am i right in thinking that transformers can step up voltage to much higher levels?

if so then what is the point in voltage multipliers? they are pretty complicated in comparison so surely it is alot simpler to use transformers?

Transformers are fairly large, expensive, and heavy. It really depends on your application.

voltage multipliers supply a DC output. auch an output is not feasible with AC output of a transformer as you need very robust and likely large diodes to form a rectifier capable of handling the extreme voltages.

if the input in a voltage multiplier was DC, would you need the diodes?

if the input to a voltage multiplier was DC then it wouldn't work.

ok, whats the best way to greatly increase dc voltage?

depends on the application.

 

its like saying whats the best way to drive. its going to vary depending on what the desired goal is.

 

what sort of load will it be required to cope with , what variance in the voltage is acceptable, how restrictive are costs etc etc.

well basically i want to make an air ionizer but with a dc power supply

What is your DC supply voltage available, what is the ionizer output DC voltage desired, at what current and what polarity ( negative ions or positive ions ) ?