[Rol]

I bought a flash diffuser to plug into Sigma 500 DG super flash head, I found the TTL pre-flash metering become inreliable, some time over expo a lot but some time under. Generally my setting is :

EV -1 at flash,
A / S mode at body (Pentax DS)
Flash zoom head is manually fixed as 28mm (if let the flash head auto zoom according to the lens, flash output is more inreliable)

Sometime I prefer to give up TTL and turn to use manual flash mode, or simply give up the flash diffuser

Isn't it 500 DG super too bad, or my setting is incorrect. I see many C Hing using SB800, 580ex with flash diffuser, they seems don't need to frequently adjust the flash output with the flash diffuser !!

Thanks for any input.

Philippe Hing, any advice ??

[Philippe]

點解你會問我既?
我冇用呢支Sigma閃燈,不過用TTL pre-flash應該係唔駛理個柔光罩的.我都有用柔光罩都係唔駛理佢的.
你係咪試過如果唔用就冇事呢?
但係我覺得用唔用柔光罩都係要成日將閃燈補償調來調去的.主體大小,顏色,測光模式等等都會影響閃燈輸出.要排除這些變素,可以試下用點測光或影大一點的主體,盡量塞滿畫面,也選顏色中性一點的物件測試,咁閃燈輸出就應該好穏定.如果咁都唔準,就有可能係支燈有問題.

[micros]

如果問題只係加o左罩後出現﹐可能係柔光罩物料太厚/太深色﹐部份 pre-flash 因此而消耗。
正因為咁﹐閃燈測光以為唔夠光﹐於是就出大力o的﹐出o黎就 over。

[Philippe]

但這正是pre-flash TTL設計原意.柔光罩厚了閃燈就會自動加強輸出,用者該不用操心.

[micros]

pre-flsh 好薄a3﹐如果柔光罩太勁﹐block 晒 pre-flash 就會出問題。