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09-10-2014, 08:17 AM   #1
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Astrophotography lenses

Hello,

I need some info about lenses for astrophotography, Do I need low light lens for astrophotography?

09-10-2014, 08:33 AM   #2
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Having a fast lens helps considerably since it allows you to use a lower ISO and/or faster shutter speed. I would look at lenses such as the Rokinon 35mm F1.4 or 24mm F1.4, or a manual Pentax 50mm F1.4. Manual focus lenses are more than adequate for astrophotography since you have to fine-tune the focus manually anyway.

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09-10-2014, 08:41 AM   #3
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QuoteOriginally posted by Adam Quote
Having a fast lens helps considerably since it allows you to use a lower ISO and/or faster shutter speed. I would look at lenses such as the Rokinon 35mm F1.4 or 24mm F1.4, or a manual Pentax 50mm F1.4. Manual focus lenses are more than adequate for astrophotography since you have to fine-tune the focus manually anyway.
Thank you for the help.

And I have also one question about the macro lenses. Which lens between the 35mm F2.8, 100mm F2.8 and the 50mm F2.8 from Pentax would you recommend?
09-10-2014, 08:50 AM   #4
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I chose wide over fast, with the SMC 17mm Fish-Eye. This will capture a whole lot of sky. Since exposure can be longer with a short-focal-length lens like the 17mm before stars show any drift the f/4 aperture is not a major issue. I also have the O-GPS1 now, for times when the 85mm f/2 or another fast prime is preferred to get a closer view of particular objects.

09-10-2014, 08:50 AM   #5
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QuoteOriginally posted by Botina Quote
Thank you for the help.

And I have also one question about the macro lenses. Which lens between the 35mm F2.8, 100mm F2.8 and the 50mm F2.8 from Pentax would you recommend?
You should post that question in a separate thread. Generally speaking the focal length you want depends on how far away from your subject you plan to/want to be. Check the spec tables in our lens database for more info.

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09-10-2014, 10:50 AM   #6
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What type of astrophotography do you want to do? Nightscapes and starscapes are not too demanding on optics, most short focal length lenses will give decent results tho you may need to stop down some.
If you want to do widefield DSO's (Deep Sky Objects) like nebulas and open star clusters, you will need moderate focal lengths (~100 to 400mm) and for planetary and/or galaxies you will need very long focal lengths (into the metres) and the optics will need to be superb for use at low f ratios.

Astrophotography is the harshest test for any lens.
While faster lenses make sense for shorter exposure times, quite often they exhibit severe aberrations that typicaly don't affect daytime photo's.
The most common are coma, where the stars at the edge of the frame are stretched, and axial and lateral chromatic aberrations where the stars will not focus correctly and have blue or red halo's. Coma and axial chromatic aberration can be reduced by stopping down, lateral chromatic aberration cannot be fixed by stopping down.

Some very expensive ED glass can be used with decent results wide-open, but more often than not you will see better results with the lens stopped down.
09-10-2014, 10:59 AM - 1 Like   #7
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@Botina, based on your questions I am assuming that you're just getting started with astrophotography and you do not own an O-GPS1 or tracking mount, but do have a tripod.

For Milky Way images, wide and fast lenses are good. Prime lenses generally have less coma distortion (stars near the corners look stretched out even when focus is good) than zooms. If you already own an 18-55 kit lens, you can start learning at 18mm and 30 second exposures. The lenses Adam mentioned above will gather more light wide open, but note you'll need to use shorter exposures because the longer focal length shows star trailing sooner. The Samyang/Rokinon/Bower 14mm f2.8 is popular for astrophotography with APS-C sensors.

Moon images can be done with any telephoto lens. 300mm is sort of the minimum for the moon.

Astrophotography of planets or dim deep sky objects is much more advanced. Start with the moon and Milky Way! Read The Backyard Astronomer's Guide: Terence Dickinson, Alan Dyer: 9781554073443: Amazon.com: Books if you want to pursue astrophotography. That book gives a through introduction to all aspects of amateur astronomy.
09-10-2014, 11:07 AM - 1 Like   #8
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John hit on something I forgot to mention, primes being better than zoom lenses. This is absolutely true. Zoom lens design is a compromise and I was never happy with any I tried.
For astro I only use prime lenses.

The image at the following link was a single 7.5 main exposure taken with a 105mm wide open (f2.8).
Coma is not too bad but there is mild axial CA evident (red halo's around the orange stars) This also means the detail in the red nebula's is not as sharp as it could have been had I stopped down to f4 or f5.6

---------- Post added 09-10-14 at 11:08 AM ----------

Sorry, forgot the link and I can't edit my previous post...
Eta Carina Nebula (Simon Williams) | AstroBin

09-10-2014, 01:12 PM   #9
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QuoteOriginally posted by AstroTak Quote
What type of astrophotography do you want to do? Nightscapes and starscapes are not too demanding on optics, most short focal length lenses will give decent results tho you may need to stop down some.
If you want to do widefield DSO's (Deep Sky Objects) like nebulas and open star clusters, you will need moderate focal lengths (~100 to 400mm) and for planetary and/or galaxies you will need very long focal lengths (into the metres) and the optics will need to be superb for use at low f ratios.

Astrophotography is the harshest test for any lens.
While faster lenses make sense for shorter exposure times, quite often they exhibit severe aberrations that typicaly don't affect daytime photo's.
The most common are coma, where the stars at the edge of the frame are stretched, and axial and lateral chromatic aberrations where the stars will not focus correctly and have blue or red halo's. Coma and axial chromatic aberration can be reduced by stopping down, lateral chromatic aberration cannot be fixed by stopping down.

Some very expensive ED glass can be used with decent results wide-open, but more often than not you will see better results with the lens stopped down.
For now I'm into the nightscapes. So I'm looking for the best lens for it.

One more question. Is the smc DA 18-135mm F3.5-5.6 WR lens enough good for the nightscapes?

---------- Post added 09-10-14 at 10:13 PM ----------

QuoteOriginally posted by DeadJohn Quote
@Botina, based on your questions I am assuming that you're just getting started with astrophotography and you do not own an O-GPS1 or tracking mount, but do have a tripod.

For Milky Way images, wide and fast lenses are good. Prime lenses generally have less coma distortion (stars near the corners look stretched out even when focus is good) than zooms. If you already own an 18-55 kit lens, you can start learning at 18mm and 30 second exposures. The lenses Adam mentioned above will gather more light wide open, but note you'll need to use shorter exposures because the longer focal length shows star trailing sooner. The Samyang/Rokinon/Bower 14mm f2.8 is popular for astrophotography with APS-C sensors.

Moon images can be done with any telephoto lens. 300mm is sort of the minimum for the moon.

Astrophotography of planets or dim deep sky objects is much more advanced. Start with the moon and Milky Way! Read The Backyard Astronomer's Guide: Terence Dickinson, Alan Dyer: 9781554073443: Amazon.com: Books if you want to pursue astrophotography. That book gives a through introduction to all aspects of amateur astronomy.
Thank you for your reply John,I'm also thinking about the O-GPS1 for the beginning. Later,when the budget will allow me to,I'll buy some telescope or a tracking mount for deep sky objects
09-10-2014, 05:09 PM   #10
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QuoteOriginally posted by AstroTak Quote
John hit on something I forgot to mention, primes being better than zoom lenses. This is absolutely true. Zoom lens design is a compromise and I was never happy with any I tried.
For astro I only use prime lenses.

The image at the following link was a single 7.5 main exposure taken with a 105mm wide open (f2.8).
Coma is not too bad but there is mild axial CA evident (red halo's around the orange stars) This also means the detail in the red nebula's is not as sharp as it could have been had I stopped down to f4 or f5.6

---------- Post added 09-10-14 at 11:08 AM ----------

Sorry, forgot the link and I can't edit my previous post...
Eta Carina Nebula (Simon Williams) | AstroBin
And yet your decription on that site is as follows:

"Single 7.5 minute exposure at f4.
Some very thin high level cloud passed through the frame.
I like what it did to the brighter stars, but overall it has made the image soft."

I see you are using the Astrotrac: Was this shot taken from the Northern or Southern Hemisphere? (Eta Carina is pretty far south so maybe not north)

If you took it from the southern hemisphere then how did you do a polar alignment?

Cheers
09-10-2014, 09:06 PM   #11
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Yes you are correct, I made an error when entering data to that site and have yet to change it.
It's easy to forget which settings were used on the fully manual lenses after a long night of imaging, don't have the luxury of exif data to check
When I inspect the raw image(5184 x 3456px) there are no diffraction spikes around the bright stars, though perhaps they are hidden by the softening from the cloud.

Yes, shot from the southern hemi, polar aligning the Astrotrac is relatively easy when using the optional wedge and polar scope. We don't have a nice bright polar star like Polaris in the north, but we do have a star named Sigma Octantis that is very close to the southern celestial pole.
09-11-2014, 01:32 AM   #12
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QuoteOriginally posted by AstroTak Quote
Yes you are correct, I made an error when entering data to that site and have yet to change it.
It's easy to forget which settings were used on the fully manual lenses after a long night of imaging, don't have the luxury of exif data to check
When I inspect the raw image(5184 x 3456px) there are no diffraction spikes around the bright stars, though perhaps they are hidden by the softening from the cloud.

Yes, shot from the southern hemi, polar aligning the Astrotrac is relatively easy when using the optional wedge and polar scope. We don't have a nice bright polar star like Polaris in the north, but we do have a star named Sigma Octantis that is very close to the southern celestial pole.
Thanks for the reply AT.

I was originally intending on an O-GPS1 but have seen great results from Astrotrac. The price put me off somewhat and i never bought either.
09-11-2014, 08:16 AM   #13
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For nightscapes the 18-135 is fine. You might find that you will need live view focusing
12-15-2014, 08:06 AM   #14
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Hello, it's me again.

Will the HD Pentax-DA 15mm F4 ED AL be good enough for starscapes?
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