Hyperfocal focusing with NEX-5 and manual lenses - crop factor adjustments?

[WideAngleWandering]

I ordinarily shoot Canon FD manual focus 35mm film SLRs. I also have a Sony NEX-5 that I started using for travel & test shots (mainly landscapes) before I start exposing film.

One of the things I like about the NEX is the ability to use my FD lenses and that I can use hyperfocal focusing via the scale on the lens barrel.

I'm wondering though, given how crop factor affects focal length, is the focus scale on my 35mm lens still accurate or does that need to be mentally adjusted as well?

 

[Pioneer]

That should be pretty easy to test. Manually focus and take a shot. The use the focus scale and take your shot. Are they similar? If so, good to go. If you pixel peep at 100% you will likely see some out of focus issues that you didn't know existed before but any prints should be quite similar.

 

[Halka]

Hey Wandering.

The focusing scale is no longer 'valid' - since the NEX's APS-C sized sensor has greater depth of field, one's first impulse could be to 'virtually extend' the focusing scale markings; however, the opposite seems to hold: Hyperfocal Focusing With APS Sized Sensors

 

[WideAngleWandering]

To test this myself I would need to put the camera on a tripod, find or arrange subjects at varying distances and use a tape measure to know how far they were from the camera, shoot the test shots and then compare on screen.

Since I'm on the road right now that would be a hassle. Much easier to ask someone who understands lenses better than I do

 

[WideAngleWandering]

Hi Halka - thanks for the link! That was very informative (and complicated). I have to decide if I want to maximize DOF with my NEX or just shoot the good stuff with my 35mm SLRs. I'm not sure if it's worth the extra math!

 

[chuck94022]

Hey Wandering.

The focusing scale is no longer 'valid' - since the NEX's APS-C sized sensor has greater depth of field, one's first impulse could be to 'virtually extend' the focusing scale markings; however, the opposite seems to hold: Hyperfocal Focusing With APS Sized Sensors

The link is an accurate description of the problem. For what it is worth, Halka's comment above is not accurate. The sensor itself does not have a "greater depth of field".

Two things happen with a smaller sensor: you have to enlarge the captured image more to get an 8x10 print, and the smaller sensor means a lens of a given focal length has a narrower field of view.

The first factor means the DoF scale on a lens barrel will be wrong, if it assumes a 35mm captured image size. It will overestimate DoF, assuming you will enlarge to 8x10 print size. It may not matter if you only show on the web for example in small enlargements. (It will also be wrong on full size sensors if you plan on much larger than 8x10 enlargements.)

The second factor means that for an equivalent field of view, you will use a shorter focal length lens with a smaller sensor camera. For some cameras, much, much shorter. Shorter focal length lenses have greater DoF. So this somewhat offsets factor one. With very small sensors, it more than compensates for the first factor. It is one reason the Nikon 1 focuses so fast. With that small sensor, most of the image is already in focus due to the large DoF of short lenses.

So in summary, the sensor itself doesn't have depth of field at all. It just forces choices that change the factors affecting DoF calculation.

 

[Halka]

I stand corrected.