# Thread: DOF calculator for a Chamonix

1. ## Re: DOF calculator for a Chamonix

No you don't need a different scale for each lens. Read up on the physics of it, it's determined by extension, and hence the same scale works for every lens.

I'm sure you can in some cases do it fine by loupe, but why bother performing what is in essence a purely mechanical mathematical task manually when a scale is faster, more reliable and repeatable? It's basically converting a focus spread based on extension into the sharpest aperture to stop down to. There needn't be any human decision making there. Likewise we could probably all make a decent guess at exposure just by eye but most of us tend to use a light meter. Same idea.

2. ## Re: DOF calculator for a Chamonix

Originally Posted by dave_whatever
No you don't need a different scale for each lens. Read up on the physics of it, it's determined by extension, and hence the same scale works for every lens.

I'm sure you can in some cases do it fine by loupe, but why bother performing what is in essence a purely mechanical mathematical task manually when a scale is faster, more reliable and repeatable? It's basically converting a focus spread based on extension into the sharpest aperture to stop down to. There needn't be any human decision making there. Likewise we could probably all make a decent guess at exposure just by eye but most of us tend to use a light meter. Same idea.
YMMV I go by the feel of an image, I don't really measure, I'm an artist, not a physicist or mathematician, I lose my creativity and the image looks like crap if I get too distracted by all the tech (to an extent). It's very rare that I shoot under F/16 ever, these were both f/22.... Everything I wanted was in focus and everything I wanted out of focus was too...

I still don't get the extension thing, f/22 in this image gave me a DOF of about 3 inches, if I were shooting a field and mountain my DOF would be multiple meters... then there's all the tilting and shifting, hard to measure all those planes, But again YMMV.

3. ## Re: DOF calculator for a Chamonix

If you don't understand it, read up in it before you discount the method. It's available on the home page. Have you seen QT's Luong's prints in person? You say you spend 15+ minutes setting up a shot (your words elsewhere on this forum) getting all the movements right. Then say you've used every movement the camera has to get it just right. Sounds like art. Meanwhile, those using other methods (dof calculator) are off setting up the next shot.

4. ## Re: DOF calculator for a Chamonix

Originally Posted by vinny
If you don't understand it, read up in it before you discount the method. It's available on the home page. Have you seen QT's Luong's prints in person? You say you spend 15+ minutes setting up a shot (your words elsewhere on this forum) getting all the movements right. Then say you've used every movement the camera has to get it just right. Sounds like art. Meanwhile, those using other methods (dof calculator) are off setting up the next shot.
If it's not broken, don't fix it...

I'm not adverse to learning I just know after 20 years of shooting film that judging by eye works just fine for me.

6. ## Re: DOF calculator for a Chamonix

Originally Posted by Bob Salomon - HP Marketing
yea, that looks way to complicated, I would surely screw that up, hope it's useful for the OP. Pretty sure by the time I worked that all out it would be midnight and I would started at 6am and have not taken my first shot yet...

7. ## Re: DOF calculator for a Chamonix

Bob's chart is complicated, which is exactly why people chose to use a simple knob-based DOF scale instead of a complicated chart where you have to measure repro ratios.

8. ## Re: DOF calculator for a Chamonix

Originally Posted by dave_whatever
Bob's chart is complicated, which is exactly why people chose to use a simple knob-based DOF scale instead of a complicated chart where you have to measure repro ratios.
So you focus on the near point and then the far point and read off the mm scale the distance between them. Set the indicated F stop for that distance on the scale and then reposition the rear standard the indicated amount on the chart.

That's how the knob type ones also work. Just it is flat and fits your pocket.

9. ## Re: DOF calculator for a Chamonix

Thanks Bob. Your input is always appreciated.

Dave

10. ## Re: DOF calculator for a Chamonix

Originally Posted by Bob Salomon - HP Marketing
That's how the knob type ones also work. Just it is flat and fits your pocket.
And because it's flat and doesn't benefit from the gearing of a knob scale it's much less precise, especially with wide lenses. Not to mention it can be lost, dropped, or forgotten. But each to their own.