Good lenses for astrophotography?

[Calculus (Yas)]

Hello all!
Been in to observational astronomy for a while and astrophotography now looks like the next logical progression!
Haven't done much astrophotography apart from a few shots of the Milky Way.
My current camera (Canon 40D) is due for an upgrade (used it for 5 years, nearly 150k shots) and hoping to get myself the Canon 6D.

1. Is 16-35 L II a good lens for wide-field astrophotography? I am thinking of getting myself this lens for daytime/normal shoots (I generally shoot landscapes) so if this lens suits both purposes then it's two birds with one stone. I already have a 24-105 but it can't do much while mounted on a crop-sensored 40D.
2. Or do you recommend a prime lens such as Canon 14mm for this?

Thanks - advice, recommendations welcome!

[skysurfer]

On a Fullframe camera like the 6D this lens has lots of vignette at full aperture.
This site: http://www.the-digital-picture.com/R....aspx?Lens=412
has an excellent preview how lenses perform in sharpness, color errors, etc.
The best value for astrophotography is NOT a FF body but a crop one.

Reasons:

- Use lenses designed for fullframe as the worst part (the edges) falls outside the cropped section.
- clip-in filters such as Astronomik CLS or Hutech LPS V2 can be fitted behind the lens
I have a 7d and 85mm f/1.8 and 70-300 f/4-5.6L excellent value for AP.
The advantage of higher sensitivity due to larger sensor is undone by more squeezing the aperture to prevent vignetting and edge softness.

Get a 70d or 7d or 60d. Cheaper body and invest in glass !

For daylight and landscapes you can use crop lenses such as the EF-S 10-22 or 15-85mm f/3.5-5.6, the latter is called 'the L lens without a red ring'. And the EF(not S) 17-40mm f/4L is of great value too.

[graphworlok (James)]

Another 40D owner here. Great camera.

I only have a few, possibly irrelevant suggestions to make

If you are looking at doing any astro work where you might want flat frames, avoid zoom lenses, unless you have a lightbox setup that lets you avoid touching the focus or zoom.

Ok, thats one suggestion. I said a few..

I like my old Pentax Takumar lenses - but the CA is noticeable (And in the event of a home invader, you can put one in a long sock and hit them with it). Dunno if that counts.

Cheers.

[dannat (Daniel)]

The 16-35 will cover both your daytime plus nighttime needs.

If you want you might also consider the Nikon 12-24/2.8, a very good glass.

The canon 14mm while wide is limiting, & you'll prob need another prime to cover all angles, maybe 20/2.8 or 28/1.8. Zoom is more convenient.

Will the 16-35 just be tripod mounted? Ie no motorized tracking

[acropolite (Phil)]

6D is an excellent choice, the 16-35 is a fairly good lens, not perfect but nothing is unfortunately. Vignetting really isn't an issue with the 16-35 on full frame, the little there is can be easily corrected in Canons DPP as can any CA and lens distortion.

[Calculus (Yas)]

Dear all,
Many thanks for your suggestions - very helpful indeed.
Skysurfer's advice re: sticking with a crop-sensor camera sounds like solid advice. I had already made up my mind for a 6D considering day-time shoots but may now have to reconsider it.

Armed with all of your advice, I can now conduct further research on what I should invest in. Cannot afford two DSLRs at the moment.

Thanks again, everyone!

[rogerg (Roger)]

Hmm, while I'd agree a crop camera is better in many ways there is no way I would give up my 6D before I gave up my 7D when it comes to astrophotography. There is barely any comparing the two in terms of noise and high end ISO colour performance. It's cheaper to buy the 6D and get 2-3 stops improved capability than to buy f/2.8 or faster L quality glass. Also, I wonder how much you'd really be missing out on if you took a 20.2MP from the 6D and cropped it - compared to the 7D's 18MP (if you're concerned about full frame distortion you can just crop it like it would be on a crop body - more or less). If I could, I would take the high ISO performance and put it in a 7D, but that's just not possible.

My impression of the 16-35 is that it doesn't receive many rave reviews. Typically reviews comment of the distorted corners. I have the 17-40 (bought it over 10 years ago) and while it has some edge distortion on full frame it is well controlled compared to the alternatives.

My Tamron 24-70 f/2.8 has different distortions to the 17-40, perhaps slightly more but they are different so hard to compare. All-round I enjoy it for it's affordability. I'd only buy it if getting a full frame.

The Nikon 12-24 f/2.8 is the class leader, but you won't have auto controls.

If choosing one lens I wouldn't go a prime like the 14mm.

My 2c worth. Not easy decisions

[rcheshire (Rowland)]

I agree with investing in glass and practice with the 40D, which is a good all-rounder for AP. Later you may wish to do a spectrum mod. I think aps-c sensors are more flexible than full frame for AP, unless you intend using a telescope.

Pixel size is also a consideration. Below is JTWs blurb on pixel size applied to the 1100D.

http://www.jtwastronomy.com/products/ultimate.html

We also chose the 1100D because of the pixel size, the main reason for a CMOS based camera's low QE is due to the industry's relentless pursuit of smaller pixels. Great for regular photography, but not for astrophotography. The 1100D has pixels of 5.2µm (surface area of 27µm²) , much bigger than the 600D or 650D (4.3µm, surface area of just 18.5µm²). The 1100D is more sensitive because of this. You may say that the max ISO is much higher on the 650/600D but this is just an off-chip amplification, ISO makes almost no difference to the sensitivity or signal to noise ratio. Taking an average European night with seeing of 1.5 arc seconds, and a fast widefield telescope (600mm) the camera is sampling almost 1:1, meaning the sensitivity is maximised and there is no data loss. If the seeing is worse or the telescope focal length is longer, you will be oversampling. The 1100D really is the best tool for the job

Hope this is helpful...