Image Circle of Petzval and Aplanat

**Richard K.** · 17-Nov-2011, 08:22

For a given focal length, say 10", I guess the Aplanat or a Rapid Rectilinear will have a bigger image circle than a Petzval?

That seems to be the case for me unless I confused the 2 negs I made of the same shot, one with a 10.5" Ross 1840s vintage Petzval, the second with a Grubb B or C (not sure which it is) Aplanatic of similar perhaps slightly longer focal length. The Ross produced an 8" circle on my 8x10 film ; the Grubb covered it without any fall-off.

I guess my question is: did I identify them correctly?

I can't get over how sharp these 155-168 year-old lenses are!!

**BarryS** · 17-Nov-2011, 08:44

Something seems fishy about a 10.5" Ross Petzval only producing an 8" image circle. Are you sure it's a 10.5" lens? Is there anything that could be causing mechanical vignetting? In general, Petzvals will illuminate an image circle very close to their focal lengths.

**Richard K.** · 17-Nov-2011, 08:55

Originally Posted by BarryS

Something seems fishy about a 10.5" Ross Petzval only producing an 8" image circle. Are you sure it's a 10.5" lens? Is there anything that could be causing mechanical vignetting? In general, Petzvals will illuminate an image circle very close to their focal lengths.

Hmmm. Thank you for pointing this out! What I did was make a couple of crude stops for it:

and attached them in the hood very close to the glass:

I guess this caused the vignetting; I'll try with no aperture disk and see if things imorove!

**goamules** · 17-Nov-2011, 11:11

Richard, you are right, a RR will give a wider angle of view than a Petzval, which is only about 20 degrees if I recall. An RR is more, and then the anastigmats even more. I was shooting a 6.5 inch Dagor last weekend that covered 4x5 easily, but a Petzval about the same length wouldn't.

**eddie** · 18-Nov-2011, 04:31

Originally Posted by BarryS

Something seems fishy about a 10.5" Ross Petzval only producing an 8" image circle. Are you sure it's a 10.5" lens? Is there anything that could be causing mechanical vignetting? In general, Petzvals will illuminate an image circle very close to their focal lengths.

huh?

a 10 inch petzval was probably originally designed for a format smaller than 4x6 inches. (as an example a dallmeyer 3b is an 11 inch lens and was designed for 4x6 inches.!

in today's accepted use of lenses and formats most 10-11 inch lenses are best suited for 5x7. i know that people use 11 inch petzval lenses on 8x10 but they are most always tight head shots with almost no DOF. a gimmick IMO. those shots are repetitious and boring. i am tired of seeing a 1mm shot of a persons face in focus and the rest falling off fast. this si what you get using a "under coverage" lens on a too large of a format. all comes down to proper tool, proper job.

as for teh OP question if he is seeing fall of i bet he shot a landscape (at infinity) Richard? whaddiyou shoot?

rat over.

if you are shooting 8x10 petzvals at landscape use a 16 inch lens already! or maybe a 14 inch lens.

here is a shot taken with a 14 inch f3 petzval on 8x10. not infinity but a full body portrait (it was actually a test shot). same lens at portrait distance.

16-18 inch petzval lenses are better for 8x10.

an 8-10 inch RR should do well on 8x10 stopped down....for a medium wide.

eddie

**goamules** · 18-Nov-2011, 07:24

Yeah, Eddie's right, you need a very long petzval for a good coverage on 8x10. Notice in my pic above, a 5" F3.6 petzval, it doesn't cover 4x5. It may barely have a 5" illumination, but about 1/3 of the edge is that darkening, super curved field, swirly nonsense some people love! So it's really a 3 1/2 to 4 inch image circle of usable image.

**Richard K.** · 18-Nov-2011, 08:06

Originally Posted by eddie

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as for teh OP question if he is seeing fall of i bet he shot a landscape (at infinity) Richard? whaddiyou shoot?

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wide.

eddie

You are right Eddie. I was shooting a cemetery scene but really just testing the lens and the Delta 100 film. Both of which I have fallen deeply in love with...ah to discover love again at my age...um....right...OK....
Man I can't get over how sharp this lens and the Grubb Aplanatic I also tested are!! The Grubb was sharp corner to corner on the 8x10 film!

**Richard K.** · 18-Nov-2011, 08:19

Addendum:

So, Eddie, are you saying that to get a Petzval that covers 8x10, it may not fit on a Sinar board? What focal length to cover 10x12 - about 18" I guess?

Seriously, after playing with just those two lenses, I can see why so many of you have big brass ones!

**cdholden** · 18-Nov-2011, 08:32

The problem with a Sinar board is that you may not get a fast petzval. There are some out there f5.6, f7, etc. I think Richard Rankin picks them out of the trees. He seems to find lots of them. Finding the ones f3-4 are going to much larger, limiting your options to the 5.5" square board..
Check out a 14" Vesta. It's f5 and is a "modified petzval", but I'm not sure of the flange diameter. If it's close, SK Grimes may be able to make a custom (thinner) flange to mount it with. I've got the 11.5" and it will fit on a Sinar board (just haven't done it yet), but Wollensak shows it for use with whole plate.

**BarryS** · 18-Nov-2011, 09:49

I stick by what I stated--In general, Petzvals will illuminate an image circle very close to their focal lengths. There's a world of difference between illuminating an image circle and providing good coverage. What people consider adequate coverage for a format with a Petzval varies considerably.

Richard stated that the Ross produced an 8" circle--referring to the illumination circle of the lens. His homemade stops placed against the front element are very likely mechanically vignetting the image circle.