21mm/24mm f/1.4 for star photography?

[lecycliste]

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There is little to choose in optical quality between the Summilux 21 and Summilux 24. For lenses of this speed they are superb. It all depends on the use you plan to take; star shots are one thing, but these lenses are too fine -and expensive- to neglect their use for the rest of your photography.

 

However, given the present-day improvements in high-ISO performance I would question the need for super-fast lenses for star photography. The Super-Elmars offer perfect edge-to-edge sharpness, minimal distortion, a flat focal plane, more so than any faster lens can offer.

 If I were to head out in the night I would take the Super-Elmar 18, a good tripod and crank up the ISO (within limits, of course ) Heck, the price difference would get me a A7SII...

 

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There are at least a couple factors in wanting to keep astrophoto exposures as short as possible. Even with an M10, noise at ISO 6400 or higher will require a fair amount of careful post-processing to reduce without messing up faint stars or blurring the Milky Way. 

 

Coma, elongation of bright stars at corners and edges, is another factor, especially wide-open, but also stopped down with some lenses. The photographer needs to research and test any lens for the aperture and subject being shot before purchase to ensure the best lens for his / her needs. 

 

Then there's exposure time and tracking. How much time would you like to spend outside for multiple mid-winter night exposures of several minutes duration? Each exposure will take twice as long as its selected time because of Leica's mandatory long exposure noise reduction (LENR) - the camera won't let you turn LENR off. If you want a staionary star shot, you'll either need to keep exposure below 400/(focal length) seconds or use a tracking mount. WIth tracking, you can keep the stars stationary, but you'll blur any foreground features. That requires shooting the stationary foreground untracked, then layering tracked stars and untracked foreground in Photoshop. 

 

Since the M10 is limited to 124 seconds in B, you won't be able to shoot anything longer anyway, even if you want to. For some Milky Way photography in dark skies, that may not be enough. The SL will let you shoot up to 30 minute exposures, buit you'd wait an hour for each shot since you once again can't disable the camera's LENR. 

 

So the best solution is an f/1.4 or 1.8 lens  to minimize exposure time. If you're going to do it cheap, a non-Leica dSLR (EOS Rebel series) with a Rokinon / Samyang 24mm f/1.4 might be your best bet. If you want to minimize multiple picture stitching, a  Sigma 14mm f/1.4 Art or Rokinon 14mm f/2.4 might work best. The Rokinon lenses have the best low-coma performance wide open, though their build and optical quality aren't as good as Leica (not surprisingly). The SIgma 14mm f/1.8 Art has more coma than the Rokinon, but is still lower than most other lenses, and its build and image quality are quite good. 

 

Edited February 14, 2018 by lecycliste

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[lecycliste]

I just pointed my 21 Summilux out the window 8s @ f/1.4 ISO 160 on a M9.

The camera is not squared so vertical perspective is what it is.

 

There is quite a bit of light pollution, but you can see Orion in the center and hopefully gauge the sharpness; degree of coma and chromatic aberration.

It seems sharp with well controlled coma to me.

 

The DNG file is here if you want to look deeper.

 

http://www.donaldingram.com/ForumImages/L1004475.DNG

 

and a full size jpg

 

http://www.donaldingram.com/ForumImages/L1004475full.jpg

 

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Looking at the corners and top edges of your picture, there's a fair amount of batwing elongation (coma) of bright stars. Rokinon's 24mm f/1.4 has a lot less coma, for 10% of the price. It's not built nearly as well (some copies show decentering), and isn't anywhere near as good for general photography, though. See a review at https://tinyurl.com/y735befw.

 

There's also a Rokinon SP 14mm f/2.4 lens with minimal coma, albeit with 1.5 stops slower speed. See a review at https://tinyurl.com/y93jxrzb.