In-camera lens compensation

Transcription

1 In-camera lens compensation High resolution sensor are really demanding when it comes to the resolution of the lens as well as to shading, chromatic aberration and distortion which are more important on DSLMs like the Sony A7 and the Sony A6000 due to the shorter flange (distance between sensor and lens mount). Most of these optical errors can already be corrected in the construction of the lens for a higher price (see Zeiss Otus). In-camera lens compensation is one mean to reduce the costs of lens construction. This article shows the effects of the three different correction parameters of the in-camera lens compensation on JPG and RAW based on pictures taken with the combinations of Sony Vario-Tessar T* FE 16-35mm F4 ZA OSS on the Sony A7 and Sony E 10 18mm F4 OSS on the A6000. Trade-Off Many DSLR (Digital Single-Lens Reflex) and DSLM (Digital Single-Lens Mirrorless) user want more and more megapixel; be it the professional photographer who wants the best possible quality for large prints or be it the ambitious hobby photographer who simply wants the best gear for his hobby or the beginner who thinks that more resolution is equal to better pictures. The trade-off between lens price and quality called in-camera lens correction is fed by the ambitions of the manufacturer who wants to build the best product possible and the photographer who wants to use the best possible lens for the lowest price. The most uncomprising lenses currently available which deliver outstanding image quality on mainly all available sensors are surely the Otus lenses build by Zeiss. Image quality, which one can expect at a price level far above the level of $ This lens are surely made for the enthusiasts which have the money and the willingness to pay the price and less interesting for the professionals that think in economic dimensions or the hobbyist with smaller budget. The later are rather interested in those lenses found at mid-range price levels which deliver the best performance in combination with the internal lens corrections as far as available in the camera firmware.

2 A note to the image material Cameras and lenses Using a full-frame lens on a camera with APS-C sensor would not really show the real amount of distortion and shading because the APS-C sensor is only using the good center part of the full-frame lens. The following drawing shows the relationship of image circle and sensor size of full-frame and APC-C sensors: The in-camera lens correction is best shown when using wide-angle focal length and surely in the outer image areas and corners of the picture. The following combinations of camera and lens have been used to create as much lens errors as possible: Sony A7 with Sony Vario-Tessar T* FE mm F4 ZA OSS Sony A6000 with Sony E mm F4 OSS

3 RAW and JPG There is an ongoing discussion whether the in-camera lens correction is applied to RAW images. All pictures have been made in RAW and JPG each with activated and deactivated lens correction to find out whether lens correction is applied to RAWs. All comparable pictures have been taken with the same event of simultaneous shutter release in Sony A7 and Sony A6000 to create the highest rate of comparability and to avoid difference in images caused by e.g. cloud moving into sunlight. The cameras have been mounted as shown in below picture and the shutter was released by a radio trigger.

4 Analysis of images Shortly after Sony started selling the lens I wrote a first Hands-on about the Sony Vario- Tessar T* FE 16-35mm F4 ZA OSS. In one of the comments of the German version of the hands-on I was asked about my opinion on the in-camera lens correction here it is. Frame 1 Chromatic aberration JPG Obj.korrektur Aus / lens corr. off PG Obj.korrektur Auto / lens corr. auto RAW Obj.korrektur Aus / lens corr. off RAW Obj.korrektur Auto / lens corr. auto

5 SEL 10-18mm F4 OSS, JPG and RAW, mit und ohne Korrektur / with and without correction The red marked area is used for comparison of JPGs and RAWs: left: lens correction off right: lens correction auto

6 Looking at the crops the JPGs shot with deactivated lens corrections there are green and purple lines next to the tree branches as expected. Surprisingly, these chromatic aberrations are not visible in the RAWs even with deactivated lens correction. Hardly believable, but I checked all RAWs one by one and this looks like the proof that the correction of CAs can t be disabled for RAWs. As a comparison below the the crops from the images shot with the FE mm F4 ZA OSS at 16 mm and at F5.6, because I made a focussing mistake taking the pictures at F4 which I realised to late, but this does not influence the assessment of chromatic aberrations. left: lens correction off right: lens correction auto Obviously the FE 16-35mm F4 ZA OSS mounted on alpha 7 shows the same results like the SEL 10-18mm F4 OSS mounted on alpha 6000 regarding the correction of chromatic aberrations on RAWs.

7 Frame 2 and 3 Shading and distortion JPG Obj.korrektur Aus / lens corr. off JPG Obj.korrektur Auto / lens corr. auto RAW Obj.korrektur Aus / lens corr. off RAW Obj.korrektur Auto / lens corr. auto

8 The following pictures show the effect of in-camera lens correction regarding corner shading and distortion. SEL 10-18mm F4 F4 JPG: SEL 10-18mm F4 F4 RAW: It is easily visible that the correction of shading is applied to the RAWs as well, whereas the activation or deactivation of the correction of distortion has no effect on the RAWs. The following comparison between JPG and RAW with deactivated correction of distortion shows, that JPG and RAW are the same. The small differences in shading are caused by the selected creative style Neutral and are not related to any lens correction.

9 Let s have a look on the same images shot with FE 16-35mm F4 ZA OSS mounted on the alpha 7. FE 16-35mm F4 ZA F4 JPG: FE 16-35mm F4 ZA F4 RAW: FE 16-35mm F4 ZA F4 JPG+RAW deactivated correction: There is a lot more image material taken from other subjects and with different apertures and focal lengths and lens correction activated or deactivated which I did not include in this article but which I provide as zip-files for download at the end of this post and which can be used for your own analysis. If you use this material for your own publications I only require being listed as reference with a link to this post.

10 Verdict Pictures are worth more than a thousand words and following this motto the diagramm below provides an overview on which correction parameter is applied to JPG and RAW when the lens correction is activated or deactivated (black means that this particular corrections shows in the pictures). Two results are quiet suprising: First is that the correction of chromatic aberrations can be deactivated for RAWs when there is a lens corrections profile for the used lens contained in the installed firmware and second, that that there is no correction of distortion in RAWs, no matter whether this parameter is activated. Lens-correction profiles can only be added to the camera with a new firmware. The alternative is to use the Sony PlayMemories Camera App Lens Compensation to create your own profile for lenses not yet supported or that will never be supported (legacy lenses) by the firmware and automatically apply the lens correction but this is a different and very interesting subject.