KUBOTEK Nikon Rayfact 80mm f/3.5 Line Scan Lens test

Kubotek Optics 80mm f/3.5 line scan lens made by Tochigi Nikon

This is the Kubotek Optics 80mm f/3.5 line scan lens made by Tochigi Nikon for factory inspection of flat panel displays. This lens was designed for Kubotek's 12K, 4μm pixel pitch line scan cameras, according to the Kubotek site, the lens can resolve 1μm defects. Lenses designed for line scan work, usually make excellent macro lenses, since they are designed to cover large format sensors with a sharp, flat field, with consistent quality from edge to edge. 

There is zero reliable information available online on Kubotek lenses, so other than the fact that this is a Nikon Rayfact private label lens, I knew nothing about it when I picked it up. 

 

Kubotek Optics 80mm f/3.5 line scan lens at minimum and maximum magnification settings

The long outer barrel with big knurled ring is turned to set magnification, twisting the barrel moves two lens cells back and forth inside the tube about 60mm, setting the magnification from 1x to 0.25x. The lens has an ultra satin finish and the control movements are very smooth and precise, this lens is very solid and has feel and fit of an extremely expensive lens. Instead of an extending barrel design, this lens uses an extra long barrel that can accommodate lens travel needed for 1x magnification.

Kubotek Optics 80mm f/3.5 lens as purchased with Kubotek line scan camera KCCD7581.

These Kubotek lenses started showing up a few years ago in different configurations, most with camera attached, some include the entire mounting bracket complete with a micrometer stage. The prices for the units are very low, but the two units that I have seen in person, have both had fungus issues so beware and make sure the seller accepts returns.

The Kubotek inspection setup with the 80mm lens from the Kutotek site:  http://www.kubotek.com/enginfo/Ehome.html  

The Kubotek inspection setup with the 80mm lens from the Kutotek site: http://www.kubotek.com/enginfo/Ehome.html 

The information in this article is from my own personal testing on my own lens. I am not receiving compensation for it. I have no business relationship with any company mentioned in this article.

TECHNICAL SPECS

Kubotek Rayfact 80mm f/3.5
Part Number:
KLN-80-F3.5-4
Type: Industrial Large format 12K Line-scan Lens
Magnification range: 1x to 1/4x
Kubotek camera sensor pixel pitch: 4μm
Focal length: 80mm
Aperture range: f/3.5 - f/11
Sharpest aperture: f/4
Lens mount: This lens has M41 P=0.5 threaded mount
Filter thread: M61mm, unknown pitch.

Other than the decal on the side of the lens, there is no information available anywhere for this lens. If you have any info on these lenses please let me know.

Kubotek Optics 80mm f/3.5 line scan lens

Magnification Range

This lens arrived mounted on a Kubotek KCCD7581 line scan camera with a flange focal distance (FFD) of approximately 36mm, that is the distance from the mounting flange to the sensor. For testing I set up the lens on a Sony A6300 body with a FFD of 18mm and a combination of E-mount adapter and 15mm of extension for another 18mm, giving me a total of 36mm from the lens to the sensor. This set-up gives me a very convenient 1x to 1/4x magnification range on the Sony A6300 sensor.

You can use this lens with cameras with a longer FFD, like a Nikon with 46.5mm FFD, but this would take you beyond 1x where image quality may vary. You could change the magnification ring setting for less than the maximum setting to take you back to 1x, but this would mean that image quality might also vary slightly, compared to what you see here.

Pushing the lens closer to 2x, I did see a noticeable drop-off in image quality, so I would not use this lens for much more than 1x magnification.

 

1X test results

Click on any image below to launch a new window with a larger version. You can right click, or two-finger click with a Mac and select the open in a new tab or new window options.

Kubotek Optics 80mm f/3.5 line scan lens at 1x with Sony A6300 body.

Click on any image to launch a new window with a larger version. You can right click, or two-finger click with a Mac and select the open in a new tab or new window options.

Kubotek Optics 80mm f/3.5 line scan lens 100% crop examples

Silicon Wafers are perfect targets for testing a lens, since they are completely flat and don't warp in the middle of a shoot, like naturals subjects tend to do. Most importantly they have a lot of ultra fine detail that can be an excellent way to check sharpness, like the numbers 1-8 in the image above.

The Kubotek Rayfact 80mm is a seriously sharp lens at 1x. From the center to the far corner the lens is able to clearly resolve the smallest numbers etched on this wafer. Chromatic aberration is well controlled overall, but a tiny amount of red fringing becomes visible along fine lines, as you move towards the corners. The CAs are mild and not as high as a consumer macro lens like the Canon MP-E 65.

The image above was made slightly stopped down to f/4, I did test the lens wide-open at f/3.5 and the results were also fantastic.

the sharpest aperture

In the 100% crops below, the Kubotek Rayfact 80mm looks perfectly sharp wide open at f3.5. The peak in sharpness looks like f/4, and by f/5.6 there is a definite drop off in sharpness on the Sony A6300 body.

TEST SET-UP 

Camera: Sony α6300, model # ILCE-6300, also known as the A6300
Sensor size: 23.5 × 15.6 mm. APS-C. 28.21 mm diagonal. 3.92 micron sensor pitch
Flash: Godox TT350s wireless flash x 2 with one Godox X1s 2.4G wireless flash transmitter
Vertical stand: Nikon MM-11 with a Nikon focus block

All of the images above are from a single file and were chosen out of a stack of images. For consistency all of images were made on a MM-11 microscope stand with two godox TT-350 flash units and X1T wireless trigger.

A series of images was shot with each lens in 10 micron steps, and the sharpest image was chosen at Photoshop at 100% view. The single RAW file was processed in PS CC with all noise reduction and lens correction turned off, all settings were zeroed out (true zero) and the same settings were used for all of the images. 

LONGITUDINAL CHROMATIC ABERRATION TEST

Coming soon...

Longitudinal chromatic aberrations or LoCAs are ugly pink and green fringing seen in the out of focus areas in front of and behind the focus point of an image.  LoCAs are common, especially with fast lenses, so chances almost all of your lenses have at least a trace, you just never noticed. The problem is that LoCAs are extremely difficult to correct with complex designs using special glass to fully correct the aberration.

The optical glass used in lenses disperses or separates light in varying degrees. This is bad for image quality because it causes chromatic aberrations or CAs, where the different wavelengths or colors end up being focused at different points. This causes unsightly fringing that will reduce sharpness and resolution. Chromatic aberrations, or CAs, are produced by a lens that was not able to bring all the different wavelengths or colors of light to focus on the same point. A low dispersion lens element, with a lower the dispersion ratio, will scatter less the light which makes it easier for the designers to correct for chromatic aberrations.

MECHANICAL QUALITY

The lens barrel has a fine satin anodized finish and is really solid and well done. The magification ring on the lens tube is very smooth and tube itself is rigid, with zero flex. This is an industrial lens designed to withstand dust, heat, shock and vibrations present in an industrial environment. Both the lens aperture ring and the tube magnification setting have lock screws. 

AVAILABILITY AND COST

The Kubtek lenses found on the used market have been pulled from factory inspection installations and are being sold by surplus dealers, usually South Korea and China, the problem with that is that these have been sitting in less then ideal conditions in the surplus dealer's warehouses, not camera shops. So condition is a big issue with these lenses. As I write this in June 2018, there are 5 ads on Ebay with Kubotek lenses and cameras ranging from $299 to 499 USD, but make sure the dealer accepts returns. 

Flare Issue

If you are thinking about buying one of these lenses, there is an issue with flare that you need to know about.  This type of central hotspot is actually common with industrial extension tubes since the inner surfaces are not flocked or treated to reduce flare. Most Schneider Kreuznach, Thorlabs and other machine vision tubes have the exact same issue.

The fix is quick and dead simple; just roll up sheet of flocking material and slip the tube into the rear of the barrel to eliminate the problem. 


The roll of flocking material would be an issue in the field if you want to change the magnification, since the lens group shifts to the rear of the lens.

 

 

 

 

 

Fungus issue

Another issue with these lenses is fungus. The lens used in this article arrived from Asia with fungus and when attempted to return, or exchange the lens, the dealer chose to credit my payment instead. With nothing to lose, I decided to disassemble the lens to check the extent of the fungus damage.

The process was pretty basic. I removed the lock screws and bosses, and then removed the black tape disks that covered the mounting screws and removed these. The front cover was held in place with 3 small Phillips head screws. Once I removed these I was able to slide the two lens cells forward and out. Both of the these cells are sealed.

With a flashlight I could see that the fungus was covering the entire surface of the lens, but I got really lucky; only on the rear surface of the lens had fungus and the layer was easily removed with lens cleaning fluid, without leaving any trace.

Reassembly was straightforward, just make sure you align the lens cells aperture lever cut-outs, I slide the cells back in. Then replace all the fasteners and the front cover to finish.

Fungus seems to be a common issue with these lenses, so shop carefully.

 

 

SETTING UP the Kubotek 80mm LENS FOR MACRO PHOTOGRAPHY

The biggest problem with this lens is mounting. The unusual M41 x 0.5 mounting threads means it's going to next to impossible to find an adapter for sale. I am having a custom adapter made right now, so I will update this page once I receive a sample of the adapter.

This lens does not come with a tripod mount, so you will have to mount the lens to the body, and install a quick release plate on the body.

This Tamron Tripod ring (made for the old 300mm, 70-210, and 80-200) fits the lens barrel perfectly and makes it very convenient to add a long quick release plate. Since the entire outer barrel rotates to set the magnification, you would have to loosen the tripod ring and only lock it down, once the ratio is set. Otherwise the camera body will turn when you change the magnification with the lens ring locked down.

There is one of these old Tamron tripod rings on Ebay right now for $18.

 

Kubotek Optics 80mm f/3.5 line scan lens with a Tamron tripod mount

Kubotek Optics 80mm f/3.5 line scan lens

THE BOTTOM LINE

This Kubotek Rayfact 80mm f/3.5 was a lucky find. It's is a unique lens with a really useful magnification range an excellent performance from 0.25x to 1x, even at a wide-open aperture. The lens is an excellent buy if you can find a clean one without glass condition issues.

The main problem with this lens is mounting, but I am having a custom adapter made right that should be available for sale in the future.

What I really like:
Fast f/3.5 aperture
Consistent center to corner performance
Price vs performance value
Excellent fit and finish
Solid heavy duty design

What I dislike:
The entire outer barrel rotates to change magnification
The 41mm lens mount thread size
Lack of tripod mount
 

Kubotek and TOCHIGI NIKON

The Japanese Kubotek corporation started out manufacturing industrial inspection equipment for factory automation, now it looks like their main business is developing CAD/CAM software products for design, engineering, and manufacturing.

The Tochigi Nikon Corporation is best known for their Rayfact brand high-precision, high-quality industrial-use lenses made in Japan. They are the makers of the famous Eco-Glass versions of the famous Printing Nikkor 105mm F2.8, and Printing Nikkor 95mm F2.8.

LINKS FOR MORE INFO

Kubotek Inspection Optics page (in Japanese) :

http://www.kubotek.com/optics/next_g/il_aoi_optics.html

Kubotek english website:

http://www.kubotek.com/enginfo/Ehome.html