A&M/LOMO 80/600 Vs Takahashi FS78 Vs Equinox 80ED
發表於 : 2010-02-08, 19:00State of the art, classic and bargain: A&M/LOMO 80/600 Vs Takahashi FS78 Vs Equinox 80ED
At the end of last December, I was told there is short tripod for HEQ5Pro. I was delighted by this news and asked Galaxy to reserve one set for me. This is by all mean improve the portability of HEQ5Pro. At the same time my friend Xiaoer needed to buy a new refractor which is used to couple with the LS75F. We went to Galaxy and shopped. When we arrived Galaxy, we were tempted by those scopes put messily on a table! A&M/LOMO 80/600, Tak FS78 and Pentax 75SDHF etc. Our curiosity drove us to try those scopes. Due to our background, doing experiment is kind of fun. If we can perform a star test and do some celestial observations, it would be great! However, the sky sucked almost for the whole winter, it is difficult to find clear skies for testing the scopes! So we tried an alternative, indoor test! Star test is a simple and accurate method to test and collimate telescopes. Instead of using a real star, Sirius or Vega, to perform star test, we used an artificial star. Basically it generates a spot of size 50um. When place it a several tens meters apart, the angle sustained will be smaller than the Rayleigh resolution. In our case, the spot size is 50um and the distance is 25.3m. The angle sustained is 50x10^-6/25.3 = 1.98x10^-6. Roughly all the aperture of all the tested scope is 80mm. The theoretical limit of the resolution, Rayleigh resolution, is 1.2x550x10-9/80x10^-3 = 8.25x10^-6. So the artificial star is virtually a star now! There were some advantages of using artificial star.
1. In Hong Kong, it is sadly that we cannot have bright real stars when in needed.
2. Even the telescope is the same, different nights would result in different star test result. The seeing, the turbulence of atmosphere, affects a lot.
3. Real stars are moving, but artificial star is stationary. One can perform high power magnification without caring about the tracking. Collimation is possible by using artificial star too!
The artificial star we used is not white light, but R, G & B. This is a big advantage that we can test the color correction of the scopes in three widely separated wavelengths in the visible spectrum. Well! The artificial star is very good in testing telescope. But it got a big disadvantage! It costs you for more than HK$2000! Worth it or not, you think about it!
OK! Back to our main course, the optical performance of A&M/LOMO 80/600 Vs Takahashi FS78 Vs Equinox 80ED. We used TV Everbrite diagonal and Pentax XO 2.5mm eyepiece to boost the magnifications above 200X for all scopes. All three scopes gave very good green diffraction pattern, especially the A&M/LOMO. It just standout! Its’ 2nd diffraction ring was almost invisible. This result was quite expected as all telescopes are optimized for green light. We next turned the star test to red light. The red light performance is corresponding to most DSO and Ha performance. The A&M/LOMO gave excellent diffraction pattern. Both Tak FS78 & Equinox 80ED gave very good diffraction pattern. It seems that Tak FS78 gave a bit better performance than Equinox. Finally we turned the star test to blue. A&M/LOMO gave very good diffraction ring. While both FS78 and Equinox 80ED gave good diffraction pattern. It seemed that Equinox gave a bit better performance than Tak FS78.
Summary Table:
1 means excellent & 5 means bad (Subjective 5 points scale)
Green Star Test
A&M LOMO 80/600 1+
Tak FS87 1
Equinox 80ED 1
** 1+ means excellent. Textbook like diffraction ring!!!
Red Star Test
A&M LOMO 80/600 1
Tak FS78 2
Equinox 80ED 2
** It seems that FS78 is a bit better than Equinox 80ED, but not sure. A side by side test is needed.
Blue Star Test
A&M LOMO 80/600 1
Tak FS78 2
Equinox 80ED 2
** It seems that Equinox 80ED is a bit better than FS78, but not sure. A side by side test is needed.
The use of artificial star is very convenient. The seeing is not an issue and the result is reproducible if other controllable factors, say distance and brightness, are fixed. The result is quite obvious that the A&M/LOMO is by all mean the winner. All three RGB star tests of A&M/LOMO are way ahead Tak FS78 and Equinox 80ED. It is hard to differentiate Tak FS78 & Equinox 80ED, because we didn’t set all scopes side by side and do comparison. From the very beginning, we started the test after a casual talk. So no serious preparation was done. Only one tripod was used. This means we need to swap the scopes and memorize the star test result for a particular scope and do the comparison. Unless the result is very outstanding like the case of A&M/LOMO, otherwise it wouldn't be very reliable to tell the difference. In other words, there would not be big different in Tak FS78 & Equinox 80ED. If one really wants to differentiate them, a side by side artificial star test is needed.
Apart from the optics, I like the Feather Touch focuser of the A&M/LOMO the best. I have an Equinox 80ED, mounting a heavy DSLR for high magnification would be difficult. Although the dual speed focuser of Equinox is not bad, Feather Touch is just gorgeous! Try it for imaging and you will know it. It is tough and accurate. The Tak FS78 focuser is a bit behind among these three scopes in nowadays standard. So which one I would choose? If I have money, I will go for A&M/LOMO. It is state of art. However, if you are a collector or Tak fans, go for FS78. It is a classic. If you are a pragmatic user, Equinox 80 is the one to opt! It is a real bargain. Which one you would opt? Ask yourself?
At the end of last December, I was told there is short tripod for HEQ5Pro. I was delighted by this news and asked Galaxy to reserve one set for me. This is by all mean improve the portability of HEQ5Pro. At the same time my friend Xiaoer needed to buy a new refractor which is used to couple with the LS75F. We went to Galaxy and shopped. When we arrived Galaxy, we were tempted by those scopes put messily on a table! A&M/LOMO 80/600, Tak FS78 and Pentax 75SDHF etc. Our curiosity drove us to try those scopes. Due to our background, doing experiment is kind of fun. If we can perform a star test and do some celestial observations, it would be great! However, the sky sucked almost for the whole winter, it is difficult to find clear skies for testing the scopes! So we tried an alternative, indoor test! Star test is a simple and accurate method to test and collimate telescopes. Instead of using a real star, Sirius or Vega, to perform star test, we used an artificial star. Basically it generates a spot of size 50um. When place it a several tens meters apart, the angle sustained will be smaller than the Rayleigh resolution. In our case, the spot size is 50um and the distance is 25.3m. The angle sustained is 50x10^-6/25.3 = 1.98x10^-6. Roughly all the aperture of all the tested scope is 80mm. The theoretical limit of the resolution, Rayleigh resolution, is 1.2x550x10-9/80x10^-3 = 8.25x10^-6. So the artificial star is virtually a star now! There were some advantages of using artificial star.
1. In Hong Kong, it is sadly that we cannot have bright real stars when in needed.
2. Even the telescope is the same, different nights would result in different star test result. The seeing, the turbulence of atmosphere, affects a lot.
3. Real stars are moving, but artificial star is stationary. One can perform high power magnification without caring about the tracking. Collimation is possible by using artificial star too!
The artificial star we used is not white light, but R, G & B. This is a big advantage that we can test the color correction of the scopes in three widely separated wavelengths in the visible spectrum. Well! The artificial star is very good in testing telescope. But it got a big disadvantage! It costs you for more than HK$2000! Worth it or not, you think about it!
OK! Back to our main course, the optical performance of A&M/LOMO 80/600 Vs Takahashi FS78 Vs Equinox 80ED. We used TV Everbrite diagonal and Pentax XO 2.5mm eyepiece to boost the magnifications above 200X for all scopes. All three scopes gave very good green diffraction pattern, especially the A&M/LOMO. It just standout! Its’ 2nd diffraction ring was almost invisible. This result was quite expected as all telescopes are optimized for green light. We next turned the star test to red light. The red light performance is corresponding to most DSO and Ha performance. The A&M/LOMO gave excellent diffraction pattern. Both Tak FS78 & Equinox 80ED gave very good diffraction pattern. It seems that Tak FS78 gave a bit better performance than Equinox. Finally we turned the star test to blue. A&M/LOMO gave very good diffraction ring. While both FS78 and Equinox 80ED gave good diffraction pattern. It seemed that Equinox gave a bit better performance than Tak FS78.
Summary Table:
1 means excellent & 5 means bad (Subjective 5 points scale)
Green Star Test
A&M LOMO 80/600 1+
Tak FS87 1
Equinox 80ED 1
** 1+ means excellent. Textbook like diffraction ring!!!
Red Star Test
A&M LOMO 80/600 1
Tak FS78 2
Equinox 80ED 2
** It seems that FS78 is a bit better than Equinox 80ED, but not sure. A side by side test is needed.
Blue Star Test
A&M LOMO 80/600 1
Tak FS78 2
Equinox 80ED 2
** It seems that Equinox 80ED is a bit better than FS78, but not sure. A side by side test is needed.
The use of artificial star is very convenient. The seeing is not an issue and the result is reproducible if other controllable factors, say distance and brightness, are fixed. The result is quite obvious that the A&M/LOMO is by all mean the winner. All three RGB star tests of A&M/LOMO are way ahead Tak FS78 and Equinox 80ED. It is hard to differentiate Tak FS78 & Equinox 80ED, because we didn’t set all scopes side by side and do comparison. From the very beginning, we started the test after a casual talk. So no serious preparation was done. Only one tripod was used. This means we need to swap the scopes and memorize the star test result for a particular scope and do the comparison. Unless the result is very outstanding like the case of A&M/LOMO, otherwise it wouldn't be very reliable to tell the difference. In other words, there would not be big different in Tak FS78 & Equinox 80ED. If one really wants to differentiate them, a side by side artificial star test is needed.
Apart from the optics, I like the Feather Touch focuser of the A&M/LOMO the best. I have an Equinox 80ED, mounting a heavy DSLR for high magnification would be difficult. Although the dual speed focuser of Equinox is not bad, Feather Touch is just gorgeous! Try it for imaging and you will know it. It is tough and accurate. The Tak FS78 focuser is a bit behind among these three scopes in nowadays standard. So which one I would choose? If I have money, I will go for A&M/LOMO. It is state of art. However, if you are a collector or Tak fans, go for FS78. It is a classic. If you are a pragmatic user, Equinox 80 is the one to opt! It is a real bargain. Which one you would opt? Ask yourself?
