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05-20-2018, 08:52 AM   #1
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Image ghosting when doing water splash photography with K-1

Hi, I've just been doing some water splash photography and had rather unexpected results.

My camera is a K1 set to record DNG to card 1 and JPEG to card 2 and is in manual mode with IS and most other options turned off such as (lens correction, AA sim, d-range, noise reduction etc). I just want the camera to take images without any intervention and all sort any issues later in post.

For the first image (IMGP0052.jpg) the camera was set to iso100, 70mm, f8, 1/125 with the HD Pentax-D FA 24-70 f2.8 lens fitted, the Yongnuo 560III was set to 1/128 (minimum) power so the T1 time is pretty quick (1/23041), a fake ice cube was dropped into a glass of water and an image taken. However the water splashed seem to have a ghost, there is one bright image and then offset from this is a darker version. The distance of the offset is not consistent, some are further apart than others, also the ghost are not exactly the same shape. Looking at the ghost images its as if the camera took two images a short time apart and thats why the water droplets have moved (gravity) and are a slightly different shape. The glass however is perfectly sharp with no ghost.

I took a second image (IMGP0060.jpg) iso100, 160mm, f8, 1/50 with the HD Pentax-D FA* 70-200 f2.8 with a blue gelled background but with the same speed light power (1/128) and had the same ghosting result so I feel its not a lens issue. I also tried turning IS ON, no change so switched it back OFF.

Does anyone know whats happening?, is the camera recording some kind of internal reflection, is it related to the shutter mechanism? or is it due to internal processing on the camera?. Any help greatly appreciated.

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05-20-2018, 09:13 AM   #2
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QuoteOriginally posted by johngreenphotography Quote
Hi, I've just been doing some water splash photography and had rather unexpected results.

My camera is a K1 set to record DNG to card 1 and JPEG to card 2 and is in manual mode with IS and most other options turned off such as (lens correction, AA sim, d-range, noise reduction etc). I just want the camera to take images without any intervention and all sort any issues later in post.

For the first image (IMGP0052.jpg) the camera was set to iso100, 70mm, f8, 1/125 with the HD Pentax-D FA 24-70 f2.8 lens fitted, the Yongnuo 560III was set to 1/128 (minimum) power so the T1 time is pretty quick (1/23041), a fake ice cube was dropped into a glass of water and an image taken. However the water splashed seem to have a ghost, there is one bright image and then offset from this is a darker version. The distance of the offset is not consistent, some are further apart than others, also the ghost are not exactly the same shape. Looking at the ghost images its as if the camera took two images a short time apart and thats why the water droplets have moved (gravity) and are a slightly different shape. The glass however is perfectly sharp with no ghost.

I took a second image (IMGP0060.jpg) iso100, 160mm, f8, 1/50 with the HD Pentax-D FA* 70-200 f2.8 with a blue gelled background but with the same speed light power (1/128) and had the same ghosting result so I feel its not a lens issue. I also tried turning IS ON, no change so switched it back OFF.

Does anyone know whats happening?, is the camera recording some kind of internal reflection, is it related to the shutter mechanism? or is it due to internal processing on the camera?. Any help greatly appreciated.
Forgot to mention there I was using two speed lights, one to the left side of the glass to illuminate the glass and another also on the left but pointing towards the backdrop. Both speed lights were fitted with Good X1 receivers and were triggered using Godox X1 hotshoe mounted trigger. This was a photo workshop with Canon, Nikon and Sony but none of the other cameras showed the same ghosting issue.
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05-20-2018, 09:15 AM   #3
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The normal explanation for ghosting is too much ambient light - what was the situation in your set-up here?
05-20-2018, 09:44 AM   #4
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QuoteOriginally posted by johngreenphotography Quote
Forgot to mention there I was using two speed lights, one to the left side of the glass to illuminate the glass and another also on the left but pointing towards the backdrop. Both speed lights were fitted with Good X1 receivers and were triggered using Godox X1 hotshoe mounted trigger. This was a photo workshop with Canon, Nikon and Sony but none of the other cameras showed the same ghosting issue.
Welcome to the Pentax Forums!

Assuming all cameras were using the same exposure settings, the obvious blame would go to the lighting (not the camera's fault). That being said, what the examples show is not classic ghosting. Instead, it almost looks like two separate exposures (one flash and one not) taken a short time apart. Do you have an out-of-camera file to share? Such would have intact cameramaker information in the EXIF including whether a composite mode was being used.

May I also ask how exposure was being triggered and which variant Godox X1 (O, F, C, or N) was being used?


Steve


Last edited by stevebrot; 05-20-2018 at 09:55 AM.
05-20-2018, 10:04 AM   #5
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Perhaps the two flashes were set to different modes or did not trigger at the same time.
05-20-2018, 11:38 AM   #6
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QuoteOriginally posted by photoptimist Quote
Perhaps the two flashes were set to different modes or did not trigger at the same time.
After a little experimentation on my end, something like that is what I am thinking. The spacing is too close for composite. I am wondering about the setup of the X1 TX and the group configurations.


Steve
05-20-2018, 11:49 AM   #7
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QuoteOriginally posted by johngreenphotography Quote
Forgot to mention there I was using two speed lights, one to the left side of the glass to illuminate the glass and another also on the left but pointing towards the backdrop. Both speed lights were fitted with Good X1 receivers and were triggered using Godox X1 hotshoe mounted trigger. This was a photo workshop with Canon, Nikon and Sony but none of the other cameras showed the same ghosting issue.

My guess is slight delay in when the backdrop flash was firing.



In your first sample, the brighter half of each ghost pair is from the flash aimed at the water, and the darker ghost is the flash aimed at the backdrop. That's assuming the frame was not rotated - it looks like water was sprayed sideways with gravity carrying the drops downward.


It's less obvious in the second sample photo because slower exposure speed allows more time for the drops to move, leaving more separation between ghost pairs. This time the bright ghosts are below their dark siblings, suggesting that the drops were splashing upwards if you had the same flash delay as in the first photo.
05-20-2018, 12:02 PM   #8
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the ghost drops are lit from a different angle suggesting some synching issue with your triggered lights. start there. good luck.

05-20-2018, 12:03 PM   #9
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QuoteOriginally posted by photoptimist Quote
Perhaps the two flashes were set to different modes or did not trigger at the same time.
I like this explanation (different trigger times) - accounts for the different separations between various blobs and slightly different shapes. Would also explain why the (stationary!) glass is sharp.

Can you do it again? If so, try a shot with just one light!!

Do you have any way to make high speed light measurements? If so, you should be able to see two separate flashes. I have measured optical flash response time (i.e. one flash triggers the second one with its light flash) to be tens of microseconds.

How is the initial exposure triggered?
05-20-2018, 12:13 PM   #10
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Thanks All.

ffking - the ambient light was low, we were in a studio with blacked out windows etc, so the speed lights were the main source of light.
stevebrot - the images are crops from the original .DNG files, there was no compositing used, the EXIF info showing up on these images above seems to be correct. I couldn't say what variant the X1 was, the studio owner is a Canon user though.

I think the main conclusion is the background speed light even though it was on a wireless trigger on the same group/channel as the glass speed light was still firing a fraction of a second later. As DeadJohn noted in the first image the water droplets are falling, so the darker image is below. On the second image the water was still rising out of the glass so the darker image is above. Shutter speed shouldn't have too much of an influence, the point of the slower shutter speed is to show that its the flash T1 duration that will freeze the action, shutter speed is predominately there to influence the ambient. To me the distance offset of the darker image between the two images is fairly comparable, plus I think its dependant on where the water is in its cycle, for example has it reached as high as it can and is about to start falling down etc.

I think for future I may look at some PC sync cables, or a continuous light for the background. One thing that was mentioned during the workshop was that if two speed lights are used, they need to be at the same power otherwise it starts producing black lines?, unfortunately we didn't have time to explore this...something for next time.

Many thanks everyone for you input, for a little while I though my K-1 was having a bad day :-( but the sync issue seems the most logical.
05-20-2018, 01:41 PM   #11
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Pixel shift is off?
05-20-2018, 11:35 PM   #12
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Yep I think sync is slightly deferent with your two flashes.
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