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Does using a lens adapter change the field of view?

I recently bought a Sony NEX-5, an extra Minolta MD 50mm 1.7/f lens and a MD to E-mount adapter and I was wondering, as the adapter increases the distance between the sensor and the lens by ~10mm, does this effectively make my 50mm lens a ~60mm lens? Or am I just misunderstanding things?

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up vote 6 down vote accepted

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).

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That's very interesting about the crop factor, I hadn't really read up on that before. I guess that's why it can feel a bit claustrophobic when using that lens indoors. It does take some beautiful profile pictures but sometimes it feels like I need to be taking them from the other side of the room. Making me seriously consider also getting the 16mm 2.6/f Sony lens. – Ross Anderson Oct 20 '11 at 11:21
    
I have the 16/2.8 E-mount, as well as a bunch of MD lenses, and the pancake can't hold a candle to the manual lenses as far as optical quality is concerned, and autofocus at 16mm is pretty superfluous (even at f/2.8 the hyperfocal distance is about 4.5m, at reasonable apertures everying is in focus). Unfortunately it can be difficult (and expensive) to find true UWA for 35mm cameras (since they cast a larger image circle, a 16mm for full frame is many magnitudes more expensive to produce) but you might want to try Minoltas 20 or 24/2.8, or the suprisingly awesome Sigma 24/2.8 for MD mount. – Tzarium Oct 20 '11 at 11:43
    
Thanks very much for your suggestions :) – Ross Anderson Oct 20 '11 at 12:21

If the adaptor is a good one no characteristics of the lens will change. The lens will be placed in exactly the correct spot it should be, and all will be functioning as normal.

Some mounts however don't have an easy conversion with optics correcting focal shift. If those optics aren't included, then the converter will act like an extension tube. This will move the focus of the lens, and usually mean you can no longer focus on infinity.

Having a quick google of MD to E mount adaptors it seems that they do allow you to focus to infinity without adaptors, so it should be business as usual with no adjustment to what you see.

Difference in sensor size between cameras may effect your FoV however

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The answers you've gotten are correct, a standard/correct adapter does not change the focal length.

It is worth noting however that there are some adapters called Speed Boosters which are designed to do exactly that. They counteract most of the "crop factor" caused by the smaller sensor. They aren't cheap, but it's always good to know your options. For Minolta MD to Sony NEX

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... as the adapter increases the distance between the sensor and the lens by ~10mm, does this effectively make my 50mm lens a ~60mm lens? Or am I just misunderstanding things?

You're misunderstanding things.

The Minolta MD/MC registration distance (or flange focal distance)--that is, the distance from the mount flange to the sensor, is 43.5mm. If the lens is held closer than this distance, it will focus past infinity. If the lens is held farther away, its near-focus capability is increased, but it can't achieve focus to infinity (think: macro extension tubes).

Sony E-Mount's registration distance is 18mm.

Your adapter ring makes sure that the distance the lens is held from the sensor doesn't change. Its thickness makes up the 25.5mm difference, so that a Minolta MD/MC lens is mounted on your NEX, the lens's mount flange is still held 43.5mm away from the sensor in your camera, so that the lens can achieve focus to infinity.

However. This only holds true for simple ring adapters. If there are optical elements in an adapter ring, then the focal length of the adapted lens does change.

Some adapting combinations--where the adapted mount has a shorter registration distance than the mount being adapted to--require a glass element in the adapter to act as a short teleconverter so the lens can still focus to infinity. This type of adapter effectively increases the focal length of the lens, and reduce its maximum aperture, just as any teleconverter does. There are also the wide-angle adapters known as Speed Boosters which do the opposite--reduce the focal length and increase the maximum aperture.

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