Blogipity

Here’s a nice comparison of Tamron AF 17-35mm f/2.8-4 Di LD Aspherical and Canon EF 17-40mm f/4L USM. I really enjoy reading these amatuer lens reviews/tests.

PhotoReview has a nice piece titled, 6-megapixel DSLR or 8-megapixel Digicam Which Should You Buy?, that does a good job of countering the megapixel fetishism that many consumers have. Perhaps consumers should start asking about how big cameras’ sensors are?

My night’s surfing of dpreview forums has yielded one more gem. Can anyone guess what this sound is?

To answer the question, this is the sound of a Canon 50mm 1.8 mk II focusing.

Andrew’s Magnificent MTF Comparo-meter provides a Web interface to compare the MTF charts for 2 Canon lenses.

Another great dpreview post: Re: How to read CANON’s MTF chart: Canon SLR Lens Talk Forum: Digital Photography Review

1. On the Canon MTF charts, the distinction between thick and thin lines is the spatial frequency to which the lines apply, the thick lines being for 10 cycles/mm and the thin ones for 30 cycles/mm.

Comment: The MTF at a low spatial frequency is indicative of the dilution of contrast (by such phenomena as internal scattering of light, or “lens flare”. I ideally, that property would me measured at zero spatial frequency, but we cannot measure MTF at zero frequency, so we use the MTF at a low spatial frequency.

The “sharpness” of the lens is indicated by the way the MTF “holds up” as the spatial frequency increases (that is, for “finer and finer detail”). To really understand this, we would need to see a plot of MTF vs. spatial frequency. The normal MTF chart published by Canon (and most lens manufacturers) plots MTF against distance from the center of the frame, with spatial frequency as a parameter (reflected by different sets of lines), and for only one “higher” spatial frequency.

2. The distinction between the black and blue lines is the lens aperture to which the lines apply, the black ones at the maximum aperture of the lens and the blue ones at f/8.0

Comment: It is of course common that the MTF performance of the lens, at any given spatial frequency, will decline with increasing aperture (at least in the aperture range where diffraction effects are not controlling).

3. The distinction between the solid and dotted lines is the orientation of the path across the image to which they apply, or looking at it another way, the orientation of the pattern of test lines to which they apply, the solid lines to the meridional case and the dotted lines to the sagittal lines.

Explanation: The distinction only applies when we are not at the center of the frame. (This is why the meridional and sagittal MTF curves coincide on the MTF chart at zero distance from the center on the Canon-style MTF chart.)

The meridional test pattern comprises lines that are perpendicular to a radius from the center of the frame. If we had a test pattern of concentric circles, its lines would be meridional. Thus the meridional MTF would be taken for “travel” along a path across those lines, which would be a path along a radius from the center of the frame.

The sagittal test pattern comprises lines that are along a radius from the center of the frame. If we had a test pattern of radial lines (a “sunburst” pattern), its lines would be sagittal. Thus the sagittal MTF would be taken for “travel” along a path across those lines, a path at right angles to a radius, a path along a circle centered on the center of the frame.

Comment: The distinction between meridional and sagittal MTF reveals the presence of the aberration called “astigmatism”.

From: Couple of neat tricks with polarizer: Canon EOS 300D Forum: Digital Photography Review

Polarizer in my regard is the most versatile filter you can put on you camera and with digital cameras it is probably the only one you ever need. besides serving its primary function of removing the glare from semi-reflecting objects (water/glass) it can be used as a density filter, warming filter, sky haze filter, etc.

Here’s just some of the neat tricks you can have by using the polarizer (most of them are highly usable in everyday photography):

1) on a sunny day look through polarizer at the sky. Now start rotating it - the sky will turn increasingly blue - giving it a very desired deep and saturated feeling. Notice that the best effect will be achieved when you are looking at the sky approximately 90 degrees from the sun. The closer you turn to the sun - the lesser effect will be

2) reverse the polarizer (rotating ring towards eye/lens) and start turning it - you will see that colors looking through it will distinctly become warmer/colder. To use your polarizer as warm fiilter on the camera you would need to buy a reverse ring (they are very inexpensive but well worth it)

3) stack two polarizers together: one in normal position and the second one in reverse. Now start rotating the second polarizer - you will see that looking though it the scene will become increasingly darker until you will achieve a complete darkness. Thus you can use two stacked polarizers as a variable density filter. You can use it to achieve long exposures during day time for various creative effects!

4) if you have LCD monitor try looking at it through the polarizer. Now start turning the polarizer and you will see that at some point the screen will turn complete dark. Search on internet for explanation on why this is happening!