How to Use Extension Tubes on Film Cameras

Extension tubes are simple mechanical devices that let you to focus your regular or macro lens closer to your point of interest. This can help you fill more of your frame with your tiny subject.

The tubes work similarly to the native camera focusing mechanism, moving the lens further from the film plane. However, you’ll need to consider some limitations and calculations while using this tool.

In this article: Extension tubes vs. native focusing. Bellow extension factor and exposure compensation. Stacking extension tubes. How to find your extension tube(s) length. How long do your extension tubes need to be to achieve the desired magnification? How much additional magnification can you get with your extension tubes? Loss of image quality with extension tubes. Exceptions to the formula calculations and lenses that do not work with extension tubes. Support this blog & get premium features with GOLD memberships!

Extension tubes vs. native focusing.

Extension tubes can help you make extreme close-ups with regular lenses or improve the effect with the macro lens you already have. However, there are some downsides to using them.

The extension tubes in the graphic above (Asahi Pentax Auto Extension Tubes) are made specifically for Pentax K-mount cameras with a mechanical coupling for the aperture. This lets you focus and frame your shot with the blades fully open and have them quickly contract during exposure. However, this isn’t always a given; thus, you should check for that functionality before you buy the tubes.

If you want to switch from the close-ups to a normal focal range up to infinity, you’ll have to remove the extension tubes and re-mount your lens.

As your lens gets further from the film plane, the amount of light it delivers diminishes, which can make focusing difficult (as your viewfinder becomes dimmer) and manual exposures tricky. There are also other calculations you may need to do, which I explain further in this guide.

Extension tubes are also not very practical with short focal lengths and have limited usefulness with all types of lenses. I will explain this further below.

But despite those shortcomings, extension tubes can make shots that are either impossible or exceptionally expensive with native optics without spending too much money.

Extension tubes are not the same as close-up filters — there are no glass elements, which can be considered an advantage. Magnification filters are prone to introducing aberrations and thus decreasing the overall sharpness of your image. Instead of bending the light, extension tubes physically crop your lens’ output without losing any of the resolution (although there could be some loss of quality as the extension tubes push your lens to do more than it was designed for).

Bellow extension factor and exposure compensation.

All focusing systems produce some amount of light loss as the lens extends to focus closer on the subject. For example, Mamiya RZ67, which has very long bellows, prints the calculations on its body for quick reference. But most cameras ignore this property as the lens’ extension isn’t typically long enough to warrant exposure re-calculation.