Vari-ND

My cheap 77mm vari-ND filter arrived today, so when there is some sunlight, a test video will be created. This filter will enable one to use a wide aperture, 1/50s shutter in sunlight to give both the correct exposure and shallow DoF.

Two new videos

I have just made another two basic videos to showcase the difference in both depth of field and field of view between the Canon 550D and Canon 5Dmkii. With the 5Dmkii being a full frame sensor one must compensate between the two cameras by either adjusting the focal lengths of the lens differently, or by positioning the 550D further back from the subject.

The first test was to place the two camera bodies as close to each other as possible and the same distance away from the "30cm" marking on a tape measure. Focal length was then adjusted to approx. 70mm on the 5Dmkii and 43mm (approx.) on the 550D, thus providing the same field of view. Secondly, the same focal length was set on both cameras to show the difference in field of view / depth of field for both camera bodies.

The second test was using to try and demonstrate the difference in camera position required to give the same field of view for the same focal length setting. The 5Dmkii was positioned approx. 75cm from the subject (in this case a plant!) and the 550D was positioned approx. 120cm from the same subject (i.e. to take into account the x1.6 crop factor).

In each case the ISO values were set identically on both cameras, the same 24 to 105 f/4 L lens was used (set to f/4) and the shutter on both was set to 1/50s.

Videos are available on the usual www.vimeo.com/digitalvideoslr pages.....

Sensor size and DoF

Have just been considering the effect of sensor size and the depth of field achievable for the same focal length and the same aperture. I have just been using an on-line depth of field calculator (www.dofmaster.com), which interestingly stated that for the same distance to subject, using the same focal length and aperture, the depth of field will be shorter on the cropped sensor camera compared to the full frame. However, one has to remember that on the cropped sensor camera, the effective field of view will be greater (x1.6 crop for example) resulting in a shorter DoF since the magnification will be greater. If however, the distance to subject is increased for the cropped sensor to provide the same effective field of view for both cameras (and to compensate for the magnification due to the cropped sensor). then the DoF will be shorter for the full frame sensor.

Example: (using the DoF master software)

Full frame 5DMKII with 50mm f/2.8 lens with a distance to subject of 10 feet:

Depth of field: 2.06 feet

APS-C 7D with 50mm f/2.8 lens with a distance to subject of 10 feet:

Depth of field: 1.29 feet

However, one must remember that the 50mm lens on the APS-C camera will behave more like an 80mm lens (50mm x 1.6), meaning the field of view will be "closer" and the DoF will be shorter (as DoF is also a product of focal length too). Therefore, if we "move" the APS-C camera further away from the subject to say 16 feet, then the field of view for both cameras, with the 50mm lens should be the same and hence the DoF on the APS-C camera should be deeper than the for the full frame.

A test video needs to be created for this.... watch this space!

Also, to provide approximately the same DoF for both sensors, as well as as moving the cropped sensor further away from the subject to provide the same field of view, one can decrease the aperture of the lens on the full frame sensor too.

Vari-ND

I can feel another video coming on. I have just purchased a 77mm Vari-ND filter which will be useful for well lit situations where the shutter needs to be kept at 1/50s (PAL) and the aperture of the lens needs to be wide open too. It's only a cheap filter, but I am hoping that for demonstration purposes, it will be reasonable enough.

Video will be posted on this Blog and via Vimeo as usual, hopefully within a few days.....

Canon 6D

17th September saw the announcement by Canon of the new 6D FULL FRAME DSLR camera! The specs look good and one wonders now whether to purchase one of these instead of the new Canon 5D MKIII or the MKII!