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Orion
Lens: 135mm Camera: K-x Photo Location: Manistee, MI ISO: 6400 Shutter Speed: 1s Aperture: F2.8 
Posted By: justDIY, 01-20-2010, 10:53 PM


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There is a lot wrong with this picture, and I'm hoping the gurus can point me toward relevant websites so I can do a better job next time I get a clear night sky.

After having no luck with either of my kit lenses, I mounted up my Sears 135mm f2.8 M42 prime (older than I am by a good margin!). With the first picture, I was blown away by how much faster this lens is than the kit. So I spent a good while fine-tuning the focus and bracketing with various settings.

This is a single exposure that I fine tuned a little in PP (my neophyte tool: picasa).

My biggest question is: Some of the stars look like proper pin-pricks, while others look like spheres of light surrounded by a halo. What causes this? Is this because they're over exposed (blown out)?
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01-21-2010, 07:29 AM   #2
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You need to stop down 1 to 2 stops. Don't shoot wide open. Unless you have a ED lens you will get some chromatic abberation or purple fringe around brighter stars. Stopping down helps. Good shot anyway.

William
01-21-2010, 10:15 AM   #3
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At a shutter speed of 1 second you might also have some slight motion blur. You can try speeding up the shutter speed 1 stop at a time until the brighter stars are sharp. You might lose the dimmer stars though. A very good effort and better than most of mine.
01-21-2010, 02:01 PM   #4
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Greater intensity of light from the larger and brighter stars will etch a greater footprint on the sensor and even produce star streaks if the exposure is long enough (just like with street lights).

Reservations as above for your next trial.
You generally have up to 30 seconds with a wide angle lens, and proportionally less time with a 135mm to capture stars without appreciable rotation.

04-05-2010, 01:57 PM   #5
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At that focal length, it doesn't take much time for your stars to streak and look blurry. The Orion Nebula in the middle of the sword looks great, though!

Edit: and good call Ash, about the stars with greater intensity. Orion is composed of some of the most intense stars in the sky. I love the Orion Constellation!!
04-05-2010, 08:08 PM   #6
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I'm no guru. But I think there is a lot right with this picture. Looking at the full size
image, I see no sign of motion blur. However, the brightest stars do seem to have a bright
purple halo around them. So go ahead and trade another second or two of shutter speed
for a step or two in aperture as WillCarney suggested.

I'm surprised you couldn't get the 18-55 kit lens to cooperate. My 'Orion Rising' shot
was 20s at 24mm f4 iso 800. Since you are successfully shooting iso 3200 here, you
should have ample room to replicate my shot, trading f-stop for iso.

As for relevant websites, I found this one inspirational if not educational.
I found the site owner congenial and helpful as well.

Have fun and good luck with your astrophotography adventure.
04-05-2010, 08:13 PM   #7
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Astrophotography can be a real struggle, but I think you did quite well. At 135mm you will get motion blur very quickly, and wide open the lens will exhibit some CA (purple fringing) around the brighter stars. Unfortunately our planet likes to revolve around its axis and there's really not a lot that can be done about that other than attempt to compensate for it; if you are willing to shoot wider images google "barn door tracker" and you can find instructions for building a pretty simple device that will let you do multi-minute exposures at wider angles.

Also, isn't Orion absolutely spectacular? Even with the naked eye, it's quite the sight, and with a basic telescope you can spend hours marveling over the nebula (M42) in the "scabbard". Astronomy is a great hobby to get into and it's amazing the things you can see even with fairly basic gear; we just spent some time this evening looking at Saturn through my 8" reflector (cost $375 used, a lot less than many lenses) and the entire family enjoyed it. Yeah, you don't get the colorful views you do when shooting pictures, but there's something to be said for seeing things with your own eyes.

04-08-2010, 02:39 AM   #8
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Some tips
You are using a 135mm lens, that reduces the exposure time drastically for having pinpoint stars in the image.
Find out what that time is and use it.
Use the highest ISO available, even if you get noise.
Stop down the lens so that you won't get ant flares (comet like coma) on the stars close to the corners (sagittal coma that is) or other lend abberations. This is lens dependant so you might be able to use your lens at full aperture.
Take several shots (5-10 or as much as you like). You might need to adjust the frame as the Earth rotates, but it doesn't have to be a perfect re-framing.
Shoot RAW, use the RAW converter of your choice, adjust the image to your likeness and save the results as 16bit TIF files. But you can also use the RAW files for the next step.
Use Deep Sky Stacker (freeware) to align and stack the images. It's rather easy to use.

Additionally, Deep Sky Stacker software above can work with dark frames (put the cap on the lens and take several shots with the same ISO and exposure time as the ones with the stars), flat frames (use the same ISO and exposure, either defocus the lens to the other end or target the lens to a flat and even colored surface (dark white/grey)) and bias frames (use the same ISO and the shortest exposure time the camera can deliver).
Dark frames are used to 'map out' noise and hot/dead pixels.
Flat frames are used to adjust for eventual vignetting and such.
Bias frames are used to reduce any inherent problems with the sensor (hot/dead pixels and such).
Take all the shots described above in the same sitting, 2-3 of each, before and after the stars photo session
If you-re really prone to learning astro-photo, you can use software as Iris, Registax, K3CCD Tools that give you some more control on the post processing.

For a 1 second shot at ISO 6400 you have a lot of information in the picture there, and more can be pulled out by post processing as described above.
04-08-2010, 03:14 AM   #9
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QuoteOriginally posted by WillCarney Quote
You need to stop down 1 to 2 stops. Don't shoot wide open. Unless you have a ED lens you will get some chromatic abberation or purple fringe around brighter stars. Stopping down helps. Good shot anyway.

William
I actually thought that was a nebula or something.
04-08-2010, 03:55 AM   #10
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QuoteOriginally posted by jct us101 Quote
I actually thought that was a nebula or something.
There is ofcourse the Orion nebula in the image and there is quite some additional nebulosity in the field. BUT the blue halos around the bright stars are simply a lens effect, i.e. the poor correction of a simple achromatic lens. I find it quite severe for such a short focal length.

You can avoid that by stepping down. But then your expsoure time would need to go up and that ead to star streaks/trails instead of the nearly pin point stars you achieved.

All in all I find the image very(!) good for a 135mm lens on a resting (non-tracking) camera. Well done.

Ben
04-08-2010, 04:53 AM   #11
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I do like this shot with a bit more adjustment.

I do see the CA in the top 1/3 of the frame but it does look like a nebulae in the bottom of the constellation. Is that the nebulae? I would love to pull that in a bunch closer.
Anyone have an idea what FL would be needed to get more detail out of that?
04-08-2010, 05:28 AM   #12
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QuoteQuote:
Anyone have an idea what FL would be needed to get more detail out of that?
The image below is shot with a Nikon D40 and a 12"/300mm diameter Meade telescope f/10 (3000mm f.l.) @ f/6.3 (~1900mm f.l.) using a focal reducer. It's a little too tight for the nebula(s).
Something like ~1500mm would have been more appropriate, but nevertheless the nebula is so wide even a 500mm would get a pretty nice pic.
There are 3 x 15 sec. images@ISO 800 stacked with DSS I mentioned above.


BTW, the image is a 50% crop.
04-08-2010, 08:38 AM   #13
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QuoteOriginally posted by Nomad Quote
I do like this shot with a bit more adjustment.

I do see the CA in the top 1/3 of the frame but it does look like a nebulae in the bottom of the constellation. Is that the nebulae? I would love to pull that in a bunch closer.
Anyone have an idea what FL would be needed to get more detail out of that?
I thought I had posted this one already, but maybe not. It's a composite image of 60ish exposures, using the same 135mm lens, full crop of the nebula area. Shorter exposures have lost some of the rich color seen in the single long exposure, but the stacking has brought out some of the fainter cloud.

I really needed to rig-up an interval timer for the K-x, as pressing the remote button over and over again in 12 degree weather gets tiresome pretty quickly.

Good 'seeing' is out of the question for the next six months in my area however I do look forward to trying again next winter!

04-09-2010, 05:54 AM   #14
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I have used a K20 and several expsoures of different lengthes, to keep detail in the bright central part of the nebula and at least try to show some fainter nebulosity.

The images are combined in Photoshop. I think, its five expsoure of between 15 s to 30 s at ISO 800 and ISO 1600 - there is some noise, which I find not worse than in film days.

Taken through a tracking 100mm (diameter) f/6 semi-Apo telescope.



Note, that there are still some slight blue halos around the brightest stars left. The scope is not a full apo…
Ben

Last edited by Ben_Edict; 04-10-2010 at 07:01 AM.
04-09-2010, 05:30 PM   #15
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nice work Ben.

I have a tracking telescope too, a 4.5" newt. only problem is the focusing assembly is crippled, it only accepts 1" eye pieces (or some other strange size). The eyepiece holder is removable, so I need some sort of "cap" that has a K mount bayonet on one side and the other is whatever pitch thread the eyepiece holder attaches to the focus tube with. As light as the K-x is, esp with lithium batts, the scope shouldn't hardly notice it is there.
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