Saturday, September 26, 2009

Spotting photographic equipment scammers

1. Go to nexttag or some other site and figure out the price range of the product
2. Go to several different resellers and check the prices.
3. Do a search with the reseller's name along with the phrase 'bait and switch'
4. Find the product on amazon, adorama, ritzcamera and keh.com
If the
1. Price of the product is much below (say 30%) the well know retailers' prices
2. Accessories are correspondingly more costly
3. Extended warranties are correspondingly more costly
4. website sells the same product at a higher price and it looks like one is body only and the other is kit (but the website does not tell you)
Then be wary. They could be
1. Trying to bait and switch you (sell you another product after saying out of stock)
2. Trying to sell you over priced accessories and warranties to make up
3. Selling a used or refurb kit as new
4. Just plain old scam you - take your money and not deliver the product.

Tuesday, September 22, 2009

Macro lens

A lens of a given focal length has a certain field of view. If you can focus the lens close enough, you can get large reproductions of objects. Such lenses are called macro lenses.

Maximum reproduction ratio

1:6.6 maximum reproduction ratio -> 10mm object will take up 1.515151515151 (sorry had to do that) mm on the sensor.

DX sensor on D40 23.7mm -> 3008 pixels so 1.51 mm -> 192 pixels -> about 1in for a 200dpi print.

So with the 50mm 1.8 AF-D lens if you shoot at the closest distance (about .5m) a 1cm object can be printed at 1in decently. Not that you would want to use this lens that way...

Latex math: Vertical bar

Like that used for indicating the evaluation of integrals between limits:

\bigg|

as in

\frac{\rho}{4\pi}\left(-\frac{1}{r}\right)\bigg|_{r_{0}}^{\infty}

from a hint here from robphy

Friday, September 18, 2009

50mm f/0.7

Its billed as the world's fastest lens. A limited number were built for NASA (glamor portraits in outer space - astronauts photographed only by the light of their own instruments) and Stanley Kubrik snagged a few to make some obscure movie shot mostly by candle light (yep, he spent all his money on those fancy high speed lenses and couldn't afford real lighting).

Here is a picture of one. And here is a page by the guy who modified the lenses for Kubrik.

PS. You've probably figured out I was kidding about some of the stuff about astronaut portraits and Kubrik running out of money...

Thursday, September 17, 2009

How the D40 handles a multi dimensional problem

There are three dimensions to exposure:
1. Aperture
2. Shutter speed
3. Sensitivity
In film days adjusting sensitivity on the fly was not practical, so you basically had a two dimensional plane once you loaded film.

The life of the camera computer was easy when you set the camera to A or S modes: all it had to do was adjust the free variable to maintain correct exposure. In M mode the camera merely informed you of exposure letting you roam freely in this 2D space.

The D40 can be setup exactly this way if you select fixed ISO. If you select auto ISO, however, the camera now is handed two free parameters (for A and S) and one free parameter (for M). How does the D40 deal with this?

For A mode the computer minimizes ISO and maximizes shutter speed. You can set a lower limit for Shutter speed and upper limit for ISO and the camera will drop shutter speed until it hits the lower limit and the start to bump ISO.

For S mode the computer minimizes ISO. It will maximize the aperture until it reaches the lens' limit. The it bumps ISO.

This all sounds sensible, but what about M mode? This is funny. In M mode you no longer have the freedom to mess with exposure - the camera runs loose with ISO changing it to give you correct exposure regardless of your A and S combination. Eventually it hits the camera ISO limits and starts to show you over- and under-exposure.

M mode with auto-ISO will enable you to play with particular shutter (motion capturing) and aperture (DOF) combinations for your subject that would normally be inaccessible to you (cumbersome with manual ISO, impractical with film).

Everything you wanted to know about flashes

(But couldn't find on google because it thought you were looking for compact flash memory cards)

http://repairfaq.cis.upenn.edu/Misc/strbfaq.htm

Hopefully you find this link if you are looking for
1. Photographic flashes - AKA:
2. Strobe
3. Strobelight
4. Flash
5. Camera flash
6. Compact flash (Hell why not)

Wednesday, September 16, 2009

IR Remote for Nikon

I didn't buy this for my Film SLR because I cost too much. Currently Nikon's brand (ML-L3) costs $15 on Amazon/Adorama etc. and on Nikon Mall costs$20. However, if you look here (bestofferbuy) you can get an 'alternate version', called the YN ML-L3, for $4.80 and free shipping. I was a little wary at first and wondered if this was a scam, but I decided to try it out and ordered two (aha, see how this works, they price it less and that gets the sucker customer to buy more). I guessed it would take a long time to get here, but it took about a week and a half. I tried out the first one and it works fine. The unit comes with battery installed but with a plastic tab to keep it from discharging. These shady Chinese operators are moving upscale. (Actually it ships from Hong Kong. Don't know if that's any different anymore). I have plans for the other one. An intervalometer costs an insane amount of money. Say like$140. What I want to do is order a 555 and some pots from Digikey and modify the second remote for time lapse photography. Who knows, I may even get fancy and use a crystal and a binary decade counter with BCD encoding for accurate timing...

Tuesday, September 15, 2009

BR2A

Any Nikon camera with lens info contacts (e.g. any DSLR and any newer Nikon) needs the BR2A reverser, rather than the BR2 to reverse lenses.

Tuesday, September 8, 2009

Rotated text in Firefox with CSS

-moz-transform: rotate(-90deg);

Monday, September 7, 2009

Rounded borders in Firefox

CSS3 supports divs with rounded borders, but for now Firefox lets you use something like
-moz-border-radius: 2em;

Grouping results in rails

I needed to group records by year. From this post and the enumerate module docs we end up with
   entries = Entry.find :all, :order => 'date DESC' entries.group_by do |entry|   entry.date.year end
The group_by returns a hash with keys corresponding to the result of the block (i.e. the year)

Sunday, September 6, 2009

What will 6MP get you?

So, how big a print can I make with a 6MP (3000x2000pixel) image, if I assume that the image is meant to be seen all at once?

From wikipedia (eye acuity) we find that a human with 20/20 vision can resolve 2 arcminute per line pair. This means two pixels separated by 2/60 = .033 degrees they can be seen separately

Then a 1000 pixels can subtend 1000/2 * .033 = 16.66 degrees, so a 6MP image can subtend 50x33 degrees.

At a distance of .3m (arm's length) this works out to .358m x .195m (14.3"x7.8")

At a distance of 1m this works out to 1.192m x .65m (47.5"x25.87")

I don't think this is too shabby.

Thursday, September 3, 2009

D40 quick controls

1. Set Fn button to control ISO
2. Set AE/AF lock to AE only
In A/S (Aperture/Shutter priority) modes
1. Wheel alone controls Aperture(Shutter)
2. Wheel + function controls ISO
3. Wheel + (+/-) controls exposure compensation (I keep forgetting this)
In M (Full manual) modes
1. Wheel controls shutter
2. Wheel + (+/-) controls aperture
3. Wheel + function controls ISO
4. Exposure is indicated on the bar graph
In Auto mode you only get to control ISO

Wednesday, September 2, 2009

Digital vs FIlm and Point and Shoot vs SLR

I'm sure Google crashes when you do this search. But here's what I think:
1. The only way to get photographs you attach to is to take a lot of them as often as possible, look at the results and link it with what you did.
2. Digital makes this process cheaper and faster. Digital gives you instant feedback. From the instant LCD display, to the home viewing on the big monitor to the prints at the dime store.
3. More pictures, more fun.
4. I think the guys who say 'all you need is a pinhole' are right. Really. It ain't the camera. I have photos I treasure from my Dad's Exakta RTL (with a busted exposure meter), from point and shoot Yashikas and Kyoceras, and from my Canon A510. From my D40 so far I have perhaps two photos I treasure for artistic reasons (out of may be 500). The camera and the lens just don't matter. Just take a lot of photos. And have fun.
5. UPDATE: One thing though - the D40 has really good low light capability. I took several indoor shots with room lighting and they came out gorgeous handheld. My point of comparison is with a Canon A510 so current P&S may have improved.

Tuesday, September 1, 2009

The moon and six pence

Photography increases my admiration for the human visual system. I look up into the night sky and I see the full moon, I see the stars around it and the houses below. Then I put my camera on a tripod and try to capture the same scene. WOW! The moon is BRIGHT! I mean you could shoot it hand-held (1/30th even at f13). But wait, at that exposure the stars are gone, not to mention the house. I go down to 1" at f13. Now I get the stars, not really the house and the moon is one big halo with no internal structure.

Shutter mechanisms

I got fascinated by the camera shutter mechanisms and started to do some reading:
1. A great set of images of a shutter opening and closing. Read the tech details of how it was done.
2. A very nice writeup with attractive hand drawn sketches of the principle of the focal plane shutter and some funny effects that occur with fast moving objects or flash use.
I wanted to know more about the shutter mechanism.
1. Nikon has two pages with tiny drawings [1],[2]
2. A search on google images with the word "shutter mechanism" and filter by line art gives interesting results
3. An example of how shutter speed knobs interact with the actual shutter is given here.