Hello
I'm new into the micro/macro fotografie. And I would like to know more about reverse Lens photography. Since I have to save first for a MP-E65 Lens, I first like to try with a reverse Lens. I have a Tamron 90 mm MAcro lens, and on top an Old FD 50 mm f1.8 lens, but placed in reverse.
Problem is that my images are not sharp. I think that is the couse of the reverse lens, but how can I help this out? My reverse lens is full open @ f1.8 and Focus is set on the closest distance as possible. Also My tamron lens is set al Close focus distance, and a aperture of about f5.6.
Can Anyone help me pls with this?
Kind regards.
How to work with Reverse Lens
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Ichthyophthirius
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Hi,
Not my area, really, but I would have thought that you put the focus of both camera lenses to infinity. That creates an afocal space between the two lenses: https://en.wikipedia.org/wiki/Macro_pho ... eMacro.png
Not my area, really, but I would have thought that you put the focus of both camera lenses to infinity. That creates an afocal space between the two lenses: https://en.wikipedia.org/wiki/Macro_pho ... eMacro.png
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rjlittlefield
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In addition to the focus issue identified by Ichthy, your choice of aperture settings is not ideal. In most cases it is better to stop down the front lens, not the rear lens. The reason is explained in our FAQ: Stopping down a lens combo.
Note that when both lenses are focused at infinity, the magnification will be simply:
magnification = rearFocalLength / frontFocalLength
In this case, when the front lens is stopped down, then the effective aperture seen by your sensor is equal to
effectiveFNumber = frontFNumber * magnification
So, setting your front lens aperture to f/5.6 will give you an effective aperture of 5.6*90/50 = f/10.
Setting the front lens to f/8 will give you effective f/14, which is probably a better value to start with. You might even go down to f/11, giving effective f/20, which will give you some additional depth of field at the cost of a little sharpness from diffraction.
Many people are confused by the bit about "* magnification", because the commonly quoted formula for a lens that is focused by extension is
effectiveFNumber = lensFNumber * (magnification+1).
Just recognize that both formulas are correct, but they apply to different optics. When reversing one lens in front of another, with both lenses focused at infinity, you want the simpler formula without the "+1".
--Rik
Note that when both lenses are focused at infinity, the magnification will be simply:
magnification = rearFocalLength / frontFocalLength
In this case, when the front lens is stopped down, then the effective aperture seen by your sensor is equal to
effectiveFNumber = frontFNumber * magnification
So, setting your front lens aperture to f/5.6 will give you an effective aperture of 5.6*90/50 = f/10.
Setting the front lens to f/8 will give you effective f/14, which is probably a better value to start with. You might even go down to f/11, giving effective f/20, which will give you some additional depth of field at the cost of a little sharpness from diffraction.
Many people are confused by the bit about "* magnification", because the commonly quoted formula for a lens that is focused by extension is
effectiveFNumber = lensFNumber * (magnification+1).
Just recognize that both formulas are correct, but they apply to different optics. When reversing one lens in front of another, with both lenses focused at infinity, you want the simpler formula without the "+1".
--Rik