Coating scratches in refractor... effect on images

I've been having some trouble lately getting a good telescope. The last few units I received (vendor's name withheld) have all had problems. Example, one Maksutov I received had grease on the secondary, the replacement Mak had a loose rear mirror cell that wouldn't tighten down, and collimation was way off.

Now, I received an achromatic refractor which had some sort of residue all over the primary. Instead of sending it back again, I decided to just clean it myself. I suppose due to my frustration, I didn't take the time to clean it carefully, and as such managed to put a few very light scratches in the coating. Of course, these scratches are only noticeable when shining a flash light down the tube.

However, since this being my first refractor (I've owned plenty of newts, and know how to care for my optics), I'm a little concerned that image degredation might occur.

I reassembled the doublet, and recollimated and so far star tests seem okay. Advice? Suggestions? Should I worry about it, or just let it go... the telescope is a fast 80mm f/5, so I'm doing mostly widefield viewing with it. No photography.

Thanks!

If all the coating on that surface was gone, you'd probably suffer a loss of 4% of total light throughput. If you removed 0.01% of it, which would be very obvious and ugly looking, you'd loose 3%x.01%=.0004% of throughput, not measurable, much less noticeable. The outer surface is the most benign place to increase reflection, since the reflected light goes back out into the universe, instead of bouncing around in the scope eventually to your eye. 80mm f/5 scopes are so much fun! My bro-in-law has one. We put a 22 Panoptic on it and have a ball, the images are just about perfect!
Ron

James Sarte said:


Now, I received an achromatic refractor which had some sort of residue all over the primary. Instead of sending it back again, I decided to just clean it myself. I suppose due to my frustration, I didn't take the time to clean it carefully, and as such managed to put a few very light scratches in the coating. Of course, these scratches are only noticeable when shining a flash light down the tube.

Thanks!

Maybe you scratched it.
Maybe you didn't.
Maybe there aren't any scratches.

The "flashlight test," which is what you have done, is a sure way to make any lens or mirror look HORRIBLE. Don't do it. Don't worry. And don't take anything apart again. If you put scratches in the coating (which I doubt unless you use a piece of sandpaper for a cleaning tissue), they will have zero effect on images. Just get outside and enjoy your wondeful telescope; no obsessing allowed!

8)