NX200 test shots - lenses, focus, and ISO 400

Started Nov 9, 2011 | Discussions
Andrew Westlake Senior Member • Posts: 2,928
NX200 test shots - lenses, focus, and ISO 400

OK, with the latest round of test shots up, it's time to explain what's been going on.

The first round of shots were taken with the Pentax 50mm F1.4 on the Samsung NX-K mount adapter. The lens was set to F8, but what has become clear is that it was actually stopped down to about F11. This had three consequences:

  1. Longer shutter speeds

  2. Extended depth of field

  3. Very slight softening (mainly visible as loss of contrast) due to diffraction

These gave rise to various erroneous interpretations on these forums:

From 1) it was assumed that the NX200 mis-reported its ISOs, whereas in reality it is, just like pretty well every camera out there, within 1/3 stop of the ISO 12232:2006 SOS spec that's relevant to our testing methods. (Never, of course, to be confused with DxOMark's saturation-based test, which gives different answers.)

From 2) it was assumed the lens was front focused, causing the images to be soft. This was incorrect - the lens was correctly focused, but DOF extended further forward. Most of what people considered to be incorrect focus was simply the result of high ISO noise reduction (noone was ever able to demonstrate an obvious problem with the ISO 100 shot). The addition of RAWs should now make that more clear.

With the new round of shots taken with the NX 60mm macro, we're confident the aperture setting is now correct (F8), and shutter speeds consequently match other cameras to within 1/3 stop at any given ISO. However the longer focal length and larger aperture inevitably combine to reduce DOF compared to the previous set. Most obviously, the Queen of Hearts and corner checkerboards are now just beyond the depth of field, and look slightly soft as a result. There's little we can do about this given the 3D-nature of our test scene.

The ISO 400 shots have been withdrawn because we've identified slight motion blur at the shutter speed used (1/80 sec). The pattern is highly consistent between all of the duplicate shots we took, despite the fact that the camera is (as always) on a heavy studio tripod, with OIS turned off and using the self-timer for release. Note that the blur is so slight you'd never notice it in real-world shots - you can only see it when you place the ISO 200, 400 and 800 shots side-by-side and pixel-peep intensely. It's important to understand that it's unlikely to have any real impact in practical use. However it was clear from comments that it was immediately being massively over-analysed, so we withdrew the shot to avoid confusion.

As for what's causing this blur, our current working theory is that it may be shutter-induced vibration. This would explain why it affects only a narrow range of shutter speeds, and appears pretty consistent in both amplitude and direction from shot to shot. The relatively light bodies and double shutter action (close then open) makes this type of camera theoretically more prone to this effect than either SLRs or compacts (which use in-lens rather than focal plane shutters).

It's not just theory, either; we've seen essentially the same effect previously with the Olympus E-PL3 and E-PM1. However on these cameras it can be mitigated using Olympus's 'Anti-shock' setting, which closes the shutter, waits a specified time, then opens the shutter again to make the exposure. The NX200 has no analogous setting.

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Nikonworks Senior Member • Posts: 2,202
Re: NX200 test shots - lenses, focus, and ISO 400

Thank you for the clarification.

strata83 Contributing Member • Posts: 720
Re: NX200 test shots - lenses, focus, and ISO 400

Thank you for clarification.

I must add that I also have noticed some blurring in my shots taken at the shutter speeds between 1/80 and 1/160. What is more strange is that it appears to affect only one half of the frame.

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Robert N Senior Member • Posts: 2,007
I don't get it.

With the new round of shots taken with the NX 60mm macro, we're confident the > perture setting is now correct (F8), and shutter speeds consequently match other > cameras to within 1/3 stop at any given ISO. However the longer focal length and > larger aperture inevitably combine to reduce DOF compared to the previous set. > Most obviously, the Queen of Hearts and corner checkerboards are now just beyond > the depth of field, and look slightly soft as a result. There's little we can do about > this given the 3D-nature of our test scene.

Isn't the focal length completely irrelevant as long as the magnification (framing of the scene) and the aperture is the same?

BTW: Thanks for your efforts!

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OP Andrew Westlake Senior Member • Posts: 2,928
Re: I don't get it.

Robert N wrote:

Isn't the focal length completely irrelevant as long as the magnification (framing of the scene) and the aperture is the same?

Not quite; the DOF/magnification thing is an approximation (although a pretty good one). But it's important to understand that there's there a key conceptual difference between depth of field (i.e. which regions of the scene front-to-back fall within a certain standard for sharpness) and the appearance of background blur (essentially definable by the diameter of the blur circle from an out-of focus point light source). The latter increases with longer lenses - so if you do the classic demo of shooting a portrait at 35mm and 135mm using the same subject magnification and aperture, the latter will have a visibly more-blurred background despite DOF being near-identical. Much the same potentially happens here - the effect isn't going to be huge, but then again the blur of the QoH isn't huge either (indeed by normal print standards the card is within DOF).

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Ariston Senior Member • Posts: 2,401
Re: NX200 test shots - lenses, focus, and ISO 400

Andy Westlake wrote:

OK, with the latest round of test shots up, it's time to explain what's been going on.

The first round of shots were taken with the Pentax 50mm F1.4 on the Samsung NX-K mount adapter. The lens was set to F8, but what has become clear is that it was actually stopped down to about F11. This had three consequences:

  1. Longer shutter speeds

  2. Extended depth of field

  3. Very slight softening (mainly visible as loss of contrast) due to diffraction

These gave rise to various erroneous interpretations on these forums:

From 1) it was assumed that the NX200 mis-reported its ISOs, whereas in reality it is, just like pretty well every camera out there, within 1/3 stop of the ISO 12232:2006 SOS spec that's relevant to our testing methods. (Never, of course, to be confused with DxOMark's saturation-based test, which gives different answers.)

From 2) it was assumed the lens was front focused, causing the images to be soft. This was incorrect - the lens was correctly focused, but DOF extended further forward. Most of what people considered to be incorrect focus was simply the result of high ISO noise reduction (noone was ever able to demonstrate an obvious problem with the ISO 100 shot). The addition of RAWs should now make that more clear.

With the new round of shots taken with the NX 60mm macro, we're confident the aperture setting is now correct (F8), and shutter speeds consequently match other cameras to within 1/3 stop at any given ISO. However the longer focal length and larger aperture inevitably combine to reduce DOF compared to the previous set. Most obviously, the Queen of Hearts and corner checkerboards are now just beyond the depth of field, and look slightly soft as a result. There's little we can do about this given the 3D-nature of our test scene.

The ISO 400 shots have been withdrawn because we've identified slight motion blur at the shutter speed used (1/80 sec). The pattern is highly consistent between all of the duplicate shots we took, despite the fact that the camera is (as always) on a heavy studio tripod, with OIS turned off and using the self-timer for release. Note that the blur is so slight you'd never notice it in real-world shots - you can only see it when you place the ISO 200, 400 and 800 shots side-by-side and pixel-peep intensely. It's important to understand that it's unlikely to have any real impact in practical use. However it was clear from comments that it was immediately being massively over-analysed, so we withdrew the shot to avoid confusion.

As for what's causing this blur, our current working theory is that it may be shutter-induced vibration. This would explain why it affects only a narrow range of shutter speeds, and appears pretty consistent in both amplitude and direction from shot to shot. The relatively light bodies and double shutter action (close then open) makes this type of camera theoretically more prone to this effect than either SLRs or compacts (which use in-lens rather than focal plane shutters).

It's not just theory, either; we've seen essentially the same effect previously with the Olympus E-PL3 and E-PM1. However on these cameras it can be mitigated using Olympus's 'Anti-shock' setting, which closes the shutter, waits a specified time, then opens the shutter again to make the exposure. The NX200 has no analogous setting.

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Andy Westlake
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thank you for this Andy. atleast everything is clear now. with regards to camera blur, I believe the only way to overcome this probably is either to shoot at faster shutterspeed (1/200 atleast) or activate OSS in some lenses. on an interesting note, since the shutter could be causing such vibration, maybe the OSS could had helped on the tripod setup? will you consider experimenting on this? considering you got the 60mm with OSS function?

Billx08 Forum Pro • Posts: 11,373
NX200 test shots - lenses, focus, and ISO 400, part 1 of 2

Andy Westlake wrote:

OK, with the latest round of test shots up, it's time to explain what's been going on.

The first round of shots were taken with the Pentax 50mm F1.4 on the Samsung NX-K mount adapter. The lens was set to F8, but what has become clear is that it was actually stopped down to about F11. This had three consequences:

  1. Longer shutter speeds

  2. Extended depth of field

  3. Very slight softening (mainly visible as loss of contrast) due to diffraction

These gave rise to various erroneous interpretations on these forums:

From 1) it was assumed that the NX200 mis-reported its ISOs, whereas in reality it is, just like pretty well every camera out there, within 1/3 stop of the ISO 12232:2006 SOS spec that's relevant to our testing methods. (Never, of course, to be confused with DxOMark's saturation-based test, which gives different answers.)

No, not everyone assumed that the ISOs were mis-reported. I've already written that based on the very large difference in the reported shutter speeds in the ISO 100 photos, that the aperture must have been smaller than f/8. It would have been more accurate to write "From 1) some of you assumed that the NX200 mis-reported its ISOs"

From 2) it was assumed the lens was front focused, causing the images to be soft. This was incorrect - the lens was correctly focused, but DOF extended further forward. Most of what people considered to be incorrect focus was simply the result of high ISO noise reduction (noone was ever able to demonstrate an obvious problem with the ISO 100 shot). The addition of RAWs should now make that more clear.

No again. From the comparison crops that I previously posted, the NX200 photo is front focused, irrespective of any greater DoF due to the smaller aperture. The two photos that I posted showed the comparisons where the selected locations (top right corner - most distant from the camera, and bottom left - closest to the camera) show much more detail in the NX200 sample, more than what I think would arise from using f/11 instead of f/8. But even so, if the NX200 photo was not front focused, and the greater DoF explains all, then similar results should have been seen in the top right corner crops, but here the NX100 did much better than the NX200, which did pretty poorly, about as blurred as the NEX-5N. Assuming that the NEX-5N was properly focused, this would be consistent with the NX200 being front focused and its greater DoF (due to f/11 being used) making its image comparable to what the NEX-5N produced. When I posted the comparison crops I included links to the studio comparisons so that others could see for themselves, but now that the original NX200 studio photos have been removed from the database and where the NX200 image would have appeared, all that now shows is "No sample", and the images from the NX100, NEX-5N and E-PL3 show nothing at all. I can understand how coding peculiarities might have produced this result, but it seems like it would have been better if all of the crops that could   be shown were   shown. Here is what I previously posted, including the now useless links :

http://www.dpreview.com/reviews/studiocompare.asp#baseDir=%2Freviews_data&cameraDataSubdir=boxshot&indexFileName=boxshotindex.xml&presetsFileName=boxshotpresets.xml&showDescriptions=false&headerTitle=Studio%20scene&headerSubTitle=Standard%20studio%20scene%20comparison&masterCamera=samsung_nx200&masterSample=sam_7087&slotsCount=4&slot0Camera=samsung_nx200&slot0Sample=sam_7087&slot0DisableCameraSelection=true&slot0DisableSampleSelection=true&slot0LinkWithMaster=true&slot1Camera=samsung_nx100&slot1Sample=sam_0166&slot2Camera=sony_nex5n&slot2Sample=dsc00774&slot3Camera=oly_epl3&slot3Sample=p8100509&x=1.017828200972447&y=1.703045685279188

http://www.dpreview.com/reviews/studiocompare.asp#baseDir=%2Freviews_data&cameraDataSubdir=boxshot&indexFileName=boxshotindex.xml&presetsFileName=boxshotpresets.xml&showDescriptions=false&headerTitle=Studio%20scene&headerSubTitle=Standard%20studio%20scene%20comparison&masterCamera=samsung_nx200&masterSample=sam_7087&slotsCount=4&slot0Camera=samsung_nx200&slot0Sample=sam_7087&slot0DisableCameraSelection=true&slot0DisableSampleSelection=true&slot0LinkWithMaster=true&slot1Camera=samsung_nx100&slot1Sample=sam_0166&slot2Camera=sony_nex5n&slot2Sample=dsc00774&slot3Camera=oly_epl3&slot3Sample=p8100509&x=-0.35714931250403464&y=-1.7851722758741508

Billx08 Forum Pro • Posts: 11,373
Re: NX200 test shots - lenses, focus, and ISO 400, part 2 of 2

(continued)

With the new round of shots taken with the NX 60mm macro, we're confident the aperture setting is now correct (F8), and shutter speeds consequently match other cameras to within 1/3 stop at any given ISO. However the longer focal length and larger aperture inevitably combine to reduce DOF compared to the previous set. Most obviously, the Queen of Hearts and corner checkerboards are now just beyond the depth of field, and look slightly soft as a result. There's little we can do about this given the 3D-nature of our test scene.

Thanks for pointing this out. I didn't see cues (or clues) that would have made it obvious that the Queen of Hearts is positioned so far in the background, and to my eyes (the same ones that are more sensitive to brightness differences) it appeared not to be "slightly soft" but grossly soft.

The ISO 400 shots have been withdrawn because we've identified slight motion blur at the shutter speed used (1/80 sec). The pattern is highly consistent between all of the duplicate shots we took, despite the fact that the camera is (as always) on a heavy studio tripod, with OIS turned off and using the self-timer for release. Note that the blur is so slight you'd never notice it in real-world shots - you can only see it when you place the ISO 200, 400 and 800 shots side-by-side and pixel-peep intensely. It's important to understand that it's unlikely to have any real impact in practical use. However it was clear from comments that it was immediately being massively over-analysed, so we withdrew the shot to avoid confusion.

I never saw these motion blurred photos and think that it would be useful if DPR would make these available somewhere (with an appropriate disclaimer) so that the "pixel-peepers" might be able to judge for themselves whether the blur is so noticeable that it causes massive over-analysis (which I also haven't seen) or so unnoticeable that it would never be noticed in real-world shots.

As for what's causing this blur, our current working theory is that it may be shutter-induced vibration. This would explain why it affects only a narrow range of shutter speeds, and appears pretty consistent in both amplitude and direction from shot to shot. The relatively light bodies and double shutter action (close then open) makes this type of camera theoretically more prone to this effect than either SLRs or compacts (which use in-lens rather than focal plane shutters).

It's not just theory, either; we've seen essentially the same effect previously with the Olympus E-PL3 and E-PM1. However on these cameras it can be mitigated using Olympus's 'Anti-shock' setting, which closes the shutter, waits a specified time, then opens the shutter again to make the exposure. The NX200 has no analogous setting.

If your theory is correct, and I assume that it is, then do you think that the only practical way to fix or minimize it would be for a firmware upgrade to add a similar "Anti-shock" setting, assuming that a firmware fix could work? Also, how wide is the range of the affected shutter speeds? DPR didn't pull the ISO 200 or ISO 800 comparison images, so either the increased blurring didn't extend to 1/40th or 1/160th, or if it did, the blur was sufficiently attenuated to be much less noticeable. The NX100 has five shutter speeds that lie between 1/40 and 1/160 so I'd guess that the NX200 also can use these shutter speeds. If so, it would be nice if current NX200 users (there are a few) know whether they should try to avoid 1/50 - 1/125, 1/60 - 1/100, or just 1/80.

OP Andrew Westlake Senior Member • Posts: 2,928
Re: NX200 test shots - lenses, focus, and ISO 400

Ariston wrote:

with regards to camera blur, I believe the only way to overcome this probably is either to shoot at faster shutterspeed (1/200 atleast) or activate OSS in some lenses.

We can't shoot at faster shutter speeds without using a larger aperture, which will give insufficient depth of field. Turning on image stabilisation on a tripod opens up a whole can of worms - we'd much rather not go there. However what we can do is shoot at a slower shutter speed by reducing the scene illumination, so that's looking like the most likely solution at the moment.

(To pre-empt the idea that noise is dependent on light level and shutter speed, and this would skew the results, this isn't really true. The reason why it's often believed to be true is because the visibility of noise is highly dependent upon the colour temperature of the light source, and low light levels are strongly associated with low-colour temperature artificial light. However the higher noise in images shot under such lighting isn't because of the light level per se , but because the blue and green channels have to be amplified much further to achieve correct white balance.)
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OP Andrew Westlake Senior Member • Posts: 2,928
Top corners as proxy for focus, and curvature of field

Billx08 wrote:

From the comparison crops that I previously posted, the NX200 photo is front focused, irrespective of any greater DoF due to the smaller aperture. The two photos that I posted showed the comparisons where the selected locations (top right corner - most distant from the camera...)

Sadly, your use of the top corners as a proxy for focus falls foul of a not-entirely-obvious issue - that of curvature of field. It's been apparent to us from the start of shooting this scene that those regions are highly variable in sharpness, indeed far more than would be expected. What we also know is that if you compare different lenses on the same camera, those regions vary far more than any other. The obvious conclusion is that curvature of field is confounding the results here, so we don't pay any attention to them. The pertinent point to note is then that the NX200 was originally shot with the Pentax 50mm F1.4, whereas the NX100 used the Pentax 50mm F2.8 macro, which unsurprisingly is better-corrected for flatness of field. So your observations, while initially persuasive, aren't entirely correct.

If you want to compare focus, use the angled ruler at the lower center of the frame; it's a far better indicator.

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Andy Westlake
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OP Andrew Westlake Senior Member • Posts: 2,928
Re: NX200 test shots - lenses, focus, and ISO 400, part 2 of 2

Billx08 wrote:

Thanks for pointing this out. I didn't see cues (or clues) that would have made it obvious that the Queen of Hearts is positioned so far in the background, and to my eyes (the same ones that are more sensitive to brightness differences) it appeared not to be "slightly soft" but grossly soft.

That is, of course, a matter of language, and how one chooses to interpret pixel-level sharpness on a high pixel count sensor compared to looking at the image as a whole (which provides more context).

If your theory is correct, and I assume that it is, then do you think that the only practical way to fix or minimize it would be for a firmware upgrade to add a similar "Anti-shock" setting, assuming that a firmware fix could work? ... it would be nice if current NX200 users (there are a few) know whether they should try to avoid 1/50 - 1/125, 1/60 - 1/100, or just 1/80.

As I made absolutely clear in my first post, I don't think you'll ever see this blur as a problem in real-world shots (we've shot the camera extensively outside the studio and never identified it), so there's no obvious need for NX200 owners to avoid any shutter speeds at all. It's visible in our test shots because they have extremely fine high contrast detail such as the coins on the Martini bottle, and (slightly ironically) because they're shot under such controlled conditions, and scrutinised so closely, that any slight discrepency in sharpness gets blown out of all proportion.

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Fred Briggs
Fred Briggs Senior Member • Posts: 1,023
Re: Top corners as proxy for focus, and curvature of field

Andy ,

Thanks for all the work on this and the very useful explanations of the issues. Looks like the shutter flutter or whatever it is could be a design problem which would be a shame as the camera looks quite promising.

Regarding focus accuracy, would you consider putting up a picture of the test scene taken from above so that people can better appreciate the depth of field/field curvature issues which many are mistaking for out of focus problems?

Fred

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Ariston Senior Member • Posts: 2,401
Re: NX200 test shots - lenses, focus, and ISO 400

Andy Westlake wrote:

We can't shoot at faster shutter speeds without using a larger aperture, which will give insufficient depth of field. Turning on image stabilisation on a tripod opens up a whole can of worms - we'd much rather not go there. However what we can do is shoot at a slower shutter speed by reducing the scene illumination, so that's looking like the most likely solution at the moment.

I understand and thank you for that. although if ever dpreview decides in the future just for the sake of sharing or as a sidenote if you observe that OSS helps a lot on a tripod setup, it would be greatly appreciated for any info. I don't have the 60mm OSS lens and can't test it, so I can't comment on the issue on the matter on how it would affect the image.

also, considering that dpreview does lens review as well, you might want to consider including that area (OSS) as well. if it does help a lot when doing handheld and as well as mounted on a tripod.

(To pre-empt the idea that noise is dependent on light level and shutter speed, and this would skew the results, this isn't really true. The reason why it's often believed to be true is because the visibility of noise is highly dependent upon the colour temperature of the light source, and low light levels are strongly associated with low-colour temperature artificial light. However the higher noise in images shot under such lighting isn't because of the light level per se , but because the blue and green channels have to be amplified much further to achieve correct white balance.)

I don't argue with this.

Billx08 Forum Pro • Posts: 11,373
Re: NX200 test shots - lenses, focus, and ISO 400, part 2 of 2

Andy Westlake wrote:
. . .

If your theory is correct, and I assume that it is, then do you think that the only practical way to fix or minimize it would be for a firmware upgrade to add a similar "Anti-shock" setting, assuming that a firmware fix could work? ... it would be nice if current NX200 users (there are a few) know whether they should try to avoid 1/50 - 1/125, 1/60 - 1/100, or just 1/80.

As I made absolutely clear in my first post, I don't think you'll ever see this blur as a problem in real-world shots (we've shot the camera extensively outside the studio and never identified it), so there's no obvious need for NX200 owners to avoid any shutter speeds at all. It's visible in our test shots because they have extremely fine high contrast detail such as the coins on the Martini bottle, and (slightly ironically) because they're shot under such controlled conditions, and scrutinised so closely, that any slight discrepency in sharpness gets blown out of all proportion.

I agree, that in "real-world" shots most photographers probably wouldn't see any differences. But some of those real world shots might be taken by demanding landscape photographers using the same 60mm lens or one of the wide angle pancake primes, also using good tripods, and some of them through many years of experience are able to see minute flaws that would escape the notice of most other photographers (think Thom). So I still think it would be reasonable to tell us what you've discovered about the effects of shutter speeds, including reiterating how insignificant the problem actually is. If people will blow that out of proportion, what of it? Isn't that the normal state of affairs in the forums?

Identity Senior Member • Posts: 1,065
Re: NX200 test shots - lenses, focus, and ISO 400, part 2 of 2

Andy Westlake wrote:

As I made absolutely clear in my first post, I don't think you'll ever see this blur as a problem in real-world shots (we've shot the camera extensively outside the studio and never identified it), so there's no obvious need for NX200 owners to avoid any shutter speeds at all. It's visible in our test shots because they have extremely fine high contrast detail such as the coins on the Martini bottle, and (slightly ironically) because they're shot under such controlled conditions, and scrutinised so closely, that any slight discrepency in sharpness gets blown out of all proportion.

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Andy Westlake
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I wonder if the rigid studio tripod mount is actually contributing to the shutter shake? When handheld, or on an el-cheapo tripod like I have, the vibrations may actually be damped because the entire camera body is free to move slightly.

Have you guys ever had to put so much effort in to getting a good consistent set of test shots as this NX200?

OP Andrew Westlake Senior Member • Posts: 2,928
ISO 400 crops - 1/80sec blur

Just to illustrate the issue we encountered with our ISO 400 shots, here are the relevant image crops (I'm not going to post the full image). Left to right is ISO 200, 400, 800 (1/40, 1/80, 1/160 sec respectively), top row is jpeg, bottom row is raw.

In the raw file especially, ISO400 is anomalously soft - but you'd probably not notice this outside of these highly-controlled tests. Do bear in mind we're staring at 100% crops out of a 20MP files here - these crops are a tiny fraction of the full image area. If you move a couple of meters/yards back from your screen to simulate more sensible viewing conditions, you'll see no difference at all.

We see similar blur in all our studio shots taken at 1/80 sec when we stare at them this closely, but as yet haven't investigated any further.

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Ariston Senior Member • Posts: 2,401
Re: ISO 400 crops - 1/80sec blur

Andy Westlake wrote:

Just to illustrate the issue we encountered with our ISO 400 shots, here are the relevant image crops (I'm not going to post the full image). Left to right is ISO 200, 400, 800 (1/40, 1/80, 1/160 sec respectively), top row is jpeg, bottom row is raw.

In the raw file especially, ISO400 is anomalously soft - but you'd probably not notice this outside of these highly-controlled tests. Do bear in mind we're staring at 100% crops out of a 20MP files here - these crops are a tiny fraction of the full image area.

We see similar blur in all our studio shots taken at 1/80 sec when we stare at them this closely, but as yet haven't investigated any further.

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Andy Westlake
dpreview.com

what is odd is the one taken at the lowest ISO (200) is sharper despite having the slowest shutter speed. could it be the camera is counteracting with the steadiness of the tripod setup? or a bug somewhere between the camera firmware associated with the OSS lens? or the lens needs a firmware update.

OP Andrew Westlake Senior Member • Posts: 2,928
Re: ISO 400 crops - 1/80sec blur

Ariston wrote:

what is odd is the one taken at the lowest ISO (200) is sharper despite having the slowest shutter speed.

This isn't particularly odd - it's analogous to what happens with mirror slap-induced blur on SLRs. You only see blurring across a narrow range of shutter speeds, because the vibration quickly dampens out. So at slower shutter speeds, while the vibration is still occurring, it's across a relatively small proportion of the overall exposure and doesn't visibly affect the image.

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Billx08 Forum Pro • Posts: 11,373
The tale told by the angled ruler

Andy Westlake wrote:

Billx08 wrote:

From the comparison crops that I previously posted, the NX200 photo is front focused, irrespective of any greater DoF due to the smaller aperture. The two photos that I posted showed the comparisons where the selected locations (top right corner - most distant from the camera...)

Sadly, your use of the top corners as a proxy for focus falls foul of a not-entirely-obvious issue - that of curvature of field. It's been apparent to us from the start of shooting this scene that those regions are highly variable in sharpness, indeed far more than would be expected. What we also know is that if you compare different lenses on the same camera, those regions vary far more than any other. The obvious conclusion is that curvature of field is confounding the results here, so we don't pay any attention to them. The pertinent point to note is then that the NX200 was originally shot with the Pentax 50mm F1.4, whereas the NX100 used the Pentax 50mm F2.8 macro, which unsurprisingly is better-corrected for flatness of field. So your observations, while initially persuasive, aren't entirely correct.

It probably escaped your notice, but I previously wrote that Samsung's 60mm macro should provide better results with the NX200 due to its flatter field.

If you want to compare focus, use the angled ruler at the lower center of the frame; it's a far better indicator.

I did just now, and thanks for the suggestion. Doing my pixel-peeping best examining the top of the ruler I couldn't see any difference between the initial NX200 ISO 100 photo and the revised ISO 100 photo, so I thought that perhaps you were right all along, that the earlier NX200 photo was properly focused. But when I looked at the bottom of the ruler in the photo that I fortunately downloaded, it was really obvious that the earlier photo shot with the Pentax 50mm f/1.4 was front focused because the bottom of the ruler was very sharp, and the bottom of the ruler shot with Samsung's 60mm macro lens is so soft that you can hardly notice the lines at all, softer than I think could be attributable to only the 60mm len's smaller DoF. Unfortunately more worms are spilling out of the can because using the ruler as a guide, the PEN E-PL3 appears to be very strongly back focused, so perhaps this can of worms should be set aside before your testing schedule gets thoroughly disrupted.

Laurie899 Regular Member • Posts: 150
Re: NX200 test shots - lenses, focus, and ISO 400

Andy thanks for the time and effort in clarifying and educating - much appreciated.
Are you able to say when the in-depth review willl be published.

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Samsung NX20 Samsung NX 18-55mm F3.5-5.6 OIS Samsung NX 50-200mm F4-5.6 OIS Samsung NX 12-24mm F4-5.6 ED Fujifilm XC 16-50mm F3.5-5.6 OIS
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