would think there would be a difference throughout ( not least due to 13-bit v true 14-bit). Whether or not we would 'see' that difference in print is another question ..
Once amplified above about ISO 200 or 400, the noise floor of the sensor signal has been raised comfortably above the noise floor of the 13-bit ADC, so I would expect little or no difference at higher ISO speeds. At least this is so if the higher ISO speeds are implemented with sufficient analog gain before ADC rather than just bit shifting.  I think that this is what testing indicates, but if I am wrong, I am sure that someone like Iliah can correct me.

This 13 vs 14 comparison can drift into the realm of the spurious claims that 16-bit ADC gives an IQ advantage over 14-bit ADC in an MF back that has less than 13 stops of engineering DR (and as with all recent sensors, an even smaller photographically useful range.)

Combined with my previous arguments for skepticism about that "outlier" DxO DR measurement at ISO 200, the observations of Lloyd Chambers strengthen case that it is either a measurement error or sample variation. If the latter, this could be an illustration of the hazard of testing only one camera of each model, in contrast to what Roger Cicala at Lens Rentals can offer with his testing of multiple lenses.
« Last Edit: December 11, 2013, 09:19:04 AM by BJL » Logged
ErikKaffehr
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« Reply #105 on: December 11, 2013, 11:48:06 AM »
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Hi,

12, 13 or 14 bits just affects the blacks. Sony uses some compression for the lighter part of the image, but I am quite sure that shot noise, that is natural variation of light arriving at the sensels absolutely dominates over the quantisation error introduced by mapping algorithm.

Best regards
Erik



If you consider what Iliah says in this thread,  http://www.luminous-landscape.com/forum/index.php?topic=84842.msg687161#msg687161 ,  I would think there would be a difference throughout ( not least due to 13-bit v true 14-bit). Whether or not we would 'see' that difference in print is another question ..
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Telecaster
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« Reply #106 on: December 11, 2013, 02:27:39 PM »
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I kept many of my old manual focus lenses as I may be reasonably ruthless in discarding cameras that I no longer need, I am a mug for keeping my glass. And what have I got - a rather large collection of primes including a 200 / 4 and a 300 / 4 plus a 28 - 85 and a 50 - 135 zoom. No extremely heavy or long zooms that marketing departments would have you believe that you not only need but that you aren't complete as a person let alone a photographer without.

Hehe, that's my approach too. An exception was Canon EF lenses...sold most of 'em (when I gave up on the cameras) due to their relatively non-adaptable nature. At the time anyway...no A7(r) or other mirrorless mounts in 2006. Kinda wish I'd kept the 100/2, though, as it made a lovely people-pic lens. My single Big Gun is a Nikkor 400/3.5, which I bought mainly for adapted telescope use...which I haven't gotten around to yet! Makes pretty Moon pics on micro Four-Thirds cameras, though, and with the 2x TC I can just resolve Saturn's coarse ring structure.

I went through a bout of long lens fever c. 2007/8, and ended up mostly with photos where I let the lenses tell me what to do rather than vice versa. It got so bad that I'd try to use a moderate wide lens, say 35mm, and it would look to me in the finder like a fisheye. Ugh... Of course there are people who make the big glass sing. I'm just not one of 'em.

-Dave-
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CptZar
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« Reply #107 on: December 11, 2013, 03:12:21 PM »
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I'm not a subscriber to Lloyd's site. Could you be a bit clearer. Do you mean that Lloyd has compared the  DR of the A7r with that of the D800 at ISO 200 and found no difference? There should be no noticeable image quality differences between the two cameras at all other ISOs.

At all ISOs, including ISO 200,  the Color Sensitivity, SNR at 18%, and Tonal Range should be approximately the same for both cameras. It's the DR at ISO 200 which is the anomaly.

I quote:

"As in the blue crop, ISO 200 is hard to distinguish from ISO 100. Which in practice is highly useful for that extra shutter speed. And it might well be that the Sony 8-bit compression makes ISO 200 truly as good as ISO 100 anyway (low level noise compressed away).

Most striking perhaps is the absence of any significant pattern or streaking noise even at ISO 25600 and even when the individual color channels are examined (including the red channel). In this regard the A7R *blows away* all Canon sensors of any resolution, and appears to be no less good than the Nikon D800E. In context, this is a true state of the art performance and speaks highly of sensor quality in the real world."

By the way...
If the DR of ISO 200 was smaller than at ISO 100 shouldn't the RAW Histogram in RAW Digger reflect that?

Best regards

Jan
« Last Edit: December 11, 2013, 05:12:18 PM by CptZar » Logged

Ray
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« Reply #108 on: December 11, 2013, 06:34:25 PM »
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I quote:

"As in the blue crop, ISO 200 is hard to distinguish from ISO 100. Which in practice is highly useful for that extra shutter speed. And it might well be that the Sony 8-bit compression makes ISO 200 truly as good as ISO 100 anyway (low level noise compressed away).

Most striking perhaps is the absence of any significant pattern or streaking noise even at ISO 25600 and even when the individual color channels are examined (including the red channel). In this regard the A7R *blows away* all Canon sensors of any resolution, and appears to be no less good than the Nikon D800E. In context, this is a true state of the art performance and speaks highly of sensor quality in the real world."

By the way...
If the DR of ISO 200 was smaller than at ISO 100 shouldn't the RAW Histogram in RAW Digger reflect that?

Best regards

Jan


Without a clear description of Lloyd's methodology and the type of images he used for comparison purposes, I'm still none the wiser.

If both cameras at ISO 200 have similar SNR, tonal range and color sensitivity, as well as identical resolution, one would not expect to notice any significant difference in most images compared.
A difference in DR of 0.71 EV would only be noticeable in situations where ideally one needed to bracket exposures to create an HDR image, but was unable to do so for whatever reason, such as lack of a tripod and/or lack of time due to a changing scene.

In such circumstances a choice of ISO 200 might be preferred in order to get an adequate shutter speed for a hand-held shot, in conjunction with a good DoF at a small aperture. If one were using the A7r with an adapter, the circumstances where one would need to use ISO 200 would occur more frequently because one wouldn't have the benefit of image stabilization, even if the attached lens did have that feature.

Now it is certainly possible that DXO have either made a mistake during their testing, or they have accurately tested a faulty, or below-average camera body.

It would be interesting if someone could take the trouble to do a specific DR test at ISO 200, comparing shots of a very contrasty scene, such as the view out of a window on a bright day, exposing for the sky. The quality of the detail in the relatively poorly lit room would be ideal to reveal any DR difference of 0.71 EV, if such a difference exists.
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JimVehe
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« Reply #109 on: December 11, 2013, 07:24:14 PM »
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My experience agrees with Michael. 35 f2 ASPH, 50 f2, 90 f2 APO all work fine.  I have seen some color casts on images with the 18 f3.8 Super Elmar but not all. What diffusion filter are people using with Adobe's DNG Flat field plug-in?
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johnvr
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« Reply #110 on: December 12, 2013, 12:24:48 PM »
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Question for people using the A7r, do you notice jagged edges in your EVF, for example when viewing text or branches against a light background? I do, and I wonder if it's normal or a fault of my camera.

Thanks
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jrp
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« Reply #111 on: December 12, 2013, 01:13:56 PM »
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There is a series of tests here: http://blog.kasson.com/?p=3877 (a series of blog posts)

Fixing with the various plug-ins seems problematic as you need to know which aperture you used.
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chrisgibbs
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« Reply #112 on: December 13, 2013, 12:53:10 PM »
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>You push a totally dark image all the way up, and there is no color bending. It stays absolutely clean. Impossible on the 5DIII which will then always give you color artifacts.<

Good to know, also one of the big plusses of the Nikon D800 sensor over our 5D3's! ~Chris
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photodan
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« Reply #113 on: December 13, 2013, 05:00:17 PM »
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Quote
Question for people using the A7r, do you notice jagged edges in your EVF, for example when viewing text or branches against a light background? I do, and I wonder if it's normal or a fault of my camera.

I have noticed the same thing as have, especially on branches & leaves on trees at a distance.
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