0

Context

So I've seen teleconverters that go onto telephoto lens to increase the perceived focal length of the lens. This allows a lens to focus at one or more additional focal lengths with a cost that it might not be as sharp as a lens dedicated to that focal length.

Question

I've seen, I'd assume, crappy wide angle converters sold on eBay. Is there a reason why first party manufacturers, such as Canon, Nikon and Sony, aren't making them for their wide angle lens? Given how people do buy teleconverters when they need a reach, I can see a market of people, repurposing their wide angle lens to get even more in the shot, at a reduced sharpness I'd assume.

EDIT: Sony does make them for their 16/20mm APS-C pancakes as well as their 28mm full frame prime but I don't see them used a lot??

  • They make them for video and some compacts. But as they're front mounted like macro screw-in lenses, you might be better off looking at filter manufacturers. In general though, wide zooms for DSLRs aren't too expensive, and most people will have them -- a wide angle adaptor can't reasonably be better than a lens designed to do that angle in the first place. – Chris H Feb 4 '16 at 15:54
  • I'm going to guess that's why we see lots of teleconverters and not wide angle adapters (WAA). Buying another teleprime can cost a few grand. A wide angle lens, probably less so? – unsignedzero Feb 8 '16 at 15:21
  • yes my wide zoom cost about 1/4 my telezoom (both sigma IS for Canon) and arguably the wide zoom is a better lens. – Chris H Feb 8 '16 at 15:37
1

Unlike teleconverters, which crop the angle of view provided by a lens, a wide angle converter needs to expand the field of view (FoV) provided by a lens.

Assuming the lens in question projects an image circle just large enough for the sensor on the camera in question, there's nothing to be gained by placing such a converter between the lens and camera body because the resulting image would look something like this:

Crop lens on FF sensor

This is an APS-C lens mounted on a full frame camera. The white lines show the area covered by an APS-C sensor. Pretty much all of the light circle is already in use on an APS-C camera. Expanding the FoV from behind the lens will only reveal the dark areas, not more of the scene.

In order to increase the field of view, an converter needs to be placed in front of the lens so that light from a wider area can be gathered by the lens' front element. Several third party sellers make such adapters. They can vary widely both in terms of price and quality. But even the best will deliver a fairly significant hit in terms of image quality.

Some camera makers do make other kinds of screw-on adapters to enable closer focus for macro work. Canon, for instance, offers the 250D and 500D closeup lens in several sizes. These work fairly well with little image degradation. The fact that camera and lens makers don't offer the same type of adapter to increase the FoV is an indicator that wide angle adapters come with a greater sacrifice in image quality.

  • Nice mess. Do all closeup lens adapters "widen" the FoV? I presume the amount is what the "+X" designation is for? – unsignedzero Feb 5 '16 at 5:48
  • Closeup adapters don't widen anything. They allow closer focus for macro work. They also eliminate infinity focus with most lenses. The +x.x for closeup lenses is measured in diopters, the same measure used for reading glasses. They are mentioned to point out that although camera/lens manufacturers do offer first party screw-on closeup lenses (which don't degrade IQ terribly), they don't offer screw-on wide angle adapters (which do tend to degrade IQ significantly). – Michael C Feb 5 '16 at 6:48
  • I presume as with everything, modifying the lens in some fashion, via TC, the closeup filters, or related will degrade IQ, especially if it a third party item? – unsignedzero Feb 7 '16 at 5:29
  • Not necessarily. The best lenses have more elements and groups than their inferior cousins because the additional elements and groups correct the aberrations introduced by a single thin lens. This is more and more true the larger the diameter of the lens' objective is. – Michael C Feb 7 '16 at 8:48
  • 1
    @Michael Clark - re. your last point: yes indeed, adding any non-matched supplementary lens to the equation introduces some field curvature, meaning that the light passing through the supplementary lens and hitting the front lens element already has some degree of chromatic aberration, which at best remains uncorrected by the time it hits the film plane; at worst it is amplified as it passes through the camera lens elements. – HamishKL Feb 7 '16 at 9:39
0

The big name brands actually do make exactly what you're describing - wide angle converter lenses, to be screwed into the front of a lens (usually with an adaptor ring), however these are exclusively intended for use with non-interchangeable lens cameras and/or video cameras. Similarly, they also make supplementary teleconverter lenses as well. This doesn't mean you can't screw one into the front of an SLR lens and get some kind of useful widening of the FOV, but they aren't designed for this and results vary from lens to lens. In my experience the big name brands like Nikon, Canon & Sony make very good quality supplementary lenses that have noticeably less chromatic aberration than the zillions of generic counterparts out there.

Here's an example from Canon.

  • And like everything with compound lenses, the larger the front diameter of the lens in question, the more things need additional correction to maintain the same level of IQ. – Michael C Feb 7 '16 at 8:53

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.