How to Test a Cheap Wireless Photo Flash Trigger
My journey to understand and diagnose the effects of a faulty wireless flash trigger and the difference in behaviour between film and digital photography
This article started out as a review of the Neewer/Andoer PT-16GY for part 3 of my DIY Studio Strobe series but when using them produced unexpected and puzzling results, I began investigating. This article describes what I learned and what I wish I’d known before I wasted quite so much film.
Neewer PT-16GY: Low-Cost and Low Speed
If you are looking around for a low-cost wireless flash trigger and receiver for use with a vintage flash then the Neewer PT-16GY feels like a good choice. The receivers have a PC sync socket, as well as a built-in hot shoe; and the product specification claims the receivers are compatible with an impressive number of older flash accessories.
The Neewer PT-16GY is an older product and is no longer listed on Neewer’s website. The same product is still listed on Andoer’s website. It can be purchased on eBay in the US for around $20 and imported direct from China for around €15 plus taxes.
The main drawbacks that I’ve found with the PT-16GY are build quality and issues problems syncing above 1/60th on film cameras.
I chose the PT-16GY because it claims to be compatible with a huge range of cameras and flash accessories and the receivers include a PC flash sync socket of the type that was the de facto standard for flash accessories from the 1950s — 1990s.
Flash Synchronisation Issue
Reviews of the PT-16GY suggest that customers have experienced various issues including flashes not always triggering at short distances and flashes not syncing correctly leading to partially exposed images.
I was aware of theses issues when I bought my PT-16GY but my thinking was that Neewer have a reasonable brand, wireless triggers are simple enough devices and if necessary, it’s straightforward to return things that don’t work.
Spoiler Alert: I was wrong! They are easy to return which is fortunate because I’ve tried both the Neewer and Andoer versions and they both struggle to sync at speeds over 1/60 second.
The series of images above is taken from the second test roll I shot using the Andoer PT-16GY with my Nikon F80D SLR and a DIY studio strobe based on a Vivitar 283. The series was taken using Ilford FP4 Plus at “box speed” (ISO 125) exposed at 1/125 second.
The issues visible in the series above look similar to what I’d expect to see when trying to use flash at a shutter speed that’s faster than the camera’s flash sync speed. In fact, the first test roll had similar issues because I mistakenly shot it at 1/250 second which is higher than the maximum flash sync speed of the F80D.
Flash Sync Speed
The maximum flash sync speed for the Nikon F80D is 1/125 second. This means that a frame of film exposed at 1/125 second or slower should be correctly exposed using flash. Whilst a frame of film exposed at a higher shutter speed will have some or all of the frame incorrectly exposed because some of the light is blocked from reaching the film.
Digital SLRs and nearly all 35mm film SLRs and rangefinder cameras use what is known as a focal-plane shutter. Professional medium format film cameras use a different type of shutter called a leaf shutter which allows them to sync at higher speeds.
The focal-plane shutter is located inside the camera body, directly in front of and parallel to the film or sensor and consists of two “curtains”. At slower shutter speeds, the “front” curtain moves to expose the film or sensor and then the “rear” curtain moves to cover up the film or sensor thus ending the exposure.
At higher shutter speeds, the rear curtain beings moving whilst the front curtain is still moving, and the film or sensor is exposed by the light entering the “slit” between the two curtains as they travel across the film or sensor.
The Nikon F80D has a vertical focal-plane shutter that uses two metal blades as curtains. Shutters with curtains that travel vertically allow for faster flash sync speeds, since the curtain has to travel a shorter distance: for 35mm film a vertical curtain has to travel 24mm instead of 36mm for a horizontal curtain. Older cameras used shutter curtains that traveled horizontally and thus were limited to flash sync speeds of 1/30 second or 1/60 second.
If I were using an unfamiliar or untested vintage camera then I’d be inclined to think that there was a problem with the camera. I bought my F80D for a black and white photography course I studied in 2005 and it’s been in regular use ever since, so I know the camera isn’t the issue.
If it’s not the camera, is it the flash?
If the shutter is fully open when the flash fires, then the film frame or sensor will be fully illuminated. The images below shows that the rear curtain was in motion when the flash triggered. The top part of the frame is black because that area of the film was obscured when the flash fired.
To understand why, we need to explore a little of how an electronic flash works. The peak intensity of the burst of light from a flash like the Vivitar 283 is fixed. When you reduce the power of the flash the peak intensity remains the same but the duration of the flash is reduced, so that overall it contributes less light to the exposure.
If your subject is stationary and the flash triggered whilst the shutter was fully open then the burst of light from the flash illuminates all of the film frame or sensor. There is no way to know if the burst happened at the start of the exposure, or sometime later.
At full power, the duration of the flash from a Vivitar 283 is 1/2000 second or 0.5 milliseconds. At half power the duration of the flash is 1/4000 second (0.25ms). In comparison a shutter speed of 1/125 second equates to a 8ms exposure, so even at full power the flash is only active for fraction of the time the shutter is open.
Most vintage cameras trigger the flash at the at the start of the exposure. This is referred to as front-curtain sync to differentiate it from rear-curtain sync where the flash is triggered just before the rear curtain begins to move. My Nikon F80D supports rear-curtain sync flash but the problematic images were all taken with front-curtain sync enabled.
No, the Trigger Struggles with Film
If it’s not the camera and it’s not the flash then it must be the cheap wireless trigger. Time to return it and get my money back.
I’m an engineer at heart, so before returning my PT-16GY, I decided to investigate further and see if the issue is reproducible with the smaller sensors often used in DLSRs and mirrorless cameras.
My Nikon D300S DSLR has a similar vertical focal-plane shutter to my F80D. The main difference between the two is that the D300S is not a full frame camera, it uses a sensor that is physically smaller than a 35mm film frame. This means that the rear curtain on the D300S shutter has travel a shorter distance and therefore at will start moving slightly later than the rear curtain on the F80D. So, if the flash is being triggered late then the effects may be less obvious.
The images taken with the D300S and Vivitar 283 flash show none of the issues found in the images taken with the F80D. The PT-16GY works OK at 1/125 second with a DSLR with a smaller sensor.
Additional the maximum flash sync speed for the D300S is 1/250 second, so I wouldn’t expect to see an issue at 1/125 second. I was able to reproduce the issue with the D-300S at 1/250 second though not as often as I with the F80D at 1/125 second.
Trying out the Neewer PT-16GY (and wasting more film)
Optimistically, I used the refund from the Andoer PT-16GY to buy a Neewer PT-16. Maybe I’d just been unlucky with the Andoer version?
I tried the first Vivitar 283 with the F80D again with the Neweer PT-16GY. The results appeared slightly better but examining them more closely, 33 of the 37 frames in this fourth roll showed signs of the synchronisation issue. The series above uses the second of the two PT-16GY receivers. The first of the two receivers stubbornly refused to trigger reliably, leaning to my third test roll being mostly black frames.
How to Waste Less Film When Diagnosing a Faulty Trigger
Instead of wasting rolls of film, I could have diagnosed the issue by shooting a simple pattern of black and white bars.
You can do this by shooting directly at softbox with a mask in front of it. I use a 60cm x 60cm softbox with a piece of black A1 size foam board with 3cm wide slits as a mask. You could also stick parallel, vertical strips of black duct tape to the softbox.
The important things are:
- You shoot in landscape orientation if your camera has a vertical focal-plane shutter or in portrait orientation if your camera has a horizontal focal-plane shutter.
- That the white bars (unmasked areas of the softbox) stretch from top to bottom of the picture and thus to the edges of the negatives. Like a 2D barcode you find on groceries.
This way there is no need to scan/print the negatives:
- Correct: all the negatives should look like the same uniform height barcode. If the black bars on the negative (unmasked areas of the softbox) each stretch all the way from one side of the negative to the other then the trigger worked as expected at that shutter speed.
- Faulty: some negatives have shorter bars. If the black bars on the negative (unmasked areas of the softbox) don’t stretch all the way from one side of the negative to the other, then the flash fired after the rear curtain started moving.
- Faulty: no bars are visible. If the negative is white (transparent) then the flash either: wasn’t triggered (you’ll have seen this when shooting the test) or was triggered after the camera’s shutter was closed.
Example
To demonstrate this, below is a side-by-side comparison of a Bresser T-13 (which I use for triggering mains powered, vintage studio strobes) at 1/60 and 1/125 second and the Neewer PT-16GY at the same shutter speeds, 1/60 and 1/125 second.
As a visual marker when cutting the negatives and to make it easier to correctly frame the mask, I the first 2 frames of each new test combination where shot with just a modelling light (ringed in blue).
The next 3 frames (ringed in green) were shot with the modelling light and flash. If the rear curtain is shadowing a significant part of the negative when the flash is triggered then the white bars will be darker but still visible.
The final 3 frames of each new test combination (ringed in orange) were shot with just the flash. I shot 2 additional frames of the Neewer PT-16GY at 1/125 second as this is the one I expected to have problem results
The none of the negatives for the Bresser T-13 tests showed signs of issues. The negatives for the Neewer PT-16GY test at 1/60 second also showed no signs of any issues. However, in 3 of the 5 frames shot with the Neewer PT-16GY at 1/125 second (ringed in red) the tops of the black bars are missing.
Final Thoughts
Cheap universal wireless flash triggers are just that: cheap. It should not be surprising if a manufacturer didn’t test their trigger with a 35mm film camera at 1/125 second shutter speed. After all, customers using a DSLR with a smaller sensor or a higher maximum flash sync speed likely won’t see this issue. Neither will customers with a vintage 35mm camera that has a maximum flash sync speed of 1/60 second or less.
