RF 10-20 f/4 L vs RF 15-35 f/2.8 L...

[sedda]

OK, so the obvious... The 15-35 is faster at f/2.8. The 10-20 is wider, more unique, and if paired with a 24-105 f/4 L will give a photog everything they need between ultra, ultra wide and medium telephoto. It's also more expensive.

Not so obvious...? The 15-35 can be a decent walking around lens, including up to that 35mm street photogs allegedly love, whereas the 10-20 is more specialized.

So, I ask for debate and thoughts, one way or the other. I'm not at all committed to buying either, but if I do, I can't imagine a situation where I'd want both; and I **bleep** sure don't want to pay for both! Now it's your turn...

[ebiggs1]

It's really not a hard decision. Do you need or want ultra WA or is WA enough. The 15-35mil is going to be the more friendly lens to live with if your lens inventory is few. They really are not comparable because they are designed for a different use. If you already have the 24-105mil then the 10-20mm probably makes more sense, if not the 15-35mm does.

[shadowsports]

Greetings,

I own the RF15-35 and find it to be wide enough for my needs.  It's image quality is very good to superb.  I have a Rokinon 12mm for EF if I need wider, but doubt I ever would.  It's a pretty specialized lens and provides 180* FOV. I bought it because it doesn't put a black ring around images.  It's good for special effects and astro.  

It has a protruding convex objective like the RF 10-20.  That lens sits at 130* so it's very good for UW and doesn't skew the horizon.  DPP, Lr and PhotoLab all have lens corrections for it.  It's solid at constant F4.   So to Ernie's point, if you need UW, and want a high performing lens where F4 is enough and don't mind the bubble on the front, it's a great lens.  I found I preferred the flat front on my 15-35 and the extra stop of light.  

[Tronhard]

Just to throw a wildcard in.   I was originally considering the RF10-20 to add to my 24-105 etc., but in the end I went for the RF 14-35L f/5 IS USM because:

• It was wide enough for my purposes and had reach up to the longer FL
• Its front element allowed the use of conventional 77mm filters without adapters
• It was significantly cheaper than the alternatives
• It was much more compact and lighter to carry.

Like many lenses now, the 14-35 takes a shot somewhat wider than the specified FL, about 11mm, but uses that extra capacity to do some significant pixel wrangling - in-camera as JPGs or on import to PP software - to produce clean, straight, sharp and essentially distortion and vignetting-free images.    This is becoming more common, using computational algorithms similar to those that have been applied to cell phones for some time.  It allows lens makers to achieve very wide angles without the massive and complex optics of previous lenses.  The new approach allows the lenses to be much more compact, lighter and cheaper than would otherwise be the case, and they can be improved over time via firmware updates.

For my purposes, I have been extremely happy with the results, however each of us must find the solution to fit their own circumstances.