Too large of a sensor??

[smellzlikefish]

I was recently shooting blue sharks off Rhode Island with some seasoned pros (note: I am not seasoned nor a pro) who were damning the large sensors of their video setups. This flew in the face of everything I had ever learned, but they held firm. I believe their argument was that they got less depth of field with larger sensors underwater. Could someone help me understand why larger sensors may be a disadvantage?

 

[DazedAndConfuzed]

depth of field is determined by the focal length of the lens and aperture.

Thus if you put a 24mm f2.8 lens (which has great depth of field even shot fully open) from a full frame camera onto P&S camera with a 1/3" sensor, whose sensor size is 1/64 of a full frame camera and its dimension is 1/8 as long& wide, 98% of the image projected by the lens is not used, thus 24mm lens actually is the equiv of a 200mm telephoto lens, while preserving the same depth of field.

Thus for these new skool pros who are use to iphone videos, going from a 2mm f4 lens to a imax camera with a 100mm f4, they can't not 'not bother with focusing' anymore and have to do real videography work. Maybe they need a dome lens where it is back to focus free shooting.

 

[smellzlikefish]

It may not have been a depth of field issue, but they were cursing larger sensors for video work. I know one of them brought up write speeds as an issue (makes sense), but they had a whole list of complaints. If I could remember the conversation better, I'd love to elaborate. I do know that one shoots regularly for Discovery, one has his own show with international viewership and the other works sometimes for Nat Geo. I don't think any of those applications utilize Iphone videos.

 

[Blackwood]

I was recently shooting blue sharks off Rhode Island with some seasoned pros (note: I am not seasoned nor a pro) who were damning the large sensors of their video setups. This flew in the face of everything I had ever learned, but they held firm. I believe their argument was that they got less depth of field with larger sensors underwater. Could someone help me understand why larger sensors may be a disadvantage?

Sensor size doesn't really affect DOF (which is an optical property). More appropriately, in order to achieve the same composition with a larger sensor, you either need to get closer or use a longer lens than with a smaller sensor. That's why DOF is "reduced" - they're comparing different formats with a common framing.

I guess it depends on what you are going for. As was alluded to above, many UW videographers want a wide DOF focused at the hyperfocal length so they can essentially set it and forget it. Shooting with a narrow DOF means actively changing focus. Above water, portrait and abstract shooters often crave narrow DOF. When I photograph my son, I often have his eyes sharp with a DOF only a few inches wide (tip of the nose to back of his ears). Everything else is progressively OOF. Landscape artists on the other hand want very wide DOF, and shoot fairly narrow apertures to achieve it.

Examples (exit data available):

 

[DazedAndConfuzed]

Imagine what the guys shooting Imax 3D had to complain about. film reels that holds 3 minutes of film, camera the size of a dishwasher. But that's the nature of the beast. I wish I had a camera that intercepted my optic nerve and took pictures based on what I am seeing, but it doesn't exist and I have to lug a unhydrodrynamic contraption around.

 

[Blackwood]

What's the problem?

 

[Interceptor121]

I think the poster may refer to people that have switched from a normal video camera like a canon XA10 to a DSLR to take video
With a traditional video camera you have focal lengths between 5 and 50 mm this together with a wide angle lens like a fathom soon gives you infinite depth of field and basically you don't need to focus
With a DSLR you need a dome port and a fisheye lens if you want to have the same ability but then your lens is set for the dive and this for video is not good.
If you have a zoom lens behind a dome say a 14-42 most of the time you will need to focus and still you don't get the same flexibility of a normal video with small sensor

 

[smellzlikefish]

I think Interceptor nailed it. Thanks.

 

[DazedAndConfuzed]

I thought anyone worth their salt would have been using the Sony HDW-F900-3 and now the Red One or Epic. Or I guess the DSLR is kind of the poor-man's Red. All large sensors. The Red 5k will eat thru memory though.