Over - Under -shot not in focus?

[privatebydesign]

Ok imagine over distance is ∞ and under distance is 0.5m, where I put the two arrows, turn your focus so the two arrows are equal distance from the focus line, the small numbers below, 8 in this case, are the minimum dof needed to encompass both over and under, but I would recommend at least f11.

Here is your picture edited, I have moved the focus ring to where you would need it to be with the above numbers.

 

[fiend]

Ok imagine over distance is ∞ and under distance is 0.5m, where I put the two arrows, turn your focus so the two arrows are equal distance from the focus line, the small numbers below, 8 in this case, are the minimum dof needed to encompass both over and under, but I would recommend at least f11.

Here is your picture edited, I have moved the focus ring to where you would need it to be with the above numbers.

Aaah, sweet! that explains it! Sounds good. Is the distance "below" equal to distance above?
I've read something about an "virtual image" that you focus on so the distance below is not the same as above.

 

[Drizzt321]

Ok imagine over distance is ∞ and under distance is 0.5m, where I put the two arrows, turn your focus so the two arrows are equal distance from the focus line, the small numbers below, 8 in this case, are the minimum dof needed to encompass both over and under, but I would recommend at least f11.

Here is your picture edited, I have moved the focus ring to where you would need it to be with the above numbers.

Aaah, sweet! that explains it! Sounds good. Is the distance "below" equal to distance above?
I've read something about an "virtual image" that you focus on so the distance below is not the same as above.

The search term you're looking for is Zone Focusing, or Scale Focusing (https://en.wikipedia.org/wiki/Scale_focus, http://digital-photography-school.com/ultimate-guide-to-zone-focusing-for-candid-street-photography). I've become better at it since getting my 120 folder that I have to set the focus manually on the lens before using the viewfinder to approximately frame. Unfortunately most lenses these days don't have any kind of decent focusing scale, although with a fisheye like the one you have unless you're just a few feet from the lens you can pretty easily get acceptable focus to infinity stopped down a fair amount.

 

[privatebydesign]

Ok imagine over distance is ∞ and under distance is 0.5m, where I put the two arrows, turn your focus so the two arrows are equal distance from the focus line, the small numbers below, 8 in this case, are the minimum dof needed to encompass both over and under, but I would recommend at least f11.

Here is your picture edited, I have moved the focus ring to where you would need it to be with the above numbers.

Aaah, sweet! that explains it! Sounds good. Is the distance "below" equal to distance above?
I've read something about an "virtual image" that you focus on so the distance below is not the same as above.

No the distances are very different, because of the "virtual image". Underwater the water and port combine to make a lens that makes everything seem much closer to the camera (it creates a "virtual image"), over water the dome is just a piece of clear plastic and does not affect focus distance.

So you need a dof that covers both actual (above) and apparent (underwater) distances, even when they are the same physical distance from the camera.

Typically a domed port underwater will focus at 1- 1 1/2 times its size, but this is vary variable depending on focal length, distance from lens to port etc etc. So your 8" port will focus at infinity at around 8"-12"! However the above water portion of the image will focus normally. As you can see you need massive dof to cover both these figures.

 

[Drizzt321]

Ok imagine over distance is ∞ and under distance is 0.5m, where I put the two arrows, turn your focus so the two arrows are equal distance from the focus line, the small numbers below, 8 in this case, are the minimum dof needed to encompass both over and under, but I would recommend at least f11.

Here is your picture edited, I have moved the focus ring to where you would need it to be with the above numbers.

Aaah, sweet! that explains it! Sounds good. Is the distance "below" equal to distance above?
I've read something about an "virtual image" that you focus on so the distance below is not the same as above.

No the distances are very different, because of the "virtual image". Underwater the water and port combine to make a lens that makes everything seem much closer to the camera (it creates a "virtual image"), over water the dome is just a piece of clear plastic and does not affect focus distance.

So you need a dof that covers both actual (above) and apparent (underwater) distances, even when they are the same physical distance from the camera.

Typically a domed port underwater will focus at 1- 1 1/2 times its size, but this is vary variable depending on focal length, distance from lens to port etc etc. So your 8" port will focus at infinity at around 8"-12"! However the above water portion of the image will focus normally. As you can see you need massive dof to cover both these figures.

Ah, that's what he meant by "virtual image", interesting. Good to know.

 

[Lyle Krannichfeld]

Hi there, old post but worth posting.

Some quick tips:

Camera on manual
f16 or as close as you can get
Expose for the above
Focus below (either on manual focus or AF, you can pre-focus and re-compose, or select the lower AF points)
If you don't have a lot of light in the water you'll need strobes to bring in detail and even things out, and in this instance you generally need a LOT of light due to the wide angle. I use 2 older DS125's (now 160's) and they are usually on close to full power for over/unders.

I don't suggest Rainx. Spit works (spit on it before you get in, wipe it around and let it dry). Lasts 30 minutes or so with good results. Or slice a potato and wipe it around before getting in.

Lyle