pixel density

On Fri, 4 Mar 2005 wrote:

You have to realize that a 2x will use up a lot of light. You need to
halve the exposure time, for the same image stability, and you need 2
stops more to get the same exposure.

One stop.

KeS

In article rq-jvgu.arg,
wrote:
On Fri, 4 Mar 2005 wrote:

You have to realize that a 2x will use up a lot of light. You need to
halve the exposure time, for the same image stability, and you need 2
stops more to get the same exposure.

One stop.

Nope - two stops. A 1.4x costs you one stop.

In message
rq-jvgu.arg,
wrote:

On Fri, 4 Mar 2005 wrote:

You have to realize that a 2x will use up a lot of light. You need to
halve the exposure time, for the same image stability, and you need 2
stops more to get the same exposure.

One stop.

A 2x doubles the width and the height of the focused image center,
increasing the area 4x, which is a 2-stop loss of light.

You may also need to stop down the lens beyond this to maintain local
contrast; depending on the conditions, a 2x will generally cost you
anywhere from 2 to 5 stops of light, if used optimally. I generally
only do it when I am shooting in direct sunlight, or under a light haze.
--


John P Sheehy

..::SuperBLUE::. wrote:
How does pixel density influence the resolution at super telephoto?
For example: Is it better to buy a:

1. Nikon 8800 with a teleconverter
2.Olympus e300 2x crop factor
3.Canon 350d 1.5 or 1.6 crop factor
4.Panasonic FZ20 with a 2.8/420mm x teleconverter?
5.7mpix consumer camera disassembled and lens replaced with a 35mm
slr lens

Lens options:
1.Opteka/Exakta/Samiyang/Vivitar/whatever 650-1300mm f/8-f16 lens
(1300mm
f/8 EFL Olympus) (teleconverter???) 250 Eur
2.100-400 f/5.6 with 1.4x teleconverter 500 Eur
3.80-200 f/2.8 Tamron or Tokina with a 3x Kenko teleconverter 600 Eur
+ 250
Eur
4.600 mm f/8 mirror
5.50-500mm f/6.3 Sigma with 2x and 1.4x teleconverters
6. A diy project of makeing the lens myself from components (found a
front
lens 17cm diameter)
7. A telescope with an adapter 6 inch 1200 f/8 refractor 500 Eur +
adapter

My goal is to get an image similar to the one from 20x50 binoculars
or
better.
50mm lens is normal 1x, then 1000mm is 20x normal???

Auto focus speed or manual focus feasibility are also important. Canon
300D might be affordable to you. For AF, you need f/5.6 or better.
Affordable good lenses include 400/5.6, 300/4, and 200/2.8. All 3 has
the same physical lens openning of about 70mm. So with tele converters,
they can be effectively the same as 400/5.6, (300/4 + 1.4x or 200/2.8 +
2x), to keep AF. With the 1.6x cropping of 300D, it is equivalent to
640/5.6. If 43mm is 1x (the diagonal of the 36x24 frame), 640mm is
about 15x, close to your 20x binocular.

If you want more reach than the 15x, you can stack on more TC, 400/5.6
+ 1.4x, 300/4 + 2x, or 200/2.8 + 3x (2x + 1.4x). The result will be
smaller than f/5.6 so you would lose AF on 300D. You can block some
lens electric contacts to fool the camera about TC to retain AF, or use
some 3rd party TC that does not transfer those contacts.

If MF is OK for you, then 600/8 mirror is OK.