What is a Raynox?
Raynox is best known for their high-quality achromatic close-up lenses. Raynox performance is decent enough with APS-C and smaller sensors, but when you use the same lens with a infinity corrected microscope objective for photography they perform surprisingly well.
A detailed overview of the Raynox close-up lenses is available here on Closeuphotography.com: https://www.closeuphotography.com/raynox
Raynox as a Tube Lens
The term tube lens comes from microscopy and has become a standardized term for an infinity-corrected tube lens designed for use with a infinity-corrected objective to create a certain effective magnification ratio. An objective lens creates an image of an object at infinity and a tube lens is designed to refocus the collimated light rays into an image on the sensor. Raynox have become popular tube lenses for a couple of reasons, they don't cost a lot, less than $100 USD, and the image quality really is surprisingly good. Raynox are almost impossible to beat from a performance vs dollar standpoint.
TECHNICAL DETAILS
Raynox 208mm +4.8 (43mm mount)
This lens is labeled the RAYNOX MACROSCOPIC LENS MODEL M-150, and is sometimes sold labeled the Raynox 35mm MacroExplorer Model CM-2000 1.5X lens.
This is the most commonly used Raynox since the most common tube lens focal length used by Mitutoyo and most other manufacturers is 200mm.
Strength: +4.8 diopter
Focal length: 208mm
Optical Design: 2-group/3-element, Multi-coated optical glass elements
Chromatic Aberration Control: Very good when used as a tube lens
Normal Set-up:
- Infinity focus
- Normal mount
- 50mm from tube lens to objective
Optional Short Focus Set-up:
- Short focus, 144 mm extension from sensor to lens
- Normal mount
- 50mm extension from tube lens to objective
- 178mm effective FL lens, .86x magnification factor
Lens mount: 43mm x 0.75
Filter threads: 49mm x 0.75
Raynox 125mm +8
This lens is labeled the RAYNOX MACROSCOPIC LENS MODEL M-250, sometimes sold labeled the Raynox 35mm MacroExplorer Model CM-2000 2.5X lens.
The is also popular Raynox and is used to push down the magnification of a infinity-corrected objective where you can change the tube lens focal length to create different magnification ratios at the camera sensor, without compromising the color correction.
Strength: +8 diopter
Focal length: 125mm
Optical Design: 2-group/3-element, Multi-coated optical glass elements
Chromatic Aberration Control: One of the best corrected tube lenses available
Set-up:
- Infinity focus
- Normal mount
- Minimal space between lens and objective
Lens mount: 43mm x 0.75
Filter threads: 49mm x 0.75
These lenses where made in the 1990s so some samples have light haze, so I would recommend buying from a seller that offers returns.
Raynox 170mm +5.9
This lens is labeled RAYNOX DIGITAL CAMERA MACROSCOPIC LENS 2X, also the 35mm Microscopic Lens 6x model CM-3500, and was also sold as the Raynox video microscope lens 35x.
The 170mm Raynox is an excellent tube lens but these can be a little tricky to find since they are no longer in production. 170mm makes a nice focal length to slightly push down a infinity-corrected objective.
Strength: +5.9 diopter
Focal length: 170mm
Optical Design: 2-group/3-element, Multi-coated optical glass elements
Chromatic Aberration Control: One of the best corrected tube lenses available
Set-up:
- Infinity focus
- Normal mount
- Minimal space between lens and objective
Lens mount: 37mm x 0.75
Filter threads: No Filter Threads. The lack of front threads makes the lens installation more difficult but there are work-arounds, I use the rear section mount from a Sigma Life-Size Attachment closeup lens to give me 52mm threads.
The Bottom Line
All three of the Raynox lenses here are all excellent tube lenses. They are easy to find and they cost very little, about $70 new. The only downsides with these lenses are the small size threads. My studio set-up is based on 52mm x 0.75 threads so a lens like the Thorlabs ITL200 with a 52mm threaded Thorlabs adapter works better for me. But from an optical standpoint its hard to beat any of these three Raynox lenses.
Raynox Pros and Cons
Pros
-Low price
-Easy to find new
-Very good to Excellent image quality
Cons
-5 different names for the same lens can make shopping difficult for the beginner
-Small mounting thread size
-Plastic body
Things I dislike about Raynox Lenses
-The 43mm mounting threads
-Raynox has 5 different names and part numbers for the same lens
WHATS A TUBE LENS ANYWAY?
To use an infinity-corrected objective for photography, you will need a tube lens in addition to the main objective, or the system will not focus, since the tube lens is a required part of a infinity-corrected optical system. The tube lens can be a telephoto lens, a close-up diopter, or a tube lenses designed for a microscope.
To find out if you need to use a tube lens with an objective, it's easy to check, infinity-corrected objectives are identified with the infinite mark (∞) on the side of the lens barrel.
The magnification obtained by an infinity-corrected objective is the ratio between the focal length of the tube Lens and the objective. The most common tube lens focal length used by Mitutoyo and most other manufacturers is 200mm. With infinity-corrected objectives you can change the tube lens focal length to create different magnification ratios at the camera sensor, without compromising the 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.
Tube Lens Test
A detailed tube lens test with image comparisons is available here on Closeuphotography.com: https://www.closeuphotography.com/tube-lens-test