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10-12-2012, 05:52 AM   #1
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low pass filter the same as an AA filter ?

was wondering if these are the same thing, as i read somewhere at some time, that the dust removal function is to clear dust from the low pass filter ?

10-12-2012, 05:17 PM   #2
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i think a low pass filter is an AA filter :

( from wikipedia ) Low-pass filters exist in many different forms, including electronic circuits (such as a hiss filter used in audio), anti-aliasing filters for conditioning signals prior to analog-to-digital conversion, digital filters for smoothing sets of data, acoustic barriers, blurring of images, and so on. The moving average operation used in fields such as finance is a particular kind of low-pass filter, and can be analyzed with the same signal processing techniques as are used for other low-pass filters. Low-pass filters provide a smoother form of a signal, removing the short-term fluctuations, and leaving the longer-term trend.

so if the dust removal function removes dust from the low pass filter ( i read that somewhere ) then without it, how does the dust get removed in the k-5 ll s ?
10-12-2012, 05:56 PM   #3
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QuoteOriginally posted by dh4412 Quote
if the dust removal function removes dust from the low pass filter ( i read that somewhere ) then without it, how does the dust get removed in the k-5 ll s ?
I guess there is an IR filter in front of the sensor.
10-12-2012, 10:08 PM   #4
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an IR filter , so old guy ?

10-13-2012, 04:23 AM   #5
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What is often referred to as an "AA filter" or "Low Pass filter" are actually two birefringent plates that in combination multiply the image four times, which each copy slightly shifted against the others.

The function of these plates is to combat colour moiré (which otherwise can occur with Bayer-matrix sensors) and as a result they cause a slight blurring. Appropriate levels of capture sharpening, however, can get the micro-contrast back to the same level as if the slight blurring had never occurred. I'm assuming colour photography here; if one measures black and white patterns, I'm sure one can measure better resolution for cameras like the D800e and the K-5 IIs. What the relevance of such figures is for practical photography is another question, though.
10-13-2012, 06:30 AM   #6
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While not specifically reading this, I would be very surprised if the K-5 IIs doesn't still have a optically clear cover over the sensor. The various discussed filters are simply part of this cover. Removing a filter type doesn't remove the cover (and this is a good thing). So however Pentax names the cleaning function, what is really meant is dust is (hopefully) ejected from the the protective cover over the sensor.
10-13-2012, 08:05 AM   #7
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that makes sense, a clear filter , i wonder how many filters there are now in the existing k-5, just the AA filter over the sensor ?
10-13-2012, 06:01 PM   #8
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There will still need to be an IR and UV filter - though some people have successfully replaced those with optically pure glass to record into the IR and UV wavelengths. You'll need filters for the front of the lens if you want to take images in visible-only light - or any of the other regions.

10-13-2012, 10:16 PM   #9
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so are you saying , ter-or , that the existing k-5 has an infrared filter, an ultra violet filter, and also an anti-aliasing filter , all in front of the sensor ?
10-14-2012, 06:34 AM   #10
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It isn't like these are separate stacked filters. They would all be embedded in the same single piece of optical glass that protects the sensor.
10-14-2012, 06:03 PM   #11
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Yes, if you remove that filter you'll record a much broader spectrum, and the images will be unusual. there used to be a K-20 for sale here with this modification. Of course you can't see the IR or UV, so you'd need to use Live View to know if you were recording something. It's called the Bayer Sensor, presumably for who makes it.
10-14-2012, 09:14 PM   #12
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i guess if there is a clear glass or whatever that the dust removal acts on , that kind of answers my question, i did a quick search on google but did not come up with any diagrams showing the actual arrangement of the AA or glass filter in front of the sensor. anyway, thanks for the replies.
10-15-2012, 05:12 AM   #13
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there are 2 types of filters,

optical filters which restrict the light hitting the sensor to (largely) the visible range of light.
digital filters which are used to prevent errors from sampling, in this case, between pixels and related to the pixel pitch and resolution. These are anti aliasing filters. Without them, recurring patterns at close to the pixel pitch would appear to be banded or have some other pattern because of the difference in sampling as you move across the pattern.

it is this latter type they are removing.
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