Will my depth of field change when I add a 1.4X Sony tele-extender to my 70-200mm telephoto lens? For the first time ever, I am adding a 1.4X teleconverter that adds one F stop to my...

Shooter41 Loc: Wichita, KS

For the first time ever, I am adding a 1.4X teleconverter that adds one F stop to my Sony A7R4 + Sony F2.8 70-200mm telephoto lens set-up. (I will go from F2.8 to F4.0) I need to be able to reach out from my usual 200mm shooting indoor soccer under low-lighting conditions to 280 mm. My goal is to shoot RAW instead of JPEG and reduce the amount of post-game cropping that I have to do in order to also reduce the amount of noise I get in my final images. My question to you is, "Will my depth of field increase when I go from F2.8 to F4.0, or will it stay at F2.8? Shooter41

kymarto Loc: Portland OR and Milan Italy

It just enlarges the image. DOF does not change.

Shooter41 Loc: Wichita, KS

kymarto wrote:

It just enlarges the image. DOF does not change.

THANKS!

Grahame Loc: Fiji

If we assume that your 'camera to subject distances' are going to be the same when you use the 1.4TC on the 70-200mm as they were when you do not use it, according to 'PhotoPills' the DoF will be less when using the TC. Based upon the same medium viewing distance.

That's the way I read it from the calculator.

Example:
200mm lens, 20m subject distance, f/2.8, no TC - DOF = 1.68m
200mm lens, 20m subject distance, f/2.8, 1.4TC - DOF = 1.20m (note, 1.4TC selected in calculator field)
280mm lens, 20m subject distance, f/4.0, no TC - DOF = 1.21m

https://www.photopills.com/calculators/dof-advanced

SnappyHappy Loc: Chapin, SC “The Capitol of Lake Murray”

Using a 1.4 TC will reduce your maximum aperture by about 1 stop…so your 2.8 lens will effectively be stopped down to a 4.0 max. If you are shooting wide open you will realize the 1 stop difference in aperture and DOF.

larryepage Loc: North Texas area

Shooter41 wrote:

For the first time ever, I am adding a 1.4X teleco... (show quote)

Kymarto provided the correct answer. Your teleconvertor is an external device that simply magnifies the image already finalized by the lens to which it is attached. All focus and depth of field determinations have been made before light rays from that image ever enter the front lens of the TC. Depth of field calculations depend only on the distance and aperture settimgs indicated by the lens.

One thing you will need to figure out, however, is whether your camera displays the actual f/stop to which the lens is set or to the effective f/stop including the teleconvertor penalty. That's easy to do...if the lens is an f/2.8 lens, just set your camera to manual and see whether it will allow you to set the aperture to f/2.8. If so, you will know that it is ignoring the TC loss. If not, you are going to have to remember that you can't use the displayed aperture to calculate DOF.

Ysarex Loc: St. Louis

Enlarging an image changes DOF.

DOF is measured at the final image and nowhere else.

Changing from f/2.8 to f/4.0 will increase DOF all else equal.

Changing magnification by increasing focal length will decrease DOF all else equal.

Magnification is the dominant factor controlling DOF.

Grahame has it right above. The magnification increase will outweigh the f/stop change and DOF will decrease.

CHG_CANON Loc: the Windy City

The Sony a7IV is a 33MP camera. The modest 40% increase in effective focal length of a 1.4x extender on a 200mm lens is more likely to deliver challenges when shooting indoors, rather than tangible positive differences over just cropping from the native f/2.8 @ 200mm results.

Make sure you check the return policy and due-date from the purchasing source of this extender.

larryepage Loc: North Texas area

I will not get into an argument over this depth of field question. The exact same picture elements that are in focus at a given focal length and aperture without the TC will still be the ones that are in focus if the TC is added. Photographers are famous for applying principles that well apply in one area to completely different area where they do not apply at all.. I will add to what Paul suggested that once you get your TC, just set up and conduct a quick experiment to verify the effects for yourself. Then you will know for sure.

gwilliams6

CHG_CANON wrote:

The Sony a7IV is a 33MP camera. The modest 40% increase in effective focal length of a 1.4x extender on a 200mm lens is more likely to deliver challenges when shooting indoors, rather than tangible positive differences over just cropping from the native f/2.8 @ 200mm results.

Make sure you check the return policy and due-date from the purchasing source of this extender.

You misread CHG_Canon, the OP is using his A7RIV which is a 61mp sensor camera.

Three factors control DOF, lens aperture, lens focal length. distance from lens to subject. As a Professor of Photography at a state university, I have to know and teach this to my photo students.

So yes shooting at 280mm vs 200mm will decrease DOF because of the greater focal length of 280mm, however his lens aperture will still be set at f2.8. It is just that the 1.4X TC loses one stop of light, so his exposure will be at f4 when he sets the lens aperture to f2.8 and is using the 1.4X TC. BUT his setup is not getting f4 DOF, it is still getting f2.8 DOF, but now that normal f2.8 DOF is decreased from the longer focal length.

I have the same gear.

Cheers and best to you.

gwilliams6

Ysarex wrote:

Enlarging an image changes DOF.

DOF is measured at the final image and nowhere else.

Changing from f/2.8 to f/4.0 will increase DOF all else equal.

Changing magnification by increasing focal length will decrease DOF all else equal.

Magnification is the dominant factor controlling DOF.

Grahame has it right above. The magnification increase will outweigh the f/stop change and DOF will decrease.

Three factors control DOF, lens aperture, lens focal length. distance from lens to subject. As a Professor of Photography at a state university, I have to know and teach this to my photo students.

So yes shooting at 280mm vs 200mm will decrease DOF because of the greater focal length of 280mm, however his lens aperture will still be set at f2.8. It is just that the 1.4X TC loses one stop of light, so his exposure will be at f4 when he sets the lens aperture to f2.8 and is using the 1.4X TC. BUT his setup is not getting f4 DOF, it is still getting f2.8 DOF, but now that f2.8 DOF is decreased from the longer focal length.

I have the same gear.

Cheers and best to you

gwilliams6

I show my University Photography students this when I start to teach them about DOF, and then they get shooting assignments to show they understand how to get shallow DOF, and then how to get extended DOF.

Adorama TV- with Mark Wallace, Depth of Field: Shallow or Extended DOF

https://www.adorama.com/alc/episode/depth-of-field-adoramatv/

Cheers and best to you

Also Adorama-TV's Mark Wallace talks about settings to achieve correct hyperfocal distance to get everything in focus:
www.youtube.com/watch?v=hYT54OBbrl0

CHG_CANON Loc: the Windy City

gwilliams6 wrote:

You misread CHG_Canon, the OP is using his A7RIV w... (show quote)

61MP kind of says it all, just crop. There's no way 200mm couldn't be close enough over 61MP, unless you're shooting the goal from still inside the locker room. Who cares about the f/2.8 depth of field when magnified via a extender? 'Magnified' by another piece of equipment splashing a larger image circle over the same size sensor.

Ysarex Loc: St. Louis

gwilliams6 wrote:

Three factors control DOF, lens aperture, lens foc... (show quote)

No, that's not correct. You're confusing f/stop and aperture -- mixing them back and forth (just like the video you posted). F/2.8 is not the lens aperture. It's an exposure factor derived from the lens aperture and focal length combination -- focal length / lens aperture = f/stop value. Common DOF equations (the ones we use) don't take a value for aperture (eg. aperture diameter) but do take a combination f/stop value and lens focal length value. With the 1.4 extender the f/stop value changes from f/2.8 to f/4 because the focal length really is increased. DOF is then calculated using the f/4 value in the equation.

Grahame provides a clear example in his post above and used one of the better DOF calculators available that allows for the 1.4 extender to be entered as a variable. Grahame and that calculator have it right.

User ID

Grahame wrote:

If we assume that your 'camera to subject distance... (show quote)

That might be correct calculation but it doesnt apply here. The OP was cropping tighter, which decreases DoF the same as adding a TC. The TC is just a substitute for cropping. The loss of DoF is about the same either way.

Acoarst the TC is losing half the light transmission vs cropping instead. Since the TC is part of a noise avoidance scheme, raising the ISO is of the table, and since DoF is a concern, a wider aperture is off the table, so the shutter must be slowed by a full stop, which is a bad idea with an action subject.

PhotoPills is just a calculator. It deals in numbers and dimensions, not in in logic or common sense. That stuff is BYO.

The bottom line is that the TC is really just a no-gain waste of money in this particular scenario.