Five random photography questions I dont know answers to.

[Innocence]

"Brand new to photography, or brushing up on some of the basics? Don’t be shy! " Haha, I'm holding nothing back!
Here we go...

Please tell me if my questions make no sense, or if I' m just missing something. :lmao:

1/ What is the difference between ring / micromotor USM?

2/ What on earth is the crop factor, and how does it affect how I shoot photos? (or how lenses work..."effective focal lengths..?" I read a bit, and there just seems to be a lot of flame fests and I understand nothing haha)

3/ In what situations besides taking photos of fast moving things would you want higher shutter speed? ie what benefits are there which I'm not aware of?

4/ a) how does a camera autofocus?
IF it does so by changing the fstop...focal length and aperature
THEN:
b) how do prime lenses autofocus? :/

5/ What is ISO? Happy for a technical explanation, and how is GRAIN generated at higher ISOs.

 

[Rob]

1. AFD was the original (noisy and crap) type motor which does not allow auto/manual override, was discontinued about 1995. This has been superceded with ring USM which is fast and quiet and allows simultaneous auto/manual focussing and a switchable button. Micro USM is a cheap version of ring USM and is seen mostly on cheap zooms. It does not allow auto/manual focussing and is a bit noisy and crap.

2. There is a lot of nonsense talked about the crop factor. Basically, most digital cameras have sensors smaller than a bit of 35mm film would be. This therefore means that you don't get the same end result. Read about the only sensible piece on it here: http://www.millhouse.nl/digitalcropfactorframe.html It does not mean that your 200mm lens turns into a 300mm lens, it just means you get a smaller subsection of the same image cf 35mm film.

3. Generally the faster the shutter speed, the less movement affects a shot. With people, animals, action and hand-holding the camera, there is an element of movement which may be shown in an image as blur. Therefore, you should always shoot at the fastest setting possible for the effect you wish to create in order to ensure that the shot is not subject to motion blur.

4. http://travel.howstuffworks.com/autofocus1.htm Use google for this type of question.

5. ISO is the sensitivity of your film/sensor. With film, more sensitive particles tend to be bigger, hence 50 ISO will be sharp, but insensitive, whereas 3200 ISO will be grainy, but will work in near darkness. With digital cameras, it's noise, not grain.

Rob

 

[Big Mike]

5. A digital camera's sensor records the light and sends that information to the camera's processor. To increase the ISO (the sensitivity), the camera amplifies the signal from the sensor. The more amplification, the more distortion. This distortion is manifested into digital noise in the image.

 

[Innocence]

Thanks Rob! And Mike!

For Q4, it said that the AF moves the lens in and out to get the sharpest focus. What does moving the lens in and out mean? And is it possible to do with a fixed focus lens?

 

[zedin]

What it means by moving the lens in and out is that the motor in your camera is shifting the glass elements inside the lens. In the old days (well and still when using view cameras) you focused the image by moving the lens closer or farther from the plane of film. Now most of the 'in and out' is just done by roatating the bits of glass inside the lens to get the same effect.

 

[Rob]

Thanks Rob! And Mike!

For Q4, it said that the AF moves the lens in and out to get the sharpest focus. What does moving the lens in and out mean? And is it possible to do with a fixed focus lens?

Think about an old fashioned telescope where you pull or push it open and closed to focus/zoom. Now imagine that motion controlled by a screw-thread using a twisting motion to move forward and backwards. Now imagine that screw-thread is attached to a tiny set of motors.

A fixed focus lens is fixed. I suspect you mean a prime lens (such as a 50mm f1.8 ), or a fixed focal length lens? The answer is yes for a prime lens, it works the same way.

Rob

 

[LWW]

3/ In what situations besides taking photos of fast moving things would you want higher shutter speed? ie what benefits are there which I'm not aware of?

The only way to get a higher shutter speed and a proper exposure under any given circumsatnce is to use a larger aperture opening (smaller f number).

The side effect of this is that you get a much shallower depth of field.

Even when shooting an immobile inanimate object a faster shutter speed can give a better result. Not because the shutter speed is faster but because of the side effect of blurring the background and making the subject *POP* in the photo.

Examples to follow as I dig them out.

LWW

 

[LWW]

LWW

 

[LWW]

Notice the barn door which is nearly invisible unless pointed out.

LWW

 

[LWW]

LWW

 

[LWW]

See how the room is not seen at all.

And here is Saddam at a little distance and shot with at f16.

LWW

 

[lorrir]

Q2
When I was in college I shot with a film camera and developed in the darkroom at school. I was taught to crop in the camera and "touch up" cropping in the enlarger. Simple enough if I wanted 8X10 or 5X7 I did it in the enlarger. I then bought a Canon 10D. I was still cropping in the camera. When I went to crop to an 8x10 or 5x7 in photshop I had cropped out too much in the camera. It all had to with the sensor size of the digital camera. I like the distance I get out of my non digital lenses, but would prefer a "film size" sensor.

Lesson learned... I still crop in the camera but leave a little bit of extra room for formatting to the standard photo sizes.

Good Luck

 

[ksmattfish]

...but would prefer a "film size" sensor.

The dimensions of a print are determined by aspect ratio. A frame of 35mm film and the 10D sensor both have the same aspect ratio of 2:3, even though the 10D sensor is smaller. 2:3 aspect ratio makes 4x6, 5x7.5, 6x9, 8x12, 10x15, etc... prints. You can get a "film sized" sensor in the 5D, but it's still a 2:3 aspect ratio, meaning it would make the same sized prints as the 10D or 35mm film.

8x10 is a 4:5 aspect ratio, and 5x7 is a 5:7 aspect ratio, and 11x14 is yet another different aspect ratio of 11:14.

More info with an example here:

http://www.mattneedham.com/faq.html#ratio

 

[lorrir]

Matt,

Great example!


Lorri

 

[ksmattfish]

5/ What is ISO? Happy for a technical explanation, and how is GRAIN generated at higher ISOs.

ISO stands for International Standards Organization.

Film emulsion is made up of silver halide crystals. The larger the crystals, the less light is needed to expose the film properly. Large crystals make larger grains of silver during development.

Tabular grain films (Tmax and Delta) have a flat crystal that exposes more of the surface area of the crystal to the light. This allows for the use of smaller crystals at the same ISO.