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Optivelox SS04U Light Sensor Review

George Vittman reviews the Optivelox SS04U Sensor light meter for Android smartphones and tablets.

|  Optivelox SS04U in Exposure and Light Meters
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While reviewing a studio flash unit, I came across the Optivelox SS04U sensor, which I feel an obligation to present, as a budget friendly alternative to, for example, the 10x more expensive Sekonic L-885D.

The Optivelox SS04U, an upgrade to the former SS04, consists of a sensor, which plugs into the USB port of any Android phone, and measurements are controlled using the Lxmeter app, available from the Google Play Store. The SS04U is an incident light meter for both flash illumination and continuous light, is a reflective light meter using the mobile’s built-in camera, and it is to my knowledge the only existing device for Android phones offering measurement of flash durations, i.e. t0.5 and t0.1. I have used the device for verification of the Nikon SB-910 Speedlight, the Elinchrom Pro HD studio flash, and for measuring the Nikon D810 shutter times. All Optivelox SS04U measurements presented in this review were done using a Galaxy Note 3 and/or a Google Nexus 7 (2013), both running Android v6.01.


The Optivelox SS04U – Lxmeter combo - Configuration

As a default when opening Lxmeter, the illumination at the sensor location is shown and expressed in a user-selectable standard unit, Lux, ft candle or EV @ ISO 100 (Figure 1).

Figure 1

Figure 1: Startup page showing illumination expressed in a user selectable unit

The Lxmeter dashboard is user-friendly and complete. At startup, 2 menus are accessible (Figure 2). A function menu, allowing for a choice between Ambient light, Flash, Accumulated Flash and Remotely Triggered Flash (Bluetooth) to be measured. And secondly, the main configuration menu, allowing for sensor selection (internal or Optivelox SS04U), the management of a file archive and the global sensor and measurement parameter configuration.

The RT Flash option is only indicated when the mobile is Bluetooth enabled.

The settings menu with included sensor configuration is depicted in Figure 3.

Figure 2

Figure 2: Lxmeter menus at start-up: function menu and configuration menu


Figure 3left Figure 3right

Figure 3: Lxmeter settings with included sensor configuration


EXPOSURE MEASUREMENTS - Incident light metering

Scrolling the startup page to the left brings the user to the camera related incident light measurement module. Four priority modes are available, Aperture (F), Shutter (T), Aperture & Shutter (F&T), or alternatively a no-priority, manual mode (Figure 4). After the result of a measurement is displayed, the user can change the prioritised parameter, in order to update the recommended camera setting. The measurement is continuous unless a HOLD button is pressed to freeze the display.

Figure 4

Figure 4: Incident light measurement display, here using aperture priority, indicated as [F]

The F, T and ISO resolution can be set to 1/3, ½ or 1 stop.

Table 1 compares shutter durations obtained in aperture priority mode (f/2.8) for both the Sekonic L-758DR and Optivelox SS04/Lxmeter, when using a variable continuous LED light source as illumination. The partial discrepancy is attributed to the built-in camera profile used by default by the Sekonic L-758DR, whereas for the Optivelox SS04U no camera correction was applied, and the absolute illumination values were used.


Table 1: Incident light metering results obtained in aperture priority mode

Besides the measurement of continuous light, the same evaluation can be done for flash illumination, whereby T values in the range from 125 s to 1/16000 s can be selected. The Optivelox SS04U handles High-Speed Sync without any issue.

Table 2 shows a Nikon SB-910 flash exposure measurement comparison between the Sekonic L-758DR and the Optivelox SS04U, as a function of the set power level, and using shutter priority mode. Compared are the returned aperture values for 1/250 s and 1/1000 s, the latter being the low limit for the Sekonic L-758DR. For the Optivelox SS04U also the result for a 1/8000 s shutter time is added.


Table 2: Flash exposure measurement Sekonic L-758DR vs Optivelox SS04U

It can be observed that for a T of 1/250 s and also for 1/1000 s, the flash duration (Table 2, 2nd column) stays shorter than the T value, which then does not impact the required aperture. Applying this to photographing a moving image, it will be the flash that freezes the motion. This changes for a shutter time of 1/8000 s, and for power levels above 1:16 when it will be the shutter that freezes action.

The difference between the Sekonic L-758DR and the Optivelox SS04U can again be explained by the default camera profile used by the Sekonic. Figure 5 compares 2 out-of-camera test shots, taken with a Nikon D810, of an Elinchrom Pro HD eliminated scene, using a 1/250 s shutter time, ISO 64 and an f-stop as recommended by either the Sekonic L-758DR, f/4.5, or the Optivelox SS04U/Lxmeter, f/6.3. The conclusion regarding the better exposure setting is left up to the reader, as there is the dependence on the mood that the photographer wants to express in his work of art. The subject is, by the way, my regular model, friend Joe, in his avocado tree.

Figure 5left | 1/250 sec | f/4.5 | 58.0 mm | ISO 100
Figure 5left | 1/250 sec | f/4.5 | 58.0 mm | ISO 100
Figure 5right | 1/250 sec | f/6.3 | 58.0 mm | ISO 100
Figure 5right | 1/250 sec | f/6.3 | 58.0 mm | ISO 100

Figure 5: Test shot using the by Sekonic L-758DR and Optivelox SS04U recommended values

A flash accumulation mode is provided, which is useful for multiple exposure applications or in situations where multiple flashes are fired at non-coincident times. The flash accumulation can be done automatically or can be done manually, meaning that for each flash to be fired the START button is pressed. This can be useful in case a scene manipulation is required in between flash pulses.

Reflective light metering

Concerning this aspect, the reflective light metering is implemented in Lxmeter, by using the mobile’s built-in camera, but the measurement accuracy strongly depends on the mobile's on board image sensor. The comparison with a reference meter being mobile brand and model dependent, an evaluation will be omitted for this review.

Flash duration

Figure 6

Figure 6: Additional menu allowing the selection of a graphical representation

The Lxmeter configuration page for the SS04U allows for a selection of a time resolution, 16 µs or 8 µs. For measurement of ultra-short flash waveforms, an HS option is provided, hereby making the measurement precise down to 2 µs, resp. 1 µs.

Upon available flash pulse data, a new menu is added to the main page, allowing for a choice of the graphical representation of the results (Figure 6). Available are t0.5, t0.1, Full, Flash and Global, of which the first 3 are the ones important for photography. The graphs t0.5 and t0.1 show the respective flash duration, while the Full shows all flash pulses measured in the 1 s interval after triggering the sensor (Figure 7). Also shown, both in flash exposure and flash duration measurements, is the percentage flash to total illumination.


Figure 7

Figure 7: Graph display mode Full showing flash strobe, with flash pulses spaced at 0.05 s.


Figure 8

Figure 8: Graph menu allowing to save data/graph

The graph window can be resized using the standard zoom function found on mobile phones. Tapping the Y-axis brings up a graph option menu, which includes the possibility to save data and/or graph for a more detailed post processing (Figure 8).

As a test case in evaluating the measurement of flash durations, the results for the Nikon SB-910 speedlight are presented next. The by Nikon-specified “approximate” values for t0.5 (flash illumination above 50% of maximum) and the measured values are given in Table 3, together with the measured, for freezing motion critical time that the illumination is above 10%, t0.1. A few of the measured curves are illustrated in Figure 9.


Table 3: Specified and measured flash durations for the Nikon SB-910


Figure 9a
Power 1:1

Figure 9b
Power 1:2
Figure 9c
Power 1:4
Figure 9d
Power 1:128

Figure 9: Illustration of the SB910 flash measurement results


Feature comparison Optivelox SS04U/Lxmeter vs Sekonic L-858D

To resume the Optivelox SS04/Lxmeter capabilities it might be useful to examine a feature comparison with the Sekonic L-858D, which as a matter of fact just had a serious price drop.

Comparison Table
Comparison Table

The reader may notice a small contradiction in this review, in that all measurement results presented compare the Sekonic L-758DR with the Optivelox SS04U/Lxmeter combo. The L-858D is supposed to have improved sensitivity over the L-758DR, but I do think that we can extrapolate the final conclusion also to this latest Sekonic Speedmaster.


Optivelox SS04U Conclusion

When not being branded at carrying a big name around, the Optivelox SS04U/Lxmeter combo is found to be a valuable alternative. Pros include the versatility in measurements, the very compact form factor for carrying along (delivered in 4.5 x 5.5 x 3.5 cm storage box), the compatibility with any Android mobile phone or tablet (display size and display quality!), the possibility to store flash data for post-processing, and last but not least the very attractive price tag for the budget oriented photographer. Real cons have not been found, and it has to be mentioned that the Optivelox developer is open to adding new features on customer demand.


George Vittman

George Vittman is a French Alps based electronic engineer and image sensor specialist, who identifies job and hobby as one, and who expresses his passion for technology and nature through his photography. Describing subjects as Creatio Ex Nihilo, created from nothing and simply being there, George tries to replicate and immortalise what his eyes see and enjoy by squeezing out the edge of technology.

George is in his past author of countless educational/expository articles in international magazines, discussing numerous subjects, going from electronics to equestrian and photography. He loves the country life and likes to relax within nature. For him, living is learning, as also expressed 2500 years ago by Socrates “I know one thing, and that is that I know nothing”.


DISCLAIMER NOTICE: The author is not affiliated with any of the brand names mentioned in this write-up, nor is he being compensated for using their name.

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