Focussing with Extension Tubes

Question

I bought a set of extension Tubes to use with my Nikon D5300 and 35mm f/1.8 lens. However, it seems that the only option to focus is to change the distance to the subject. This is very inaccurate and difficult, especially when using more than two of the tubes (It is a set of 20, 36 and 12mm tubes).

Is there any possibility to have better control over what is in focus? I imagined something that moves your camera over a set of rails like this one. Is there any existing workaround?

Also, is focus stacking possible with extension tube? (as you have to change distance, which changes field of view and perspective)

Answer 1

The only option to focus is to change the distance to the subject.

Basically, yes.

Is there any existing workaround?

A. Some rails are indeed one workaround rather than moving the tripod. There are some simpler models, like just a sliding plate on the head, like this one of the same brand.

B. Some other has some sliding bellows for both elements, the lens, and the camera.

C. But you can also use just a sheet of paper if you are on a table for example. Put the camera on a paper, a napkin or some smooth fabric and move it.

D. Another workaround is to move the subject, but of course, it depends on what your subject is.

E. If you are in a garden, one trick is to balance the tripod. Put two legs pointing to the front and the last leg pointing backward. If you extend or contract a bit this leg you will be also moving a bit forward and backward the camera. You need to compensate also the tilt of the head, but you have some more control than moving the tripod.

F. Another way to keep better focusing is by closing the aperture. Yes in some cases you need a great amount of light to compensate. So you probably need to fire a flash, or having some bright beam pointing at your subject. You could use some bright led lamp. Nowadays is easier and safer to have bright lights.

is focus stacking possible with extension tubes?

I suppose you always have some limitations because of the change of perspective, but focus stacking as far as I understand drop the zone that is not in focus. What you could have is some overall deformation.

Answer 2

You can still focus using the lens manual focus or even the autofocus but the ring drastically reduces the range of possible focus distances, so the subject-camera distance must already be in that range.

In addition the effect of the ring increases with the ratio of ring size to focal length. If you have a short focal length and a big ring the proper focus range can be very small... and inside your lens.

So in practice moving the camera or the subject is necessary, even if you can sometimes still use the AF to improve the focus.

If you want to do focus stacking, you will need something more accurate than a pair of plain rails, you need "focusing rails" with a screw drive or a rack to be able to accurately and regularly step the camera on the rails. Changing the rings is IMHO out of the question, you are not likely to obtain the very same framing after changing the rings.

Answer 3

1. When using extension tubes, the effectiveness of the focus ring on the lens is reduced.
2. For macro work, the focus ring and length of the tube impacts your magnification significantly. Unlike normal distance photography, where object distance affects most of the magnification while focus does little, macro is the reverse, i.e. focus affects most of the magnification while object distance does little. Hence most of the time you would choose a magnification and compose by adjusting the focus ring and tube length, then move the object or the camera to get in focus. Rafael's tool is created for exactly this purpose.

Answer 4

For macro work, the maximum magnification only occurs when the lens is focused at the minimum distance (e.g. 1:1); and at any other (longer) focus distance you get less magnification. So "macro rails" are often used to move either the camera/lens or the subject (using the rail as a focus stage); and having fixed focus is not an issue.

But there isn't really any significant difference for focus stacking compared to lens based focus shift. If you use lens based focus shift it changes the magnification ratio overall, and the relative magnifications through the scene; which causes relative shifts in size/composition. You loose maximum magnification, but it can be easier/better if you have the ability to make such small focus changes (many modern lenses make this very difficult).

If you use position based focus shift instead the magnification ratio remains constant, but the perspective changes causing relative magnification changes; which causes relative shifts in size/composition.

Answer 5

At high magnification, specially for focus stacking, one needs to avoid any movement of the camera by accident in-between frames. For Nikon you have various options, from most expensive to cheapest, and all of them effective: a motorized focusing rail (e.g. Stackshot from Cognisys, or a similar one from Weemacro or the very expensive new Novoflex one), a focus-staking extension tube from Helicon Focus, a Remote controller specific for stacking running on a computer or cell phone, such as Helicon remote, any other camera tethering software that allows remote manual focus.

With the motorized rails you can use any objective, even microscope objectives, and extension tubes without electronic connection. Macro photography using tethering or remote control without a rail, either through USB or Wifi will require a lens with autofocus and extension tubes with electronic connection to the lens.

Earlier I used quite frequently for focus bracketing with my Olympus camera a free tethering software from Olympus, that lets me manually step the focus point frame by frame, tedious but it works. Surely there are equivalent software for Nikon (even Lightroom or Capture One might work).

Recent Olympus cameras can be programed to do focus bracketing with many steps, and this is easy and very fast and what I tend to use nowadays. Some years ago when using a Nikon D7000 I found Helicon remote to be handy to control focus in camera or the Stackshot rail to do focus bracketing. All in all much depends on the magnification you aim at, at moderate magnification even manual focusing rails can be used with care and patience if the camera is on a sturdy copy stand or heavy tripod (macro rails like those from Sunwayfoto's or Really Right Stuff are good for this). As told in other answers, you can use such rails also to get the distance to within the range where autofocus or manual by wire focus will be in range.

For a whole system of modular rails, bellows, etc. Novoflex has the most comprehensive and unified approach, and they have added quite a few interesting new pieces of equipment in the last year, but at very high prices. Other supplier is Hejnar photo also makes a large array of different high precision manual focusing rails.

I mentioned above different brands as examples of what are the options. There are other alternatives that may be better or worse, cheaper or more expensive, but the companies I mention have web sites where the equipment is clearly described.