Reverse mounting a lens
Macro photography is fun... but a good macro lens is expensive (as all good lenses are). So if you want to try it, but don't have the cash to do it... just flip your standard lens around... no, i'm not kidding!
Anyone can reverse mount a lens by just holding the front of the lens to the camera. This can be a bit cumbersome and tricky to use, so i would not generally recommend it, but i have used it in a pinch for short periods of time with success. I would recommend buying a reversal ring however. These little rings are cheap (around 10 euros) and have a filter thread on one side that attaches to the front go your lens, and on the other is a lens mount so you can connect it to your camera, reversed. This is no secret really and has been around for a long time, but I am still surprised at how few people know it or at the least use it.
How does it work?
What makes a macro lens a macro lens is it's ability to focus on things very close. The closer you get to a subject, the larger it is projected onto your sensor and the larger the resultant image.
Now think of a normal lens... light enters the front and is projected or 'focused' onto your sensor. In short every one of your lenses has the ability to focus light from the back of your lens onto your camera sensor. This sensor is very close to the back of your lens. So by reversing your lens, you reverse the 'flow' of light, allowing you to focus on very close objects. Sounds perfect right? Well, sadly no.
When you revers mount a lens you loose conventional focus control. By that I mean neither auto-focus or manual focussing the lens will change the focus of the subject. This is because under normal situations with a lens mounted normally, your camera sensor is always the same distance from the lens mount, and all lenses are calibrated to project the light at that distance. You might think that your normal focusing should still work by focusing the light onto the sensor (since it is now reversed)? That is not the case, because your focusing system is not designed to focus on something as close as the sensor would be, and if it did, it would already be a macro lens, and this who exercise would be moot! So, how do you focus?
Well, you have a fixed focal plane at a fixed distance from the reversed lens. Unlike in normal situations where you can change the distance the focal plane using AF or manual focus, here you move it by, moving. You have to move the camera and lens closer and further away to the subject to get it in focus. This is not so bizarre, Canon has a MP-E 65 f/2.8 lens that uses the same method of focusing.
Which Lenses are best
Now, I have simplified the whole situation for ease... mine and yours. But there is another aspect that you need to know. This technique only works well on wider angle lenses... the longer the focal length of the lens, the less well it works. This is to do with the optical ability of the front of the lens being able to project the image on the sensor. The bottom line is the wider the better, but as a guide, I have used my 50mm f/1.8 like this for years and with great success. So, anything 50mm or wider and you are all good! :)
The relationship between depth of field and distance is well known. The close you are to your subject, the smaller the depth of field. So now you are really close to your subject, you are going to have TINY depths of field... so small, it is very tough, especially since you have to focus in a strange way too... so what to do? Easy, change the aperture... but you can't, since you have no electronic connection with your lens.... So how do you change the aperture so you get more than just the left eyebrow of that ant in focus?
- Option 1 is to put the lens back on your camera the correct way round, select the aperture you want (f/8 or higher is a good starting point), hold down the DOF preview button whilst removing the lens (the camera has to remain on all the time), then mount it reversed. ugh... tedious, can be fiddly, but doable.
- Option 2 pick up a cheap 2nd hand old manual-focus lens. These all had aperture rings on the lens, that allowed you to change the aperture whenever you wanted to. It does not even have to be a comparable lens to your system, since you won't be mounting it normally anyway! :) I would recommend any old 50mm lens, which you can pick up for 10-20 euros easily! You will then have a dedicated macro lens too... ;)
Great, you have a reversed lens on your camera, it is at a good aperture and you are focusing by rocking back-wards and forward. You will now notice how dark the image is. You are going to need a lot of light for macro photography, mainly due to the large f-value you will have to adopt. Here are a few tips to help you on this.
- Use a tripod... it will allow you to have longer more managerial shutter speeds
- Use any torch as a light source... I frequently use the flash on my smartphone to light my macro work. No need to buy extra flashes at this point.
- Bunk the ISO if all else fails.
This is not a practical solution if macro is your main area... there are many specialised lenses that are easier to use. However, this is so cheap and works very well (if you have the time to deal with the fiddly focusing) it is almost stupid not to at least try it. I use it for my macro work, which is not a lot, and i am generally very happy with the results! :) For 10 euros, you can convert you kit-lens into a macro, for a little more you can pick up a second have MF lens. Try it, go out, and shoot! Explore the little world around you! :)