If a TTL and a non-TTL flash are strapped together in a softbox, will TTL expose correctly?

I have recently sold all my Yongnuo speedlite kit and bought into Godox, for their integrated radio system.

I have, so far, an AD200 strobe, a TT685-F speedlight and an X1T-F controller (Fuji system). All work absolutely flawlessly together, but I could do with another speedlight, at least until I can justify a second AD200 😉.

My quandary is, should I get another TT685 (TTL)? or will the TT600 (non-TTL), at half the cost, suffice?

I expect to use the two speedlights, strapped together, in a modifier on those occasions that I need a bit more grunt as a fill/edge light to compliment the AD200.

If used thusly, will TTL calculate the flash exposure correctly if one speedlight is non-TTL? In other words, will it compensate for the lack of adjustment? Or should I bite the bullet and stop expecting miracles, even from this excellent system?

2 Answers
2

What you want to do will not work. Here's why:

If you want to use TTL and non-TTL flashes together in this way, it's probably time to learn how to use all of them by controlling the power manually. TTL is far from perfect. It is useful in situations that are changing rapidly, such as event photography where the subject distance may be changing constantly.

In a situation with a fixed modifier you're almost always better served to set the power manually for the sake of consistency from shot to shot. If you are using the modifier in a more 'run-and-gun' setting, such as the dance floor at a wedding reception, then you need to use two TTL flashes in the modifier so that both of them fire and are accounted for by the camera during the calculations made between the pre-flash and the main flash when the shutter opens.

You are basically asking two questions here.

The answer to one question is; no having a TTL and a manual flash in the same modifier won't work properly. When the camera is doing the TTL measurements, it does not know the second flash is there. During the actual exposure the camera is surprised with extra light, and the shot will be over-exposed.

The other question is, should i buy the TT685 or the TT600. Definitely the TT600 (or two of them, if you want to spend some money).

There are two reasons:

1) If you have a multiple light system, you usually have a subject that does not move a lot and you have time to set flashes manually. In those cases manual is more suitable because it is more consistent.

2) It is generally not very useful to have more than 2 TTL flashes, because TTL works by measuring flash light reflected of the subject. If a flash is behind, or on the side of the subject, TTL does not work well because there is little light reflected on the subject towards the camera.

It is my opinion that one TTL flash is almost essential, for those times where you don't have time time to set it up manually, like a party. Two of them could be useful in some quite unusual circumstances, but more is definitely not useful.

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