Lens advice - Oly 25mm f1.9 or Pan 20mm f1.7

Started 3 months ago | Discussions thread
OP khcan Junior Member • Posts: 27
Re: Lens advice - Oly 25mm f1.9 or Pan 20mm f1.7

Androole wrote:

khcan wrote:

Androole wrote:

khcan wrote:

traveler_101 wrote:

I've looked through the responses this far and not surprisingly opinions vary considerably. Comparison is made much harder because of the different focal lengths. For me 25 is better for composition; narrow means you must exercise more control over the frame. On the other hand if I need wide, I reach for the 17mm which gives a moderate wide angle. The 20 is neither here nor there.

In terms of the quality of the lenses they render differently. Both are very, very good. I am not sure if the 20 is actually sharper; it might be, but it is certainly much cooler, while the 25 is bolder. Better colours with the 25, I think - but of course we are wading here into subjective preferences.

Finally and I think the decisive factor for why I sold my 20 in favour of the 25 we come to focusing - speed and stealth. You get both with the 25/1.8 and neither with the Panasonic 20. It is clunky, noisy and quite a bit slower than a contemporary m43 lens. After all, the 20 was one of the earliest lenses for the system.

I think that's a good summary of the factors I need to weigh, the possible limits of the 25 focal length vs the limits of 20's clunk and speed. I've seen some threads and/or flickr groups (can't remember which) that had so many outstanding pictures using the 25mm.

Of course, another option is to save some money and just get a Canon EOS 100 w the kit lens. There are so many choices and it's really tough to weigh the options with such little experience using different systems.

Note that the EOS 100 with the 22mm/f2 has the same disadvantages as the 20mm/f1.7 in terms of focus speed (and will result in nearly identical low light performance and depth of field, since you are trading a slightly slower lens for a slightly larger sensor).

With many (if not all) fast pancake lens designs, it seems like they tend to use a "unit focus" architecture, where they need to have the entire lens group move forward and back to focus. Most modern non-pancake lenses have a single lightweight focusing lens or group of lenses that is internal and is designed to be moved very quickly.

So it's the classic trade-off scenario, where you can't really get both. Tiny (thin) size or fast focusing speed, hard to get both. (Given a roughly "normal" focal length and a fast aperture around f/2, that is)

That's what I figured, but I wasn't sure if the larger sensor gave me comparable low light performance with the kit lens 15-45mm f/3.5-6.3.

I've never used a prime before so it makes me a little nervous

It's not perfect, and there are a lot of caveats to keep in mind, but a rough back-of-the-napkin approach to seeing what sensor size does to your low light capabilities is to divide the aperture of the lens by the relative crop factor of two sensors you're comparing.

If that sounds like gobbledygook, here's a quick demonstration.

Micro Four Thirds = 2.0x Crop Factor

Canon APS-C = 1.61x Crop Factor (Sony / Nikon / Pentax APS-C is 1.54)

2/1.61 = 1.24x Relative Crop Factor between M4/3 and Canon APS-C

So now with the lenses...

If you were comparing the Canon 22mm/f2 to the Panasonic 20mm/1.7:

f2 / 1.24 = f1.61 "equivalent" on M4/3

So you can see that's very close to f1.7, which is what you have with the Panasonic. That's a difference of just under 1/6th of a stop, which is technically referred to as a "smidgen."

With the f3.5-6.3 kit lens, you can go through the same exercise.

You end up with a f2.8-5.1 "equivalent" lens. In that case, the Panasonic f1.7 prime lens gets dramatically more light.

~1.5 stops on the short end, and just over 3 stops on the long end. So to compare the quality, imagine setting your camera to ISO 800 to simulate how it would look with the prime lens, and then bump it up to ISO 2000 or ISO 6400, and that's how the Canon with the kit lens would look, by comparison...

As you can see, a fast prime lens totally transforms the low light image quality equation. It's huge. If you were talking about comparing a fast prime on M4/3 to a big pro f2.8 zoom on a full-frame camera, that would make sense. But the difference between M4/3 and APS-C, especially Canon APS-C, is pretty small, so the aperture on the lens is the dominant effect.

Not sure I could duplicate that (without a handy crop-factor ref guide), but it makes sense. I had crossed the Canon off my list before (don't remember why) and I'll do so again. Thank you!

 khcan's gear list:khcan's gear list
Olympus OM-D E-M10 II Olympus M.Zuiko Digital ED 14-150mm 1:4-5.6 Olympus M.Zuiko Digital 25mm F1.8 LG G5 +1 more
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