I have the file for the next phase which is the erecting lens version but I can't get it down small enough to get it submitted.
Mike

Quote:


Yes and no, depending...

A converging lens, DCX or PCX, will focus a collimated beam to the focal point of the lens at its focal distance. Collimated light travels parallel to the focal axis. The light rays from an object at an infinite distance from the objective lens are considered to be traveling to the objective lens as a collimated beam of light. 

If the next lens is a DCX and is placed at the proper spacing, the converged rays from the objectives focal point should converge again at your DCXs back (rear) focal point, toward the ocular end.

However, if your next lens is a PCX, and depending on how you orient it, your point image coming from the objective focal point could be converted back into a collimated beam, which would be imaged to infinity, and not the focal point of your next lens downstream.  

My post about splitting a DCX into two PCXs was a hint. With the orientation of the two PCX halves from the DCX kept unchanged, and when slowly separated, you should have collimated light between the two halves. Now combine that idea to obtain an effective focal length to replace a DCX lens that you can't order in exactly the focal length you want, and you've got a possible work-around. 

Selecting a lens is kinda like selecting a new canister powder. You need to gain an understanding of its particular properties, as compared to others, and experiment a bit to see if its suitable. 
Snell's Law and ray diagraming is an important part of understanding the particular properties of a lens. 

Mike,
Good articles, Thank you. Emphasizes the importance of baffles (stops, learned a new word) and a test setup. Edmund (Anchor) experimental lenses can vary by 10%, so a test setup is important.  Deadeyes's aluminum angle is about as easy as any.
Chuck

Frank,
Look at the cut-away pictures of modern scopes that depict the various lens cell configurations. You'll often see DCX and PCX lenses combined (as well as other lens types), some touching, some with a separation, and in several different orientations. How you arrange the particular lenses is determined by where you need the rays to go as they travel through the scope. 

If you can find a PCX lens that looks like it will do about the same thing you're damaged and unavailable DCX lens did, go ahead and give it a try. It may come close, or not quite close enough, and then you'll need to experiment to get it to work properly with your existing lenses.

One advantage a PCX often has is that when it is used to focus collimated light rays, it often produces a sharper focal point, reducing spherical aberration. 

But remember, the path of light rays that were converged to a focal point inside the scope and are now spreading apart as they travel from that single point source to your PCX, are not traveling at the same angles as a set of light rays in a collimated beam, and the angles as they exit the PCX will likely be different. 

Learning Snell's Law and applying it to make ray diagrams (and to do the math) is a big part of paying your dues.


Chuck,
Baffles, stops, and diaphrams are kinda similar. Lasers use them to help keep the individual light rays bundled into the single beam, and there is a lot of good info in that area of optics that is useful for managing the light rays traveling through telescopes.