Depth of Field & Crop Sensor

Leica CL + Voigtlander Skopar f2.5

One thing that worried me about switching from a DSLR system to the Leica CL, was that the crop sensor would not allow me to get a sufficiently shallow depth of field using the lenses I already owned, necessitating a new lens purchases. I was already planning and calculating in my head which lenses I might need to save up for, and drove my husband a little nuts obsessing about this topic.

In theory, my concern was justified. To get the look I wanted for my knitwear photos, I typically used an aperture between f2 and f4 on my DSLR + 50mm lens setup. Assuming I understand the conversion correctly, in order to get the equivalent on the crop sensor CL, I need a 35mm lens that goes down to f1.4, which is not a lens I currently own.

The nicest 35mm lens I have access to, is the Voigtlander Skopar f2.5 - which I understood to be the equivalent of f4 on a full-frame. That means the lowest f stop I am now able to go down to, is at the high end of my preferred range. Sounds as if ideally I need a different lens. But one thing giving me hope, was this: When taking a few knitwear test shots with the Skopar earlier, I did not notice the DOF limitations being a problem. But those photos were rushed. So I decided to withhold judgment until my next photoshoot, which was scheduled for today. The weather again was horrendous, and after less than 30 minutes we had to call it a day. But in that time I did have the presence of mind to test whether I could get the look I wanted when photographing from different vantage points and distances in relation to the subject.

The image at the top of the page is not intended as a fabulous example of a product photo, but I chose it because it illustrates the DOF effect at f2.5 very nicely. The model is holding her hands quite close to her face. The binoculars and mittens are in focus; her face is not. And neither is the bit of her shawl that is dangling directly behind the mitten. This does not look like an f4 photo to me, no matter what the crop sensor conversion charts indicate.

So… I don’t know. I do have my theories as to why the DOF appears shallower than it ‘should’ be, considering I am using a crop sensor. But I am weary of contributing to the already extensive collection of of misinformation on such topics available on the internet, so I will keep those theories to myself for the time being. For now I am just glad that I do not need a new lens.