Choosing a Lens

There are many lens comparisons. Had some questions from a different perspective. (Note i am looking at the 17-50 sigma/tamron and the 15-85 canon vs 17-70 sigma)

How does the number of blades in the aperture, min f stop (i.e. f22 vs f32) and groups/elements of the lens. Low dispersion vs UD affect the image. Just trying to understand so that i can make a decision on lenses.

If this has been discussed, sorry.

Lastly, plan on using this on a APS-C camera.

If you have more blades in the iris of the lens, the aperture will be more circular. The more circular the aperture the smoother the bokeh. When stopped down, with less blades, when you shoot lights, you will get less points on the starburst. I personally like more points on the startbursts from lights.

Purplecow wrote in post #13240603
When stopped down, with less blades, when you shoot lights, you will get less points on the starburst. I personally like more points on the startbursts from lights.

Just to specify, you do get more points with more blades. The number of points is double the number of aperture blades. However, with an even number of blades the opposing "points" will be on top of each other, so it will appear as if you have less points. For example, the Canon 10-22 has 6 blades, so 12 pointed stars. But the points are superimposed on each other, so the result is a 6 pointed "star" whereas the tokina 11-16 has 9 blades, which is an odd number, and this produces 18 pointed "stars". Personally, I hate this many points

Minimum f stop doesn't really affect image quality at other apertures.

Low dispersion and UD elements are special glass that makes the lens better at correcting aberrations, which means better IQ.

But looking at these "features" will not help you see which lens produces better IQ. It is a combination of all the factors together that gives a lens its "look". And whether you prefer the look of one lens over another is entirely subjective. I'd advise you to go look in the sample image threads of all those lenses and decide based on what you see there which lens you like best.

Of course, first you'd have to decide whether you want constant 2.8 aperture, or more range.

The sigma 17-70 OS is a great choice IMO because it combines the best of both worlds. It has a faster aperture than the 15-85, and it has more range than the 17-50's.

Thanks guys/gals. So many good choices and with all the comparisons i thought I'd look at another aspect. Learned something new about lenses today (Star burst points).

I was leaning towards the 17-70 for the exact reason you(Sirrith) mentioned. There is one on the forum for 250 shipped (Not OS though) . Need to sell my 24-105 first.

I'd stay away from the non-OS, the OS version doesn't go for that much more, and its better in several important ways: HSM, OS, IQ, aperture are all improved over the old non-OS version. MFD takes a slight hit, but thats not really an issue, you can still get crazy close with the OS version. Here are a few pictures from it, its been my perfect travel lens:

IMAGE LINK: http://www.flickr.com …s/noobography/5​954382990/

IMAGE LINK: http://www.flickr.com …s/noobography/5​953817023/

IMAGE LINK: http://www.flickr.com …s/noobography/5​954381726/

IMAGE LINK: http://www.flickr.com …s/noobography/6​217471240/

Sirrith wrote in post #13240966
I'd stay away from the non-OS, the OS version doesn't go for that much more, and its better in several important ways: HSM, OS, IQ, aperture are all improved over the old non-OS version. MFD takes a slight hit, but thats not really an issue, you can still get crazy close with the OS version. Here are a few pictures from it, its been my perfect travel lens:

IMAGE LINK: http://www.flickr.com …s/noobography/5​954382990/
IMG_7076 by noobographer, on Flickr

IMAGE LINK: http://www.flickr.com …s/noobography/5​953817023/
IMG_7384 by noobographer, on Flickr

IMAGE LINK: http://www.flickr.com …s/noobography/5​954381726/
IMG_7090 by noobographer, on Flickr

IMAGE LINK: http://www.flickr.com …s/noobography/6​217471240/
IMG_9174 by noobographer, on Flickr

thx for the input. luv the notre dame photo. my main use is travel than sports.

eos650 wrote in post #13240526
There are many lens comparisons. Had some questions from a different perspective. (Note i am looking at the 17-50 sigma/tamron and the 15-85 canon vs 17-70 sigma)

How does the number of blades in the aperture, min f stop (i.e. f22 vs f32) and groups/elements of the lens. Low dispersion vs UD affect the image. Just trying to understand so that i can make a decision on lenses.

If this has been discussed, sorry.

Lastly, plan on using this on a APS-C camera.

Don't mean to derail your question, but you have a sweet lens with that 24-105. If your gear list is accurate, I'd be looking at a 70-200 as your next lens.

mckinleypics wrote in post #13241133
Don't mean to derail your question, but you have a sweet lens with that 24-105. If your gear list is accurate, I'd be looking at a 70-200 as your next lens.

I am looking for something wider. I keep saying some day i will get a full frame but will prob not do it. I have access to a 70-200 2.8 IS that I am using for soccer but do not want to travel w it. I find on the aps-c the 24-105 is not wide enough often times. The lens really woke up w the 7D, i took some shots w it and i was surprised at the improvement over 50d that i had. I recognize it was prob just my lack of knowledge of using the camera (50D). One of the other options was to keep the 24-105 and pick up the 17-50, thus the carousel go's round again.

I would sell the 24-105. No point keeping it around and having a standard zoom as well. You can always buy it back when and if you do go FF.

Sirrith wrote in post #13241246
I would sell the 24-105. No point keeping it around and having a standard zoom as well. You can always buy it back when and if you do go FF.

That was/is my first option. I will be putting up on craigslist later this week.

eos650 wrote in post #13240526
There are many lens comparisons. Had some questions from a different perspective. (Note i am looking at the 17-50 sigma/tamron and the 15-85 canon vs 17-70 sigma)

How does the number of blades in the aperture, min f stop (i.e. f22 vs f32) and groups/elements of the lens. Low dispersion vs UD affect the image. Just trying to understand so that i can make a decision on lenses.

If this has been discussed, sorry.

Lastly, plan on using this on a APS-C camera.

not sure on the number of aperture blades and low dispersion UD but the Tamron 17-50 2.8 has a constant f 2.8 which is useful


XSi (450D) with Tamron 17-50 2.8 non-vc

ISO 1600
43mm
(cropped)

eos650 wrote in post #13241186
I am looking for something wider. I keep saying some day i will get a full frame but will prob not do it. I have access to a 70-200 2.8 IS that I am using for soccer but do not want to travel w it. I find on the aps-c the 24-105 is not wide enough often times. The lens really woke up w the 7D, i took some shots w it and i was surprised at the improvement over 50d that i had. I recognize it was prob just my lack of knowledge of using the camera (50D). One of the other options was to keep the 24-105 and pick up the 17-50, thus the carousel go's round again.

In that case I LOVE my Tokina 11-16 2.8!

Not sure why you have both 28-135 and 24-105.... They duplicate each other pretty heavily, so unless you need one to back up the other for business purposes, can't see a lot of reason to have both.

That said, if you want wider, and like one or the other of what you've got, why not just get a wider lens to complement what you have, rather than overlap it to a large degree?

There are some great ones to choose among (and possibly going FF someday maybe just doesn't cut it, since you are considering mostly "crop only" lenses already, and can alway sell those off if/when you ever do go FF).

There are a number of very nice lenses that you might consider to complement what you have:

Sigma 8-16 (extremely wide, leaves a big gap between it and your current lenses)
Canon 10-22 (probably the best, but also fairly high priced)
Sigma 10-20 (there are two versions now, one has fixed f3.5 aperture but is more expensive)
Tamron 10-24 (widest focal length range, but some say it's a bit soft between 20 & 24mm)
Tokina 11-16/2.8 (the only f2.8 lens in the group, but very narrow focal length range, big gap)
Tokina 12-24/4 (nice range, nice price, fits in well with your zooms... this is the lens I bought and use)
Sigma 12-24 (this is pricey, it's actually a FF lens if that's what you must have, has some distortions, but can be corrected with software)

I wouldn't recommend a 15 or 17 or 18 to whatever, unless you are planning to replace your existing zooms and trying to have just a single lens.

Not everyone likes/needs/uses longer teles. There are many to choose from, though it sounds as if your biggest concerns are wider, not longer. If you ever do want a longer lens, I'd also suggest 70-200... especially the f4 IS version if you want to travel with it. Unless you suddenly decide to become a bird/wildlife photographer, in which case 200mm isn't going to be long enough and you probably should look at Canon 100-400 IS, Sigma 120-400 OS or 150-500 OS, even though they are considerably bigger and heavier.

In addition to the number of apertures blades (more blades = more round opening = more better bokey), some lenses have specially curved blades that further make for nice background blur.

f22 and f32 really aren't very relevant when shooting with a crop sensor camera. On 7D or T2i, you will start to see loss of fine detail in your images at apertures smaller than f7.1. It will be minor at f8 and f11, so those are still very usable, but at f16 and even more at f22 it will show up more and more, so you might want to avoid using those f-stops. Besides, small f-stops are great for showing off how much dust is on your sensor.

Don't worry about the number of elements and groups, or too much about whether or not the lens includes UD, ED and other specialized types of glass and elements. Instead look at images made with any particular lens you might be considering... Search the the Lens Sample Archive right here on POTN for user submitted images from just about any lens imaginable. That will likely tell you more than just about all the discussion and specifications you might find to read.

If you replace your current mid-range zoom, you might be concerned about having a larger aperture (f2.8) and USM (or HSM if it's a Sigma)... Those are both desirable items on a mid-range.

However, if instead you complement your current mid-range with and Ultrawide zoom, these things are a bit less critical. f2.8 isn't all that important on very wide lenses because you are usually stopping that type of lens down anyway, there's never a great deal of background blur possible with them, and short focal length lenses are more easily handheld steady at slower shutter speeds. USM focus is less necessary because Ultrawide lenses only need to move their focusing groups slightly to achieve focus, so can be very fast and responsive without it. Also, USM focus can be more accurate, but the deeper depth of field of an Ultrawide lens tends to hide minor focus errors anyway.

So, you can possibly economize a bit by not spending the extra charges for some of these features on Ultrawides, yet still get a very usable lens.

A lot of wider lenses are variable aperture... You'll see something like "f3.5-f5.6" in the description and right on the lens' name ring. Non-variable lenses are usually more expensive to make and buy, plus tend to be larger and heavier. Whether or not a lens' aperture varies might not matter to you. One common area where a variable aperture can be a problem is when using manually set flash or studio strobes. It's a bit of a pain and can lead to some exposure errors to have to adjust everything after zooming the lens (and the aperture changes). On the other hand, if like most people you use modern eTTL flash in the usual ways, it will automatically compensates for any changes in aperture, so doesn't matter.

Image quality is the most overriding concern I have when considering a lens, but other less citical things I look at include...

-Filter size... is it the same as some of my other lenses, so they can share filters I already have?
-Lens hood or other accessories... are they included or additional cost?
-Size, weight.
-Ergonomics or functionality... such as how AF is turned on/off, the direction focus/zoom rings rotate, etc.
-Build quality... hoping for a durable lens that won't get dust inside too easily.
-Reliability... for example, does the lens have a history of calibration issues, or get out of calibration easily... and/or are there a lot of reported failures.

Have fun shopping!

amfoto1 wrote in post #13251167
Not sure why you have both 28-135 and 24-105.... They duplicate each other pretty heavily, so unless you need one to back up the other for business purposes, can't see a lot of reason to have both.

That said, if you want wider, and like one or the other of what you've got, why not just get a wider lens to complement what you have, rather than overlap it to a large degree?

There are some great ones to choose among (and possibly going FF someday maybe just doesn't cut it, since you are considering mostly "crop only" lenses already, and can alway sell those off if/when you ever do go FF).

There are a number of very nice lenses that you might consider to complement what you have:

Sigma 8-16 (extremely wide, leaves a big gap between it and your current lenses)
Canon 10-22 (probably the best, but also fairly high priced)
Sigma 10-20 (there are two versions now, one has fixed f3.5 aperture but is more expensive)
Tamron 10-24 (widest focal length range, but some say it's a bit soft between 20 & 24mm)
Tokina 11-16/2.8 (the only f2.8 lens in the group, but very narrow focal length range, big gap)
Tokina 12-24/4 (nice range, nice price, fits in well with your zooms... this is the lens I bought and use)
Sigma 12-24 (this is pricey, it's actually a FF lens if that's what you must have, has some distortions, but can be corrected with software)

I wouldn't recommend a 15 or 17 or 18 to whatever, unless you are planning to replace your existing zooms and trying to have just a single lens.

Not everyone likes/needs/uses longer teles. There are many to choose from, though it sounds as if your biggest concerns are wider, not longer. If you ever do want a longer lens, I'd also suggest 70-200... especially the f4 IS version if you want to travel with it. Unless you suddenly decide to become a bird/wildlife photographer, in which case 200mm isn't going to be long enough and you probably should look at Canon 100-400 IS, Sigma 120-400 OS or 150-500 OS, even though they are considerably bigger and heavier.

In addition to the number of apertures blades (more blades = more round opening = more better bokey), some lenses have specially curved blades that further make for nice background blur.

f22 and f32 really aren't very relevant when shooting with a crop sensor camera. On 7D or T2i, you will start to see loss of fine detail in your images at apertures smaller than f7.1. It will be minor at f8 and f11, so those are still very usable, but at f16 and even more at f22 it will show up more and more, so you might want to avoid using those f-stops. Besides, small f-stops are great for showing off how much dust is on your sensor.

Don't worry about the number of elements and groups, or too much about whether or not the lens includes UD, ED and other specialized types of glass and elements. Instead look at images made with any particular lens you might be considering... Search the the Lens Sample Archive right here on POTN for user submitted images from just about any lens imaginable. That will likely tell you more than just about all the discussion and specifications you might find to read.

If you replace your current mid-range zoom, you might be concerned about having a larger aperture (f2.8) and USM (or HSM if it's a Sigma)... Those are both desirable items on a mid-range.

However, if instead you complement your current mid-range with and Ultrawide zoom, these things are a bit less critical. f2.8 isn't all that important on very wide lenses because you are usually stopping that type of lens down anyway, there's never a great deal of background blur possible with them, and short focal length lenses are more easily handheld steady at slower shutter speeds. USM focus is less necessary because Ultrawide lenses only need to move their focusing groups slightly to achieve focus, so can be very fast and responsive without it. Also, USM focus can be more accurate, but the deeper depth of field of an Ultrawide lens tends to hide minor focus errors anyway.

So, you can possibly economize a bit by not spending the extra charges for some of these features on Ultrawides, yet still get a very usable lens.

A lot of wider lenses are variable aperture... You'll see something like "f3.5-f5.6" in the description and right on the lens' name ring. Non-variable lenses are usually more expensive to make and buy, plus tend to be larger and heavier. Whether or not a lens' aperture varies might not matter to you. One common area where a variable aperture can be a problem is when using manually set flash or studio strobes. It's a bit of a pain and can lead to some exposure errors to have to adjust everything after zooming the lens (and the aperture changes). On the other hand, if like most people you use modern eTTL flash in the usual ways, it will automatically compensates for any changes in aperture, so doesn't matter.

Image quality is the most overriding concern I have when considering a lens, but other less citical things I look at include...

-Filter size... is it the same as some of my other lenses, so they can share filters I already have?
-Lens hood or other accessories... are they included or additional cost?
-Size, weight.
-Ergonomics or functionality... such as how AF is turned on/off, the direction focus/zoom rings rotate, etc.
-Build quality... hoping for a durable lens that won't get dust inside too easily.
-Reliability... for example, does the lens have a history of calibration issues, or get out of calibration easily... and/or are there a lot of reported failures.

Have fun shopping!

Andy, first and foremost, thanks for your input. I know there are a ton of threads on "which lens", that is why I decided to look at other aspects or specs of teh different lenses. And of course cost.

The 28-135 was a gift so I do not want to get rid of it. I have use of a 70-200 f2.8 IS that i have been using for soccer. Theres also another 24-105L in the family so that was the reasoning to sell my 24-105 as I can borrow if need be. That is def a plus with an extended family and 6 family members(nephews and niece) w canons ranging from a Xti to a 5D MkII. That left me w choosing the 17-50 or the 17-70.

I use to travel a lot and I took 2 lenses with me for my eos. They were a 28-70 and a 70-200 (Very old canon lenses). I never took the 28-70 off. That was the reasoning for going w the 17-50 on an aps-c (7D) camera. I like to travel light.

As u mentioned about filters, the 17-50 sigma is a 77mm lens so i am covered filter wise, but is 200 more than the 17-70. It also comes w a lens hood, another plus.

I plan on trying both out at the store. Ultimately, it comes down to IQ as u mentioned and the characteristics I am looking for btwn the 2 lenses (2.8 aperture or the reach)

eos650 wrote in post #13253011
As u mentioned about filters, the 17-50 sigma is a 77mm lens so i am covered filter wise, but is 200 more than the 17-70. It also comes w a lens hood, another plus.

I plan on trying both out at the store. Ultimately, it comes down to IQ as u mentioned and the characteristics I am looking for btwn the 2 lenses (2.8 aperture or the reach)

IQ should be slightly better on the 17-50, its just normal, since its a higher end lens in the lineup. Whether the difference is worth the price and 20mm on the long end is your choice, and trying them out at the store is a great plan. Also, all sigma lenses come with hoods, that includes the 17-70, not just the 17-50.