A quick help needed !

[Alexz]

I'm toying to my Shen-Hao 4x5 shooting some extreem closeup in our studio at work. In particular, I'm willing to test how my Clatar-II 90mm/6.8 will work on maximum closeup I can get with it which turns to obtain about 3:1 maginfication. I managed to focus at the distance of about 7-8cm with bellows almost fully extended (focused by back), now need to calculate bellows factor for exposure.
According to Steve Simmon's book, I have to square bellows extention value (measured by tape to be around 280mm from the shutter to the film plane) and then divide it on squared lens focal length thereby obtaining the necessary exposure correction in stops. Doing that for this particular case I get about 9.6 stops to add to the orginal exposure !!! (f/22@8) Can it be true ?!?! Sounds like I messed up with this approach...or this is likely to happen in such extreem closeups and magnifications ?

Thanks, Alex

 

[Konical]

Good Afternoon, Alex,

I haven't done the calculation, but the compensation doesn't seem too far out of line; remember that 1:1 is already two stops. With a 90mm, aren't you running into problems with the lens being so close to the subject that the body of the camera interferes with positioning lights properly?

Konical

 

[Huub S]

You didnt make a mistake, its true. And dont forget to calculate Schwarzschild aswell!

Huub

 

[Brickbird]

Alexz--You have roughly a 4" lens extended out to an 11" lens focal length. A 4" lens to 8" is 2 stops and 8" to 11" is one more stop. So open up 3 stops for the bellows extension. Inches works like f-stops. So f4(4 inches) to f8(8 inches) is 2 stops then f8(8 inches) to f11(11inches) is one more stop. That's how I do it and it seems to work every time. It becomes f8@8.

Brickbird

 

[Dan Fromm]

Alex, it appears that you can read.

Save your shekels until you can afford a copy of Lester Lefkowitz' book The Manual Of Closeup Photography. Then buy one and read it. Learning that way really is quicker than learning by trial, error, and begging strangers for help. It also gives a much better, um, grounding.

It is possible that you're relatively a beginner or, if an experienced photographer, don't have a good, um, foundation. If so, buy a copy of A. A. Blaker's book Field Photography and read it.

 

[Alexz]

Thank you all, I re-read books paragraph talking about this issue - I was mistaken, the autor calculates exposure multiplication factor rather then actual correction in stops.
I.e. the factor obtained is about 9.6, at exposre f/22@8 gives about 1.2 sec exposure (at f/22) which is close to 3 stops addition as Brickbird suggested by his (or her ) method. Luckily, the film reciprocity still holds at this exp. times (currently I use Kodak E100s), so no need to compensate for that.
Konical, thans for bring lighting issue to my attention, but as I mentioned I do that with studio setup - on large-scale copy stand equipped with dedicated daylight lighting (similar to Macro lighting setup), so I was able to position lights so that they do not interfare with camera.
Huub, thank you also, but I indeed screwed up in my frst evaluation obtaining 1 min exosure , 9.6 turns to be not the stops but rather a factor to multiply the original exposure.

 

[Brickbird]

To do it your way would be the extension is roughly 7"x7"= 49" divided by 4" lens squared=16". 49 divided by 16=3 stops. Still works either way. You are extending 7" past your 4" lens length to 11". You really have a 3.5" lens but 4" works ok.

 

[John_Brewer]

Hi Alex

I always have a scientific calculater in my camera bag. When you get your exposure factor find the log and divide by 0.3.

So in your case log 9.3 = 0.968
0.968/0.3 = 3.23 stops

Hope that's of help.

J

 

[Alexz]

Thanks Dan, don't really get you what fundation you're talking about. All of my experience (quite extensive one, must admit, also lots of self-learning since 1997) comes from 35mm (and some, though quite limited from MF), and so far I have never got into Macro or closeups at all, neither had an interest in such.
Just recently somem interest has been raised in my mind to LF closeups (not too extreme though) thanks to particular project I was trying to assing myself, and BTW part of which will be devoted to the learning process and hopefully fun that is involved into it...
One more thing Dan, please do not take it personally, but if I'm not mistaken this is not the first time you trying to help me in, xmm a bit aggresive manner. Of course, I appreciate your assistance, including book advises, but please, if you feel you're not willing to help in a particular advise related to the asked question and my primitive questions a bit irritate you, feel free just to pass on it...

Regards, Alex

 

[Bob F.]

I use this: (http://www.salzgeber.at/disc/index.html) Quickdisk. The page also has the formula for calculating the exposure compensation by using the bellows extension and focal length of the lens if you want to do the maths (it is the same formula you already have).

Cheers, Bob.

 

[Alexz]

Thank you Bob, the formula there is exactly the one used in Steve Simmon's book and the one I referred to. The disk however (and I'm aware about it) apparently is useful up to 1:1 and doesn't go beyond this magnification (cause providing up to 4 times (2 stops) correction).

 

[Bob F.]

Sorry - forgot it only goes to 1:1.... . Still, you have the formula and John Brewer showed how to convert the multiplication factor to stops (though I'd have done it as 9.3 = 8 (3 stops) + 1.3 (a bit more) ... ).

Have fun, Bob.