Understanding Crop vs Full Sensors

by Amy Bish

When DSLRs first came out, the term crop sensor was introduced to the public. What exactly is a crop sensor though?

A crop sensor is basically just a smaller sensor compared to the full sensor that more expensive camera bodies sport. These full sensors were created to mimic the film size on your old film SLR so that their previous lineup of lenses acted the same on DSLRs.

The main thing a crop sensor affects is the amount of image captured when shooting. Let’s take a closer look:

Restoring an Under Exposed Image in Lightroom

Now say this photograph was shot with a full sensor at 400mm. The corresponding lines on here show how different crop sensors would perform when capturing this image with the same lens, focal length and distance:

– Entire Image: Full Sensor
– Black Line: 1.3 Crop Sensor
– Gray Line: 1.5 Crop Sensor
– White Line: 1.6 Crop Sensor

Note: If you’re shooting with any size of crop sensor you will not see the full sensor image when shooting with your camera. What you see is 100% of what you get after taking the photo. Also, there are lenses created for use only on crop sensors. They’re less expensive and act differently on your crop sensor camera than lenses compatible with full sensors.
However, in this article I’m going to assume you’re only using lenses that work with the full range of DSLR sensors.

At first this makes a lot of people assume that your crop sensor increases the focal length of your lens, but that’s just not true. A 400mm lens on a crop sensor camera is still a 400mm lens. The difference between the images captured occurs because your crop sensor decreases the area of recorded light from the actual amount your lens shines into the camera.

Still confused?

Look again at the picture above. It is an image comparing all the different sizes of sensors. The entire picture is full sensor, the black line indicates a 1.3 crop sensor, etc. When the shutter is open and your lens shines light into the camera, it will always shine in enough light to fill a full sensor. The crop sensor makes it so you’re recording less of that area of light; how much less depends on the size of your sensor!

Now that we know how they work, let’s look at crop vs full sensors and see what else they affect. All comparisons done below are with the same lens, focal length and distance from your subject:

Closest Focusing Distance

Many people who are just told their crop sensor increases their lens’s focal length worry that their focusing distance will change. Although now that you know how a crop sensor affects images you’ve probably guessed that the minimum and maximum focusing distance will not be altered.

Aperture

Your aperture value will stay the same on a crop sensor. However, the depth of field an aperture value creates will change going from crop to full sensor.

Depth Of Field

If you were to crop your full frame image down to the area your crop sensor covered, your depth of field would then be identical for both sensors. Without cropping, when shooting with the same variables your crop sensor would have less depth of field. If you used the same focal length but shot at different distances for the same field of view, the crop sensor would then have more depth of field. Are you confused yet? Check out this article on depth of field.

Hand Held Shutter Speed

The rule of thumb for shooting hand held with your camera is the minimum shutter speed should equal 1/focal length to rule out camera shake. However, that’s when you’re shooting with a full sensor camera. If you have a crop sensor take 1/focal length x crop sensor. For example: I’m shooting at 400mm with a Canon 7D which has a 1.6 crop sensor. Therefore, my minimum shutter speed would be 1/400 x 1.6 which equals 1/640. These speeds are only a guideline though, view your images afterwards at 100% to see if you need to be shooting faster.

Usable ISO

When I say usable I mean ISO settings that don’t have a lot of grain. If you compare a new 18MB crop sensor with a new 18MB full sensor camera, the full sensor camera will allow you to shoot with higher ISO settings without seeing as much grain. This is because the amount of space each MB is packed into varies; more sensor space per MB will give you less grain.

Imperfections In Your Lenses.

If you’re ever read reviews for lenses, they sometimes vary from positive to negative for things like vignetting and soft focus near the edges. Chances are the positives are using a crop sensor and the negatives are using full sensors. One of the nice things about shooting on a crop sensor is that you’ll cut out unwanted effects near your frame edges where lens quality is known to usually be weaker. However, a crop sensor will enlarge any defects in the middle of your lens.

Crop Sensor Camera Lenses

These are new on the market and aren’t compatible with film SLRs. Lenses are usually a larger investment into your photography than the actual camera, because they’re something you’ll still be using 10 years or more down the road. That said, if you ever want to switch to a full sensor camera anytime in the future, be careful purchasing these because they only work with crop sensors.

Wildlife & Sports Photography

For some people it makes sense to use a crop sensor for wildlife and sports photography, especially when you’re starting out because you have to invest less money into longer telephoto lenses and teleconverters to stretch your reach. Since your crop sensor automatically records a smaller area of light than your lens sends into the camera, it becomes a beneficial feature when using telephotos because the subject will be larger in the frame than it would on a full sensor camera.

Landscape Photography

If you fancy using wide angle lenses the image they’re meant to have recorded on a full sensor camera will automatically be cut with a crop sensor, making your landscapes a bit less impressive and you’ll need wider lenses to match what a full sensor camera would capture at the same distance.

Image Quality

A bit of rehashing from the Usable ISO section, but a new full sensor’s image quality will be better than a new crop sensor’s which is why they do cost more. However, a crop sensor’s quality is not to be laughed at – there are some very high quality crop sensor cameras on the market right now with a lot of bells and whistles that new full sensor cameras include.

Full Sensor Trade Up

Now that you’ve read all this you might be dying to trade up to a full sensor. Just be warned; to get all that premium quality out of a full sensor camera you may need to upgrade to premium lenses, longer telephotos, and teleconverters. Like I said above, full sensor cameras also have the ability to show more negative qualities in lenses. See what all you’d want to upgrade before making the switch.

If you’re shopping for a DSLR, I hope that you now understand one of the biggest differences in the camera market right now between the models out there. Depending on your use crop sensors can be a pro or a con to your photographs. If you already own a DSLR, maybe you’ve learned something about your full or crop sensor when comparing them. While it’s definitely easy to get caught up in the full and crop sensor debate and want more and better equipment, don’t forget the number one ingredient of every great photograph is the photographer!

Amy Bish is a nature and wildlife photographer from Pennsylvania. Having earned a dual major in photography and design at Edinboro University, when not out shooting she enjoys writing and featuring inspirational photos on her blog. You can find her work online at http://www.aforaperture.com

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6 Comments

Ally said:

Great information. Thank you for a well explained post!
Sue Block said:

I have a Nikon D700 and have a 24-70mm lens which I love.

I am going on a trip to to Namibia – Is it important to purchase a compatible 70-300 mm lens or will my 18-200mm crop lens provide a respectable quality outcome to photographing wild animals?

Sue
Amy Bish said:

Sue -

As I’m sure you know your D700 has a full sensor at 36.0 x 23.9mm and is considered Nikon’s FX series.

Unlike a lot of camera manufacturers, Nikon will let you use DX lenses on a lot of FX bodies which is a great option if you’re missing that length in an FX lens. It comes with some drawbacks though.

When you mount your 18-200mm DX crop lens on your FX D700 it will do one of two things:

- Automatically crop the edges of your sensor out.
- Use the full sensor but you’ll see about 1/2 of the image blacked out.

It does this because a DX lens is built to create an image only large enough for DX sensors, which are smaller then FX sensors. If your camera chooses to automatically crop the edges out, it can create the illusion of magnifying your field of view just like crop sensors do. However, it will convert the useable area of your 12.1 MP FX sensor into a 5-6 MP sensor making your images smaller!

If it was me heading to Namibia, I would splurge on a new FX lens that was at least 300mm for capturing wildlife. A 300mm FX lens will give you around the same field of view as a 200mm DX lens, but you’ll be taking full advantage of your FX sensor giving you double the image size!

Good luck with your decision and most of all enjoy Namibia.
Bill Jones said:

Great information Amy!
Amy Bish said:

Ally & Bill –

Thank you both!
Edward Gill said:

Amy

Nice article although your connection of crop sensor to depth of field is incorrect as written. Depth of field is determined by the lens focal length, aperature used, and distance to subject – as explained in the article you linked to. The size of the sensor has zero effect on the depth of field for any given combination of the three factors mentioned above. Where sensor size comes into play is in Field of View (FOV). For example a 50mm f1.4 lens wide open focused at 10 feet will have give the same depth of field (or focus) regardless of the sensor behind it but it will have a varying FOV depending upon the sensor size (up to the image circle of the lens). For a Canon 1.6 crop sensor the FOV will be equivalent to an 80mm lens but the depth of field will still be that of a 50mm lens at the given aperature and focus distance. Example, an 80mm lens at f2.8 on a full frame camera focused at 10 feet will have roughly 0.25 ft depth of field (0.01mm circle of confusion). To get the same FOV and depth of field on a 1.6 crop sensor you would need to use a 50mm set at f1.2. The 80mm at f2.8 on the crop sensor would still have 0.25 ft depth of field but a FOV equal to a 128mm lens.