about DSLR

DSLR
This is my guide for shopping DSLR (digital single lens reflector) lens and accessory.
The target machine is Canon 500d/T1i, which is classified as consumer DSLR. Other option may be 550d/T2i, which is newer. This ASP-C cropped frame machine. Real focal length is 1.6x the focal length marked on lenses.
I get 500d, which is best with EF-s lens. Here is a list of options I can upgrade the lens from the kit lens, which is EF-s 18-55 IS.

In EF-S lens range, there are three options consider most widely here for an upgrade still in wide-mid-telephoto range:
• EF-S 17-55mm f/2.8 IS USM, priced over $1,000. This is the best lens in this range. It provides the best IQ. But it lacks of range and also tagged high price. Note that this lens is the only constant aperture lens in the EF-s line. There is dust issue about this lens, but it can be solved by using UV filter.
• EF-S 15-85mm f/3.5-5.6 IS USM, priced over $700. The corresponding hood is 78E, the diameter for the lens is 72mm. Cost for lens, hood and UV filter would be just under $800.
• EF-S 17-85mm f/4-5.6 IS USM, priced over $400

Among all these three lenses, 15-85 would be the proper one after judging price, focal length range and IQ. But 17-55 definitely has the best reputation for image quality.

There are also wide to ultra-telephoto range lens, EF-S 18-135mm IS and EF-S 18-200mm IS. These lenses built quality is normal and believed comparable to kit lens 18-55 IS.

There are several ways to buy the lens, including eBay online shopping, online store and local store. Here some local stores are listed while I don’t have hand on experience of shopping with them yet.

First store I shall talk about is B&H, its tag is fair and often regarded as the baseline for deals. It has both online and local store. The store has pretty long history through.

Second, some reliable stores are 17photo.com, J&R, Ritzcamera, Calumet, Willoughby’s, tristate and 42th street photo.

There are also good online shopping stores like Amazon.com, beachcamera.com, newegg.com, dell.com, onecall.com, sigma4less.com, ibuydigital.com, samys.com and buy.com. Note that ibuydigital.com has the lowest tag for EF-S 15-85 while it may be a gray market item. All online store reputation can be checked on review site like, resellerrating.com, pricegrabber.com

Another item that is popular with lens is UV filter (ultraviolet filter). It’s a piece of glass used to prevent ultraviolet light through, which may cause blue foggy image. In reality, UV filter is used to protect expensive lens, to prevent first contact with other surface in situation like accidentally dropping. UV filter is specified by its diameter. The diameter for EF-S 15-85mm f/3.5-5.6 IS USM is 72mm. There are several UV filter brand and people believe more expensive filter means better filter. Hoya, Tiffen, B+W are common brands for UV filters. The cost for a good multi-coat filter would be up to $60.

Another protection to the lens and also good stuff for the photograph is the lens hood. The lens hood item number for EF-S 15-85mm f/3.5-5.6 IS USM is EW78E. Original brand hood is overpriced so get a cheap one.

There are also other accessories that are necessary for everyday shooting with DSLR, like tripod, flash, fast lens, underwater gear and bag. And in the following paragraph, we will talk about specification about these items that can guide the shopping.

Although tripod is not that important since the age of digital SLR, it’s still necessary for marginal light shooting or long time exposure. Any tripod will do the work, but more expensive tripod from Gitzo (best tripod), Bogen (best value/price) can provide better head which allows flexible adjustment and steady support.

For Canon DSLR, current line of flash is made of Speedlite 580EX II, Speedlite 430EX II and Speedlite 270EX. For macro shooting there are MT-24EX and MR-14EX. 580 comes with weather seal.

Below it’s a figure from Wikipedia which shows the common aperture size. Aperture controls the amount of light come through the lens. So aperture with larger size allows more light coming through so it allows shooting in dark place and faster shutter speed. Depth of field (DOF) is also determined by aperture, aperture with larger size will decrease depth of field. Aperture is often judged by speed and lens is called fast or slow by their aperture. Prime lens often has faster aperture than zoom lens. As far as I know, lens with aperture faster than f/2.8 can be considered as fast lens.


Underwater gear is helpful when shooting with water. There are two kinds here. One is waterproof gear and the other one is underwater gear. The latter one is more expensive that is often listed over the price of the camera. It gives control for each button of the camera while waterproof gear often is a water sealed plastic bag with hard housing for attached lens.

kernel develop from zero

from:
http://www.julienlecomte.net/blog/2007/07/3/
http://www.omninerd.com/articles/Installing_GRUB_on_a_Hard_Disk_Image_File
http://kbarr.net/bochs
http://thestarman.pcministry.com/asm/mbr/PartTables.htm
http://members.iinet.net/~herman546/p20/GRUB2%20Bash%20Commands.html

make a fire ready disk image:
1. get a disk image file. There are two ways to get a empty disk image.
One is:
$ dd if=/dev/zero of=disk.img count=10080
The other one if Bochs is installed:
$ bximage: hd, flat, 1500, c.img
cyl=3047
heads=16
sectors per track=63
total sectors=3071376
total size=1499.70 megabytes
2. After having a disk image， we need partition table in it.
$ fdisk disk.img

x -> Extra functionality
c 10 -> 10 cylinders
h 16 -> 16 heads
s 63 -> 63 sectors per track
r -> Return to main menu
n -> Create a new partition
p -> Primary
1 -> Partition #1
1 -> First cylinder
10 -> Last cylinder
a -> Set bootable flag
1 -> Partition number
w -> Write partition to disk
3. to setup the loop back device.
first to find where the first partition start:
$ fdisk -l -u disk.img

Device Boot Start End Blocks Id System
disk.img1 * 63 10079 5008+ 83 Linux

Given one block is 512 bytes size.
Then, 63 * 512 = 32256
$ losetup -o 32256 /dev/loop0 disk.img
4. format the disk image
$ mkfs.ext2 /dev/loop0
5. mount the disk
$ mount -o loop /dev/loop0 /mnt
6. install GRUB
7. umount disk
$ umount /mnt
8. Detach the loopback device:
$ losetup -d /dev/loop0
9. Finish up the GRUB installation:
$ grub --device-map=/dev/null

device (hd0) disk.img
geometry (hd0) 10 16 63
root (hd0,0)
setup (hd0)
quit
10. Setup your .bochsrc file in the same directory as your disk image:
megs: 32
romimage: file=/usr/local/share/bochs/BIOS-bochs-latest, address=0xf0000
vgaromimage: file=/usr/local/share/bochs/VGABIOS-elpin-2.40
ata0-master: type=disk, path="disk.img", mode=flat, cylinders=10, heads=16, spt=63
cpu: count=1, ips=15000000
mouse: enabled=0
log: out.bochs
boot: disk