Using Raynox Close-Up Filter As Tube Lens
Overview
Many people started out macro photography with close up filters, some are cheap one and some are not so cheap, such as Raynox DC-150 and/or DC-250. These close up filters are very convenient to use, simply screws it onto a (usually) telephoto (zoom) lens. The results can be stunning as evidenced by many beautiful images shot with Raynox close-up filters.
There is another use for Raynox close up filters: it can be used as tube lens for infinite microscope objective! From my last blog post, I mentioned a pretty good article about microscope objectives, Understanding Microscopes and Objectives by Edmund Optics. From there, we know that an infinity corrected objective needs a another optical piece, called tube lens, to project an image onto a surface, in our case image senor of our DSLR camera. Raynox close up filter can do just that, projecting light rays onto camera sensor when positioned correctly and it has been proven the results are excellent, even for high end expensive APO objectives. Cool, right!
So theoretically the purpose of tube lens is to focus light beams coming out of microscope objectives onto our DLSR sensor, therefore, it is necessary to position the Raynox (as tube lens) at right position so that its focal plane coincides with the sensor plane. To do this, the Raynox must be placed at its focal length distance from the sensor. For Raynox DCR-150, the focal length is approximately 208.33mm and it should be placed at 208.33mm away from the sensor. For Raynox 250, the focal length is 125mm, therefore it must be placed at 125mm away from the sensor plane.
To place the Raynox at particular distance, we can either use extension tubes with helicoid to fine tune the distance. Or we can use bellows to achieve the same result. There is also another dimension of this matter -- either use the Raynox in reverse or normal position. Both work fine and I personally believe it is just a matter of preference, though some swear that it is best to use Raynox in reverse and insist so.
Using Raynox As Tube Lens (Normal Orientation)
Both Raynox 150 and Raynox 250 have 49mm female filter thread in front of it and 43mm male thread at the end. In this blog, I am trying to find a generic solution so that this approach can be used for other type of cameras. So here is one way of assembling it together with a M42 male thread at the end.
Picture 1
In the above picture, the whole assembly before the helicoid ends with a male M42 thread. Why? Because it is easier to adapt this approach to different camera types. In the above picture, it is for Canon camera. For Nikon camera, you can get extension tubes for Nikon, then a Nikon to M42 adapter (AI-M42) and mount that assembly onto the Nikon extension tube, same with Sony with Nex mount, or Olympus. etc
Here the purpose of the helicoid is to fine tune the position of the Raynox referenced to the camera sensor plane. This 12-17 helicoid is very light and smooth. For Raynox 150, here is the list for complete setup:
1x 37-RMS adapter
1x 49-37 step down ring adapter
1x 42-43 step up ring adapter
1x 12-17 M42 back to back helicoid
1x EOS-M42 adapter
4x #3 extension tubes of 28mm long
1x #2 extension tube of 14mm long
1x #1 extension tube of 7mm long
1x male EOS mount end of extension tube
1x female EOS mount end of extension tube
For other camera types, similar configuration with exception of extension tubes. Most camera extension tube are made up of five segments, the male camera mount, the female camera mount, one #3 of length 28mm, one #2 of length 14mm and one #1 of length 7mm. For the above setup for Raynox 150, 4 sets of extension tubes are used because 4 #3 segments are used.
Using Raynox As Tube Lens (Reverse Orientation)
There are discussions of using Raynox as tube lens in reverse position. It has been shown that this reverse configuration is superior than normal position, however, I personally have not experienced this.
Picture 2
As can be seen here, it is a little complicated than the normal position setup. One particular thing worth mentioning is the 62-58 step down ring. This particular step down ring has M58 thread threaded through, so you can thread a M58 end on either sides of the ring, so basically it serves as a M58 female to female adapter ring.
Things used in this configuration
1x 37-RMS adapter
1x 58-37 step down ring adapter
1x 62-58 step down ring adapter
1x 58-42 step down ring adapter
1x 42-43 step up ring adapter
1x 49-49 male to male adapter ring
1x 42-49 step up ring adapter
1x 12-17 helicoid with M42 on both sides
1x EOS-M42 adapter (for other camera type, use appropriate adapter, such as AI-M42 for Nikon)
4x EOS extension tube #3
1x EOS extension tube #2
1x EOS extension tube #1
1x male EOS mount end of extension tube
1x female EOS mount end of extension tube
Again, here the assembly from the RMS objective to 42-49 adapter ring can be used for different camera type. For example if a Nikon extension tube and an AI-M42 adapter are used, this assembly can be mounted to a Nikon camera. Same goes with Sony or Olympus camera.
Using a Bellow
Since a bellow allows us to adjust the position of a lens (assembly) easily, the helicoid and extension tubes are not needed. So with an EOS-M42 adapter (or AI-M42 for Nikon, Nex-M42 for Sony, M4/3-M42 for Olympus, etc), we can mount the assembly onto the bellow with ease.
Focusing to Infinity
After everything is set up, it is time to do the most important thing -- focusing to infinity by turning the helicoid. With Raynox mounted on a camera, point it at something as far away as possible, it is recommended to turn on live view and use the max digital zoom to help focusing. Here is an example: the red little thing next to the digital zoom box is about 2 kilometers away and it is actually very small in the frame but with help of digital zoom, it is blown up with fine details -- the Raynox is position at the right place that focuses parallel (almost, light ray from 2km away) onto the sensor.
Conclusion
Though for many people who stick to one type of camera, it is still a good idea to end with a male M42 for the front assembly because it is easier to find the rest of parts -- extension tube and camera specific mount to M42 adapter. Of course, you can use M42 extension tube through out, but you might end up vignette for some full frame cameras.
And the most important thing after setting it up is to make sure it focuses to infinity because an infinite microscope objectives converts lights as if they come from infinity (hence the name infinite objective).
