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Strobe and exposure

strobe; position; exposure

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#1 Trwen

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Posted 05 July 2014 - 03:46 AM

My set up is: Canon S120, Canon housing, single Inon 1200S strobe mounted on 2 x 5" arms, Fantasea Nano focus LED mounted on cold-shoe top of housing.

 

Issues are: diving in fairly murky water (meaning a lot of floating plankton and debris) and this year, due to violent storms in spring, vis around 3-5m max. 

 

Current settings on camera are Manual, Auto focus on, ISO 100, f6.3, shutter speed 1/500, point AE focus, minimum flash power. On strobe the setting is Manual, with magnet in, and flash strength 5.5

 

 Exposure problems - the top third of a lot of photos is over exposed. I've read loads (feeling quite confused) about single strobe positions for macro pix and understood that the closer the subject, the closer the strobe to the camera - this makes sense. However, this does seem to produce a hotspot or flare (not sure which).

I've attached a typical photo with above problems

 

I am also having problems with backscatter - due I'm  sure to positioning of strobe.

 

I have heard that you set your camera settings before you go in and alter exposure for different shots with the strobe strength..is this the best place from which to start?

 

I tend habitually to take macro shots from around 3-6" away, most often on short animal turf on rock/boulder, aim the focus light directly at subject and use my focus light with shutter halfway pressed down to focus the camera lens ...and from there on  I'm lost about how/where to focus the strobe (which doesn't have an aiming light). Can anyone draw a diagram for me from which strobe position and distance from camera to start, given all the above criteria? When sites mention angles of 45degrees, they fail to mention 45degrees from what.

 

I know I'm probably asking too much but some help would be greatly appreciated! IMG_0881.JPG

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#2 ChrigelKarrer

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Posted 05 July 2014 - 05:24 AM

Trwen,

welcome aboard!
 

1° Problem: Hotspot
    There are two possible solutions, the focus light or the strobe itself
    The white hotspot is most likely the light from your Nano LED focus light, even if this focus light should switch off when you take the picture but
    something probably don't work well.
    If the same issue occurs when you don't use the focus light it is the position of your strobe and only the lower intensity border of the strobe beam hit the coral

    while the center of the strobe beam hit above and lead to the overexposed area.

 

2° Problem: Strobe positioning
very near macro with a external strobe (if not a ring strobe) is difficoult using 1 strobe only as he has to be positioned very near the port.

     Using only 1 strobe in a 45° angle mostly lead to ugly shadows of the opposite side of the motive, positioning it above may work better.

 

3° Problem: Backscatter

     To reduce backscatter you need to position the strobe(s) at a 45° angle regarding the lens and as far out as possible so

      that the motive is hit only by the borders of the strobe beam

          

           \   o    /

o=Lens     \ + / = strobe(s)

 

 

Remarks:

- why don't you use sTTL? The S120 and the S2000 should work perfectly together using Tv or Av, Av to control depth of field, Tv to control dark backgrounds

- play with the exposure control settings: matrix, center weighted or spot  to see what gives you the best results

- backscatter and macro is difficult to control, photoshop is your friend ...

- If viz is good, the mix of the internal strobe and a external strobe can lead to very nice pictures

 

Chris


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#3 timthefish

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Posted 05 July 2014 - 08:58 AM

That focus light should not cause a hot spot, I have the same one and don't have any problems. It looks more like strobe aiming to me but I am no expert. What was the ambient light like, how deep were you? I dive in similar conditions and with a compact. Yesterday I had to be at f8 and 1/800 and strobe power around 1/4 or it was blown out.

#4 Trwen

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Posted 05 July 2014 - 09:31 AM

Yes, first things first...I'll try next with my focus light out and see if it replicates problems,  in similar conditions.

I take your point about the strobe focus being too far above and therefore being too bright for the background.

Can't afford 2 strobes and a lot of my fellow divers seem to only use one, so will have to keep trying for the moment.

OK, I see what 45 degrees angle is meant.

Thanks very much

 

 



#5 Trwen

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Posted 05 July 2014 - 09:38 AM

Timthefish

OK, I did check that the focus light went out and it did -   I had that problem before and it was due to my focus light not 'seeing' the strobe either due to low batteries in focus light, or angle of strobe to focus light. That seems to be working now.

I think what I'll do is alter strobe power for the moment....

We weren't very deep (12m) and ambient light meant I could easily see things without a light...so inference is I had the strobe on too high power.

Tomorrow will tell.

Thanks



#6 timthefish

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Posted 05 July 2014 - 10:21 AM

Have you tried your kit on the comfort of your own home? Try in a darkened room that will allow a bit of practice, set up a little model and snap away. I think it is because of the ambient light and strobe aim. If it is really bright underwater just use the strobe to get the colours back. I would be surprised if you were using more than half power even at 1/500

#7 samplin

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Posted 05 July 2014 - 11:19 AM

I looked at the EXIF file and you shot this at 1/1000 of a second at f6.3 woth ISO 100.. 

There is no way the focus light could be that strong to blow out that much..

 

My guess is strobe power and loaction..

 

Joe


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#8 cneal

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Posted 05 July 2014 - 12:55 PM

Can the camera and strobe sync at 1/1000? Most cameras can not. I would suggest trying a more normal 1/200.

 

I looked at the EXIF file and you shot this at 1/1000 of a second at f6.3 woth ISO 100.. 

There is no way the focus light could be that strong to blow out that much..



#9 samplin

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Posted 05 July 2014 - 01:41 PM

You are thinking about cameras with moving shutters. I  pretty sure the S series have electronic shutters 

I have a S100 and shoot at high shutter speeds to drop the background to black on macros. 


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#10 Nautilus Cairns

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Posted 05 July 2014 - 08:55 PM

I have an S95 and like the S100 it can shoot with a strobe at high shutter speeds. I also have S2000 strobes and I would say that you may have the strobe power  too high when you are only 3" to 6" from the subject or maybe the strobe is too close to the subject.

 

I suggest for shooting macro  you try using STTL with  the strobe output strength at the C position on the EV controller. Try it in different positions but only change one thing at a time and look at the results. You will need to have the camera flash settings set to maximum so the strobe can set the strength through STTL.

 

Also suggest you close down the aperture to f8 to maximise depth of field.

 

Try playing around at home like Timthefish suggests, but don't fire off too many flashes in quick succession out of water. (see the Inon manual).


Edited by Nautilus Cairns, 05 July 2014 - 08:56 PM.

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#11 Trwen

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Posted 07 July 2014 - 07:00 AM

Timthefish

Yes, I have done a lot of playing about in a darkened room at home. Yesterday I tried again at both 30m and 8m and I think you're right that I have the strobe on too high as even at 30m I got some white outs.....I did try turning it down, but then the review photo looked too dark. If I have to have an error, which is best, over or under exposed?



#12 Trwen

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Posted 07 July 2014 - 07:08 AM

Samplin

Thanks for that...I have eliminated the focus light as an issue yesterday, so now I know it must be my strobe strength or position! Unfortunately yesterday I was not diving with people who wanted to hang around while I played with different settings (non-photographers), so I had to grab what I could; I left the settings the same and merely changed angle and position of strobe. Slightly better on some, so now I need to power down on the strobe. I see others have suggested different settings and will reply to them too.



#13 timthefish

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Posted 07 July 2014 - 01:17 PM

Difficult I would go for under exposed but it's down to choice of subject. Sometimes they make nice black and white shots or moody shadows. Should not take too much fiddling to get it right though. I used some simple things to start me off. I set a shutter speed to either freeze it or isolate it. Aperture to set depth of field, big number big dof small number small dof. Then imagine pointing a torch at the subject to highlight it's best attributes. All you need adjust is the strobe power. Adjust one thing at a time and review the changes, once you understand the effect of the change you will be well on the way. I am no expert but this last couple of years my pics have improved massively. I have practiced and read a lot. I did a lot of practice in a darkened room as the weather was so bad I couldn't dive

#14 Interceptor121

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Posted 07 July 2014 - 11:52 PM

Two suggestions - 1 close the aperture to f/8 second the strobe power is too much. Out the strobe right on the port aiming forward and start from the minimum until you expose correctly 5.6 is too high due to close distance you are looking at two stops reduction at as minimum so from 4 going down as you have a highly reflective bottom. In doubt is better to have a darker picture than one with blown highlights

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