What's the equivalent focal length when 210mm lens used with a 6x7 rollfilm back?

210mm lens is considered not long enough for portrait. If it is used with a 6x7 roll film back, will it be close to 300mm? This way not only could save the cost of another expensive lens but also avoid the need of a extra long rail.

It's the eqiv of a 105mm in 35mm format, about twice "normal". It's close to 300mm (about twice normal) if you're talking about the 4x5 format.

The actual usable area on 4x5 film is 4.6875x3.6875, by my measurements. Your question implies that you want to fit a photo taken with 6x7 (2.25x2.75) film onto a 4x5 format. Since the ratio of width to length is larger for 6x7 (2.25/2.75)than that for 4x5 (3.6875/4.6875), I would use the ratio of widths of the two formats (versus the ratio of lengths) to address your question.

The ratio of usable widths between the two formats is 3.6875/2.25=1.64. Multiplying by this factor, one would conclude that the equivalent focal length on 4x5 for a 210mm used on 6x7 would be 210x1.64 which is 344mm. The one assumption I'm making is that the length of 6x7 format is 2.75", since this is the dimension published by Linhof. (I don't have a 6x7 to measure.)

This level of detail may seem kind of ridiculous, but I think it's appropriate. Otherwise, answers can vary widely.

If you go here and down;load the excel spread sheet, you can work out equivelent focal lenthgs in any size and for most main formats to your hearts content. for both 4:5 aspect ratio prints and for negative diagonal. Great fun...

http://www.smu.edu/~rmonagha/mf/lenses3.html

Tim A

One of the advantages of a 4x5 camera is that you don't have to use the whole ne gative. There is no rule which says you can't shoot a portrait with your 210 fr om a distance which gives good perspective, and then enlarge the section of the negative you want. Of course, if you already have a 6x7 rollfilm back, that is easier to develop.

210 is about twice the focal length of the "normal" lens for 6x7 (which can be a nything between 80mm and 105mm), so it is fine for portraits. It also may make a perfectly good portrait lens for 4x5 in spite of "rules" to the contrary -- t ry it and see if you like the results.

Aaron: All the formulas aside, a 150mm-180mm is considered a good protrait (head and shoulders) for 6x7 format. Since the normal focal length for 6x7 is 90mm, the 150-`180 is double the normal focal length. The old formula for film size and focal is that the length plus the width of the film size is a good start for portrait length, while the diagonal of the film is about the length of the normal lens, give or take a couple of mm. A 180mm on 6x7 would be about the same as a 100mm on 35mm or 300mm on 4x5. A 210 will work fine, in fact may be a tad long. Hope this helps, Doug.

Aaron: All the formulas aside, a 150mm-180mm is considered a good protrait (head and shoulders) for 6x7 format. Since the normal focal length for 6x7 is 90mm, the 150-`180 is double the normal focal length. The old formula for film size and focal is that the length plus the width of the film size is a good start for portrait length, while the diagonal of the film is about the length of the normal lens, give or take a couple of mm. A 180mm on 6x7 would be about the same as a 100mm on 35mm or 300mm on 4x5. A 210 will work fine, in fact may be a tad long, but o.k. if you have plenty of room. Hope this helps, Doug.

A 210mm is fine for portraits. This is my standard 4x5 portrait lens. Of course, I do not get in my subject's face.

You asked: "What's the equivalent focal length when 210mm lens used with a 6x7 rollfilm back?"

A 210mm lens is always a 210mm lens regardless of the film size used. The only thing that will change is the relationship between the focal length of the lens and the film size. So, for example, a 100mm lens is telephoto on a small format camera, normal on a 6x7 camera, and wide angle on a large format camera -- but it's still a 100mm lens. (I know, I'm ignoring the differnt coverages required for each of these formats -- there's probably not one lens that can really be used on all three formats.) So, I think the right way to ask your questions is "Is a 210mm lens on a 6x7 camera good for portraits?" The answer to that question is yes. I use a 135mm on my Pentax 67 for "head and shoulders" portraits with great success. A 210mm lens sould work well. Good luck!