Jump to content


Photo
- - - - -

Auto exposure?


  • Please log in to reply
2 replies to this topic

#1 tc_rain

tc_rain

    Sea Nettle

  • Member
  • Pip
  • 14 posts

Posted 17 November 2011 - 07:14 PM

I am trying to understand the difference and the advantages / disadvantages of using an electrical sync cord over a fiber optic cable on a point and shoot camera. The camera housing is an Olympus PT-030. It has an Inon bayonet mount where the fiber optic cable just pushes through a bushing in front of the onboard camera flash or I could get a Heinrichs Weikamp replacement bulkhead . I will be attaching a S&S YS-110a. If I use the sync cord and the Heinrichs Weikamp replacement bulkhead will I get somewhat of an auto exposure with it for macro shots? With the fiber optic cable will my only option be to manually adjust the power settings to control the flash intensity? Sorry, I am really new at this and the articles I read just confused me further I think.

#2 rtrski

rtrski

    Great White

  • Member
  • PipPipPipPip
  • 1000 posts
  • Gender:Male
  • Location:Texas, USA
  • Interests:Slowly learning digital photography and underwater digital photography. Like drinking from a salt-water firehose... ;-)

Posted 18 November 2011 - 01:38 PM

With the H-K you should (I believe) pick up "TTL" capability thru the electrical sync. However...for macro, TTL often doesn't help.

TTL works by giving the strobe a 'quench' signal to truncate the flash before it's been on for it's full duration, but once it thinks the light thru the lens is enough to properly expose the selected region (spot, etc). And at macro distances, the subject is so close, the quench can't happen fast enough.

With fiber optics, it is possible in some situations to get an effective TTL behavior - Inon strobes for example can perfectly 'mimic' your onboard flash's preflash/flash/quench times. I don't know if that's true of the Sea and Sea's. But again...for macro type distances, regardless of whether you're getting an electrical or optical 'TTL' imitation...there's just not time to damp down the strobe before the subject gets overexposed, and as such manual control is usually the way to go, anyway.

Current rig: Sony SLT-alpha55 in Ikelite housing, Sigma 105mm f2.8 DC Macro w/ Ike 5505.58 flat port or Sigma 8-16mm f/4.5-5.6 DC HSM behind UWCamStuff custom 5" mini-dome. Dual INON z240 Type IVs triggered with DS51 for TTL mimicry, or DS51 alone with home-made ringflash assy for macro.

 

Topside, unhoused: Sony SLT-alpha99, Sigma 150-500mm + 1.4TC (Saving for Sony 70-400 G2), Sigma 15mm diagonal fish, Sony 24-70mm f2.8 CZ, Tamron 180mm f2.8 Macro...all the gear and nary a clue...


#3 tc_rain

tc_rain

    Sea Nettle

  • Member
  • Pip
  • 14 posts

Posted 18 November 2011 - 02:29 PM

With the H-K you should (I believe) pick up "TTL" capability thru the electrical sync. However...for macro, TTL often doesn't help.

TTL works by giving the strobe a 'quench' signal to truncate the flash before it's been on for it's full duration, but once it thinks the light thru the lens is enough to properly expose the selected region (spot, etc). And at macro distances, the subject is so close, the quench can't happen fast enough.

With fiber optics, it is possible in some situations to get an effective TTL behavior - Inon strobes for example can perfectly 'mimic' your onboard flash's preflash/flash/quench times. I don't know if that's true of the Sea and Sea's. But again...for macro type distances, regardless of whether you're getting an electrical or optical 'TTL' imitation...there's just not time to damp down the strobe before the subject gets overexposed, and as such manual control is usually the way to go, anyway.


Thanks for the reply. Earlier today I found a great site (www.uwphotographyguide.com) that really helped explain things that I could understand.