Close -up photography

[david_henderson]

Hi. I've very recently acquired a macro lens and extension tube for

my Bronica to enable me to carry out a personal project. I'm new to

close-up photography. I've done quite a bit of research here and

elsewhere about how best to use these, and the adjustments to

exposure I have to make , but there's a couple of things puzzling me.

 

First, I understand that when using an extension tube I'll lose

infinity focus. However in reality I don't seem to be able to focus

the camera well other than at or near minimum focus distance. This

is the case with each of my lenses. Is this what you'd expect from

a 36mm tube?

 

Second, I'm using magnification to work out exposure adjustments,

since despite having a metered prism I prefer to use a handheld

spotmeter. So for example if I set my 110 macro lens to its closest

focus distance I get 1:4 magnification and a need to increase

exposure by a little over a half stop. Now if I add the 36mm

extension tube that increases magnification to 1:1.5 and a total

exposure adjustment of +1.5 stops. I can get in even closer if I

add in my 2x teleconverter(I knew I'd find a use for this

sometime!). This takes magnification to 1.4:1 and reading this off

my table gives an exposure adjustment of +2.5 stops. But hold on,

that's only one extra stop for the 2x TC. Surely I need 2 stops for

the TC alone so + 3.5 stops in total ? Or do I? I've tried to

work this out for myself using my metered prism. That told me that

the answer is three stops so right between the two. Fact is that

the prism measures to the nearest half stop and is next to useless

for this sort of comparative purpose.

 

Can someone who knows put me straight please?

 

Finally I can use tables to give me dof data for any of my lenses

including the macro because the lens tells me (near enough) what my

focus distance is. However when I fit the extension tube all this

disappears because the focus scale on the lens isn't accurate any

more. How do I work out dof when I have the extension tube? Do I

simply measure/estimate the actual distance from film plane to

subject when in sharp focus and plug that into the dof formula?

 

Thank you.

[brooks short]

David,

 

You could measure the film to lens distance to guesstimate an exposure factor for the bellows extension and you could use dof tables to estimate the depth of field...All of which will still be a best guess.....

 

OR...

 

You could buy a polaroid back for your Bronica and shoot a polaroid test and see exactly what the proper exposure and depth of field will be.