Does an MD-to-E mount adapter change focal length or field of view?
Asked 10/20/2011
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I’m using a Minolta MD 50mm f/1.7 on a Sony NEX-5 with an MD-to-E mount adapter. Since the adapter adds about 10mm of physical distance, does that effectively turn the lens into a longer focal length, or change the field of view?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
14y ago
2 Answers
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The adapter bridges the gap in flange distance (distance between mount and sensor/film) between the NEX native E-mount (18mm), and the MD/SR mount (43.5mm). Therefore, the focal length of the MD lens isn't affected, it's still at its native flange distance from the sensor.
If you were to adapt an MD lens to a mount with longer flange distance (i.e. canon EF, 44mm), the net effect would be that of an extension tube, equivalent FoV but the focus range would shift, allowing a closer minimum focus (and therefore, increased maximum magnification) but losing the ability to focus on infinity.
However, your FoV IS affected by the APS-C-size sensor in the NEX-5, causing an effective 1.6x crop in FoV (about the same as an 80mm lens in your case).
Originally by user5016. Source · Licensed CC BY-SA 4.0
user5016
14y ago
0
Generated from our catalog & community — verify before relying on it.
A normal MD-to-E adapter does not change the lens’s focal length. Its job is simply to place the Minolta MD lens at the correct flange distance for the Sony E-mount camera, so the 50mm lens remains a 50mm lens.
What does change is the field of view from the Sony NEX-5’s APS-C sensor. Because the sensor is smaller than 35mm film/full frame, it crops the image compared with what the same lens would show on full frame. So your 50mm will give a narrower field of view, roughly similar to an 80mm lens on full frame.
If an adapter does not maintain the correct optical spacing, it can behave more like an extension tube: focus shifts closer and infinity focus may be lost. But a proper MD-to-E adapter is designed to preserve normal operation, including infinity focus.
One exception is focal-reducing adapters (often called Speed Boosters), which use optics to alter the image and can change the effective field of view. A standard mechanical adapter does not.
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