March 06, 2015, 12:53:36 PM

Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.

Messages - Passport

Pages: [1]
C-mount Pentax 8-48mm f1.0

And this one is real.  Even if Sigma did announce an F1.4 zoom, it still wouldn't be the fastest.

Lenses / Re: Would a 14-28mm f/1.8 be possible?
« on: February 15, 2013, 10:12:38 AM »
Of course it's possible.  Just don't assume a 24 by 36 sensor/film size.  You can buy a used BOLEX KERN Vario switar Zoom 12.5-100mm f : 2 Lens for under $800 on Ebay today.

Lenses / Re: Please explain the need for f2.8 zooms
« on: January 30, 2013, 09:44:24 PM »
Faster lenses also allow you to see the image more clearly in the view finder.  You generally get better photos if you can see the composition.  The shallower depth of field enhances the distinction between what is in or out of focus making focus acquisition more precise.

If the object is to compare sensors of equal number of pixels for sharpness and nothing else, why not provide a colimated light soure to adjacent pixels in a checkerboard pattern such that neighbors get alternately 0 photons and photons beyond saturation.  Take the digital data and blow it up any number of times, 5, 10, 1000, or a billion.  Sensor size is immaterial if you remove all the optical variables.  The digital data will be identical regardless of sensor size.  Prints made from either sensor will be identical.

Pick a limited number of variables and you could have the alleged photocopier.

Pick a realistic number of variables and we are beginning to talk photography.  Pick your poison and make your pitch.

Generally, system resolution is calculated by taking the reciprocal of the sum of the reciprocals of the elements of the system.  For simplicity, if you have film or a sensor that will resolve 100 line pairs per millimitre and a lens that will resolve 100 line pairs per millimitre, the best that can be hoped for is (1/100+1/100)^-1.  That is 50 line pairs per millimitre.  In reality you need to add contrast factors, paper resolution, printer resolution.  Back in the day I added enlarger lens resolution to the calculations.

Take a lens that has infinite resolution and a sensor that has 100 lp/mm and you get 100 out of the system.  Take a sensor with 100 billion pixels and feed it an image with 100 lp/mm lens and you get a resolution approaching 100 lp/mm out.  A larger sensor has more millimitres than the small one hence a higher total number of line pairs.

Numerous factors including optical diffraction limits, lens abberations and sensor noise give larger sensor of comparable technology with identical pixel count and proportionately larger pixels an advantage in resolving detail.  Mechanical accuracy of mount alignment and distance to sensor proportionately favours the larger sensor as well.

Third Party Manufacturers / Re: Is it hard not to buy 3rd party lenses now?
« on: December 26, 2012, 04:25:28 PM »
8-16 Sigma zoom on a T1i is a combination that works well.  The Canon 10-22 doesn't match the width and the copy I borrowed did not perform any better.  I've had the Sigma on many dozens of flights and on hundreds of construction sites.  It still looks new and the images it takes get some publication in specialty magazines and a few of our boardrooms. Autofocus is kind of wasted on a 8mm f4.5 crop sensor lens but I generally let it do its thing and it's snappy enough for the mostly stationary subject matter it is used for.  It was real hard not to buy this lens.

Pages: [1]