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PostPosted: Sun Oct 07, 2007 7:14 am 
DavidL wrote:
Hi Ant1
Not every day you planned to get ONE camera and end up
getting TWO
from amongst the BEST of Both P&S and DSLR World !
Congrats..
Now go out and enjoy shooting ! :)


You're not wrong! How do these things creep out on you?... I just wanted initially to get a camera that was giving me more control, that's all. And now, my wallet has taken a severe beating! :shock:

On another subject: Wanting to protect my investment in the lens, I fitted the UV filter that came with the lens - a gift, so to speak, from the retailer. However, having read about the quality of various brands of filters, and not wanting to compromise the quality of the lens, I took some test shots of the same subject, using a tripod and live view in order to get the best possible comparison. Well, what a difference! The lens came with a Hoya HMC UV filter, and I could not believe how degraded the image quality became with it. When I transferred the test pictures onto my computer, I could really analyse them in detail.
There were two differences between with and without the Hoya HMC UV filter. The first difference was in exposure. With the filter on, the image was around one stop more exposed than without. The shot without the filter was more dramatic, more vivid, less washed-out. Second - and that's the killer - I zoomed in on the top-right edges of the picture that contained foliage. The picture without the Hoya HMC UV filer was much, much more crisp and detailed. I'm talking about a huge difference here, not just details. So back to shopping I go (will this ever end?...). I heard that B&W UV filters are the go. Any recommendations as to which UV filter - and brand in general -will give me the best picture quality, that is, a picture that is at least not worse that without the filter? I understand that adding glass to the light path will compromise to a certain extent the picture, but which is the one that I should get? Your recommendations are appreciated.

Ant1


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 Post subject:
PostPosted: Sun Oct 07, 2007 7:16 am 
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Hi Ant, some filters can certainly degrade your image, but that's a bit disappointing coming from a Hoya as they're normally quite good. Any chance of you posting shrunken versions of your photos with and without the filter to illustrate it?


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 Post subject:
PostPosted: Sun Oct 07, 2007 8:40 am 
Gordon Laing wrote:
Hi Ant, some filters can certainly degrade your image, but that's a bit disappointing coming from a Hoya as they're normally quite good. Any chance of you posting shrunken versions of your photos with and without the filter to illustrate it?


Sure. The first link is of a crop of the image I took. It's the top-right corner of the picture, with the Hoya HMC UV filter on:
http://farm3.static.flickr.com/2010/150 ... ef50_o.jpg

The second picture is of the same crop taken from a different image taken a few seconds later, but this time without the filter on:
http://farm3.static.flickr.com/2272/150 ... ff74_o.jpg

I don't think that Hoya necessarily makes "bad" filters. From what I read,though, they make different grades of filters, eg consumer grade, a "Pro" grade, and so on. The "HMC" UV filter I have is the consumer grade, from what I gathered - the bottom of the range. Maybe one of their higher-end filers would possibly be better. However, I only read good reviews about B&W and Heliopan, so I think this is the way I will be going. After all, why have a top-grade lens, only it to be compromised by a lesser optical component in the chain?


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 Post subject:
PostPosted: Sun Oct 07, 2007 10:45 am 
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Oh boy that looks dramatic! :shock:
I use Hoya "HMC" and "superHMCpro" filters and never ever encounter something like this. You've certainly had a look at the filter, that there is no smear? You should see this difference when looking with the naked I through it...

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 Post subject: Filters
PostPosted: Sun Oct 07, 2007 11:08 am 
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Hi Ant,

If it wasn't for the fact that you are happy with the image quality at the centre of the "with filter" picture I would have guessed there is a focussing error with that picture.

Until very recently I used a B+W UV filter on my EF 24-105 lens but have now decided to leave it off. My admittedly very non-scientific impression is that the filter causes a loss of sharpness in the corners when the lens is at the wider focal lengths. That extra couple of flat surfaces in front of the lens can also reflect light back to the digital sensor which is itself more reflective than film.

I will keep the filter but from now on it only gets fitted in those rare situations where I know the lens might be at hazard from dust, moisture or marks (pets and children).

Bob.

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 Post subject:
PostPosted: Sun Oct 07, 2007 11:25 am 
Bob
Are you saying you encountered such err... 'effects' before ?
Is it specific to the Lens or Camera body ?
Seeing that both are same body and lens.

I would assume Gordon's reviews did not include any filters so as to maximise the sharpness, and every detail can be scru·ti·nize


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 Post subject:
PostPosted: Sun Oct 07, 2007 11:57 am 
There is always the possibility that I did something wrong when taking the picture, which would account for the differences in the crops. If that's the case, I would appreciate your feedback. I have to admit that, looking at the cropped pictures, it might look like the one with the filter on would have been totally out of focus, and not just the cropped part.

In this context, I downloaded in the links below the full images from where the crops were taken. You can judge for yourselves and, once again, do not hesitate to comment so as to improve my abilities, if that's what it turns out to be.

This first picture is the full image. Lens WITHOUT filter (the crop was taken from the top-right corner of the picture):
http://farm3.static.flickr.com/2336/150 ... abe5_o.jpg

This picture is the same, but this time with the UV filter ON (crop was taken from same area as pic above):
http://farm3.static.flickr.com/2023/150 ... 6468_o.jpg

Note that I did not change a thing between the two shots, except for taking the UV filter off very carefully so as not to move the camera from the tripod. But even if that would have been the case - that I would have moved the camera - then the picture without the filter should have been the one out of focus, because I took first a picture with the filter ON (in focus), then with the filter OFF (which thus should have been out of focus because of movement). I thought it might have been the wind that caused the blurriness, but then look at the railings next to the foliage...Just as blurred.
Also, note(a) the difference in sharpness of the bricks in the centre of the pictures and (b) the difference in exposure between the pics with the filter on (more washed out in my opinion) and without (more saturated).

Oh dear...my first day on this forum, and I feel like I opened a can of worms already. Gordon, is this out-of-topic?


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 Post subject:
PostPosted: Sun Oct 07, 2007 12:34 pm 
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To my eye it seems that the lower left corner is comparable but the upper right is the corner to watch. This is incredible if the filter does not show clear signs of smear in on corner. Just like a decentering defect of the lens.
At least it confirms that it was not shake (would have influenced the whole pic) and most probably not defocus (should also have a similar effect in all corners, although the picture-plane is slightly tilted: left=closer/right=further).

I think you simply have to repeat testing.

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 Post subject:
PostPosted: Sun Oct 07, 2007 8:01 pm 
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Hi everyone - in resposes to David's question, we never use filters when testing lenses.

Personally speaking, I'm like Bob - I avoid filters these days unless it's a polariser or I know the lens wil be at risk, such as from poor weather, or splashback from any nearby action... I would recommend fitting a lens hood though as these can protect your front element (a litte) from sideways prods and knocks!


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 Post subject:
PostPosted: Sun Oct 07, 2007 8:12 pm 
Gordon Laing wrote:
Hi everyone - in resposes to David's question, we never use filters when testing lenses.

Personally speaking, I'm like Bob - I avoid filters these days unless it's a polariser or I know the lens wil be at risk, such as from poor weather, or splashback from any nearby action... I would recommend fitting a lens hood though as these can protect your front element (a litte) from sideways prods and knocks!


Gordon what do you mean with 'these days' ? That you used to use filters but not anymore now ?


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 Post subject:
PostPosted: Sun Oct 07, 2007 8:27 pm 
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When I first started with an SLR in my teens I wouldn't dream of going out without a filter - I think most people used them back then. But about 15 years ago I stopped, partly out of paranoia about IQ and partly after seeing most pros using their lenses in a care-and-filter-free attitude!

So today I'm a filter-free fellow, again unless it's raining, I'm in a risky situation or I'm using a polariser...


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 Post subject:
PostPosted: Mon Oct 08, 2007 3:48 am 
tombomba2 wrote:
To my eye it seems that the lower left corner is comparable but the upper right is the corner to watch. This is incredible if the filter does not show clear signs of smear in on corner. Just like a decentering defect of the lens.
At least it confirms that it was not shake (would have influenced the whole pic) and most probably not defocus (should also have a similar effect in all corners, although the picture-plane is slightly tilted: left=closer/right=further).

I think you simply have to repeat testing.


So I did...I took some new shots of the same vista for consistency. This time I set the timer for 2 seconds to avoid camera shake when pressing the shutter, as I noticed in live view how sensitive it is to the slightest shake, yes, even that of shutter release (an endorsement for live view, I suppose...). Although not as dramatic as the first test, there is nonetheless a difference in sharpness between this particular UV filter ON and OFF the lens.

This first shot is the top-right crop, taken without UV filter:
Image

This second shot is with the Hoya UV filter ON the lens:
Image

Link to the full picture, UV filter OFF:
http://farm3.static.flickr.com/2090/151 ... e570_o.jpg

Link to the full picture, UV filter ON:
http://farm3.static.flickr.com/2346/151 ... bbeb_o.jpg

Although ok in the middle on the image, the sharpness deteriorates towards the edges, albeit not as dramatically as the first batch I took earlier. This, as I mentioned, might have been due to camera shake - even on a tripod - as the shutter was released, whereas this new lot was taken with a 2 sec timer.


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 Post subject:
PostPosted: Mon Oct 08, 2007 5:01 am 
Hmm
It does looks like sharpness towards the edges is taking a beating WITH the UV. I'm surprised !
Have you any other lens to test further ? Besides the 24-105.


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 Post subject:
PostPosted: Mon Oct 08, 2007 7:45 am 
No, the 24-105 is my only lens. As I mentioned in another post, I had a point and shoot and just wanted to upgrade to "something else" that was giving me a bit more control than what a p$s does...and I ended up with the EOS 40D AND a p&s with control (Canon G9). So, finance-wise, this is it for the moment. No more lenses for a while.

Plus, I really like the 24-105. Granted, the f/4 does annoy me sometimes as I wish I had more light coming into the lens. An f/2.8 - such as the 24-70mm "L" lens would be good. But, from what I read, the 24-70 is way heavier, more expensive and does not have image stabilisation. And, besides, the noise on the EOS40D is really well controlled, such as in situations where a higher ISO might be needed to compensate for the slower lens. It's always a compromise in the end, isn't it?

But are you suggesting that another lens might have produced a different result with the UV filter I used? I do not see why that would be the case, though. Let's say I had a 24-70mm L lens. Why would the UV filter not degrade the sharpness at the edges by the same amount as it does on the 24-105? Of course, I'm not pretending to be an expert here, so I only go by logic. Maybe there is another explanation?


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 Post subject:
PostPosted: Mon Oct 08, 2007 8:25 am 
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Hi ant, out of curiosity, could you try repeating the test with the lens at 24 and at 105mm?


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