Friday, 12 February 2016

Fisheye Lens for Suitable for Infrared Photography: Kelda 6.5 mm f/3.5

From ePhotozine
I have been looking for a fisheye lens for infrared photography. I found it difficult to find out which fisheye lenses, if any, show a ‘hotspot, and I was reluctant to buy a second-hand Nikon or one of the still relatively expensive ones from the second-line manufacturers.

A couple of weeks ago I saw in ePhotozine that Kauser International were offering a Kelda 6.5 mm f/3.5 fisheye for APS-sized DSLR sensors for £129. Now, I am usually very wary of buying a cheap lens. The reviews of most reveal poor optical performance. However, the earlier review in ePhotozine of this lens showed it to be remarkably good at f/8 and f/5.6. I then found that this lens is or has been sold by a number of companies, some in slightly different configurations, starting, it seems with Samyang and described either as 6.5 or 8 mm focal length. Although Samyang appear to make their lenses in Korea, the Kelda is described as made in China. 

I ordered one (with a Nikon mount) on the grounds that if it proved not to be suitable for infrared, then I had lost very little. It arrived from Kauser virtually by return. It looks like the early model Samyang. The fact that it is manual focus with a manual aperture ring is no hardship. I was impressed by the build quality: a solid feel, smooth focusing ring and half-stop clicked aperture ring. The supplied plastic front lens cap has a faux spatter-coated sheet metal look. On this model the petal lens hood seems to be fixed (well, I can find no way to remove it and the plastic flange extends below the front element of the lens) even though the box states that it is removable.

The first test was my usual shot out of the window lens test. The weather has been so foul and so dull that a meaningful test was out of the question. However, at first glance I could see no sign of a dreaded hotspot. Yesterday, however, the weather was fine, and on the way back from the post office I stuck the lens (attached to my 590 nm infrared converted Nikon D80) into the Auld Kirk to check that it really was suitable for infrared. As you can see from the following Lightroom, Photoshop and Viveza-processed shots, there was no sign of a hotspot.

Reviewers of this lens in it various guises have commented, hardly surprisingly, on the flare when shooting against the light. With this lens’s coverage of 180° on the diagonal of the sensor, it is hard to avoid getting the sun (or one’s own shadow) in the frame. Reviewers have also marked the lens down for its lack of a depth-of-field scale. With the enormous depth of field of this lens (whether it is nominally 6.5 or 8 mm focal length), that absence, together with the absence of an infrared focus mark, is completely irrelevant. At f/8, the hyperfocal distance is about 30 cm which means that when focused at that mark, everything is in focus from the end of a six inch rule to infinity.

The Samyang fisheye lens family to which this version clearly belongs is noted for the stereographic projection of the image. The advantages of this projection over others are shown here.

In conclusion, I have a fisheye lens that works for infrared with an optical performance (ePhotozine used Imatest) that hits excellent between f/5.6 and f/11 with minimal chromatic aberration at f/11. I would rate this lens at the price I paid as a bargain. So far, so very good.