I bought a carbon telescope with a view to restoration. I am thinking of buffing down and recoating with XCR Epoxy. The telescope was obviously left outdoors at some point, some of the bolts are rusty and the Aluminium end caps are bubbling under the paint (powder coat?). I have attached pictures of the carbon, and was wondering if anyone could say what the white marks are? It must be some kind of water damage i think, and thought it might be best to get a second opinion of what, if anything, can be done about them before actually doing anything. I think I will re-coat anyway as there are loads of pinholes.

It's not water damage... to me it looks like they used an in-mould clear coat and then got voids underneath. But you say it has pinholes too, which would rule that out. 

Looks to me like a typical clear gelcoat followed by a mediocre hand layup. You will need to sand back the gelcoat to get it fixed.

Thanks for the replies so far. Yes, sanding back the gelcoat agreed. It doesn't seem very thick though. You can see how the white marks go round the tube in kind of lines following the weave. Do you know what it is that causes it?

Heh heh mediocre hand layup. Yes, it probably is mediocre, but how can you tell?

Regards, and stay safe.

Visually. By the amount of of pinholes. From a technical point of view it will be fine, especially since there will be only little and mostly static loads in this application.
The lines are a common pattern of bad wet layup. There was plenty of air trapped under the first layer, and it's stretched out along the brush strokes.
From what I can tell this is only a visual defect. And before you start sanding off the gelcoat, I would like to say, that it takes some practice to get back to such a smooth, shiny surface. Cylindrical objects are even more difficult, since you will easily detect every plateau from the sanding process. Plus polyester surfaces are a dream when it comes to polishing. It is difficult to get epoxy resin to that grade of shine. It might be, that you will end up without the pinholes, but with a less pleasant look nevertheless.

Yeh as above, I would leave it. Especially because these voids will be trapped in the low spots between the fibres, so to remove them will mean you are very likely to hit the fibres in the process and effect their appearance. 

Not an easy job, and a perfect example of why in-mould coatings aren't a great idea unless your production techniques are flawless to begin with.

I had a feeling the Mark's were between the fibres. And lines of air caused by a brush make perfect sense. Glad I checked first, I will probably leave it. I know all about the difficulties sanding cylinders, I recently made a large tube mould from scratch. Thanks Oekmont and Hanaldo