Question about L lenses & Sharpness

[lmelendez]

Hi there

I have a quick question about something I read here. I saw a thread that said that primes will give you the best quality in terms of sharpness. So, does that mean that the Canon 85mm f1.8 lense will give you better quality (sharpness wise) than the 70-200mm f2.8 L used at 85 mm ?

Thanks!

Leo.

[Adam Hicks]

According to this site it will http://www.photozone.de/2Equipment/easytxt.htm#Zstd

And logic says it should. Especially with both lenses at f2.8.

[lmelendez]

Thanks Adam!

[Mike Panic]

keep in mind however that most lenses, even L glass is not its sharpest wide open. they are generally thier sharpest 1-2 stops closed from wide open, and from f/8 to f/11 or so

[lmelendez]

keep in mind however that most lenses, even L glass is not its sharpest wide open. they are generally thier sharpest 1-2 stops closed from wide open, and from f/8 to f/11 or so

Thanks Mike,
I read about that too a few days ago and I am currently playing with my lens to find the best point (in terms of sharpness).

Leo.

[DaveG]

Hi there

I have a quick question about something I read here. I saw a thread that said that primes will give you the best quality in terms of sharpness. So, does that mean that the Canon 85mm f1.8 lense will give you better quality (sharpness wise) than the 70-200mm f2.8 L used at 85 mm ?

Thanks!

Leo.

This tends to be one of those recurring issues. Are zooms softer than primes? Of course they are, so on an optical bench the answer is yes. Yet in a photograph that you or I took at 1/500 of a second (at the 85mm focal length) with either the lens at f5.6, then there won't be any difference at all.

My point is that the lab is testing mines per millimeter of sharpness and while that's all well and good you can't see the difference between the slightly superior 85's and the zooms.

I use this analogy all of the time, usually about the future MP cameras, but it seems to be appropriate for this discussion as well: If you are buying stereo gear and you are in the shop you have to remember that you can hear 7, you own 8, and they're trying to sell you 9.

Have a look in a bunch of photography magazines at the library. The lens used is usually sited underneath the photograph and I suspect that the 70-200 Canon would be used a lot. So do they look soft to you?

I've got tons of pictures with my 70-200 f2.8 L that are dead soft. And tons more where they are razor sharp. There is a heck of a lot more going on with image sharpness than the inherrent LpMM capability of a lens.

[Longwatcher]

check the following page out

http://wlcastleman.com/equip/reviews/70_200/index.htm

It indicates that at f5.6 and f8 the 70-200/2.8 out resolves the 85/1.8, but otherwise the 85/1.8 wins. I should point out it is not favorable to IS version of 70-200, but that is with IS on. I personally like the results of my 70-200/2.8L IS so I am not really careing as it works great for what I use it for.

As for Canon's results they show a higher sharpness for the 70-200's across the board, but the contrast is not as good, meaning the bokeh should be better on the 85/1.8.
70-200/2.8L
http://consumer.usa.canon.com/ir/controller act=ModelDetailAct&fcategoryid=150&modelid=7341

70-200/2.8L IS
http://consumer.usa.canon.com/ir/controller?act=ModelDetailAct&fcategoryid=150&modelid=7469

85/1.8
http://consumer.usa.canon.com/ir/controller?act=ModelDetailAct&fcategoryid=152&modelid=7311

Just my research.

[lcoleman]

Longwatcher wrote:

"...but the contrast is not as good, meaning the bokeh should be better on the 85/1.8."

How are contrast and bokeh related? My understanding of bokeh is the quality of the out of focus part of the image. I have read about the quality of the glass, the shape and number of aperature blades, etc., but never heard of contrast of the lens being a major factor. How does this play into the bokeh?

[Longwatcher]

I have read several articles that descibes what affects bokeh and how to find out for yourself ahead of time. I also rechecked and realised I got somewhat confused. It is the meridonial and sagital lines that are the solid/broken lines that can help determine bokeh. I knew it was the solid/broken lines, I just got messed up on what they meant.

links to one of my sources:
MTF
http://luminous-landscape.com/tutorials/understanding-series/understanding-mtf.shtml
Bokeh
http://luminous-landscape.com/essays/bokeh.shtml

While one factor is the number and shape of blades (the more the better usually); this affects the overall shape of the blurry part. A circle is usually best (but not always)

The other factor is how well the center and edges of the blurriness shows up.

For the second part, you can get an idea of how this will be from the MTF charts. If the solid and dashed line (of the same color/thickness) are nearly on-top of each other, you should have good bokeh as far as the center/edge of the blurry spot is concerned. If they separate then it will theoretically not be as good. However, I also know you want some separation although not a lot since you want the edge to be fading just a very little bit more then the center, but not a lot as then it would look wrong. It would also look wrong if it was even all the way across, although theorectically that is what the lens designer's are going for in a perfect design if humans didn't have an opinion. And of course, sharp edges won't look good either. Usually.

Bokeh depends a lot on the shot, but the MTF can at least give you an idea of how a lens will perform as compared to others, not only in sharpness, but in bokeh as well. However as is mentioned on the link on MTF, it can be different from shot to shot, depending on focal length, aperture and lens construction.

Or so I have read and seen for myself.