I don't get it - Please help the newbie

[steve simmons]

If you have 17" of extension wth an 8.25/210 lens then add two stops.

steve simmons
www.viewcamera.com

[NikoSperi]

You'd go all the way to f-8-2/3?!? Oh dear... I'm lost

Just for more info I measured my bellows extension from the center of the lens to the center of the GG - I got 17 inches. And I was no more than 2 - 2 1/2 feet from my subject.

Ok, 17 inches bellows draw... on what focal length lens? 8.25" (210mm)? That would mean a 4.25x factor, or just over two stops. So f/25 would need to become f/11 about.

[Bruce Osgood]

You'd go all the way to f-8-2/3?!? Oh dear... I'm lost

Just for more info I measured my bellows extension from the center of the lens to the center of the GG - I got 17 inches. And I was no more than 2 - 2 1/2 feet from my subject.

Okay, let me get the numbers right. You're 24" - 30" from the subject. This only means you are less than ten times the F.L., so compensation is needed.

The formula is: EXTENSION LENGTH^2 / LENS LENGTH ^2

The draw you measured is 17". Squared is 289
Your lens (210mm) = 8.25 inch or rounded 8". Squared is 64

289/64 = 4.5 stops compensation

So, an exposure of f-25 @ 1/60 would or could be either f-25 @ 1/3 second OR f- between 5.6 and 8 @ 1/60, OR a combination of each.

In my earlier message I simply picked a number out of the air as bellows draw, not thinking, I'm sorry I did that.

[Gary892]

Jim, I am looking for 12x20 film holders for a 12x20 korona. If you see any please let me know.

Thanks

Gary

[Gary892]

Whoops, wrong thread. A senior moment. cheeezz.

Gary

[steve simmons]

Lets clarify a few things

early in the thread she said she was using strobe with a 210m lens. So

you can not compensate with shutter speeds

giving a formula with a 6" lens as an example may not be helpful.


I would still suggest using the general rule of thumb I posted earlier as it applies to all focal lengths (yes, even telephoto lenses) and all films.

steve simmons
www.viewcamera.com

[mikeb_z5]

I do it steves way.

[Digidurst]

Lets clarify a few things

early in the thread she said she was using strobe with a 210m lens. So

you can not compensate with shutter speeds

giving a formula with a 6" lens as an example may not be helpful.


I would still suggest using the general rule of thumb I posted earlier as it applies to all focal lengths (yes, even telephoto lenses) and all films.

steve simmons
www.viewcamera.com

Yes, Steve, we don't want to complicate things - might send me right 'round the bend! LOL Really enjoying your book, by the way.

Thanks everyone for the help so far

[jnanian]

Yes, Steve, we don't want to complicate things - might send me right 'round the bend! LOL Really enjoying your book, by the way.

Thanks everyone for the help so far

another to remember way to do it - - think of your focal lenght as an fstop, so you are using a 8 1/4 " lens ( think f 8 + a little bit ) then at 11 ( + a little bit) " it will be one fstop more you have to open up, ( or one shutter speed more to compensate ) then at 16" ( + ...) you would open up 2 fstops, 22 " ( + ... ) it would be 3 and so on ... since you are using a leaf shutter you can compensate mostly by shutter speeds, so can stop down more and not worry about depth of field.

[MurrayMinchin]

Is anybody else getting a throbbing headache? Run with Steve's plan!

I keep an actual wooden ruler in my camera bag that has the bellows extension compensations marked right on it (in 1/2 stop increments) for each of my lenses. All I do is hold one end at the lensboard and see what compensation is needed (for that lens) by seeing which compensation number is closest to the film plane.

The less I have to fumble over numbers while being creative, the better!

Murray

(Added later) Start your measurement from the "nodal point" of the lens...(the point at which the image inverts within the lens)...so if you've used swings or tilts, measure from where the lens meets the lensboard. Same goes for the film plane...(measure for the middle). That'll get you in the ballpark.