DIY Lunar Filter

[Buzzard75]

I have a nice 80mm spotting scope that works great for the moon. Problem is, it's really bright. The other problem is it uses proprietary eyepieces. The easiest thing to do would be to construct a filter for the objective, but not sure what to use for filter media. The only thing that comes to mind is window tinting material. Anyone have experience making such a filter?

[Prador]

What about a budget ND filter used for photography? Maybe bodge it to the end without coming into contact with the objective lens.

[Buzzard75]

17 minutes ago, Prador said:

What about a budget ND filter used for photography? Maybe bodge it to the end without coming into contact with the objective lense.

I'm not worried about it coming into contact with the objective. It has an extendable light/dew shield that normally sticks out a centimeter or two past the objective. I'd just need to find one large enough and with a fairly low transmisivity.

[Buzzard75]

Got home and checked the scope again. It does actually have threads on the objective so a photography filter may just work. The problem is, the threads appear to be slightly larger than the 82mm of a standard filter so I have no idea if an 82mm filter is going to fit. Next size down is a 77mm and next size up is a 95mm. I bought an 82mm anyway. If it fits, if fits. If it doesn't, I'll make it fit or find some other use for it or someone else who can use it.

[Buzzard75]

Didn't work. ? As I suspected, the thread on my scope is slightly too large to fit the 82mm filter. Oh well. I should still be able to tape it on or something. As I have no intention of using this for anything other than my little spotting scope for public outreach or personal observation, I'm not too concerned about the adhesive sticking to the filter and the filter housing itself is slightly larger than the actual clear objective so it shouldn't be an obstruction.

[brown_rb]

What about about a step ring. Something like this?

https://www.ebay.com/itm/82mm-to-86mm-82-86-82-86mm82mm-86mm-Stepping-Step-Up-Filter-Ring-Adapter/162062737509?hash=item25bbb12065:g:Da8AAOSw~gRV5XCz:rk:6:pf:0

 

[Buzzard75]

4 hours ago, brown_rb said:

What about about a step ring. Something like this?

https://www.ebay.com/itm/82mm-to-86mm-82-86-82-86mm82mm-86mm-Stepping-Step-Up-Filter-Ring-Adapter/162062737509?hash=item25bbb12065:g:Da8AAOSw~gRV5XCz:rk:6:pf:0

 

Oooh, that might work. I didn't even know that was a thing. Won't do me much good for tomorrow night, but I might have to get me one of those.

EDIT: I looked at it a little bit closer and I think I might need it to go the other way. The filter is too small so I need something that has a larger thread on the bottom that would screw into the scope. I'll look for a step-down ring

[Prador]

What about wrapping some foam-like material around the circumference of the filter (thickness to suit) and gently press into the dewshield?

[Buzzard75]

28 minutes ago, Prador said:

What about wrapping some foam-like material around the circumference of the filter (thickness to suit) and gently press into the dewshield?

The threads fit inside the dew shield and the threads on the scope, but the housing of the filter does not. The OD of the filter housing is about the same as the OD of the dew shield. It mates up pretty nicely with the dew shield actually. There are not a lot of threads sticking out of the filter to be able to wrap anything around to give it a firmer fit, good thought though. I'll just secure it with several pieces of tape for tomorrow and get myself a step-down ring for future more permanent use.

[Rusted]

Find a bit of tube which fits over the dewshield.
Cardboard, metal or PVC plumbing? Empty food can? Drinks bottle?
Empty tablet or detergent bottle with the end cut off?
Glue or tape a disk onto the end with a neat hole to take the filter.
A threaded adapter will give you something to hold it more firmly in place.
If you don't have one then temporarily sandwich the filter between two [end] disks taped in place.