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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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04-09-2010, 05:47 PM   #16
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Very beautiful shot, the colors are great and you managed to capture the stars very well. Sure makes me wish I could go out and try this but its been really cloudy lately.

04-10-2010, 07:06 AM   #17
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QuoteOriginally posted by justDIY Quote
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.
If the scope is older or a Japanese one (Vixen?), they may have some strange focuser size. Perhaps you can simply mount the camera + lens piggypack onto the scope? Many scope's mounting rings have extra photo threads, to allow mounting a second scope or a camera. That would be much easier to do, than using the scope as a lens and on top you could use the scope for guiding.

Ben
04-10-2010, 01:09 PM   #18
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QuoteOriginally posted by justDIY Quote
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.
Possibly it takes .965" eyepieces, which have been used for quite some time in cheaper scopes.
04-10-2010, 01:21 PM   #19
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QuoteOriginally posted by pingflood Quote
Possibly it takes .965" eyepieces, which have been used for quite some time in cheaper scopes.
The 0.965 eyepieces need not be cheap. I have a couple of Pentax Orthos in that size (not antique, ones) and most of my Zeiss Orthos are also that size. It is just yesteryears standard.

Ben

04-11-2010, 05:26 PM   #20
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QuoteOriginally posted by Ben_Edict Quote
The 0.965 eyepieces need not be cheap. I have a couple of Pentax Orthos in that size (not antique, ones) and most of my Zeiss Orthos are also that size. It is just yesteryears standard.

Ben
That is true, but today .965 is pretty much the domain of the "575x" department store scope.

Speaking of scopes, my "grab and go" should show up tomorrow: Sky-Watcher 80mm f/11 on an AZ4 mount. Just want something I can throw outside for quick looks when I don't want to set up the 8" dob.
04-11-2010, 07:49 PM   #21
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Please stop with these images. I am developing TBA.

First word: Telescope.
04-12-2010, 03:01 AM   #22
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QuoteOriginally posted by rparmar Quote
Please stop with these images. I am developing TBA.

First word: Telescope.
Once TBA starts, it can even worse, than LBA, at least for your pocket… I have currently 5 scopes, starting with the bigger 10 inch Cassegrainian and going down to the small Pentax 75 SDHF apo, which is just such a neat piece of optical and mechanical engineering. I would like a really big photographic telescops, though...

Ben
04-12-2010, 06:25 AM   #23
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Yes, you get that first scope and five minutes later "aperture fever" sets in, and before you know it you're changing cars because that 30" Obsession won't fit in your sedan....

04-12-2010, 06:43 AM   #24
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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)?

This is generally caused by an affect called coma. It is often present in short focal length telescopes and camera lenses. Some manufacturers make coma correctors while others offer real expensive lenses that correct it internally.

William
04-12-2010, 07:23 AM   #25
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QuoteOriginally posted by WillCarney Quote
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)?

This is generally caused by an affect called coma. It is often present in short focal length telescopes and camera lenses. Some manufacturers make coma correctors while others offer real expensive lenses that correct it internally.

William
In this case the halo is simply the residual colour of the simple lens used - namely the typical blue halo of an achromatic lens. Coma would be rare with a 135/2.8, I think. Also the slight elongation of the stars is due to the Earth's rotation. For real pinpoint stars you cannot go over app. 15s expsoure time with a 35mm lens and not over 2.5s with that 135mm lens.

Ben
04-14-2010, 05:46 PM   #26
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wow...much better than i could ever capture...keep it up
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