7Artisans 7.5mm F2.8 Fisheye Lens and De-Fishing

I recently traveled to southern Africa and decided to add the 7 Artisans 7.5mm f2.8 fisheye lens by to my lens collection primarily to perform some astrophotography and because the price was really attractive. My initial impressions of the lens are very favorable, it is well-made, small and fairly light. This 7.5mm is a fisheye lens that apparently has a maximum angle of view of 180 degrees. With 11 elements arranged into 8 groups, it also has a 12-bladed iris. It is a lens requiring manual focus and aperture adjustments although the price of $140 makes it a no-brainer to add to my lens collection. It is about 2.5 in wide and long and weighs 9.7 oz due to a mostly aluminum construction. I thought I would share some photographs and techniques using this lens on my Lumix GX8 camera.

Sample Images

The 7artisans 7.5mm f2.8 Manual Lens for M4/3 feels solid and well made. The aperture ring is snappy and the diaphragm blades are clean and well formed. The lens mounted fairly snug on the Lunix GX8, and the focus ring is smooth and hitch-free. Overall, the quality is more than acceptable. As you can see in the photos above, the lens is sharp, edge to edge, athough I had stopped the diapham down to f20. There is a little chromatic abberation in the second photo in the trees which I left in to demonstrate. You will need to set the GX8 to “no lens”, it will ask for the length of the lens (8mm is the smallest available so I chose that) and l turned on manual focus aid “AF Mode/MF”, with the “MF Assist Display” option set to “FULL”, and “Peaking” set to “LOW” and red.

Macro Images

I really love this lens for macro work, stopped down it has an incredible depth of field. Full disclosure, I shoot in RAW and these photographs have been “prettied up” for publication without any attempt to de-fish the images. Shooting with this manual lens was much easier than I had imagined. Focusing with the peaking turned on is usually pretty easy with this lens. For the most part, you only really have to focus on things that are relatively close, because the “infinity range” starts less than a meter out. Stopped down to F4, the 7Artisans has a great DOF for outdoor shots.

De-Fishing

According to Wikipedia, the fisheye lens had its “first practical use was in the 1920s for use in meteorology to study cloud formation giving them the name ‘whole-sky lenses’.” As a result, they’re excellent for photographing the night sky. The large field of view that they offer allow us to not only see a huge amount of the night sky but also let us use relatively long exposures, up to 30-60 seconds without significant star trailing. Now if only that horizon wasn’t so curved and fishy. The process of reducing distortion in a fisheye lens is called de-fishing as illustrated above. I will descuss three de-fishing options which are also described in an excellent video by Ian Norman at “Lonely Speck” listed below.

Rectiliniar De-Fishing in Lightroom

The first method of correcting the curved horizon is found in the Lightroom lens correction utility. The 7Artisans 7.5mm lens is relatively new so I adjusted the Rokinon 7.5mm lens profile with a slight tweek. You can see that the closer the horizon is to the center of the photo the less curvature occurs. The rectalinear correction straightens the horizon but causes a reduction in the field of view to 80-90 degrees with distortion and smearing in the corners of the image. These are clearly not characteristics desirable in astrophotography. Note the distortion of the reeds and buildings in the corrected photo above. Obviously, this method is not what we are looking for.

Imadio Fisheye Correction

 

There is a $30 plugin filter for Photoshop that performs a much better de-fish with little to no loss of field of view and no stretching in the corners. This trick is accomplished by de-fishing in one direction at a time. As you can see in the above photo the field of view is preserved and the buildings are now straight and undistorted. Pay particular attention to the rocks on the shores in the bottom corners of the image, no distortion and no smearing.

Technique with Imadio

The technique to using this filter is a little more complex than words can convey, I highly suggest you watch the video below. That said, I will givyou an outline of the steps involved. The intallation provides three filters, the one you will use for the GX8 is Fisheye-Hemi 2. Natively, this filter only straightens vertical lines, to get it to de-fish the horizon, we will trick it by enlarging the canvas vertically by 225%. The steps are as follows:

• Import the file into photoshop and double click on the layer to change it from “background” to “layer 0”.
  Go to Image/Canvas Size and in the dialog change to percent from inches and enlarge the “Height” to 225%. Change the “Anchor” up for a horizon in the upper part of the picture, down for a horizon in the lower part of the picture. Click ok.
  Move the photo up or down the enlarged canvas to the approximate position of the horizon in percentage terms. This is tricky and may require some trial and error to get a straight horizon.
  Go to Filters/Imagio/Fisheye-Hemi 2 and click. You will see the result, if you are happy, crop the picture from the expanded canvas and save it!

Photoshop Warp

You can do a very similar de-fish using the tools native to Photoshop. First turn the layer from “background” to “layer 0” as we did before. Than go to Edit/Transform/Warp. Use the adjustment points to straighten the horizon. The horizontal FOV will reman the same and there is no blurring in the corners. Crop the image or fill in the sky and you are done.

Astrophotography

When I was in Africa, I had a chance to try the 7Artisans 7.5 f2.8 at night. Because there were many predators around, the choice of location was limited and I had no view of the Milky Way. However, with the lens mounted on the Lumix GX8, with ISO 1600, wide open at f2.8, focused at infinity and an exposure of 25 seconds, I was able to capture a very satisfying night sky. The photo above is not stacked, it is a single exposure for inspection. Note the upper right and left corners where the stars are slightly distorted since I did not de-fish the image. The center stars are point sources with actually nice brightness for a single exposure. This lens is a very nice option for m4/3 cameras since you get a very reasonable exposure time due to the very short 7.5m lens.

Overall I am very pleased with this inexpensive, bright and well built fisheye lens. It has some limitations but overall the positives far outway the negatives. As always, I hope you enjoyed the post, please leave a comment.

References:

Using Manual Focus Lenses on the GX8: https://www.dpreview.com/forums/thread/4011926

De-Fishing a Fisheye Lens: https://www.lonelyspeck.com/defish/

Imadio Fisheye Correction: https://imadio.com/products/prodpage_hemi.aspx