AA filter and MF vs dslr sensors

[rodcones]

Hello, just joined after lurking a while, And jumping in the deep end with this :-)

I've wondered about one of the reasons for digital MF's superior image quality being the lack of an AA filter and, although I think I understand its need wrt moire, there's a common sensor aspect which increases my doubt .

 Now, until recently the dMF backs have really been "DX" framesize wrt 645 film as we have the DX dslr wrt 35mm, but stll larger than dslr and the bigger capture framesize will stay play a major role in large print quality as it's "nearer thy goal than wee". :-)

However, the matter of pixel density and size is the salient point of my query. Allow me to lay out my reasoning even if you know this already.

In film days your 'blads, bronicas and mamiyas et al were going to show up your F2's and M5's by 12x16 (A3) and no contest as you got to A2. Now, film is film and Velvia, Ektachrome, Pan F etc are exactly the same in each's different film size and if you cut a 10mm square from the centre of 35mm, 220 and 5x4, any forensic exam would show them identical.

A real experiment might be complicated by finding a maker who made 645 and 35mm plus lens adapters allowing 1 lens use on each body but we can stick with 645 makers who provided a 35mm back. So we have a suitable lens, 645 body, 645 and 35mm backs with same film, tripod, lighting and a subject. Let's suppose this is a pretty girl and we'll take a face shot with portrait orientation to maximise frame usage, as this helps towards evenening out the comparison.

So, with 645 back oriented portrait, we compose so that the top of head/hair and bottom of chin are just inside frame. With a non-permanent marker, write 645-F on her forehead. Take 1 shot A.

Now put on the 35mm back. Move tripod as required so framing is same as above. Wipe the forehead and write 35. Take 1 shot B.

Now put the 645 back back on. I confess to no MF experience but I'm sure one can do the next operation easily. Re-compose so that the face will occupy the same area on the 645 film as it did with the 35. Change forehead to 645-35. Take 1 shot C.

When printed to A2, shots B and C will be indistinguishable and inferior to A. The lens was the same, the film was the same so the capture medium had the same density but A started out nearer the "goal" size.

OK, back to digital and the relevance of the above to my salient point mentioned at the outset. Certain DX dMF backs in xxMp size had the same pixel density/size as FX dslr and in particular the Canon 5d at about 8.2micron.  36/8.2 = 4.39 24/8.2 = 2.92, multiplied = 12.8.

I'm willing to be corrected but, leaving post-capture electronics and processing aside, this to me is the  same "film", aka capture medium density. I'd like to see a similar trial but is complicated because there are no "35mm" capture backs for dMF bodies! :-)

With a suitable lens and adapter it could be done and would take the size out of the equation leaving the AA filter, or lack of, as the only
quality factor.

Which then begs the question: if the sensor has the same pixel size  why does the dslr have an AA filter?

[Doug Peterson]

Which then begs the question: if the sensor has the same pixel size  why does the dslr have an AA filter?

Easy.

dSLRs service a very very broad market most of which have no idea about AA filters or Moire. The typical dSLR user would FREAK out if they saw moire.

Digital backs tend to service much more knowledgeable IQ-conscience customers who (especially with the advent of 6.8 and 6 micron sensors which very rarely exhibit moire) are willing to tolerate the occasional moire nuisance in exchange for higher absolute IQ.

The better question is why dSLR manufacturers don't do small-runs of AA-less dSLRs and I think the reason is that the niche who would tolerate slight nuisances for higher IQ are more likely to go to low end DBs (to gain the advantages of larger sensors, higher DR, better lenses, ability to use tech cameras etc etc) than high-end dSLRs with no AA filter, especially now that full kits of each are in the same ball park.

It would be very interesting to hear the total volume of conversions on high-end dSLRs that MaxMax (or other 3rd party AA removers) do in a year.

Doug Peterson (e-mail Me)
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[Graham Mitchell]

Which then begs the question: if the sensor has the same pixel size  why does the dslr have an AA filter?

Probably to prevent a million consumers from going to their dealers and complaining about their 'faulty' cameras.

As to your other point, yes there will be an optimum pixel density beyond which if you want more resolution the answer is to go larger. The question is whether that limit can be contained on a 35mm format sensor for your needs, or not.

Personally I like the larger format partly because of the larger viewfinder image that entails, and the narrower DOF. However I wish that a standard size would be settled so that lenses can be designed with a sufficient image circle without being much larger than necessary (which is the norm at the moment). So, either more large (645 size) sensors or smaller (and/or faster) lenses please. At the moment it's still a little messy.

[Doug Peterson]

When printed to A2, shots B and C will be indistinguishable and inferior to A. The lens was the same, the film was the same so the capture medium had the same density but A started out nearer the "goal" size.

Don't forget that a lot of factors play into IQ and even if you match the lens, subject size, and sensor pixel size that other things like A/D conversion (both bit depth and component quality), software refinement (better/worse algorithms and how much an algorithm is tuned specifically to a particular sensor), CMOS vs. CCD architecture, microlenses or lack there of, etc etc all play in to the various attributes of IQ.

Even pixel size can be deceiving. The P25+ and P45+ are 9 and 6.8 microns respectively. However the "wasted" space between pixels which was not light-sensitive was reduced so dramatically between the two chip generations that both chips have roughly the same light-sensitive surface area per pixel. Throw in shape of the pixel as a variable and the ability to combine photosites into larger "virtual pixels" with Sensor+ and your head is sure to spin.

We all wish you could distill all of this into a few numbers (like dXo does) but the richness/fidelity/quality of MFDB files come from the cumulative sum of many many factors.

Doug

Doug Peterson (e-mail Me)
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[rodcones]

Even pixel size can be deceiving. The P25+ and P45+ are 9 and 6.8 microns respectively. However the "wasted" space between pixels which was not light-sensitive was reduced so dramatically between the two chip generations that both chips have roughly the same light-sensitive surface area per pixel. Throw in shape of the pixel as a variable and the ability to combine photosites into larger "virtual pixels" with Sensor+ and your head is sure to spin.

Right, I get what you're saying. And a side issue is maybe honing Googling skills to be able to find a succint bunch of relevant material.  

I've seen the stuff concerning the M8 when it first appeared and other related points but taking in what you mention on microlenses and live/wasted space there's no _cohesive_ material which really explains this aspect of digital technology. Unless it's amongst the other few hundred Google hits I don't really have time to investigate!  

And although I started by talking about certain DX MF backs, now, as you say, the newer with 6.8/6micron size are on a seemingly pixel-size par with the 2XMp dslr flagships. So is it really the on-chip processing (or off) that's controlling their moire or a whole micro physical architecture difference causing the dslrs to require the AA filter still?

[Doug Peterson]

Right, I get what you're saying. And a side issue is maybe honing Googling skills to be able to find a succint bunch of relevant material.  

I've seen the stuff concerning the M8 when it first appeared and other related points but taking in what you mention on microlenses and live/wasted space there's no _cohesive_ material which really explains this aspect of digital technology. Unless it's amongst the other few hundred Google hits I don't really have time to investigate!  

And although I started by talking about certain DX MF backs, now, as you say, the newer with 6.8/6micron size are on a seemingly pixel-size par with the 2XMp dslr flagships. So is it really the on-chip processing (or off) that's controlling their moire or a whole micro physical architecture difference causing the dslrs to require the AA filter still?

Anytime a repeating subject pattern lines up with the pixel array you will get moire. An AA filter slightly softens the image to greatly reduce (though not wholly eliminate) the chance of moire. The smaller the pixel size the less probability a subject pattern will match it closely enough to generate moire. The 6 micron sensors in the P40+ and P65+ are very unlikely to moire.

Another way to think about it is is for a given sensor and subject (generally the fixed variables in a shoot) any camera will moire at multiples of some calculable distance to subject (e.g. 12 ft, 24 ft, 36 ft) and a smaller micron size means a higher base distance to subject and therefore less chance you will randomly find the "sweet spot" for moire.

On a side note, you can accomplish something similar to an AA filter to combat moire by stopping down a bit past the diffraction limit of your lens (which will soften the image slightly).

Generally speaking moire is more talked about than it is a real-world problem. If you shoot a LOT of fashion/fabric and you have a large-micron sensor you will run into it with some relative frequency. Otherwise you will very rarely experience it. And the upshot is higher sharpness and the ability to actually realize the "stated" resolution of your camera.

Doug Peterson (e-mail Me)
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[narikin]

Generally speaking moire is more talked about than it is a real-world problem. If you shoot a LOT of fashion/fabric and you have a large-micron sensor you will run into it with some relative frequency. Otherwise you will very rarely experience it. And the upshot is higher sharpness and the ability to actually realize the "stated" resolution of your camera.

I got hit by a couple of really strong moired images in some street photos with my P45+ the just yesterday. some guys shirt and my sensor interacted to make an extremely vibrant moire pattern, which was almost impossible to dial out with C1 4.8's moire tool. (at least with my limited attempts)

[Carsten W]

I'm willing to be corrected but, leaving post-capture electronics and processing aside, this to me is the  same "film", aka capture medium density. I'd like to see a similar trial but is complicated because there are no "35mm" capture backs for dMF bodies! :-)

In which sense do you mean "35mm capture back"? If you mean with a Canon/Nikon sensor with AA filter intact, you are right, but there were some 36x24mm sensor backs early on, I am pretty sure.

[Doug Peterson]

I got hit by a couple of really strong moired images in some street photos with my P45+ the just yesterday. some guys shirt and my sensor interacted to make an extremely vibrant moire pattern, which was almost impossible to dial out with C1 4.8's moire tool. (at least with my limited attempts)

Any back CAN show moire and it can be extremely frustrating. Still, specific instances aside it happens far less on a 45+ than on a 25+ and even less with a 65+.

In which sense do you mean "35mm capture back"? If you mean with a Canon/Nikon sensor with AA filter intact, you are right, but there were some 36x24mm sensor backs early on, I am pretty sure.

Absolutely, but the comparison would be a bit unfair since all the components of those systems are many years old.

[James R Russell]

Any back CAN show moire and it can be extremely frustrating. Still, specific instances aside it happens far less on a 45+ than on a 25+ and even less with a 65+.

Absolutely, but the comparison would be a bit unfair since all the components of those systems are many years old.

When the last two peoples are left on this earth, I am positive that one will be a canon user the other a larger than smaller sensor rep and they will be arguing about the lack of aa filter, the threedeeness of a larger than smaller sensor file, the ability to hold, not hold highlights and the larger than smaller sensor rep will end the conversation with, "wait until version 19.6 of he software comes out, then you'll see a real improvement in moire correction, not that "our" cameras really show moire.

I'm sure all of this is important to the people that make and design cameras, I know it's important to the people that market and sell cameras, but does it really matter to a photographer?

Today I have 19 photographs going out for mounting for a show, from projects shot in 2008.

They're shot with a p21, p30, 1ds1, 1ds2, 1ds3, d700, d3 and a Leica, oh yea and one is even with a Nikon D90.

At no time during the selection of these photographs, by me or the judges did anyone notice, or care about the camera, the ad convertor, 14 bits, 12 bits, 16 bits.

At no time during the shooting did the AD, the client, the publisher, the stylist, the producer, the printer, the webmaster, or the caterer think about camera choice either.

Now as a photographer, I used each camera for a reason.   Sometimes because I just wanted to, sometimes because some focused faster than others, in one instance because I only had the canons with me,  but 90% of the time because for whatever scene I was shooting, that specific camera's images looked pretty.  If highlights were blown, then I balanced the light to level them, if the lens choice was limited I went to a system that had more offerings, if the lcd wasn't readable, I either put up a computer or shot a different camera,  but that's my job, that's what is expected of me.

I believe with all my heart and soul that in a few years that photographers will look back on this time and asked "why did photographer care about this stuff?"


JR

[Doug Peterson]

I believe with all my heart and soul that in a few years that photographers will look back on this time and asked "why did photographer care about this stuff?"

Right with you.

That's what I think Ansel Adams and all his fruitless concern about the technical attributes of his camera end-to-end workflow. Didn't that guy know that technical mastery of your equipment doesn't help you be a more creative and profound creator of images?

Doug Peterson (e-mail Me)
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[James R Russell]

Right with you.

That's what I think Ansel Adams and all his fruitless concern about the technical attributes of his camera end-to-end workflow. Didn't that guy know that artistry and technical knowledge of your equipment are completely different pursuits and never overlap.

Ok, so Ansel Adams used a what . . . p65, p45, p . . .



JR

[Doug Peterson]

Ok, so Ansel Adams used a what . . . p65, p45, p . . .

:-P

He sure as heck "rolled his own profiles" though :-).

Doug Peterson (e-mail Me)
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[snickgrr]

The fiftieth anniversary of Robert Frank's "The Americans" is exhibiting currently at SFMOMA....the exhibit as well, of course, the photographs sent chills up my spine.  I cried at a couple of shots.  On doing some research to send to my girlfriend before we went I came across this quote.

"Quality doesn't mean deep blacks and whatever tonal range. That's not quality, that's a kind of quality. The pictures of Robert Frank might strike someone as being sloppy - the tone range isn't right and things like that - but they're far superior to the pictures of Ansel Adams with regard to quality, because the quality of Ansel Adams, if I may say so, is essentially the quality of a postcard. But the quality of Robert Frank is a quality that has something to do with what he's doing, what his mind is. It's not balancing out the sky to the sand and so forth. It's got to do with intention." (Elliott Erwitt)

[tho_mas]

I believe with all my heart and soul that in a few years that photographers will look back on this time and asked "why did photographer care about this stuff?"

As much as I agree... the answer is: because there are different kinds of photography. What I've seen of you by now is that you always create a certain look - may it be mellow or glossy - but (correct me if I'm wrong) one of your main means of expression is narrow DOF.
I have a print of a portrait I took some years ago with a 10MP DSLR and a 1.4/85 at f2 or f2.8. It's a 90x60cm print and beyond any doubt (at least from a technical standpoint). I could print it even bigger. Much bigger probably.
But if you shoot stuff that demands for heavy tripod, no wind, small apertures and and and and and... you obviously care about certain aspects of technical quality.
And it's not necessarily a self purpose. Maybe you "need" that quality because you want to show, express, visualize something. And this "something" is connected to the content you want to show/create or, simplified said, connected to your "emotion" for that particular stuff you are shooting.
It's hard to imagine that Gurskys pit stop works (8 meters wide) would be that outstanding if the people in the Photograph would be smaller. When you stand in front of the image you feel like standing right in front of that pit stop. And the viewer therefore gets a position he would never achieve in "real life". Gursky wouldn't take a D40 for that stuff (I guess) ...
So... you are right. But...

[James R Russell]

As much as I agree... the answer is: because there are different kinds of photography. What I've seen of you by now is that you always create a certain look - may it be mellow or glossy - but (correct me if I'm wrong) one of your main means of expression is narrow DOF.
I have a print of a portrait I took some years ago with a 10MP DSLR and a 1.4/85 at f2 or f2.8. It's a 90x60cm print and beyond any doubt (at least from a technical standpoint). I could print it even bigger. Much bigger probably.
But if you shoot stuff that demands for heavy tripod, no wind, small apertures and and and and and... you obviously care about certain aspects of technical quality.
And it's not necessarily a self purpose. Maybe you "need" that quality because you want to show, express, visualize something. And this "something" is connected to the content you want to show/create or, simplified said, connected to your "emotion" for that particular stuff you are shooting.
It's hard to imagine that Gurskys pit stop works (8 meters wide) would be that outstanding if the people in the Photograph would be smaller. When you stand in front of the image you feel like standing right in front of that pit stop. And the viewer therefore gets a position he would never achieve in "real life". Gursky wouldn't take a D40 for that stuff (I guess) ...
So... you are right. But...

I agree.

I;m not saying not to by a pee 65 a pee 40 a hasselblad, leaf or a sinar.

All I'm saying is regardless of where these web discussions go, it's always a comparison between a Japanese dslr vs. a digital back and they both have their merits and their issues.

I can give you just as compelling story why a photographer would get use out of both systems, and turn the conversation around as to why a used 1ds1 will shoot 99% of every photograph ever taken.

It's all personal preference, nothing more, nothing less.

JR

[tho_mas]

It's all personal preference, nothing more, nothing less.

Yes.
I sold my entire DSLR sytsem back in the days because I needed the money to get the P45 (refurbished) payed.
The last weeks I noticed that I actually gave up one part of photography: hand held and spontaneous (re-) acting. With the P45 I'm determined to use a tripod and mirror lock. So I thought about the Sony A900 and 3 lenses. Then I looked at my cases and bags and imagined all that stuff you need in addition like batteries, cables and so on.
As I never used sensitivity beyond ISO400 (rarely ISO800) the last 25 years and (if needed) am used to use a monopod I finally thought about the P21+. No other lenses, no other batteries... just that small black clump in my case and I can shoot hand held. And if you look at the Phase site and the current product line published in their flyers you'lll see that the P21+ silently fades away. So I thought good time to buy one. Now or never. And I did.
Some will say that's totally stupid as DSRLs are so fast and easy to use and reasonable priced. But a A900 with 3 lenses (the 3 I would have taken) is more expensive. Plus the accessories.
I tell you what: I fell totally free and immune to updates/upgrades as now I have a dead system (Contax) which I like very much and two discontinued backs which I also like very much. Sole updates come from Phase weekly with C1.48657ß09%.201. And if that "shit" will not break, I'll use it for many, many years (I hope). Even a P65+ isn't tempting me as I feel the P45 is not the limiting factor... it's the lenses (not in single shots but when stitching based on movements with the tech camera). And finally... with the P21+ the continious mode of the Contax makes sense again :-)
But hey - my "needs" are definitely very far from yours - I'm aware of that.

[rodcones]

Doug wrote
"Anytime a repeating subject pattern lines up with the pixel array you will get moire. An AA filter slightly softens the image to greatly reduce (though not wholly eliminate) the chance of moire. The smaller the pixel size the less probability a subject pattern will match it closely enough to generate moire. The 6 micron sensors in the P40+ and P65+ are very unlikely to moire."


Yes, that's what I read and still in a "thinking out loud" fashion I keep wondering about the necessity and whether X's 8/7/6micron sensors are so different from Y's 8/7/6's that X needs it and Y doesn't


carstenw wrote
"n which sense do you mean "35mm capture back"? If you mean with a Canon/Nikon sensor with AA filter intact, you are right, but there were some 36x24mm sensor backs early on, I am pretty sure."

I meant a proper dMF back which would have a 36x24mm sensor as you say though I only know about what's current from the major makers' sites.


James wrote
"When the last two peoples are left on this earth, I am positive that one will be a canon user the other a larger than smaller sensor rep and they will be arguing about the lack of aa filter, the threedeeness of a larger than smaller sensor file, the ability to hold, not hold highlights and the larger than smaller sensor rep will end the conversation with, "wait until version 19.6 of he software comes out, then you'll see a real improvement in moire correction, not that "our" cameras really show moire." etc etc

Sure enough, I didn't intend to begin another of the usual tech squabble fanboy sort of thing that can go on although some of the previous threads I've seen in here about narrow technical merits can be interesting enough if not seen totally as a "that makes it better/worse for ...". Mind you, whatever discipline or pursuit, there has to be a foundation of science and accuracy about the materials and "workings".

Although there isn't a "creativity" sense perhaps, for those who know how to use 2 and 4 wheel machines to get round circuits with greater skill and artistry than the rest of the grid, never mind the rest of us, I don't know if they get into discussions about whether... it's late and I can't conjure up whatever tech points but I'm sure you all know what might be involved with a bike or car being more easily hustled,  or as more of this thread says, people just get on with using the gear and not giving it a second thought.

[yaya]

You can buy an 11MP 24X36 back for next to nothing, borrow an MF body with A lens (one that can be adopted to your 12MP DSLR) and do some tests. (oh yes you'll need a model and a sharpie)

Then tell us what you saw and what you think.

Welcome on board BTW:-)

Cheers, yair

[rodcones]

hi there,  well now I suppose I could but it was really a hypothetical kinda q that's been niggling.


yair wrote
     "You can buy an 11MP 24X36 back for next to nothing, borrow an MF body with A.."