Which pen wrote which?
Can you tell the difference? Can you guess which pen I used in writing specimen 1 and 2? What's really the difference in using oblique pen and straight in Copperplate script? Can we use straight pen in writing slanted script like Copperplate and Spencerian? You may have observed that the shades in 1 is thicker than 2 making the entire length of the name longer as well.. But apart from that and looking from afar, not much difference, right?
Zooming in a bit.. We can now observe that the shades in 1is more defined than in 2 and you can now see the "ragged" edges on the right side of the shade better. Why so? It is because of the reason that 2 points of the nib forming the tip must be parallel to the slant you are working on for it to yield crisp edges.
I'm not saying that using oblique holder will never yield that ragged edge -- it can also result to that if the nib point is not parallel to the slant as well BUT it would mean less wrist adjustment and paper adjustment if one is using an oblique.. The very reason why the oblique pen was created.. Having said those.. The answer to question 3 is YES. You can use both oblique and straight pens in writing slanted scripts like Copperplate but if you're very particular to crisp edges and ease of writing slanted scripts and want to achieve both, OBLIQUE PEN will work better for you. I have seen great calligraphers use straight holders in Copperplate but it's never without ragged edges or more bending at the wrist when writing. But then again ... It's a matter of preference and what works well with you. I hope this helps.
Gail here crash blogging at The Curious Artisan.