Banding in my images when attempting flash photomicrography:

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MicroMan2
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Banding in my images when attempting flash photomicrography:

#1 Post by MicroMan2 » Fri Dec 30, 2022 3:23 am

Hello I recently made a Flash Photomicrography setup using a 50/50 beamsplitter. My camera is a Canon 60D with an external flash-sync cord attached to a Yongnuo Speedlite NW-580. The flash unit is not recognized by the Canon 60D so changing flash unit settings on the camera's end is not feasible. At 1/400 exposure time, I am having issues where parts of the image are not exposed. It is a distinct, linear region that only increases as the exposure times get faster. I think this has to do with how the flash unit's signal is delayed and that the flash is not fully captured. Has anybody experienced or known of this error.
Here is an image describing the error: https://photos.google.com/share/AF1QipP ... pITXo2Q0FB

Scarodactyl
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Re: Banding in my images when attempting flash photomicrography:

#2 Post by Scarodactyl » Fri Dec 30, 2022 5:28 am

I think this is normal if your shutter speed is too fast.

MicroMan2
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Re: Banding in my images when attempting flash photomicrography:

#3 Post by MicroMan2 » Fri Dec 30, 2022 7:16 am

I would like to know then what exposure times can freeze most motion. With this limitation in mind, I can only feasibly go to an exposure time of 1/250 sec with my camera.

viktor j nilsson
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Re: Banding in my images when attempting flash photomicrography:

#4 Post by viktor j nilsson » Fri Dec 30, 2022 9:14 am

It's not the shutter speed that freezes motion - it's the flash. The duration of the flash is extremely short when used at 1/8 power or less. What you need to do is reduce the power of the continuous illumination. Then set an exposure time that's long enough to trigger the flash (say 1/160s). The goal is to make sure that the continuous illumination adds as little as possible to the image exposure. In other words, with the flash off, you want the image to be almost totally dark. And then you want the flash to go off in the middle of the exposure, and provide almost all the light. You need to find the ISO setting that's low enough to keep the image dark enough with continues light, and high enough to let you use the flash at reduced power. (Full power is usually 1/200s or so, which is too long to freeze movement).

Alexander
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Re: Banding in my images when attempting flash photomicrography:

#5 Post by Alexander » Fri Dec 30, 2022 9:46 am

MicroMan2 wrote:
Fri Dec 30, 2022 7:16 am
I would like to know then what exposure times can freeze most motion. With this limitation in mind, I can only feasibly go to an exposure time of 1/250 sec with my camera.
1/250 is the fastest speed that opens the shutter fully on the 60D. Shorter times do not open the shutter fully which results in banding. The second shutter is closing in before the first one opened fully. That's how fast shutter speeds are achieved on DLSR's. A small window moves over the sensor. That results in banding because the flash burns only for a short time and the light hits not all of the sensor. This is getting worse with faster shutter speeds.

Use 1/250 on the 60D to limit the permanent light as much as possible and you will achieve your freeze. In case your objects are not frozen properly increase ISO to have the flash fire for a shorter period of time.

MichaelG.
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Re: Banding in my images when attempting flash photomicrography:

#6 Post by MichaelG. » Fri Dec 30, 2022 10:03 am

Alexander wrote:
Fri Dec 30, 2022 9:46 am

[…]

Use 1/250 on the 60D to limit the permanent light as much as possible and you will achieve your freeze. In case your objects are not frozen properly increase ISO to have the flash fire for a shorter period of time.
.

Spot-on, Sir … very succinct

MichaelG.
Too many 'projects'

MicroMan2
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Location: Canada,Alberta

Re: Banding in my images when attempting flash photomicrography:

#7 Post by MicroMan2 » Fri Dec 30, 2022 7:26 pm

Thank you very much for the input!

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