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Old Apr 25, 2010, 5:29 AM   #41
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... but Mr. P want's photos of the lighting. Once he's got the stage in focus, he can (and should) turn off the AF (along with the AE, so the areas that are properly illuminated won't be overexposed against the black background.) So that's not a factor, and, optically, the 35/2.0 is better.

The store was quite kind in letting him swap the Canon for the Pentax and back again. Perhaps they'll also let him try different lenses.
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Old Apr 25, 2010, 10:06 AM   #42
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According to SLRGear.com, the Canon EF 35mm f/2, wide open, has less vignetting and is sharper than the Sigma 30mm f/1.4 EX DC HSM at f/2.0, and it's sharper and has less chromatic aberration than the Canon EF 28mm f/1.8 USM at f/2.0.
My two cents worth...

When I look at the blur charts for the Sigma 30mm f/1.4 when set to f/2, compared to the Canon 35mm f/2 at f/2, I'm seeing less than one blur unit difference on average in the corners, with very similar looking charts.

But, unless you are photographing a brick wall or something similar, you probably don't care about the extreme corners anyway, as those areas are typically going to be out of focus (or unimportant) compared to the primary subjects you're interested in for many types of shooting, especially since you may want to leave a bit of room for cropping anyway when framing.

Also, shooting a test chart from 5 feet or 6 feet away is not the same thing as shooting a stage from 30 or 40 feet away.

Optical characteristics of lenses tend to change some with focus distance (especially with internal focus lens designs), and things like curvature of the focus plane at closer focus distances come into the picture (with wider lenses tending to have more issues in that regard).

I've seen more than one reviewer photographing real subjects (versus test charts at close range) that think the Sigma 30mm f/1.4 is a better lens optically at f/2, compared to the Canon 35mm f/2 at f/2 (and f/2 is where the OP is likely to be using a lens in a low light theater environment).

For example, note the comments about the center crops in this photo:

http://www.pbase.com/lightrules/image/45926000/original

Or, note the comments in this one showing left edge crops, at a more realistic focus distance of a real subjects, versus a test chart from 5 or 6 feet away. ;-)

http://www.pbase.com/lightrules/image/45926001/original

Or, note the comments from a different reviewer comparing these two lenses:

http://www.whichlens.com/index.php?b...&c=1&tb=1&pb=1

The Sigma would also give you a wider angle of view (meaning that you could fit more of the stage into the frame without backing up quite as far). For uses other than shooting theater (for example, taking photos at parties and family gatherings indoors where you may not have a lot of room to back up), I'd personally prefer a wider angle of view (as sometimes it can be tough to fit everyone into the frame).

The Sigma is also twice as bright (meaning that the AF sensors see a brighter subject when attempting to lock focus). That can help with focus accuracy in low light (especially since it appears to be relatively sharp in the center of the lens, even wide open at f/1.4).

In other low light conditions, the extra stop of brightness could come in handy, allowing you to shoot at apertures like f/1.4, f/1.6, or f/1.8 (whereas the Canon starts off at f/2), so you'd get faster shutter speeds when needed in conditions where DOF or corner sharpness isn't a big issue.
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Old Apr 25, 2010, 10:37 AM   #43
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If the lighting get a bit low, and he want to take a photo in the dimer lighting, it will be a bit of a problem with that lens. It may be slightly optically better then the sigma or the canon ef 28 f1.8. But the AF OOF will cause more of an issue. You may loose a little bit optically with the sigma and the ef 28, but you should gain with the numbers of keepers with less OOF shots. The canon ef 35 f2.0 is not a great perform when not in well lit environments. That was what I found out when I had it. I agree it is a very sharp lens in the day light.
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Old Apr 25, 2010, 12:30 PM   #44
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If the lighting get a bit low, and he want to take a photo in the dimer lighting, it will be a bit of a problem with that lens. It may be slightly optically better then the sigma or the canon ef 28 f1.8. But the AF OOF will cause more of an issue. You may loose a little bit optically with the sigma and the ef 28, but you should gain with the numbers of keepers with less OOF shots. The canon ef 35 f2.0 is not a great perform when not in well lit environments. That was what I found out when I had it. I agree it is a very sharp lens in the day light.
You've missed the point for the theater shots, Mr P is working on a tripod, fixing the focus and leaving that well alone, the focus can be done very accurately in live view with MF. This negates the whole focus issue allowing this great lens to be used.

If however the desire for AF is brought back to the table then I would go back to my original suggestion of the Sigma 30mm f1.4.
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Old Apr 25, 2010, 12:53 PM   #45
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I just see it a bit differently. As sometimes you want to swing the tripod to a different point. And that will throw the focus slightly off, then you will have to refocus.
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Old Apr 25, 2010, 1:01 PM   #46
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What I know is that SLRGear.com uses consistant methodology when testing lenses.

What I don't know is how LightRules tests lenses. At the very least, I'm troubled by how the 30mm lens and the 35mm lens seem to have exactly the same angle of view. The edge crops have identical views, even though the 30/1.4 should have a left edge that was 7% further to the left. Was the original image from the 30/1.4 cropped so the view would match that obtained from the 35/2.0? If so, then what we're using to compare wouldn't actually be the "left edge", would it? Possibly the 30/1.4 was moved closer to get the same basic image as the one obtained with the 35/2, but then the difference in the subject distance would come into play, wouldn't it? Or perhaps some form of digital magic was performed to make the angles of view appear equivalent. Whatever happened, it causes me to have enough doubt about LightRules' conclusions that I would not base a purchasing decision on them, especially in the face of the contradictory evidence presented by SLRGear.com.

I'm not saying that LightRules isn't correct. I'm saying that this constitutes a "peer review" process, and I have some doubts.

And, of course, Mr. P has had the option, in the past, to try and return different gear, and perhaps his local vendor won't mind allowing him to do it again in order for him to be assured that he got the best tool for what he wants to do.

And sharpness asside, I'd still be troubled by the vignetting of the Sigma 30/1.4 and the CA of the Canon 28/1.8, especially in the extreme lighting Mr. P will be using.
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Old Apr 25, 2010, 1:05 PM   #47
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Quote:
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During the dress rehearsals of the show I will have a camera sitting near me on a tripod, focussed to cover the full width of the stage. ...
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I just see it a bit differently. As sometimes you want to swing the tripod to a different point. And that will throw the focus slightly off, then you will have to refocus.
But that's not how Mr. P sees it.
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Old Apr 25, 2010, 1:08 PM   #48
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The best answer for those issues is either the 24 1.4L or the 35 1.4L they are the best for this type of lighting. But the vast majority of us need to live with compromises.
the 35 f2 you give up on AF, the 28 1.8 or the sigma 30 you take a bit more distortion. It the distortion that much great, I did not think so between the 35 and the 28 looking at some photos I took with both lenses on my eos 1.
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Old Apr 25, 2010, 1:10 PM   #49
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All 3 lenses will work. But it comes down to Mr.P preference on which one's compromise will be most acceptable. Each has it's short falls.
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Old Apr 25, 2010, 3:47 PM   #50
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What I don't know is how LightRules tests lenses. At the very least, I'm troubled by how the 30mm lens and the 35mm lens seem to have exactly the same angle of view.

[snip]

Possibly the 30/1.4 was moved closer to get the same basic image as the one obtained with the 35/2, but then the difference in the subject distance would come into play, wouldn't it?
That's the way you should test lenses if you want to compare subject detail from an image. The same thing would apply to testing lenses with any kind of MTF test chart. If the subject is not occupying the same percentage of the frame, then you'll have more pixels representing your subject in one image versus another and you can't compare things like lp/mm from a chart. So, you move the camera closer or further away to the same subject or chart if testing different focal length lenses so that your subject (or chart) occupies the same percentage of the frame.

I see he mentioned that in this test (using different focus distances):

http://www.pbase.com/lightrules/image/62468514/original

But, I don't see any mention of how he got the crops to look the same from the other test and it mentioned 100 feet away.

http://www.pbase.com/lightrules/image/45926000/original

I'll send him an e-mail with a link to this thread and see if he responds. If so, then perhaps we'll have a better idea of how he performed the testing with that first set of crops. fstopjojo (the owner of that lightrules album we're discussing) is a member here, although he hasn't posted in quite a while.

If memory serves, he had a lot more photos online at one point. So, he may have removed some of them to save album space. He also had more than one copy of the Sigma 30mm. The first copy had some front focus issues if memory serves (which was a common problem with the first production run of it), but the second copy was fine.

But, he's not the only one to see the same type of thing with that lens (Sigma 30mm f/1.4 sharper than the Canon 35mm f/2 when both lenses are at f/2).

See the comments in another review for another example of that, where the reviewer said this:

"The Canon is soft at f/2.0 and f/2.8 but shows similar performance at f/4.0 to the Sigma at f/2.8"

http://www.whichlens.com/index.php?b...anon_ef_35mm_f

Unfortunately, that reviewer's albums are not online with the sample photos he used to evaluate them. But, if you look at the car crops from fstopjojo, that looks to be about right (at least at the focus distances he used):

http://www.pbase.com/lightrules/image/62468514/original

So, I've got a feeling based on the types of comments and test results I'm seeing from more than one reviewer comparing these two lenses (as compared to slrgear.com's results with them), that the Sigma is sharper at f/2 as focus distances get further away, since the other two reviewers were shooting outdoor subjects versus test charts.

But, the tests at slrgear.com look pretty close at f/2 anyway from looking at their blur chart with both lenses at f/2, where the OP is more likely going to be using a lens like that. There is very little difference between them at f/2 with whatever focus distance they used to get their test charts in the frame (my guess is that they were probably around 6 feet away with lenses that wide). But, given that optical characteristics can change with focus distance with some lenses, I wouldn't put my faith in just one test using charts and software to compute lens performance.
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