by Rich Neuschaefer
| Tele Vue TV-76 | 76mm f/6.3 doublet APO refractor | Bogen 3021 aluminum tripod / TV Tele-Pod head |
|---|---|---|
| Takahashi FS-78 | 78mm f/8.1 doublet APO refractor | Tele Vue Gibraltar alt/az mount |
| Leica Televid 77 APO | 77mm f/5.7 triplet APO refractor | Manfrotto CarbonOne 441 tripod / Bogen 3130 head |
Montebello Open Space, Palo Alto, California
With the permission of the park management our observing group uses the Montebello OS parking lot for small star parties. Montebello is near the top of the ridge, in hills a few miles west of the city of Palo Alto.
We had a clear, cool evening. Dew was not a problem. The test period was from 6:30 pm PST to 8:30 pm PST. The seeing was quite good during that time. After 8:30 pm the seeing quickly degraded to the point it was not good enough for testing these telescopes.
The Moon was large, 12 days old and well up in the East. Jupiter and Saturn were high overhead.
I started by comparing the two compact scopes, the TV-76 and Leica 77. The highest power eyepiece Leica offers is a 20x-60x zoom. I used the Moon as a test target. It was easier to use than Jupiter or Saturn because it was not as high overhead. The Leica has the eyepiece at a 45 deg angle. It is not easy to use when pointing nearly straight up. At 60x, both the Leica 77 and TV-76 gave sharp, high contrast, color free images.
At this point, I felt time would be better spent comparing the TV-76 and FS-78 since they both will accept eyepieces that give more than 60x. I should say that it would have been easier to do a comparison of these two telescopes if I had found a way to mount them side by side on my Astro-Physics 900GTO mount. The TV-76 arrived only a few days ago and were lucky to have a good night for testing. So, I went with the small alt/az mounts I had available. Also, these are the mounts I will usually be using with these telescopes. The TV Gibraltar held the FS-78 quite well. The Bogen 3021 tripod / TV-76 combo became much more useable with I put Celestron vibration damping pads under 3021s legs.
There were six people at the star party. Three of us spent the most time comparing the TV-76 and FS-78. Two other people also helped.
The big problem was finding a way to get the same magnification with virtually the same type of eyepiece. I started out using a 5mm Tak LE eyepiece plus a TV 2x barlow, in the TV-76 and a 7.5mm Tak LE plus Celestron 2x Ultima barlow in the FS-78. This didn't not give magnifications that were close enough for a good comparison. It gave the TV-76, 192x and the FS-78, 168x. Looking at Jupiter through TV-76 at 192x gave a view that was a little too dim for me to easily see band detail. A little less power, like 168x with the FS- 78 was a better choice. The difference in magnification was just too much for a useful comparison, even when looking at the Moon.
Fortunately one of the testers came up with the idea of using his Tele Vue Zoom Nagler eyepiece. This would let us get the same image scale in each telescope and use the same eyepiece and barlow. I was using a Lumicon 1 1/4" mirror diagonal in the FS-78. It handles the short Celestron barlow better than the long TV 2x barlow. So, we put the TV zoom Nagler in the 2x Celestron Ultima barlow and move the eyepiece plus barlow to the scope we were testing.
By the time we came up with the idea of using the TV zoom Nagler, Jupiter was so high became too difficult to observe with the alt/az mounts. So, we concentrated of looking for fine detail on the Moon. Schroter's Valley was in good position. There are little craters near this large rill. There are also a number if small craters on floor of the walled plain Schickard.
After much going back and forth between the two telescopes with the TV zoom Nagler we came to the conclusion that both telescopes showed virtually the same amount of lunar detail.
When placing the bright limb of the Moon in the center of the field of view, all three telescopes showed no false color.
Two of the testers mentioned they preferred the feel of the TV-76 focuser. My Tak FS-78 is a few years old, I may need to refresh the lube on the drawtube. The FS-78 focuser was smooth but a little stiff compared to the silky TV-76 focuser.
These three telescopes are virtually the same in aperture. They all have fine optics. However, they are tools for different jobs. The Leica Televid 77 APO is an outstanding spotting scope. It is designed to be carried long in the field for terrestrial viewing under adverse conditions. The TV-76 is a rugged astronomical travel scope that can also be used for terrestrial viewing. The Tak FS-78 is a well built astronomical telescope. It can be used for terrestrial viewing. It is portable, but it was designed to be treated with the care usually given an astronomical telescope.
I went into the comparison thinking the FS-78 would have an edge in image quality mostly because of its longer focal ratio. I was surprised that the fast, f/6.3, doublet TV-76 performed so well. I'm glad it did. I've liked the TV Pronto for years, but always wished it had a little more aperture and was color free. The TV-76 fills the bill.
Thanks to James T., Phil T., Heidi & Issac K. for their all their help with the three inch APO shootout.