Killfitt-Makro-Kilar D 1:2.8/4 cm

Focal length: 40mm

Mount: Exakta
Aperture: F 2.8 - F 22
Min focus distance: 0.05m (!)
Length (from flange): 39/78mm
[+ 26mm for the adapter], rear element protrudes 10mm
Diameter: 62mm
Weight: 166gr.

Some pictures:

A7 and the lens.

Lens not extended

Lens fully extended.

Sample pictures: You may click on the sample image (except closest focus) for full resolution. The full resolution image opens in a new window, so you can keep it open for comparison. Focus is on the satellite dish to the right of the big solar panel near the center of the photo.

F 2.8.

F 8.

F 22.

Closest focus is only 7cm from outermost edge of the lens, F 8. Focus on the program wheel of the camera.

This is a very unusual lens. I had the 3.5 version in stock, it escaped going with the lot when I gave my Exaktas and Bessamatics away. The glass sits deep inside (no shade necessary) and it's a real good macro lens. The 2.8 version is extremely expensive nowadays and obviously prone to glass problems. So it took me some time to put my hands on a reasonably priced one and I had to return several lenses to their sellers. My 2.8 version extends a lot more than my 3.5 version, so magnification goes down to 1:1.1. This means real macro photography without additional macro gear.

On my A7 the lens focusses from infinity down to less about 7cm from the filter thread. Picture quality is soft towards the edges wide open and it's a bit difficult to focus, between sharp and blurred are only fractions of a mm. It's o.k. at F 8, but there is still a hint of softness towards the edges. 
At F 22 there is no diffraction. A very nice lens for a botanist or a entomologist.