How do you get from photo to canvas?

[Garth Herrick]

I have a large sheet of home made carbon paper, I use over and over. It's a sheet of tracing paper rubbed over with a conte crayon; occasionally it needs renewing. Over this I position a photo reference printed on very thin paper, over the photo I place a very thin sheet of acetate to protect the photo reference, and through all this I trace with a glass pen for sharp clean gray lines. This process works best on an oil primed canvas, as the lines need no fixing whatsoever.

The main downside I find for myself is if I draw in too much minute detail, it tends to hamper being able to paint broadly at first because I am worried about losing/hiding all the traced lines.

Another approach which seems to avoid this problem is the technique Thomas Eakins apparently used. He simply placed a small dash or line to mark an edge, corner, or peak of a curve, and connected all the dots as he painted. This way you can paint broadly at first, and hone in on the detail by eye later.