Orion/M42, how to increase Nebulosity

dhein (David) · #1 11-11-2009, 12:14 AM

Hi all,

I've recently purchased a C8 Scope + CG5 mount in order to explore Astrophotography. I've always had a passion for Photography & general interest in Astronomy, so it seemed like a great combo.

I've attached one of my first attempts at Photographing M42. My biggest disappointment is the lack of nebulosity. I actually stumbled accross an example by Noel Carboni here http://ncarboni2.home.att.net/The_Sw...rion_Small.jpg and followed the exact set-up he quoted, being -

Piggyback with Canon (500D in my case)
300mm Lens (Canon 70-300 @ 300mm DO Zoom)
1600 ISO
22 x 30 second shots
6 x Dark Frames (not specified, but realise these are needed)
Stacked (DeepSky in my case)
Enhanced in Photoshop

However it's pretty obvious comparing my attempt, that I haven't been able to capture nearly the amount of nebulosity. I even downloaded his own photoshop actions to try & optimise as best as possible. After an hour of trying everything I could via levels, exposure, saturation etc - it's pretty clear that I just haven't captured the level of nebulosity he has.

So my question (long winded as it is!) ... how do my results vary so much if I follow the same exposure times & method.

Can anyone shed some light or offer tips ?

Any help is much apprecaited.

Cheers
David

Tandum (Robin) · #2 11-11-2009, 12:28 AM

I think that 70-300 canon lens is about F5.6 while your C8 is F10. I think that puts you 2 F stops away from the canon lens which means you need 4 times the exposure so 120 seconds not 30 to get to the canon lens.

dhein (David) · #3 11-11-2009, 12:44 AM

Thanks for the feedback Robin. Re the F Stop. I actually shot this using the Canon piggbacked on the scope. Isn't F5.6 a wider (more open) aperture than F10 - so would require less exposure rather than more?

I suppose the other thing I still can't resolve is that the other chap I linked to used the same settings that I did, yet got a drastically better result.

Anyway, I'll keep pushing along .. lots to learn!

Cheers
David

Quote:

Originally Posted by Tandum

I think that 70-300 canon lens is about F5.6 while your C8 is F10. I think that puts you 2 F stops away from the canon lens which means you need 4 times the exposure so 120 seconds not 30 to get to the canon lens.

Tandum (Robin) · #4 11-11-2009, 12:54 AM

I read it wrong. I thought the Carboni shot was with a canon lens and yours was with the C8. What did he shoot it with? 30seconds isn't enough. Try 5 minutes.

Octane (Humayun) · #5 11-11-2009, 01:11 AM

Also, your Canon lens has such a small aperture compared to an 8" telescope.

The telescope is going to gather a lot more light a lot quicker than a tiny lens.

Also, 30 second exposures aren't going to reveal much nebulosity. You need to be taking at least 5-minute exposures to get decent nebulosity.

Having said that, at 5 minutes, the core of the nebula is going to be blown out (saturated). You can take shorter -- 10 to 15 second -- exposures and mask them in Photoshop.

Regards,
Humayun

dhein (David) · #6 11-11-2009, 01:32 AM

So just to clarify, when you say 5 minutes, you mean lots of 5 minute shots and stack them? (my shot was 11 minutes in theory if you times out 22 x 30 sec shots .. but I'm still not quite up to speed with the true capabilities of stacking).

I note he also used ISO 1600 .. is it generally better to stick with higher or more moderate ISO.

Cheers
David

Quote:

Originally Posted by Octane

Also, your Canon lens has such a small aperture compared to an 8" telescope.

The telescope is going to gather a lot more light a lot quicker than a tiny lens.

Also, 30 second exposures aren't going to reveal much nebulosity. You need to be taking at least 5-minute exposures to get decent nebulosity.

Having said that, at 5 minutes, the core of the nebula is going to be blown out (saturated). You can take shorter -- 10 to 15 second -- exposures and mask them in Photoshop.

Regards,
Humayun

Tandum (Robin) · #7 11-11-2009, 01:42 AM

5 minute subs means lots of shots, 5 minutes each. The longer the exposure the more detail you'll capture. The more subs you get the cleaner the image. The FAQ for deepskystacker explains the maths better.

The higher the iso you use the more noise you will need to deal with in the result. When I was using a 40D I stuck with 400iso and extended exposure if I wanted more detail. I think exposures over 15minutes proved problomatic by way of guiding and noise. I found that at 400iso, with exposures of 10minutes each, the images I got from the 40D where easier to manage, noise wise. Trial and error really.