Wanted 30x Microscope Objectives

Jem · Post by **Jem** » Thu Apr 28, 2011 3:06 am

Hi all

I'm in need of a couple of decent quality 30x microscope objectives. They must produce a nice reasonably clean expanded beam when a laser is shone through them.

I have some 20x and these don't expand the beam enough, I also have some 40x and these expand the beam too much and waste loads of precious photons. I guess 30x should be just perfect for my needs

They're for my holography setup and they'll be used in a spatial filter. I don't want any that are scratched etc. Even though i'm using a pinhole to clean up the beam there are limits

Please PM me if you have any laying around (in some nice protective packing of course). I'm in the UK, so as well as a price I would also need a shipping cost.

Cheers

Jem

holomaker · Post by **holomaker** » Thu Apr 28, 2011 6:15 am

hi Jem, these 30x are rare and super hard to find. why dont you place a weak lens on the output side of the spatial filter and simply adjust the divergence that way? If the correct lens is used(like a Meniscus) no artifacts will be seen from this lens as its not going to focus anything just slightly bend it ...............

Ed Wesly · Post by **Ed Wesly** » Thu Apr 28, 2011 6:41 am

Or why not put a weak lens on the input side of the microscope objective? Since most laser beams don't entirely fill the entrance aperture of the MO, pre-spreading the beam will fill it up, resulting in a wider spread. A little trick TJ showed me.

You will need a longish focal length for the pre-spreader. I use a negative 100, but wish I had longer. If you consider that the incoming laser beam is collimated, then its image spot will be formed one focal length away from the lens on the image side, or as close to the MO as it can possibly be. A beam diverging from a negative lens will be interpreted by the MO as being nearer, and the image will be thrown further from the MO, possibly more than the travel in the focusing axis of the SF.

Hope this helps solve your recurring dilemma!

Jem · Post by **Jem** » Thu Apr 28, 2011 7:17 am

Thanks guys

I was just trying for the easy option in hoping to pick up a couple of objectives. I work in Ophthalmic Optics so I have (plastic ophthalmic) lenses coming out of my ears, if I don't manage to pick any 30x's up i'll have a play around and surface/cut myself some appropriate AR coated lenses to fit into the back of each objective.

It's frustrating that I can't just move the SF/Mirrors either forward or backwards, but as my table is so small i'm prety much limited with my options.

In other news, and following on from all my stability issues (which are now hopefully cured), i'm now producing nice, bright and clean H1 Master transmission holograms (well, five so far if that qualifies me

). I'll shortly be moving on to trying to produce reasonable H2's

I think one of my big steps forward in brightness (apart from stability) was the change from a fast developer (Zip 1) to a slower developer (CW-C2), i'm using the old Agfa film. I now have my exposures down to below 5 seconds and deveopment time is around 2 minutes in CW-C2, bleaching in EDTA takes around 1½ minutes.

Thanks to all on here who have offered advice in the past, and particularly to John Sonley who lives local to me, his help and assistance has been invaluable, I consider him my holography mentor as well as a good friend.

Cheers

Jem

Dinesh · Post by **Dinesh** » Thu Apr 28, 2011 1:21 pm

Jem wrote:AR coated lenses

You're sure you want it AR coated? You're hitting the lens with coherent light. If you're hitting it with red, AR coating will not affect it and if you're hitting it with green, you'll lose a lot of light off the front surface. Assuming that the AR coating is coated for green.

Jem · Post by **Jem** » Thu Apr 28, 2011 4:38 pm

Dinesh wrote:
Jem wrote:AR coated lenses
You're sure you want it AR coated? You're hitting the lens with coherent light. If you're hitting it with red, AR coating will not affect it and if you're hitting it with green, you'll lose a lot of light
off the front surface. Assuming that the AR coating is coated for green.

Good point Dinesh. I'll get some transmission curves for the various coatings we use and see what the losses are at various wavelengths. I'm currently using a 35mW HeNe although I do have a C315m as well. Using the HeNe allows me to compare results directly with John, plus it's easier for him to troubleshoot my holograms as he's used a HeNe for many years.

I appreciate your input though.

Kind regards

Jem