I am trying to figure out if these 13mm condenser lenses available from amazon would work for a build of the low-cost microscope:
The lenses are described based on their “beam angle” (15, 30, 45, 60, 90 or 100 degree) and I am unsure which one would be most suitable, as the description does not mention their focal length.
Or would these be a better alternative, even though they are 12.5mm in diameter:
Thanks in advance, this is my first build and I am still sourcing out all the required parts.
Hi @ricardd. The condenser lenses are the hardest thing to find unfortunately.
For the optical purpose they need a large clear diameter and short focal length. The OpenFlexure design uses a type of lens with a flange on. The actual curved lens part is maybe 11mm diameter, with a flange all around. The focal length is 5mm.
If you are using a high resolution objective, 40× or more, then this is very important. For 20× or for the low-cost optics you can do well with a longer focal length condenser lens.
For the physical fit in the condenser, the lens needs to have 13mm outer diameter. To work with the push-fit it also needs to have the thin outer flange region.
Most of the vendors listed on the OpenFlexure website have the lenses, and if you are getting any of the electronics then it is easy to get the lens as well. Otherwise it can be a bit of a search, and the lenses are more likely available in 100s direct than to find them on Amazon.
If you are doing the soldered LED and Sangaboard compatible microcontroller setup, rather than buying the electronics, then modifying the condenser makes a bit more sense. If you are willing to use a little epoxy to glue around the edges of a lens, then the push-fit is not important. As I also put earlier, for low magnification the focal length is also not so important, but you do want it as short as you can. Because the LED in our condenser is only about 35mm away from the condenser, a focal length of about 10mm is the maximum that will give a focus on the sample.
As to the lenses that you link, the first ones are probably a lens with a spacer. If a lens is very close to an LED the light will still diverge, as you move the lens away then the beam becomes more focused. Have a look at the pictures, I would expect that the ‘wider angle’ ones have a smaller spacer part, which is what you want. In use you would put the spacer towards the sample. The second lenses have no flange, the focal length is not stated, but they look to be not very curved, so will have quite a long focal length.
I had a look at the first set. There are some good photos that are clearly different for each version, not a generic for the overall style.
It seems that the spacer is the same on all of the different angles, but the lens changes. The 15 degree ones are the most ‘bulged’ so have the shortest focal length. You could try sanding off most of the spacer part, which would give you a flanged lens that should fit. Obviously you would need care not to scratch either side of the actual lens part.
I suppose only the UK is this kit available. This would be really useful for the manual microscope.
For manual you need current limiting, preferably on the LED board.
I’ve had the first ones in my microscope and they work alright. Pic in thread below
In the post above that one I can see that the lenses fitted without removing the spacer part, it is clearly there sticking out below the condenser.
Did you get the 15 degree version?
Yes, 15 degrees. The spacer sticks out from the bottom and the lens is smaller than the regular OFM lens, but it works fine. I also had a 30 degrees version I didn’t try, which I think would bring the condenser up a bit, since you see it almost touching with 15.
Edit: also the way the lens sits in there, with a bit of force you can push it out by the spacer and put in the regular lens. I’ve changed mine to get rid of the plastic sticking out once I got them.
Thank you @WilliamW and @adamglia for the relevant info, I will order the lenses with 15° angle and go from there.
@j.stirling I have gathered most of the other parts and that kit would probably be prohibitively expensive to ship to Canada.
I will keep you posted with the build. It is very encouraging to have the developers replying here in a timely fashion and with clear answers and directives.
I do ship that worldwide. However, one concern with it is that the LED board doesn’t have current limiting, so for manual setups it requires at least an extra resistor and a bit of soldering or a breadboard.
I don’t know what is the best way to handle that, maybe having a separate current limiting component that could be added in line so that it is connected directly to the Pi? It could be a little PCB or even just a resistor (or a constant current diode, but for a manual setup resistor is likely fine) inside a short cable extension. That way people can switch to the motorised version with Sangaboard easily.
Other option is to re-make the version of the LED with the constant current driver (maybe with a solder bridge bypass if people want to switch), but I think that was deemed possibly confusing in the past.
We are derailing @ricardd’s thread rather here! The current (v7.0.0-beta5) instructions for the illumination for the Manual suggest adding a current limiting resistor in the wire when using the LED PCB: Assembly Instructions.
Personally I use PCBs with constant current drivers, the previous round version, as I still have several. Your design with D-shape for the LED-only board, to make it different from the round board with current limit, I think gives the opportunity to have both versions in the wild. It then depends on what the demand might be to see whether it would be worthwhile for people to sell them. I do find them useful in all sorts of places that are not microscopes - there are many other mini LED boards available, but with these I know they have a really flat spectrum for optical experiments. Plus of course I have some in the cupboard…