Is this use of optocoupler wrong?
You did not provide a datasheet link or a part number for the opto, but I can make some educated guesses. First, the 470% CTR is a suspiciously high number as a guaranteed minimum at 5mA LED current for a phototransistor output isolator. If it's actually a Darlington output, then you'll need to modify the circuit to get to work reliably as the saturation voltage will be too high. 

Suppose it's something like the excellent FOD817D (the D is important) which has a CTR range of 300-600 with 5mA in. That is specified with Vce of 5.0V and you require less than 0.5V for it to work reliably. The effective CTR will be much lower. Figure 3 shows you that you can typically expect it to handle 2.5mA at the output (good design will add a substantial amount of margin for aging, temperature and unit-to-unit variations, so maybe 0.8mA is safe). You are at 250uA, so the particular part I mention should be more than okay. 

Suppose you are using a Darlington type or an optoisolator that is not as high performance? 

Well, you need to add some voltage drop between the optoisolator collector and the transistor base. Since you have plenty of voltage (12V supply) and the optos are specified at 5V, you could insert a 5.1V zener diode between the opto as so..







simulate this circuit &ndash; Schematic created using CircuitLab

The Vce of the opto is about 5.6V at the threshold, and the zener diode I suggested has a 5.1V breakdown at 50uA (the circuit switches at about 60uA) so all the parts are well specified. Nominal base current is similar to your circuit, about 180uA. You'd really like to see more like 2-4mA maximum for the transistor to be well saturated, so maybe you can increase the 1K to about 3.6 to 5.2K. If you really need the 1K then increase the base current using the method I illustrated above, use a MOSFET or darlington or a really high performance BJT. 

TL;DR: There are a couple of things that look marginal in this circuit, the real optoisolator drop at saturation and the base current of the output transistor. They both should be fixed.