Does my Secondary Mount weigh too much?

[michael8554]

I'm restoring a 1970's 205mm F8 Newtonian.

The secondary holder is made from solid 2" diameter aluminium bar and the two parts, fixed and adjustable, without the secondary mirror, weigh 450g/1lb.

Should I bother to lighten it by some strategic drilling?

It would reduce the load on the spider which might be flexing, and perhaps improve cool-down time?

Cheers

Michael

[NGC 1502]

Hi Michael. Difficult to say what's best. It does sound heavy though. Can you see the spider vanes flexing with gentle pressure ? I'm sure most will flex if you try. You could, as you suggest, remove some material by drilling, but I think that's only worth doing if you can get rid of a substantial amount, and just a few holes may not do that. And you will probably wish to leave it neat looking, even if that doesn't affect the view through the scope.

As for cooldown, I expect you are worrying about a big lump of cooling metal right in the light path. But I think it's likely that the primary will take longer to cool than the secondary and mount.

So if it were my scope, I'd leave it as it is, and see if there are any issues.

Sounds like a great scope, all the best with the renovation, Ed.

[michael8554]

Thanks for the response Ed.

At present the scope is a box of bits waiting to be assembled so I'm only guessing that spider flex is going to be a problem.

My thinking is that collimation will change with declination.

You're right about keeping it neat so three holes 120 degrees apart down the length of the bar will loose about a third.

Great scope?

I hope so, but any time you want to swap with your 10" F4.8 let me know...:-}

Thanks

Michael

[swamp thing]

As long as the spider vanes are (relatively) tight. You shouldn't have any problems with flexing.

Most can be tensioned once in position. It doesn't need to be like a guitar string, just pulled up to remove any flexing.

Just keep an eye on the position as you tension it. Working opposites to keep the position correct.

Four vane spiders are a lot easier to tension than threes for this reason.

Regards Steve