Depth of field is a function of focal length, aperture and desired
resolution typically called (confusingly) the circle of confusion (which
is the inverse or resolution).
When dealing with a crop sensor camera, when you compute depth of field
you use the actual focal length and aperture of the lens or, in this
case, what's coming out of the converter. In this case 355mm and f/5.6.
But, also when dealing with a crop sensor camera, one cannot use the
conventional circle of confusion numbers or tables based on same since
most of these are based on 35mm. For example, a typical (and slightly
loose value) for 35mm resolution is 30 lines/mm or a CoC of 1/30 =
0.033mm. Since prints from crop sensor cameras need to be enlarged more
than 35mm the resolution requirement need to be increased by the crop
factor. For example, the Fuji APS-C sensor with 1.5X crop factor needs
a resolution value of about 45 lines/mm (CoC = 0.022) and 4/3 images
need 60 lines/mm (CoC = 0.016).
But all of these Resolution/CoC values are based on making an 8x10 print
or magnification of approx. 8X from 35mm. If you're making smaller
prints or doing just web images you can use lower numbers... unless
you're eagle-eyed Moose in which case you need to double everything. :-)
Chuck Norcutt
On 9/10/2014 3:12 AM, SwissPace wrote:
Thanks Moose for saving me the explanation, what it means is though that
I can use my ultrawides on the XT-1 camera as if it were full frame
gaining a stop in the process. Which means I no longer need to hold onto
my canyon gear and sell it to recover some of the costs of moving to Fuji.
What I haven't researched or thought about yet is what the speedbooster
does to the depth of field.
On 10/09/2014 05:03, Moose wrote:
On 9/9/2014 7:38 PM, Chuck Norcutt wrote:
What is the effective focal length and speed of the combo?
"Mounted between a mirrorless camera and a SLR lens, Speed Booster®
increases maximum aperture by 1 stop (hence its name), increases MTF
and makes lens wider by a factor of 0.71x."
Thus, 500/8 becomes 355/5.6. FOV eq. depends on the sensor size With a
1.5x APS-C sensor, it goes back up to ~532 mm eq. The Speedbooster
becomes just that, increasing speed by one stop, while leaving FOV
essentially the same.
So What Moose
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