Birds n bugs's Blog

One of the options to shoot closeup is to add magnification in front of your existing lens.  There are lens attachments called closeup filters or positive diopter lenses.  They are all the same thing but some are better than others.

The typical positive diopter lens is sold as part of a kit and often comes with it’s own case.  Here’s an example of a set of B+W single element closeup lenses.

The kit shown here is a pretty normal item and usually sells for less than $100 for the whole kit.  These kits are almost always single element lenses.   Each lens is identified by a number which indicates it’s magnifying power.  A kit usually has +1 to +4.  The lenses can be stacked, that is more than one put on your primary lens at a time.

All of the single element lenses will have problems with spherical and chromatic abberations because different colors of light focus at different planes.  Better closeup lenses have two elements and are usually referred to as apochromats.  The two elements are used to correct the spherical and chromatic abberation and generally do so very well.

Because they have two elements, they are thicker and heavier.  It’s pretty obvious when you compare the two.  A single element lens is no thicker than a filter while the apochromats are twice as thick.  The two element lenses may be referred to as doublets by some.

Nikon used to make two element apochromat lenses which were designated 3T and 4T in 52mm sizes and 5T and 6T in 62mm sizes, etc. but, these are no longer in production.  Nikon also made single element and referred to them as No. 0, No. 1 and No. 2. The lower magnifications didn’t need as much correction as the higher.

Canon still makes the 250D and 500D in a number of filter sizes.  The 250D is designed for short lenses and the 500D for longer lenses.  There are other vendors of true apochromats as well

The magnification that you will get with these lenses is a function of the focal length of the primary lens.  It will be different between a 50mm and a 135mm for example.

Pros

• These are relatively cheap and easy to use. 
• Because they are stackable you can often get just the right magnificaton.
• There isn’t much distortion of image quality at lower magnifications
• There is little effect on the f-stop

Cons

• You will lose infinity focus with the lens in place
• The focus range can be small and may need multiple tries to get the right combo
• At stronger magnifications, some chromatic and spherical abberation can occur

I don’t have any examples of the use of these lenses since I moved to digital.  I found them fine for occasional use but, my interest in closeup work led me to better options fairly quickly.  The set shown was purchased to allow some closeup work with a Mamiya 645 film camera.

Reversing rings are lens attachments that permit a lens to be turned around so that the front element of the lens is aiming into the camera and the rear element is aimed at the subject.

There are actually two types of reversing rings. One permits you to reverse a lens directly onto the camera body. The Nikon model for this is the BR-2 or BR-2A with the A model being used with newer film cameras and all Digital SLRs.

The other type reverses one lens onto another so that the lenses are facing each other. This type of reversing ring uses the filter threads to allow the connection. If you are using two lenses with different filter sizes then you will need a step up or step down adapter. This picture shows the two types of reversing ring. The top ring is the Nikon BR-2A reverse on camera ring. The bottom ring is a Bowers MC52-52 lens on lens reversing ring.

The lenses are a 55mm f3.5 Micro-Nikkor and the 18-55mm digital kit lens.

Reversed Lens on Body

First let’s look at a lens reversed on the camera with the Nikon BR-2A.  Since the 18-55mm f3.5-f5.6 lens is widely available today I will use it as the example.  Here is the reversing ring and the 18-55mm mounted on a D90.

Here it is shown with the reversing ring on the front of the lens.  Note that the reversing ring has the F-Mount bayonet flanges.  The next picture shows the 18-5mm reversed on the D90 body.  You can see the electrical contacts that allow communications and control between the camera body and the lens.  Since these are not connected in this position, all focussing and aperture control must be done manually.

Because of the loss of communications and connection, the camera can no longer control the aperture of the lens.  On Nikkors, this control is performed by the position of a lever.  The lever is normally in the closed (fully stopped down) position when the lens if off the camera.  Once mounted, a lever on the camera body holds the aperture open.  In normal on camera operation, when focussing or metering, the lever is held down to allow those function to be performed at full aperture.  When the shutter is released, the lever is permitted to move to a position which represents the desired shooting aperture.

When reversed, this is lost and we must control the aperture ourselves.  Unfortunately, the full range of f3.5 to f22 only takes a movement of about 1/4 inch.  I certainly can’t control this with any accuracy or precision so, the solution I use is to wedge the lever in the fully open position with a small piece of card.  Like this:

It certainly isn’t elegant but, the lens is now wide open and ready to use.  Nikon makes a BR-3A ring which mounts on the lens and allows the lever to be locked open or closed but, the bit of card works just as well.

So, how does it work?  Well, it does allow you to move much, much closer to your subject.  I set up a small demo with the D90 and reversed 18-55.  Here is what the setup looked like at 18mm.

The two pictures below show the ruler  at the minimum focus distance at 18mm and at 55mm.  The bottom pair show the closest focus I could achieve with the lens reversed at 18mm and 55mm.

Normal Mount 18mm image on the left, 55mm on the right

Now reversed in the same order

Surprised?  Notice that the 18mm position provides a much greater closeup capability.  In fact, it’s beyond 1:1.  Just as the position is reversed, the function is as well.  The WA side of the lens creates a larger image circle and your sensor is actually cropping it.

I apologize for the fuzziness of the WA image.  I didn’t have a remote handy as was pushing the shutter by hand.

Reversed Lens on Lens

I only have two lenses with 52mm filter sizes at the present time.  The 18-55 and the 55mm f3.5 Micro-Nikkor.  The 55mm is a non-AI lens and had never been modified.  I usually use it on a bellows but, that’s another topic for another time.  Just for demonstation purposes, I mounted the 55mm reversed on the 18-55mm.  As I expected, this was not a good combination.  While I did get slightly better magnification and retained exposure control the images were just small circles in the center of the sensor.  This method works best when the reversed lens is a wide angle.  But, just to show you how the rig looks, here it is.

And, the highly vignetted images that were the result of this are:

As I said, this was not a good combination for shooting and I only did this to show the configuration.  The 55mm f3.5 is an old Non-AI lens of metal construction and is heavier than the 18-55mm.  I was a bit hesitant to mount this and made sure the 18-55 barrel was as far back as it could go to make sure the weight didn’t hurt anything. 

After writing the above, I realized that I had an old 135mm f2.8 noname telephoto which could be used with the 18-55.  I dug it out and mounted it on the D90 with the 18-55 reversed at 18mm.  The results were now a lot better with a lot higher magnification.  I didn’t have much time to setup for various reasons but, the rig looked about the same while the images were no longer vignetted.

I had to invert the target ruler because the range was so close that I was bumping into the shelf it was on before achieving focus.  The viewfinder was very dim and the extra light was needed behind it.  But, as you can see, much higher magnification was achieved using a telephoto as the on-camera lens and a wideangle as the reversed lens. 

If you want to pursue lens to lens reversing, I would recommend the widest angle old lens with an aperture ring to use as the forward lens.  G mount lenses can be used since the actual aperture control will be on the camera side lens.

There is always a lot of interest in getting closer to a subject, particularly in nature photography. One reason is that getting closer reveals more detail and it is amazing how complex some seemingly simple things are. For example, there is often a confusion over the difference between WORKING DISTANCE and MINIMUM FOCUS DISTANCE .

The Working Distance is the distance between the front element of the lens and the subject.  Other things can change this,  For example, if you are using accessories like the Nikon R1 closeup lighting kit or a ringlight, the lights will be forward of the front element and will intrude into and reduce the working distance.  The working distance will also vary by magnification ratio.  In the case of the picture below, the lens is set to a 1:1 ratio and the working distance is about 6 inches.

Minimum Focus Distance is always marked as one of the specifications for a lens. What it means is the distance from the subject to the focal plane of the camera. The focal plane of a camera is the location that any lens is focused on. On film cameras, it was often called the film plane on digital, it’s sometimes called the sensor location or plane. The plane is marked on most cameras. The standard symbol is a circle with a line through it where the line is the location of the plane. Here is the focal plane mark on a D300.  You can see it on the left below and behind the top LCD.  On the D90, the focal plane mark is on the right side between the function dial and the prism.  It’s black on black so it’s difficult to see.  The minimum focus distance is always calculated or measured at the maximum magnification of the lens.  In this case, A 105mm f2.8 Micro-Nikkor that is 1:1  and the Minimum Focus Distance is about one foot.

The Magnification Ratio is a comparison of the image on the sensor or film plane and the actual subject.  If a lens has a magnification ratio of 1:1 it means that the image of the subject will be the same size as the original subject.  If the ratio is shown as 1:2 then the image of the subject will be one half the size of the original subject.  So, it’s easy to think of the colon as a slash and see that 1:2 is the same as 1/2 when reading specifications. So at 1:4 the image on the sensor would be 1/4 of the size of the original subject.

And, then there is Bellows Extension Factor.  With in camera metering  the bellows extension factor does not need to be calculated and the aperture adjusted to accomodate it.  We now get our light measurements at or near the focal plane so the loss of light from extending the lens forward is accomodated automatically.  That doesn’t mean it isn’t a factor. 

I often see posts on photography forums about lenses that don’t appear to be the proper aperture.  A typical complaint might be “I bought an f2.8 lens but I can only set it to f4.0 when I’m shooting macro.”  This usually occurs with an internal focus lens which doesn’t seem to be extending to focus.  The effect is the same though. 

In order to focus close, you have to move the lens closer to the subject than the focal plane.  As that happens, the amount of light at the plane is reduced by the inverse of the square of the distance (the inverse square law).  That means that if you are twice as far from the focal plane, you get only one quarter of the light energy on the sensor.  This actually happens at every focal length and magnification but becomes most apparent only in situations where the lens is extended far from the focal plane as it is in closeup work.  If you look at the figure below, the left rectangle represents 1 unit of light, in a straight line at twice the distance, the same amount of light energy is spread over 4 times the area.

Because of this, the effective aperture of a lens is reduced. Some lenses report this as a part of the cameras data included in pictures and some only record the nominal f-stop of the lens.