Question about effect on Depth of Field of Zoom vs Macro

[dlwalke]

Just did an experiment in my apartment (will be glad when wetsuit season gets here) and it seemed as if I got better depth of field when I was about 4 ft away and used zoom vs 8 inches away using macro (with these settings, object was scaled to same size). Does this make sense?

 

[Cacia]

I too, eagerly await the answer....

 

[alcina]

Why not post your results so we can all see And let us know which camera you are using....

 

[herman]

One problem with doing this is, you just added 3 1/2 ft of water between your lens and the subject. This will effect all of your settings and increase the chance of introducing back scatter into the photo.

 

[Warren_L]

Just did an experiment in my apartment (will be glad when wetsuit season gets here) and it seemed as if I got better depth of field when I was about 4 ft away and used zoom vs 8 inches away using macro (with these settings, object was scaled to same size). Does this make sense?

With all else being equal, I typically find that there is less DOF in macro mode. But as herman points out, you have much more water involved in the equation so your quality of light may be different. What camera/lens are you using?

 

[devolution365]

Usually with macro shots topside (flowers and the like) a shallow depth of field is preferable. That's why your camera is making that decision "for you". You'll have to see if there's a work-around with your camera. I'm new to underwater photography, but I just work around mine (I take into account the fact that on macro I have to be pretty accurate about focus and not mind the background being blurred or deal with the blue.) A future strobe will allow me to zoom a bit instead of getting so close, but I have no idea when I'll get around to purchasing one (my wish list is pretty long).

 

[MarkH]

Was the aperture (f-stop) the same?

 

[Tortuga Roja]

DOF is tetermined by a few factors. Loss of DOF occurs
1) if you are closer to the subject
2) the focal length of the lens is longer (zoomed in)
3) the aperture is larger (smaller f-stop)

In the experiment, we really don't have enuf info about other factors like light and aperture but you can figure that when you were closer and zoomed wide, the DOF gained from your shorter lens length (#2) was offset by your closeness to the subject (#1). Whether it was a complete wash would probably take some physics calculations that I don't understand and don't particularly ever want to.

But getting closer, besides lessening the crap between the lens and the subject, also allows your strobe to do more lighting, which allows you to use a smaller aperture (bigger fstop) (#3). So to gain DOF closer rules again.

If you want less DOF, you could turn the strobe down.

"Get close & shoot up" is still the best UW photo mantra going.

 

[RiotNrrd]

Depth of field is a funciton of f-stop and distance - think of it like a percentage. The focusing distance is also logarithmic, I think (or maybe it's a square relationship?). So if you have (for example) 25% on either side of the focus point, and you are focused at 4 feet, you have a "focus" between 5 feet and 3 feet (but because of the log, it's probably more like 6 feet and 3.5 feet). If you are at 8 inches, then it's probably something like 12 inches and 7 inches. So while proportionally the DoF is the same, your closeness skes it to be "worse" when close in macro mode. Make sense?

 

[RiotNrrd]

Tortuga Roja - good point on the lighting. Didn't think of that part.