10x only or not?

[cpsTN]

While observing a Rotifer in water from snow, I wasn't able to reach focus with the 40x objective and 10x EP. I WAS, however, able to reach focus with both the 20x objective and 20x eyepiece for the same power of 400x. I know about the 500-1000x NA rule. Since both configurations reached the same power, how is this working if the "law" is 10x EP only?

[Oliver]

I would guess that the lower depth of field of the 40x objective caused you to have focusing problems. It might (as a matter of fact) have been in focus, but because of the lower depth of field areas above and below the focus plane might have interfered, and therefore given you a subjective impression that it is out of focus. The resolution would still have been higher for those part that are in focus (compared to the 20x objective 20x EP), but the subjective impression was that it is overall more blurry due to the lower depth of field. I guess.

Oliver.

[cpsTN]

Thank You, Oliver. That's the problem I see with Microscopy. It's not like telescopy, a hobby of mine since 1986. Many times, the focus area itself seems microscopic too! lol Was I actually getting 400x with the 20 obs and 20 EP?

[apochronaut]

There isn't really a 10X eyepiece law, just a caution that 15X and 20X may be overstepping logic, when it comes to resolution and since you have some astronomy experience perhaps it would help if the microscope parameters were translated into a telescope framework. This may be of some help.

A 10X eyepiece microscope eyepiece has a focal length of around 22.5mm. A common lower power telescope eyepiece is around 25mm. Using a 20X microscope eyepiece is like using an 11mm telescope eyepiece, and the image quality degradation that can occur with it's improper use is similar.

Yes; it is a benefit to use a 20X objective with a 20X eyepiece because of better W.D. and better depth of field but the trade off in resolution is usually not worth it. You can get around that by purchasing apochromat objectives, just as in astronomy an apo refractor eclipses an identical diameter and focal length achromat and will perform better with shorter focal length, eyepieces.

However, using a 20X eyepiece with a 20X .40, even .50 objective, is not going to give you the resolution that a 40X .65 will with a 10X. If you were to use a 20X .65 apochromat with a 20X eyepiece you probably would get the same resolution, maybe even better but the apochromat would have a W.D. closer to that of a 40X, so a tradeoff exists, no matter how it is sliced.

[Dale]

and buying the apo would stimulate our economy to no end.......

[cpsTN]

and buying the apo would stimulate our economy to no end.......

Yes, but it would blow MY economy sky high! lol
I just started paying on a bankruptcy, $1300/mo on a $20k income. That's why I'm asking so many questions. My income tax, which I will get to keep, is about the only time I can buy anything, so I want to buy as few times as I can.

[apochronaut]

Apochromats aren't as expensive, as used objectives, as most people think. If you are searching for modern infinity corrected objectives, then the prices are likely going to be high, of course but even in that category of objectives , there are often less expensive ones. I 've paid 100.00-150.00 for several and as low as 50.00 for a planfluorite, simply because I looked for them. If you take the position that they are unobtainable and never look, you will never find them.
If you have a fixed tube microscope of 160mm, there are lots around and at good prices too.
http://www.ebay.com/sch/i.html?_nkw=apo ... mfe=search
http://www.ebay.com/itm/Bausch-Lomb-Apo ... Sw3ydV5kh9

2 of these are for 160mm tube. sell the others for 30.00 each.
http://www.ebay.com/itm/Bausch-Lomb-Obj ... Sw4UtWSMHm
http://www.ebay.com/itm/SPENCER-OBJECTI ... SwiwVWTgGS

Unfortunately, from a technical point of view, there is no way around your ongoing desire to raise the magnification by the use of 20X eyepieces but to couple them to an objective , that has the capacity to utilize the extra magnification.