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I have bought this 0.15x fish-eye lens adapter on eBay:

photo of a fisheye lens adapter, on dark cloth

But it turns out to be practically unusable with any camera. I thought it was a clone-of-a-clone of the (in)famous Kenko 0.15x adapter, which is sometimes wrongly credited as 2001's HAL. Here's footage on the web: as Kenko 1, as Kenko 2, as Soligor, compilation of several brands 1, compilation of several brands 2, as Weltblick, but lacking more info. Plus some meta-info, as Spiratone, Spiratone, but 0.16x, claims that they're clones.
The footage all looks like i would expect it, and as I know it from my other (0.45x, 0.42x, 0.3x) fish-eye adapters: a circular wide angle image that is cropped more or less.
The articles I've read tell you to use these adapters in front of a lens between 30 and 200mm; most people seem to use a 50mm.

Now, when I try to use it with any of my cameras (a system compact, a Digi8 camcorder, a APS-C DSLR with zoom lense), I get terrible results. The circular image is tiny, unless I zoom in, but then it gets cropped (in a different way).

Example shots, Sony RX100 at 28/60/70mm (equivalent).

montage of three shots with circular image on a black backdrop that gets bigger from left to right, you can see a balcony with a bike

With my DSLR, with a Sigma 18-50mm (28-70mm equiv.), this is even worse; even at 50/70mm it looks like the leftmost shot.

Before you say, wait the RX100 doesn't have a screw mount, here I hold a terrible, dirt-cheap 0.42x adapter in front of it, at 28mm:

a circular fish-eye image of said balcone with bike, this time crisper

Note how the image, for what it's worth, is even more wide-angle, at a "worse" factor (0.42>0.15).

So I've noticed, this adapter's entry pupil rear opening (? sorry?) is kind of small, 10mm, compared to the "front openings" of my cameras. And the Sony at 20mm did much better than the DSLR at 60mm. (Although note that the 10mm seems to be normal, when I compare it to the other clones.)

photo of rear side of the lense with a ruler for scale; lens says diameter 49 and JAPAN

So I hold it in front of my semi-old iPhone, at "50% zoom":

again, circular fish-eye image of the balcony; at wider angle, but behind a yellow-ish greasy fog

Getting there... save for the greasy lens, this looks like a wider angle than the 0.42x. Still, the lens can't "see" the whole virtual image, the outer ring is always blocking its crisp edge, and producing a blurry/feathered edge.
Looks like I need a small lens AND I have to get as close to the lens as possible.

So I grab an old, terrible webcam: 40mm-ish and a 1.5mm aperture. I file down it's plastic case, get basically inside the adapter, this is the image i get:

montage of 4 fish-eye shots, all digital and blurry, with feathery black circular edge; showing some grass, a window, a monitor with a checker pattern, and a hallway

Still not the full image! Still blurry edge! What the!

And even when I push my own eye real close to it, I can never see the full, circular, virtual image; that ring is always blocking parts of it, like it sits "too far within the lense".

Thoughts:

  • not all these clones are equal (which are, though?)
  • do the "better" clones have wider rear openings?
  • this adapter just can't be meant to be used with filed-down webcams and smartphone cameras, can it - they just didn't exist when it was made!

To boil it down to one question:

Is my lens broken, a hoax, or am I doing something wrong?

Bonus, if you've made it this far: I had already bought this adapter once, like 20 years ago, off of eBay, with the same result but resold it at a profit :)

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    \$\begingroup\$ You need to set the focal length scale on the adaptor (green numbers) to match the focal length of the lens it is attached to along with the aperture... have you done that? \$\endgroup\$
    – Steven Kersting
    Commented Apr 6 at 16:32
  • \$\begingroup\$ @StevenKersting I had tried that, should have mentioned it -- it changes nothing, optically. As far as I can tell, the focal length ring shifts the aperture ring (min. f/3.5 at 30mm, f/22 at 200mm). The aperture ring does have an effect, I can see a diaphragm closing. But setting it to anything else than "open" (so f/3.5, or f/22, resp.) makes the problem worse as the circular image gets even smaller... more like cropping than aperture. \$\endgroup\$
    – kubi
    Commented Apr 7 at 12:19
  • \$\begingroup\$ Just an idea (my understanding of optics is not good enough to judge whether it really makes sense or not): could the smaller (than full frame) image circle of your APS-C lens somehow restrict the image circle of the combination of the adapter and the lens? Someone on Pentax Forums seems to be having the same problem on an APS-C zoom. Do you have a full frame lens to try it with? Or a prime? Not sure why a prime would make a difference, but zooms can be weird. I don't know. \$\endgroup\$
    – Steadybox
    Commented Apr 11 at 2:56
  • \$\begingroup\$ Perhaps you could try a macro extension ring behind the lens as well. Just to see what happens to the image circle. \$\endgroup\$
    – Steadybox
    Commented Apr 11 at 2:57
  • \$\begingroup\$ @Steadybox a macro ring between adapter and lens increases the distance, making things worse (closer=better); between lens and camera, well it would make it macro, which seems irrelevant (my zoom's macro doesn't help whatsoever). Full frame or prime seems only to matter w.r.t. the entry pupil size - here the tiny sensors did better... \$\endgroup\$
    – kubi
    Commented Apr 11 at 17:40

2 Answers 2

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Perhaps the OP's situation is different.

For other people who come across this post seeking to understand : If the intermediate lens (ie the lens between the Weltblick/Spiratone auxiliary lens and the camera body) isn't set to f/2 or larger aperture, the field of view of the results will likely be reduced.

On my D850, 50mm f/1.8, Spiratone 0.15x (same appearance at the Weltblick):

@ f/1.8 - no vignetting

@ f/2.0 - no vignetting

@ f/2.8 - some vignetting at the other edge

@ f/4.0 - field of view definitely smaller, vignetted by the smaller aperture

@ f/5.6 - field of view even smaller

and same for subsequent smaller apertures. F/22 is really small.

The auxiliary lens instructions say to set the intermediate lens to it's max but makes no mention of the required max to ensure full field of view.

Based on my quick test, it's my expectation that if the max of the intermediate lens is less than f/2.0- f/2.8, you will likely see some reduction in recorded field of view. This may vary by focal length.

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I had what looks to be the same issue. The aperture of the intermediate lens is vignetting the image. Shoot in full manual and set your intermediate lens to max (f1.8 or so), and the image circle and viewfinder POV are the same. If you shot the intermediate lens at say f/16, you'll see the vignetting effect pretty clearly. Also didn't seem to matter if I left the UV filter on the intermediate lens or not.

BTW, the aperture / focal length setting on the Spiratone is just a f stop scaling calculator - I don't think it does anything optically. I set mine to 30mm and f 5.6 for funsies. Nikon D850, Nikon 50mm f/1.8.

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  • \$\begingroup\$ thanks, that's unfortunately not it. aperture of the "intermediate" lens has no effect on the vignetting. we might have different lenses - in my Weltblick, the ring does close an internal diaphragm (there's an adjacent second ring which is only a calculator, indeed, though) \$\endgroup\$
    – kubi
    Commented May 21 at 20:36

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