I have tried to use ZENITH lens in vacuum chamber. The out-gassing from the lens barrel was critical. So the maximal preasure did not exeed 10^-4bar.

Thank you Andrey. I will modify the lens assembly to add vent holes and perform a vacuum bake out prior to use. Hopefully this will reduce the outgassing. However there may be certain substances within the lens assembly, such as grease, that might continually outgas. In this case a complete disassembly, clean, and reassembly might be necessary.

Bear in mind that optical elements may be held in place with adhesives. Typical optical adhesives soften at around 50C, and therefore may not survive a bake.

Totally agree with David and Andrey. Optical performance will be ok, but outgassing is definitely an issue, both due to barrel, interspaces and adhesives. Try to use fixed focal lenses rather than zooms where you will have a lot more components, complexity, grease and sensitivity to misalignments. And if you dismantle the lens be very careful on re-mounting (order of surfaces, centering, placement, planarity), and look for someone having done it before if you are not yourself experienced.

I've had good luck with a basic 4F optical system, with all of the lenses and camera exterior to the vacuum chamber. This work was done at 10^-9 Torr.

The real question is: what is the vacuum that you require?

What is the nature of the imaging?

What are the other constraints?

Thank you for the latest updates. The lens I have purchased for this test is of fixed focal length. The lens will form part of a metrology camera system being used to monitor the position of a small target located inside the vacuum chamber, which ideally, should operate at 10^-7 mbar, at room temperature. The main issue raised here appears to be outgassing which we will need to carefully monitor. Unfortunately the metrology system cannot be located outside the vacuum chamber as to perform reliable position measurements the camera, lens, and target all have to be mechanically linked on a common mount within the chamber.

You can certainly have a stable fixture mounted outside of the chamber; I used a mechanical clamping system and a small optical breadboard. This was self-calibrated with a TEM grid target that was mounted on an XY-theta stage.

I've also seen small vacuum chambers mechanically mounted in holes cut in an optical table.

But I may not be understanding all of your requirements.

Another option is to enclose your lens system withing its own mini chamber which is vented to the outside. For example it could replace one of the windows.

As previously mentioned, if the adhesives survive the baking, the outgassing might be a problem. A lot of commercial assembly have brass, which will outgas. You can find some values from NASA and ESA. They measured outgassing values for different alloy.

http://outgassing.nasa.gov/

http://esmat.esa.int/Services/outgassing_data/outgassing_data.html

Another option, if the lens assembly is simple enough, could be to custom make a new casing (choosing a metal/alloy with low outgassing), and rebuild the lens assembly in it. Also mentioned here by Santiago Royo, this re-assembly can be very sensitive to misalignments (dependent on the complexity of the lens assembly).

Good luck.

You can buy single optical elements from a company like Thorlabs or Edmunds or very little money, place them in a lens tube, and then mount the lens tube with a C mount adapter or similar. If you put the lens in the mount yourself you can simply not add any glue or oil (which is unnecessary for fixed focus custom lens designs). Performance will not be as good because the design won't be well optimized for the application, but unless you need high resolution or large field of view this may not be an issue.

To minimise the out-gassing of our lens barrel in the vacuum chamber we have drilled a number of vent holes in the barrel. To work out where to drill the holes, without prior knowledge of the lens positions (proprietary information), we took an X-ray of the lens, as shown in the attached picture. We drilled the vent holes in locations to allow trapped volumes of air to escape. The lens barrel is now in a vacuum chamber undergoing testing to determine the amount of out-gassing versus time. If the levels of out-gassing are found to be acceptable then no further modification of the lens barrel will be needed and we will be able to use it in our vacuum camera facility.