How can I use a beam splitter behind a camera lens without losing so much light?
Asked 3/9/2011
2 views
2 answers
0
I’m placing a beam splitter between a camera lens and the imaging sensors/cameras. In my current setup, adding the beam splitter increases the distance from the lens to the sensor, so I can only reach focus by adding a diverging lens in front of the main lens. That works, but it causes a significant light loss. Is there a better way to achieve focus in this kind of optical path? For example, would a relay lens or other transfer optics be a better approach? I’d prefer an established solution rather than designing something from scratch.
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
15y ago
2 Answers
2
The problem is that placing the beam splitter between the lens and the cameras increases the distance between the lens and the sensor to the point where you can focus only at very close distances.
One solution is to buy a lens for a large-format or viewfinder camera: these are designed for greater lens-to-focal plane distances and many of them have largish maximum apertures. There's a good market in secondhand lenses. See Ken Rockwell's article for a start. The Ebony site has a good discussion of lens extension and points out that retrotelephoto lenses can be used to get greater extension (than their nominal focal lengths indicate).
Originally by user1356. Source · Licensed CC BY-SA 4.0
user1356
15y ago
0
Generated from our catalog & community — verify before relying on it.
The core issue is the extra optical/mechanical distance introduced by the beam splitter. Moving the sensor farther behind the lens shifts focus so much that a normal SLR lens may only focus very close unless you add corrective optics. Your diverging lens restores focus, but it also costs light.
A more practical option is to use a lens designed for a longer flange/focal distance, such as a large-format or view-camera lens. These lenses are intended to work with greater lens-to-image-plane distances, so they can better tolerate the extra spacing caused by the beam splitter without needing a front-mounted diverging element. Some retrotelephoto designs can also provide more back focus than their nominal focal length suggests.
So yes, relay/transfer optics are one possible route, but the simplest established solution from the answers is: use a lens intended for longer extension rather than adapting a standard SLR lens with a diverging lens in front.
Recommended products
UniqueBot
AI15y ago
Your Answer
Related Questions
Can a beam splitter send one lens image to both an infrared and a visible-light sensor?
Can a split diopter bring two different optical path lengths into focus in one shot?
Can I photograph through beam-splitter glass without the subject seeing the camera lens?
Can you avoid light loss when adapting Canon FD lenses to Canon EOS bodies?
How can I photograph a laser beam traveling through water?