Newbie with some basic questions, help is appreciated!

[Eugene1]

Hi all,
I'm new to the underwater photography world so apologies if these are basic questions. After reading information online, I seem to find on a lot of websites that f/8 is recommended for underwater photography with wide angle shots. However, I don't get it....

- I am planning to buy an Olympus 8mm f/1.8 fisheye lens. Isn't the f/1.8 very useful to keep ISO low and get a higher quality image? Why would I want to shoot this lens at f/8 considering that the fisheye has a lot of 'natural' depth of field, even at f/1.8..? What is the reason that high aperture numbers are recommended for underwater work?

- Furthermore, the use of strobes is also recommended. What about shots close to the surface? For example close up fisheye shots of sharks/dolphins near the surface? Isn't that nicer with natural light? Or is a strobe always recommended?

- Lastly, when making split images (top/under) during daylight hours, are strobes needed? Or only when the 'under' shot is too dark?

Hope someone can help me with this!
Thanks in advance

 

[bvanant]

Sort of in-order.
1. F1.8 has very shallow DOF even on a wide angle lens. To get sharp corners f8 is appropriate. The reason that the 1.8 is nice is that is the aperture that the lens uses to focus. I will try to post some images (on land) showing DOF fall off with aperture.
2. Strobes are necessary if you are trying to have a foreground subject that is lit in front of a wreck or reef. Of course natural light at the surface is a great way to shoot but for shooting a fan say deep in front of a wreck, you need the strobe. Many really wide wreck or reef shots are shot only in natural light but strobes definitely help with many (NOT ALL) shots.
3. Over-unders typically have a very bright over and a much less bright under. If the under part has a definite subject then a strobe helps, otherwise a variable filter can help.

Bill

 

[JamesBon92007]

I agree with everything bvanant said but want to clarify one point (which was implied) and that is: color. With natural lighting the water absorbs all the red in fairly shallow depths with yellow being the next to go. A red filter can help a lot to restore the lost color at depth and a typical strobe with give you nice, colorful results.

Personally I generally like to get as much depth of field as possible so I shoot with a higher F Stop. But heck, sometimes getting something's eye in focus and everything else out of focus can be very effective. It's been a while since I did any still photography underwater but I seem to recall using f11 a lot. But that was with film. Digital is still somewhat of a mystery to me.

 

[Eugene1]

Many thanks Bill & James, your advice is highly appreciated!
I will be shooting with a m4/3 camera, therefore f/1.8 will give equal DoF as f/3.5 on full frame. Thus, am I right stating that I could potentially shoot the fisheye at f/2.8-4 (FF f/5.6-8) to still get nice DoF underwater? I thought the f/1.8 would be very handy with dolphins portraits (no background) that move quite fast.
A question about the red filter James: can't I adjust this in RAW afterwards? Or is that very tricky?
Thanks again both!

 

[bvanant]

White balance certainly works in raw, but getting the color close is pretty much important for good photos. I don't understand why you think f/1.8 would be better for dolphins than f/6 say. It all depends on the available light. You won't get "nice" DOF until you get to 5.6 or 8 if you want the corners of your frame sharp. I will post some pictures tomorrow with the 8 mm fisheye.
For a red filter just get one mounted to a flip adapter.
Bill

 

[PatW]

Generally when you use a wide angle lens you want a large depth of field, usually from the subject to infinity. So you would shoot at a higher f stop of at least 8. Also wide angle lenses usually work better optically at f stops of 8 or higher. The big deal of the 1.8 minimum f stop is the lens focuses wide open. The low f stop allows more precise focus under low light.

Now photographers will use low f stops of 4 or less with macro lenses. Macro lenses are close up lenses. Macro lenses tend to be very good optically so they perform wide open. Often the subject in a close up has a cluttered and distracting background so you can emphasize the subject by using a low f stop. But that is a different thing entirely.

I would suggest that you do topside shooting with your camera. It is really important to understand f stops, iso, shutter speed, lenses, focal length, depth of field, composition and lighting. Scuba diving is complex enough without trying to learn photography in a low light and murky conditions. It really helps to know what you are doing before you dive,

 

[Eugene1]

Thanks a lot guys! I fully understand the importance of DoF and how aperture affects it. The reason I thought the f/1.8 would be handy is that it allows for more light and therefore a higher shutter speed (fast dolphins at the surface). Hence I could use a lower ISO if not using strobes. I know that ultrawides/fisheye automatically have a lot of DoF, therefore I didn't understand why f/1.8 could not be used for fast moving subjects (since the lens has a large DoF of itself). Furthermore m4/3 f/1.8 has equal DoF as f/3.5 on FF. But I guess I sould stick to f/5.6-8.0 then, thanks a lot!!

 

[bvanant]

I think your assumption about DOF is not as warranted as you think. By all means get the 1.8 lens (it is spectacular) but don't expect sharp corners at f/1.8.
Bill