Adapting GFX: Test Shots vs Real World and Lessons Learned

Despite white wall tests of the Canon EF 28mm and 135mm lenses showing acceptable levels of vignetting, my first real world use of them ended in failure.

First, to address testing: while everyone and their sister are reviewing gear on youtube and will spew off useless bullshit in order to make themselves seem smarter despite proving a tenuous grasp on the concepts they attempt to explain, only real world use can help you determine if something will work for your use case. It’s why I refuse to say definitively if any lens will work in this database I’ve started. I leave the judgment up to whomever stumbles across this blog. While the white wall shots showed an acceptable level of vignetting for my own use, real world performance proved that is not the case. The first dry day in weeks allowed me to try out both the 28mm ƒ/1.8 and 135mm ƒ/2L. The results were laughably bad when it came to vignetting, resolution and distortion, especially at the extreme edges. The level of detail was also noticeably less than that of my Fujifilm lenses when zoomed in, though it was by far the least of the issues. They clearly underperformed and it was obvious when compared to Sigma’s Art lenses. The edges were soft and distorted throughout the focal and aperture ranges and wasn’t acceptable, especially in the 135/2L, a focal length I bought especially for panoramas.

Which brings me to the second point: these lenses were very unpredictable on the adapter. Changing settings would cause the lenses to drop focus, even in fully manual mode. Going from DOF preview, shooting and out of preview mode would cause them to change focus for no reason. Despite direct focusing, the lenses could not be completely powered off in manual focus. It’s completely unacceptable and even if there were no serious vignetting and detail issues, the inability to get consistent, repeatable performance is a dealbreaker. I’m also aware the adapter factors into this and a change of adapter may be forthcoming.

I’ve learned my lesson. The Sigma 50/1.4 Art I’ve been borrowing has none of these issues, so I’ll be going with them instead, despite the 90 degree focus throw making it difficult to grab focus, the completely unusable behavior in continuous focus and incompatibility with eye AF. My passion is in landscapes and astro… there are no eyes I need to focus on anyways.

It seems the claims Sigma’s made in the past about utilizing a larger, projected image circle to enlarge the “sweet spot” and provide better edge and corner performance isn’t just marketing BS. This choice is likely why Sigma Art lenses tend to have slightly darker exposures of about 1/3 stop, when compared to a lens of the same focal length and aperture setting, that’s consistent across their lens range. That larger imaging circle means reduced light intensity projected onto the sensor when compared to a similar lens with a tighter imaging circle. If this doesn’t make sense, compare the performance to that of a “speedbooster,” where reducing the imaging circle to fit a smaller sensor increases light intensity; that’s where your “extra stop of light” comes from as it increases the total amount of light reaching the sensor.

As such, I’ve already put in an order for the 35/1.4 and 85/1.4. The 28/1.4 and 135/1.4 will come later when I find them either on sale or used.

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