Televue NP 101 & my homemade TMB 115
Posted: Wed Sep 06, 2006 1:35 pm
The Televue NP101 refractor happened to stay with me for a while and I quickly grabbed this chance to do an amateurish test from a Steve’s point of view.
APOs are good at image sharpness, contrast and being able to be pushed to extreme. In order to find out the hair splitting differences, both scopes are tested at high magnification.
Combination A: Televue NP101 (fl=540mm, f ratio=5.40) + Nagler Zoom ep (3mm fl), exit pupil: 0.56 mm, Power: 180 X
Combination B: TMB115 (fl=805mm, f ratio =7.0) + tmb monocentric 4 ep (4mm fl), exit pupil: 0.57 mm, Power: 200 X
Testing object: “The SPIRE” Building near Bukit Timah, it is approx. 2600 meters away from my balcony. There are plenty of pinpoint light sources that is good to do collimation and a wealth of details on the attic such as water marks (low contrast) and lettering (high contrast) that tells when the building was built (2002/03751).
1. Finishing & workmanship: Being the high end Televue refractor, the NP101 is truly a piece of art. Holding it at hand gives me a feel as if it was an antiaircraft missile, the black anodized dew shield and focuser are of matt finishing which is quite different from TV’s earlier models whose paintings are very glossy and gives a less professional feel. The focuser is still the rack-and-pinion, however it works surprisingly well with the fast f 5.40 incident light cone whose focal plane is paper-thin. My homemade TMB115 only outshines the Televue in two aspects: 1) the retractable OTA and the 2) dual speed focuser that makes focusing at high power much easier.
2. Star test: (done by using terrestrial pin point light source such as a mercury lamp, so it is not a real star test). Just same as what was reviewed by S & T years ago, there is nothing imperfect with NP 101 given its aperture, both inside and outside-focus diffraction rings are highly symmetric and shows no color at all. I also cannot find the asymmetric and color on tmb 115’s diffraction ring however its interferometer test report does state a 0.03 rms and a 95.6% strehl.
3. Image contrast and sharpness: A close match
4. Resolving power: tmb 115 slightly outperforms, providing more successful glimpse showing the subtle details on water marks and lettering on “The Spire” ‘s attic.
5. Lens coating and reflection: the NP101 is better than tmb 115, giving a deeper and fainter green reflection off the optical surfaces. The tmb shows a brighter and blue reflection that seems more superficial.
6. Color bias: the tmb 115 exhibits a cooler image.
7. Compatibility with Nagler T5/31 eyepiece: the behemoth eyepiece handles both scopes well, showing almost identical visual performance. I guess it is the flat field given by NP101 that helps retain the edge performance, however the NP101 does give a larger TFOV which I think is more useful at Mersing.
I didn’t see any magic things happened on either NP101 or tmb 115 bearing in mind that they are highly famed by apo fans. In this case, physics and aperture simply rules.
My sincere thanks to Andrew (Tachyon) who helped me go through the custom clearance and an anonymous amateur who provided the fund.
APOs are good at image sharpness, contrast and being able to be pushed to extreme. In order to find out the hair splitting differences, both scopes are tested at high magnification.
Combination A: Televue NP101 (fl=540mm, f ratio=5.40) + Nagler Zoom ep (3mm fl), exit pupil: 0.56 mm, Power: 180 X
Combination B: TMB115 (fl=805mm, f ratio =7.0) + tmb monocentric 4 ep (4mm fl), exit pupil: 0.57 mm, Power: 200 X
Testing object: “The SPIRE” Building near Bukit Timah, it is approx. 2600 meters away from my balcony. There are plenty of pinpoint light sources that is good to do collimation and a wealth of details on the attic such as water marks (low contrast) and lettering (high contrast) that tells when the building was built (2002/03751).
1. Finishing & workmanship: Being the high end Televue refractor, the NP101 is truly a piece of art. Holding it at hand gives me a feel as if it was an antiaircraft missile, the black anodized dew shield and focuser are of matt finishing which is quite different from TV’s earlier models whose paintings are very glossy and gives a less professional feel. The focuser is still the rack-and-pinion, however it works surprisingly well with the fast f 5.40 incident light cone whose focal plane is paper-thin. My homemade TMB115 only outshines the Televue in two aspects: 1) the retractable OTA and the 2) dual speed focuser that makes focusing at high power much easier.
2. Star test: (done by using terrestrial pin point light source such as a mercury lamp, so it is not a real star test). Just same as what was reviewed by S & T years ago, there is nothing imperfect with NP 101 given its aperture, both inside and outside-focus diffraction rings are highly symmetric and shows no color at all. I also cannot find the asymmetric and color on tmb 115’s diffraction ring however its interferometer test report does state a 0.03 rms and a 95.6% strehl.
3. Image contrast and sharpness: A close match
4. Resolving power: tmb 115 slightly outperforms, providing more successful glimpse showing the subtle details on water marks and lettering on “The Spire” ‘s attic.
5. Lens coating and reflection: the NP101 is better than tmb 115, giving a deeper and fainter green reflection off the optical surfaces. The tmb shows a brighter and blue reflection that seems more superficial.
6. Color bias: the tmb 115 exhibits a cooler image.
7. Compatibility with Nagler T5/31 eyepiece: the behemoth eyepiece handles both scopes well, showing almost identical visual performance. I guess it is the flat field given by NP101 that helps retain the edge performance, however the NP101 does give a larger TFOV which I think is more useful at Mersing.
I didn’t see any magic things happened on either NP101 or tmb 115 bearing in mind that they are highly famed by apo fans. In this case, physics and aperture simply rules.
My sincere thanks to Andrew (Tachyon) who helped me go through the custom clearance and an anonymous amateur who provided the fund.
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