Panasonic Lumix S 18 mm f/1.8
7. Coma, astigmatism and bokeh
The Panasonic Lumix S 18 mm f/1.8 dealt with this task more or less sensibly only in an area covering the APS-C sensor, where the point-like sources of light are very slightly deformed even in the frame corners.
The situation changes drastically when you pass to the corners of full frame. In this case the points turn into a significant pie that, additionally, features slight wings, so it's evident there are a lot of problems. Both Sony models we use here for comparisons also had problems with coma correction but in their case the size of deformations wasn't so conspicuous.
Please Support UsIf you enjoy our reviews and articles, and you want us to continue our work please, support our website by donating through PayPal. The funds are going to be used for paying our editorial team, renting servers, and equipping our testing studio; only that way we will be able to continue providing you interesting content for free. |
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
| Center, f/1.8 | Corner APS-C, f/1.8 | Corner FF, f/1.8 |
|
|
|
| Center, f/2.5 | Corner APS-C, f/2.5 | Corner FF, f/2.5 |
|
|
|
In order to present a comprehensive performance in this category we also decided to show crops of photos of the sky taken from the right-hand upper corner of full frame. This time, however, we show shots by f/1.8, f/2.5 and f/3.5. The tests performed on images of stars is always a tad more demanding, here for example you can notice a more distinct structure of deformations of the point-like image of a star. It is clear that even on stopping down the aperture by 2 EV coma is not corrected completely, remaining as the only aberration and its effects still remain visible in a form of a slight 'commas'.
| Corner FF, f/1.8 | Corner FF, f/2.5 | Corner FF, f/3.5 |
|
|
|
Astigmatism, understood as an average difference between vertical and horizontal MTF50 function values, amounted to 6.7%. It is a result that we consider to be low so in this testing category the lens should be praised.
Now let's deal with out-of-focus areas positioned far away. With such an wide angle of view we didn't expect any miracles and yet the Panasonic managed to surprise us in an unpleasant way. Circles of light, generated by this lens, are really weak. Not only the presence of aspherical elements caused a distinct onion-ring bokeh effect but also you can notice a lot of heterogeneities in light spread. Add to this a bright rim which intensity increases on stopping down and you know situation is rather difficult.
The fact that mechanical vignetting disappears completely on stopping down the aperture by two full steps is a kind of consolation.
| Center, f/1.8 | Corner APS-C, f/1.8 | Corner FF, f/1.8 |
|
|
|
| Center, f/2.5 | Corner APS-C, f/2.5 | Corner FF, f/2.5 |
|
|
|
Center, f/3.5 | Corner APS-C, f/3.5 | Corner FF, f/3.5 |
|
|
|
