08-27-2018 09:25 AM
Thanks. I'm not "having a go" at anyone in particular. It just seems that there are a lot of assumptions made and when we are new to a piece of technology, trying to get accurate information for one particular aspect of that technology is very hard to achieve.
I'll keep looking
08-27-2018 11:22 AM
Not a video, but here's an article that may be helpful: https://luminous-landscape.com/focusing-tilt-shift-lenses/
I have yet to find a decent video. I generally find (a) the "miniature" effect, or (b) someone who explains how to maximize the focus but explains the concept while not providing the steps to follow to achieve the results.
When I noticed the the index marks on the tilt-angle and verified that those marks are, in fact, degrees of tilt, I realized their *must* be a reason that the lens makers mark the degrees ... so I went in search of a formula. That was a less-straight-forward search than I would have expected. Originally I found articles that just hinted around at it. I ultimately found enough info that I was able to derive the formula and then did a bit of testing to make sure it worked. I eventually did find articles that gave the formula and confirmed that I what I found was correct.
So this article linked above is actually pretty good. It does give the formula. It also offers some practical advice where you don't use the formula. It could be improved with a diagram.
At the bottom of the article, the author has a list for a few lenses... 24mm, 45mm, 90mm, and 150mm (Canon's lenses are actually 17mm, 24mm, 45mm, 50mm, 90mm, and 135mm.
Anyway... the correct tilt-angle is based on knowing the focal length of the lens (that's easy to know ... it's either 17, 24, 45, 50, 90, or 135) and also the distance from the lens axis to the desired plane of focus. And since the units need to be the same and the lens is in millimeters, the distance from the lens axis to the focal plane *also* needs to be in millimeters.
The average human is 1.8 meters tall. If you were taking a photo of landscape while holding the camera at eye-level... it's *probably* about 1.7 meters from your eyes to the ground.
The tilt formula is: arcsine(tilt-angle) = lens-focal-length ÷ distance from lens-axis to desired focal plane
If the lens a 90mm tilt shift and the distance from the lens axis to the ground is 1.7 meters (1.7 meters = 1700mm)
Then it's: arcsine(tilt-angle) = 90 ÷ 1700
Your mobile phone probably has a calculator on it that can do sine / arc-sine. Divide 90 by 1700 and take the arcsine of the result. It turns out it works out to 3.03° (3° is close enough).
So right away, you should be able to put the tilt-angle to 3° down, place the camera on a tripod, and just focus and everything should come to focus.
The idea behind having a lookup table for your lenses and common heights you might use (eye-height, waist-height, knee-height, etc.) is that if you do this a lot, you start to just know about how much tilt to dial in based on how you want to set up the shot.
If you don't have a lookup table... I have seen people explain that you should focus on a near subject and tilt until the far subject is also in sharp focus. I've also seen the opposite... focus on the far object and adjust tilt until the near object is in focus. The "problem" with both of these... is that the NEXT step is always go back and double-check the original focus point to see if it is still in focus... followed by advice to adjust the tilt-angle ... or tilt the whole camera ... or re-tweak the focus...
When I read this I translate it to mean "just fiddle with stuff until it works".
I recognize that you *can* get focus across the entire field by using either technique and fiddling with controls until you get the result you want. But using a quick-lookup table or the math will quickly get you to the correct angle and now it's just a matter of focus (you should not have to re-tweak the angle).
Two generalizations... (1) the closer the camera is to the desired plane of focus, the more tilt it will require, and (2) the higher the focal length of the lens, the more tilt it will require.
If you were using a 24mm tilt-shift, then the amount of tilt needed if the camea is on a tripod at eye-level to shoot a flat field (the ground beneath your feet) is just fractionally less than 1° (remember that the 90mm needed about 3°). But if that same 24mm lens was at knee-level (say 500mm above the ground) ... now it's a 2.75° tilt. (divide 24 by 500 and take the arcsine of the result).
08-27-2018 11:56 AM
Nice bit of Maths, Tim.
Now, don't get me wrong, I can follow the maths but when I'm out in the field, that is the last thing I need to be thinking about.
I'm a simple guy. I need a simple way of getting that front to back sharpness. Fore example, I struggle with hyperfocal focussing on an "ordinary" lens. If the chart says focus on 45feet, my problem in the field is "where is 45 feet from the lens"?
This is why I am looking for a quick and simple method of getting the job done rather than getting a calculator out or getting a chart out.
Why does it have to be quick and simple? I have my wife telling me from behind "haven't you taken that picture yet". I know, we've all had that experience. So, quick focus on subject, jiggle the tilt knob, take picture. But where do I focus. This is what nobody is telling me.
08-27-2018 12:36 PM
And still nobody has answered my initial question.
Where in the frame/scene do I focus, whether it's quick or not.
I'm sorry. but, my frustration is getting the better of me.
08-27-2018 02:03 PM
There is another article ... this one is my favorite as it also includes interactive examples. I tried to find this earlier but their website was unreachable.
Here’s the link: https://www.cambridgeincolour.com/tutorials/tilt-shift-lenses2.htm
They have different articles for using shift... the article above specifically deals with tilt ... including instructions on how to do this in the field.
Be aware that using tilt has a bit of a learning curve. Don’t expect to be able to do this in a hurry at first. As you do it more often, you start to get a bit more comfortable at knowing about how much tilt will be needed for a given situation. It is generally NOT a type of photography you do when rushed.
This is why I suggested calculating the tilt amounts for common camera heights such as the height of your eyes, your waist, your knees, etc.
08-27-2018 03:12 PM
Please, gents, don't get me wrong. I am very grateful for your input. I realise that we are all in this together. I realise too that it is a steep learning curve and, maybe I am in the minority on this. I just like taking landscape photos and it seemed such a simple question.
As I said in an earlier post, when using an "ordinary" lens my comment about not being sure where the hyperfocal point of focus was located (my example was 45feet) I should have then said that the quick reference about 1/3rd of the way in from the bottom of the frame using the grid in live-view is the way to estimate that hyperfocal point and I was wondering if there is a quick ready-reckoner for tilt.
I realise that very few shooters will own a TS lens but everyone in videos seems to concentrate on the shifting of the focal plane but hardly ever mentions where the focus point should be.
Tim: I will look at the link you have kindly found for me and again, I am very grateful for all your comments.
08-27-2018 09:19 PM
First, I adjust the “bellows”, and then I adjust for critical focus. Adjusting focus, and then adjusting the tilt-shift without refocusing will almost always result in an OOF photograph.
The T-S lens alters the distance between the lens elements and the image sensor slightly. If you focus when the lens is “normal”, then why should it still be in focus after you have introduced tilt and/or shift?