To play devil's advocate, if I were to go along with this notion and say that the lens has changed qualities and now inherent the DoF of the faster lens it has appeared to become, wouldn't the focal length change be directly proportional to the gain in sensitivity? For instance, because of the inverse square law, a 2x teleconverter loses 2-stops of light, because the surface area is four times as large. So playing with this reasoning, theoretically, this lens were to have shallower depth of field, but at the same time inversly be a wider focal length of proportional means, and we know that wider focal lengths have deeper stops.
Lol. Something to think about.
I assumed the lens would keep it's same properties, the only difference is that we see more of what used to fall off the sensor, thus it's more of a FoV change than it is a DoF change. It's the CoC part I've got to figure out. I love this talk though. Good way to start my brain in the morning. Thanks to everyone who is participating. Can't wait to figure this all out.
Results 11 to 17 of 17
05-16-2012 06:36 AM
Last edited by Ryan Patrick O'Hara; 05-16-2012 at 06:48 AM.
05-16-2012 06:39 AM
05-16-2012 06:23 PM
- Join Date
- Apr 2011
only caveat is that if you can't get a picture out of the lens because of other aberration problems, depth of field
might not be that important.
therefore the f number will be the original f number divided by two.
This does not mean that you have four times as much light hitting a particular pixel. The doubling of light
goes by f/2.8->f/2.0->f/1.4->f/0.98->f/0.7. An f/0.7 lens is four times as bright as an f/1.4. That's also a
good idea of how much harder it is to make an f/0.7 lens than an f/1.4.
The brightness goes like (f#)^(-2). The inverse square law doesn't work on images and the actual math is a great
way to ruin a perfectly good weekend. If you want to see the proof it's equation 2-77 in
So the size of the image doesn't really determine the brightness. It's dependent on magnification which
is dependent on focal length which is dependent on f/number which controls brightness.
05-24-2012 11:29 AM
Before I upload photos and information, just wanted to say that so far, my initial tests have been interesting.
I've been using a f/2.5 105mm lens to test, and so far have gained a stop and a half - a stop and a quarter range on it. At an f/4, I got it to match my Cooke Panchro/i at T/2.8.
The Nikon was definitely the way to go. Because of flange distance, the Nikon has one the longest/deepest, while the camera I'm using (NEX-5 right now, later the GH2) is short. This allows me room to add elements in the middle. Sadly, because of where I have to place the focal reducer, it does not reduce to the amount it does in telescopes. It was advertised to gain at least two+ stops in telescopes, of course placed differently in the assembly. I think a f/10 - f3.3. Instead, I'm seeing a stop and change.
I will be keeping at it, but it seems if the f/1.2 50mm follows suit, we may be looking at something below a f/1 but not a .7. Maybe a .8 or so.
I've taken apart about $2,000 worth of lenses I no longer use. They are really quite fun to take apart. It's a learning experience and I'm having fun.
Not giving up yet.
06-14-2012 03:49 PM
- Join Date
- Apr 2011
Interesting project. AFAIK, Zeiss simply used a focal reducer for the Planar f0.7 to reach its fast aperature.
I've been playing around with some fast lenses myself recently, including this 60lb 130mm f/0.7 monster. Covers 80x80mm sensors!