Why Full Frame cameras are better than Crop Sensor cameras for controlling light.

I briefly owned a Sony A7R2 and the 85mm f/1.8 lens. I took some great photos with that setup that I really love, but I didn’t love the Sony A7R2 itself. I was on the fence about selling it for a long time.

When I learned that the 56mm f/1.2 lens from Fuji had the same field of view and depth of focus on Fuji’s APS-C crop sensor camera as the 85mm f/1.8 on Sony’s Full Frame sensor camera — my decision was made.

I sold the Sony camera and lens, and bought the Fuji 56mm f/1.2 lens. Since the two lenses were equivalent in both depth of focus and field of view, it was a 1:1 swap. (Ignoring the megapixel difference between the two cameras.)

The next week I used the Fuji lens on a photoshoot and I couldn’t get the exposure right. Everything was too bright — not just a little, but like 2+ stops too bright.

Then I realized — this lens is an f/1.2 lens, one stop brighter than the Sony. And the Fuji camera has a base ISO of 200 vs. Sony’s base ISO of 100. Of course everything is 2 stops too bright, this whole setup — for a given shutter speed — is 2 stops brighter at the lowest ISO and widest aperture.

Because I was shooting with studio strobes, I couldn’t use shutter speed to make the images darker, and I wanted to shoot wide open at f/1.2 for a shallow depth of focus.

The Fuji would need to go to ISO 50 to make up for the 1 stop increase in aperture. It will do ISO 100 in “L” (low) mode, but that wouldn’t be enough for me. Sony’s camera goes to ISO 50 — and I’ve done tests, the dynamic range actually increases at ISO 50 on the Sony, so there’s little to no loss in quality.

This means that for a given field of view and depth of focus, you have more ability to control the light on a full frame camera than on a crop sensor camera.

They keep making these super fast lenses for crop sensor cameras (APS-C and Micro Four Thirds) to make up for the fact that they’re not full-frame sensor cameras, but it’s not the same. Fuji is coming out with a 33mm f/1.0 lens — with a depth of focus equivalent to a 50mm f/1.5 lens. I suspect this is because they’re threatened by Nikon’s new lens mount, which will allow Nikon to make very, very fast lenses.

They want you to believe the lenses are equivalent because their angle of view and depth of focus, but for controlling light, they are not the same. This is probably why Fuji are also so keen on introducing electronic shutters — when shooting at f/1.0 outdoors, you’re going to need that super fast electronic shutter to get proper exposure at a wide aperture.

Why a $90 piece of glass is better than a $500+ new studio strobe and accessories

In frame: Fuji X-Pro2 with 56mm f/1.2 lens and B+W 3 stop ND filter. Photo taken with my Sigma DP3 Merrill and my perfectly good studio strobes.

I immediately knew what my solution should be — buy a Neutral Density filter for the lens.

I posted about the issue on the Fuji forum on DPReview and the answer came back — “get better studio strobes.” A response that baffled me. Not just because my gear is just fine thank you very much, but because it belies a lack of understanding of the basics of light control and why an ND filter is preferable to more expensive studio strobes.

So I present to you — reasons a $90 3 stop Neutral Density Filter is better than a $500 studio strobe.

1. I don’t have to buy a new set of studio strobes.
2. I can better control the ambient light vs. the studio strobes at wider apertures. (At f/1.2 and ISO 200 and 1/160 sec — safe sync speed — some ambient light was creeping into my images.)
3. I can use the ND filter outdoors to shoot at wider apertures (or slower shutter speeds).
4. I can use the ND filter indoors to shoot at wider apertures (or slower shutter speeds).
5. An ND filter will take up less space than a new studio strobe + accessories, and I don’t want to clutter my life with more things.
6. An ND filter is portable. Studio strobes — less so.
7. Assuming I leave it on most of the time, it will protect the front element from dust and the elements.
8. It’s less expensive.
9. I don’t want to have to learn to use new studio strobes. Not that they’re complicated to learn, but fewer buttons = happier life.
10. Color temperature may not be consistent between my existing strobes & new strobes (though hopefully they should be), so all my preset white balances may need to be recalibrated each time I switch.
11. Cool looking “black” lens is a conversation piece.

The only drawback I can see to buying a 3 stop ND filter is that it may affect autofocus performance for a given amount of ambient light.

Light control is one of the most fundamental aspects of photography & knowing what tool to use to control the light — what tool gives you the most flexibility and utility — is a fundamental part of being a photographer.

Side note: I’m aware of High Speed Sync. I’ve done plenty of work where I’ve used strobes to overcome the sun, but I prefer leaf shutter or electronic shutter cameras for this. Every system has a limit where the ratio of ambient to strobe hits a wall and you can’t darken one without darkening both.

As the shutter speed increases, the rear curtain chases the front curtain across the sensor, exposing only a tiny sliver at a time — there is never a moment where the full sensor is exposed where a strobe could fire.

This means HSS will produces a series of pulses to expose each section of sensor. This results in a loss of power that’s much greater than if you used a Neutral Density filter to darken the scene & fired the strobe for a given exposure value at regular sync speed.

HSS has its uses, and I’m not totally against HSS, but you should know the limitations of a system before believing the hype.

Addendum:

I recently shot the Canon 85mm f/1.2 lens on my Sony body, and at ISO wasn’t enough to get the exposure I wanted. Luckily I was able to go down to ISO 50 if need be on the Sony. The Fuji is not friendly to studio setups if you want fast apertures that require low ISOs. Also I found that when switching between lenses, the B+W 3 Stop ND filter wildly threw off the white balance vs a lens that didn’t have it — so it seems the B+W filter isn’t truly “neutral” after all.

Further Reading

Micro Four Thirds cameras are better at Low Light (busting the Full Frame Myth).