To my great surprise I found that the 18-35mm with MC11 combo held focus as I zoomed. Each time I made sure to zoom in and out again several times to see if the lens held focus. I did a series of shots with each adapter, making sure to check focus was accurate by viewing on my 55 inch 4K television. I got together a Metabones MKIII adapter, a Sigma MC11 and a Sony LA-EA3 adapter for my A-mount 18-35. To test this I set about assembling a small collection of other adapters to test with my Sony a7R II. What if it was my adapter that was out and not my lenses? What if other adapters were more accurate than the Metabones I’ve been using to begin with? The Sigma MC-11, Metabones MK III, Metabones MKIV and Sony LA-EA3 E-mount adapters This got me thinking more about adapters. With many PL cine lenses, and several of the better PL lens adapters, it is possible to make these adjustments. With ENG lenses, operators routinely check and tune the backfocus of their lenses using Siemens star patterns. It is a well-documented fact that professional video lenses require backfocus adjustments, and cine lenses often need shimming, to get them to hold focus while zooming and have accurate witness marks. The Sony a7R II with my Sigma 18-35mm lenses and various adapters So, as far as he was concerned the base lens itself was parfocal, but the backfocus of his adapter needed to be set first (something that he could do only because he was using a Speedbooster, and not a regular adapter). By a process of trial and error he moved the Speedbooster lens elements forwards and backwards (which is a relatively straightforward user adjustment) until the Sigma held focus. He further explained that to get it to behave this way he used a Metabones Speedbooster on a Blackmagic BMCC MFT. Reader Anthony Brown got in touch to say that he was 100 percent certain that his copy of the 18-35mm lens held focus while zooming, and sent me a video to prove it. There was always a noticeable shift with my Metabones MKIV Smart Adapter. With all of my regular setups using Metabones adapters on A7 series and FS series Sony cameras I had previously thought that the lenses didn’t hold focus perfectly when zooming. Up to this point I had assumed that my copies of the lenses did not hold focus perfectly when zooming. Just how well did they hold focus while zooming? Naturally, I wanted to try and verify what other people were seeing for myself. I have stills versions of the 18-35mm f1.8 in both Canon EF and Sony A-mount. Surely they would have even better tolerances than their stills counterparts? Furthermore, the cine versions cost many times more and are made from precision-made metal parts. The cine lenses share exactly the same optics so, the reasoning goes, they should perform in the same way. The Sigma 18-35mm f1.8 is a popular choice for video shooters. This is because several users have reported that their copies of the stills versions of the lenses actually hold focus when zoomed in and out. The recent statement by Sigma that the upcoming cine versions of their 18-35mm and 50-100mm lenses are ‘near parfocal’ has caused some confusion to potential buyers.
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