Assymetric Tilts

[KJK]

I know this has been gone over many times before, and I understand the theory of Assymetric tilts. But what I can't figure out is how Sinar gets them to work on their cameras becasue the tilt mechanism is entirely below the film plane and therefore seems more like a base tilt than an assymetric tilt, which I would assume should be located at some point about 1/3 the way up from the bottom of the lower edge of the film.

If a person wanted to incorporate these assymetric tilts in a camera, is there a mathematical formula for where the pivot point has to be, what the arc of that pivot has to be, and then where the focus point are on the ground glass?

 

[rusty71]

WHOA! It's late, and glancing over recent posts, my tired eyes deleted the "L" in your subject line....
Sorry, wish I could help you out with the Sinar. But thanks for the giggle.

 

[plungefrog]

The Sinar tilt axis (on the P/P2/X series) is indeed located 1/3 of the way up the focus screen.The mechanism uses a geared drive which is located in an arc described by the base of the standard.The drive is self-arresting,the tilt axis does not require a support of its own.The location of the arc is largely dictated by the size of the standard.Some models of Sinar (the Norma for example) have ordinary base tilts.

 

[AgX]

Actually I'm not qite sure about the term assymmetrical tilt. Could also just mean that the tilt axis does not meet the optical axis.

Anyway, the Sinar mechanism you are referring to is different in that way, that it does not employ a mechanical axle to pivot the standard, but rather a virtual axle. It does so by employing a roller-segment type of joint. You must not look at that physical joint, but rather where the axis of this roller-segment is to be found.

Furthermore, the mechanical type of joint has nothing to do with what optical kind of tilt (or swing) you gain. With both type of joints you can place the tilt axis deliberately while engineering.

There are cameras (Horseman types eg.) where a real axle is employed, but a shift mechanism is placed between the standard and the axle. Thus enabling you to place the tilt axis at your choice.

 

[David A. Goldfarb]

Actually I'm not qite sure about the term assymmetrical tilt. Could also just mean that the tilt axis does not meet the optical axis.

Generally, cameras that advertise "asymetric tilts" put the tilt axis somewhere on the groundglass. Base tilts are asymmetric in the general sense of the term, but in the context of describing a view camera, these are generally just called "base tilts."

 

[AgX]

Yes, David, in my first sentence I meant `off the optical axis but still on the groundglass´. I have to think more, before posting...

However there were constructions with central tilt but still off the groundglass. I don't know whether this has a special term to it. But the more terms, not only in English but in our very own language, the more complicated this thing gets. For instance, in my post I had it about the standard, but actually meant that frame pivoted to the standard and itself holding the filmback...

 

[reggie]

If Edward Weston didn't have it, do you really need it?
Spend your $$ on film and paper.

-R

 

[Tom Duffy]

If Edward Weston didn't have it, do you really need it?
Spend your $$ on film and paper.

-R

Don't knock it if you haven't tried it. Bet you a dollar that I can set up and take a picture in half the time you can... and get everything in focus.

 

[Peter De Smidt]

Yep, they're great!

 

[dslater]

Don't knock it if you haven't tried it. Bet you a dollar that I can set up and take a picture in half the time you can... and get everything in focus.

Hi Tom,
This is the first I've heard of asymmetric tilts. What are the advantages over base tilts and axis tilts?

Thanks,

Dan

 

[KJK]

Tom

my sentiments exactly. I have owned and used a Sinar 8 x 10 F2 camera in the past. It had base tilts, WHICH ARE NOT the same as ASYMETRIC tilts. What I am getting at here is that I would like to incorporate some sort of Asymetric tilt into a field camera (without having to resort to buying a an Ebony) and all I want to know is whether there is a mathematical formula for what the circle of tilt has to be (i.e how far forward the top has to go and how far back the bottom has to go, and how far off the film plane it has to be in order to use basically the same sort of set up as sinar does (i.e focus on the 1/3 line, tilt the front, transfer to the back, and your done)

Dan

The advantage is the speed in which you can work becasue you are not having to constantly refocus everytime you tilt or swing the camera.

 

[dslater]

Tom

Dan

The advantage is the speed in which you can work becasue you are not having to constantly refocus everytime you tilt or swing the camera.

I thought that what axis tilts were for?

 

[AgX]

...all I want to know is whether there is a mathematical formula for what the circle of tilt has to be...

Rodenstock once offered a calculating disc on this, solving some of your problems.

 

[Peter De Smidt]

You might try emailing Leonard Evens. He's a Professor Emeritus in mathematics at Northwestern University. He's a large format photographer, and I've seen him take part in these types of discussions.

 

[KJK]

I thought that what axis tilts were for?

No. With axis tilt you are also constantly refocusing because as you tilt for either the far or the near the other side of it goes out of focus. So now you have to refocus and then redetermine whether your tilt or swing is correct. If its not then you have to retilt or reswing, and then refocus again. Many many moons ago when I was at Brooks Institute we spent a whole semester learning how to refocus after swinging or tilting!!!!

 

[Ole]

With the sharp focus at the tilt axis you won't have to refocus regardless of where the tilt axis is - presuming your tilt axis also passes through the front (?) node of the lens. The only camera I know of where the tilt axis is repositionable with regards to the lens is the Carbon Infinity, and I can assure you that if everything is set up correctly there is no refocussing after swing or tilt. Then shift and rise can be applied after the swing/tilt/focus!

 

[KJK]

Look, you have two axis. horizontal and verticle. and you have three methods of swinging and tilting. you have base, you have center, and you have asymmetric. with base and center swing you have to refocus after tilting, then adjust, then refocus etc. You definitely do with center swing (i.e. on the lens axis or nodal point) becuase when you tilt you change the position of the image circle thereby resulting in unsharpness.

 

[Ole]

... with base and center swing you have to refocus after tilting, then adjust, then refocus etc. You definitely do with center swing (i.e. on the lens axis or nodal point) becuase when you tilt you change the position of the image circle thereby resulting in unsharpness.

No. You change the position of the image circle with all three versions, there is no "magic" difference between center and asymmetric tilt.

If changing the position of the image circle mattered, you would have to refocus after shift and rise too, which you definitely don't (assuming a lens with a fairly flat field).

 

[dslater]

I think we need to be clear about something here - are we talking about front tilts/swings or rear tilts/swings? From the talk about the lens nodal point, I assume we're talking about front tilts/swings correct?

 

[Ole]

Most of the time, I've been discussing front movements. The rest of the time it makes no difference which end you swing.

 

[Nick Zentena]

If changing the position of the image circle mattered, you would have to refocus after shift and rise too, which you definitely don't (assuming a lens with a fairly flat field).

You're going to make me setup the camera to try now aren't you. :rolleyes:

Won't enough rise/shift change the distance between the film plane and the lens? Shouldn't that require a change in focus?

 

[Peter De Smidt]

What's important for the rear standards is whether the axis of rotation lies on the film plane. If it doesn't, then any tilt or shift will require refocusing. Some center tilts, for example, do not pivot on the film plane. These will require more refocusing than others. Regarding front focus, I assume that this needs to be at the nodal point of the lens, and this will be slightly different with different lenses. On my Sinar P, though, I don't need to refocus when I tilt the lens, but maybe I my lenses have a similar nodal point. For example, I don't own any telephoto LF lenses, which is different from long focal length lenses.

 

[Ole]

You're going to make me setup the camera to try now aren't you. :rolleyes:

Won't enough rise/shift change the distance between the film plane and the lens? Shouldn't that require a change in focus?

No, it won't. The on-axis distance is constant (assuming your standards are straight - and a reasonably flat-field lens), and the rest is taken care of by the (aforementioned) flat field.

Just last week I took a shot with a 210mm Angulon on 8x10" film: First I focused on the subject, then I decided I wanted the framing a bit different and shifted the lens up by 20cm (on vertical 8x10" film, 20x25cm). The very top was soft since the lens isn't entirely flat-field outside of about 480mm image circle, but the rest was just as sharp.

Since I also happen to own that greatest of all "toys" for playing with shifts, swings, tilts, axis placements and internodal distances (the Carbon Infinity), I've played around with just about any conceivable movement and combination of movements, including changing the distance between pivot pint and lens nodes.