petzval focus shift?
Hello all knowledgeable souls,
I have just taken delivery of my beautiful 12x10 twin sliding box camera with an 1855 petzval 18 3/4" f4 lens. I have been told to expect a focus shift if I load panchro film into the back. How pronounced will this be, and can I just stop down (well, waterman down) to cover the shift?
Will the shift be constant for different subject distances?, and would I still have the shift if I used ortho film or paper?
Thanks for your help, as ever,
Early Petzval lenses suffered from terrible chromatic aberrations; Since daguerreotypes are only blue sensitive this was less of a problem than it would be today with panchromatic film, but there was notable focus shift. By the mid-1840s most Petzval lenses had been redesigned (achromatized?) which reduced chromatic aberration, and removed focus shift. Now, the adjustment was for ortho materials so there may be a residual affect.
I have used Petzvals from the 1850s with modern film and have not noticed any focus shift. I have seen some banding and other signs of chromatic aberration. Of course these lenses were ground by hand, so each is unique and has its own "personality" (read; aberrations)
ps: are you sure the lens is really from 1855? 10x12 would be a pretty rare size in the 1850s.
The lens was not originally designed for 10x12, that is the size of camera I have had built around it.
Encouraging news, thanks.
In case, I guess you can adapt a blue filter to fit the lens and emulate a "blue&UV-sensitive" film.
Hmmm ! This thread has sparked my interest as I have several Dallmeyer Patent Portrait lenses (waterhouse stop versions) from a 3B to a 6D from the 1860's as well and three earlier Lerebours et Sectretan petzval lenses (no aperture adjustment less a brass cap that fit's over the front element with a smaller hole in it on one version ) from the approx 1840's and 1850's. Coverage of the Lerebours ( again I have three--2 small and one rather large) is yet unknown but I estimate about 8 inches in FL for the smaller ones. The large Lerebours et Secretan will hopefully have enough coverage for 8x10 but is yet unknown and has a FL of about 290 mm from the rear cell and the lens is about 9 inches in physical length. It is a real beauty!!
I have an old CC Harrison made around 1849 and the focus shift when shooting wetplate on it is pretty significant, I usually focus 1/4" or more past what I want to be sharp and that works. With film there's not much focus shift since modern film is pan.