Orion/M42 via T1i/50mm lens/DSS

[mtbdudex]

Having some success with M31 using my T1i/50mm f1.4 prime lens a week ago, I decided to try Orion/M42.

Taken Oct 17, 2010, 500 (2) sec exposures @ ISO800, 40 darks, 25 bias, shot via T1i+50mm f1.4 prime lens on tripod.
DSS took quite a while to crunch this.

Not much PP here; adj levels, added some saturation/vibrancy.

Full output:


Crop1


Crop2 of M42


I seem to be getting massive overexposure of the stars using this technique, guess ISO800 @ f1.4 and 2 sec does it.
When I use show hot/cold areas the stars are overexposed.
If others try this lower ISO (ISO 400) and/or f 1.8 just to limit the star overexposure.

[tkerr]

2 Second exposures?
500! plus Darks and bias, yeah, I would think DSS is going to take quite a bit of time to register and calibrate then stack all that.
Keep in mind stacking multiple exposures will improve your SNR, but it doesn't necessarily increase the image data, That is a result of exposure!

The stars don't really look over exposed, but they do look slightly out of focus as well as some Chromatic Aberration(color Fringing) from the lens you are using, which is giving the stars that bloated blown out look. Nonetheless, only 2 second exposures you captured quite a lot of image data.
Imagine what you would get with much more exposure than just 2 seconds.
With a 50mm lens you should be able to get longer exposure without discernible star drift.

[VIGER]

Cool stuff. I wonder how it would of come out using the Canon 20D IR mod that I have for sale ( plug ) i the FS: adds.

Good shot. Keep it up.

[trailblazer87]

Barnard's Loop would probably show up with that many exposures, especially with the IR. That sounds like a worthy endeavor.

[mtbdudex]

Tim - thx for feedback;

I'm trying this again this morning right now, very clear/dark skies (moon set, sun still below horizon)
1st attempt: 50mm prime f1.4 @ f1.8, ISO 200, 5 sec exposures for 20 minutes will give 240 frames vs 500 frames above, that will be done @ 5:15am EDT.
(DSS should crunch a little faster....)
2nd attempt: 15-85mm lens @ 85mm, f 5.6, ISO 800, 4 or 5 sec exposure for 20 minutes.
btw, I went back into my editing program, Apple Aperture and tried to see if exposure was being blown out anywhere on single frame as captured, here is what I find:
Whole image:


Crop of area shows red hot spots on M42 and bright stars.


Crop with -1.0 exposure applied showing red "hot spot" gone by M42


Crop with -1.75 exp applied showing re "hot spot" of stars gone also


This seems to show the camera settings I used over exposed M42 by 1 stop, and the bright stars by 1.75 stops, am I correct?

As noted, when I stack them I'm getting this weird purple fringing, that is over exposure or as you state Chromatic Aberration of the 50mm f1.4 prime lens I have?

I also double checked focus for these 2 new attempts; I pick a bight star, manual focus 10x live view, back-forth until the star is smallest.

Tim-I'm learning as I go here, so thx for patience with my q's.
(and others here in the forum I see you answer)

[tkerr]

Originally Posted by trailblazer87

Barnard's Loop would probably show up with that many exposures, especially with the IR. That sounds like a worthy endeavor.

Barnard's loop is very faint, regardless of how many 2 second exposures used in a stack it will be very hard to get it to show up. There is a point at which the number of light frames with such a short exposure time won't produce any significant returns. 500 x 2 seconds is still a 2 second exposure.

You cannot stretch out image data that is not there. If you want more depth and saturation so those very faint objects reveal themselves, you will need to extend the exposure time per each frame.
Quite Frankly, nonetheless, I am extremely surprised at the amount of data that was captured in just 2 seconds.

Some good reading:
http://ccdastrophotography.com/article.php?id=5

http://www.cloudynights.com/ubbthrea...2/Main/3902239

[tkerr]

Originally Posted by mtbdudex

Tim - thx for feedback;

This seems to show the camera settings I used over exposed M42 by 1 stop, and the bright stars by 1.75 stops, am I correct?

The Orion Nebula is one of those objects with such a dynamic range that you are going to over-expose certain areas when you try to properly expose others, and vise verse.

Originally Posted by mtbdudex

As noted, when I stack them I'm getting this weird purple fringing, that is over exposure or as you state Chromatic Aberration of the 50mm f1.4 prime lens I have?

The lens is probably just one cause, and probably the primary cause for the color fringing, however, the atmosphere will also have an effect on it. If you are shooting your images of the Orion Nebula when it is closer to the Horizon, you are shooting through more atmosphere than you would when it is straight over-head. The air we breath and look through is full of water and other particulates that mess with the refraction of light, and then there is the atmospheric turbulence that will only compound the effects..

[mtbdudex]

Tim - thx for explain on tradeoff of exposure choices and color fringing.

Here is the re-shoot from the morning:
Taken Oct 19, 2010 5am EDT, 212 (5) sec exposures (17.7 min total exposure time) @ ISO200, 31 darks, 23 bias, shot via T1i+50mm f1.4 prime lens @ f1.8 on tripod.

Full output:


Crop1


Crop2 of M42


While bright stars less "blown out" definitely LOST some detail in M42

Just being a engineer and testing my equipment:
I'll take shot @ 5 seconds, 6 seconds, 8 seconds, and 10 seconds seconds to see where image movement becomes visible also, not just full image but crops down to 1024 pix wide as well.....if someone else has already done that would save me a little time....

Then, at 5 second baseline + max exposure w/o "bad" movement when crop:
I'll do as a test is try just 10 frames each @ (plus 5 darks/5 bias for each)
-ISO200, 50mm f1.4 prime lens @ f1.8 (baseline to compare)
-ISO400, 50mm f1.4 prime lens @ f1.8
-ISO800, 50mm f1.4 prime lens @ f1.8

just to satisfy my curiosity of sensor noise vs increased photon capture...learning about my equipment abilities at same time.

I read the Canon 50mm 1.4 prime is slightly soft @ f1.4, that's why I'm shooting @ f1.8, however if that is not an issue for astrophotography than I'd shoot @ f1.4 instead for the test.

Hopefully for people with just a Rebel body and 50mm lens this is worthwhile info as well.
Other note:
I am find this helpful in learning the sky, rather than jumping to some telescope, books recommend people use a binocular to view the sky, a 50mm lens + DSLR for me is serving that purpose.

[SteveInNZ]

I'm all for encouraging people to experiment, so take these numbers as a guideline, for verification or just ignore them.
M42 is at -5 degrees declination so plugging your lens and camera into my handy spreadsheet, I get 4 pixels of movement in 5.2 seconds. You'll have to decide how small a detail you want and multiply/divide accordingly.
What normal folks call soft and nice bokeh, tends to translate to vignetting and spherical aberration in astrophotos. OTOH, that's 70% longer exposure times and I guess that for this technique, it is probably the more important factor.

[mtbdudex]

Originally Posted by SteveInNZ

I'm all for encouraging people to experiment, so take these numbers as a guideline, for verification or just ignore them.
M42 is at -5 degrees declination so plugging your lens and camera into my handy spreadsheet, I get 4 pixels of movement in 5.2 seconds. You'll have to decide how small a detail you want and multiply/divide accordingly.
What normal folks call soft and nice bokeh, tends to translate to vignetting and spherical aberration in astrophotos. OTOH, that's 70% longer exposure times and I guess that for this technique, it is probably the more important factor.

Steve- I'm trying to grasp your technical #'s with visuals....

Full images 4752 x 3178 reduced to 1024 for web viewing (posting 5sec, 10 sec, 15 sec), honestly can't really see movement here @ 1024 pix at all:
(shot with ISO100 due to bright moon)

50mm f1.4 @ f1.8 IMG_8438 5 sec


50mm f1.4 @ f1.8 IMG_8441 10 sec


50mm f1.4 @ f1.8 IMG_8443 15 sec


Simple conclusion:
I can't see any drift/motion posting 4752 x 3178 reduced to 1024 for web viewing...my take and opinion
(already knew that from taking wide field images, just never did side-side comparison myself)

Next post will show crops .....

[mtbdudex]

Now crop a 5, 6, 8, 10, 13 and 15 sec exposure to 1024 wide:

50mm f1.4 @ f1.8 IMG_8438 - 5 sec crop


50mm f1.4 @ f1.8 IMG_8439 - 6 sec crop


50mm f1.4 @ f1.8 IMG_8440 - 8 sec crop


50mm f1.4 @ f1.8 IMG_8441 - 10 sec crop


50mm f1.4 @ f1.8 IMG_8442 - 13 sec crop


50mm f1.4 @ f1.8 IMG_8443 - 15 sec crop


Just my visual observation (I'm sure there are detailed studies somewhere where people have discussed and "agreed" some formula/rule like SteveInNZ has)

If I'm doing Astrophotography with 50mm lens in general I'd shoot up to 8 sec exposure IF I was going to also crop the full image (my T1i 15MP 4752 x 3178 image) to 1024 wide, if not then 10 or even 13 second may suffice, depends on how much "sky"/object you want to show in the crop.

Ok, I'm done for tonight with this little endeavor.

Simple math for 85mm lens?
If I say 8 sec "works" for 50 mm lens can I do 50mm/85mm times 8 sec = 4.7 sec so 5 sec would be "my equivalent" acceptable for 85mm lens based on above...correct?

[mtbdudex]

SteveInNZ, can you post a link to that handy spreadsheet or PM me it?

As a point of reference, I also shot the moon tonight with my T1i + 50mm prime.
Full size:


Cropped to 1024 wide, posted 1024 wide:


Compare to M42 cropped 1024 wide, posted 1024 wide


relatively speaking, M42 and the moon appear the same size to our eyes...kinds puts that into perspective for me.

[ebann]

Originally Posted by mtbdudex

SteveInNZ, can you post a link to that handy spreadsheet or PM me it?

[snip]

+1 me too!

[jsigone]

surprised you're getting that much CA on the lens. I'd try to stop it down to 2.8 or 3.2 to help the stars from bloating.

[SteveInNZ]

ebann,
You'll need to send me a PM with an email address.

The spreadsheet is far from anything fancy. (In fact, it's close to embarrassing). It's just a personal tool I use to throw numbers into to test ideas, camera/lens/telescope combinations, etc.

Steve.