Question about Samyang 16mm f2 lens on crop sensor camera

HenryHunt · Mar 12, 2017

Hi!

I'm going to Yosemite in the summer and would like to do some astrophotography there, but am finding it difficult to choose a lens. I have a Canon EOS 60D and 700D and have am currently thinking the Samyang 16mm f2 because of its wide angle and wide aperture. I initially decided on the Samyang 14mm f2.8 but changed to the 16mm because it was specifically designed for APS-C sensors and the 14mm is not and would give a smaller field of view.

However, the product page on the Samyang website says that it has an equivalent focal length of 24mm on APS-C sensors. How can it not be 16mm on APS-C if it's a 16mm lens designed for APS-C sensors? Will it actually be 16mm when used on my two APS-C cameras or will it be 24mm? If it is 24mm then which lens would you suggest, the 14mm or 16mm?

Additionally, if you would recommend a better (< £300) lens for astrophotography for APS-C cameras then please say.

Thanks

fmw · Mar 12, 2017

I would opt for a wide angle zoom designed for the APS-C sensor.

Derrel · Mar 12, 2017

Focal length is focal length, and is mostly specified accurately by the lens maker (but not always!) But, the basic concept is to take the focal length, 14mm or 16mm, and to mutiply that by your camera model's FOV factor, typically 1.53 for Nikon, 1.6 for Canon. Lenses made for DX-sized sensor cameras do NOT have a "fudge factor" built in, but are specified by their actual focal length, such as say 10-22mm zoom, or 10-24 zoom, or 12-24mm zoom, etc. A 16mm lens for APS-C will be the same focal length as a 16mm for full-frame; neither one will give a wider field of view on your APS-C sensor camera.

As fmw mentions, there are some nice wide-angle zooms designed for APS-C sensor cameras.

HenryHunt · Mar 12, 2017

So what you're saying is that the focal length on all lenses is specified for full frame, and the amount of crop on the sensor just affects how much of the frame from that lens you can capture? So does that mean that my 18-55mm kit lens isn't actually 18-55mm on my APS-C cameras, it's 28.8-88mm effectively?

Sounds like I just got confused by focal lengths on a crop sensor vs full frame. What does it mean when the lens says it is designed for APS-C then?

Derrel · Mar 12, 2017

HenryHunt said:
So what you're saying is that the focal length on all lenses is specified for full frame, and the amount of crop on the sensor just affects how much of the frame from that lens you can capture? So does that mean that my 18-55mm kit lens isn't actually 18-55mm on my APS-C cameras, it's 28.8-88mm effectively?

Sounds like I just got confused by focal lengths on a crop sensor vs full frame. What does it mean when the lens says it is designed for APS-C then?

Hi Henry,
Yes, you got it right, the 18-55mm lens for your APS-C camera has the 28.8-88mm effective angles of view, as would be spec'd for a 24x36mm camera using 135 format film. Your confusion is very common, and has been since crop-framed camera were introduced and manufacturers and customers had to adapt legacy 35mm lenses to the then-new digital SLR cameras.

Some people have started referring to lenses for APS-C sensor cameras as having an "eView", or "35mm film equivalent view". I have noticed this new lingustic trend mostly among users of Fuji and Olympus and Panasonic cameras, many of whom learned photography decades ago, and who think of lenses in old-school ways like, "I want a 35mm eView lens for my Fuji," or, "I want an 85mm eView lens for my Fuji." You'll see this trend fairly often at The Online Photographer, and it is one way to remind people that the focal length of some lenses will be modified by the camera it is used on.

When a lens states Designed for APS-C, it means first and foremost that the lens is hopefully, optimized to be used on a small,digital sensor and not a film-optimized lens design.Optimized for APS-C also hopefully means high optical performance across a 29mm diameter APS-C image circle. Many APS-C designed lenses will NOT project the 43mm diameter image circle needed to cover full frame (FF,FX, or 24x36mm, same size), so if used on an FX camera, these lenses will usually show blackened corners of the picture outside of the APS-C sized area at most focal length settings.

Digital sensors are very flat and very thin, and field curvature that older film lenses sometimes had can really hurt performance, espcially on old, film-era wide-angle lenses. Digital sensors like light rays that come in at straight angles, not glancing angles, as much as possible, across the entire image area. Digital sensors are shiny and reflective, and some old-design film-era lenses had an iris that sometimes would cast a ghost dot of the light coming through the aperture and into the empty film chamber area, and digitally-optimized lenses were developed almost a decade ago or more, to combat that issue of "red spot flare". The focal length ranges needed for APS-C are also different, so the film-era 24-70mm f/2.8 zoom has been shifted to a 17-50mm or 17-55mm f/2.8 lens length in the "designed for APS-C" lenses.

HenryHunt · Mar 12, 2017

Great, thanks for that information. I think I'll go ahead with the Samyang 16mm f2 then as its wide, has a large aperture and has very little optical problems. Great for astrophotography