90mm ~f/2.2 from plano-convex lens

[enzodm]

In the past I already attempted to build one objective from a meniscus lens, but I never finished the work (small lens, short focal length, some difficulties).
Recently I bought a plano-convex lens with 90mm focal length and 42.5mm diameter (this one), close to some well known thread size , so I did it again. The result is here: an M42 helicoid plus a couple of short extension rings, and the lens trapped between two M42-M52 step-up-down rings, with some black cardboard iris.



This is one picture taken around f/5 (PP: only a small increase in exposure):



Fully open, contrast is very low, but maybe there was also some light leak, I have to try again. I did not try yet smaller apertures.

[kansalliskala]

try a newspaper test, put a newspaper on a wall, set camera on tripod and see if it is sharp on any distance?

that will help of engineering it further

[kds315*]

You can add a iris to the front, that will increase sharpness if so wanted, but why,
it is a great soft focus lens as is!

[enzodm]

thanks to both and yes, I'm aiming more at a portrait lens than at a blade, although checking if closing gives more sharpness is always interesting.
By the way, there is already an iris, placed just behind the lens (without, it is ~f/2.2). I wonder if there is a better place... Closer to the sensor? Or in front?

[bang2]

The work and the result, for me are both 'two thumbs up'.