Wrong, Jack.
O says it takes a time of d/c for O' to go from O to the burn mark, remember?
And SR tells us that O' says it takes a time of d/cλ between O' passing and the burn mark passing.
Almost. In this case v is in the opposite direction to the positive x direction, so t' = (t + vx/c²)λ
Let's see where that takes us. The burn mark meets O' at:
$$t = d/c$$
$$x = -vd/c$$
Now let's find t':
$$t' = \gamma(t + \frac{vx}{c^2})
$$t' = \gamma(d/c - \frac{v^2d}{c^3})$$
$$t' = \gamma \frac{d}{c}(1 - \frac{v^2}{c^2})$$
$$t' = \gamma \frac{d}{c}(1/\gamma^2)$$
$$t' = \frac{d}{c\gamma}$$
What do you know?
t' = d/cλ, just like we said.$$
$$
I am OK with your calculation.
It is consistent with the fact that the light beam in O' starts at O' and ends up a distance d/λ from the B< which has been my point all along.
What do you know?
However, when O' moves to the BM, the O from has the light beam d + (v/c)d down the x-axis.
Note the disagreement.
I have a different way to put it. Let me see what you do with this.
Assume the standard configuration using O and O'
Each agree in their own frames they will start a clock at co-location and stop the experiment when the time reaches an agreed upon d/c where d is some chosen agreed value between the two.
When the experiment ends, they mark a measuring rod in their own frames only describing the positions and distances.
Here is what O marks.
BM-------(v/c)d-------O>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>d
Here is what O' marks.
O'>>>>(v/c)d>>>>O>>>>>>>>>>>>>>>>>>>>>>>>>d
They get back together after the experiment with their rods in the same frame and compare them.
BM--------(v/c)d--------O>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>d..Measuring rod of O
O'>>>>>(v/cd>>>>>O>>>>>>>>>>>>>>>>>>>>>>>>>d..............................Measuring rod of O'
By matching up O and O', they find two different light paths.
All is consistent with SR with the following conditions met in each frame.
1) Light is measured c in each frame
2) The light emission point in the frame is located at the observer in the frame.
3) O and O' are separated by their relative motion caused by v. While light moved d, the frames diverged by (v/c)d
4) Light travels d in ct.= c(d/c)
Hence, SR is the theory of two different light paths.$$