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Looking for advice re existing scope

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This is my first post apart from an introduction in the “Welcome” forum. Apologies in advance for the lengthy description below!

I have an F5 8.5 in Astrosystems (UK) reflector (David Hinds mirror) on a Vixen SP mount, which I’ve had for some years. It has not been used that much for a variety of reasons, one of which was that I was never convinced the performance was quite what it should be.

Basically, the cool down time seems too long for an 8.5 in; at least an hour, but even up to 2 hrs brings further improvement. Also, I just cannot see any real detail when viewing Saturn or Jupiter. I can see the Cassini division OK but not much other detail, and on Jupiter I can see 2 belts but not much else on the surface.

I think I am right in saying the OTA was originally described as being permanently collimated and as a result I never tied to make any adjustments. However, over the past few months I have discovered how the collimating system works and the scope clearly had been slightly out of collimation. Although it is better now I suspect it is still not perfect. Unfortunately the weather has been diabolical for a while where I am and so I’ve not been able to fully test the extent of any improvement. The cool down issue I suspect is due to the fact that the mirror is not “open to the air”. The tube is entirely closed at the mirror end and the mirror appears to be “glued” to the rear plate with some sort of material in between. Finally, the spider is a 2 vane spider with relatively thick vanes.

I am looking to improve the performance and as I see it have a number of options:

a) Put the mirror in a proper cell and open up the rear of the OTA. Also replace the spider with something with thinner vanes.

:D Accept the OTA as it is and think about buying another “cheap” scope for planetary use – but I don’t want long cool down times

c) Sell the scope as it is and replace it with something else

Any thoughts and suggestions would be much appreciated including views on how modifying an OTA along the lines in a) may affect its resale value. On the latter point I am thinking of the impact of having to drill holes in the OTA and possibly damaging paintwork etc, etc.

Thanks in anticipation,


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I would suggest getting the 'scope collimated as a first option. I don't know about the David Hinds mirror's quality but they have a good reputation so I would be surprised if its no good.

Next step would be to find out if your eyepieces are of reasonably good quality as they would have a negative effect on image quality if the are no good.

Then I would investigate the relative costs of a 9 point cell from Orion compared to a Skywatcher 200mm f/5 OTA complete.

Captain Chaos

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