VynZ Modern Life

All things modern.

Full-frame lenses on crop-sensor bodies – a comparison.

There are loads of opinions on the internet about what happens when you use full frame lenses on crop sensor camera. The reason why people would want to do this is that they want to invest in full frame lenses but only use them on a crop sensor body for the moment. When they do finally upgrade to a full frame body, they would already have suitable lenses.

In theory, it should work just fine. In fact using a full frame lens on a crop sensor body should give very good results as it only requires the centre portion of the image circle to be used and this is traditionally the ‘best’ part of the image. But does this work in practice?

I happen to have both a full frame and APS-C body. Both use the same Sony E mount so I can use the same lenses on either. Also I happen to three zoom lenses, one made for APS-C and two designed for full frame. I can therefore test the various combination as follows:

Sony 7R with 16-50 APS-C lens, 24-70 FF lens and 16-35 FF lens

Sony a5000 with 16-50 APS-C lens, 24-70 FF lens and 16-35 FF lens.

To keep as much constant as possible:

  • I used the exact same scene and lighting for al the photos. I chose an indoor scene so that I could control the light and test the sharpness as well as the noise levels at a midrange ISO
  • Set both cameras to Manual with F=5, S= 1/30, ISO=2500
  • Dynamic Range Optimiser on both cameras set to OFF
  • All photos taken at 24mm with the distance to the subject being varied to keep the field of view constant
  • All photos were taken handheld

The results are presented first with the whole image, and then followed by 100% crops, they are crops of the same portion of the image and so are different sizes. If you would like to see for yourself you can download the full size images by licking on them below. So first the full images:

Sony A7r with 16-50 APSC in crop mode: Down_Arrow_Icon

Sony A7r with 24-70 Down_Arrow_Icon

Sony A7r with 16-35 Down_Arrow_Icon

Sony a5000 with 16-50 APS-C Down_Arrow_Icon

Sony a5000 with 24-70 Down_Arrow_Icon

Sony a5000 with 16-35 Down_Arrow_Icon

…and now the 100% crops:

16-50mm comparison Down_Arrow_Icon

16-50

*It may seem strange that the image from the a5000 is larger here but it’s because when using an APS-C lens, the a5000 can use its full 20 mPx but the a7r is limited to 15 mPx in crop mode.

24-70mm comparison Down_Arrow_Icon

24-70

16-35mm comparison Down_Arrow_Icon

16-35

You can probably come to your own conclusions by looking at these photos. From my point of view there is no difference in exposure. However I do notice a very slightly elevated noise level when using the FF lenses on the APS-C sensor. This could be just down to sensor technology as the sensor in the A7r is by all counts a much better sensor as can be seen by direct comparison on DXOMARK.

Sensor comparison for a5000 and a7r

a5000 vs a7r sensor

While we are on the DXOMark website, lets see what they say about using the full frame on crop sensors. Looking at the 24-70mm, DXOMark rates it at 15 pMpx on the a7r but only 7 pMpx on the a5000. Similarly the 16-35 rates at 16 pMpx on the a7r but only 8pMpx on the a5000. The 16-50mm APS-C lens rates as 7 pMpx on the a5000. This would explain why the photos taken with the a5000 with the kit 16-50 and the much more expensive full frame lenses look so similar. Comparing the images from the a5000 and the a7r using the same lens however, the increase in sharpness is clear.

From these results it seems that if you want to build your camera kit slowly, it is perfectly fine to buy a cheaper crop sensor body now and future proof by buying compatible FF lenses. The only drawback doing this would be that you will need to carry around larger lenses for the time being.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Information

This entry was posted on 23 February, 2015 by in Technology and tagged , , , , , , , , , , .
%d bloggers like this: