PDA

View Full Version : Ha with a DSLR?

renderwerks
24th of April 2009 (Fri), 13:06
Can this be done?

I mean, shoot with a Ha filter with a DSLR on mono?

I'd just try it, but I'd have to buy a filter... not so inexpensive.
chris.bailey
24th of April 2009 (Fri), 13:15
You can do it with a OSC CCD so I dont see why not. Think it may be more successful with a modded DSLR but...

Not sure I would set to Mono but would shoot raw and process as mono.
troypiggo
27th of April 2009 (Mon), 07:01
No you can't with an unmodded DSLR. There is a filter on standard DSLRs in front of the sensor that blocks Ha, IR and UV range. Putting a Ha filter will filter the light coming in, but the sensor filter will block the Ha light too. That's what they talk about when "modding" DSLRs. They either swap the standard filter for one that does allow Ha through it, or they swap it for just plain glass which allows all light through including IR and UV.
hollis_f
27th of April 2009 (Mon), 07:27
No you can't with an unmodded DSLR. There is a filter on standard DSLRs in front of the sensor that blocks Ha, IR and UV range. Putting a Ha filter will filter the light coming in, but the sensor filter will block the Ha light too. That's what they talk about when "modding" DSLRs. They either swap the standard filter for one that does allow Ha through it, or they swap it for just plain glass which allows all light through including IR and UV.

I thought that Ha (656 nm) was still within the optical. After all, you can see an image through an Ha filter, can you not? Does the sensor filter really remove some real, visible, red light?
troypiggo
27th of April 2009 (Mon), 08:14
I believe the Canon filter cuts in/out right around there. See here. The Baader filter is one of the ones you can swap into your camera.

http://www.ezystyles.com.au/ACF.jpg
hollis_f
27th of April 2009 (Mon), 08:48
I believe the Canon filter cuts in/out right around there. See here. The Baader filter is one of the ones you can swap into your camera.

Very interesting, thanks. I didn't realise the Canon filter chopped out so much visible light. So the Baader really is the only way to go. I'm getting my 20D modded with an 720 nm filter - so that'd block the Ha as well.
SteveInNZ
27th of April 2009 (Mon), 15:29
The graph shows %Transmission. The standard Canon filter crosses the Ha line at about 25%. That's 2 stops, so doing the filter mod gains you 2 stops worth of Ha. It's not like the standard filter blocks it out completely as anyone who's taken a picture of M42 can show.
Although if you're doing a couple of hours worth of exposures, 2 stops makes a big difference.

Steve.