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Author Topic: 1Ds MKIII and Optical Low Pass filtering  (Read 149883 times)

John Sheehy

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1Ds MKIII and Optical Low Pass filtering
« Reply #100 on: October 26, 2007, 05:46:53 pm »

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Yep, I've got over $40,000 invested in Canon bodies and lenses, over $35,000 invested in Nikon and Kodak lenses and bodies and about $5,000 invested in Sigma so I have a huge economic investment in Sigma.

I wrote, "You have some kind of psychological or economic stake in the Sigma camera ...".  Do you know what the word "or" means, and how it is different from the word "and"?

The psychological part was the part I was leaning towards.  A psychological investment does not necessarily parallel an economic one.  A psychological one could simply be a need to identify with something perceived as the under-dog, non-mainstream, or something like an ego thing relating to the questioning of your perceptual faculty.

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I use what works and I know what my images look like. You see "aliasing" everywhere you look. Fully half your posts on dPReview involve some discussion of aliasing and about 100% of your post concerning Sigma/Foveon concern your obsession with trying to convince people of the poor performance of the Sigma cameras. I'm not the one writing "ridiculous things" John, look in the mirror.

I am just trying to bring some honesty into the the threads where aliased photography is praised.  I'd hate to see someone rush out and buy an aliasing camera and a cache of proprietary lenses because of fanatical claims, and then find out they don't like it.  A person has a chance of listening to claims like yours, and my objections, and look closer to see if what I am saying is true or objectionable to them.  Not everyone likes mortar that disappears and reappears in different parts of walls, or the edges of roof tiles that come and go due to luck of alignment, or natural textures that should have equal angles of opportunity being emphasized horizontally and vertically.  They may not start noticing these things until after they have made an investment.  And there are lots of folks who had Sigmas and could deal with the aliasing; if you don't remember those posts, then your memory is very selective.

IMO, people who see aliasing as image detail are living in a state of ignorant bliss.  Are they lucky that they're not bothered?  I don't know ... but I suspect that if they can't notice that points and edges are in the wrong places or inconsistently present at all, they can't be fully appreciating what I know of as Reality; they're just satisfying a need to feel like they have succeeded in focusing on the print or screen.

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Nasty "aliasing" yep, that's your subjective opinion. It's not shared by the majority. In fact the "majority" of people listening to your constant obsessive/compulsive rhetoric about aliasing whom I've had conversations with think you are trolling the majority of the time.

And who do you converse with?  Other fanatics.

I doubt that any more than a small minority of people who read my posts think I'm a troll, and I'm not a troll, because I say what I really think; not what I think will stir people up as an end in itself.  

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You're all talk and no show, John.

Show what?  Did I ever say, "Lin, my pictures are better than yours"?  It's just like you to shift contexts to create illusions.  I've said times before, that a camera is capable of taking great photographs despite artifacts.  AOTBE, however, I don't want aliased capture.

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You talk the talk but you don't walk the walk.

What walk did I claim to be doing but am not?  Again, you are trying to create illusions.  You are coming across as a megalomaniac who thinks that he can bend reality through his mighty implications.

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Were are your superior samples of CFA images with no aliasing. Where are your comparison shots of Foveon and CFA images? Were are "any" images you've taken?????

None of your business, and that is irrelevant.  Again, you are trying to create an illusion; the illusion that we are having a photo competition, when in fact, I was only talking about aliasing and resolution.

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I'll give you this, you really do like to talk - LOL
[a href=\"index.php?act=findpost&pid=148661\"][{POST_SNAPBACK}][/a]

I do like to write - about things that I have taken a special interest in.
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Ray

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1Ds MKIII and Optical Low Pass filtering
« Reply #101 on: October 27, 2007, 02:15:10 am »

It's such a pity that Lin seems to have taken offense at what is merely a bit of robust criticism.

I actually quite admire the Foveon system. In my view, that's what a pixel should be, a composite of a red, green and blue element. I was quite dismayed when I first learned that most digital cameras have to interpolate the other 2 colors from surrounding values. I thought that was sort of cheating   .

Unfortunately, all systems have their weaknesses and I guess Foveon's is the absorption of the blue and red light that takes place as it passes through the layer(s) of silicon above. Without some technological breakthroughs I would guess that a 10mp sensor would be too noisy in the red and blue channels, unless the sensor size were increased. A 12mp full frame 35mm Foveon sensor might be viable though.
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Graeme Nattress

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« Reply #102 on: October 27, 2007, 09:24:12 am »

The advantages of the Foveon (and clever it is) are the co-sited nature of the components, so no interpolation is needed to figure what's going on where. The disadvantage is that silicon is used as a colour filter, silicon is  not a terribly good colour filter. That leads to issues with noise, which is a shame.

Foveon does not have the advantage that it does not require an OLPF, which is how Sigma configure their Foveon cameras. Foveon themselves in their white papers state quite clearly that their Foveon sensor still requires an OLPF.

Graeme
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bjanes

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1Ds MKIII and Optical Low Pass filtering
« Reply #103 on: October 27, 2007, 10:14:14 am »

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Foveon does not have the advantage that it does not require an OLPF, which is how Sigma configure their Foveon cameras. Foveon themselves in their white papers state quite clearly that their Foveon sensor still requires an OLPF.
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Aliasing can be nasty, especially when it produces colored moiré patterns with Bayer pattern sensors. Fortunately for Sigma, the moiré with their sensor is monochrome.

Whether or not aliasing is readily visible depends on the nature of the subject. It is quite visible with regularly repeating patterns near the frequency of the sensor grid, such as fabrics or the tiles on a roof. Most naturally occurring objects such as landscapes do not have such patterns. An exception is feathers photographed close up.

The Nikon D70 has a weak OLPF and in my personal experience, I have never noted moiré in landscapes, but it has ruined some family pictures where strong moiré appeared in fabrics. The D200 has a weaker OLPF and moiré is less of a problem, but more sharpening is required.

The best sharpening algorithm for images degraded by OLPF is of interest. Bruce Fraser used unsharp masking with the radius selected according to the resolution of the sensor and the amount according to the strength of the filter.  Jonathan Wienke has been experimenting with a deconvolution algorithm rather than unsharp masking and has reported good results. Comments on this matter are welcome.

Bill
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John Sheehy

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1Ds MKIII and Optical Low Pass filtering
« Reply #104 on: October 27, 2007, 09:33:06 pm »

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Aliasing can be nasty, especially when it produces colored moiré patterns with Bayer pattern sensors. Fortunately for Sigma, the moiré with their sensor is monochrome.

It is possible to get moire that is colored, however.  the difference is, true color moire can occur with B&W subjects.  An LCD color display, shot at pixel-pitch-to-dot-pitch ratios near unity will result in color artifacts not directly representative of the subject as well, although they will not look as bizarre as when they are demosaiced from a CFA:



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Whether or not aliasing is readily visible depends on the nature of the subject. It is quite visible with regularly repeating patterns near the frequency of the sensor grid, such as fabrics or the tiles on a roof. Most naturally occurring objects such as landscapes do not have such patterns. An exception is feathers photographed close up.
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I think it varies greatly with the viewer, too, and this, perhaps, is the reason why people feel so differently about aliasing.  I can see aliasing in totally randomly-arranged subject lines and textures.  I can see it quite clearly, even in sand.  I see it as a propensity for things to line up and snap to a grid, and it looks very unnatural to me.  I don't even have great eyesight; it's a brain-thing, IMO.  My brain sees the weightedness of points and edges of light and dark, and sees them as artifically distributed.  The "sharpness" of aliased imaging is about as useful to my brain as looking at an analog image through a sheet of glass with little magnifying glasses in rows and colums that show you only the center of the dots, but fill them out.  Sharper transitions, but more erroneous representations of the areas.

Another problem with aliased capture, especially with aliased capture at low pixel resolutions, is that the captured image is very fragile in terms of freedom of resampling; you can not properly resample the low-res, aliased image at ratios like 60 to 80%  or 120% to 170% and keep any of that content (real or fake) near the nyquist.  It's re-distributed at lower frequencies, whereas, with a pixel-softer but higher-MP image, you have much greater flexibility as you are not smearing and redistributing anything at the original nyquist, because there is almost nothing there.  One option is to use nearest neighbor, as that always maintains or increases pixel contrast in the result in randomly distributed subjects, but that results in even more aliasing, and this time, snap to left, snap to right, snap up, and snap-down to the new grid, depending on column and row in the original, as opposed to just snapping symmetrically in the original capture.
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Ray

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1Ds MKIII and Optical Low Pass filtering
« Reply #105 on: October 28, 2007, 01:03:42 am »

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Another problem with aliased capture, especially with aliased capture at low pixel resolutions, is that the captured image is very fragile in terms of freedom of resampling; you can not properly resample the low-res, aliased image at ratios like 60 to 80%  or 120% to 170% and keep any of that content (real or fake) near the nyquist.  It's re-distributed at lower frequencies, whereas, with a pixel-softer but higher-MP image, you have much greater flexibility as you are not smearing and redistributing anything at the original nyquist, because there is almost nothing there.  One option is to use nearest neighbor, as that always maintains or increases pixel contrast in the result in randomly distributed subjects, but that results in even more aliasing, and this time, snap to left, snap to right, snap up, and snap-down to the new grid, depending on column and row in the original, as opposed to just snapping symmetrically in the original capture.
[a href=\"index.php?act=findpost&pid=149103\"][{POST_SNAPBACK}][/a]

John,
That all sounds very nasty. One wonders how those very demanding MFDB users cope with all these problems. I think the pixel density of a 22mp digital back is no greater than that of the SD14 and I'm getting the impression that aliasing from Bayer type sensors that don't have an AA filter could be worse than aliasing from Foveon type sensors, at least with regard to color.
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Jonathan Wienke

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1Ds MKIII and Optical Low Pass filtering
« Reply #106 on: October 28, 2007, 02:18:01 pm »

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Another problem with aliased capture, especially with aliased capture at low pixel resolutions, is that the captured image is very fragile in terms of freedom of resampling; you can not properly resample the low-res, aliased image at ratios like 60 to 80%  or 120% to 170% and keep any of that content (real or fake) near the nyquist.  It's re-distributed at lower frequencies, whereas, with a pixel-softer but higher-MP image, you have much greater flexibility as you are not smearing and redistributing anything at the original nyquist, because there is almost nothing there.

Capturing at a high enough sampling rate that there is little near-Nyquist signal is a good way to increase the fidelity of a sampled waveform. Witness the growing popularity of 48-96KHz sample rates in digital audio as an example. Even though 44.1KHz is technically enough to capture up to 20KHz without aliasing, the fidelity of the recording suffers as you approach Nyquist. I use this principle when stitching panoramas; I upsize the source images to the largest ACR output dimensions before feeding them to the stitcher program to be bent, folded, spindled, and mutilated. The stretching and warping inherent to stitching is less destructive to the images as a result, and it is possible to make alignment adjustments <1 pixel (relative to the original resolution) when specifying anchor points and making any manual alignment adjustments after stitching (I always output to a layered PSD file so I can manually align and blend the layers together).
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John Sheehy

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« Reply #107 on: October 28, 2007, 09:47:14 pm »

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Capturing at a high enough sampling rate that there is little near-Nyquist signal is a good way to increase the fidelity of a sampled waveform. Witness the growing popularity of 48-96KHz sample rates in digital audio as an example. Even though 44.1KHz is technically enough to capture up to 20KHz without aliasing, the fidelity of the recording suffers as you approach Nyquist.

Frequencies near the nyquist, and near fractions like 3/5, 2/3, 4/5, and 3/4 of the nyquist suffer amplitude problems, and a sampled frequency sweep near these values results in periodic amplitude modulation.  The things the don't tell you in basic sampling theory.

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I use this principle when stitching panoramas; I upsize the source images to the largest ACR output dimensions before feeding them to the stitcher program to be bent, folded, spindled, and mutilated. The stretching and warping inherent to stitching is less destructive to the images as a result, and it is possible to make alignment adjustments <1 pixel (relative to the original resolution) when specifying anchor points and making any manual alignment adjustments after stitching (I always output to a layered PSD file so I can manually align and blend the layers together).
[a href=\"index.php?act=findpost&pid=149195\"][{POST_SNAPBACK}][/a]

Same goes for rotation, perspective correction, CA correction, lens correction, etc, etc.  While not quite the same thing as originally sampling at a higher rate, I like to upsample images before doing these things (if not already oversampled), to reduce the damage.
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EricV

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1Ds MKIII and Optical Low Pass filtering
« Reply #108 on: October 29, 2007, 01:41:05 pm »

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I can see aliasing in totally randomly-arranged subject lines and textures.  I can see it quite clearly, even in sand.  I see it as a propensity for things to line up and snap to a grid, and it looks very unnatural to me.  I don't even have great eyesight; it's a brain-thing, IMO.  My brain sees the weightedness of points and edges of light and dark, and sees them as artifically distributed.  The "sharpness" of aliased imaging is about as useful to my brain as looking at an analog image through a sheet of glass with little magnifying glasses in rows and colums that show you only the center of the dots, but fill them out.  Sharper transitions, but more erroneous representations of the areas.[a href=\"index.php?act=findpost&pid=149103\"][{POST_SNAPBACK}][/a]
This sounds more like a description of pixelation than aliasing.  If I photograph a single thin hair against a dark background, with a lens which out-resolves the sensor, the image might well be a single pixel wide, with all sorts of artificial looking consequences (jaggies, snapping to grid).  Some people probably find these artifacts as objectionable as aliasing.  The cure in both cases is the same -- blur the optical image so that it no longer out-resolves the sensor.  However, in this case (unlike aliasing), the blurring can also be performed after the fact, on the digital image.
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Graeme Nattress

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« Reply #109 on: October 29, 2007, 01:45:48 pm »

What you describe as pixilation is actually aliasing.

Graeme
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Ray

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1Ds MKIII and Optical Low Pass filtering
« Reply #110 on: October 29, 2007, 05:15:34 pm »

No-one has really explained how photographers who spend spend huge sums of money on MFDBs and associated equipment in order to get the ultimate image quality, manage to deal with this very prevalent and nasty aliasing.

The only reasonable explanation I've heard so far is that professional photographers know what they are doing and deal with it by either reducing its effect through software or by recognising and avoiding situations where aliasing is going to be a problem.

Since time is money and quality is paramount for the professional, an extra couple of thousand for an AA filter on top of the $30,000 or so for the average MFDB would be money well spent, I would have thought, in order to avoid the hassles of aliasing, if it's as bad as Graeme, John and Joanathan claim.
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John Sheehy

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1Ds MKIII and Optical Low Pass filtering
« Reply #111 on: October 30, 2007, 09:02:05 am »

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No-one has really explained how photographers who spend spend huge sums of money on MFDBs and associated equipment in order to get the ultimate image quality, manage to deal with this very prevalent and nasty aliasing.
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I haven't really noticed any correlation between "professionals with MF digital" and the interest in details such as RAW data, and there aren't a lot RAW files available to examine, so there is a bit of a dearth of useful infomation.

The internet is full of all kinds of stuff, but very little of it is RAW files, especially RAW files shot for specific tests.  Conversions have too much opportunity to hide artifacts.
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Jonathan Wienke

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« Reply #112 on: October 30, 2007, 11:43:40 am »

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No-one has really explained how photographers who spend spend huge sums of money on MFDBs and associated equipment in order to get the ultimate image quality, manage to deal with this very prevalent and nasty aliasing.

An AA filter is only needed when the lens outresolves the sensor. When a lens is designed to cover a larger image circle, the LP/mm where MTF is 50% decreases. Medium format lenses can resolve more total detail than a DSLR lens, but do so with a lower MTF at a given LP/mm than the equivalent DSLR lens. Given that DSLRs and MFDBs have pixel densities in roughly similar ranges, the MFDB is less likely to encounter aliasing because the lens is less likely to outresolve the sensor, meaning an AA filter isn't necessary. And if aliasing does occur, it's less noticeable when part of a 39MP image than part of a 10MP image, even if it's the same on a per-pixel level.

The other factor to consider is that software is getting better at dealing with color aliasing (moire) during Bayer interpolation and later on in the workflow.
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Tim Gray

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1Ds MKIII and Optical Low Pass filtering
« Reply #113 on: October 30, 2007, 12:02:43 pm »

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An AA filter is only needed when the lens outresolves the sensor. [a href=\"index.php?act=findpost&pid=149564\"][{POST_SNAPBACK}][/a]

So at the end of the day, ___IF__ it's determined that, for example, the 1ds3 is lens limited, ie the sensor outresolves the lens(es) then it would be appropriate to wonder if an AA filter is necessary?   And not to give Canon credit where they probably don't deserve it, ___IF___ we assume Canon executed a well engineered design of the sensor/AA filter "system" in the 1ds3 then the fact they included an AA filter means that the sensor does not out resolve the lens(es)?

(Ignoring for the moment whether __some__ lenses do or some don't outresolve...)
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Graeme Nattress

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« Reply #114 on: October 30, 2007, 12:20:49 pm »

Given that the 1Ds MKII has the same pixel pitch (or thereabouts) of the 20D, I don't think the sensor is out-resolving the glass. I don't think it's lens limited (certainly not in the centre of the image).

Graeme
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Jonathan Wienke

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« Reply #115 on: October 30, 2007, 01:14:29 pm »

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So at the end of the day, ___IF__ it's determined that, for example, the 1ds3 is lens limited, ie the sensor outresolves the lens(es) then it would be appropriate to wonder if an AA filter is necessary?

Yes it would. An AA filter is probably still appropriate, but it doesn't need to be as strong as on previous models, given that the likelihood of resolution being lens-limited is much higher. The more pixels you put behind a given lens, the weaker the AA filter needs to be to avoid aliasing.
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JeffKohn

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1Ds MKIII and Optical Low Pass filtering
« Reply #116 on: October 30, 2007, 02:34:15 pm »

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Yes it would. An AA filter is probably still appropriate, but it doesn't need to be as strong as on previous models, given that the likelihood of resolution being lens-limited is much higher. The more pixels you put behind a given lens, the weaker the AA filter needs to be to avoid aliasing.
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This is what's puzzling about the impression Michael initially posted, because he felt that the AA filter on the 1Ds3 was stronger than the 1Ds2, not weaker. I don't recall hearing compaints about the 1Ds2 filter being too weak, so if Michael's impression is true you have to wonder what Canon was thinking.
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Jeff Kohn
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Jonathan Wienke

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1Ds MKIII and Optical Low Pass filtering
« Reply #117 on: October 30, 2007, 04:47:12 pm »

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This is what's puzzling about the impression Michael initially posted, because he felt that the AA filter on the 1Ds3 was stronger than the 1Ds2, not weaker.

And note that Michael removed those comments because he decided they were not accurate...

Also keep in mind that if the AA filter in the 1Ds-III is the same strength per-pixel as the 1Ds-II, it is still weaker overall on a per-image basis.
« Last Edit: October 30, 2007, 04:49:53 pm by Jonathan Wienke »
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JeffKohn

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« Reply #118 on: October 30, 2007, 08:14:56 pm »

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And note that Michael removed those comments because he decided they were not accurate...
Has he said that his observations about the relative AA filter strengths were not accurate? I thought he removed all the AA discussion from the review because his comments about in-camera JPEG being the reason for AA filters were inaccurate.

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Also keep in mind that if the AA filter in the 1Ds-III is the same strength per-pixel as the 1Ds-II, it is still weaker overall on a per-image basis.
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I guess we'll just have to wait for some real, technical reviews to see.
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Jeff Kohn
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Ray

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1Ds MKIII and Optical Low Pass filtering
« Reply #119 on: October 31, 2007, 01:59:00 am »

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An AA filter is only needed when the lens outresolves the sensor. When a lens is designed to cover a larger image circle, the LP/mm where MTF is 50% decreases. Medium format lenses can resolve more total detail than a DSLR lens, but do so with a lower MTF at a given LP/mm than the equivalent DSLR lens. Given that DSLRs and MFDBs have pixel densities in roughly similar ranges, the MFDB is less likely to encounter aliasing because the lens is less likely to outresolve the sensor, meaning an AA filter isn't necessary. And if aliasing does occur, it's less noticeable when part of a 39MP image than part of a 10MP image, even if it's the same on a per-pixel level.


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Those photographers who have invested in the new Digitar and Rodenstock lenses which have a reduced image circle more appropriate for the 'cropped' MF format of the P22, P25 and P45 must be hopping mad at the amount of aliasing they are getting. Some of those new MF lenses have an MTF response higher that that of any 35mm lens that I've seen. Their performance looks more like that of the Zuiko lenses for the 4/3rds format, you know, something like 70% MTF at 60 lp/mm (can't remember off-hand the precise figures).
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