Good morning from Madrid, I am building a OFMv7 manual as a first step to build an high resol OFM later. A question, I have several PMMA lens 10 mm diam and 4.5 mm thickness, are they suitable for the OFM? (I know I will have to re-adjust them to the condenser´s lens 12.7 mm space).
Thanks
Have your lenses got a flat rim around the edge? The standard condenser lenses that we use have a rim that is about 1mm, so the actual lens part is only around 10mm. The height of the lens is only partly important, what is the focal length? If you point the curved side at something far away out of the window, how far is the image from the lens.
I gather from you other posts that you are not using higher power lenses than ×40. With the low cost optics or with ×20 and ×40 objectives the illumination does not need to have a very high numerical aperture, so the condenser lens large diameter and short focal length are less critical.
Hi William,
my lenses have not rim around, they have 10 mm diameter exactly. I will try to buy other ones as yours.
Yes, you can calculate the focal length and it is dependent of diameter and thickness (to calculate the radius of curvature, R) and then calculate the focal length (f= R/n-1) for PMMA with a refraction index (n) of 1.49. Then, effective focal length is 10.86mm and 8.6mm the back focal length for 10 mm diameter and 3.5mm thickness.
Moreover, I have a problem with the 3D printed piece named “condenser”. The ring to place the lens in the condenser top part is poorly fixed to the structure and finally always ends as a loose piece apart. I am trying to design a smaller ring to place my 10mm-lens and insert al this in the ring at the top of the condenser. The problem is that I can´t know where exactly the lens is placed or if it is in a correct distance.
Thanks for your help and your time.
Note: I am building the OFMv7 manual version with c-270 Logitech webcam.
That is a longer focal length than the specification, but shoild be plenty for the C270 lens.
Could you print a ring, 10mm id, 12/13mm OD and 1mm thick and glue to your lens? Would end up being a shape that should fit. With care to to use too much glue 
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Thanks again William. I am trying to solve this issue. But, I do not why the internal rim becomes loose after print the condenser`s structure. Perhaps, I will need to glue also the rim to the condenser or change some parameters in my 3D printer. I will be playing searching for the best solution. Regards from Spain.
Could you post a photograph of the problem? It sounds as though the layer adhesion in the print is not good. In the main body that can cause hidden problems in the actuators as well.
That is the internal part that supports the lens? In that case it is fairly wide and should not come adrift. The outer shell part that grips the lens is much thinner and I would expect to have more problem if the layer adhesion is not good.
This is most likely to be an issue with your printer, either alignment, temerature, or settings. I have been fortunate so far that I have not needed to find out what causes or cures such issues.
I don’t see how it could be in the slicing, but it might be worth looking at the layers at that level in your slicer software, to look for any odd tool paths or voids.
