Originally posted by ghelary Your math are shoddy at best, lets review a bit the problem:
- 1. 645 and 35mm image ratios are different. Calculating a "crop factor" is a matter of personal taste, comparing 645 to 35mm is like comparing 6x6 and 6x7. What is the crop ratio of 6x6 compared to 6x7?
- 2. Once you have chosen a crop ratio (roughtly 1.3) you can determine equivalent FOV (diagonal, in length or in height) and equivalent focal length.
- 3. But to determine the equivalent apertures to obtain the same DOF, you cannot take the aperture number and divide it by the crop ratio.
DOF is much more dependant on distance to focus, than on aperture so you have to set before the distance of focusing to make comparisons.
DOF is a very complex subject, and get you things right, I suggest you have a look at this series of articles from the
The Online Photographer
DOF is a very complex subject where focal length, distance to focus, capturing technology (film, digital, size of grain/ nb of pixels), aperture and size of print all play an important part. For the larger prints, the "look" of MF is definitively different than 35mm, which is different than APSC.
Personnaly, I gave up on making knowledgable calculations of equivalence etc... What is important is knowing what you can get from your equipment and knowing what equipement your need for the result you want to achieve.
1. and 2. Maybe you don't have seen my 645D "equivalent" lenses table. I have posted the table here (april 2010) and in this thread.
https://www.pentaxforums.com/forums/attachment.php?attachmentid=78820&d=1293059317
As you can see there is a 35mmFF "equivalent" focal length for the horizontal, vertical and diagonal ratio.
Note also that I say in my post "same" "equivalent" (not same and equivalent) and "MORE OR LESS".
"Personnaly, I gave up on making knowledgable calculations of equivalence etc... What is important is knowing what you can get from your equipment and knowing what equipement your need for the result you want to achieve."
I agree. Because that I have used on film these formats:
35mm (Canon, Olympus)
35mm panoramic (Noblex)
4.5x6cm (Fuji and Pentax)
6x6 (Rolleiflex)
6x7 (Mamiya)
6x9 (Cambo)
5x12 panoramic (Noblex)
9x12 and 4x5" (Linhof, Arca-Swiss)
13x18 (Arca-Swiss)
8x10" (Arca-Swiss)
Now, on digital, I use 3 formats:
4/3 Olympus
APS-C Canon
35FF Canon
And Maybe 33x44mm Pentax in the near future...
"and knowing what equipement your need for the result you want to achieve."
One example:
Linhof Technika V, Nikkor T-ED 500/11, Sinar panorama 6x12 back, Fuji Velvia:
Luna sobre Aneto-Maladeta :: Fotonatura.org
Ramуn