ISO Torture Test: Sony A77 vs Pentax K-5

We’ve done an ISO Torture Test on the Pentax K-5 previously, when we compared it to the Nikon D7000, but now there’s a new kid on the block, the Sony A77, and we’ve put it through it’s high ISO paces against the well respected Pentax K5. So how does it stand up? Let’s find out!

Items Used in This Review

First, I believe it is important to note that the Sony A77 has 24.3 megapixels on an APS-C sensor, while the Pentax K-5 has only 16.3. More megapixels on the same size sensor may indicate the tendency to introduce more noise into images. The other important factor to consider is that the Sony A77 is a translucent mirror camera, which means it splits the light between the image sensor, and a phase detection autofocus sensor. Roughly 70% of the light goes to the image sensor, and 30% to the autofocus sensor. Ultimately that means that the image sensor receives less light than a standard SLR, so you may need to reach to a higher ISO (or a slower shutter speed) to get to the same exposure of a normal SLR. Now, onto the tests.

In this test, I used a Pentax K-5 with the Pentax 50mm f/1.4 lens, and a Sony A77 with the Sony 35mm f/1.4G lens. All shots were taken at f/1.4, in a fairly dark room with only one very dim light lighting the subject. Because these lenses are different focal lengths, the framing is slightly different, but I tried my best to match between cameras as best I could. Both cameras were shot in Fine JPEG mode, with noise reduction turned off on the K-5, and turned to “Low” on the A77 (noise reduction cannot be turned off completely on the A77). The images were taken straight from the cameras, resized in Lightroom, and uploaded here. No post processing was done at all.

Sony A77

Sony A77: ISO 100

Sony A77: ISO 200

Sony A77: ISO 400

Sony A77: ISO 800

Sony A77: ISO 1600

Sony A77: ISO 3200

Sony A77: ISO 6400

Sony A77: ISO 12,800

Pentax K-5

Pentax K-5: ISO 100

Pentax K-5: ISO 200

Pentax K-5: ISO 400

Pentax K-5: ISO 800

Pentax K-5: ISO 1600

Pentax K-5: ISO 3200

Pentax K-5: ISO 6400

Pentax K-5: ISO 12,800

100% Crop Comparisons


First Place: Pentax K-5

The Pentax K-5 has always been great in low light, and even managed to beat out the fantastic Nikon D7000. It’s victorious here again, showing fantastic results all the way up to ISO 12,800. Fortunately, the K-5 gives you the ability to turn off noise reduction entirely, ridding your images of any sort of detail smearing. The result is immediately noticeable, as you retain sharp details all the way up to the native ISO cap of 12,800. The images at 12,800 certainly aren’t beautiful, but could be usable with some serious post processing.

Second Place: Sony A77

While the Sony A77 pulled off fairly respectable results up to ISO 1600, it really starts to fall apart quickly at ISO 3200. It has two things working against it in these tests, I believe. First is the fact that the sensor has a significantly higher megapixel count than the Pentax K-5, and cramming more pixels onto an APS-C sensor will generally add to the noise. The other issue I noticed though, is the inability to be able to turn off noise reduction. Sony’s noise reduction smears the details quite severely, even at the “low” setting, and renders the image pretty much unusable.


At the end of the day, you’re trading resolution for high ISO performance with these cameras. The Sony A77 doesn’t perform nearly as well as the Pentax K-5, but if having 24mp files is important to you, it’ll absolutely satisfy your needs. That being said, the slightly older Pentax K-5 performs significantly better in low light, producing usable results all the way up to ISO 12,800. At 16mp, you won’t get the resolution of the Sony A77, but it may be a trade off you’re willing to accept. Both are fantastic cameras in their own respect, and both are quite a lot of fun to shoot with in all scenarios.

Sony A77 on B&H
Sony Alpha 35mm f/1.4G on B&H 
Pentax K-5 on B&H
Pentax 50mm f/1.4 on B&H 

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