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Solution to 39mm to 52mm Macro Coupler?

Started 9 months ago | Questions thread
3D Gunner Senior Member • Posts: 1,025
Re: Solution to 39mm to 52mm Macro Coupler?

gardenersassistant wrote:

In the setup I described I certainly got severe ("looking through a porthole") vignetting at the widest angles (lowest magnification), but having got past that I didn't notice any issues. (This was all at f/45 full frame equivalent btw.)

Up to a point, the close-up lenses can be equated with objectives, but are not the same thing from the multiple points of view.
Let's see a practical example.

In the two images, I put a 50mm lens (at f/2.8) with extension tubes to get a 1:1 magnification, over which I inverted a 23mm lens at f/4 (maximum for this lens).
In the image on the left, between the lenses is just a 52 to 52mm coupler, in the image on the right I added an additional 9mm extension.
As you can see, in the first image the vignetting is small, but at a distance of only 9mm more it is already significant, and at +5mm it is also visible, but smaller.
You can also see less magnification as the distance between the lenses increases.
So, with the basic 60mm f/2.8 lens (instead of 50mm f/2.8) and with the inverted 23mm f/1.7 lens, at apertures wider than f/4 it is expected that vignetting will not occur using the 52-52mm coupler + 39-52mm step up ring, but at apertures smaller than f/4 I think vignetting can occur.

Also, image sharpness seriously deteriorates outside the central area if the distance between the lenses increases!

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