Canon 70 - 200mm 2.8 USM IS lens as a Tube Lens?

[Joe Sukenick]

I am using the Canon 70 - 200mm lens as a tube lens with a Mitutoyo 20x M Plan objective and getting acceptable images (I think) with this setup. I'm shooting a Canon 5D MK II in live view with a Stackshot controller and stepping motor driving an Olympus BHMJ focus block that steps the camera horizontally.

Is there an optimal distance from the shoulder of the objective to the front element of the Canon lens for best results? The Mitutoyo is currently mounted and secured in a hole bored in a flat metal screw-in lens cover. The objective threaded portion sits inside the lens cap about 6mm from the Canon's front lens element. Is there an optimal distance to mount the objective from the front lens element for the Mitutoyo and other infinity objectives for the best results or does it not matter?

Can anyone comment on how the 70 - 200 Canon lens performs as a tube lens compared to the famed "Morphanon" I've read so much about here? The Canon is set at 200mm, focus at Infinity and f/3.5. Is this the best setting for the lens?

The help and instructional information provided by Rik and so many others on this site is phenomenal. Thank you to all!

[abpho]

Welcome to the club.

If it works then you have the best settings. Are you getting proper coverage with this setup? Ie: How are the corners of the image (for lighting, sharpness, etc) on the full frame? Stopping down the tube lens typically does nothing since the objective is the limiting factor already. Make sure you have IS turned off.

[Joe Sukenick]

Abpho, thanks for the welcome and reply.

To cover the full frame sensor, I have to be right at 200mm or vignetting starts to creep in. There is very slight image degradation at the corners but it's not noticeable unless I do serious pixel peeping. The IS kept off.

[rjlittlefield]

Is there an optimal distance to mount the objective from the front lens element for the Mitutoyo and other infinity objectives for the best results or does it not matter?

It doesn't matter much. As short as possible will minimize the chance of vignetting. Be sure that everything possible behind the objective is flocked to minimize the chance of multiple reflections causing glare & loss of contrast.

Can anyone comment on how the 70 - 200 Canon lens performs as a tube lens compared to the famed "Morphanon" I've read so much about here?

As far as I can tell from reading other people's tests, the morfanon is famed primarily for its excellent cost/performance ratio. The images from all tube lenses are remarkably similar. This is because at rated magnification, infinity objectives stop down the optical system to an effective f-number around 18-20 (depending on objective). At such a small aperture, most aberrations get cut way down except for CA.

The help and instructional information provided by Rik and so many others on this site is phenomenal. Thank you to all!

Thank you for the kind words. Yes, this is a very unusual community!

--Rik

[Joe Sukenick]

Rik,

Thanks for the reply.

Be sure that everything possible behind the objective is flocked to minimize the chance of multiple reflections causing glare & loss of contrast.

It will be interesting to see if the flocking improves the image quality. I have shot enough without it to have a good baseline.