Discover HD 25mm F1.8 MF APS-C Review

Discover HD MC 25mm F1.8
a.k.a. Zonlai/Kenro/Zhongheng

My Discover HD 25mm F1.8 arrived today. This is a small all-metal MF lens with a native E-mount. I purchased this silver version new for $75 shipped from an eBay seller based in California. It feels nicer than the Neewer 50mm I had--no roughness in either the focus or aperture throws. Both are very nicely damped.

7 elements in 5 groups
12 aperture blades
MFD 180 mm (170 mm measured)
140g
46mm filter thread
clickless aperture

The center sharpness is good wide-open, but the corners are quite dark and mushy. It has a similar amount of barrel distortion as the 16-50PZ, 18-55 SAM, and Minolta AF 24mm F2.8.

It seems to let in much more light than the printed aperture numbers report. It is not quite as bright wide-open as the 58mm F1.4, but it is much brighter than other F1.7 and F1.8 primes. The numbers printed on the aperture scale are off more than a full stop comparing both exposure and visual aperture measure. F/4 on the scale seems to be closer to f/2.8--f/16 on the scale is more like f/8. I redid the charts using equivalent exposures to adjust the aperture instead of relying on the printed aperture scale.

Sony 16-50mm F3.5-5.6 PZ OSS
Sony DT 16-50mm F2.8 SSM
Sony DT 16-105mm F3.5-5.6
Sony DT 18-70mm F3.5-5.6
Sony DT 18-55mm F3.5-5.6 SAM II
Sony DT 18-135mm F3.5-5.6 SAM
Tamron AF 18-250mm F3.5-6.3 Di II LD Aspherical
Minolta AF 24mm F2.8
Sigma AF 24mm F2.8 Super Wide II
Minolta AF 24-50mm F4

These are raw captures with the A5000 using a 24" 1920x1080 monitor with focus magnification for focusing. The A mount lenses are mounted with a LA-EA1. The test chart is about a meter away from the camera.

F2.8 Center


F2.8 Extreme Top Left Corner


F2.8 Top Left Corner


F2.8 Bottom Right Corner


The Sony DT 16-50mm F2.8 SSM is crazy sharp wide-open at this focal length. It really has no competition here for image quality. The Discover is matching the performance of the old 24mm F2.8 primes except in the extreme corners.

F4 or F4.5 Center


F4 or F4.5 Extreme Top Left Corner


The old Sigma Super Wide II is considerably brighter in the corners than all the others.

F4 or F4.5 Top Left Corner


F4 or F4.5 Bottom Right Corner


F5.6 Center


F5.6 Extreme Top Left Corner


F5.6 Top Left Corner


F5.6 Bottom Right Corner


This is wide-open showing the vignetting and distortion


Stopped down to F2.8 using the exposure (a bit past F4 on the printed scale)


Compared to the Sony DT 16-50mm F2.8 SSM wide-open


My lighting is not super even. Here is the DT 16-105 at 24 mm F8


Edited by QuietOC - 29 July 2017 at 16:30

addy landzaat wrote: QuietOC wrote: The field-of-view matches my Minolta AF 24mm F2.8 on my test chart. That might just be from the Minolta having to stick out so far. Ehm, you do know that is inconsequential, don't you? The field of view is at the sensor side, not on the front lens side. Anyway, the corners aren't that good. Did you take some (real) pictures?

Its bit "inconsequential" that a 25mm lens gives approximately the same field of view as a known 24mm lens as it implies the new lens actually gives slightly wider angular coverage than its specification.

The corners look pretty terrible - though in low light applications at large aperture it may not matter as they would be out of focus anyway in many cases.

addy landzaat wrote: QuietOC wrote: The field-of-view matches my Minolta AF 24mm F2.8 on my test chart. That might just be from the Minolta having to stick out so far. Ehm, you do know that is inconsequential, don't you? The field of view is at the sensor side, not on the front lens side.

I am using the apparent size of the test chart as my measure of field-of-view, but telephoto and retrofocus lenses start their fields-of-view at different reference points. A retrofocus design makes the sensor appear to move forward like it is sitting 24 mm from the front element. I just need an infinite test chart and these problems would go away.

Ah, real pictures
Colours seem to be old fashioned, is that because of the lens or because of a camera setting?

addy landzaat wrote: Ah, real pictures Colours seem to be old fashioned, is that because of the lens or because of a camera setting?

I was wondering the same - is this lens signature or just post processing!

I also have a Kaxinda 35mm F1.7 coming from China. The rear element on that one is more recessed.

The Kaxinda models seem to be ones being sold here under the Meike and Neewer brands. There are a number of these small manual focus lenses for mirrorless cameras. 24, 25, 28, 34, 35, and 50 are the focal length choices. Well, there is a 12mm F2.8 and some fisheyes too, but the former isn't much cheaper than the faster Samyang.

The Zonlai branded lenses have the aperture control ring at the end of the lens.

Edited by QuietOC - 29 December 2016 at 01:26