Telecentric Lenses

[JohnBar]

I would like to see some images taken with Telecentric lens and a comparision to standard lens of equal focal length and stop.

As I understand a Telecentric lens has the iris at the front instead of buried among the elements and I wonder what advantages there are if any

[iangreenhalgh1]

Never seen a lens with the iris at the front, that would cause severe vignetting I think.

[JohnBar]

Check this video at 2:29

http://www.youtube.com/watch?v=MpZOFJg9SAA

[visualopsins]

There is explanations & example photos:

http://www.edmundoptics.com/learning-and-support/technical/learning-center/application-notes/imaging/telecentricity-and-telecentric-lenses-in-machine-vision/?&viewall

[JohnBar]

Yes I have seen that, they mainly use diagrams


I wanted to see ordinary images like flowers, pets, headshots maybe with background Bokeh

[berraneck]

[JohnBar]

@berraneck

it does if you read the edmund optics link above and I quote


"It occurs when the system stop is placed at the front focal plane of the lens, resulting in an entrance pupil location at infinity. A shift in the object plane does not affect image magnification."

[kds315*]

Maybe you would enjoy finding out what a "front focal plane" of a lens is and where it is located, BEFORE you judge on others

[berraneck]

sorry, there was no intent to judge anyone. maybe it´s just my english.

[SXR_Mark]

[JohnBar]

Mark

Schneider seems to think object space telecentrics ARE very useful for photography. Watch the video above

So please stop posting misinformation

[sichko]

I thought the video was talking about image space telecentrics. Avery talks about even illumination of the sensor.

When Avery talks about the aperture being "in front" he means that the aperture ring is in front of the focus ring ? If you go back a few seconds from 2.29 you can see some glass in front of the iris. Google "Schneider Cine Xenar" and you'll find lots of pictures showing this more clearly.

[JohnBar]

[sichko]

[visualopsins]

Telecentric lens I know in use were attached with short tube to front of standard 35mm camera lens (Canon FD 2.8/35); the 35mm lens was attached to FD-C adapter and to a C-mount camera. IOW, the telecentric attachment acts like a close-up lens, with special properties:

[dnas]

[fermy]

[visualopsins]

EO Imaging Lab Module 2.2: Telecentricity (video)

[tromboads]

Yes. It is very limited for general photography! As it cant perceive objects larger then the entrance pupil, Unless you want to photograph things what, 3-5" wide that is.

[Aanything]

[fermy]

So is Schneider guy on drugs then? Look at 3:18 in the movie. They specifically highlight that telecentric lenses provide the same magnification regardless of distance, which means that their lenses must have cylindrical FOV. No doubt they would film some great movies with lenses that have a 10 cm cylinder as a FOV.

[sichko]

[SXR_Mark]

[sichko]

[SXR_Mark]

@ Sichko

The point you are making is (I believe, apologies if I am wrong) that, for a lens that is telecentric on the image space, the size of the image is independent of the position of the image plane (from the lens). Yes, this is correct. (sorry if I didn't get the point you were making before).

Image space telecentricity = exit pupil at infinity = image size independent of image plane distance

If the lens is conventionally entocentric on the object side, the image size still depends on the object distance. The lens still sees a normal perspective and has a field of view that extends beyond the lens diameter. Olympus 4/3 lenses are designed to be telecentric in the image space (at least the expensive ones are) but they still behave like perfectly normal camera lenses. With a camera lens, one does not really know that the lens is telecentric in the image space.

@Everyone

The issue causing confusion here is that the Schneider video suggests that the lenses are telecentric in object side. Now, the guy talks about the lens giving even illumination. This means they are telecentric on the image side, just like the Oly lenses. This is fine and is a good idea.

But then you get the following two slides in the video





This is pretty unambiguous to me. It says these lenses are telecentric in the object space.

Object space telecentricity = entrance pupil at infinity = image size independent of object plane distance = no perspective = FOV is a cylinder equal to lens diameter

Making a photography/cine lens like this is stupid. Firstly it says this is MORE NATURAL!! Really. I see in perspective and I think everyone else does too.

Next, the aperture on these lenses is right at the front (someone pointed out there is glass in front of the aperture but this is probably a plane filter to protect the aperture blades). But a telecentric lens has the entrance pupil (the image of the aperture as viewed from the front of the lens) at infinity. Since there are no optical elements in front of the aperture on these lenses, the entrance pupil is exactly where the aperture is and definitely not at infinity. It is clear the these lenses CANNOT be telecentric in the object space. This is of course a huge relief to anyone who is thinking of buying one as it means they will be able to make video of more than just ants.

So why does the video have those two slides? My bet is that it was but together by marketing people who:

heard the lenses were telecentric
looked up what that meant in the Schneider catalogue
found information in the section on machine vision lenses
thought the same benefits must apply to these lenses.
didn't realise the lens was only image-side telecentric

OK, maybe I'm being too cynical. Maybe Schneider have discovered some great way of making a pseudo-telecentric lens that has a meaningful field of view. I wait to be educated.

Mark

PS I've just realised there is a reference to wikipedia at the bottom of those slides. Doh. That says it all. Marketing people!!