If my understanding is correct, crop factors can be applied wherever you want to apply them. Going from FF to DX requires a crop factor of 1.5, which is a ratio used to give the equivalent focal length, aperture and possibly other equivalent values, where the FF values provide the reference point.

Going from MF to FF would also require a crop factor, which in this particular case would appear to be 3.5. However, if you wish to continue the practice of using FF as the reference point, the process you would be looking at would be going from FF to MF rather than the other way round, in which case the 3.5 would have to be inverted - i.e. 1/3.5.

According to my 23 year old Casio calculator (still going strong), that gives a factor of 0.286. Applying that to the 150mm lens, it would have an equivalent focal length of 42.9mm (before anybody says "focal length is focal length", I'm referring to the 35mm equivalent focal length). In other words it would provide the same angle of view as a FF lens with a focal length of 42.9mm - which is something a bit wider than a FF nifty fifty.

I am just wondering what the reason is for not downloading a poster's photo and showing what you mean when critiquing it. When teaching painting and drawing, I hardly ever worked on a student's drawing, and if I had to, I erased my work. A person's work is theirs only. However, in digital photography, the original would not be altered if I copied it and showed what I meant.

I would much prefer someone show me exactly than have to hope I've translated their words properly in a critique.

Am I missing something?