Please explain: Moon Reflection

[wino david]

I recently got back from a trip to West Texas where I had a great opportunity to shoot the night sky. For the record, this was my first attempt to take night shots of the sky.

However, I noticed an anomaly when I'd get the moon in the shot I got a weird multi-colored reflection of the moon. To my eyes, it looks like the moon is reflecting off the filter on the lens, but is this really what's happening? If so, I thought the coating was supposed to minimize this type of thing?

I used a 50L lens with a B+M UV coated filter.

Example 1: f/4 @ 15s
http://farm3.static.flickr.com/2731/4143543321_27275a3f23_o.jpg

Example 2: f/2.2 @ 10s
http://farm3.static.flickr.com/2505/4144304448_fdc32f6aa4_o.jpg

[VIGER]

Easy resolved.

Dump the B+M UV filter .... We have cover this common problem often.

Cheers

[Adrena1in]

I don't mind internal reflections like that sometimes, but I can see why you'd want to remove it.

However, I'd love to see the same type of shots without the filter. Because I think those shots are pretty impressive. You've captured a lot of stars very "near" the moon, and if I were to take such exposures at f/4 and f/2.2 with any of my unfiltered lenses the moon would just wash the whole image out!

[wino david]

That's what I suspected.

Does anyone know of a UV or clear filter that could be used without causing a reflection? Or is the issue just inherent in all filters at night?

[VIGER]

All filters at night. Get a good lens hood to protect the lens instead.

Good picture in a dark area it seems.

[PM01]

Even the best filters (custom scientific, baader, IDAS LPR) will still introduce some reflection in the optical chain. The only instance that I've seen that had zero reflections on a tough target would be a triplet oil spaced system without a field flattener, that is, zero reflections from the optics themselves.

The coverslips of some CCD chips (kodak/dalsa, etc) can still throw a reflection, and they're extremely well coated! In some angles the coverslips look like they disappear!

It's all about the air to glass interface. If it's soaked in optical oil as an interface, you generally won't get reflections.

But then that opens another can of worms...!

[VIGER]

I doubt that a my filter inside the body of the camera produces such flares of that intensity one day.

For DSLR and purposes the front filter remove would solve this problem and focus issues. The phenomena comes from the front lens reflectin on the inside of the filter. Like an audio feeback with a microphone and an amplifier. This is how I understand the issue.

[wino david]

That is really interesting! Just when you think you've heard it all...

I'll try again with the filter removed and see if I have better luck. Thanks for the replies!

[PM01]

A good read.

http://www.astrodon.com/articles_faq/articles_faq/press_release:391,355,49

[VIGER]

Thanks it confirms what I was saying - The drawing illustrates what I was writing. It's exactly what could happens when you had a filter to a telephoto. This bouncing effect.

Never had a CCD halo like describe in the article. Don't have the SBig either. I have seen it in CCD pictures but never in DSLR pictures.