Carton 100mm f/13 Achromat refractor and Takahashi TSA-102S.
Here are some of the findings I obtained.
Star Test - Carton, extremely nice ring patterns each side of focus, the lens does show a very
slight amount of Over-correction. In focus on Vega, a very tiny amount of C.A. Visible.
Tak - Perfect ring pattern. Vega is pure white with absolutely no trace of C.A.
Double -stars - The Carton is one sublime double star splitter, with beautiful star images
and extremely delicate first diffraction ring. Only when viewing brighter stars like Rigel
and Alpha Gem did I detect just a small trace of C.A.
Tak - Yet again a superb scope on the doubles, simply beautiful eyepiece views.
Conclusion - Both instruments as good as each other. Apart from the small trace of C.A.
on the brighter stars, I could not detect a difference between the scopes.
Diffraction ring and colour the same in both scopes. Only at the very higest power did the
Airy disk in the Carton start to take on a yellowish tint (normal for an Achromat).
I kept going from each scope trying to find a noticeable difference, but in the end I
simply called it a draw. For example on the difficult (for a 4 inch) eta Gem, the views
were identical, which was the case for all the other stars observed.
Jupiter - With the planet close to opposition this was a very good time for the 4 inch scopes.
I always tend to use a yellow filter for the planets as it helps me see more detail, even with the Tak
I stick the filter on.
Carton - Without the yellow filter, a very tiny amount of a C.A. is visible around Jupiter,
also extremely small amount of light scatter. Background is a wonderful solid black.
The eyepiece view has a warmer tone when compared compared to the Tak.
With the yellow filter, wonderful planetary views. The belts displayed bays and notches
running along their length. Festoons easily seen, along with a belt in the Equatorial Zone.
Both the N.E.B and S.E.B. showed quite a large amount of internal structure and detail.
The rift in the S.E.B. showed considerable detail for a 4 inch scope.
Nice views of the Great Red Spot, with pale orange colour visible. Smaller oval BA visible.
Then joy upon joy I even observed 3 white ovals in the southern hemisphere belt.
Tak - as the above but no C.A. visible around the planet. I've yet to see any C.A. on
any object I observe with the scope, even Sirrius and Venus are totally C.A. free images.
Conclusion - Both instruments the equal of each other in the amount of detail visible.
The Tak does seem to take higher powers slightly better, but it is of no advantage as
it is empty magnification. Both scopes gave some really wonderful detailed views,
very good considering they are only 4 inches.
The Moon - Three words to say hear regarding the Carton views, APO, APO, APO.
Observing at 40x, the views were quite simply stunning. The moon had a 3D like appearance
(yes, I know it is not real, but that is how it appeared) against the purist jet black background.
Only when you increase the magnification do you start to pick-up a very slender C.A. fringe on the limb.
No C.A. is visible across the lunar surface, the shadows are black with Lunar features razor sharp.
The contrast in the Carton is extremely good. On the night of the Full Moon, I observed at low magnification
with binoviewers. The views were outstanding, sharp details visible, the crater rays were a staggering
sight to behold. Different colouration hues in the Mare regions clearly visible.
Tak - I'm starting to sound like a broken record, but again the same as above, but without any C.A.
The views of the craterlet markings and albedo features exactly the same in both scopes.
The Carton lens is one superb piece of glass, it never did a task better than the Tak, but it
was the equal of the Tak.
The Tak has the advantage that it is easier to transport and may not be affected by the breeze so much,
and if you want to get into A.P. then I guess you would go with the TSA.
So far in my life, this Carton has to be the finest Achromat refractor I have so far used.
It is a clear notch up from the fine and wonderful Towa, circle K and Vixen scopes that I used
for many many years.
Now we come to the cost. All the parts for the Carton build were obtained used, and the total build cost me
180 U.K. pounds. I guess the price for a used TSA or FS scope would be anywhere from
1,000 to 1,500 U.K. pounds.
After the seeing the views I've had with the Carton, I would say that the build was a bargain.
This whole exercise does bring up for me the question regarding lens coatings.
The Carton appears to have a single coating of MfG with a Bluish tint in the reflected light.
The Tak is Multi-coated with a Greenish tint.
Yet if the multicoating has an advantage, I am not seeing it in the visual observations.
A few years ago I repeated the exercise with my old Towa 80mm f/15 scope, in that test the Tak
had a clear advantage over the Towa, and even my Sky-watcher Achromat with coated optics
showed a better view when compared to the Towa.
I'm not sure what the engineers at Carton were doing back in the 70s and 80s, but they were doing something
very right indeed with this lens.