DOF - Close Up Shot of Toys - How DOF changes when switching lens

[personalt]

I was shooting some of my sons Thomas Trains close up yesterday using my 35mm f/1.8. I was changing the f stop and looking at the changes in DOF and comparing it to what i see my DOF calculator. This is something I had played with while shooting random pictures but just taking the exact same shot(fixed object - shooting from a tripod) at increasing (or decreasing) f stops is a good begineer exercise.

I was wondering how the DOF would changed if I switched lenses to my 24-100mm and zoomed to 100mm, stepping back to frame the picture in exactly the same manor(Thomas the train taking up about 3/4 of the image). From what I read - if I increase my distance to counter-act the increase in zoom I am making two inverse changes and should have basically the same relative depth of field as i had on the 35mm.

That being said - when shooting close ups (in my son's toys and action figures) is there some reason to step back and zoom in with 100mm rather then get closer and use my 35mm? My 35mm goes to f/1.8 while my 24-120mm is in the f/5.6 range depending on zoom.

 

[cgipson1]

Wide angle lenses have an inherently wider DOF at the same aperture, than a 100mm would for instance. If you want shallow DOF, it is much easier to achieve with a longer lens... and you won't have the barrel distortion that often happens with WA lenses used at close range.

 

[KmH]

With the subject scale the same in the image frame and f-stop the same, using 100 mm the DoF is the same as when using the 35 mm.
To keep subject scale the same in the image frame when using the 100 mm you move back and use a longer point of focus distance.

You can verify the DoF numbers using an online DoF calculator. Compare the total DoF using 35 mm, f/4, and a focus distance of 4 feet, to 100 mm, f/4 and a focus distance of 11.4 feet.
100 mm at 11.4 feet would give the same subject scale in the image frame that 35 mm and 4 feet gives.
You should also notice that the DoF distribution does change some by being closer to 50/50 with the longer focal length lens. http://dofmaster.com/dofjs.html

What changes is how much background elements are magnified. The 100 mm magnifies them more. So, if the background elements are out of focus the magnification makes the background elements appear more out of focus when they aren't.

 

[Derrel]

Shooting from farther away with a longer lens focal length creates a picture where the background angle of view is narrower in angle than when shooting from closer, using a wider-angle lens. So..if yuo want to show "less background width", then shoot with the longer focal length lens, from farther away. If you want to show MORE background....use the 35mm lens from close range.

For, let's say a shot of Thomas and James AND IN THE BACKGROUND some of those troublesome trucks...use the 35mm f/1.8 lens!!!

Depth of field behaves in a very strange,strange manner at very close-in distances...depth of field is almost entirely "the same" when the focusing distances are very,very close, as they will be when photographing small toys like the Thomas-sized toy trains. Image MAGNIFICATION is what determines depth of field in close-up photography. When an image size is identical between a 35mm or a 70mm macro, or between a 60mm macro and a 180mm macro, the different lenses will produce basically the same depth of field on a close-up shot of a tiny toy, like a Thomas or James!! I know this from actual experience, and have compared the 60mm Micro~Nikkor macro vs the Sigma 180mm EX APO Macro lens, when BOTH LENSES were used to create a frame-filling shot of the same toy...of course the camera-to-subject distances were at factors of 1x and 3x, respectively, but the SAME SIZED toy was created. Again, this is when shooting at very close-in distances. (I actually expect/anticipate some disagreement with this from those who have not actually observed this, but whatever...)

Anyway....for shooting toys and toy railroad "sets" or set-ups or layouts...you can get different background angles of view by varying the focal length and shooting distance.At so-called "normal shooting distances", the background angle of view is a pretty good reason to vary focal length. My son LOVED the Thomas trains, videos, and track!!! We had many,many wonderful hours with Thomas and James and the gang!!!