Understanding Full Frame

[Dave Throgmartin]

You can still use the outer focus points at wide apertures on the 5D2. It's just that the cross type focus sensors are only active at f/2.8 and wider, but the outer focus points aren't cross type anyway.

If I'm shooting at 85mm and f/1.4 on my 5D2 for example, I just use the focus point closest to the area I want the subject in and adjust from there, rather than using a centre focus point and recomposing. Gets me pretty close.

Ok, that's what I was wondering if the corners of the AF points get you close enough to the points you want for it not be an issue with focus accuracy. Thanks!

Dave

[FastGass]

One other note, while 1.6 uses the "sweet spot" in a lens you are for the most part better off using the longer lens on a FF to get the equivelant focal length and DOF. I say "for the most part" because I don't know if this would apply to all lens/body combinations. Daniel would probably know.

John.

[Keith B]

I came across one of Daniel Browning's posts on another forum and this is what he said:

100mm f/4 on APS-C has the same angle of view as 160mm f/6.4 on FF35.
100mm f/4 on APS-C has the same depth of field as 160mm f/6.4 on FF35.
100mm f/4 on APS-C has the same diffraction as 160mm f/6.4 on FF35.
100mm f/4 on APS-C has the same total amount of light as 160mm f/6.4 on FF35.
100mm f/4 on APS-C has the same noise as 160mm f/6.4 on FF35.

Hmmm? I was once slammed on here by one of the brainy folks that a statement I made about a 85 1.2 on a 7D would have similar FOV and similar DOF as 135 2.0 on a 5D. DOF was the contested part. I guess if another brainy guy says it with all the fancy numbers and lingo it's ok. Oh well.

[DavidEccleston]

It all depends on the framing. If you keep the same framing, you need to move back with the 7D, thus increasing DOF, making your lens appear to have a smaller aperture.

If you just keep everything in place and live with the cut off edges (as you would in any case where you're using a 7D instead of an extender for example, or pretty much any wildlife situation), the DOF will be the same, or even slightly thinner with the 7D, as the same size CoC will be viewed larger on the 7D.

So, you're both right.

[Steph]

And for those of you who like a bit of Maths, all is explained here (http://en.wikipedia.org/wiki/Depth_of_field)

[HDNitehawk]

Sorry, my intent was that the awesome 35L when used on a crop doesn't appear like it would be quite so awesome any more, given Daniel's work up it would now be:

35 x 1.6 = 56mm focal length
56mm focal length / 25mm pupil = f/2.2 aperture

compared to full frame. It appears the 50mm f/1.4 that is much cheaper would be able to provide the similar (maybe better) results on a full frame camera than what could be achieved on the crop with the 35L.

Dave

I think this logic for the 35mm works, butto a less extent for many other lenses.

The 35mm L is a great lens on a FF camera. What makes the 35mm a great lens, and a very creative tool is its high image quality at the wider apertures. On a full frame camera it can be used to really set individuals or your subject apart and gives a fair bokeh. Because of the deeper DOF with the crop camera you lose some of the 35mm's creative ability. Keep in mind that the 35mm shot at F/1.4 on either body, the IQ will be very low. You need to get up to F/2.0 or better, and of course the higher you go the deeper DOF you get.

But the same scenario has less impact the longer the lens, even though it is still there.

I think given the choice, a 7D with a 35mm or a 5D II or III with a 50mm I would go with the 50mm on a FF. However I wouldn't go with the 50mm F/1.4.