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.

 

[itsdoable]

The shutter should be open or closed, not stuck half way. They get stuck half way when the lube gets thick, or contaminates the blades. The shutter needs a CLA. You can probably get it working temporarily by removing the lens cells, and flushing the shutter blades with solvent (lightly with isopropyl alcohol), but that would only make it work for a few months. A proper CLA is called for.

The lens is a 90mm, which covers 6x9. Is that the view of the ground glass, or is that the 4x5 adapter view? I don't have a Horsman so I can't tell. The lens is optimized for f/8. Sharpness only at the center is a sign of field curvature, or astigmatism and/or coma, which is a sign that the lens elements are not assembled correctly (spacing, or flipped element). Field curvature can be access by focusing new the corner.

 

[OAPOli]

1. That's not normal;
2. If I understand correctly, by "preview iris" you mean the shutter blades? At B the shutter should open completely as long as you're holding the release lever;
3-4. That's not normal. Coverage for the 90mm at f/5.6 is 130mm. I have this lens and use it on a 612 camera.

The shutter needs a service and I would think that the lens was assembled incorrectly. Maybe one of the elements is flipped or as @koraks suggested maybe the rear group is from a different lens. Here is the configuration:

You can also try to measure the lens board to film distance which is 92.6mm. The specs are found here: https://butkus.org/chinon/horseman/horseman_vh-r/horseman_vh-r.htm

 

[abruzzi]

I have a Super 90mm and yeah, it looks nothing like that, it (like all the 6x9 lenses from Horseman) is actually quite nice. If you post a clear photo of the rear of the lens I'll let you know if it looks like mine. Alternatively, search for "Horseman super 90mm" on ebay and you'll find some for sale in Japan and see if your rear group looks like the lenses on ebay. Unfortunately, unlike some manufacturers Horseman (Topcon) didn't seem to put serial numbers on both the front and rear groups. That would have made it easy to match.

I know a decade ago it was a thing to reverse elements intentionally to create swirly bokeh (or in really swirly distortion), but it doesn't seem like it would be very easy to do with this lens.