Fused Silica single lens tests II, 150mm plano-convex

[ulf]

I showed an ad hoc image with shot with my Fused Silica 150mm Ø50mm plano-convex lens from Oriel in Jonathan's topic about his 40mm lens.

https://www.ultravio...dpost__p__33743

The focus setting then was similar to the last refocussed one in the sequence below.

 

Now I have made some tests with different apertures from f/8 and up. Without any limiting aperture the lens is ca f/2.3 and show massive spherical aberration making it very soft and hazy.

For the second test I used an U-360, 2mm + S8612, 2mm stack.

 

It is interesting to see how much focus shift and sharpness improvement I got at fully open (lacking) aperture.

[JMC]

Looks nice and sharp when stopped down Ulf. I must try a longer focal length lens with my setup at some point.

[ulf]

One thing that intrigues me is that the branch starting just a bit left of the center at the bottom edge is reasonably sharp in all but the fully open aperture-images.

That branch is actually a three at 1/4 of the distance to the house I focussed on. At f/32 it has motion blur due to the 13s exposure time.

[Stefano]

I never saw a GIF (is it a GIF?) on this forum. Very interesting, you are getting really good, distorsion-less images with just one lens, quite impressive.

[dabateman]

That 135 format coverage looks good. Imagine just cutting out the center with 2x crop. That would equal what I am looking at with my lenses on the EM1.

I don't know if my 25mm lens cover a 135 format sensor. I will have to test them on my DF, to know. Also I haven't tested to see if they will go to infinity.

[Andrea B.]

That is interesting, Ulf !

I was wondering how diffraction might be playing a role here at the apertures beyond f/16? It appears that each stop down sharpens more even at f/22 and f/32. I think I was expecting a step backwards at some point as the apertures grew smaller.

 

 

Between f/22 and f/32 some one raised a window covering.

[Andy Perrin]

Andrea, I noticed that too. I think it might be that the aberrations of the lens are still bigger than the diffraction effects even out to F/32 in this case.