Focal Length Equivalent

[barry685]

I am trying to determine the correct focal length lens to purchase that would cover the groups that I photograph in my studio.

Using a Mamiya 645 with a P21+ back I need to purchase a 35,45, or 55mm lens. I would prefer the 55mm.

I looked at the metadata on some files that were shot with a 24 -70mm Canon lens mounted on a 5d, and found the widest focal length that I have used is 51mm. Most of the group shots were 54-60 mm.

Barry

 

[Guy Mancuso]

Hmm than a 80mm which is considered normal is equal to i think 52mm in FF. There is a calculator at CI . let me find it. Here check this out and download it

http://www.captureintegration.com/tools/our-tools/

 

[Jack]

Barry, the answer may be different depending on how/if you cropped your 5D frames. IOW the 5D is a 3:2 aspect ratio frame while the DB is a 4:3 ratio. *IF* you cropped the 5D to 4:3 then the calculation derives a slightly different answer than if you didn't.

Bottom line is if you compare total sensor diagonals, the P21 is about .79x for 35mm equivalent, give or take depending on how/if you cropped your 5D. So the 55 would be about a 43 on your P21...

What you (and the rest of us) probably want is a 65 and they don't make it. Good news is the DB is somewhat more crop-able than a DSLR, so you can shoot looser and crop. Other alternative is to learn to shoot from a little further away and go with the 80. At the end of the day, 70% of my shooting is done with the 55 or 80, and the next 20% with the 150 (but I'm shooting with the 1.1 crop sensor).

Hope that helps ,

 

[Dale Allyn]

Doug at Capture Integration posted an Excel spreadsheet which calculates FL equivalents in this forum some time ago. I'm traveling and don't have the file on my laptop, but perhaps someone will post a link or Doug will post it again.

If you don't have Excel you can use NeoOffice (Mac) or OpenOffice (Mac and PC) to use the file. Both are open source, i.e. free. I don't use MS apps. but the file is compatible with NeoOffice. I assume it will also work with OpenOffice but I have not yet tried the newly release Mac version.

Edit: I'm typing slow and I was distracted!!! Guy and Jack's replies beat me (again).

 

[jmvdigital]

Medium format and 35mm (i.e., 5D) focal lengths do not equate. The P21+ has a crop factor of 1.3x as well. Typically, I've found a good rule of thumb for 645 to 35mm lens conversion is to multiple the medium format lens focal length by 0.59 to get it's 35mm equivalent. Confused?....

The standard 80mm lens on your P21+, would be equal to about 61mm on your 5D ((80mm x 1.3) x 0.59).

The 55mm lens would be equal to about 42mm on your 5D (too wide). The 35mm and 45mm would also be too wide.

The standard 80mm that comes with most Mamiya/Phamiya kits would be perfect it seems.

EDIT: LOL! Me too.

Edit: I'm typing slow and I was distracted!!! Guy and Jack's replies beat me (again).

 

[barry685]

Barry, the answer may be different depending on how/if you cropped your 5D frames. IOW the 5D is a 3:2 aspect ratio frame while the DB is a 4:3 ratio. *IF* you cropped the 5D to 4:3 then the calculation derives a slightly different answer than if you didn't.
Hope that helps ,

Jack,
Good point. I actually crop my groups based on a 8x10 aspect ratio & have drawn lines on the focusing screen to indicate that. So now what?

 

[barry685]

The standard 80mm lens on your P21+, would be equal to about 61mm on your 5D ((80mm x 1.3) x 0.59).

The 55mm lens would be equal to about 42mm on your 5D (too wide). The 35mm and 45mm would also be too wide.

The standard 80mm that comes with most Mamiya/Phamiya kits would be perfect it seems.

EDIT: LOL! Me too.

Justin,
Your findings match the C1 Conversion program. I actually would end up needing a combination of the 55 & 80 to cover all the possibilities. When using the 55 I would just have to get closer to the subjects. The most common focal length that I used with the 5d is about 54mm which the 80 mm mamiya lens would not be wide enough for.

 

[barry685]

Hmm than a 80mm which is considered normal is equal to i think 52mm in FF. There is a calculator at CI . let me find it. Here check this out and download it

http://www.captureintegration.com/tools/our-tools/

Thanks Guy,
That is just what I needed.

 

[Jack]

Jack,
Good point. I actually crop my groups based on a 8x10 aspect ratio & have drawn lines on the focusing screen to indicate that. So now what?

Given that, my best advice is to start with the 55 and take it from there --- HoweverButt, note that for portrait work that is slightly wide and may give you some of the dreaded "bulbous nose" effect...

 

[barry685]

Jack,
The 55 & 80 would primarily be used for groups only. I also have a 150 3.5 & am going to buy a 105-200

 

[Jack]

Gotcha. Then start with the 55

 

[lance_schad]

Barry here is a great focal length calculator to download for future reference.
http://www.captureintegration.com/tools/our-tools/
You simply enter in the focal length in the filed that corresponds with what you want to cross reference it from.
So let say you are used to using a 90mm on 4x5, put 90mm in the 4x5 field and all the other ones populate with the corresponding focal lengths for the other formats.

L

 

[barry685]

Thanks Lance,
Got it already. It is exactly what I needed.

 

[Wall-H]

Can anyone please send me this tool ? I'm trying to access the link and it seems broken?

 

[daz7]

divide the larger sensor sensor's diagonal by the smaller sensor daigonal and multiply your preferred lens length by that ratio.
In your example, 55mm/43mm = 1.28 multiplied by your favourite focal length on a 5D (55-60mm) shows that you should be looking for a lens of roughly 70-75mm for your P21 sensor to roughly match it. Considering difference in a picture ratio, I'd say the lenses within the 65mm-75mm bracket should be fine.

You will never match the look exactly because of a different picture format (1.5x vs 1.3) but you can get quite close.