Focusing/noise

[kathywilson]

I recently bought a 20D with the kit lens, and a telephoto - the 28-

135mm/3.5-5.6 IS USM lens. I can't seem to get decent focus (using

auto-focus) from either of them. All of the images - at any setting -

need more sharpening than I thought they would - moreso even than

the 5mp A95 I replaced. I do landscapes - nothing moving.

 

 

In addition - there is a significant amount of noise at ISO 400, and

even noise at ISO 100, which according to the tests would seem to be

unlikely.

 

 

Throw in the fact that right from the factory the sensor has more

dust and crud on it than the lint filter in my dryer, and two dead

pixels as well.... well, to say I'm worried about the purchase I've

jut made would be putting it mildly. Can anyone give me any

tips/advice/a sedative and assurances all will be well...?

 

thanks,Kathy

[jnicholson]

Hi Kathy, first off are you shooting in RAW? If so, the camera hasn't done any sharpening on the RAW image.

 

I had a similar sense as you describe when I switched from the G3 to the 300D. I think there are two issues at play here. First, with the A95 you really weren't having to deal with DOF at all, whereas with you new combination you do. I also suspect, though offer no absolute proof, that the DSLR's do less in-camera sharpening by default than do the P&S's.

 

I have a love-hate relationship with my 28-135. I love it enough to consider taking only it and a 50mm on our European vacation this year, leaving all my L lenses at home. I hate it because more than once I've had a batch of soft results with it. However, I think the soft results are more my doing. I suggest that as you begin using this lens you act very deliberately at first. Give the lens time to do its thing before you press the shutter button all the way.

 

Regarding the noise with the 20D. Everyone says it's much better than prior cameras in this range. I've had mixed results. There are some situations where its noise performance is, well...crappy. For the last several months I've been doing everything in RAW and, thinking about it now, I haven't had the same sinking feelings regarding noise in that time.

 

Did you buy the camera new? They definately pick up dust on the sensor although you'll find you can shoot for a long time before it becomes an issue. Just use a Sensor Swab and Eclipse fluid. It's easy to clean. With respect to the dead pixels, I'll bet nearly every camera ships with a dead pixel or two. If it's only single pixels it's not a big issue (my opinion anyway).

 

All that whining said, I really think the 20D is an excellent choice. It's a very nimble performer. I think you'll find you'll get used to it quickly, especially the differences between using a P&S and a DSLR.

 

Good luck and have fun. Look forward to seeing your 20D shots.

[jnicholson]

Hope that didn't sound like I meant you were "whining". I meant my whining.

[kathywilson]

LOL - no, I didn't think you meant I was whining, Jamie. I actually appreciate your response! I think I'm suffering the proverbial "buyer's remorse" somewhat. I haven't had this long, but I love it already - what I first thought would be too heavy, is now perfect. Picked up the A95 and it felt like a kid's toy <g> I'll keep a close eye on the RAW files and see if the noise is less - and you could very well be right with the DOF thing. "Slow down" will be my mantra :) Thank you for the reassuring words!

[andre_mcnichols]

You've got to be very careful with your focus on a DSLR, the low DOF makes it easy to miss your intended target. I can confirm that it does a lot less sharpening than the A95, which allows you to have more control over image quality when you do your postprocessing. Try shooting raw and then playing with the "sharpness" slider on the raw converter... You should also watch your aperture as some lens tend to be much softer when fully open.

 

I'm surprised that you can see so much noise, you should get less noise at iso 800 with your 20D than at iso 200 with the A95. Keep shooting and get used to your equipment, you picked a fine tool but it takes time getting used to it. Have fun!

 

Andre

[andrew robertson]

Also, you need to make sure that the camera isn't in 'all points' auto selection AF mode.

Who knows what it focuses on then?

 

Get a blower bulb, some Eclipse, and some PecPads to clean your sensor. The dead pixels

are to be expected and won't be seen in prints, especially if you shoot RAW (which you really

should).

[bennyboy]

Hi Kathy, I can't wait to see what you can come up with now you've got a DSLR! I wonder if you might let us know what settings you are typically using for your landscape photos, eg F stop of around f/8 to f/11, MLU enabled to counteract mirror slap, tripod mounting etc. (I assume you're using a small aperture since you've noticed sensor crud) Also what is your workflow in getting the RAW images into photoshop? I've noticed that Adobe Camera Raw has a default sharpening value of 25 - setting it to zero can make a noticeable difference.

[mike_smith2]

Kathy

 

RAW files have no sharpening at all, in addition the image quality is degraded slightly by an anti -alias filter in front of the sensor that reduces moire patterning. Your digicam would have had quite aggressive sharpening as default and no anti alias filter in front of the sensor so straight out of the camera the images will look completely different.

 

If shooting RAW, Canon have a recommended initial/first pass sharpen procedure to overcome the AA filter softening as follows -

 

(i) In you RAW converter software turn off all sharpening when producing the TIFF

 

(ii) in Photoshop do a first pass unsharp filter with settings of 300%, 0.3 radius, 0 threshold

 

Opinions are mixed as to whether you should reduce any noise before or after this sharpen step, either way this default first "pass setting" is a good starting point to refine the image.

 

Mike

[jnicholson]

Mike, that's great info. Thanks for sharing.

 

Ben, I use Adobe Camera Raw. I remember reading somewhere, I think it was the book "Camera Raw", that the sharpening capabilities of Camera Raw were not its strongest feature. The suggestion was to do your sharpening in PS. That seems to marry well with what Mike suggests.

 

Kathy, Pec Pads and Sensor Swabs are made by the same company. For the sensor I'd stick with Sensor Swabs. In both cases you need Eclipse fluid.

[kathywilson]

Wow, thanks everyone! I was shooting jpg images with the problems I mentioned above, and the noise/focus wasn't as sharp as I'd hoped even on f22 - though it was significantly better at iso 100/f22 than iso400/f11. But knowing now that RAW is, well, precisely what it says -raw <G> I'll not worry about applying a lot of sharpening when processing those images. 300% wow! Though, sounds like the A95 did that for me. I've got a rocket blower coming soon, and will search out a source for the Eclipse stuff. Thanks again for the valuable assistance!

[ian riches]

f/22 will never give you an optimally sharp image on a 20D, due to diffraction effects. (See <a href="http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00DhKN&tag=">here</a> is you want to find our more about diffraction.)<p>

For optimum sharpness from your 28-135mm, you'll want it set around f/8-ish. Unless you *really* the depth of field that f/22 gives (and you sometimes might in a landscape or macro shot), or you *really* need the accompanying slow shutter speed for the effect you are looking for, then there's no reason I can think of to shoot at f/22.<p>

 

Photozone tends not to test non-macro lenses such as your 28-135 at such small apertures as f/22, but the physics works just the same for macro lenses. Look at the graphs <a href="http://www.photozone.de/8Reviews/lenses/canon_50_25/index.htm">here</a> to see how sharpness typically first rises as you close down the aperture, and then falls away again as the aperture keeps getting smaller.

[kathywilson]

Ian - wow, I don't believe I understand a word of that. I mainly shoot landscapes. When you want things sharp from front to back - wouldn't you use the "largest" number you can? (which is the *smallest* opening, right?)

 

My camera appears to go to f35 - which are numbers much higher than the f numbers on the lens itself which says 3.5 - 5.6, and then there's mm - which I think is the length of the lens... after that, I'm lost. I don't get why my lens says f3.5 - 5.6, and then on the lcd read out starts talking f5 - f35 (or f29... forgot what the largest number was). Are they different things?

[kathywilson]

wow, I don't believe I understand a word of that. I mainly shoot landscapes. When you want things sharp from front to back - wouldn't you use the "largest" number you can? (which is the *smallest* opening, right?)

 

My camera appears to go to f35 - which are numbers much higher than the f numbers on the lens itself which says 3.5 - 5.6, and then there's mm - which I think is the length of the lens... after that, I'm lost. I don't get why my lens says f3.5 - 5.6, and then on the lcd read out starts talking f5 - f35 (or f29... forgot what the largest number was). Are they different things?

[conraderb]

Kathy - Ian is correct.<BR><BR>

 

conrad puts on white lab coat and begins to lecture to college physics 101 class<BR><BR>

 

There is a phenomenon in physics called diffraction, and can be demonstrated seen when you move (propagate in physics terms) waves (ie. light waves/sound waves) through a medium (ie. water or air) and they pass through a very small opening. the phenomenon that you will see is that once the wave has passed through the opening, it will tend to spread outwards and diminish in intensity.

<BR><BR>

a diagram:

<BR><BR>

these are waves of light

<BR><BR>

||||||||||||||||<BR><BR>

||||||||||||||||

<BR><BR>

this is the barrier w/ a very small opening, which is analogous to a lens at a very high f-stop.

<BR><BR>

_____ _____

 

<BR><BR>

 

this is what happens

<BR><BR>

||||||||||||||||<BR><BR>

||||||||||||||||<BR><BR>

||||||||||||||||<BR><BR>

_____ _____<BR><BR>

| <BR><BR>

/|\<BR><BR>

//|\\<BR><BR>

///|\\\<BR><BR>

<BR><BR>

 

Now, image that this is your sensor:

<BR><BR>

SSSSSSSSSSSSSSSSSSS<BR><BR>

<BR><BR>

put it all together:<BR><BR>

 

||||||||||||||||<BR><BR>

||||||||||||||||<BR><BR>

||||||||||||||||<BR><BR>

_____ _____<BR><BR>

| <BR><BR>

/|\<BR><BR>

//|\\<BR><BR>

///|\\\<BR><BR>

SSSSSSSSSSSSS<BR><BR>

<BR><BR>

the light that is supposed to make a sharp image is overlapped by other lights, and overall sharpness is reduced.

<BR><BR>

there is a formula that determines how much diffraction happens, but for the purposes, let's just say that it does occur at some point, and that f22, while is will give you maximum DOF, will ALSO reduce the overall sharpness. of course, whether or not you can see it when you are pixel peeping is another question.

<BR><BR>

read pages 235-251 for monday.

[conraderb]

Okay - my graphic didn't work. see this graphic:

<BR><BR>

<a href="http://www.gcsescience.com/Diffraction-Water-Waves.gif">here</a> for more info.<BR><BR>

 

Kathy - the 3.5-5.6 or whatever shows the maximum aperture of the lens. anything that says 'mm' after it refers to the focal lenght, which is basically how much of the scene will be seen by the lens. you might want to read some basic photography literature - look for the terms f-stop and aperture (they are the same thing).

<BR><BR>

16mm = wide on the 20D camera. 200mm = telephoto on the 20D camera.

[kathywilson]

Conrad - thanks :) You did clear that up, though I'm afraid the professorial lab coat didn't help with aperture/fstop. While I do get mm - focal length. I do not get why my lens says f3.5 - 5.6, and then proceeds to tell me I took my image at f22. Am I being obtuse? <g> The learning curve on the science of our particular art is rather steep... Though, I did argue for more control, and now that I have it I hardly know what to do with it! :)

[conraderb]

Kathy -

 

Aperture on a lens can be changed, anywhere from 1.4 to f64 or more, depending on the lens.

 

The aperture rating on your lens is just the MAXIMUM aperture. Why not write the entire range? b/c most photographers only care about the maximum aperture - the bigger the aperture (lower number), the more light the lens can bring in, and the better it will perform in low light.

 

If you don't believe me, look in your viewfinder. the number on the immediate LEFT of the -2...-1...0...+1...+2 scale is the f-stop/aperture.

 

if you still don't believe me, put your camera in manual (M) mode, and then find the black button right next to the lens mount. hold the camera lens with your left hand in a way so that your palm is supporting the weight of the lens (ie. the fingers point in a counterclockwise direction), and the button will be near your thumb.

 

once you find the button, hold it in and twirl the big black wheel on the back of the camera as you look in the viewfinder. you will see that is gets darker and lighter. why? you are 'stopping down' the aperture to the point where it is when the camera takes the picture.

 

now, holding that button down, look into your lens (ie. yo uare goinjg to take a picture of your face). you should see the aperture move aroudn as you twirl the wheel.

 

why don't you see the aperture change when you take pictures normally? because the aperture is automatic - it does not change until a moment before you take the picture, so you might not ever realize that it is there.

 

You should do some more reading about aperture and the mechanics of cameras - it would really help you. I highly recommend the national geographic field guide to photography. Buy it! Best $30 you will invest in your photographic education at this point.

[bennyboy]

There are some really good resources in the learn section on this site, it's a very good place to start. Lens, light, exposure should be required reading.<br><br>

 

This book, is probably the most useful book purchase you can make, it's highly recommended by many on this site and led me to purchase it:<br><br>

 

<a href=http://www.amazon.com/gp/product/0131896091/002-5560697-0812052?v=glance&n=283155>Photography (8th Edition) by Barbara London & John Upton</a><br><br>