CV 125/2.5 on GFX 100 at 1:1 and beyond

This is one in a series of posts on the Fujifilm GFX 100. You should be able to find all the posts about that camera in the Category List on the right sidebar, below the Articles widget. There’s a drop-down menu there that you can use to get to all the posts in this series; just look for “GFX 100”. Since it’s more about the lenses than the camera, I’m also tagging it with the other Fuji GFX tags.

I’ve been posting a lot recently about the 120 mm f/4 GF macro lens for the GFX. I found it a good performer at 1:2, at minimum focusing distance (MFD) with no extension tubes, but that it had really soft edges and a lot of focus curvature at MFD with 36 mm of tubes. In this post, I tested it at 1:1 with a 45 mm tube,a and found it credible on-axis but soft on the right edge of the frame.  I reported those results numerically and visually, using the time honored sharpness target of a banknote. The 120/4 GF was soft in the corners and edges at MFD with 18mm, 36mm, and 45mm of extension by tubes.

For copy applications, and for some 3D subjects that require extension tubes, the 120/4 GF just isn’t cutting it.

So I decided to look for an alternative. The first lens I tried works much better than the 120/4 GF for close focusing, as you’ll see if you read on. My first candidate was the Cosina-Voigtlander (CV) 125 mm f/2.5 Apo-Lanthar. My copy is in a Nikon F mount. I put a FotoDiox F-to-G converter on the back of the lens, a Fuji 45 mm extension tube behind that, and mounted the stack to a GFX 100. I set the lens to indicated f/5.6. Using a Cognisys rail, I made a series of 160 exposures with an 80 micrometer (um) shift between one. I brought the images into Lightroom, turned off sharpening, and found that I just needed to first 60 or so images, so I consigned the others to the bit bucket. I exported the files as TIFFs, brought them into Helicon Focus, and stacked them with the default B algorithm at default settings.

Here’s the setup (the image shows the 120/4 GF on the camera):

The CV 125/2.5 covers the GFX sensor perfectly.

Here’s a sample image from the stack.

The ruler was used to set the distance so that I got 1:1 magnification.

Here’s the far right edge at 150% magnification:

And here’s the same edge at the same magnification with the 120/4 GF:

The difference is not subtle.

In the lower right corner with the CV 125:

And in the same place with the 120/4 GF:

Now let’s compare the right edge of the CV 125 with the center of the 120/4 GF.

The GF is better.

What if we set the CV 125 to MFD?

Not bad at all.