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Canon EOS Crop Sensor for HD
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Old August 9th, 2011, 03:38 PM   #1
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Request for help in choosing a better lens

Hi there ...

I've been using the new Rebel 3ti with the stock 17-55mm and the 55-250mm and I'm far from impressed with the resolution, but what can one expect from what are, essentially, cheap lenses? I'm shooting movies and not stills at all.

I've been told by a kind person who responded to a previous post who recommended the Canon EF-S 15-85 IS lens.

Does anyone else out there own the Canon EF-S 15-85 IS lens? Will it make a substantial difference to my results? It retails for about $750 which is about 3 x the cost of each of my other lenses but I realize that the sky is the limit when it comes to lens prices.

But I really must get hold of something better than what I currently own.

I'm not impressed with the IS on my current lenses and I doubt if the IS is much better on the 15-85mm, so, if there is a better chunk of glass around that $750 price without IS, I would consider that too. I'm not familiar with all the adapters and so on, so any advice from you people who are far more knowledgeable than me would be welcome.

It has to be a zoom.

Thank you,

Harry.
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Old August 10th, 2011, 10:04 AM   #2
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Re: Request for help in choosing a better lens

IS lenses like the canon 70-200m 24-105, 24-70 are very costly because of the demand and build quality.

IS will be paying a lot.

A good zoom i have is 17-50 2.8 non VC. THE VC i find makes the image soft. Critical aperture is important with these lenses. If you use cinema PL glass like CP.2 shooting wide open at T2.1 its sharp. However with some lenses that are cheaper can get distortion so best stopping down to like f4 to make image sharper.

However Sigma do some great third party zooms like 17-70, 18-50, 70-200mm.

I would recommend a wide to normal perspective so 17-50 Tamron or 18-50 Sigma F2.8. Fast lens too. The 24-70 canon is very nice and the 17-40 f4 is very nice but quite pricey. 17-40 not as bad price wise, because its f4 same with 70-200 mark 2 f4 lenses cheaper of course than f2,8

What do you need that is the question?

what zoom range canon 18-55 and 18-200 are shocking and very soft. Tokina 11-16mm is great for ultra wide shots which is about 600 dollars. I am from UK (But its 400 GBP here roughly)

Also ask yourself. Do you want fast lenses? to give you that option of shallow dof? or do you want a wide range of focal lengths. Remember zooms are not there to be used as a zoom there to get optional focal length if that makes sense?

Any more questions please ask. But look at sigma 17-70 or Tamron 17-50 2.8 lenses first quite cheap too and very good quality.

Thanks

Ollie
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Old August 10th, 2011, 06:48 PM   #3
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Re: Request for help in choosing a better lens

Thank you very much for your detailed reply which is greatly appreciated.

I'm relieved that you agree with me about the dreadfulness of the Canon 18-55mm and 18-200mm. At first I thought it was some mistake I had made in the camera settings or that my eyes had taken a turn for the worse, but ultimately came to the conclusion that they belong on a Pixelvision.

So, if you'd be so kind as to put up with another question from me:

If you had the choice, based purely on optical quality, would you buy the Sigma 17-70mm that you mention or the Canon 15-85mm IS?

I don't need a fast lens, but the nature of my work is unsuited to primes.

Thanks for the advice,

Best

Harry.
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Old August 11th, 2011, 06:49 AM   #4
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Re: Request for help in choosing a better lens

I'd wouldn't be too quick to blame any softness on your lenses - the 18-55 kit lens, though cheaply built, actually has decent sharpness - certainly much more than the t3i is capable of resolving in video mode.

The DSLR's are quite soft in video mode, and also present a number of focus challenges, so it's quite possible that these factors are contributing to your soft video.

Having said that, better lenses are never a bad idea. The Tamron 17-50 f/2.8 is a great lens and excellent value. There is also a VC (Tamron's name for IS) version which is a little less sharp than the older non-VC model.
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Old August 11th, 2011, 09:25 AM   #5
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Re: Request for help in choosing a better lens

I have the Tamron non vc and agree its sharper.

the 18-55 is soft you have to really stop down again this is due to the price.

Using cp.2 wide open they are very sharp would it expect that for a pl mount lens.

You get what you pay for, but some great starter len 17-50 is get to start or 17-70.

then push to telephoto using 70-200 sigma 2.8
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Old August 11th, 2011, 10:43 AM   #6
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Re: Request for help in choosing a better lens

John, why do you say that DSLRs are quite soft in video mode? I'm shooting at 1/50th - it's the same sensor and the same optics. Why would a shot done in still mode be any sharper?

Harry.
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Old August 11th, 2011, 10:32 PM   #7
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Re: Request for help in choosing a better lens

Harry, I say it because it's true. And a still photo would be sharper because it is 18mp as opposed to the ~2mp image of HD video. But I suspect I took your questions a little too literally!

I think what you might be trying to ask me is "why do the DSLR's produce a video image that is softer than other HD video." The answer to that question lies in the way the video is sampled from the sensor. The Canon DSLR sensor's have a native Resolution of 18-21mp. To get the 1920x1080 image, they use only some of the pixels and throw away the leftover data - this is the quickest and simplest way to get a HD image from an 18mp sensor 30 times every second with minimal processing power.

But, unless the sensor's horizontal and vertical dimensions are exact multiples or 1920 and 1080 respectively, it is not mathematically possible to pull an exact 1920x1080 pixels by using a consistant line-skipping method (eg every 3rd or 4th line). What their chosen method results in instead is a lower resolution image which then needs to be scaled up to fit the 1920x1080 file.

This is an oversimplified explanation and there are far more things going on than I can understand, but essentially it comes down to the sacrifices that have to be made in order to pull a 1920x1080 image from an 18mp CMOS chip.
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Old August 11th, 2011, 11:01 PM   #8
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Re: Request for help in choosing a better lens

Wow! That's awful - so there is this massive technical compromise going on. I had no idea. I am an idiot. But I have no shame, so I ask questions. And, fortunately, people like you are generous enough to provide answers which I can then repeat to my co-workers and sound like a big shot.

Well, tomorrow my "on approval" Canon 15-85mm IS lens arrives. And all I can say is that it had better be better looking than the dreadful kit lens (18-55mm IS). I tried an 15-85mm in a retail shop here in LA and, like a slut, ordered from B&H in NY over the internet. I have learned to hate that kit lens. I may burn it.

I need not only a little more resolution, but more levels of contrast and subtlety of color.

Thanks so much for the advice to one and all.

I will report back in case anyone is interested.

Best

Harry.
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Old August 12th, 2011, 04:47 PM   #9
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Re: Request for help in choosing a better lens

The Canon 15-85mm IS arrived. I can detect no difference in resolution between it and the kit 18-55. So - John - you are absolutely correct on that score. But there is an enormous difference in build quality and the wide angle is excellent - no distortion at the edges of frame that I can see.

I'll be using this on a job next Wednesday where I have previously done a whole lot of video on the kit lens, so I am hoping that the color and overall "look" will be better. It had better be.

Harry.
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Old August 13th, 2011, 08:54 AM   #10
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Re: Request for help in choosing a better lens

Don't despair; as you said, there's a lot more to a lens than just sharpness. The 15-85 is quite a popular lens and, even if you didn't get the expected sharpness increase, it's sure to have a lot of benefits over the kit lens. Color, contrast and build quality, as you say, are all equally important factors with lenses and you'll likely enjoy some increases in quality in these departments, as well as the larger range of the 15-85.

While the Canon's are quite soft in video mode, the good news is that (as with lenses) sharpness is not the be all and end all of video quality. The colour reproduction, DOF capabilities, dynamic range and low light capabilities mean that you can still capture amazing looking HD footage, even if it is barely sharper that 720p.
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Old August 13th, 2011, 10:28 AM   #11
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Re: Request for help in choosing a better lens

One of my favorite lenses for the 7D is the Tokina 11-16 f2.8. If you're looking for a nice wide angle lens, that one seems to be a favorite.
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Old August 17th, 2011, 09:08 PM   #12
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Re: Request for help in choosing a better lens

Hey - John and others who replied to my cry for help.,

I just did a day using the Rebel 3Ti and my newly acquired 15-85mm IS and, after giving me all that welcome advice, you'll be pleased to hear that the results exceeded my expectations. Color rendition is far better than with the kit lenses and with that comes a perceived sharper image.

In addition, the 15mm end makes hand-held a far better ride - but I guess that's obvious.

Money well spent.

Thanks to one and all for the advice.

Best

Harry.
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