This is an edited extract from an article I wrote for N Scale Railroading about Depth of Field and using Helicon Focus.

Depth of field is probably the single most important parameter in model railroad photography. It is useful to understand why.  Two factors affect depth of field, aperture and focus distance. When we a photograph a prototype railroad scene with a locomotive, we usually need to stand well back from the subject to make sure that it can be fully captured in the frame. As the focus point of the subject moves away from the camera the effective depth of field increases. Most DSLR camera lenses have a scale engraved on the lens body to show how the depth of field changes with aperture and focus.

Eventually the focus point reaches the hyperfocal distance, the point of focus where everything from half that distance to infinity falls within the depth of field. Usually prototype rail photographs have the subject and background scenery in the hyperfocal region. The bottom line effect is that most of the scene is in sharp focus.

If we attempt replicate the same composition in a model railroad setting, we find that we are not in the hyperfocal region. Our depth of field is only a few inches deep. It is a property of camera lenses that the depth of field region shrinks as the focus point moves closer to the camera. This region shrinks faster than the scale distance diminishes. Therefore, not all of the image will be in sharp focus. This is particularly severe in N scale models because the camera must typically be placed very close to the models to replicate a prototype shot, such as a three quarters trackside view of a passing train.

To increase depth of field to simulate the hyperfocal region we use as small an aperture (also called f-stops) as possible since the smaller the aperture size - the greater the depth of field. Pinhole lenses were popular because the small aperture of the pinhole allowed for great depth of field. Unfortunately, pinhole lenses were hard to come by, tricky to make and difficult to use because of the dark image in the viewfinder. Furthermore, there is a limit to the sharpness obtainable from small apertures. There is a point where the aperture gets so small that the light diffracts as it passes through the hole and the overall image loses sharpness.

It is the size of the aperture that governs depth of field. Aperture sizes associated with an f-stop vary from camera lens to camera lens. In other words, f22 on one camera may not have the same size aperture as f22 on another. To understand the process requires the use of the simple formula, f-stop (N) equals lens focal length (f_l) divided by the actual aperture size (D),

N = f_l/D.

The table below shows aperture sizes for the two cameras that I have tested.  You can see that the Canon Rebel XT at f29 and 27mm focal length has the smallest aperture at 0.931 mm, and therefore greater depth of field than the 50mm macro lens at f32.

You can compute the aperture size for your camera by applying the formula. Be careful in comparing lens and f-stops as some manufacturers report equivalent focal length when describing their lenses and not the actual focal length, especially for the compact digital cameras. The equivalent focal length is the comparable focal length for a "conventional" 35mm film camera lens.

The recent arrival of Helicon Focus software changes the calculus of depth of field. Although the optical properties of the individual images do not change, Helicon Focus uses post image processing of multiple exposures with different focus points to construct an image that is sharp all over. When used in model railroad applications, Helicon Focus allows us to create model railroad images that simulate the hyperfocal sharpness of a prototype image. 

I have found my macro lens very useful when combined with Helicon Focus. The ability of the macro lens to focus just an inch or so in front of the lens means that I can capture images where virtually the whole image is sharp, from immediate foreground to distant background

Bernard Kempinski

 www.alkemscalemodels.com

 

Personal Layout Blog: http://usmrr.blogspot.com/

 

Bernie and Charlie, excellent thread!

This technique is being termed "focus stacking" and you can google on that term to find many tools.

Helicon is but one tool and it costs $115 for a permanent license, or $30 for a one year license - and it's available for a free 30 day trial.

Another competing tool that's open source (free) is CombineZM. Has anyone tried this product? I've heard it's harder to use than Helicon, so I guess you get what you pay for.

There are other tools as well listed in Wikipedia, but I'm less familiar with those.

The promise of focus stacking tools for getting absolutely stunning model railroad images is exciting. I've seen this topic discussed elsewhere and some seem to feel it's something of a "cheat" and not a "real" image taken with old school methods. To that mindset, I have to observe that it's all art and even the old techniques aren't the real thing - they're all some abstract representation of reality. One could even argue that the old school methods introducing blur outside the depth of field is actually distorting reality more!

I personally love the stunning images possible with all the new tools. If the main point is communicating undistorted information, the focus stacking technique gives you cleaner, clearer visual information in the image. And being a visual sort of guy, I just love that!

I tried CombineZ but was not impressed. It is not as easy to use as Helicon Focus.  I have been so satisfied with Helicon Focus, that I really didn't see the need to try other sources. I bought the Mac version for about $90 IIRC.

Bernard Kempinski

 www.alkemscalemodels.com

 

Personal Layout Blog: http://usmrr.blogspot.com/

 

Maybe we'll have to do a bake off at some point with all the tools and report on it in MRH. Could be useful info and as a magazine that depends on high tech delivery methods, I would expect our readership to be more skewed in interest to using techy tools in their modeling and sharing.

I don't abide by this notion. As I stated in my post above, focus stacking is a technique that allows model railroad shots to more realistically simulate the hyperfocal effect of a prototype shot. I feel that it is no more cheating than using paint to make a model more realistically look like a prototype, assuming that realism is what we are striving for.

On the other hand, here is a photo-technique website where the author is demonstrating a way to make actual photos look like models -the reverse of what we are trying to do. He basically does this by selectively blurring areas of an image using masks and blur tools.  Here is a link to his website.  http://www.recedinghairline.co.uk/tutorials/fakemodel/

Bernard Kempinski

 www.alkemscalemodels.com

 

Personal Layout Blog: http://usmrr.blogspot.com/

 

Some of us are reaching the age where we can see our models much better in photographs than we can by looking at the layout itself.  It's a scary thought, but maybe the only time I will ever get to see even my tiny layout entirely in focus is through using one of these programs . . .

I find that by placing a camera within a scene on my layout I get views of locations on my layout that would be difficult or impossible to see in person.

Regards,

Charlie Comstock

If you're going to all the trouble to build nicely detailed and weathered models, why not enjoy the visual satisfaction of that effort every way possible?

Focus stacking and railfan viewpoint images of your layout does that marvelously. More eye candy, yum, yum!

Hey Bernie, how'd you get the light on that great picture with the A-B-A units to look so much like sunlight? That was shot indoors wasn't it? Or was it? The combination of light, depth of field, modeling and composition make that picture look like you were shooting REAL trains! N-scale, freakin' just about unbelievable...

Charlie

So how do you keep your camera in a rock solid position between photos, realizing that you've got to both change the focal point and trip the shutter?

Are you hooking the camera up to a computer via USB and controlling it that way?