Lensbaby Burnside 35mm F2.8

Aberrations

No lens can be totally free of optical flaws. The following list describes the main defects that a lens can suffer from.

Name
Description
Chromatic aberration Different colors do not have the same focus point. The result is colored lines (usually red or green) on edges showing a sharp transition from clear to dark tones, and a general decrease of the sharpness. Occurs mostly at wider apertures. Easy to correct via software. Mitigated by the use of achromatic lens elements. In simple terms, lateral CA occurs in the in-focus zones, while longitudinal CA occurs in out-of-focus zones.
Purple fringing Sometimes caused by chromatic aberration effects. Can also occur because the RGB color filters in front of pixels create differences in pixel sensitivities. Creates a purple band on edges showing a sharp transition from clear to dark tones. Occurs mostly at wider apertures. Easy to correct via software.
Flare Internal reflections on the various lens elements cause a decrease of contrast, the apparition of a bright veil, or ghosting. Occurs if an image includes bright light sources, especially if the light source is near the edge. Using a lens hood helps to control flare. Better lens coatings greatly reduce the effect.
Ghosting A type of flare causing artifacts (orbs) to appear on an image including bright light sources, especially if the light source is near the edge. Can be used artistically.
Coma Flaws in the optical design cause point sources (such as stars) located on the sides of the frame to appear elongated. Dependent on the lens design.
Distortion Straight lines appear curved. Dependent on the lens design. Tested in another page.
Spherical aberration Light rays hitting the sides of the lens do not have the same focus point as those passing through the center. Mitigated by the use of aspherical elements.

Not all of those optical effects are easy to test independently. Purple fringing and chromatic aberrations are almost always coupled, and will be tested together. Flare and ghosting will also be measured as a pair. Distortion will get its own page later in this review. The other aberrations will not be formally tested as their effects are both harder to isolate and generally better controlled by design.

Flare

Flare will affect images in which a bright light source, such as the sun, is present in the frame or near its border. The use of a lens hood helps reduce the effect for side lighting, as does a recessed front element. High-quality lens coatings play a very important role in minimizing flare, by improving light transmission and minimizing internal reflections.

The Burnside 35 is advertised to feature multi-coatings, which is pretty much a given in 2018. As a moderately wide lens, flare is likely to be present but not overly distracting. The lens does not ship with a hood but the front element is significantly recessed, which should help keep things under control.

Flare Test one - Center-of-Frame Sunlit Flare, secondary iris open

As usual, we used the sun as our light source for flare testing. It is bright and covers a wider range of wavelengths than most artificial light sources. We offset the sun slightly in order to see eventual ghosting which could be hidden if there was a straight line between the light source and the sensor.  We kept the secondary iris open, so the Burnside will behave like any regular lens. You can click on the thumbnails for larger views.

F2.8
F4
F5.6
F8
F11
F16

The Burnside produces surprisingly good results with the Sun in the center. The hint of a ghost appears below the center at F11 and is more visible at F16, and a halo surrounds the Sun at F16, but apart from that there is nothing to see. Excellent.

Flare Test Two - Edge of Frame, secondary iris open

For this test, we placed the source in the top right corner of the frame, directly illuminating the sensor. You can click on the thumbnails for larger views. We looked at both the APS-C and full frame fields of view. The secondary iris is again open.

Full frame

F2.8
F4
F5.6
F8
F11
F16

Ghosting appears in the form of one single flattened circle wide open, and is visible until F8. Again, these results are beyond expectations.

APS-C

F2.8
F4
F5.6
F8
F11
F16

APS-C is basically a crop of the full frame field of view. As such, the same observations apply. F16 however shows a surprising purple streak at the bottom right. This did not occur in other circumstances or with the full frame crop size. Moving the Sun closer to the center (since the APS-C format is in fact a crop of the full frame) seems to create this problem at F16.

Flare Test two - Center-of-Frame Sunlit Flare, secondary iris closed

The settings are identical to the previous test except that the secondary iris was fully closed for this test. You can click on the thumbnails for larger views.

F2.8
F4
F5.6
F8
F11
F16

Closing the secondary aperture has no effect on flare.

Flare Test Two - Edge of Frame

Again, the settings are identical to the previous test except that the secondary iris was fully closed for this test. You can click on the thumbnails for larger views.

Full frame

F2.8
F4
F5.6
F8
F11
F16

The results are still identical to those of the previous section. Note the effect of closing the secondary iris on the shape of the Sun and its rays: it becomes elongated and seems to follow the curve of the iris.

APS-C

F2.8
F4
F5.6
F8
F11
F16

There is still no difference with the aperture closed or open.

The same purple streak is visible at F16.

Chromatic Aberration Test

For this test we used a well-lit, sharp transition from dark to bright, in order to make manifest any chromatic aberration present in the image.

We then looked at three parts of the image: the focus point, the top and the bottom (beyond and before the focus point). We tested the cop size of a full frame and APS-C sensor. The center point is the same. You can click on the images to see 100% crops, and navigate by using the left-right arrows.

Full Frame

Center
Top
Bottom
F2.8 F2.8 Center F2.8 Top F2.8 Bottom
F4 F4 Center F4 Top F4 Bottom
F5.6 F5.6 Center F5.6 Top F5.6 Bottom
F8 F8 Center F8 Top F8 Bottom
F11 F11 Center F11 Top F11 Bottom
F16 F16 Center F16 Top F16 Bottom

Results are again excellent. There is nothing to mention apart from the slightest chromatic aberration at the bottom at wide to medium apertures. It is hard to notice and should have little impact in practice.

APS-C

Center
Top
Bottom
F2.8 F2.8 Center F2.8 Top F2.8 Bottom
F4 F4 Center F4 Top F4 Bottom
F5.6 F5.6 Center F5.6 Top F5.6 Bottom
F8 F8 Center F8 Top F8 Bottom
F11 F11 Center F11 Top F11 Bottom
F16 F16 Center F16 Top F16 Bottom

The APS-C crop helps with CA. The slight CA mentioned in the full frame section is not visible here. We couldn't ask for more.

Verdict

The Burnside produces results above expectations for both flare and chromatic aberration. CA is almost absent, except a hint at the bottom of the full frame crop. Flare is limited to a single spot at wider apertures, and a purple streak at F16 on APS-C. The position of the light source will have a strong impact: the streak is not present in our FF tests.


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