older Portrait lens question

[MenacingTourist]

I've been enjoying the learning curve being new to this format and now have some questions about older lenses. Some of the lenses I've read about in forums or looked at on ebay only list the size in inches. The lens that came with my GV showed 190mm as well as 7 1/2". Am I correct that 7 1/2" has something to do with bellows extension? Would a longer inch size indicate a longer lens? For example, would an 8" lens relate to a 210mm? I believe my maximum bellows extension is 12". If a lens shows 13" will it not work with my setup?

I'm interested in portraits and like what I've read about the older lenses being softer and having some "character". The lower price of these softer and older lenses are nice too. I'm waiting on a polariod back to do tests with the lens I have so I won't be making any lens purchases for the next couple or three months. Basically, I'm forced to be patient but want to learn what I can so when I'm able to do something I'm armed.

Thanks for your help and let me know if I need to clarify these questions any more.

 

[r-brian]

Lens focal length is measured in millimeters (metric) or inches (English). There are 25 mm per inch (technically 24.7). Divide mm by 25 and you have length in inches. Multiply inches by 25 and you have length in mm.

Brian

 

[Ole]

Eh - there's 25.4 mm in an inch. Otherwise correct

Since your max extension is 12", you cannot focus any closer than infinity with a 12" / 300mm lens - unless it's a telephoto lens. I'd advice you to stay below 240mm (9 1/2") or so to be able to get closer.

A good portrait lens could well be a 210mm or thereabouts.

BTW, many older Europena lenses were marked in cm, not mm. So if you see a 21cm Heliar for salr, you'll know that it's an old uncoated superduper portait lens

 

[jimgalli]

Your 190 at f4.5 will make nice portraits. Another neat item is a sliding back that splits the 4X5 area into 2 2.5X4 frames. 2 portraits on each sheet. But it also makes that 210 or 240 seem ever so much longer because of the different aspect. 210 Heliar is a killer lens for portraits.

 

[BradS]

Hmmm....

Here is a formula that explains the relationship between the focal length of a lens, the distance between the lens(object distance) and the length of bellows (image distance).

(1/focal length) = (1/object distance) + (1/image distance)

Amoung other things, the equation shows that for any given lens focused at infinity, the distance between a point in about the middle of the lens and the film plane is exactly equal to the focal length of the lens. Thus, if your bellows can extend a maximum of 12 inches, then you would not be able to focus a 13 inch lens at infinity -- let alone anything closer than that. To focus closer, you always have to extend the bellows.

If this is just so much mathematical gibberish, may I suggest that you try a few "hands on" experiments with the kit you have....I'll assume that you have a 190mm lens

Set your camera up and focus on something far away -- at least a few hundred feet -- then, your bellows draw would be about 190mm or, about 7.5 inches (about the same as the focal length of your lens). Now, with a twelve inch bellows (12inches = 304.8 mm) and a 190mm lens, the closest you can focus is about, 504.5mm or, about 20 inches away. The equation above can be used to predict this....

1/190 = 1/x + 1/304.8
solve for x....

(1/190) - (1/304.8) = 1/x
so,
x = 1/{(1/190) - (1/304.8)}
x = 504.5 mm

so, focus on an object about twenty inches in front of the camera and see if it doesn't take just about 12 inches of bellows.

 

[jimgalli]

Brads post is excellent. Also bear in mind that when you're focused at something close and your bellows is at 12", you no longer have a 7 1/2" lens, you have a 12" lens. So the aperture scale for 7 1/2" no longer works. Easily fixed if you think in inches though. The difference will be the same as f7 1/2 to f12, about 1 1/3 stops.

 

[MenacingTourist]

What can I say? This forum is excellent! Thanks for making the learning curve a little less curvey

I've made lots of notes in my "photo note/sketchbook" and I'm going to mess around with what Brad suggested but I'll have to do it inside. Everytime I go outside I end up shoveling the driveway (18" in two days).

Thanks again.

Alan.