Solution to 39mm to 52mm Macro Coupler?

3D Gunner wrote:

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!

Thanks for the informative examples. That is very helpful. Here are some examples from the setup I was referring to.

For reference, the focal length of the camera lens (Panasonic FZ200) varies from 4.5mm to 108mm. The close-up lens is mounted on a fixed tube and the camera lens extends/contracts behind the close-up lens as the camera lens focal length changes. The maximum distance between the camera lens and the close-up lens is around two inches at the minimum focal length of 4.5mm.

First, the "porthole" vignetting.

With a 58mm Canon 500D. (The tube has a 55mm thread and a 55-58 step up ring.)

With a Raynox 150 (which has a significantly smaller diameter than the 500D).

With the 500D, the hard vignetting disappears somewhere around 16mm. Here it is at 14.5mm.

Here at 16.9mm the hard vignetting is gone. The top left to bottom right dropoff looks more like uneven lighting than vignetting to me. This was all very "quick and dirty": I was using a single table lamp for illumination and the lamp and camera were at (different) large angles to the piece of paper, and the angles varied from shot to shot as I was doing these shots hand-held.

Here it is at 35mm. It was similar at larger focal lengths.

With the smaller diameter Raynox 150, there was vignetting all the way out to 108 mm. Here it is at 108mm.

Here it is at 50mm. As you can see from the different corners being affected, this is partly an issue with the close-up lens not being exactly centrally mounted. I was using the clip-on adapter, which has a bit of slack as to positioning. Step ring mounting would be better in this respect.

As to image sharpness deterioration outside the central area varying with the distance between the camera lens and the close-up lens, in this case we need to be a bit careful with interpretation for a couple of reasons: close-up lenses tend to be softer in the corners; and here we are comparing across different magnifications. With those qualifications in mind, here are four examples using the Raynox 150. The distance between the camera lens and the close-up lens gets smaller as the focal length gets larger.

These were done with the camera on a table, using a 10 second timer.

35mm

56mm

93mm

108mm

It looks to me as though the behaviour of the two different setups we are illustrating differs significantly.