2/3" lens on 1/2" camera DOP question

[Sam Kim]

Do you calculate the DOP off of the 2/3" lens of the 1/2" sensor?

We're in disagreement right now and would like some clarification. Base it off the image being projected onto the sensor or the size of the chip itself?

Edited April 8, 2010 by Sam Kim

[Noah Yuan-Vogel]

Do you calculate the DOP off of the 2/3" lens of the 1/2" sensor?

We're in disagreement right now and would like some clarification. Base it off the image being projected onto the sensor or the size of the chip itself?

 

Most of the characteristics of your image will be dependent on size of the chip, including DOF. Lens format (2/3", 35mm, etc) only generally describes the largest format imaging plane you can put the lens on and still be sure the image circle cover it throughout its zoom/focus range and tells you the image plane format that the lens is optimized for. The only characteristics that might be affected by the lens format are vignetting (not relevant here) and sharpness. Some lenses designed for 2/3" 1080p might look soft on a 1/2" 1080p camera since the lens MTF stays the same but 1/2" camera has smaller photosites, effectivey blowing up the lens's image a bit more, however this might be somewhat balanced out by the fact that MTF is usually higher in the center of the lens, which is the part you are blowing up by using a smaller sensor.

[Sam Kim]

Most of the characteristics of your image will be dependent on size of the chip, including DOF. Lens format (2/3", 35mm, etc) only generally describes the largest format imaging plane you can put the lens on and still be sure the image circle cover it throughout its zoom/focus range and tells you the image plane format that the lens is optimized for. The only characteristics that might be affected by the lens format are vignetting (not relevant here) and sharpness. Some lenses designed for 2/3" 1080p might look soft on a 1/2" 1080p camera since the lens MTF stays the same but 1/2" camera has smaller photosites, effectivey blowing up the lens's image a bit more, however this might be somewhat balanced out by the fact that MTF is usually higher in the center of the lens, which is the part you are blowing up by using a smaller sensor.

 

 

MTF?

This is how I understood it as well. Shooting digiprimes on an ex3 is extremely sharp. It's actually sharper than I want it but it's free and I can't complain with that. The other option was to shoot on the stock lens, which I don't think is that bad, but I want more control and accuracy in control, also I have no need for a zoom.

 

Thanks for the technical info. Much appreciated.

[Noah Yuan-Vogel]

Modulation Transfer Function (MTF) of the lens helps represent the measured sharpness of the lens. As I understand it, MTF actually measures the contrast rendered by imaging systems and/or imaging components at different spacial frequencies which is directly related to how we perceive sharpness and detail. This might help better describe it: http://www.normankoren.com/Tutorials/MTF.html .

[Kyle Bourgoin]

MTF?

This is how I understood it as well. Shooting digiprimes on an ex3 is extremely sharp. It's actually sharper than I want it but it's free and I can't complain with that. The other option was to shoot on the stock lens, which I don't think is that bad, but I want more control and accuracy in control, also I have no need for a zoom.

 

Thanks for the technical info. Much appreciated.

 

Could through on a pro mist filter to tone down the sharpness a bit.

[Chris Keth]

I think you'll find that the sensor size doesn't even factor into the equation for depth of field. Things are complicated a little by a sensor of relatively low resolution.

 

The best thing for you to do is to shoot a newspaper test. Lay a sheet of newspaper out on a table next to a tape measure. Set the camera up a little higher than the top of the table so you can fill the frame with the newspaper. Shoot it at a wide enough stop that you can clearly see what is and is not in focus. Set the focus exactly at a distance that is engraved on the barrel. Looking at the test will give you a focus distance, close limit, and the far limit. Compare this "real world" situation to tables and/or a depth of field calculator and you will be able to find the circle of confusion that works best for you.

[Noah Yuan-Vogel]

I think you'll find that the sensor size doesn't even factor into the equation for depth of field. Things are complicated a little by a sensor of relatively low resolution.

 

True, but in practice sensor size will affect focal lengths used and circle of confusion which are factors in the equation. I think it is quite reasonable to talk about sensor size as having a direct and inversely proportional relationship to DOF since it will be very probable in most normal systems that do not have wildly unusual CoC or optics.

[Chris Keth]

True, but in practice sensor size will affect focal lengths used and circle of confusion which are factors in the equation. I think it is quite reasonable to talk about sensor size as having a direct and inversely proportional relationship to DOF since it will be very probable in most normal systems that do not have wildly unusual CoC or optics.

 

You're right; I'm just being proper. I usually reply to at least one thread per month that stems from someone simply having no clue of the physics of optics and of the factors that affect focus.

Edited April 21, 2010 by Chris Keth

[Sam Kim]

i get it now. did a bit more research and talked to a few people about it all. thanks guys for uber tech answers. this is why this site is so great. cheers.