Use of flash in regards to vibration

[bs0604]

At the recommendation of forum member mawyatt I purchased a Godox SK300II flash to use with my extension tube/Mutotoyo objective. Previously I had been concerned about vibration causing blurring of the images. I notice on the B&H site where I purchased the flash, that the flash duration is 1/800-1/2000 second. When I take a picture without flash and only room lights on there is not enough light to enter the microscope objective and my pictures are black. I am shooting in manual mode and as I would think that with the use of this flash and its short "on" duration it doesn't much matter whether I set my camera speed to 1/250 sec or 1 second. (My camera does not synch flash beyond 1/250). The effective exposure time is only going to be 1/800 to 1/2000 sec in view of the ambient light alone not being enough to pass through the microscope objective and register on the camera sensor. Thus, vibration problem effectively solved. Is my thinking correct?

[mawyatt]

I wouldn't go so far as saying your vibrations problems are all solved with the strobe, but your thinking seems correct.

Camera induced vibration comes from the mirror moving (DSLR), then the mechanical front curtain starting the exposure and finally the mechanical rear curtain terminating the exposure. The mirror induced vibration can be eliminated by using delayed exposure, which delays the front curtain exposure start by a predetermined amount. With strobe/flash you can use a much longer exposure (assuming dark environment) to allow the front curtain induced vibration to subside before triggering the flash which creates the image. Some cameras have a Rear Curtain trigger which triggers the strobe/flash just before closing the rear curtain.

External vibrations often have less effect on the image with strobe/flash since the effective exposure image capture is short, similar to having a shorter camera exposure but without the less light captured effect.

Best & Happy New Year,

[Lou Jost]

Generally, for high-magnification work, you will see sharper results if you use a shorter flash duration. I like to use the second- lowest power setting available on the flash. If I need more light, I use more flashes. Nowadays I don't use the lowest setting because, as Mike has shown, flash power can vary between shots, and this is worse at lower power settings. But Mike has also shown that the Godox strobes are stable, unlike Yongnuo flashes, so maybe those could be used at the lowest power without risk.

[mawyatt]

Lou,

I've found the Adorama Studio Strobe 300 (Godox SK300II) to have good repeatability between flash outputs at all settings, I generally use 1/16 to 1/4 settings. They are specified as 2% variation, which you normally don't see this spec in a low cost strobe.


Best & Happy New Year,

[Lou Jost]

Yes, I remember those helpful tests, and I bought one of those strobes (actually the 400 model) based on your recommendation. But I haven't used it yet. I look forward to it!

[rjlittlefield]

I've found the Adorama Studio Strobe 300 (Godox SK300II) to have good repeatability between flash outputs at all settings, I generally use 1/16 to 1/4 settings.

With most consumer-grade flashes ("speedlights"), the flash duration drops in close to direct proportion to the power setting. Do I understand correctly that these units have minimum around 1/2000 second, even on their lowest power setting?

--Rik

[mawyatt]

I've found the Adorama Studio Strobe 300 (Godox SK300II) to have good repeatability between flash outputs at all settings, I generally use 1/16 to 1/4 settings.

With most consumer-grade flashes ("speedlights"), the flash duration drops in close to direct proportion to the power setting. Do I understand correctly that these units have minimum around 1/2000 second, even on their lowest power setting?

--Rik

Rik,

I don't have access to an oscilloscope now, so can't say for sure. Think this is the case, the 1/2000 at minimum power (300/16 or 18.75WS). This would be 1/2~1/3 power on a typical speed light and probably faster than a speed light at this power level.

Best & Happy New Year,

[Lou Jost]

That might be an important drawback of strobes. I used to do telephoto bird photography with flashes, and I think photos at 1/16 power were notably sharper than photos at full power or half power. Movement at high magnification

[mawyatt]

That might be an important drawback of strobes. I used to do telephoto bird photography with flashes, and I think photos at 1/16 power were notably sharper than photos at full power or half power. Movement at high magnification

Lou,

The speed lights are very slow at full power, I recall something ~1/250 second. This is ~60WS at full power, whereas a 300WS strobe would be at 1/5 power and possibly faster, of course a 600WS strobe would be at 1/10 power. There are strobes that use IGBT that are faster than speed lights over most of the power range and can produce 10X the speed light power, but more expensive (~$500) than the strobes discussed here.

The important thing to consider is not the back off power setting of the speed light or strobe, but the actual output power required. If you only require 1WS then a speed light at 1/64 power will be very fast, probably faster than a strobe, however if you require 60 or 30WS then the speed light will be slow and the strobe faster.

Since I often use lots of levels of diffusion and thus lose lots of power, and not having to deal with overheating, long recycle time, uneven output and batteries, the strobes were the better solution for my application. For a long S&S session I'm not sure the batteries would last the entire session since these sessions may require 6,000 images.

Best & Happy New Year,

[Lou Jost]

if you require 60 or 30WS then the speed light will be slow and the strobe faster

Mike, to get more power I just use more flashes at their fast setting, and I can also extract the flash tube and put it very close to the subject to get extremely high light intensities with low power. I use extended battery packs to solve the battery capacity problem.

[iconoclastica]

With what frequency can you fire these speedlights without them overheating?

[Lou Jost]

When they are at their lowest power setting, and when an external battery pack is used, I think I used to give them about 4-5s. It also helps to move the flash tube outside the unit.

The flash that was more likely to overheat was the camera's built-in pop-up flash I used to trigger the main flashes.

[mawyatt]

Lou,

Using more speed lights or strobes is a good idea by allowing you to spread out the light sources and keep the individual power lower for a faster response.

Even with the external battery pack, you still have to deal with batteries, the potential overheating, uneven outputs, and don't think the pack would allow deep S&S sessions without depleting the batteries.

Speed lights have their advantages though; they are small, portable and easily configured around your macro setup. I have and use speed lights for cases outside the studio macro use, where they are invaluable for certain applications.

Best,

[Lou Jost]

You are right that the battery packs would not be able to supply a deep stack-and-stitch operation of 6000 shots or so. They can do a couple of thousand shots though, at lowest power.

One advantage of using lots of flashes at once is that the shot-to-shot variation should average out across flashes (most of the time).

[iconoclastica]

Even with the external battery pack, you still have to deal with batteries

This one is easily overcome by soldering an external power supply to the battery connectors. I have a 5.8V 3W leftover PS connected to a unit with the flashtube wired outside the unit. Can't test the heat though, for the recharging time is about 10seconds and there's no manual power setting possible.

At least it needs a faster supply.