Cheap ebay Ha filter?

[cometcatcher (Kevin)]

In my travels I came across some interesting cheap filters on ebay. Sellers advertise them as IR infrared filters, but I noticed that one of their IR filters has 650nm on it. With Ha at 656nm I thought this might make it for a wide band Ha filter. At $15 including free freight from China it was cheap enough, although I don't know why I bought it since my DSLR isn't sensitive to Ha anyway lol.

Since I couldn't find any with a 48mm thread, I bought a 46mm filter and 46-48mm step ring. It perfectly fits into any 2" filter thread now.

I might mess about with it if it's clear later and see how it goes.

[nebulosity. (Jo)]

Thats cool Kevin, be interested to hear how it goes.

Jo

[Sylvain (Jon)]

Love the creative thinking mate!
Good on you

[astroron (Ron)]

Hi Kevin,Is #3 taken at night,and did you take it?
What camera was used? as you say,
Quote)
although I don't know why I bought it since my DSLR isn't sensitive to Ha anyway lol.
Excuse me if I am reading this wrong.
BTW nice clean nails
Cheers

[cometcatcher (Kevin)]

Hehheh, I haven't done any gardening for a while Ron, hence the clean nails.

#3 was taken with the DSLR that isn't sensitive to red, in the daytime. Had to slow the shutter right down to get anything out of it. The white flowers in the pic are pink.

[astroron (Ron)]

Originally Posted by cometcatcher

Hehheh, I haven't done any gardening for a while Ron, hence the clean nails.

#3 was taken with the DSLR that isn't sensitive to red, in the daytime. Had to slow the shutter right down to get anything out of it. The white flowers in the pic are pink.

Thanks Kevin
Cheers

[cometcatcher (Kevin)]

Had a bit of a play with M42. This is a single 6 minute exposure with an unmodified Pentax K-x, the second frame converted to grayscale. Just cropped and resized, no stretching. Taken in full moonlight.

I think this filter may actually work, but not a good test with my equipment. It does seem to cut through the moon skyglow.

[pdalek (Patrick)]

A quick spectrum test.
Put a dvd disk shiny side up on a table and have the room light on.
Move about at a distance of an arm length until you can see one or two red stripes going from centre to edge.
Works well with light shining from behind over shoulder. Can do outside using sun.
Bring filter up to eye. If the line changes to a spot, then narrow band filter. If the line looks much the same then coloured glass.

If coloured glass then could be similar to R25 photographic filter or one of the Schott RG6xx. May or not pass IR, the Schott glass which you can see through does.

Another test is to check with 630nm laser pointer, but most are 650nm. A true H-alpha filter will block most of the 630nm light.

[cometcatcher (Kevin)]

Okay, interesting results. I also have a 30nm Ha filter and a GSO red filter.

With the red laser pointer the GSO red filter lets through all the light, the 30nm Ha lets through most of the light and the ebay 650nm filter blocks about half the light. Also tried a CLS filter. The CLS lets through more laser light than the ebay 650.

The DVD test was a bit vague. I used a DVDR. Out of the 3 filters, the ebay 650nm filter showed a thin red line, not a spot as such. With the other 2 filters the line was thicker.

[pdalek (Patrick)]

I took some pictures. The light is from right of frame. White compact fluoro so red not great. Would have used sun but for clouds. Very deep red at left of stripe, orange at extreme right.
1 - no filter
2 - 7nm Ha
3 - red channel of 1
4 - red channel of 2

[cometcatcher (Kevin)]

My line appears to be a bit longer so I think wider than 7nm.

[DavidU (Dave)]

Interesting thread. Great stuff