Macro Photography Tools and Techniques

   

This Macro Photography Series consists of 6 Parts. You can use the Blog Archive links to access any chapter, as well as my other posts. I recently re-formatted this Series so that the chapters can be read in order. I learned that the only way to do this on Blogger was to change the publishing dates to flow concurrently. Don't be misled by those posting dates. This thing was not written in 6 days!

The information and photos in this Macro Series represent a compilation of years of research and field experience.

Enjoy the series, and please leave a comment at the bottom if you like what you see. 

                     Macro Photography 
                    Tools and Techniques
                                 Part #1
                               
Introduction:
As anyone who has ever picked up a camera knows, bigger is almost always better. Filling a frame with as much of a subject as is technically possible ranks highly among every serious outdoor photographer’s aspirations. While easily fulfilled during every day shooting scenarios (at least most of the time),  the challenge of filling our frame with our subject becomes increasingly more difficult to accomplish as the size of our intended quarry diminishes into the unforgiving realm of the macro world.

In this Series, we will focus upon understanding the fundamentals and challenges inherent in creating high-quality, in-camera macro imagery in the field. We will attempt to acknowledge most of the obstacles Mother Nature appears to enjoy hurling into our paths as we delineate the tools and skills requisite to conquering them. We will detail specialized equipment and techniques required to resolve the adversities of effective lighting, both natural and applied. We will offer strategies for recognizing or crafting practical backgrounds which help to define and accentuate our minuscule works of art.
We will analyze some of the more popular macro subjects found in nature and offer demonstrated shooting tips, stealth techniques and suggestions helpful in transforming the mundane into masterpieces worthy of praise.
We will discuss the fine art of composing tiny landscapes…a  practice which can best be defined as “creating something from nothing“. This acquired skill can prove extremely valuable in salvaging those days when there really is, “…nothing to shoot”.
Throughout this text, a familiarity in photographic technique and its nomenclature will be beneficial…particularly as applied to modern film and digital SLR applications.
We will try to dissuade a dependence upon technology, and create a more comfortable mind-set toward applying manual camera settings for ultimate control…while translating some of macro photography’s most cryptic vernacular into more digestible provisions.

Along the trail, we will meet up with Bugsy.
He’s a fictional, but intrepid nature photographer who is beset with many field challenges which he has to resolve through innovation. How he imaginatively conquers his countless macro photography dilemmas should be an inspiration to us all!

If your concept of "photography" involves holding up your cell phone and pushing a button...you likely won't gain much from this Series.
I've been referred to as That Old Fart from the Old School...but I believe that inspirational, creative imagery requires empirical knowledge gained through years of practical experience.

Therefore, you can expect extensive discussion into expanding upon what you should already know about composition, critical focus, exposure, and depth of field control.

Like the ingredients in a stew, these fundamentals represent photography’s building blocks, so it stands to reason that a mastery of these basic essentials applies as much to macro photography as to any other form. (…only closer).

              A Macro Photographer's Arsenal

The first installment in this series outlines tools and materials which might typically be found in an outdoor macro photographer's gear bag. As mentioned, future posts will elaborate further into actual shooting scenarios, field challenges, and advanced photographic techniques designed to maximize potential.

The Macro Lens:
The true macro lens is an extremely versatile piece of equipment. This specialized lens has the ability to focus from as close as a few inches away from the subject (at 1:1 life-size) all the way to infinity.
(The idiom “life-size” reverts back to the film era and accurately defines the size relationship between an actual object and its reproduced likeness on film. “True life-size” indicates that the object size, as photographed on a film strip or slide, is exactly the same size as in real life.) 

The extreme range of focusing capabilities prompts many photographers into replacing their standard (kit) lenses with macro lenses as part of their every day, “walk around” camera systems.
When choosing any photographic accessory, quality and practicality should be foremost in the mind of the prospective buyer. This is particularly true when choosing a macro lens, since a poor choice can often lead to disaster.
Don’t be misled by generic lens manufacturers who misappropriate the idioms  “macro capabilities” or “close-focusing” when describing their modestly-priced zoom lenses. More often than not, these lenses are of poor optical quality, and most cannot focus closer than around ¼  life-size.
True macro lenses are manufactured in fixed focal lengths. The most commonly available lens sizes range from 60 mm to 200 mm. While focal lengths and working distances may vary, all macro lenses will have the same range of focusing capability…from 1:1 life-size (or 1:2 on some models) all the way out to infinity. Most name brand and high-quality generic lens manufacturers employ specialized glass, which helps optimize corner-to-corner sharpness from the lens’ minimum focusing distance throughout its entire focusing range. So while there may be other options for close-up photography, it’s wise for the serious nature photographer to own at least one true macro lens.
Which focal length to select will depend heavily upon one’s intended quarry. While a 60 mm macro lens is an acceptable focal length for wildflower photography, it may not be the most practical choice for shooting insects and the other skittish little creatures we  encounter in nature. A much better focal length for insect photography would fall into the 105 mm to 200 mm range. The same 1:1 ratio could be achieved…but at a much more effective working distance.
Lens manufactures will usually list the “Close-focus Distance” in their specifications, but don’t confuse this with the actual “Free-working Distance”.
By definition, “Close Focus” is the measured distance between two critical focus points…the subject and the film plane or sensor (when the lens is focused to its closest parameter). Conversely, the free-working distance of a lens is measured between the subject and the front of the lens barrel when the lens is focused at 1:1. While specified distances may vary slightly, dependent upon the lens manufacturer, the average working distance with a 60 mm macro lens focused at 1:1 is around 3 inches from the subject. With a 200 mm macro lens, a photographer can focus to 1:1 from over a foot away from his or her quarry.
So it stands to reason that if the nature photographer had to select only one true macro lens for all-around use, a longer focal length lens might be the sensible choice.

Close-up Filters

Close-up Filters (Diopters):
Magnifying (close-up) filters, which can be attached onto the front of just about any lens via the threaded filter ring, represent a cheaper alternative to investing in a true macro lens. They are typically sold in sets, representing varying diopter strengths, and can be used singularly or stacked together. The quality of the glass used in magnifying filters can vary from dreadfully poor to really good, depending upon the manufacturer and price range.
The obvious advantages are the lower price and ease of use. Since close-up filters can be applied to any lens which accepts the same filter thread, they allow the budget-minded macro photographer to utilize a non-macro lens he or she may already own to magnify an image beyond its standard close-focusing parameters.
The glass filters are clear so there is minimal light loss and, with a little practice, it’s generally easy to achieve acceptable results while shooting hand-held in decent light.
But as in all photography, there are trade-offs to consider. Magnifying filters are only functional when shooting close, so if a situation changes abruptly and a photographer needs to quickly react and recompose, the lens with the applied magnifying filters will lose its ability to focus on distant objects.
The filters will need to be removed to allow the lens to focus normally.
Since the filters add more layers of glass, the integrity of an otherwise stellar lens may be compromised. Adding additional layers of glass can increase the possibility of chromatic aberration (color shift), and lens flare. When several of the close-up filters are stacked, vignetting (…that dreaded darkening of the corners) is a common anomaly.
Finally, magnifying filters are designed to achieve their most effective levels of sharpness when the subject is in the center of the frame. (As we know, positioning our point of interest dead-center in the frame may not always be desirable.)

Reversing Rings:
Another inexpensive alternative for shooting close is to mount a standard lens onto the camera body backwards by using a reversing ring.
Reversing rings are readily available in a variety of lens mounts and filter thread sizes. By design,  they are all basically the same. A threaded flange on one side of the ring accepts the filter threads inside the front of the lens barrel. On the other side of the ring, a compatible lens mount attaches the reversed lens to the camera body.
(When shopping for a reversing ring, be sure to select a manufacturer’s compatible lens mount and filter thread size to accommodate the lens or lenses you intend to use.)
Lenses most practically used in reverse for macro photography have manually operating aperture control capabilities and are of short focal length (20 mm to 60 mm). It’s true that any focal length lens can be reversed with the proper ring, but longer lenses are also heavier lenses. The excessive weight of a heavy lens could add undue strain to the delicate threads of the lens barrel and increase the possibility of the threads jamming…making it difficult to remove the ring after the macro shoot.
It’s important to remember that a reversed lens is more vulnerable to damage, since the rear glass and delicate pins and contacts are exposed. G-Series (gelded) lenses are pretty much worthless when reversed. The rear contacts are no longer attached to the camera body so there is no communication mechanism to control the aperture settings.

How does reversing a lens increase magnification?
To explain this concept fully requires an understanding of focal points and how lens extensions relate to life-size ratios. (Unless you’re the Professor of Physics at the local college, the cerebral gymnastics of trying to calculate the math can drive you batty.) To put it simply, we are extending the rear lens element at a distance equivalent to the lens’ focal length. In FX (or 35 mm) format with a reverse-mounted 50 mm lens, this equates to around 1:1 life-size. Mounting a shorter focal length lens in reverse can increase the image size beyond life-size. (On a DX digital body, with its smaller sensor, the crop factor permits subject magnifications up to around 3.4X with a reversed 20 mm lens.)
Unlike the magnifying filters, no additional glass elements are applied so the integrity of the primary lens’ quality is not compromised. Since the focusing ring becomes useless, critically focusing on a macro subject with a reversed prime lens can only be performed manually by moving the camera forward or backward. This process can prove to be quite cumbersome in the field with a tripod mounted camera.
This focusing handicap has a redeeming benefit though. Since we’re forced into moving our cameras and tripods to focus manually, those old manually focusing film camera lenses we all have lying around can be put to good use.
(Some photographers mount a zoom lens in reverse…then use the zoom feature to critically focus rather than trying to move the camera and tripod back and forth.)

With a reversed lens, we are restricted to only one working distance, one critical focus point, and one magnification ratio which as mentioned, will vary depending upon the focal length of that specific lens.
The simplest method for determining how a given lens will perform in reversed position is to conduct a simple test with a flat subject, such as newspaper page.
While looking through the viewfinder, gradually move the camera and reversed lens closer toward the printed page until you see the text pop into focus. With the camera and lens stationary, it’s easy to determine the exact position where the text appears sharpest. You can then measure the distance between the rear element (which is now in front) and the subject in focus. This measurement is the only working distance achievable with that particular reversed lens.
As in all macro applications, depth of field parameters will be extremely narrow. The reversed lens should be stopped down to squeeze out as much depth detail as possible.
(It’s not advisable to stop any lens all the way down, though, since image quality may suffer.)
Since the automatic diaphragm function will not operate when the lens is mounted in reverse, the viewfinder will darken considerably as the lens is stopped down. Ideally, overall composition and a critical focus point should be determined with the camera tripod-mounted and the lens aperture at its widest setting. Once accomplished, the lens can be stopped down to the desired setting, and the scene can then be metered for proper exposure.

              Extension Tubes and Bellows Assemblies:
These two popular macro accessories are similar, in that they are hollow, glass-free spacers which are mounted between the lens and the camera body. Their primary function is to extend the rear lens in graduated distances away from the film plane or digital sensor. The result is an increase in subject magnification.
The degree of magnification is determined by two factors; the focal length of the lens, and how far the lens is extended.
 (To better understand how lens extension increases image size, we need only think back to our slide show days. Remember how moving the screen further away from the slide projector made the image bigger? The same thing is going on inside our camera when we extend the rear lens element further from the film plane or sensor.)

Extension Tubes

Extension tubes are fixed sizes and are typically sold in sets of three…usually 12/20/36 mm. They can be used singly or stacked together for up to 68 mm of lens extension. With most brands of extension tubes, auto-diaphragm functions remain operational. This is a benefit over other macro systems, since focusing and composition can be performed with a much brighter viewfinder…even when the lens is stopped down to the shooting aperture.
TTL Metering will function as well, since the meter is reading only reflected light which is passing through the lens…regardless of whatever accessories have been attached. Attaining a critical focus point is best performed manually though, even when utilizing an auto-focus camera system. The primary reason for selecting our point of critical focus manually, is that depth of field will be exponentially minimized, and our machine doesn't really know which portion of our scene we think is most important.
We should also keep in mind that extending any lens farther away from the camera body will change its focal range. To better explain focal range and how dramatically this range is affected, let’s assume that the normal focal range of a 105 mm macro lens is from 12” to infinity. If we were to stack 68 mm of extension tubes, the focal range (the distance between the subject and the film or sensor) would be limited to around 6” to 10”, between its closest parameter and the infinity setting. Given that, the implementation of extension tubes (or bellows) are only viable options when shooting in macro, and the extension accessories must be removed to permit the lens to perform within its normal focusing range.

                                                     Macro Bellows with 105 mm Lens

A bellows assembly, unlike a set of extension tubes, is fully adjustable and can extend a lens further away from the camera body throughout a wider range of distances...typically from 50 mm to 190 mm or more. Depending upon the focal length of the lens, optical magnification ratios of 10X or greater are achievable when both the bellows and the lens focusing ring are fully extended. A typical bellows assembly is equipped with a built-in focusing rail which can be tripod-mounted. The focusing rail allows the entire tripod-mounted, camera-bellows-lens combination to be easily adjusted back and forth to establish critical focus on a key element.

When discussing the use of a bellows for shooting macros in the field, you will likely hear assertions that a bellows system is “Bulky and cumbersome”, “Too delicate”, “Outdated” and, “Not practical for outdoor use”, to name a few. For the most part, these claims are at least somewhat accurate.
Bellows assemblies are indeed bulky and can be considered a bit cumbersome to control.
And delicate?…Definitely true. But since we've trained ourselves to be so cautious with our expensive equipment while we’re out in the wild, we can easily adjust our behavior to safeguard even our most fragile of accessories.
And yes, as mega-pixel resolutions continue to increase in the ever-evolving digital age, a macro bellows unit can probably be considered outdated and may eventually become obsolete. It’s so much easier to achieve extreme magnifications by enlarging an image digitally that many have forgotten the advantages of extending their macro lenses to magnify their subjects optically.
Digitally enlarging a small portion of an image taken at 1:1 with a true macro lens can indeed enlarge that part of the frame to beyond life-size, but as we know, this process utilizes a smaller portion of the sensor and a mere fraction of the available pixels.  Extending the same lens to enlarge the subject optically utilizes the entire sensor and ALL of its pixels. And best of all…with so many pixels gathering data, we can still opt to apply our digital techniques to enlarge an extreme macro image even further with very little loss in detail. (…as long as we don’t get too greedy.)
Finally, the claim that a macro bellows is not practical for use in the field was likely penned by someone who had never learned to use one. Like any piece of specialized photographic equipment, extensive field practice is recommended when attempting to use a bellows to chase finicky bugs on a windy day.
By far, the most challenging obstacle to overcome when attempting to shoot natural light macros with a fully extended bellows, is maintaining sharpness and composition when we’re faced with a subject that won’t sit still.
Quite often, we are dealing with shutter speeds of several seconds due to extreme light loss and depth of field which is measured in microns. In extreme macro, even the slightest of breezes can result in our subject dancing around in the viewfinder in and out of focus …even in and out of the frame.

Using the Macro Bellows Effectively
A macro bellows, as mentioned before, is a hollow, adjustable accordion-shaped tube with a lens mount on one end, and a camera body mounting flange on the other. For consistently producing greater than life-sized images (without cropping), no other tool in the serious macro photographer’s gear bag is more treasured.
When shopping for a macro bellows system, there are two important points to consider. Foremost, is that the lens and camera mounts have to be compatible with the camera system upon which it will be used. The second key component is that the unit must be equipped with a built-in focusing rail and a tripod mount. By shopping around, it’s relatively easy to find a high-quality used bellows and (focusing) rail system for a few hundred dollars. It’s also wise to acquire and permanently affix a 12 mm extension tube to the camera-side flange to simplify mounting of the camera body onto the bellows. This spacer proves particularly beneficial when attempting to attach the current crop of hefty, ergonomically designed DX-DSLR’s.
(Note: When attaching a 35 mm film camera (or full-frame, FX-DSLR) onto a macro bellows, avoid using the 12 mm spacer mentioned earlier or extreme vignetting will occur. The body of the camera should be attached directly onto the mounting flange of the bellows. If the camera body has an optional battery pack installed, this may need to be removed before the camera can be fitted onto the bellows.)
Once installed, the bottom of the camera body should not contact any portion of the focusing rail or it will not move freely.
On the other end of the bellows, a mounting flange accepts any compatible lens to complete the system.

The Macro Bellows…Pros and Cons:
Each piece of equipment has it’s good side and its bad side. It’s always at the discretion of the individual to differentiate between good and evil.  The outdoor macro photographer weighing these decisions ultimately determines whether or not this particular tool will be practical for his or her macro needs. For the sake of fairness…we’ll list the macro bellows’ bad points first:

1)  “Bulky, Cumbersome, Delicate, Difficult to Use”
These despondent lines of reasoning were discussed earlier…and they’re true. Using a bellows assembly in the field is challenging work. But with practice, handling the various array of knobs, levers and controls will become much easier.
2)  All Manual Operation
Forget about your auto-settings. You will need to feel comfortable setting the aperture and shutter speeds manually. Critical focusing will be performed manually as well, by moving the entire camera/bellows/lens assembly back and forth.…a process made simpler via the focusing rail.
3)  Minimal DOF and Available Light  
Both will become progressively worse as a lens is extended further. Depth of field will be almost non-existent when most lenses are extended to the most extreme distance on the bellows. Massive light loss will necessitate ambient light exposure times of several seconds. Longer focal length lenses (in the 100 to 200 mm range) will in both cases, offer much more latitude on the bellows than standard or wide-angle lenses.
4)  Camera-shake and Subject Movement will be Amplified   
Again, these sharp image killers will intensify exponentially for each additional millimeter we extend our lens. Controlling all movement during a multi-second, exposure is the bellow assembly’s most challenging aspect. The camera’s timer and/or mirror lock-up functions will definitely be utilized to their full potentials in natural light.
5)  Critical Focus Must Be Attained with the Lens Wide Open   
Due to substantial light loss, it becomes difficult to see the image through the viewfinder when a fully extended lens is stopped down to its shooting aperture. Since the lens is not connected to the camera body, the auto-diaphragm function becomes inoperable, so the scene in the viewfinder gets progressively darker as we stop down the lens. We must therefore, compose and critically focus on the key element in our scene with the aperture at its widest setting. We then, have to stop the lens down to the shooting aperture, meter the scene, set the appropriate shutter speed, set the timer, and press the shutter…ALL without touching the focusing ring or moving the camera. If all goes as planned, the timer will run out and the shutter will open and close before a bug flies off or re-shifts its pose…and before a puff of wind starts to jiggle things around. Needless to say, this takes patience…and lots of practice.
6)  Dust and Dirt on the Lens will be Visible in the Photo  
When we mount our lenses directly onto our camera bodies, tiny specs of material on the exterior elements aren't really much of an issue. The dirt and dust are thrown so far out of focus that they become indiscernible. When we extend those same dirty lenses on a bellows in extreme macro, those specs will show up in every photograph as black spots or hazy glitches which will need to removed later with software. Unless you enjoy spending time on the computer zapping out ghosts and goblins, it’s wise to carry along a good blower-brush or cleaning kit…and keep those lenses clean.
7)  Image Quality Can Deteriorate in Extreme Macro  
Whenever we try to push a lens, or any piece of equipment, too far beyond its intended parameters, something invariably has to suffer. Image sharpness and overall quality are foremost in the minds of all determined macro photographers so it stands to reason that we want our extreme macro images to be the best they can be. While magnification ratios of 15X and beyond are possible on a macro bellows, image quality will suffer and color shifts typically occur at the more extreme magnification levels. These aberrations, like many others, are progressive and will vary, based upon the optical quality of the lens, the harshness of the light, and an individual photographer’s technique. In practice, we learn which lenses in our arsenals perform best, and we ascertain exactly how far we can push their fragile limits. Empirical wisdom should eventually take precedent over greed, as we learn exactly when to back off on the throttle.…before our equipment starts fighting back.
8)  “G-Series” (Gelded) Lenses Cannot be Used with a Bellows  
Gelded lenses have aperture rings which are internally controlled by electronic contacts on the camera body. For this reason, only lenses with manually-controllable aperture rings will work on a bellows assembly. When considering a bellows purchase, it’s wise to pick up a few used manual-focus macro lenses to use with it. These lenses are relatively cheap in today’s market, and they all have manually operable aperture rings. The better quality, “name brand” used lenses perform very well when extended.
9)  Limited Exif Data will be Recorded
Since the lens is not connected directly to the camera body, internal communications supported by the lens’ contact points, such as focal length and aperture setting, will not record accurately. (The embedded data will default to the lens information supplied by whatever lens was previously attached directly to the camera body.) The maximum aperture and focal length of that previous lens is what will be recorded.
Any data supported by the camera body, such as file format, shutter speed, ISO, white balance, etc.,
will record as normal.


OK…now that we've sufficiently outlined the negative aspects to owning and operating a macro bellows system, let’s explore a few of its benefits:

                                                            Cabbage White Butterfly at @ 3.5X 
                                            105 mm Macro Lens with Bellows Extended to 190 mm 

1) Bigger is Better
The ultimate goal of the macro photographer is to get close enough to his or her subject to record its most intimate details. A bellows system allows the photographer the ability to see the macro world in an entirely different perspective. As mentioned before, when we extend our lenses, we are enlarging our subjects optically, rather than digitally,…and utilizing ALL of our available pixels.
2) Versatile and Adjustable  
Another redeeming quality is that the ability of the photographer to be flexible in his or her macro renditions is not compromised . It becomes simple to increase or decrease the magnification of macro subjects by extending or contracting the bellows. An insect photographer can reduce the bellows extension to document the subject within its surroundings, then extend it for a few full-frame, full-bug views…then, expand even further for those intimate close-ups of only its eyes…so close that he can often see his own reflection staring back at him.
All of these varying perspectives can be performed without changing the camera position.
Most bellows systems also allow for easily adjusting from landscape to portrait format (…from horizontal to vertical), by flipping a lever and rotating the camera body 90 degrees. This feature proves beneficial during those compositions when a subject is resting up and down, rather than east to west.
3)  A Bellows has No Glass Elements   
Compounding multiple layers of additional glass between our sensor and our subject typically degrades image quality. Many photographers have tried attaching magnifying filters and/or teleconverters to their macro lenses, aspiring to enlarge their images a little further than their equipment would normally allow. More often than not, they were disappointed when viewing the results. Applying additional glass opens the door toward color shifts, flare, poor focusing capabilities, as well as other optical aberrations.
The ability to physically extend a stellar lens far beyond its designed parameters to optically enlarge an image (…without adding any more glass), is likely the bellows most valuable attribute.
The bottom-line consensus when attempting to enlarge any macro subject is that…“Less glass is always better”.
4)  A Bellows/Focusing Rail can be Tripod-Mounted  
It’s certainly no secret that a macro bellows requires tripod use. On the bottom of the focusing rail, a threaded flange accepts the same thread as most standard tripod heads. If their intended quarry that day involves mostly macro work, many photographers carry their bellows permanently affixed to their tripod, with the camera body and lens attached. Matching quick-release devices mounted onto the bellows, and also bottom of the camera body, allows the photographer to switch things around in a hurry if the need arises.
5)  A Multitude of Magnification Ratios at your Fingertips  
Greater than life-size optical magnifications are easily achieved with just about any compatible lens which is mounted onto a macro bellows. A short focal length lens (in the 35-60 mm range) will produce very high magnification ratios (..up to around 12X), when coupled with a DSLR with a DX sensor. The trade-off will be DOF which is measured in microns and a very limited working distance. When the subject is in focus, it will be nearly touching the front of the lens barrel.
Shooting Tip: A short focal length lens will actually perform better and allow for greater working distance when mounted onto the bellows backward with a reversing ring.
Conversely, a longer lens (150-200 mm) will have far less magnification possibilities but will provide a lot more working distance and much better depth of field control. For all-around use, a true macro lens falling within the 85 to 105 mm range seems to provide the perfect compromise for use on the macro bellows. A 105 mm macro lens, with both the focusing ring and bellows fully extended, can produce dramatic, optical magnifications above the 4X range on a DX sensor. This combination provides acceptable depth of field control and a manageable working distance of around 4 inches away from the subject.
6) It’s Never Too Small
Photographers who arm themselves with a macro bellows system are no longer limited by the size of their intended subjects. Even the tiniest specs of life can be explored. Put simply…if you can find it, it can be photographed. Fascinating, often rare and exotic, life forms can be enlarged to show intimate detail which many have never witnessed.

As mentioned earlier, extending the lens to enlarge a macro subject optically has distinct advantages over attempting to achieve the same result by digitally enlarging a tiny portion of the frame.


             Calculating Life-size Ratios with a Macro System

        1:1 Lifesize

Mathematically calculating "accurate" life-size ratios with an extended macro bellows can result in mental gymnastics best left to brainiacs with nothing better to do.
My system is pretty simple. I roughly divide the millimeters of extension into the focal length of the lens I'm using, then estimate from there.
In other words....
A 105 mm lens extended 190 mm on a bellows would yield @ 1.81X magnification (190/105=1.809)
This calculation is close to accurate with a full-frame (FX) sensor with the lens barrel focused to infinity.
When considering crop factors for DX cameras and additional lens-barrel extensions, my brain starts to hurt, so I usually just estimate.
If you are really serious about how much actual magnification you are getting with a particular lens, prop a ruler onto a steady surface, focus the lens at it closest parameter on the millimeter scale of the ruler, and snap a photo.
You can then count the millimeter marks you see in the frame and divide that into the mm length of your sensor to get true life-size reproduction information for that lens.
(...that's the easy way.)

© Bob Cammarata 2015
bobcammarata.blogspot.com

No portion of this material may be copied or used without permission

Go To Part 2 of this Series