EF 50mm F/1.4 wide open to boost red channel only?

[Jannis]

So, i just had a though here, but i have no idea if it's possible.

Now, i have the 550D, and the EF50 1.4.

This lens need to be stopped down to about 2.8 to have nice and round stars.

However, i was planning on giving bernards loop a go. While i know i need to stop it down to get nice stars and star colors, i was curious if i can take some shoots with it wide open at 1.4 for the red channel only.

As my 550D is unmodded, it's not so sensitive to the red, so a boost there would be nice, and my thought was this:

1. take a bunch of frames at f/2.8-3.5 and stack it to get a nice starfield with M42 and posseboly the flame/horsehead in it.

2. Take a bunch of frames at 1.4 and stack these, ignoring the insanely ugly stars this creates.

3. Take the stacked pic, open it in PS, and split the color channels.

4. As the stars will probably be bad in the red channel too, try to clean it up and remove most of the "red stars", if not all the stars.

5. blend in this red channel, wich hopefully have a significantly higher level of red in the HH, M42 and bernards loop, wich the previously stacked version shoot at f/2.8-3.5

6. throw the PC out of the window as this whole thing didn't work? n_n"

Edit: note i won't be usign any filters, as i simply don't have any yet - neitehr can i aford any at the moment. >_<

[jgs001]

Jannis, you shouldn't need to do that. Stop the lens down to f/3.5 on your HEQ5 you should be able to hit 5 minute exposures. With that I was able to get the Heart and Soul nebs on my unmodded 450d. The only trouble I think you'll have is the red CA around the stars at f/3.5. I'm planning on stopping it down further next time.

I did a widefield Orion a couple of years ago with the nifty fifty (f/1.8) at f/3.2 and Barnards Loop was clear... just a shame how bad the coma was.. I had to crop a lot of the image out. I'm goina to try it again this year... I figure, 5 minute subs at f/4 with the f/1.4 will get it nicely. Let me know if you'd like me to dig out those two images as examples.

[Jannis]

Thanks for the tip. Yes, i guess you're right on that the HEQ5 would be the best bet.

Though, the reason for my thoughts is that i can't really get a nice wide-fied from where i'm usually imaging, as i have trees and stuff in the way. But i have a nice and darker place to go to, but i don't usually take anything but a standard tripod there - limiting me to about 5 sec exposure - wich is why i thought maybe at 1.4 i'd be able to capture it with enough frames (as i was able to easily capture the HH with 5 sec exposures at f.2.8 (well, with 530 frames howevere, but.. lol).

M42 looks horrible though, and stars are rather ugly, but this was mainly just a test to see what could be captures with 5sec exposures anyway, on a very windy night, and i didn't process it very carefully. But i'm guessing if i reprocess this from scratch, and pay more attention to have a nice M42, and better looking stars, then i'm allready with how the HH and flame looks. And if i could also get bernards loop in there, it would be very nice i think.

I'll see if maybe i could take my HEQ5 out there though, as there's simply a no brainder what's best of a bunch of 5s subs or a bunch of 5 min subs...

[jgs001]

Ah... I see the challenge... an HEQ5 is not easily portable... not compared to a camera tripod. I've taken to using an Astrotrac, and that is portable, and allows 5 minute subs with a 50mm without issue.I know it's a load of money (like the polarie and the Iopteron variant) but...