DSLR Lens for Astronomy/Birding

[pevsfreedom]

Hi

I wanted to ask if something like this would yield any decent types of results for tri-pod / canon T3i use for astronomy with maybe a hint of birding on the side. 

[sigma 70-300mm f/4-5.6 DG Macro Telephoto Zoom Lens for Canon SLR Cameras]

http://www.amazon.com/Sigma-70-300mm-Nikon-Digital-Cameras/dp/B0012X43P2/ref=sr_1_1?ie=UTF8&qid=1425682800&sr=8-1&keywords=300mm+lens+sigma

Would something like this put me in the 'ballpark' to image things like galaxies?

What considerations are there to take when using a camera lens without any sort of guiding / EQ mount? I assume quick short subs are necessary?

Thanks. I want to maybe buy a cheap lens like this before I dive into an APO scope.  

[Ags]

If you mean this lens i think it is not a good choice for astronomy:

http://www.photozone.de/canon-eos/326-sigma-af-70-300mm-f4-56-apo-dg-macro-test-report--review?start=1

The lens is very soft at 300mm of-center according to the review, and it has strong chromatic aberration.

Also, 300mm will not get you very close to most galaxies. I think at that focal length, you would be restricted to the Magelanic Clouds, and the Andromeda and Triangulum galaxies.

[Leveye]

Zoom lenses of this nature have a tendency to "creep" as you point them skyward and not stay focused unless locked into position some way. For birding yes for Astro i say no. Look at either older Nikkor or Ashai/Takumar prime lenses. No creeps there.

[pevsfreedom]

Thanks for the answers. 

[Thalestris24]

The more expensive 'APO' version of the lens might be better. You might be able to use it for widefield astro if you can do something to hold focus. At 300mm you're limited to about 4/3 = 1.3 secs exposures without star trails. At 200mm, about 2 secs. It's quite restricting without a tracking mount but one way to start learning.

Louise

Edit: just to mention - you always use camera and lens in manual mode for astro imaging

[pevsfreedom]

The more expensive 'APO' version of the lens might be better. You might be able to use it for widefield astro if you can do something to hold focus. At 300mm you're limited to about 4/3 = 1.3 secs exposures without star trails. At 200mm, about 2 secs. It's quite restricting without a tracking mount but one way to start learning.

Louise

Edit: just to mention - you always use camera and lens in manual mode for astro imaging

Yeah I've figured out the last part on my last night out. Did 40-50 shots with different settings to figure things out, the 10 minute exposure was a laughable effort, but a teaching one . Had decent widefield success with ~10 second exposures and low apertures. 

[kor84]

I came across this the other day https://m.youtube.com/watch?v=e0JSTF8SGi4 I think it's worth a watch.

[Rihard]

Hi

I wanted to ask if something like this would yield any decent types of results for tri-pod / canon T3i use for astronomy with maybe a hint of birding on the side. 

[sigma 70-300mm f/4-5.6 DG Macro Telephoto Zoom Lens for Canon SLR Cameras]

http://www.amazon.com/Sigma-70-300mm-Nikon-Digital-Cameras/dp/B0012X43P2/ref=sr_1_1?ie=UTF8&qid=1425682800&sr=8-1&keywords=300mm+lens+sigma

Would something like this put me in the 'ballpark' to image things like galaxies?

What considerations are there to take when using a camera lens without any sort of guiding / EQ mount? I assume quick short subs are necessary?

Thanks. I want to maybe buy a cheap lens like this before I dive into an APO scope.  

Hi,

I used to own the Apo version of that lens (still inexpensive) with the Nikon mount. The optics were very good, and although I'm no expert there was no noticeable chromatic aberration or distortion.

I found these pics on Astrobin:

http://www.astrobin.com/gear/15241/sigma-70-300-sigma-70-300-f4-56-dg-apo-macro/

As already mentioned it would not keep the focus if pointed to the sky

An alternative would be using an adapter and old screw mount (M42) lenses. You can get a fast, prime lens for a very cheap price.

Best Regards