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Selecting the Proper Brick Wall for Photographic Tests

Published April 1, 2021

Many amateurs test their lenses by taking pictures of the nearest brick wall without logically thinking about what information that particular wall provides. Done properly, a brick wall test can provide a superb evaluation of your lens. But a poorly done brick wall test is really no better than taking cat pictures without first measuring whisker length and diameter.

The first rule of testing is you MUST know what you are measuring, so let’s approach things a bit more scientifically. Today, through the barely understandable magic of scientific principles and higher order mathematics, we will discuss how to perform (dare we say it?) the PERFECT brick wall lens test.

Historical Attempts at Brick Wall Tests

Brick wall testing has a long and not colorful (cause it was black and white back in historical times) history. As we all know, the first brick wall test was performed by Niepce in 1826.

Nicephore Niepce, 1826

Niepce, as can be seen in the image above (1), demonstrated that unless the wall was at perfect right angles to the camera, it does not provide an effective test. Later efforts by Doerr (1850s) placed the wall at a more correct angle, but his use of weathered, sun-baked mud brick provided insufficient detail for effective testing.

The Alamo, by H.A. Doerr, 2012.3033.0018. National Museum of American History.

Modern Brick Wall Selection

All brick wall testers owe a debt of gratitude to these efforts by pioneers like Niepce and Doerr. But today’s amateur home tester has choices that simply weren’t available to these first testers.

Currently Available Brick

As Doerr demonstrated, proper brick composition is an important factor in brick wall testing. We all know the five common brick types, but a quick review doesn’t hurt. They are burnt clay, sand-lime, engineering, concrete, and, of course, the classic fly-ash brick. Sand-lime and fly-ash bricks are compressed and chemically bonded, rather than baked (2), giving them a smooth, strong surface that can be easily colored. This makes them quite useful for building purposes, but their surface is too smooth for effective lens testing. We recommend you avoid walls made with these bricks.

Luckily, burnt clay brick is used in the vast majority of modern brick walls. Burnt clay brick has enough irregularity on its surface to provide fine detail suitable for photographic testing. All burnt clay brick is not alike, however, so let’s cover some of those differences. No one wants to be ‘that tester’ who posts a brick wall image without identifying the brick class and grade used in testing.

Bricks are graded as either 1st, 2nd, or 3rd class. First-class bricks are uniform in size and color, have sharp edges, and (I kid you not) are supposed to make a ringing sound when you clang them together (3). I guess they get used in rich people’s houses and stuff; I’ve never seen any. Second-class bricks are pretty good; they may have slightly irregular edges, are not as uniform in color, but still, make a ringing sound when you clang them. (I wonder if ‘brick clanging’ is still done by a highly skilled human, like wine tasting, or if it’s become robotized.) Second-class bricks are what you see in most neighborhoods; they are only half the cost of a first-class brick but still look decent. Third-class bricks are near-rejects and kind of suck. Interestingly, they are used both in inexpensive buildings and costly Chicago renovations where buyers confuse bad quality with “looks like the original brick.”

Anyway, given the amount of money, most of you spend on lenses, chances are you can’t afford to live in a neighborhood made of first-class brick. That’s just fine; those second and third-class irregularities provide the fine details that are best for testing.

The Color Trap

Here’s where most of you run into trouble and don’t even realize it. We generally take photographs in white light, which is all of the light colors mixed together (4). What color are bricks? Yeah, red, mostly. In other words, they are monochromatic. Using monochromatic light is one of the best ways to cheat when you want to make a lens look better than it really is; it masks chromatic aberrations.

I know what you’re thinking: the mortar will give a more balanced color spectrum, right? Not so fast, my friends. As Reinhorn, et al. have shown (5), the typical brick wall shows a large red spectrum, but the mortar, rather than providing an even light, shows several spikes at specific wavelengths. It does not provide smooth, even spectra.

Reinhorn, et al. Optical Engineering v55. 2016

Obviously, the proper thing to do when selecting a brick wall for testing is to evaluate the color with a spectrometry camera, such as the Horiba Symphony II that Reinhorn used. We do realize its $12,000 price tag would be burdensome to all but the most enthusiastic brick wall testers, however, and luckily there are alternatives.

In the Southern U. S. almost all brick is made from good, old, high-iron, deep-red Georgia clay. You can find some white-painted brick, walls, but that won’t work because the paint is smooth. Smooth means no details to evaluate.

But I have good news, fired clay bricks from other locations come in a variety of colors. Historically, this was because clays used in certain regions had low iron mineral content, making them light in color. Milwaukee cream brick, Old Chicago yellow brick, and Wisconsin silver brick are good examples of bricks providing a broad color spectrum. If you live in the Midwest, such bricks are common, and you should have no trouble finding an appropriately broad-spectrum wall for testing. For those of you living outside the U. S., Mediterranean White Clay brick also provides a good spectra.

A variety of broad spectrum brick walls are available in the Midwest, where the clay, like the inhabitant’s blood, is weak and low in iron.

Brick Size

One other point should be made while we discuss bricks from inside and outside the U. S.; brick size. In the UK, standard bricks are 215 x 102.5 x 65mm. Surprisingly, there is no standardization in the EU, and each country has its own brick size. Germany, of course, has the largest bricks in the EU at 240 × 115 × 71, because, well, it’s Germany. Russia, just as obviously, uses larger bricks than any EU country; 250 × 120 × 65. American Standard bricks measure (203 × 92 × 57 mm), smaller than almost any other country, probably because Americans are more interested in pick up truck size as a measurement of manhood*.

In some areas, ancient brick walls, usually made of flat, wide bricks are still standing. These should be avoided since their size is either measured in Roman feet (13.2 inches) or cubits. Cubits, of course, are the length from the elbow to the middle finger, a measurement far too variable for scientific testing.

Obviously, the size of the brick does not affect the accuracy of testing in any single location. But one should be careful not to compare, for example, a brick wall test done in the U. S. with one done in a country with larger bricks, unless you perform a mathematical conversion of brick size.

Surprisingly, there is an actual reason for the variation in brick size. Before insulation was a thing, colder countries tended to use larger bricks because thicker walls were more insulating.

Summary:

If you’re going to do a brick wall test, you should do a scientifically valid brick wall test. This means a wall made of fired clay brick of broad-spectrum, using Class 2 or 3 brick. Removing a couple of bricks from the wall to perform a “Clang” test is the simplest way to differentiate between Class 2 and Class 3 brick (6).

Spectrometry of the wall to demonstrate a broad color spectrum is best, of course, but the cost of spectrometry cameras limits its use to only the most dedicated brick wall testers. It is generally more cost-effective to travel to regions with broader spectrum brick.

Tests done in different countries should not be compared directly because of the variation in brick size, affecting sharpness calculations.

Following these simple, logical rules will let you perform brick wall tests equal to that of any professional lens reviewer. Anyway, Happy April Fools Day.

References:

Author: Roger Cicala

I’m Roger and I am the founder of Lensrentals.com. Hailed as one of the optic nerds here, I enjoy shooting collimated light through 30X microscope objectives in my spare time. When I do take real pictures I like using something different: a Medium format, or Pentax K1, or a Sony RX1R.

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  • Franz Graphstill

    Sounds like you are suggesting using them for macro lenses. I don’t think they offer the fine detail we’d need for macro lens assessment.

    The problem is that these bricks are notoriously monochromatic, so careful selection of multiple colours will be required to get a diverse spectrum.

    Fortunately, their colours are consistent, making results reproducible worldwide, which is not something we can say for normal brick walls.

  • Guntram Lampert

    Roger,

    thank you for your seminal introductory text on the subject that drives the development of photographic lenses to this day.
    There is always room for improvement, so here is the most advanced form of brick wall, the MTF-brick, conceived by S. Ku-brick.

    https://uploads.disquscdn.com/images/140230cee86b84f1f46ab168437effd8375929b44f710ed55ad6ed50d75d4f55.jpg

    It allows the quick and accurate determination of sagittal and tangential MTF values in one shot.

    Regards,
    Guntram

  • Guntram Lampert

    Roger,

    thanks for this introductory text on the brick wall- the basic driver of optical design, and photography in general.
    There are now advanced brick walls in existence, and I would like to introduce the MTF-brick wall:

    https://uploads.disquscdn.com/images/192d57f84c76cd80150431dc444b5f085a73567ad44789a066c5407b22419009.jpg

    This design does away with the boring “cartesian” brick wall, and facilitates sagittal and tangential measurements. A small version for macro lenses is in development.

    Regards,

    Guntram

  • Steve Tschopp

    My kids love my brick wall pictures. I thought all the flaws in the bricks at my office were meant to be decorative, it sounds like they were just cheaper, oh well. I do try to be somewhat scientific. I adjust distance vs focal length so I get the same section of bricks. Then process the same and look at file size in jpg for a metric of overall sharpness. My kids can see subtle differences in sharpness that agree with file size differences. My old eyes can’t always see the difference. Lighting of the bricks is critical. Direct sun produces more detail than clouds, and of course clouds are too variable. So a pure cloudless sky is a good reference. But, of course the location of the sun is important for shaddow size. So unfortunatly there are only a few minutes twice a year, if the clouds are right, that I can do lens comparisons.

  • Roger Cicala

    I was afraid people would miss it. Everyone missed the caption on the broad spectrum brick pic. I was expecting to get screamed at for that.

  • Roger Cicala

    Brilliant, Ilya! I’m getting you to do next April 1.

  • Chik Sum

    Nice Try and a good effort on 1st April Roger, but somehow with you in mind and brick wall test as subject, you can’t catch me as if you are serious about this https://media1.giphy.com/media/tsgNNs93oIbwk/giphy.gif

  • Ilya Zakharevich

    I do not think one really needs the full resolution provided by a spectrometer. Something with a much coarser resolution may still carry all the needed information. (Indeed, the lenses spectral characteristics should not have sharp peaks, so they “average” the spectrum anyway!)

    I expect that enough data can be obtained in a very simple way which does not require a lot of unjustifiable investments. However, it is critical to design a workflow giving reproducible results, so one can publish the results together with the brick wall shots.

    I think a simple and cheap to implement workflow may go like this:
    ?• Measure the current color temperature of the sun (using “Custom settings color temperature” and a gray card with a digital camera. (AFAIK, Sigmas do not report the color temperature, but most of the other contemporary cameras do.)
    ?• When the wall is in shadow, use a small pocket mirror to make a reflected sun spot on the wall.
    ?• Photo the reflection of the sun spot in a calibrated DVD (preferably of Redemptione de Shawsank 10th Anniversary release).

    Do you know any software which would report the spectrum given a photon produced as above?

  • sala.nimi

    With those bricks there are other kinds of health issues also, if you accidentally on tramp on a “brick”. Your family and language may suffer also.

  • Clayton Taylor

    Oh, yes, the final citation should read “Dufresne, Andrew and Redding, Ellis Boyd…”

  • Clayton Taylor

    First you shoot pictures of the brick wall. Then you determine the # of sensor pixels / brick by knowing the distance to the wall, the size of the bricks in mm (thank you Roger) and the megapixels of the sensor. Then you determine the density of the cat’s fur in follicles / cm squared, and back calculate the distance that the cat needs to be placed. Unfortunately, by the time you have finished the calculations, the cat has walked away….

  • Clayton Taylor

    Cats do not ever “work”, they tolerate us for food and shelter. Oh, wait….

  • Dave Hachey

    I knew instantly this was an April fools prank, but I decided to read it anyway. Hilarious, in a useful sort of way.

  • I came here looking for a conversion between lens evaluations that used brick walls and those that used cats. I leave disappointed.

  • Nooooo, i love this article! It fully repay me for the fact that i came here to check for new readings almost every day!

  • DrJon

    There are health and safety issues at work here… tread on a burnt clay brick and you get a foot with some dust on it… tread on one of the Danish bricks and you’re hopping around swearing with the pain…

  • Samuel H

    This is very useful but can you please check how different cats perform? Video people often test their cameras shooting their cats, and I worry some breeds will work better than others.

  • Roger Cicala

    Over 2 hours!!!! 🙂

  • Athanasius Kirchner

    After such a sagacious and well-researched piece of invaluable prose, my only question is: how long, and how much, did you need to study brickmaking and bricklaying to craft it? ?

  • Athanasius Kirchner

    They’re only good for close-up ranges, though, so they’re more of a specialist application.

  • Roger Cicala

    You made me spit my coffee!!!!!

  • Jalan Lee

    Roger, thanks for the information!

    But you are doing a major disservice to your readers in not commenting on the merits of the main brick manufacturers! Who has the superior product Shinagawa or Itochu? Of course, I prefer German bricks made by Hans Lingl Anlagenbau Und Verfahrenstechnik – the “Red Dot” is the universal symbol of quality and prestige!

  • 45Hunter

    There is so much information in this article, Roger. I will have to read it several time to feel that I have absorbed the info available to me. I suspect that I will have to leave the testing to you and your crew.
    Thank you, Roger.

  • Hüseyin Gürgah

    It was good. 🙂

  • bokesan

    It’s more like a 3d-“pop”!

  • Roger Cicala

    @bokesan But do they clang??????

  • bokesan

    This article omits a very common danish brick made out of ABS. I’m hoping for a followup covering other kinds of bricks.

  • Andreas Werle

    “Clandestine Brick Removal.” Roger you made my day. Have some restful easter holidays and stay healthy!

  • The_Incomparable_Douche

    This is excellent ammo to use against those pigheaded dilettantes on the DPR forums. Thanks, Roger!

  • Ansgar Himmel

    Thanks for the highly detailed, scientific info! Perfectly researched, as usual.
    You had me worried for a moment, about how to efficiently perform the clang test on my broad-spectrum wall of choice. But the Andy Dufresne reference cleared that all up. I’ll be off now, researching the correct, photography-grade rock hammer ?
    🙂

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