f/4.0 Lenses and astrophotography

[Sabaki]

Hi all

So with the understanding that the larger apertures like f/2.8 and bigger being ideal for astrophotography, I'm trying to gain some experienced opinions on f/4.0 for Astro.

What would one lose with a f/4.0 and how would a photographer have to compensate in order to take good images?

Just a bit of background, the economy in my country and taken a very poor downturn and our exchange rate against the US dollar has lost about 30% in the last few months.
Unfortunately it has meant that as a hobbyist, I can't justify paying the higher prices for gear right now and I've committed to the Canon EF 16-35 f/4.0 L IS

I would really appreciate some feedback please

 

[IglooEater]

I know very little about astro, but here are my guesses: on a crop body, you'll not be able to get great results simply because you'll be needing an iso of over 6400 to keep a short enough exposure To avoid star trails at short focal lengths. On a newer full frame you might be ok. I'm guessing you'll want to look into your lens' coma, because that kills for stars, turning your stars into spaceships. Coma can be helped by stopping down, but at f/5.6 you'll really have trouble getting enough light. (I believe the 16-35 is f/4 is pretty good and you shouldn't have to stop down).
These are all guesses.

If you're doing multiple exposures via tracking and stacking anything can probably work.

I'd love to here from folks with actual experience in this, as I'm thinking of doing the same thing.

 

[BeenThere]

You can try some shots with your lens at the wide end of the zoom range at f/4, ISO 6400 for 30 seconds and see how you like them. An inexpensive lens that works well and is widely used for night skies is the 14mm F2.8 Rokinon in EF mount. You may want to try this lens if your current lens does not work out.
If you use the Rokinon, I would suggest getting it ready by manually focusing on a distant point during daylight hours and tape the focus ring in place at this distant focus. Then take it out to shoot at night without changing focus.

 

[scyrene]

A few things to consider.

First, if your image does not contain foreground elements (i.e. if your shot is the sky alone, with no landscape included), you can stack. With a normal fixed tripod, you'll have to align the shots manually, or get software that does it for you, but it will clean up very well.

Second, a cheap tracking mount may be a good option, if they are available. I had an iOptron SkyTracker and it was great for shots up to ~2 minutes without noticeable star trails.

Finally, noise that would be unacceptable on most shots is not uncommon in wide angle astrophotography, especially ones with foreground elements. And more heavy-handed noise reduction is appropriate too, in my experience.

 

[timmy_650]

I have used my my 8-15 f4 with good results but that lens is wider. I do like my tarmon 17-35 f2.8 better. What your lens lack you can make up for it in PS.

 

[YellowJersey]

If you're stuck with an f/4, then I think stacking is the way to go. Hell, even if you have an f/2.8, I'd say stacking is a good idea.

As for foreground, I'd recommend using two exposures: one for the stars and one for the foreground since trying to get it all in focus may be an issue if your foreground object is close to the camera. Perhaps consider using a flash or some other external light to give the foreground some extra light so you can keep the ISO and noise down.

Here are my first two astro shots I took with my 17-40mm f/4. Had to push like crazy in post. Both are 30 seconds, f/4, 6400 ISO on 5D mkIII.

Single shot: http://meema.deviantart.com/art/21st-Century-Man-484397231

Two shots blended (screwed up the DOF for the dunes in the background): http://meema.deviantart.com/art/Can-You-Hear-Me-Major-Tom-454152854

 

[Sabaki]

Hey all

Thanks for the feedback. Seems that experimentation and stacking will have to become part of my workflow once I eventually spring for the 16-35 f/4.0 IS

YellowJersey,you have some very cool 'scapes on your DeviantArt profile! Great shots

 

[kaihp]

Jrista is probably one of the most knowledgable about astrophotography: I'd ask him.

As I recall, Jon said in an earlier thread that he hadn't tried the 16-35 f/4L IS yet, so he couldn't comment on coma etc.

 

[StudentOfLight]

Have you already looked into the Tamron 15-30mm f/2.8 VC and Samyang prime options?

Another important consideration (other than maximum aperture) is vignette. I often hear people saying there is no need for primes because modern zooms are so good. While the new pro-zoom lenses are comparably sharp at their relative maximum aperture, they usually suffer from vignette. For this reason I prefer to use a fast prime stopped down to 2.8-3.2 than a zoom wide open at its relative maximum aperture:
1) Canon 16-35mm f/4L vs Canon 15mm f/2.8 fisheye
http://www.the-digital-picture.com/Reviews/Lens-Vignetting-Test-Results.aspx?Lens=949&Camera=453&FLI=0&API=0&LensComp=282&CameraComp=9&FLIComp=0&APIComp=1

2) Canon 16-35mm f/4L (at 24mm f/4) vs Samyang 24/1.4 (at 24mm f/2, i.e. still gathers 2 stops more light)
http://www.the-digital-picture.com/Reviews/Lens-Vignetting-Test-Results.aspx?Lens=949&Camera=453&FLIComp=0&APIComp=1&LensComp=821&CameraComp=453&FLI=2&API=0

3) Canon 24-70mm f/2.8L II vs Samyang 24/1.4 (at 24mm f/2.8)
http://www.the-digital-picture.com/Reviews/Lens-Vignetting-Test-Results.aspx?Lens=787&Camera=453&FLI=0&API=0&LensComp=821&CameraComp=453&FLIComp=0&APIComp=2

4) Canon 16-35mm f/4L (at 16mm f/4) vs Tamron 15-30 f/2.8 (at 15mm f/4)
http://www.the-digital-picture.com/Reviews/Lens-Vignetting-Test-Results.aspx?Lens=949&Camera=453&FLI=0&API=0&LensComp=986&CameraComp=453&FLIComp=0&APIComp=1

Lastly I personally do not place too much emphasis on pixel level sharpness for astro landscape photos. As a matter of fact, I actually defocus the stars slightly so that they are larger than a single pixel in order to make them easier to differentiate from noise and hot pixels and to gain a bit more depth of field for foreground elements.

 

[YellowJersey]

Hey all

Thanks for the feedback. Seems that experimentation and stacking will have to become part of my workflow once I eventually spring for the 16-35 f/4.0 IS

YellowJersey,you have some very cool 'scapes on your DeviantArt profile! Great shots

Thanks!