For anybody who might be interested in such matters:
I asked Bert:
"Can you offer an opinion as to why camera lenses are usually anodized black, but camera bodies are painted black? (I think the former looks better.)"
Bert answered:
Painting is definitely the cheaper and simpler to use process. It easily produces consistent, repeatable finish qualities on just about any surface type, and that pretty much irrespective of part geometry. Paint does hide minor surface defects, so the requirements for part preparation prior to finishing are minimal. Opaque paints (pretty much the norm) also have the unique ability to produce a uniform finish across assemblies of parts made of dissimilar materials, metal and plastic for example. On the con side, paint thickness is usually significant and non-uniform (tends to fill creases and small detail; smoothes sharp edges), making it difficult to use on precision parts.
Anodizing is used mostly with aluminum alloys, although it can also be applied to titanium, magnesium, zinc, and a few rare earth metals, but definitely not for ferrous metals (i.e. steel) or brass. Finish thickness is predictable, controllable and highly repeatable, making this the process of choice for high precision components. On the other hand, this process does little or nothing to hide any existing surface characteristics, so parts generally have to undergo some more-or-less extensive preparation (cleaning, etching, sand-blasting, brushing, etc.) if a nice cosmetic surface finish is desired. Finished surface appearance can also be strongly affected by even very minor changes in material composition or contamination, generally making it unrealistic to expect nice, uniform results on cast parts. Obtaining uniform results on parts with complicated geometries like a camera body can also be challenging because of the great localized variations in the electric field within the anodization tank (especially around sharp angles). This yields varying porosity characteristics, so the subsequent dyeing (coloration) may not always yield uniform results. Cosmetic anodizing is thus at its best on of regular, symmetrical, machined parts.
As you can see, the answer to your question is both simple and complex at the same time, as it lies within the strengths & weaknesses of each process. If you carefully study the characteristics and properties of various surface finishes, then the range of application for each one becomes pretty obvious. That is especially true since there is not as much overlap in applicability domains as it might seem at first glance. Sure, almost anything is possible if you really want it, but there are usually very few truly smart combination for any given situation.
In the case of camera bodies, only some small P&S units have an anodized finish because a soft aluminum shell is not really a handicap on such lightweight devices. Small cameras are seldom subjected to rough handling after all, and the shell is not a critical component anyway (it often only covers an underlying plastic frame).
On the other hand, heavier cameras like DSLRs are expected to withstand a lot more abuse, and I doubt that the paper-thin brushed aluminum covers found on their smaller cousins would do much good here. In fact, any material that I would select for my camera body of choice would likely be unsuitable for anodizing in the first place. And even if I were to insist on using some super-resistant aluminum alloy to produce machined bodies, the amount of surface preparation that would be required to obtain a beautiful anodized finish would likely be prohibitively expensive.
Aluminum lens components on the other hand are generally machined from high quality tubular stock. Lathe operations naturally yield the nicest surface finishes of all machining operations, requiring very little surface preparation prior to anodizing. In other words, such parts meet all the requirements for anodizing, whereas paint is almost immediately disqualified because of the very tight dimensional tolerances required for lens work.
Hope this helps,
Bert
Well, that makes sense. Unfortunately, because I would really have liked a camera body to match the beautiful black-anodized finish of the Pentax Limited lenses. They are all aluminium, no plastic or rubber, and gorgeous objects.
The main problem with having a DSLR with a metallic exterior is that it would be heavy (heavier), dent easily, be less grippy, and cold to the touch (which isn't nice in the winter).
ReplyDeleteFWIW, Pentax said they designed the K-7 to match, and be worthy of mounting, their Ltd lenses. I'll let you decide if they succeeded.
I hear you.
ReplyDeleteSo what about powder coating and electroplating?
ReplyDeleteSo what about powder coating and electroplating?
ReplyDeleteAs far as I know, dry powder coatings were developed as direct substitutes for paint, primarily to reduce/eliminate volatile emissions (for environmental reasons). For the purpose of this discussion, powder coatings and paint can thus be considered equivalent.
Electroplating is a process by which a metallic coating is applied on top of a conductive surface, using electric current to promote transfer of metal from a sacrificial electrode to the target surface. Note that there also exist many electroless plating processes, which can be used instead of electroplating, or sometimes to deposit a conductive coating on non-conductive parts in preparation for electroplating.
All plating processes require the use of many somewhat toxic, often highly corrosive solutions. The need for strict environmental controls and heavy waste water processing have all contributed to make electroplating much less attractive for any applications where adequate substitutes exist. Don't get me wrong, electroplating is still very widely used for all kind of applications, from printed-circuit board fabrication to corrosion protection on aircraft components, jewelry, etc. But it is relatively rarely used nowadays for purely cosmetic applications.
As far as general characteristics go, plating is mostly used to apply very thin coatings, most often less than one thousandth of an inch in thickness. Such thin coatings won't hide surface defects the way paint does, so parts requiring cosmetic quality finishes must be prepared accordingly (pretty much the same as anodizing).
Not all metals will bond properly to all surfaces, so it is not uncommon to have several successive plating operations performed (nickel over copper over aluminum, for example (not sure about that specific combo, it's been a while since I had anything to do with plating. But you get the idea :-)). It is a complex field, and setting up a production line for high volume manufacturing is no trivial matter, but electroplating can indeed produce some uniquely beautiful finishes.