histogram_man
137 record Test of 35mm f3.5 Super Takumar lens on a reversing ring (attaching the lens with its filter thread to the lens mount via an adapter)
Taken in August 2016. It is possible to use any M42 mount lens normally on a Sony A mount with another adapter if you don't mind manual focus and exposure. The electronic viewfinder makes it more practical than it might have been otherwise and I use it quite a bit for general photography as it makes the camera very easy to carry round, being so small and light.
There are links to two pictures, one of the lens used normally and another with a close up of some flower buds in the discussions page for this topic.
Now a rather tedious and lengthy technical explanation for anyone who wishes find out more about what is going on here.
The 2 Euro coin is about 25 mm across and is slightly larger than a British 10 pence coin. On a 36 X 24 mm sensor this image is a magnification of about 1.5 and about 2.2 on the average cropped sensor. I have some modest knowledge of basic optics and was able to work out what was happening in general terms. The following are my conclusions which are for cameras with mirrors which have to use quite complicated optical designs for wide angle lenses. We can use this for our advantage to turn them into very useful macro lenses with only modest expenditure on extra hardware. Ideal for working indoors when the weather is bad.
For any type of DSLR or SLR, focal lengths below about 40 mm would cause the rear of the lens to be hit by the mirror when it flips up. The M42 Mount of this Takumar lens makes the rear of the lens body sit 45.5 mm from the sensor/film so a special optical design is needed to create a retro focus adjustment for this lens of 10.5 mm, i.e. a virtual lens or nodal point sits 10.5 mm behind the physical lens and 35mm in front of the sensor.
The front of the lens will have an obviously curved surface so it can 'see' a wide view but the rear of the first lens will be even more curved, making the lens concave. There will often be at least one more concave lens inside. To make it focus, a strong group of convex lenses will be in the rear of the lens. The effective focal length is worked out by drawing two parallel lines through the lens diagram and where it crosses the converging light from the rear elements (the nodal point) is where you take the measurement of the focal length.
As an aside, mirrorless cameras, with mounts much closer to the sensor, do not need this elaborate design except for the shortest of focal lengths.
Once the lens is attached to the camera back to front, with an adapter that screws into the filter thread, the nodal point now sits in front of the lens rather than behind it in the mirror box and creates a natural extension, allowing it to focus much closer than normal without extension tubes or bellows.
So sticking out from the camera body lens mount we have the length of the lens barrel, 34 mm, plus the 10.5 mm retro focus nodal point and we then add the 45.5 mm from the lens mount to the sensor, 90 mm in all. The subject comes into focus at 60 mm in front of the nodal point so the magnification is 90/60 or 1.5, exactly as measured by the magnification of the coin.
Longer focal length lenses work nothing like as well because they don't need retro focus construction, being naturally clear of the mirror and the longer the focal length of the lens, the closer the nodal point is to the front of the lens. There rapidly comes a point where reversing it puts the nodal point nearer to the sensor than its focal length and it won't focus at all, let alone provide any magnification. A 55mm lens only produces a magnification of about 0.38 but a small extension using the longest tube of an extension tube set brings it up to a useful 0.9 magnification.
Another useful bonus is that the design of 'normal' lenses is based on light being taken from relatively distant objects and focused on the relatively close sensor. Using the lens reversed, while it cannot compete with a lens designed for close up work, it works better back to front as the light passes through it closer to how it was designed have light pass through it.
Once we get to telephoto lenses, their optical construction uses similar retro focus principles but the other way round, placing its nodal point in front of the lens barrel rather than behind, a procedure designed to make the lens more compact. Reversing one of these would put the lens effectively in the mirror box or even behind the sensor. A huge amount of extension would be required to get the lens to focus on infinity, let alone any closer.
After adjusting the tripod and subject position, fine focusing was achieved with a budget macro rail which I have had for many years and hardly used before. It is solid enough with the relatively light and compact camera rig. Lighting was partly natural and reinforced with an LED torch kept for household emergencies and/or a cheap LED panel which I have also had for ages. The white balance was set to 'cloudy'. All taken indoors to avoid any wind movement as exposures are fairly long so ideal for a miserable day.
137 record Test of 35mm f3.5 Super Takumar lens on a reversing ring (attaching the lens with its filter thread to the lens mount via an adapter)
Taken in August 2016. It is possible to use any M42 mount lens normally on a Sony A mount with another adapter if you don't mind manual focus and exposure. The electronic viewfinder makes it more practical than it might have been otherwise and I use it quite a bit for general photography as it makes the camera very easy to carry round, being so small and light.
There are links to two pictures, one of the lens used normally and another with a close up of some flower buds in the discussions page for this topic.
Now a rather tedious and lengthy technical explanation for anyone who wishes find out more about what is going on here.
The 2 Euro coin is about 25 mm across and is slightly larger than a British 10 pence coin. On a 36 X 24 mm sensor this image is a magnification of about 1.5 and about 2.2 on the average cropped sensor. I have some modest knowledge of basic optics and was able to work out what was happening in general terms. The following are my conclusions which are for cameras with mirrors which have to use quite complicated optical designs for wide angle lenses. We can use this for our advantage to turn them into very useful macro lenses with only modest expenditure on extra hardware. Ideal for working indoors when the weather is bad.
For any type of DSLR or SLR, focal lengths below about 40 mm would cause the rear of the lens to be hit by the mirror when it flips up. The M42 Mount of this Takumar lens makes the rear of the lens body sit 45.5 mm from the sensor/film so a special optical design is needed to create a retro focus adjustment for this lens of 10.5 mm, i.e. a virtual lens or nodal point sits 10.5 mm behind the physical lens and 35mm in front of the sensor.
The front of the lens will have an obviously curved surface so it can 'see' a wide view but the rear of the first lens will be even more curved, making the lens concave. There will often be at least one more concave lens inside. To make it focus, a strong group of convex lenses will be in the rear of the lens. The effective focal length is worked out by drawing two parallel lines through the lens diagram and where it crosses the converging light from the rear elements (the nodal point) is where you take the measurement of the focal length.
As an aside, mirrorless cameras, with mounts much closer to the sensor, do not need this elaborate design except for the shortest of focal lengths.
Once the lens is attached to the camera back to front, with an adapter that screws into the filter thread, the nodal point now sits in front of the lens rather than behind it in the mirror box and creates a natural extension, allowing it to focus much closer than normal without extension tubes or bellows.
So sticking out from the camera body lens mount we have the length of the lens barrel, 34 mm, plus the 10.5 mm retro focus nodal point and we then add the 45.5 mm from the lens mount to the sensor, 90 mm in all. The subject comes into focus at 60 mm in front of the nodal point so the magnification is 90/60 or 1.5, exactly as measured by the magnification of the coin.
Longer focal length lenses work nothing like as well because they don't need retro focus construction, being naturally clear of the mirror and the longer the focal length of the lens, the closer the nodal point is to the front of the lens. There rapidly comes a point where reversing it puts the nodal point nearer to the sensor than its focal length and it won't focus at all, let alone provide any magnification. A 55mm lens only produces a magnification of about 0.38 but a small extension using the longest tube of an extension tube set brings it up to a useful 0.9 magnification.
Another useful bonus is that the design of 'normal' lenses is based on light being taken from relatively distant objects and focused on the relatively close sensor. Using the lens reversed, while it cannot compete with a lens designed for close up work, it works better back to front as the light passes through it closer to how it was designed have light pass through it.
Once we get to telephoto lenses, their optical construction uses similar retro focus principles but the other way round, placing its nodal point in front of the lens barrel rather than behind, a procedure designed to make the lens more compact. Reversing one of these would put the lens effectively in the mirror box or even behind the sensor. A huge amount of extension would be required to get the lens to focus on infinity, let alone any closer.
After adjusting the tripod and subject position, fine focusing was achieved with a budget macro rail which I have had for many years and hardly used before. It is solid enough with the relatively light and compact camera rig. Lighting was partly natural and reinforced with an LED torch kept for household emergencies and/or a cheap LED panel which I have also had for ages. The white balance was set to 'cloudy'. All taken indoors to avoid any wind movement as exposures are fairly long so ideal for a miserable day.