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Old May 26, 2006, 12:50 AM   #1
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Okay,

Just got the rebel and decided to tape newspapper to the wall and photograph it to test the lens sharpness. To do this I set the rebel on a 3001 bogen tripod and used the timer and miror lockup. ISO was 100 for all these shots. The below shot is at 50mm. According too: http://www.photozone.de/8Reviews/len...0_28/index.htm the center crops from this lens and camera should be almost equally sharp in all appertures and zoom ranges. However what i am finding is this:

2.8 is very noticible soft compared to f8. I have tried to allow AF and MF to see if I can get a difference and I have been unable to get anything in f 2.8 to rival f8. Below is an example. First one is f8 50mm. XT parameter 1 was used. No PP work other than cropping. These are 100% views.





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Old May 26, 2006, 12:50 AM   #2
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And f2.8 50mm


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Old May 26, 2006, 12:57 AM   #3
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Now please understand that this is the dead center of the image.

MTF should be around 1900 for f2.8 and 2000 for f8 (@ 50mm according to photozone). the 100 or so MTF difference between f2.8 and f8 is pretty much thruought the zoom range. Corners and extreme corners aren't being considered right now.

Am I doing something wrong? That is possible as I just got the XT and am just using it in Av mode. Again, I tried manual focus, Auto focus, tried different metering and even selecting the center AF point.

I am really beginning to be bummed out and thinking that the lens is a bad copy. Can anyone with experience with this type of thing let me know what they think?

As a side not the XT in these images seem to has quite a bit of noise (i know their exposure isn't the best, but still I wasn't expecting this):


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Old May 26, 2006, 2:43 AM   #4
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I have no experience with this specific lens, but I bought a year ago Tamron 28-75 xd F 2.8, based on exellent reviews and... was dissapointed by the softness of this lens @ 2.8-4.0. @4.5 it becomes sharp. Very similar to your lens it's in the dead center !!!!

First I blamed myself, but then I even sent this lens to calibration , and they assured me , that it's normal lens. It's just that.. I dhad a misfortune to ged a bad copy ... too late to change, but if you can - do yourself a favor and try to gat another copy of it...

As to me... Tamron is over for me... next one will be L lens , no matter what.
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Old May 26, 2006, 5:30 AM   #5
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nelmr wrote:
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Am I doing something wrong? That is possible as I just got the XT and am just using it in Av mode. Again, I tried manual focus, Auto focus, tried different metering and even selecting the center AF point.
It's your test setup...

-> the problem is in your lighting! In a controlled test at least with the MTF the 1st plot is for contrast and isn't the contrast depends on brightness??? :-)
Turn on the flash to see a big improvement :idea:
(or repeat the test using an outside wall with daylight sun..)
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Old May 26, 2006, 6:25 AM   #6
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I was shinning 400 watts of daylight bulbs at it (4 100 watt bulbs in the clamp work lamp things from home depo). Although I wasn't doing this directly, more so diffusing it off the ceiling. I was using the multi-metter mode. Perhaps I'll try changing my mettering.

Regarding MTF, I wasnt' refering the the plot charts but rather the charts on the photozone site. Perhaps you could look at them and then look at the test shots and let me know (link is in first post). What puzzles me, is that at the f2.8 crop and f8 crop were both manual focus using the same exact focus setting. In otherwords I didn't focus twice in the 2 example s above but rather once and just changed aperture and then camera compensated the shutter. As such if the lens was suppose to be almost as sharp at f2.8 then why the drastic difference? I can't image this is due to under exposure/ not enough light.

I took about 30 photos with various apertures and various whys of focusing (metering was the same though). And in every shot the f2.8 were much softer than f8, even f4 was much sharper too. Out of these 30 shots or so about 6-7 of them were f2.8 and all were soft.

If this is an OOF problem then what is causing it? It doesn't make sense that the autofocus or my manual focus wasn't correct if the f8 expsure was fine every time. If it was an OOF problem wouldn't both exposures have problesm?

I understand contrast and sharpness correlate to each other. However, this isn't an MTF/Imatest test, it's simply an visual observation and it is much more drastic of a difference than it appears to be on the photozone site.

I plan on taking some outdoor nature like shoots today and them comparing them as well.

Regarding the noise that is visible at ISO 100, am I correct in thinking that this is due to under exposure? I'll try reshooting the indoor shots as well, with and without flash.

I have 10 days to return the lens to ritzcamera. 7 day to return the camera to B&H if something is wrong. Both of these came in yesterday so the clock is ticking. Camera appears to function okay to me. I'm a bit concerned about the noise (the wall has some texture but even the outlet has noise on it). But most likely that is due to my fault for underexposing.
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Old May 26, 2006, 7:50 AM   #7
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Try in brighter light - you'll still see some differences, but IMO you'll see a big improvement @ wide open when the contrast is increased...

As to buying an L, this has been discussed many times, you'll get a higher quality build may be, but sharpness (especially in term of MTF) is not part of it - again just check the photozone charts against a 'digital' lens (i.e. previous link):
http://www.photozone.de/8Reviews/len...5_28/index.htm
http://www.photozone.de/8Reviews/len...5_28/index.htm
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Old May 26, 2006, 7:55 AM   #8
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NHL,

I will try with better lighting/metering. I hope the sharpness improves.

Just as an example, these are from another person's test online (he was comparing the 17-50 to the kit lens). Which of the too images below is f2.8? or f8? you may be able to tell but they are close. These apparently were center crops at 18mm.



I was expecting results similar to this but rather all I have seen so far suggests my copy of the lens is much softer at f2.8. Why can't anything be easy!!!

I'm not ruling out it is anything wrong that I could be doing. I'll find out this evening on my second attempt at the tests.

Note (left image is f2.8, right is f8 in case you were wondering)
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Old May 26, 2006, 8:08 AM   #9
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The above two images are properly exposed with the correct lighting (with flash at least judging from the shadow)
-> contrary to your pictures :idea:
i.e. the test conditions are different (... and why so much variability between test results)


Thrust me on this I shoot with the 100-400L IS in low light (i.e. poor contrast) all the time, but the pictures always come out sharper with the flash on, than with IS and no flash (better saturation too!!!) :-)
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Old May 26, 2006, 8:23 AM   #10
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NHL,

Thanks for responding to most of my posts lately (I hope I haven't been annoying). I deffinetly will try what you suggest. I hope that things improve, and if I can get f2.8 to look close to f8 I'd be estatic and jumping for joy

Since this is obviously my first DSLR, is it normal to get noise levels like I got when shoots are poor contrast/under exposed at ISO 100 (note, my HP laptop LCD display seems to amplify noise as I can't see as much here at work on my dual monitors, one is a Dell LCD and the other a Dell CRT)?

Nevertheless, i will work on exposure as the histogram shows I did a horriable job exposing this shot (since it is on a tripod I can do much better even without flahs, though i will try that too):


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