and for the past few weeks I have been able to test my 6inch f/15.
The lens is a 150mm f/15 Classic Achromatic from Istar Opical. I went for the lens only as the scope
needed to be made to some special requirements. Basically the front tube and lens retracts
into the rear tube section which reduces the length to a little over 4 feet when the scope is not in use.
Due to an accident in the workshop, (i.e. yours truly knock a plank of wood over and smashed
the baffle system) I have been using the scope with no baffles in place.
I also constructed this scope for Lunar, planetary and double star observing. For DSO
I use my C9.25.
Star Test: Testing shows the lens to be a very well corrected visual objective.
Nothing unusual or out of place detected in the star test.
Bright stars such as Vega and Altair show a small but noticeable amount of C.A.
around the star. The C.A. is certainly a lot less than that seen with my 6" f/8 Achromat.
All-in-all, the lens behaves much as I expected an f/15 to behave. i.e. there is C.A.
but it is a small amount and not a problem for me.
Lunar: The lens has given me some of the best lunar views I have ever had.
Detail is exceedingly crisp and sharp. At powers above 100x, you can see a very tiny sliver
of blue fringing running along the limb.
What has struck me the most with the lens is the contrast it produces, it is excellent.
The moon appears on a jet black background, different coloration hues are easily visible
on the Lunar surface. Last night I was observing Plato, with six of the craterlets/spotmarkings
easily visible, the crater floor was filled with albedo markings.
Double-Stars: Well, where do you start. The lens is a first class double star splitter.
At powers from 200 to 500x it is well on top of its game, producing an excellent spurious disk
and faint first diffraction ring. It is very good at detecting close binary stars with different magnitude differences.
Each time I have observed 99 Her, the fainter companion instantly shows itself , even in poor seeing
conditions I have had no problems seeing it.
Jupiter: I have been getting quite a few early morning observations before going to work.
First off, there is C.A visible around the disk, not a large amount but it is there.
With the planet I have tried using a yellow filter, blue 80A, Semi-Apo and contrast booster filter,
but I prefer the un-filtered view. Visible details on the planet have been excellent, with much detail
visible within the belts, the GRS showed darker detail within the spot. Festoons are nicely seen,
as well as small white ovals in the southern region of the planet.
The North and South polar regions have shown clear mottling patterns. When the seeing
conditions are good the whole planet erupts into a wealth of detail, I don't think I would be able
draw to it all as there is just so much to see.
I have used aperture masks of 127mm and 100mm on the scope and had very good results.
With the 4 inch mask, the views of Jupiter easily match the best views I had of the planet
with my Tak TSA-102.
Really looking forward to observing Mars with this scope.
The scope cost me £580 GBP to build and I have been really pleased by the views it has delivered.
Now I really must get those baffles fitted to the tube.
Here it is in the observatory.