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UltravioletPhotography

Gopro Hero 4 for UV photography/video?


enricosavazzi

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enricosavazzi

The Gopro Hero is one of the first, and probably most popular, small action cameras. Gopro updates its models about once a year, and so far they have remained slightly more advanced (and more expensive) than the competition. Many of the craziest action sports videos on YouTube have been shot with Gopro Hero cameras. Parts of some commercial TV series and movies have also been shot with these cameras.

 

The sensor is 5.76 mm by 4.29 mm, bigger than that of a typical webcam but smaller than system cameras. Interesting capabilities (not available in all models, or simultaneously) are video up to 4k resolution and up to 240 fps, up to 12 Mpixel still pictures single or in bursts of up to 30 fps, time-lapse video and still pictures, low-light mode, and quite a few other features. All solid-state (no mechanical shutter), built-in Bluetooth and WiFi. A mobile phone app can be used as remote control, or a dedicated remote is available. Some models have a built-in touch LCD screen, others can use one as accessory. There are also plenty of limitations, like no flash sync, no AF, and lens choice restricted to S-mount lenses. This is clearly not a replacement for our multispectral converted system cameras, but on the other hand it can do some things that most of our cameras cannot do, and is extremely small and lightweight.

 

Now, given that we are on the Ultraviolet Photography site, the first natural question is whether the Gopro Hero can be used for UV photography. Strictly speaking, it does not need to be converted to multispectral, since the standard lens has an IR-cut (and presumably UV-cut) filter attached at its rear. NIR and multispectral (VIS+NIR) videos after removing this filter or replacing the lens are available on YouTube, so there is no question that the camera is NIR-capable. I have no information, however, on whether it is usable in UV.

 

The second big question is whether UV-capable lenses are available for this camera. It uses an S mount (M12 x 0.5) lens attachment, and lenses of this type are hardly exciting. However, Rib-Cage makes an overpriced modification kit that allows use of S, CS and C lenses. Rib-Cage also offers an even more overpriced, already converted range of Gopro cameras. A few months ago, I did find some C and convertible to C lenses that are reasonably good in UV, and a few dedicated lenses in C mounts designed for UV imaging are also available.

 

Installing the kit involves a complete disassembly of the camera. Among other things, the sensor is moved from deep within the camera body to flush with its front plate. Therefore, before doing the modification, I would be interested in hearing whether anyone can confirm that the Gopro Hero, and specifically the Gopro Hero 4 Silver/Black, is usable in UV. There might be show-stoppers like a UV-cut coating on the sensor package. If no one has tried so far, I guess I will be the test monkey.

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No information on the Gopro 4. However, I did try a Baader U 2" over my GoPro 3 and outcome was virtually black.
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enricosavazzi

No information on the Gopro 4. However, I did try a Baader U 2" over my GoPro 3 and outcome was virtually black.

With the standard Gopro lens still in place, or removed?

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In place as far as I can recall. This was just a quick test.

 

Interesting though there are UV-capable C-mount lenses that can be used for this camera. I got one from Vivek which I'm using on my Panasonic GH-2. However, focal length is too long for the petite sensor of the GoPro.

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They have a 6 mm C-mount UV lens with aperture f/3.5-f/16 too.

 

The C-mount lens Vivek kindly gave me is 25 mm f/1.3. Works well on the Panasonic, but way too long for a GoPro.

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enricosavazzi

Among the accidental UV lenses I tested at http://savazzi.net/photography/accidental_uv_lenses1.html, I am planning to test on the Hero 4 the Mir 11 in C mount (12.5 mm f/2.2), Vega 7 in Kiev 16U mount (20 mm f/2) and the Pentax-110 18 mm f/2.8 and 24 mm f/2.8. The first two have an image circle too small for Micro 4/3, but should cover the Gopro sensor. The two Pentax actually cover Micro 4/3. The Pentax-110 24 mm f/2.8 is so minuscule that it would look too small even on a Hero. A Pentax-110 to C commercial adapter does not exist, but I might permanently epoxy these lenses into C extension tubes.

 

I would expect the Universe Kogaku lenses to cost very roughly in the ballpark of US$ 1,000-1,300. Not more expensive than a semi-pro ordinary lens for a system camera, but still a purchase to consider only if no good accidental lenses are available.

 

I have everything on order, but might decide to use the Hero 4 unmodified on a coming vacation in July, before I start hacking it. The Rib-Cage modification does not allow the use of the Gopro water-tight case, for one thing, and is essentially a one-way process. Perhaps I could make some preliminary test by just removing the Hero standard lens, though. Perhaps I will need a second Hero 4 after all?

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enricosavazzi

I mixed up company/product names in my earlier posts. The Hero modification kit is made by Back-Bone (the company) and is called Ribcage (the product). Now where did I put my UV Clavicle?

 

I think we lost a post (not mine, but I don't remember whose) in this thread since yesterday's server move. It contained price information of Universe Kogaku UV lenses in C mount, which turned out to be lower than I expected (500-750 $).

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The lost post was mine.

 

I called UKA and got a quote on their S-mount 9mm f/2.8 Miniature UV Quartz Lens of US$ 500.

 

I was told they are soon to offer other quartz S-mounts in various focal lengths from $500-$750. I do not know the focal length of the standard GoPro lens but one of these new UKA lenses might be a direct replacement.

 

I also commented that the online DIY GoPro lens removal was "cringe worthy". It appears the original lens is cemented into the S-mount threads and requires heating to melt the glue! Makes me wonder, what else melts?

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From the back of my head I recall reading the goPro lens is approx. 3 mm focal length. That would fit given the small sensor and wide angle of view.

 

Take this with a grain of salt until someone else can corroborate the info.

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I just remembered my lost post also commented that the notion that you might test the GoPro without a lens had crossed my mind as well. Should be easy enough to illuminate a PTFE or Spectralon reflector with a 365nm LED for an initial indication of UV feasibility.
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enricosavazzi

I just remembered my lost post also commented that the notion that you might test the GoPro without a lens had crossed my mind as well. Should be easy enough to illuminate a PTFE or Spectralon reflector with a 365nm LED for an initial indication of UV feasibility.

Yes, this is completely feasible.

 

I read online that the Hero 4 lens can be removed by unscrewing it without heating. Even a strong hand is supposedly enough, once the collar friction-fitted around the lens (which cannot be unscrewed but extracts by pulling straight outwards) is removed first. Strictly speaking, the lens seems to be held in place with a reversible thread sealant just to prevent the factory focus setting from changing.

 

Edit: it is actually slightly more complicated than that. The outer sleeve is held in place by three tabs that must be pushed in. It then pulls straight out. The inner sleeve can then be used to unscrew the lens.

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enricosavazzi

From the back of my head I recall reading the goPro lens is approx. 3 mm focal length. That would fit given the small sensor and wide angle of view.

 

Take this with a grain of salt until someone else can corroborate the info.

The exact focal length for the Hero 4 seems to be a well-guarded secret, but is said by independent sources to be around 2.5 mm. The lens is said to have a (diagonal?) angle of view around 170 degrees, so it should be a non-rectilinear, fisheye design, which makes the exact FL irrelevant (there is no constant relationship between FL and angle of view in a fisheye, it varies with the lens design).

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While the statement about fisheye FL vs angle of view is correct, the focal length does have a bearing on stuff like depth of field.

 

More coffee has improved my memory to give a reading of 2.8 mm.

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I read online that the Hero 4 lens can be removed by unscrewing it without heating. Even a strong hand is supposedly enough, once the collar friction-fitted around the lens (which cannot be unscrewed but extracts by pulling straight outwards) is removed first. Strictly speaking, the lens seems to be held in place with a reversible thread sealant just to prevent the factory focus setting from changing.

 

The Wikipedia shows a photo of a spring loaded S-mount lens. Something like that might allow you to adjust focus and hold your setting reasonably well.

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enricosavazzi

Gopro Hero 4, first UV light

 

post-60-0-78508800-1431798236.jpg

 

Removed the Hero 4 lens, temporarily placed a UV Rodagon 60 mm with Baader U on a focusing helicoid atop the camera, suspended a flower about 40 cm above the camera, and illuminated it with MTE 3W UV flashlight from about half a meter away. VIS color of the whole flower is yellow.

 

post-60-0-36183200-1431799262.jpg

 

Wood ceiling of my office, about 1.5 m above camera, same setup.

 

This should remove the initial doubts that the Hero 4 can do UV. Exactly how much into the UV remains to be seen, once I can mount lenses in a more reliable way. False color ranges from violet to orange depending on subject. Color balance set to native, which is pretty much normal daylight (no custom WB on this camera, of course). Of course the 60 mm lens acts as a long telephoto lens on the Hero.

 

Unfortunately no EXIF data, so exposure time, ISO etc. is anybody's guess (exposure a fraction of a second, anyway). Apparently this camera saves still pictures as a movie, where each successive frame is a separate picture. Exported to 12 Mpixel JPG with Gopro software, then reduced.

 

The built-in LCD screen is not much to look at, but the camera displays an HD live view on an external monitor that allows accurate focusing.

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Your test flower probably is a Doronicum, which is known to have near UV-black disk florets and UV-reflective ligules (ray florets). Thus this provides solid evidence that the camera can do UV to some extent.

 

Now, a shorter UV-capable lens would be nice for the camera. Do you plan on doing UV video with the GoPro?

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enricosavazzi

Your test flower probably is a Doronicum, which is known to have near UV-black disk florets and UV-reflective ligules (ray florets). Thus this provides solid evidence that the camera can do UV to some extent.

 

Now, a shorter UV-capable lens would be nice for the camera. Do you plan on doing UV video with the GoPro?

That is one of the things I intend to try. A 30 fps HD movie I tried today in very cloudy weather outdoors (juggling camera and lens in one hand and focusing with the other hand) was very noisy, so I may need to decrease fps and/or resolution. Full sunlight is probably also necessary.

 

The sensor crop factor is said to be 5.7, so a 105-135 mm would be more than enough for wildlife photography/video. The shortest UV-usable lens I have and intend to test is the Pentax-110 18 mm f/2.8, which makes a longish 102 mm equivalent.

 

Correction: I have also a Mir-11 in C mount, which is a 12.5 f/2.5.

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  • 2 weeks later...
enricosavazzi

Now I did the Backbone modification and can mount S, C and CS lenses (and M42, Nikon F and all the rest via C adapters) . A first discovery is that, for unknown reasons, each lens I tried seems to need a different infinity focus calibration. So I will need a kit of short C extension tubes and shims to calibrate each lens. Second discovery is that a monitor with full HD resolution is indispensable to focus accurately. The Android remote control app shows a time-lagged live view sufficient for framing if one is patient, but is not enough to focus and cannot be zoomed in.

 

I did some tests with a Soligor 35 mm f/3.5, which is a supertelephoto lens on this camera. The flower is 75 mm across and I placed the camera 700 mm from the subject, which is the maximum height of my macro stand.

 

It seems auto WB should not be used, except in VIS where it does a half-decent job even with the fluorescent tube I used. One shot with Baader U, MTE 365 nm LED torch and auto WB is orange like... well, an orange, the next shot neutral gray, the next pink.

 

post-60-0-93895100-1432740160.jpg

 

post-60-0-78166600-1432740764.jpg

 

post-60-0-12592700-1432740188.jpg

 

post-60-0-16250700-1432740202.jpg

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enricosavazzi

After quick tests with the Coastalopt 60 mm Apo on the Hero 4 Silver, I can report the following results:

 

- Imaging is possible with a 325 nm narrow-band (+- 5nm) filter, but not quite usable. In practice, tree branches against a clear sky are clearly imaged, but few solid objects are visible (a utility pole in my case). This suggests that the camera is not recording 325 nm, but perhaps 15-20 nm higher wavelengths on the upper tail of the filter transmission.

- Asahi Spectra XRR0340, which uses a U340 substrate with additional IR-cut coatings, gives clear images in daylight.

- Baader U also gives clear images in daylight.

So the Hero 4 records UV as low as about 340-350 nm (on the upper transmission tail of the 325 nm narrow-band filter), but the most usable wavelengths are 360 nm and higher. This is a poorer UV recording than most converted system cameras, but still usable for most common applications.

 

A UV-capable S-mount lens would make the Hero 4 an interesting UV videocamera with decent still-picture capabilities. This idea does not need the costly Rib-Cage modification kit and only removing the standard lens is necessary, no other conversion needed. A UV filter holder can be cobbled up, and 12 mm UV-pass filters can be quite cheap. There is a picture of what seems to be an S-mount UV lens on the Universe Kogaku web page at http://www.universeo...ens_assemblies/ , but no such model is described.

 

Edit: Gotcha, it is a 9 mm f/2.8, http://www.universeoptics.com/new-miniature-uv-lens/ .

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Yes, that is the Universe Kogaku lens I mentioned earlier, they told me that they would be announcing other S-mount quartz focal lengths so you might want to check back from time to time to see what they offer.
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enricosavazzi

I asked a price quote of the Universe Kogaku 9 mm f/2.8, no answer yet. More information if I do hear from them.

 

post-60-0-50639000-1433348648.jpg

 

In the mean time, I found that a Schneider Kreuznach Xenon 16 mm f/1.9 in C mount transmits plenty enough of UV for the Hero 4, and does not vignette in the corners. Now waiting for a suitable step-up filter adapter. On the Hero 4, it is equivalent to a 91 mm on "full frame".

 

I also ordered a couple of legacy 10mm lenses in C mount. If one of them works well enough in UV, I might be equipped for this FL as well, considering that the Hero 4 does not seem to record much UV below 350 nm. This would be equivalent to a full-frame 57 mm, so we are slowly getting toward more reasonable focal lengths.

 

I even have a legacy 6.5 mm lens in D mount on order. The risk is high that it will vignette, but we cannot know without trying.

 

So don't worry if you don't hear news for a while. Eventually I will post more findings.

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I asked a price quote of the Universe Kogaku 9 mm f/2.8, no answer yet. More information if I do hear from them.

 

I already asked, and was told US$ 500.

 

The D-mount is for 8mm film is it not, ~4.5-6mm wide? I think I saw somewhere that people are using D-mount lenses on Pentax Q bodies. Sensor size on the P/Q is 6.17 x 4.55 mm, will that cover a GoPro?

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