Alan,But I only focus the bellows once. That's the whole point of asymmetrical tilting. There is no second focus point with the bellows. You tilt back the back standard to get the near point in focus after you focus the far point with the bellows. Are you saying I have to check other focus points with additional bellows adjustments beside the first and only one I do now?
Alan,
Yes and yes! You use two (or more) reference points for applying the tilt. You are, even with asymmetrical tilts, whether you realize or not and even though you're not using the bellows focus. You find and focus on the far point. Then you tilt to get a near point in focus. That's correct and it's exactly what one does with any axis tilt, whether the axis is centered or not. Base tilts are a different case, because tilting moves the whole standard and so you have to refocus.
Anyway, if you think about it, when you tilt, you're moving the film further from the lens, thus changing the focus.
And, the whole point of asymmetrical tilting is to speed up applying the tilt. It has nothing to do with focusing the camera for optimum depth of field. Please understand this!
So you find you're far point, tilt till the near is in focus and you've applied your tilt. You're still only half done! And, even if you don't use any tilt at all, you still need to focus the camera (applying tilt or swing is NOT focusing!).
Now you need focus with an eye to dealing with depth of field and choosing the f-stop. For that, you need two other focus points. You want to find the nearest and the farthest points from where the plane of sharp focus is that you want sharp in the final print. We've discussed at length how to do this, especially when tilt is applied ("above" and "below," remember?).
So, find your two focus point, note the positions on the camera bed/rail, place the bellows focus (using the focus knob) halfway between those two positions and, voilà, you have the right focus.
Now, since you know the focus spread, you can use that distance to choose the optimum f-stop. See the chart above and use it, or stop down till everything looks sharp on the ground glass and then close an extra stop like Vaughn does, but, somehow, you need to find the right f-stop. Larger focus spreads need smaller apertures.
And, please understand that when you tilt the back and move it away from plumb, you will have converging verticals in the scene. That may make no difference at the beach or whatever, but with architecture, if you want the vertical parallels to be rendered parallel on the film, you should NOT use back tilt once you have the camera set up with the back plumb and level. You should use front tilt.
Got it now?
Doremus
Now, if I felt I needed tilt to help get more things closer to the plane of sharp focus, I would have simply chosen the obvious "near" points for my tilt reference points for both your images. These would be for you Chuck, the closest grass at the very bottom of your image and the very top branches of the tree.
Chuck, in your image, there's nothing below the lawn, so you'd look at the base of the building at it's greatest distance from you and the clouds at the right side of the image and see which one gave you the greatest focus spread (more later).
The object of finding the focus spread between the objects you want in sharp focus on the final print is to first make sure the PoSF is centered between the near and far objects and, second, to be able to choose the optimum f-stop based on the focus spread. And, yes, the PoSF moves around when you do this; that's kind of the object. Usually, just leaving it where it was when you applied the tilt doesn't center it between the nearest and farthest objects you want in focus.Thanks for the clarification. Maybe I missed it, but I didn't see the second focusing process when asymmetrical focusing was explained elsewhere. Others stopped when the near tilt was done. Your method does seem like a lot of extra work. Isn't there a good chance I would just screw up the original focusing for the far and tilt for the near while trying to find those other points with the second bellows focusing? Wouldn't it just be easier and safer if I just picked f22 or something a little smaller based on the depth I can calculate based on far and near distances as one would do with regular 35mm or MF cameras without standards and bellows?
Ok, I think it just clicked so I'm hoping my comments here are indicative of that, lol. Given your two points above, the take home message I am getting is with tilt, finding and establishing "a" PoSF is step one with the near and far scenarios you have been mentioning. Step two is using the knob.......or in my case, I have to move the rear standard forward or backward for my focusing action with my current lens (135mm) on my Canham..........at any rate, using the focusing action to then "place" that PoSF halfway between two locations on the GG that represent the greatest focus spread of the scene. Step three, select the optimum f/stop based on the chart you have shown. As I type this I am visualizing the angle of the tilted focus plane moving forward or backward.........it's the same visualization without tilt. With the focusing action, the PoSF moves forward or backward except it is parallel to the film plane and not tilted, duh!
As I'm thinking about the actual tilted PoSF.................I'd have to check the book, but I believe also that I've read in AA's "The Camera" that the tilted focus plane is tilted more than the actual tilt given to the standard itself.
The object of finding the focus spread between the objects you want in sharp focus on the final print is to first make sure the PoSF is centered between the near and far objects and, second, to be able to choose the optimum f-stop based on the focus spread. And, yes, the PoSF moves around when you do this; that's kind of the object. Usually, just leaving it where it was when you applied the tilt doesn't center it between the nearest and farthest objects you want in focus.
If you chose two reference points for applying the tilt that just happen to be in the right place, then your final position for focus won't be to far from that, but, as I described above, I often pick two close points, use those to apply the tilt, and then go about finding the final place for focus by looking for the far and then focusing halfway between my first position and it.
And, when you're not tilting or swinging at all, what do you do? Certainly you focus somehow. I think from your earlier posts that you guesstimate a place a third of the way into the scene and then try to focus there. That ends up being an approximation, at best, if your goal is to get everything in the image sharp in the final print. Using the near-far and then place the focus halfway between is more accurate. And, if you use the method I'm suggesting, you have the means to find the optimum f-stop as well. No guesswork there either.
As for "just picking f/22" or whatever, you can see from the above chart that in many situations, you are going to end up using smaller apertures than f/22. My most-used aperture is f/32. Sure, you can just guess at that, or use DoF tables, etc., but I don't think they are nearly as accurate or quick.
As for being a lot of extra work: It's no more work than you would do focusing the camera without the tilt; you just do it after applying tilt. And, if you can find two near reference points to use for applying the tilt, you can combine steps.
You don't have to use this method; many don't either. You keep asking me about it and I keep explainingStill, I get good results with it. I haven't had an unpleasant focus surprise for years and years. Only in the most extreme cases do I ever get an area of the print that ends up being a bit soft. But, if you can't get your head around this method, don't despair. Just do what you've been doing and refine it. Your images are well-seen.
Best,
Doremus
The biggest issue I find with asymmetrical tilt with the back standard method is that often the far object you want to focus only in is not where the axis line on the ground glass is located. So then you have to raise or lower the front standard so it lines up. Then focus. Then you have to raise or lower the front standard to frame the picture the way it was originally making sure the front standard stays parallel to the film. Then go ahead and tilt the back standard to focus the near object.There are really two issues to be concerned about, namely focus and perspective. The orientation of the film back controls the perspective. Best practise is to set up the position and orientation of the film back to get your desired shooting perspective. Once that is done, you can use the tilts or swings of the lens to adjust the plane of focus.
Changing the swing or tilt of the lens will change the focus plane, but it has virtually no effect on the shooting perspective. On the other hand, tilting or swinging the film back will change both the focus, as well as the shooting perspective. This is why you should leave the film back alone once you've got your desired shooting perspective. Think of shooting perspective the same way as you would with a 35mm camera. If you tilt your camera back to shoot a high building, the vertical lines will converge. Similarly, if you shoot a building from the side, your horizontal lines will converge. That's fine if that's the look you're after, but not so great if you're trying to avoid that. Objects can become distorted if you're not careful with the perspective. They could be elongated or shortened, and look funny.
Sinar introduced asymmetrical tilts and swings with the Sinar P. It made it easy find the tilt or swing angle by tilting or swinging the back. The key point here is that you used the back tilt or swing to find the appropriate tilt or swing angle, and then transfer that tilt or swing angle to the lens. After doing that, you'd set your film back to it's original orientation to maintain the perspective. It was never intended to be used only on the back, since this would cause perspective problems. The steps for tilt would be to focus a near or far point on the lower horizontal line on the ground glass, and then tilt the back until your other focus point was achieved. Next, you note the tilt angle of the film back from the marked scale. Use that noted tilt angle, and tilt the front standard to that same angle (but in the opposite direction). Go to the film back and straighten the tilt back to it's original position prior to tilting, and then refocus the scene. Now both points should be in focus on the ground glass, and your original perspective was maintained. This is still a relatively complex process, and may or may not be any significant advantage compared to just iteratively tilting and focusing the lens.
Field cameras with the asymmetrical rear tilt are really just a bastardized version of the original Sinar concept. Since these cameras don't have tilt or swing scale markings, there's no way to know precisely what angle they're set at, so there's no way to transfer that angle to the lens standard. You can do it all on the back, and that still might be useful if your perspective isn't important. For things like landscape work, the perspective might not be a big deal since the tilts or swings might be small, and nobody can really tell if a tree is distorted anyway. If you do it this way all the time, you're probably asking for problems. Just be aware of the perspective concerns.
Just to recap my suggestions above to maybe help clarify: If you wish to apply tilt, you need two reference points, one near the camera and one farther away. The object is to get both these points in focus by tilting (however you do that, since it varies depending on the type of tilts you have; axis, base, asymmetrical). Once you get the two points in focus, you then find two more points, that I'm calling focus points, that represent the limits of what you want sharp in the final image. One of these is on one side of the PoSF and the other on the opposite side. The object is to find the pair of points that give you the greatest focus spread (mm on the camera bed/rail). You then place focus on the rail or bed halfway between the two points and use the focus-spread distance to get the optimum f-stop from the table.
When you have applied tilt, the plane of the camera back - let's call it the film plane - the plane perpendicular to the lens axis that's exactly one focal length in front of the lens center and the plane of sharp focus end up intersecting at a line below the lens. When you focus with the camera back, the PoSF actually rotates around this line
Yes, I understand this better now.........I need to remember that when finding the greatest focus spread, I have to remember that one point on the GG is above and one point is below the PoSF. I failed to mention that in my previous comment.
This was interesting to see in that short animation in the link you provided. I incorrectly stated in my previous post that I can only use the camera back to focus the 135mm lens. This discussion has shown me that I've been achieving focus the hard way with the Canham........it suffices to say that I do not need to use the camera back the way I have been.
So, after applying tilt, moving the rear standard toward or away from the lens rotates the tilted PoSF around the hinge line, I see that now, and it explains how I've thought that the focus plane just moved weird on the GG.
When moving just the lens forward or backward.........after applying tilt...........the tilted PoSF maintains its angle and is simply moved forward or backward, just like it would be if the standards were parallel to each other.
Alan, what is nice about most 35mm and MF cameras/lenses it that they have a depth of field gauge built right in -- which are basically mechanical computers doing Doremus's work for everyone. (computations made easier by the lack of camera movements, though)
Like I have said, I am an all-on-the-GG worker, but only because I can also (through decades of mistakes) mentally relate the placement of the plane of focus in the landscape in front of me with what I am seeing on the GG.
So if I used back tilt on the back standard for asymmetrical focusing, if I subsequently move the bellow's focus closer from the original far focus point, wouldn;t my original far focus point be further away from the new focus point? Wouldn't my near tilt focus point also now be closer than where it was with the tilt? The old close focus point is also further away?
...
When moving just the lens forward or backward.........after applying tilt...........the tilted PoSF maintains its angle and is simply moved forward or backward, just like it would be if the standards were parallel to each other.
Basically the same question you two. I'll deal with this before addressing Alan's previous question.So if I used back tilt on the back standard for asymmetrical focusing, if I subsequently move the bellow's focus closer from the original far focus point, wouldn't my original far focus point be further away from the new focus point? Wouldn't my near tilt focus point also now be closer than where it was with the tilt? The old close focus point is also further away?
Alan,I really appreciate the advice and ideas. It think the problem I;m having is I don't really understand the places you pick for focus. This is when hands on with someone showing you what to do at an actual photoshoot would be very helpful. A face-to-face training class. As far as picking 1/3 down, that comes from shooting 35mm and MF which have no bellows focusing. Interestingly, my Mamiya RB67 has bellows. I wonder if I could try your aperture method with it?
The placing of the focus on the camera bed/rail halfway between the extremes of the focus spread places the PoSF in the optimum position, so that the extremes are both within (although at the edge) of the DoF. (The 1/3-2/3 DoF thing is an inaccuracy; it really doesn't help to think of it that way - see my response to you in another thread).Thanks Doremus. I have to admit it's difficult for me to see all these details. A couple of questions. Does the relocation of halfway to refocus actually move the focus 1/3 into the picture to get the DOF?
When you tilt you're bascially extending the bellows in only parts of the picture. So, there's more room for light to travel to parts of the film. Doesn't that cause falloff in the film in those areas?
Hope this helps
Thanks Doremus. I have to admit it's difficult for me to see all these details. A couple of questions. Does the relocation of halfway to refocus actually move the focus 1/3 into the picture to get the DOF?
When you tilt you're bascially extending the bellows in only parts of the picture. So, there's more room for light to travel to parts of the film. Doesn't that cause falloff in the film in those areas?
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