Trying to understand the optics on the Horseman VH. 90mm, super Topcore

[Durio]

Hello everyone,
I got my hands on a Horseman VH.
However, something seems to be wrong.

1
The preview doesn't open completely. Only about 50 percent.
Is this normal for this lens?

2
When I use setting B with, for example, aperture 5.6, the preview iris opens completely. It is then slightly larger than the aperture iris.

3
Unfortunately, the image is only sharp in the center of the focusing screen. The sharpness decreases significantly towards the edges. There is also image distortion.

4
The high loss of sharpness towards the edges is obviously not dependent on the Fresnel lens. This effect can also be seen when only the focusing screen is used.

What is normal and what is not?
-Is the 50% aperture of the preview normal for this lens?
-Is the severe blurring at the edges (visible from 1/3 of the center to the edge) normal?
-Does this lens have to be used with high apertures?

Thank you very much for your help.

 

[Durio]

 

[koraks]

Hi @Durio - welcome (back) to Photrio and to active posting on the forum!

The shutter doesn't look right the way it's shown here:

That's certainly not the way it's supposed to open on preview (or any other setting). This is a halfway-state between closed and open, so something is stuck in the shutter mechanism somewhere. Maybe it's something fairly simple like a bent preview lever. If the shutter works OK otherwise, you might work around the issue by using B mode combined with a locking cable release.

The distortion and loss of sharpness are a more serious issue. Is this lens complete; i.e. is the rear cell also present and correctly mounted inside the shutter? The severity of the problem goes far beyond a minor issue with shimming etc; it's almost as if an entire part of the lens is missing, or if the rear and front cells of two entirely different lenses are combined.