topic Re: Interest in EF lens for imaging small, moving objects in EF & RF Lenses

Interest in EF lens for imaging small, moving objects

amag — Tue, 14 Feb 2023 21:14:02 GMT

Hi, my lab is interested in purchasing a lens to image and record small, moving objects. We are looking at the EF 100mm f/2.8L Macro IS USM lens, but have a few questions:

What is the working distance of this lens? I read that the minimum focal distance is 0.3m. If I set it up so the focal point is 0.3m away from the lens, what distance before 0.3m and past 0.3m will be focus in the image? Or does this lens capture only what is at the focal point?

Also, I am interested in using a Basler Ace camera and connecting the canon lens using a lens coupler. Do you know if the use of a lens coupler would alter the working distance or other specifications of the lens?

Thank you for your help!

Re: Interest in EF lens for imaging small, moving objects

normadel — Tue, 14 Feb 2023 21:44:57 GMT

It's not the specific lens that determines depth of field. DOF is determined by two factors....aperture size and MAGNIFICATION. Macro photography, which you want to do, means high magnification...life size or higher. DOF will be measured in millimeters and fractions of millimeters. This means that you focus on a subject, or where the subject will be, but if the subject is changing distance from the lens, it will be moving in-and-out-of focus.

You can't easily follow moving subjects under these conditions. That's why macro photography is best done with camera on a tripod or other stationary holder.

Re: Interest in EF lens for imaging small, moving objects

kvbarkley — Tue, 14 Feb 2023 22:00:29 GMT

@amag wrote:
Hi, my lab is interested in purchasing a lens to image and record small, moving objects. We are looking at the EF 100mm f/2.8L Macro IS USM lens, but have a few questions:

Also, I am interested in using a Basler Ace camera and connecting the canon lens using a lens coupler. Do you know if the use of a lens coupler would alter the working distance or other specifications of the lens?
Thank you for your help!

The working distance is the minimum focus distance where it will have a 1:1 magnification.

I don't know what a Basler Ace camera is, but unless it works with EF lenses, you have no way to control the aperture or (if it is a focus by wire) the focus.

Re: Interest in EF lens for imaging small, moving objects

ebiggs1 — Fri, 17 Feb 2023 16:23:56 GMT

" DOF is determined by two factors..."

Actually DOF is determined by FL , aperture and distance from subject to focal plane.

Example if you have your 100mm lens on a FF camera like a 5D Mk IV and have it set to f4. Your subject is 10 feet away. Critical focus is 10 feet, near limit is 9 1/2 feet, far limit is 10 1/2 feet for a DOF of nearly 3/4 of a foot.

Using the same set up but moving in to 6 inches (if possible), DOF would be about 1/10th of an inch.

Re: Interest in EF lens for imaging small, moving objects

normadel — Fri, 17 Feb 2023 17:35:03 GMT

My statement is correct as you see it.

ACTUALLY, Distance and Focal Length are the DETERMINERS of MAGNIFICATION.

MAGNIFICATION encompasses ANYTHING you have/do to change subject size at the sensor.

Re: Interest in EF lens for imaging small, moving objects

ebiggs1 — Fri, 17 Feb 2023 21:46:13 GMT

Of course it was incorrect otherwise I would not have corrected you.

There are three factors that allow you to calculate the depth of field (DOF) of an image. They are the aperture (f-stop), distance from the subject to the camera (its focal plane), and focal length of the lens. Longer FL lenses correspond to higher magnification as a product of their angle of view (AOV). Wide-angle lenses I.E. short focal length have low magnification because of their AOV. All of these parameters affect DOF in their own way and magnification has to, and does, change in accordance with the three main factors in calculating DOF. However it is not a factor in the DOF equation.

Re: Interest in EF lens for imaging small, moving objects

normadel — Fri, 17 Feb 2023 22:34:32 GMT

I sent you a private message. I do not want to argue with you here.

Re: Interest in EF lens for imaging small, moving objects

ebiggs1 — Sat, 18 Feb 2023 15:03:10 GMT

Fine, I won't argue!

Re: Interest in EF lens for imaging small, moving objects

bobsfloo — Sat, 18 Feb 2023 17:06:35 GMT

The focusing range is from 0.3m to infinity, which means the object has to be AT LEAST 0.3m from the image sensor. Any closer and your image will not be in focus.

As for the camera and lens coupler you're planning to use I don't know.