The pads are from Willman-Bell I believe. They are optical polishing pads. They have an adhesive on the back and in the shape of flower petals. Be careful, they are aggressive!
So, how do you determine the F ratio? Do you just measure how deep the parabolic shape goes compared to the diameter of the glass? And what other kind of test do you perform to determine the quality of the mirror?
The F ratio is determined by the sagitta, also known as the depth. The F ratio equation is (r²/sagitta)x 4=f/l. I have a tool called a spherometer. I made it using a dial indicator and a solid piece of square wood about 20" in length. The indicator measures to .001". You have to zero on the edge of the mirror and I find the lowest spot in the center and that gives me my sagitta. ALL lenses and mirrors are first made spherical, then polished to parabola, ellipsoidal, etc.Google ronchi for tests.
How do you know where to put the secondary mirror? (I know the basics) So let's keep the secondary out of mind for simplicity. Say you have a mirror that has a 4.5 F ratio. Does that mean the light from the primary mirror comes to a point at 4.5 times the diameter of the mirror?Example: You have an F 3 mirror, the mirrors diameter is 3 inchs. Does the light come to a point at 9 inchs? Thanks!!!!
Yes you have that right. Although you have to factor in for the diameter of your tube etc. and how much back-travel or in-travel you want from your focuser.
drive is to quick
1955flashpointer 7 months ago
What material are the pads that you show?
Thanks,
Frank Spillman
spilperson 2 years ago
The pads are from Willman-Bell I believe. They are optical polishing pads. They have an adhesive on the back and in the shape of flower petals. Be careful, they are aggressive!
Messiermarathon 2 years ago
So, how do you determine the F ratio? Do you just measure how deep the parabolic shape goes compared to the diameter of the glass? And what other kind of test do you perform to determine the quality of the mirror?
ryansuperbee 2 years ago
The F ratio is determined by the sagitta, also known as the depth. The F ratio equation is (r²/sagitta)x 4=f/l. I have a tool called a spherometer. I made it using a dial indicator and a solid piece of square wood about 20" in length. The indicator measures to .001". You have to zero on the edge of the mirror and I find the lowest spot in the center and that gives me my sagitta. ALL lenses and mirrors are first made spherical, then polished to parabola, ellipsoidal, etc.Google ronchi for tests.
Messiermarathon 2 years ago
How do you know where to put the secondary mirror? (I know the basics) So let's keep the secondary out of mind for simplicity. Say you have a mirror that has a 4.5 F ratio. Does that mean the light from the primary mirror comes to a point at 4.5 times the diameter of the mirror?Example: You have an F 3 mirror, the mirrors diameter is 3 inchs. Does the light come to a point at 9 inchs? Thanks!!!!
ryansuperbee 2 years ago
Yes you have that right. Although you have to factor in for the diameter of your tube etc. and how much back-travel or in-travel you want from your focuser.
Messiermarathon 2 years ago