NGC3621Posted By Roland Christen |
>>Also the fluorite lens of the TEC180m FL is showing its strength here with less scatter than other lenses and slightly more throughput.>.
Both those statements about scatter and throughput are not correct.
1) Your triplet lens has two other elements of ordinary optical crown, so even if the fluorite was replaced by air or vacuum, the two other glasses are still there.
2) ordinary optical glass has insignificant scatter in the scheme of things. It is almost all back scatter and very little forward scatter. The light that is scattered goes in all directions, especially back out the front of the lens (that's why you can see the faint laser trace) and almost none of the energy reaches the film plane. Unlike a mirror, where almost all scatter goes into the direction of the film plane, optical glass has almost zero focused forward scatter. That's why normal optical crown can be used in coronagraphs where no scatter can be tolerated, and mirror coatings cannot be used at all due to forward scattering.
3) the light transmission of optical crown and fluorite is almost identical over the visual wavelength range from near IR to the edge of the UV. Only in the UV does fluorite transmit more light, but that is not a useable wavelength, plus the other cover glasses of a triplet absorb light there anyway. You will not be able to measure the diffrence in transmission between a fluorite and an ED oil spaced triplet.
Lenses in general, and oil spaced triplets in particular, have very high light transmission efficiency. Refractor tubes can be ideally baffled to prevent stray light. If the figuring is good, then you can get very good focused energy into the image, which allows you to stretch it to extract ectremely faint detail. It has zero to do with the fluorite, but everything to do with the way the scope is built.
Tony Hallas discovered this himself when he was experimenting with various refractors at his deep sky site. He found that he could go far deeper with a refractor than he could with his 14.5" Cass before background light intruded into the image. Example is his latest M81/82 image, among others, which shows extensive faint extra-galactic dust around those galaxies. His scope is a 206mm F8 triplet apo, non-fluorite: http://www.astrophoto.com/M81M82.htm
I also have a preliminary Rosette which he has not published yet, but which he will show at NEAF. It has faint detail in the core that I have not seen in any amateur photo. No fluorite was needed, just a well baffled oil spaced triplet refractor.
Rolando
Both those statements about scatter and throughput are not correct.
1) Your triplet lens has two other elements of ordinary optical crown, so even if the fluorite was replaced by air or vacuum, the two other glasses are still there.
2) ordinary optical glass has insignificant scatter in the scheme of things. It is almost all back scatter and very little forward scatter. The light that is scattered goes in all directions, especially back out the front of the lens (that's why you can see the faint laser trace) and almost none of the energy reaches the film plane. Unlike a mirror, where almost all scatter goes into the direction of the film plane, optical glass has almost zero focused forward scatter. That's why normal optical crown can be used in coronagraphs where no scatter can be tolerated, and mirror coatings cannot be used at all due to forward scattering.
3) the light transmission of optical crown and fluorite is almost identical over the visual wavelength range from near IR to the edge of the UV. Only in the UV does fluorite transmit more light, but that is not a useable wavelength, plus the other cover glasses of a triplet absorb light there anyway. You will not be able to measure the diffrence in transmission between a fluorite and an ED oil spaced triplet.
Lenses in general, and oil spaced triplets in particular, have very high light transmission efficiency. Refractor tubes can be ideally baffled to prevent stray light. If the figuring is good, then you can get very good focused energy into the image, which allows you to stretch it to extract ectremely faint detail. It has zero to do with the fluorite, but everything to do with the way the scope is built.
Tony Hallas discovered this himself when he was experimenting with various refractors at his deep sky site. He found that he could go far deeper with a refractor than he could with his 14.5" Cass before background light intruded into the image. Example is his latest M81/82 image, among others, which shows extensive faint extra-galactic dust around those galaxies. His scope is a 206mm F8 triplet apo, non-fluorite: http://www.astrophoto.com/M81M82.htm
I also have a preliminary Rosette which he has not published yet, but which he will show at NEAF. It has faint detail in the core that I have not seen in any amateur photo. No fluorite was needed, just a well baffled oil spaced triplet refractor.
Rolando
