[Rob22315]

Go old school - get a flash meter and meter your flash exposure, then use the settings from the meter manually entered in M mode.

[dragra]

Go old school - get a flash meter and meter your flash exposure, then use the settings from the meter manually entered in M mode.

This way OP might get the right exposure, but not the expected result. He would like to use f1,7.

[Tanzer]

Thanks for all of your replies. That is sad but nothing seems to help with this.
I will try with an external flash.

If you are going with an add-on light, you may have better luck using one of those LCD panels that offers continuous lighting, so you can meter in advance. Just turn it on before you hit the green button, and everything will fall into place.

The LCD panels don't have a lot of power compared to strobes, but at f/1.7, that is a benefit. Not sure what you are trying to photograph, the ambient lighting conditions, if you intended to balance your subject with the ambient, etc.