Long Telephoto lenses and increasing depth of field?

C Sean wrote:

So the question is when you zoom in close to your subject with a long telephoto lens, no matter how much you stop down, you can only get one subject in focus unless the subjects are perfectly lined up?

I haven't shot properly with Full Frame and less experience shooting with their standard 70-300/100-400 type lenses. However, I know several M43 members mention with long telephoto zooms, you don't need to stop down all the time and therefor it's easier to shoot with long telephoto lenses compared to Full Frame. So is there a long telephoto rule, if you zoom in close, you can only get one subject in focus no matter how much you stop down?

You will get same DOF regardless the focal length, when you have three factors same:

1. Same subject framing
2. Same format
3. Same F-stop

So in this case with m4/3 and example f/5.6, there is no difference do you shoot with 12mm or with 300mm, you are having the same DOF when the subject framing (magnification) is same.

The typical scenario is this, your subject is further but you want the same framing, so you use longer focal length. That will deliver you same DOF as you would get if you would use shorter focal length at the closer distance and frame the subject same size.

If you want multiple different subjects to be framed in same size, then you need to start to play around with multiple factors:

You can only get so far all the magnifications same, but never get the same perspective or background blur, but the DOF will be same.

Tommi K1 wrote:

C Sean wrote:

So the question is when you zoom in close to your subject with a long telephoto lens, no matter how much you stop down, you can only get one subject in focus unless the subjects are perfectly lined up?

I haven't shot properly with Full Frame and less experience shooting with their standard 70-300/100-400 type lenses. However, I know several M43 members mention with long telephoto zooms, you don't need to stop down all the time and therefor it's easier to shoot with long telephoto lenses compared to Full Frame. So is there a long telephoto rule, if you zoom in close, you can only get one subject in focus no matter how much you stop down?

You will get same DOF regardless the focal length, when you have three factors same:

1. Same subject framing
2. Same format
3. Same F-stop

So in this case with m4/3 and example f/5.6, there is no difference do you shoot with 12mm or with 300mm, you are having the same DOF when the subject framing (magnification) is same.

The typical scenario is this, your subject is further but you want the same framing, so you use longer focal length. That will deliver you same DOF as you would get if you would use shorter focal length at the closer distance and frame the subject same size.

If you want multiple different subjects to be framed in same size, then you need to start to play around with multiple factors:

You can only get so far all the magnifications same, but never get the same perspective or background blur, but the DOF will be same.

Tommi I have a general idea where you're coming from and I'd had read an article last night regarding both long telephoto lenses and depth of field. However, if I wanted to say photograph a group of people, not only would I say use the 15mm 1.7 (depending on the size of the group) but I would also close the lens down to F5.6 or F4.0.

When it comes to long telephoto lenses, if we ignore 70-200mm and the use for landscape or portrait. The long telephoto lenses often use for either wildlife or sport and in those situation, very often you can't get close to the subjects and use a wide angle lense. I imagine you can zoom out a bit to increase the DOF and crop in later if you have spare megapixels but in general use of long telephoto lenses is because you can get close to the subject by foot.

The image below was taken in South Africa last year and I can't remember if I stopped down or not. If I remember correctly the shot was taken at 400mm at either 6.3 or 8.0 or even higher. Problem is the 100-400 at 400mm generate a thin depth of field.

The options is either to use the 100-400, drive closer and scare the birds away. The other option is to jump out of the vehicle, walk up to them and scare the birds or at the sometime get killed by the bleeding and peed off cape buffalo close by.

Tommi K1 wrote:

C Sean wrote:

So the question is when you zoom in close to your subject with a long telephoto lens, no matter how much you stop down, you can only get one subject in focus unless the subjects are perfectly lined up?

I haven't shot properly with Full Frame and less experience shooting with their standard 70-300/100-400 type lenses. However, I know several M43 members mention with long telephoto zooms, you don't need to stop down all the time and therefor it's easier to shoot with long telephoto lenses compared to Full Frame. So is there a long telephoto rule, if you zoom in close, you can only get one subject in focus no matter how much you stop down?

You will get same DOF regardless the focal length, when you have three factors same:

1. Same subject framing
2. Same format
3. Same F-stop

So in this case with m4/3 and example f/5.6, there is no difference do you shoot with 12mm or with 300mm, you are having the same DOF when the subject framing (magnification) is same.

The typical scenario is this, your subject is further but you want the same framing, so you use longer focal length. That will deliver you same DOF as you would get if you would use shorter focal length at the closer distance and frame the subject same size.

If you want multiple different subjects to be framed in same size, then you need to start to play around with multiple factors:

You can only get so far all the magnifications same, but never get the same perspective or background blur, but the DOF will be same.

Yes.

You can restate the usual DOF formulas in terms of magnification rather than subject distance and focal length in which case you find that DOF is a really a function of magnification.
I prefer to think of it this way when I'm in the field using a variety of focal lengths at various distances. Estimating magnification is easier for me than subject distance and focal length. YMMV.

C Sean wrote:

However, if I wanted to say photograph a group of people, not only would I say use the 15mm 1.7 (depending on the size of the group) but I would also close the lens down to F5.6 or F4.0.

Yes, that depends from the size of the magnification that how much you need to stop down.

If you double or half the focal length, you need to double or half the distance to the subject to get the same framing as with the previous focal length, examples:

• if you take a shot with 25mm from a 3 meters and you move to 6 meters, you now need a 50mm to get the same framing. 
• If you take the shot from 5 meters with 100mm and you move to 2.5 meters, now you can use 50mm to get the same framing. 

Now, lets say that you use 25mm from 3 meters, that gives you framing of about 220 x 160 cm. At that range f/1.8 gives you about 78 cm.

If you are now photographing the same group of people and you have four people positioned together that you can fill in that 78 cm of DOF, but you find that the background is distracting, what you can do is to change the perspective. So either turn camera around the group and turn the group facing the camera until camera points toward background that has the nicer background.

Or if you can't do that, you can control the background better by using longer focal length, so instead 25mm you can go straight to example 100mm. Now you have four times narrower field of view, so what you need to do is to move four times further. So you move camera from 3 meters to 12 meters.

What you now have is same framing for the group, the background size is only 1/4 of the previous, and with f/1.8 (now a theoretical 100mm f/1.8 lens) your DOF will be the same, about 78 cm, but your background will be much different and far more blurrier.

When it comes to long telephoto lenses, if we ignore 70-200mm and the use for landscape or portrait. The long telephoto lenses often use for either wildlife or sport and in those situation, very often you can't get close to the subjects and use a wide angle lense.

Of course. But in such scenarios where you can not get the same framing (magnification) your DOF will be totally different.

I imagine you can zoom out a bit to increase the DOF and crop in later if you have spare megapixels but in general use of long telephoto lenses is because you can get close to the subject by foot.

Cropping changes the DOF.

The DOF is defined by you, the viewer, that what you find acceptable as sharp (instead blurry). And DOF changes as well by the final image size, viewing distance and your eyesight. It as well changes by the sensor Mpix count (image resolution) as well is the lens sharp or soft and many other factors, that are not related to the F-stop or camera distance.

The image below was taken in South Africa last year and I can't remember if I stopped down or not. If I remember correctly the shot was taken at 400mm at either 6.3 or 8.0 or even higher. Problem is the 100-400 at 400mm generate a thin depth of field.

The 400mm will generate same DOF as example 12mm if you would frame (magnify) the bird in same size on the frame from 4/3" sensor.

The 400mm itself doesn't make the DOF thinner, the magnification does.

The options is either to use the 100-400, drive closer and scare the birds away. The other option is to jump out of the vehicle, walk up to them and scare the birds or at the sometime get killed by the bleeding and peed off cape buffalo close by.

The point I am raising, is that the focal length doesn't change the DOF, but your magnification does. So if you are there photographing that bird with a 40-150mm, 300mm and 150-400mm with all set for longest focal length and all you are using at f/5.6.

You will get the same DOF regardless the focal length change when you frame the bird same size. Meaning you would have possibility to get closer or further to get that same framing.

So your f/5.6 is not thinner with 400mm than it is with 150mm.

So let me put it in other way:

You do not need to stop 100-400mm @ 400mm down more than you would need to stop down 35-100mm @ 100mm, if you would manage to get the same framing on the bird, as the DOF will be same.

bclaff wrote:
I prefer to think of it this way when I'm in the field using a variety of focal lengths at various distances. Estimating magnification is easier for me than subject distance and focal length. YMMV.

And it becomes very easy for fixed focal length user (or zoom user at the end of the ranges) when having a guidelines overlaid. It is already easy to imagine the frame to half of its size, just by splicing the frame vertically and horizontally to two. That is the framing if you would use two times shorter focal length.

And the Olympus "Cross Hair" overlay helps a lot in zoom usage, as you get the magnification guides, the one that resembles this from microscopes:

As with that, especially the macro, landscape, architecture and portraits photography becomes very much easier as you know how much to change camera distance, angle or focal length to get the wanted composition. And it doesn't end up just there, you can use it as well to modify your lighting equipments as you get the guidance via that for the lights angles, modifiers adjustments etc.

Extremely powerful.