I am getting ready to start another big camera. The customer has a 6D already. The catalog I have says the coverage is 18x16 with a 19 1/2" F.L. Will it cover 20x24? Does the F.L. seem correct?

www.guillorycameras.com

The focal length of a 6D is 24", 19 1/2" is the back focus.
Only experiment will show how well it covers 20x24.

Seán

"Focal gan fada, focal gan ciall"

I wouldn't think that a Petzval would cover a plate much larger than it's FL, except maybe at very close distances. I bet he could use it for the times when he is shooting a smaller plate with a reducer kit and then just use the front element alone when he'd need some real coverage. Just a thought. After all, 8D's don't fall into one's hands too often

I think a question that one has to ask is, what kind of photography is the camera going to be used for?

Portraiture, landscape, groups, still life?

Proper portrait lenses for 20x24 are almost nonexistant, Dallmeyer's D range are really designed for groups and views.

Voigtlander did produce some very long focus Euryscopes at f4.5 in the 1880s, but again, I don't think I have ever seen one on ebay for this kind of plate size.

The cheapest and most practical choice would be, IMHO, a Rapid Rectilinear.

Suitable ones do exist, I sold a 20x24 RR several years ago.

Seán

"Focal gan fada, focal gan ciall"

I use a Dallmeyer 16x18 RR on my 18x22 and it works fine stopped down without falloff.

Ill bet that lens would be fine as long as you like fall off. If not Sean is right. Get a RR.