Mitutoyo MT-1 Tube Lens Test With 5x M Plan APO
The 200mm MT-1 tube lens is made by Mitutoyo for the companie's APO infinity-corrected objectives. The lens is designed to cover the visible wavelength range with correction from 435nm to 656nm.
This is not a very popular tube lens, probably, since the cost as new is about $750 USD compared to about $60 for a Raynox +4.8 208 mm tube lens. Used units do appear on Ebay occasionally.
There are a total of 5 tube lenses sold my Mitutoyo, and the MT-1 looks like the best choice for photography. The MT-L is designed for near-ultraviolet, the MT-L4 is for ultraviolet light, MT-2 is 400mm, and the MT-40 has a smaller image field than the MT-1.
I compared 18 tube lenses in a test last month where the MT-1 performance was about average, but a re-test with the lens mounted in reverse, the lens did much better. You can see some image samples and comparison images below.
WHAT IS A TUBE LENS?
Tube lenses are a required part of an infinity-corrected optical system. To use an infinity-corrected objective for photography you must have a tube lens in addition to the main objective or the system will not focus. Infinity-corrected objectives are identified with the infinite mark (∞) on the side of the lens barrel.
Microscope manufacturers design their systems to provide the magnification engraved on the housing when they are used with a tube lens of a specific focal length. 250mm tube lenses are standard for Qioptiq, Mitutoyo, Thorlabs, Nikon, and Leica objectives, use a 200 mm tube lens as standard.
With infinity-corrected objectives you can change the tube lens focal length to create different magnification ratios at the camera sensor without compromising the axial color correction. To calculate the system magnification for different tube lens and objective combinations, you can use this simple formula; Effective magnification = Marked magnification x the new tube lens focal length/the system tube lens focal length.
Setting Up the MT-1
The biggest downside of using a tube lens like the MT-1 is the custom mount. The flange on this lens has 3-2.4 drilled holes and is made to fit Mitutoyo microscopes. Non-standard mounts are typical for tube lenses; the Nikon MXA20696 and Thorlabs ITL200 also use proprietary mounts.
The use of a non-standard mount makes things a little more difficult but not impossible. I keep a couple of Sigma LSA, Life-Size Attachment 52 mm x 0.75 mount lenses on hand, exactly for this kind of project. I pick up the Sigma LSA on Ebay for a few bucks, $20-30 and a few times the units had a little bit of haze, so rather than throw them away, I keep these for use with this kind of project.
Sigma LSA 52 mm close-up lens with a Mitutoyo MT-1 tube lens.
You can usually loosen the retainer ring by hand, if not, you need a rubber 52mm lens wrench designed to remove lens retainer rings. Once the Sigma LSA glass is removed you can use the 52mm housing and ring to hold lenses like the MT-1. It's an easy 5 minute install and you can easily mount the MT-1 in normal or reverse orientation.
Above, on the left, you can see the MT-1 mounted in reverse, flange towards sensor, and on the right, the flange side pointed towards the objective.
The diagram below shows the set-up I found best in testing. Mitutoyo's set-up on the left and best imaging set-up on the right.
Forward Or Reverse?
After spending a lot of time testing the MT-1, I have found that for best image quality the lens should be used in reverse with the lens flange towards the sensor. I know this is the opposite of what Mitutoyo recommends. Feel free to follow their instructions, but be prepared for reduced image quality compared to the proper set-up.
To compare the image quality with the MT-1 in normal and reverse I used the lens with the Mitutoyo 5x M Plan APO lens on a Sony A6300 on a Nikon MM-11 vertical stand with two godox TT-350 flash units and X1T wireless trigger for consistency and the sharpest results possible. For more details on the test set-up, see the TEST SET-UP DETAILS section below.
Un-cropped 5x showing the crop areas highlighted in blue.
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.
In the center crop area at 100% the image with the lens mounted in reverse is much sharper and cleaner with a lot less lateral chromatic aberrations. The difference between normal and reverse mounting is striking.
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.
The off-center crops also are really improved with the lens in reverse.
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.
In the corners the story is a little bit different; in reverse the corners have less CAs but the sharpness is not as good as the normal mounted lens. I would choose the softer CA free reverse image, but if corners are very important, then I would go with a more consistent lens like the Thorlabs ITL200. Note that each crop area is picked from a series of focus bracketed images, so field curvature is not an issue.
TUBE LENS TEST SET-UP
This lens was tested with 17 others as part of a tube lens test that I ran last month. For the tube and close-up lenses I shot these forwards and reversed. For all the lenses I tested without any objective extension and with my normal 75 mm (3 inches) of extension.
For this comparison I used a favorite 6 inch 150 mm silicon wafer. Silicon Wafers are perfect targets for testing a lens. Nothing beats a wafer for flat ultra-fine details, the geometrical patterns are from a few microns (μm) down down to the nano-meter (mµ) range. The best part of working with wafers is they will not warp or change shape in the middle of a test, they are perfectly flat and they stay flat.
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.
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.
Test of The Best Tube Lenses at 100%
Thorlabs ITL200 Tube Lens
Mitutoyo MT-1 Tube Lens reverse mounted
Raynox DCR-150 / Model CM-2000 1.5X / +4.8 diopter / 208mm Lens
Sigma LSA 200 mm Close-up Lens
The center crop area compared at 100% view in Photoshop.
Click on any image below to launch a new window with a larger 2500 pixel version. You can right click, or two-finger click with a Mac and select the open in a new tab or new window options.
Comparing center crops, all of the lenses are sharp at 100%, but the MT-1 looks sharpest. The Thorlabs and Raynox do best with the least amount of chromatic aberrations, but the MT-1 is better than the Sigma LSA.
All of these images in this test were processed with the settings in Photoshop with all correction turned off.
The off-center crop area compared at 100% view in Photoshop.
Click on any image below to launch a new window with a larger 2500 pixel version. You can right click, or two-finger click with a Mac and select the open in a new tab or new window options.
Off-center there is not much difference; all of the lenses have excellent detail and sharpness. The Sigma has a slightly higher amount of lateral CAs.
The corner crop area compared at 100% view in Photoshop.
Click on any image below to launch a new window with a larger 2500 pixel version. You can right click, or two-finger click with a Mac and select the open in a new tab or new window options.
In the corners things get a little strange. The ITL200 is best here, sharp and no CAs. The MT-1 is sharper than the Raynox and the Sigma but it has some CAs in here. The Raynox and Sigma show zero CAs in the corner crops.
Test CONCLUSION
The performance in the center and off-center are very good to excellent when mounted in reverse, but the poor corners hurt the overall performance compared to lenses like the ITL200 that are much more consistent from edge to edge over the entire frame.
TECHNICAL SPECS
Mitutoyo MT-1 Tube Lens
Part Number: 970208
Type: Tube Lens
Focal length: 200 mm
Optical Design: Achromat
Lens mount: 3-2.4 drilled holes
Manufacturer: Mitutoyo
Correction: Visible light
AVAILABILITY AND COST
The MT-1 sells on Edmund Optics site, new for $725 USD. For a much less cost I would recommend the Thorlabs ITL200 that is actually made by Nikon. A detailed review of the ITL200 lens is available here on Closeuphotography.com; https://www.closeuphotography.com/thorlabs-itl200/
PROS AND CONS
What I really like:
Center sharpness
What I dislike:
Cost
Image quality when mounted normally
Mitutoyo proprietary microscope flange mount
THE BOTTOM LINE
Out of the 17 lenses I tested, the ITL200 easily had the best image quality for 200 mm tube lenses. The MT-1 was not a top performer overall, but it does have great center and off-center sharpness comparable to the best lenses when used in reverse.
Also you should not forget the MT-1 lens performs better in reverse, the opposite of what Mitutoyo recommends.
Its a mystery why Mitutoyo makes and sells a non-APO corrected tube lens for their excellent APO corrected objectives.
There are a few other excellent tube lenses in other focal lengths that I have tested as part of a tube lens test. For more details the tube lens test is available here on Closeuphotography.com: www.closeuphotography.com/tube-lens-test
TEST SET-Up DETAILS
A series of images was made with each lens in 5 micron steps. This was repeated for each aperture. Then the sharpest frame was then chosen using Photoshop at 100% actual pixel view. Separate images were selected for center, edge, and corner if needed. Each image was processed in PS CC with identical settings 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. All of the images shown here are single files.
LINKS FOR MORE INFO
The MT-1 lens on the Edmund Optics site:
https://www.edmundoptics.com/p/mt-1-accessory-tube-lens/11488/
The Tube Lens test page on Closeuphotography.com: