Why do I need 35mm adapter?

[Patrik Vale]

Hi!

This may be a stupid question, but..
If I have EX-3 and Adaptimax Nikon lens adapter, I can put on a 50mm lens with f1.2 and have shallow dof, is that right?
Because as I know the lower f stop number, the shallower dof is..
If it is, why do I need a 35mm adapter like Letus, RedRock or any other?

Thanks for your replies

[Ted Ramasola]

Try reading this,

Redrock Sample Footage

The principle discussed applies to all 35adapters

Ted

[Patrik Vale]

Thanks, I was reading, but I still don`t understand why the size of the camera sensor affect the DOF?

[Brian Valente]

Hi Patrik

Chuck Westfall from Canon has a good article on this - and I am copying his input here:

The three main factors (not the only factors, but the main factors) affecting depth of field are camera-to-subject distance, focal length, and aperture. Changing any of these will have an effect on the depth of field in the resulting photograph. When shooting the same scene with both full frame and small sensor digital SLRs, typically there are two ways that photographers attempt to match the angle of view:

1. If the actual focal length is the same on both cameras, the camera with the smaller sensor must be positioned at a further camera-to-subject distance to match the angle of view. Increasing the distance while keeping the focal length and aperture the same results in greater depth of field.

2. If the distance and the aperture remain the same for both cameras, the actual focal length must be reduced on the camera with the smaller sensor to match the angle of view on the full-frame camera. Reducing the actual focal length without changing the distance and aperture also results in greater depth of field. It turns out that there is approximately a one f/stop increase in depth of field for a 1.6x DSLR compared to a full-frame DSLR when the distance and aperture are the same, but the focal length is reduced on the 1.6x camera to match the angle of view on the full-frame camera.

3. If all three factors are the same on both cameras, then depth of field is identical, but the angles of view are not.

What may be confusing some photographers on this topic is the concept of "effective" focal length vs. actual focal length. For example, it is often said that an actual focal length of 50mm on a 1.6x DSLR is equivalent to an "effective" focal length of 80mm on a full-frame DSLR. While this may be true in terms of angle of view, it is equally true that the actual focal length of the lens never changes regardless of image sensor size. When it comes to comparing depth of field, therefore, "effective" focal lengths should be disregarded.

the full article is here: Tech Tips by Chuck Westfall - The Digital Journalist (October 2007)

Keep in mind his comparisons are for two different sized chips in DSLR - APS-C (appox 24x18mm) and full frame (2x that size at 24x36mm). a 1/2" sony chip, while huge by video camera standards, is extremely small by digital SLR standards, so all his comparisons would be even more dramatic when compared with a stock Sony camera.

There are also a number of additional resources on the internet if you google depth of field and sensor size. my search results:

"depth of field" and sensor size - Google Search


Hope that helps


Brian

[Matthew Overstreet]

Originally Posted by Patrik Vale

Thanks, I was reading, but I still don`t understand why the size of the camera sensor affect the DOF?

I hope I can help. But, generally the larger the size of the sensor, whether it be a film frame or CCD sensor, the shallower the depth of field there will be... 35mm film has shallower depth of field than 16mm which has shallower depth of field than 8mm film.

In general... even 2/3" CCD video cameras are closer to 16mm if not smaller. If you attach a 50mm lens that's intended for a 35mm camera onto an EX1 with a simple converter, there's going to be a zoom or crop factor because the reality is... the EX1 does not have a 35mm sized sensor. You're not going to get the same field of view as you'd get on a true 35mm film image.

That's where the converters come into play. These converters make it so the lens projects the image on an intermediate plane, which is the same size as a 35mm frame... and then the video lens records THAT image...

Hopefully that explains it clear enough.