Focal length question: 40mm vs 35 & 50

[adan]

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Genuinely interested here, hopefully not too off topic - in the image that you says shows both (which one?), can you point out what is Moire and what is colour aliasing?

 

Are they caused by the same thing, and are some lenses better at avoiding Moire and / or colour aliasing?

 

Take a look at the second picture in the links above (50mm lens) - in the nets draped over the tower at left, on the top floor, there are eerie red/cyan "waves" in the plain brown netting.

 

That is color moiré or aliasing - the repeating grid pattern of the net is being projected onto the grid of red/green/green/blue

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pixels of the sensor with such good resolution that a single "string" of the netting is alternately blacking out red or blue pixels, creating false reds and blue-greens in what should appear as a consistent brown.

 

Moiré, the digital photography and physics effect, is named for the wave-like weave of moiré silk, which it resembles: https://en.wikipedia.org/wiki/Moire_(fabric)

 

Color moiré is just another type or subset of moiré in general, which is caused by a repeating pattern (or single dark line) interacting with the grid of sensor pixels to form an interference pattern. Usually when the two patterns are not quite in sync, in either angle or scale.

 

Now - that particular subject matter is itself physically made up of two overlapping grids in the real world (two hanging nets, one in front of the other) and that will create a moiré pattern all by itself - visible to the naked eye viewing the actual scene, and in a film photograph. Photographing it on digital just adds a yet another grid to the mix.

 

Look at this simulation - if you zoomed in on the greenish area at left, you would see it replicates the red/green/green/blue Bayer pattern or filtered checkerboard of a color digital sensor. That is the only "real" color in this image.

 

On top of that I laid down two linear textures - they can be seen "pure" against the white background at right. Black vertical lines, and black tilted lines, at a spacing of detail almost indentical to the pixel spacing. Despite those patterns being pure black, they acquire "artificial" reds and blues in bands, when overlaid on the green area. That is color moire. The single black sloped line far left also acquires alternating red/blue bands, as though it was red and blue yarn twisted together. That is color aliasing - a single-line equivalent to color moire. Finally, note that the two black textures themselves, even against pure white, will alias or moire with each other, producing the "false" pattern of gray arcs. A "subject matter moire" as with the two layers of netting overhanging the balconies in the sample picture.

 

 

Yes, some lenses are better at avoiding moiré or color moiré - but you won't like the answer. The fuzzier and blurrier the lens, the less it will produce moiré. It can't render any details fine enough to fall only on one pixel or line of pixels. Moiré is a function of a lens rendering very fine details on the same scale as the pixels on the sensor. The sharper the lens, the greater the chance of moiré occuring.

 

Many digital cameras have an anti-aliasing or anti-moiré filter on the front of the sensor, to intentionally blur the images from sharp lenses so as to avoid moiré. Leica has always chosen to not use those, preferring occasional moirés to permanent fuzziness in all images.

 

Alternatively, one can defocus the lens slightly (intentionally blur the picture).

 

Or use a Monochrom Leica, which will remove the chance of color moire/aliasing, since it has no Bayer color filter pattern.

 

And/or get a huge number of megapixels, such that no lens ever made can produce detail smaller than at least 2 pixels wide. (but we've had that discussion..... )

 

Or shoot film, which has a random pattern of silver grains, rather than a checkerboard grid of pixels.

[stephengv]

I would hardly call a 35 mm a tele lens

 

 

What  I meant was, the 28 is a wide and the 50 is a "short tele" lens, while the 35 is a compromise between the two.  

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[lct]

What  I meant was, the 28 is a wide and the 50 is a "short tele" lens, while the 35 is a compromise between the two.

 

50 as always been a standard lens for me, 75 a short tele and 35 a wide angle lens. But i pertain to the HCB generation. Well one generation after to be honest...

[cp995]

The 35mm f1.7 CV Ultron VM is as good as it gets from a 35mm focal length perspective. I just wish it was 6 bit coded...

 

My Ultron was very easy to code, as there is a "deepening" in the flange.

All you need is a blck touch-up pencil and the desired code.

If you need help, drop me a PN

[LichtUndDunkelheit]

 

I'm in the process of considering ONE of three lenses, all Voightlander (This is more about focal length vs the brand): 

 

- 35mm/1.7 Ultron

- 50mm/1.5 Nokton

- 40mm/1.2 Nokton

 

If you had to choose only one of these which would it be?

 

Why, the 40/1.2 because its the best of these lenses (and possibly the best lens from Voigtländer for Leica M overall).

[lct]

Why, the 40/1.2 because its the best of these lenses (and possibly the best lens from Voigtländer for Leica M overall).

 

The CV 40/1.2 looks softer than the CV 50/1.5 on the moiré pics above (#31) though. Reason why it shows less moiré i guess. 

[thedwp]

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The CV 40/1.2 looks softer than the CV 50/1.5 on the moiré pics above (#31) though. Reason why it shows less moiré i guess.

I think the copy I had was soft...I've read and seen so many Images that were tack sharp, thats why I was a little surprised with the results I was getting. 

[LichtUndDunkelheit]

The CV 40/1.2 looks softer than the CV 50/1.5 on the moiré pics above (#31) though. Reason why it shows less moiré i guess. 

You seem to be missing the point of evaluating all aspects of a lens in actual photographs versus looking at some graphs that tell you about some more or less obscure detail of a lens.

[lct]

You seem to be missing the point of evaluating all aspects of a lens in actual photographs versus looking at some graphs that tell you about some more or less obscure detail of a lens.

 

 I have no idea about those graphs. Which one(s) are you referring to?