Stacking lenses for macro photographing.

[anders_stavland]

<p>I have read John Shaw´s Closeups in Nature. There he mentioned focus stacking. Among his best experience was a ordinary 200 mm lens f4 as the lens mounted on camera. In front he used to reverse other lenses. He especially mentioned short mount lenses as useful for this work. As far as I have understood the term short mount lenses, both enlarging lenses and lenses used to mount on bellows are short mount lenses. Am I right? <br>

Shaw also mentioned that you have to try different combination of which lenses work together. I have no experience myself, but should like to receive recommendation from macro photographers withe experience with different lenses and combination of lenses. Which type of lenses are useful, and what combinations works well?<br>

Since enlarging lenses are rather cheap when bought used, I am special interested if someone have experience with them in front of another lens? Should the lens mounted in front of another lens be mounted reversed or not is also a question I should like to learn more about.<br>

Thanks in advance for replying.</p>

 

[alex_lofquist]

<p>Yes, the front lens should be reversed. Also, the rear lens should be set to infinity for best results. Focusing is done by moving the whole system forwards and backwards, rather than fooling around with the lenses. A rack&pinion assembly is very desirable here. While I have tried zoom lenses, my best results were with primes. I have used enlarging lenses but find them not significantly better for this configuration. I have had some lens systems work quite well and others were abominable. The greatest problems were with vignetting even when stopped down. <br /> I found it best to leave the rear lens wide open and control the aperture with the front lens, using "stopped-down" metering.<br /> Best of luck.</p>

[joseph_wisniewski]

<p>I think John Shaw is a wonderful photographer, far exceeding my abilities, and his books are classics. The worst part of his otherwise excellent "Closeups in Nature" is his description of macro stacking (note, not "focus stacking"). He basically treats the front, reversed lens as if it were a high power diopter on the rear lens.</p>

<p>Alex has many good tips. When the front lens has a larger diopter number than the rear lens, it become the dominant lens in the system, the one that determines the overall optical characteristics. The rear lens becomes an "infinity coupler", it transfers light from the front lens at a "virtual infinity) to the camera's sensor. It's just like an "infinity optics" microscope, currently the predominant technology in laboratory microscopes.</p>

<p>Basically, what determines how well lenses work for macro stacking is the location of their entrance pupils (which sounds complicated, but isn't) and their curvature of field. You can test a lens for both of these things (ask how, if you like, it's not a long procedure, I can describe it). You can also look at lens reviews. Any lens blasted in the review for something like "pronounced curvature of field", "excessive curvature of field", etc. will not couple well to other lenses. That's why the 200mm f4 that Shaw recommended makes such a great rear "infinity coupler", it's a "flat field" macro lens, it has essentially no curvature of field (they label lenses with little or no curvature of field "flat field") and its exit pupil is well forward.</p>

<p>A handy rule of thumb, here's the rear lenses, in order:</p>

<ul>

<li>macro lenses make near perfect rear lenses, they almost always have flat fields and forward entrance pupils.</li>

<li>slow and medium speed telephotos also have low curvature of field and good entrance pupils.</li>

<li>limited range zooms (70-200mm f2.8, 70-200mm f4, 70-210mm f4-5.6, 70-300mm f4-5.6 or 6.3) are tolerable, although the entrance pupil makes for more vignetting.</li>

<li>wide range zooms (28-200mm, 18-200mm, 18-140mm) are generally the worst: between the entrance pupil location and the curvature of field, they're horrid.</li>

</ul>

<p>Front lenses are similar.</p>

<ul>

<li>Simple wide primes are the best 20mm f2.8, 28mm f2.8, and 35mm f2 are classics</li>

<li>Slower normals tend to be better than fast normals 50mm f1.8 or 40mm f2.0 in preference to 50mm f1.4 or 1.2.</li>

<li>Fast normals have enormous curvature of field, they misbehave wide open, and are horrible with mostly flat subjects. They can do interesting things with flowers, when you don't care if the corners are sharp, but beware: the corners look more "smeared" than "blurred", there's often "streaking".</li>

<li>Zooms tend to perform really poorly.</li>

<li>Longer lenses perform poorly. Never use an 85mm stacked in front of a 200mm to get 2.3x, instead stick a 50mm in front of a 135mm.</li>

<li>Enlarger lenses are almost always too long or too slow.</li>

</ul>

<p>Some lens combinations behave better with an "interlens" stop. Generally, when the lenses are within 3x of each other (50mm on anything 150mm or shorter is the most common situation) if you make an aperture, a round hole cut in a piece of black card, and place it between the two lenses, then use both the front and rear lens wide open, you get superior results to stopping down either the front or the rear lens. As the ratio exceeds 3x (50mm in front of 200mm, 20mm in front of 135mm, etc). you should only control the front aperture.</p>

<blockquote>

<p>A rack&pinion assembly is very desirable here</p>

</blockquote>

<p>I think what Alex meant is that a "focus rail" is desirable here. Focus rails come in two flavors, "rack and pinion" and "worm screw". Rack and pinion are the preferred rails if you like shooting with the lens close to horizontal, i.e. you're right down at flower level. Velbon, Novoflex, Nikon, and Pentax make excellent rack and pinion rails. I tend to avoid the generic Chinese rails. You get essentially the same rail from eBay, Adorama, Deal Extreme, and Kirk: it's wobbly and awkward.</p>

<p>The worm screw rail is preferred if you're shooting more than 30 degrees up or down. Manfrotto and RRS make good worm screw rails. RRS is the king of the worms.</p>

[alex_lofquist]

<p>Joseph, you make a good point in that an iris diaphragm (stop) ought to be placed between the two lenses, closest to where the chief ray crosses the optic axis. (The chief ray represents an undeviated ray of light from a point on the subject to the image. On a thin lens system it is an off-axis straight line through the center of the lens from a point on the subject to the image.) While it may be difficult to find this exactly, it is certainly better than using either lens diaphragm to control exposure.</p>

[Jeff Lear]

<p>I've been experimenting with this a bit myself. I rented the MP-E 65 for a weekend and while I enjoyed the novelty of it, decided I would forego the $1000 price tag and attempt to make my own using things I already had. I've got a fairly descriptive overview on my <a href="http://www.facebook.com/photo.php?fbid=193821050655538&set=a.193821040655539.36966.170111329693177&type=1&theater">facebook photo page</a> if you're interested. Along with some of my <a href="http://www.facebook.com/photo.php?fbid=193244474046529&set=a.174459349258375.30203.170111329693177&type=1&theater">results</a>. In short, I have an EF 75-300 mounted normally with an EF 50 f/1.4 reversed using a couple filter rings glued back-to-back. All of that rests on an old machinist's vise or <em>focus rail</em>, as I like to call it.<br /><br />I control the aperture using the traditionally mounted lens, I've tried setting aperture with the reversed lens but it vignettes badly.<br /><br />In the end, I get greater depth of field, contrast, IQ, and versatility with my frankenmacro setup than I did with the dedicated MP-E 65 which, admittedly, was a heavily used rental and probably not in top condition, optically.</p>

[anders_stavland]

<p>Thanks Joseph for Your excellent explanation on my question. I have read elsewhere that You are going to publish a book of Macro photography. When will this happen?<br>

I have seen Your general rules about both the front lens and rear lens. I have a manual Nikon ai 200 f 4 lens. How will You rate this as a rear lens? Shaw recommends this lens.<br>

I have a Nikkor 50 mm Ai f2 and also an EL Nikkor 50 mm 2,8. The El Nikkor has been used in the darkroom for many years. Now I would try to use it in front of my 200 mm. I also should like to try a Rodenstock Rodagon 80 mm f4 enlarging lens in front of my 200 mm.<br>

Should I try to mount my enlarging lenses reversed or not?<br>

At last I also have a AF Micro Nikkor 105 2.8 D. Could this lens be useful as a rear lens?<br>

Thanks for replying.</p>