Full frame confusion

I was recently having a discussion with a colleague about full frame cameras and he started talking about cameras with frame sensors and although they are not referring to the same thing it actually managed to confuse some issues.

The main issue.. our office owns a 7D. We basically want to know if the lenses that our office already owns (that fits the 7D) will fit the 5D III if we upgrade.
A side issue, we're pretty sure that the 7D lenses actually fit my old 40D once when we were playing around with both cameras and the same lens.

It's my understanding that although some of these cameras do not have full frame sensors they are all in fact full frame cameras with respect to lens mounts.

Can anybody offer any clarification on these please?

If the lenses are EF-S, they will not work on the 5DIII or any other FF body. If they're EF (no -S) lenses, then they will work.

The 40D is a crop sensor just like the 7D, so all the lenses you have would work with both of those.

Canon EF lenses will work with full frame or crop sensor bodies. EF-S lenses will only work with crop sensor bodies.

You don't mention whether you have third party lenses, but is so, many third party manufacturers have lenses that will only work with full frame or crops cameras, you'll have to look up compatibility with those.

Hi, the 7D and 40D are APS-C (crop sensor) bodies, they are compatible with both EF (full-frame) and EF-S (crop frame lenses).

Only EF lenses will fit a 5D mkiii.

EF-S lenses are designed for the smaller footprint of APS-C bodies.

The lens mount for EF-S and EF lenses are both different.

Howeveer I don't use third pary lenses so I cannot clarify how you would determine whether they are for full frame or APS-C bodies just by looking at their designation.

What types of lenses do you have in the office?

I'm sure someone will chime in with a more detailed explanation, but basically you're dealing with two things, sensor size and lens coverage. Lenses marked with "EF" will work on any Canon camera, while lenses marked "EF-S" will only work on the likes of the 7D/40D.

A bit of a history lesson- Every Canon camera ever made since 29 years ago uses the EOS mount (EF), which was designed for 35mm film, which in turn had the same physical dimensions of modern full-frame sensors (36x24mm). When digital sensors first came along, building a sensor of the same size as 35mm film was difficult and cost prohibitive, and so APS-C was born (23x15mm).

The smaller sensors changed the way certain lenses were used since the field of view was reduced, for instance a 24mm no longer gave you a view that was nearly as wide, thus a lens like the 24-70mm lost some of it's value if you used to use it at 24mm a lot on film. To counter this, Canon designed lenses specifically for the smaller sensors (EF-S), but they still use the same physical EOS mount. A 17-55mm zoom used on an APS-C sensor would be similar to a 24-70mm in terms of field of view on full format, and so photographers got back their wide-angle capability. Additionally, since the sensor is smaller, the EF-S lenses could be designed to cover a smaller surface and be smaller/cheaper themselves as a result, but also making them unusable on cameras with larger sensors.

So you can use lenses that are intended for full format on a camera with any size of sensor, but lenses specifically made for APS-C (EF-S) can only be used on cameras with reduced size sensors, but not the rare APS-H variant that used to exist as part of the 1D line of cameras.

Wow thanks for all of your responses. I apologise for not nominating the lenses in my first post. The main lens at work is a Sigma DC 18-200mm Macro HSM. Only one of the lenses are Canon (can't recall that model off the top of my head), the rest are all Sigma or Tamron. I can look up the rest of the lenses later but for now the one above is main one in question. I'll try looking it up whether this lens is an EF or EF-s equivalent but all i can find so far is that it competes with an EF-S so I'm guessing it means that this lens is also an EF not EF-S.

Any further clarification would greatly appreciated.

The Sigma DC series are all crop - they won't work satisfactorily with a FF body; FF-capable Sigmas are DG. Tamron's Di II are also crop; the Tamron Di (no II after) does FF. You may be able to mount crop-model Sigma or Tamron lenses on a FF body, but they're not designed to cover the full 24x36 mm sensor of the FF body. Somewhere along the way you'll run into light falloff and vignetting (usually at the wide end). And no Canon EF-S, as previously noted, will even mount on a FF body.