Nikon D3 (color at left), Nikon D70-IR (infrared at right)

Contents

Introduction

Updated: May 11, 2008

This article is in progress—more is planned. Check back regularly.

This article covers the Coastal Optics 60mm f/4 UV-VIS-IR APO macro (see the brochure also). Its performance is unique, offering parfocal and true apochromatic performance from approximately 315nm (ultraviolet) to 1100nm (infrared), with transmission from 290 to 1500nm. There is no other lens available today that can offer that sort of performance, though the long-discontinued Nikon 105mm f/4 UV Micro-Nikkor offers an approximation in the UV and visible light bands. Even the legendary Hasselblad 250 SuperAchromat doesn’t claim that wide an apochromatic band. The Coastal Optics lens stands head and shoulders above anything offered to the public.

Don’t miss the lens designer notes.

Pricing and intended market

At US$4495, the 60/4 won’t find its place into very many camera bags, but for science, forensics, multi-spectral and fine-art photography, it’s a boon to have such a capable lens available. This reviewer hopes that Coastal will extend the lens line to include 24mm, 35mm, 135mm and 270mm lenses of similar quality.

For those shooting ultraviolet, it’s one of the very few options available. For infrared, it’s the ultimate performer. One lens that performs to the level of the very best lenses in ultraviolet and visible light and infrared is something you simply cannot enjoy with any other lens—and it’s a macro lens too!

Exotic optical design

With no less than five (5) of its 10 elements made of calcium fluoride, it truly is an exotic lens. By comparison, perhaps one or two of Canon’s finest lenses might be made of fluoride. In addition, the lens coatings are 12-layers and designed to handle that 315-1100nm range—conventional lens coatings attenuate huge portions of that spectral band. Even the Zeiss ZF Prototype lenses use a simpler coating optimized only for infrared.

A few other exotic lenses exist in the rarefied territory of UV-capable lenses, including the Nikon 105/4 UV-Nikkor (long since discontinued), the Pentax 85/4.5 Ultra apochromatic (circa 1975), and the (medium format) Hasselblad/Zeiss 105/4.3 UV-Sonnar. There exist other specialty lenses, most of which were made in very small numbers (and of varying optical performance), but it’s a safe bet that few to none of them offer the versatility and high performance from UV through infrared that the Coastal 60/4 APO does, especially once one considers the MTF performance and flare-resistance throughout the ultraviolet, visible and infrared spectral bands, in addition to the low distortion and pleasing bokeh. And of course, only a small handful of the potential lenses could actually be mounted on a Nikon or Canon body without modification.

For visible and infrared applications, there is also the medium-format Hasselblad/Zeiss Sonnar 250/5.6 SuperAchromat, though it is not claimed to be UV-capable (corrected for 400-1000nm), nor does its MTF look especially good in comparison to the Coastal 60/4 (even bearing in mind that it covers medium format). Anyone in the San Francisco Bay Area owning this rare lens is encouraged to contact the author—I’d like to evaluate it on my Canon EOS bodies using a Hasselblad-to-EOS adapter.

Ergonomics and build quality

Build quality is first rate. It appears that the lens is made from anodized aluminum, very robust and solid. The focusing helicoid is very smooth, with nice “throw” (albeit opposite in direction to Nikon lenses). Focus is entirely manual, but Nikon’s “focus assist” works with it.

The aperture ring offers distinct click stops, though these aren’t needed on Nikon bodies—the 60/4 is fully automatic (excepting focus); one sets the aperture on the camera body and the lens stops down electronically, just like any Nikon-made lens. And that’s in 1/3 stop increments too. The lens does have an aperture ring however, so it can also be used (with an adapter) on Canon bodies.

The one thing missing is a lens shade. However, the B+W rubber 52mm telephoto lens hood is a near-perfect match as well as offering protection to the front of the lens; it’s a must have for both reasons because unlike many macro 50-60mm lenses, the front lens is not deeply recessed in the lens barrel.

Filtration

For shooting ultraviolet and infrared images, filters are needed to block out unwanted portions of the spectrum. Filters can be internal (often with cameras converted for infrared use) or external. See the Spectral Transmission Graphs page for graphs of some common filters.

Click for details

Notes from the lens designer

These notes are straight from the lens designer, J. Brian Caldwell, Ph.D., of Caldwell Photographic Inc, in response to questions posed by Lloyd Chambers of diglloyd.com. Italicized type indicates lens designer comments.

Field Curvature

The lens was optimized for a flat image plane for both distant and close object distances, and there is very little to be gained by allowing the image plane to curve, or equivalently considering a curved object plane. If you look at the MTF curves for infinity focus that I put in the online brochure you'll see that at f/5.6 there is essentially no drop in performance over the DX format (~29mm diagonal), and only a very small performance drop in the outer parts of the FX format (43.2mm diagonal). So, at f/5.6 you probably will have difficulty detecting any field curvature at all.

At f/4 the MTF curves show a little more off axis performance drop than at f/4. You might be able to detect a very small amount of field curvature at f/4, but it will not be at all obvious. I took some images of large flat test charts, and the lens delivered sharp images at f/4 out to the extreme corners on a Canon 5D (using a mount adapter).

At close-up distances there is virtually zero field curvature, and this is one reason why the MTF curves that I show for 1:2 magnification are so flat across the field. In fact, at 1:2 and f/5.6 the lens meets the more challenging criterion for a diffraction-limited lens (Strehl ratio > 0.8) from 365nm all the way to 900nm.

Focus Shift (color dependent)

Emphasis (bold) added by diglloyd.com.

The lens is a true apochromat in the old-fashioned and more rigorous sense of the word, with three widely spaced color crossings in the UV, VIS, and IR portions of the spectrum. As you probably know, true apochromats are a surprisingly rare thing in photographic optics despite the proliferation of "apo" lenses on the market.

The MTF curves that I calculated for the UV, VIS and IR portions of the spectrum all share a common image plane. In other words I forced a zero focus shift condition on the analysis. Despite this, the MTF values are exceptionally high for all portions of the UV-VIS-IR spectrum. There is a small drop in the IR band, but this is due to diffraction. In the UV it is possible to squeeze out a tiny amount of extra performance at wider apertures by shifting the focus about 0.001", but this is really just a theoretical thing that would be very difficult to observe in practice.

Focus Shift (aperture dependent)

There is essentially zero focus shift as you stop down from f/4 to smaller apertures. I paid special attention during the design phase to ensure this.

Close Focus vs. Infinity Performance

The design is a two-group type in which the rear group is stationary during focusing. This ensures that the residual aberrations, especially coma, remain small for all object distances. As I mentioned above, the lens is diffraction-limited at 1:2 magnification at f/5.6 (~f/8 effective). At infinity focus it is close to diffraction limited at f/5.6, but the wavefront error is slightly greater than at 1:2. Nevertheless, the MTF at infinity is better than at 1:2 simply because the effective aperture close-up is about a stop slower.

In other words, performance is very good at all focus distances.

DIGLLOYD: translation: “very good” = world class.

Peak Performance

The optimum aperture is f/5.6. Opening up to f/4 or f/4.5 improves the on-axis performance very slightly, but drops corner performance. Stopping down from f/5.6 to f/8 improves performance slightly in the extreme corner of an FX frame, but drops performance over most of the field. f/11 is worse than f/8 in every part of the field.

DIGLLOYD: diffraction rears its ugly head...

Color Rendition

Color rendition in the visible should be very neutral because neither the coatings nor the optical materials impart any substantial color shading. The AR coatings are a 12-layer stack designed for good performance over an extremely wide waveband, and they have very little variation over the visible band.

We did do an end-to-end transmission measurement of a complete prototype using a spectrophotometer, and it does show a fairly flat performance from ~350nm out to ~1000nm. The coated surfaces do have a very pale color cast, but not nearly as strong as a typical multicoated lens.

The coatings are 12 layers deep, which is pretty exotic for a photographic lens but is necessary to achieve the performance we wanted over such a wide waveband. From 300-1000nm the coating efficiency is approximately 99%, meaning that there is a reflection of about 1% at each air-glass interface. This is good, but not as good as visible-only AR coatings, which can be roughly twice as efficient.

When you point the lens at the sun you will get flare, but I haven't yet done a detailed comparison with other lenses.

DIGLLOYD: field shooting shows that flare control is not perfect, but bettered by very few lenses, and is rarely a problem in practice. The 52mm rubber B+W Telephoto lens hood is highly recommended for the 60/4.

Hot spots (infrared)

Hot spotting is a completely different issue. I paid particular attention to the central hotspot issue during the design phase, and was able to keep pupil ghosting at the center of the frame to a minimum. This design approach combined with very good coating performance in the infrared pretty much solves the hot spot issue.

Using a B+W 93 filter with an unmodified D70 camera I have been unable to see any sign of a central hotspot regardless of aperture. I have done some work with tricolor IR filters from MaxMax, and these do cause a diffuse hot spot due to their dichroic nature. However, the lens is not involved in this.

DIGLLOYD: see the diglloyd Guide to Digital Infrared Photography for an extensive study of infrared hot spots with over 50 lenses.

Sensor cover glass

Emphasis (bold) added by diglloyd.com.

The lens is designed to be used with a 2mm thick plane parallel piece of glass in front of the sensor. This models the effect of the filter pack used in most cameras. If you use a camera in which the glass has been removed there will be a slight performance drop in the outer part of the field. Its a fairly minor effect, but something you should be aware of.

Also, if you use an IR modified camera which has been tuned to counter the "typical" IR focus shift error found in the "typical" photo lens you will wind up with a focusing error when using the 60/4 UV-VIS-IR. For accurate shooting in the UV and IR you need the camera to be set up for accurate focusing in the visible waveband.

Regarding the sensor glass, there are at least two distinct issues. First is the issue of visible/infrared parfocality. I purchased a copy of your excellent article on IR imaging, and its pretty obvious that most (virtually all?) lenses do not hold focus in the IR when you focus in the visible. Our lens has no focal shift between visible and IR, or between visible and UV. Thus, the ideal IR-converted camera for our lens would have a replacement sensor glass that has an optical thickness identical to that of the original filter pack.

DIGLLOYD: It is correct to say that none of the over 60 lenses tested can hold the same focus from visible through the infrared band. The 60/4 is unique in being able to achieve this. Which leads to a compromise when converting a camera: convert for the 60/4 or convert for the average lens? Recommendation: if you’re buying the 60/4, optimize for it.

In the case of your converted 5D, it sounds like MaxMax made a stab at trying to counteract the IR chromatic aberration found in virtually all photographic lenses by using a different optical thickness for their replacement sensor glass. As a result you will probably get a small focus error when using this particular camera with a perfectly corrected lens such as ours.

Of course, the technique used by MaxMax cannot account for varying degrees if IR focus shift found among different lenses, nor can it account for varying degrees of focus shift that you get when using different IR filters.

DIGLLOYD: This mirrors my research in the diglloyd Guide to Digital Infrared Photography.

The Coastal lens is adjusted to work properly with a standard F-mount, and as a result will focus correctly on any standard Nikon digital or film camera, or on any standard Canon camera with an appropriate mount adapter. Due to the extensive use of fluorite we have incorporated a small over-travel on the focus motion to allow infinity focus in extremely cold temperatures, but this is a fairly minor detail.

The second issue relates to aberration correction. Any time you place a plane-parallel piece of glass in the path of a converging light beam you introduce aberrations. Virtually all digital cameras have a cover glass of some sort. Even if you remove the filter pack there is still a thin coverslip that protects the actual pixel structures. The vast majority of digital cameras also include a filter in addition to this coverslip. In order to achieve the best possible performance in a lens to be used with digital cameras it is therefore necessary to include the effects of all this glass near the image plane, and to counteract it by proper design of the lens.

When designing the 60mm f/4 I called several people who were doing IR and UVIR camera conversions, and was told that DSLR filter thicknesses ranged from ~1mm to more than 3mm. There is no standard thickness, unfortunately. However, I had to pick something, and 2mm seemed like a reasonable compromise. It seems that this choice might be a very good match for a standard Canon 5D, since the filter pack is 1.45mm thick and the coverslip is probably ~0.5mm thick. Making a small error in filter thickness has a fairly minor effect on the aberrations, and even omitting it altogether will not cause a drastic reduction in performance. After all, any lens designed for film cameras will automatically have aberrations induced by the sensor glass when used on a digital camera, but very few people notice this effect.

The sensor glass aberration effect is much greater when the exit pupil is shorter. Quasi-symmetrical large format lenses such as the Rodenstock HR series, which have a very short exit pupil distance relative to the image diagonal, really must account for the sensor glass in order to maintain good performance in the corners. In our case the exit pupil is much further away, and my decision to account for the sensor glass is based on a simple desire to achieve the finest possible image quality. From the beginning my goal has been to achieve not just ultra-broadband correction, but also to achieve better visible band performance than any other manufacturer.

DIGLLOYD: And indeed shooting to date with other exotic lenses including the Leica 90/2 APO Summicron-R and the Leica 180/2.8 APO Elmarit-R does not suggest that the Coastal Optics 60/4 can be bettered.

Optical performance

MTF (modulation transfer function)

The Coastal 60/4 is diffraction-limited by f/5.6 across the UV-VIS-IR spectral band. A few exotic lenses approach this level of performance, such as the Leica 300mm f/4 APO or the 90/2 APO Summicron-R or the 180/2.8 APO-Elmarit-R, but none of them can do so outside the visible light range.

MTF at infinity, visible light (400 - 700nm), f/4, f/5.6, f/8

Wide open at f/4, MTF is excellent, indeed outstanding in the center, dropping off gracefully into the extreme corners. Conventional lenses stopped down 2-3 stops might show somewhat better performance in the corners in most of the visible light range, but most will also show chromatic errors that are not seen with the Coastal 60/4. One stop down at f/5.6 the 60/4 offers world-class performance; stopping down just 1/3 or 2/3 stop from f/4 yields most of this improvement.

More important for many subjects will be depth of field, which makes f/8 the optimal aperture for overall results in practice. While a graph for f/11 is not available, diffraction can be expected to reduce performance noticeably.

MTF at infinity, visible light

MTF at infinity for UV & IR, at 1:2 for visible light

Performance in the UV band is simply outstanding, and still outstanding in the infrared band, though slightly lower due to diffraction, which degrades performance with longer wavelengths.

MTF at infinity for UV & IR, 1:2 for visible light

Chromatic aberrations and distortion

This level of chromatic correction is extremely difficult to achieve, which explains why the Coastal 60/4 uses so many fluorite elements, which are expensive (and even the supply of calcium fluoride glass is limited).

Distortion is extremely well controlled for a 60mm lens.

Distortion (left) and chromatic aberrations (right)

Relative illumination and spectral transmission

See the Spectral Transmission page for more on spectral graphs. Vignetting is minimal, an excellent performance by f/5.6, the optimal aperture.

Distortion (left) and chromatic aberrations (right)

Apochromatic (APO) behavior — out of focus rendition

The “APO” designation of some 3rd-party lenses is a marketing claim of dubious technical merit.

The Coastal 60/4 offers the real deal. The magenta/green color fringing seen with conventional lenses is completely eliminated with the Coastal 60/4. Does this matter? Absolutely—the effect of the Coastal 60/4 on real pictures is an uncanny clarity, a lifelike rendition you just won’t find in conventional lenses, lenses that tinge the background with funky discolorations never seen in real life. These discolorations are especially troublesome on scenes that include out-of-focus highlights, where the oddball color fringes draw attention to themselves.

In addition to the discoloration caused by non-APO performance, the depth of field seems to be higher with the Coastal 60/4 eg at the same aperture the Coastal 60/4 offers superior depth of field. This might be due in part to the demosaicing process required for today’s digital sensors, since detail over the spectrum is blurred to a different extent by non-APO lenses—hence the color fringes.

The comparison below is with the Nikon 60mm f/2.8D, a well-corrected lens of excellent optical quality. Even so, the magenta/green color fringes of the Nikon 60mm are clearly evident, in stark contrast to the completely neutral rendition of the Coastal 60/4 APO.

    
Coastal Optics 60/4 (left), Nikon 60mm f/2.8D (right)
Both images taken at f/4

Diffraction limit

The Coastal Optics 60/4 UV-VIS-IR APO macro is diffraction-limited by about f/5.6 - f/8, depending on focus distance. Some improvement in contrast is seen by stopping down from f/4 to f/5.6. For critically-sharp images (excluding depth of field requirements), f/5.6 should be the aperture of choice at closer distances, and f/8 near infinity (Nikon D3). On higher resolution cameras such as the 21.1MP Canon EOS 1Ds Mark III, a small but observable drop in image contrast begins by f/8, due to diffraction.

diglloyd Guide to Digital Infrared

Want to take months or years off the infrared learning curve? Get the definitive Guide.

diglloyd Guide to Digital Infrared Photography

Examples and image quality

This section shows photographs taken with the Coastal 60/4 APO macro.

Color examples

Sharpening on the example images was done very conservatively to show the inherent quality; the samples can be made to “pop” with additional sharpening, but that would eliminate certain subtleties that are best left alone for showing the quality of the 60/4.

The total lack of any residual color aberrations results in very high image quality with unadulterated color, an especially lovely combination with the beautiful tonal and color quality of the Nikon D3. Especially notable is the total absence of out-of-focus green/magenta color fringes seen with most other lenses; this leads to an especially natural look.

Flowers

The Nikon D3 and Coastal 60/4 work together beautifully. The Nikon D3 offers exceptionally smooth high quality pixels, and the Coastal 60/4 contributes image rays free of virtually all aberrations, especially the disturbing magenta/green color fringes seen with so many other lenses on out-of-focus areas. The result is pure, unadulterated color.

Nikon D3. Coastal 60/4 @ f/8, ISO 1600

Nikon D3. Coastal 60/4, handheld 1/100 @ f/11, ISO 800

Nikon D3. Coastal 60/4, handheld 1/100 @ f/5, ISO 1600

 

Brick wall [Nikon D3]

Shot at f/8 for depth of field considerations. Focus was on the brick wall, but might have been slightly off. Obtaining critical focus is always a technical requirement, even with Live View.

Nikon D3. Coastal 60/4 @ f/8

This image shows the beautiful color and bokeh (background blur) possible with the 60/4.

Nikon D3. Coastal 60/4 @ f/5.6, handheld

The Coastal 60/4 provides striking color rendition; its total lack of chromatic errors means that the color comes through in all its subtlety as in this “spring green” scenery. After shooting with the lens for a while, one notice a certain dullness with many other lenses (though not all); they impart a slight veil over the natural rendition—the 60/4 always delivers.

Nikon D3. Coastal 60/4 @ f/8, handheld

The Coastal 60/4 delivers outstanding detail even on the 21 megapixel Canon EOS 1Ds Mark III, right out to the corners, though f/8 seems to be required on the Canon 1Ds Mark III to bring the extreme corners to perfection. Click to see a larger image and actual-pixels.

Canon EOS 1Ds Mark III. Coastal 60/4 @ f/8

Many lenses would have a difficult time with a scene like this: white streaks on saturated red. The chances of red/cyan color fringing would be very high. But nowhere in the frame can even a trace of such color fringing be found with the Coastal 60/4. (Note: this image was shot handheld from a car and isn't at peak sharpness).

Nikon D3. Coastal 60/4 @ f/9, handheld from car

Infrared examples

See also the following 2008 blog entries: Jan 16, Jan 18, Jan 23, Jan 27

Because most cameras converted for infrared have had their focus adjusted for “average” lenses that strongly backfocus (focus behind what is seen in visible light), the Coastal 60/4 can front-focus on some cameras since it has zero focus shift from UV through IR. This means that accurate focus might require some trial and error (shoot, zoom in on the camera LCD, adjust focus, etc). The author’s Canon EOS 5D-IR suffers from this problem but his Nikon D70-IR does not.

The performance seen in infrared is limited largely by focus accuracy (and sensor digital artifacts and Bayer interpolation). It’s a shame that a monochrome sensor is not available to exploit the stunning sharpness of the 60/4.

Red Barn. Nikon D70-IR

Hiker. Nikon D70-IR

Cliff and Ocean. Nikon D70-IR

It just doesn’t get any better than the level of detail seen in the next two images. Careful attention was paid to focus, and even though the 60/4 was stopped down beyond its optimal f/5.6 aperture, the results are still stunning. Click to see actual-pixels crops.

Miners food (Death Valley, CA). Canon EOS 5D-IR

Mining Death Valley. Canon EOS 5D-IR

Tools of the trade. Canon EOS 5D-IR

Ice in infrared false color. Nikon D70-IR

 

Moon and Plane. Nikon D70-IR

Moon and Plane. Nikon D70-IR

Beach. Nikon D70-IR

Trees. Nikon D70-IR

West Alpine Road. Nikon D70-IR

Ultraviolet imagery

As of April 2008, the author lacks UV-capable camera. The example below shows the Nikon D3 using the Coastal 60/4 with the Baader “Venus” filter (original).

Nikon D3 with Baader “Venus” filter

UV-capable lenses

If the aim is to shoot ultraviolet, there are several other options. Here are a few:

• Coastal Optics 105/4.5 APO macro (250-650nm correction)
• Tochigi-Nikon UV-105/4.5, see the specifications. This lens is very similar to the original UV-Nikkor, perhaps even the same design.
  
• A used Nikon 105/4 UV-Nikkor

All of these options are more limited in spectral range than the Coastal 60/4 APO macro. They might not offer the same level of performance in other ways as well (flare resistance, color rendition, etc).

Conclusions

The Coastal Optics 60/4 UV-VIS-IR APO macro is a reference lens for other lenses, and uniquely capable of imagery across the UV/visible/IR spectral bands simply not possible with any other lens available today. On a scale of 1 to 5, it is a 5+.

Value

While the price of the Coastal 60/4 APO is high in absolute terms, its value in relation to the unprecedented and unique capabilities it offers is in line with other specialty lenses (unless one is pricing lenses by the pound/kilogram!).

Paying for the unique capabilities of the Coastal 60/4 is no different in principle than paying US$4500 for Nikon’s 300/2.8 AF-S VR or US$8000 for the 500/4 VR—such lenses are designed to perform for specific uses, and those needing them (sports and wildlife photographers) realize that fact. The mental hangup comes from expecting a $4500 lens to weigh 6-10 pounds and be huge and heavy, which is a silly way to evaluate the value! The Coastal 60/4 is a a diamond among lesser optical gems, and worth its price.

Nit picks

Coastal should supply a lens hood with the 60/4, perhaps simply obtaining a supply of the 52mm B+W rubber telephoto lens hoods.

Coastal could broaden the market appeal of the 60/4 by offering a Canon-mount version, even if it were to be via a (certified-compatible) adapter option.

Coastal should offer filter options with the 60/4, eg those for UV and IR and visible usage on full-spectrum and/or modified cameras.

More on infrared

Want to learn all about infrared? Get the definitive Guide.

diglloyd Guide to Digital Infrared Photography

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See also:

Search for infrared at diglloyd.com

Digital Infrared

Infrared Contamination—Good Color Gone Bad

Zeiss ZF Prototype Lenses for Infrared

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