How can I use a non-TTL lightmeter beyond its built-in ISO range?

Question

Some introductory information first: I got into photography a few months ago and I have very basic knowledge on the matter so be patient - the answers may be obvious for you. The camera is Zenit 11 - Old Soviet SLR with no electronics. It has a light meter that does not measure through the lenses and the light indicator is not in the viewfinder but on the top of the camera - similar to this one. It has a small needle that moves according to how light the scene is and a small circle that you move by rotating one of the two rings on the "calculator" part of the meter to match the needle. The inner ring is used to select the ISO/ASA of the film and has markings for the aperture sizes, the outer ring has the shutter speeds. Once you match the needle with the circle, you can view what combinations of aperture and shutter speeds you can use for the current scene.

I've used the camera for around 8 rolls of film so far and the light meter is very handy and still works and feels accurate (based on the resulting photos). However it has a limitation - The ISO/ASA selection goes only up to 500 and I want to use it with faster films like 800 ISO. Is there a way to use it with faster films? Let's say I put an ISO 800 film but set the meter to ISO 400 and then if it says that I can use shutter speed 125 with aperture 8, how do I compensate ?

My second issue with it is that it does not measure through the lens. I want to experiment with extension tubes for macro stuff and I have 9mm 16mm and 30mm extension tubes that can be used in different combinations. The lens is a Helios 44m-4 58mm f/2 . I guess using it with an extension tube will cause less light to get to the film which the meter does not take into account. Since the only thing I can "set" on the meter is the ISO, is there a way to calculate a different ISO selection for the meter that will give "true" results when an extension tube is used? I am looking for a formula or something. For example, let's say I have ISO 200 film in the camera and the meter shows that I can use shutter speed 250 with aperture 8 for the current schene. Now if I screw the 16mm extension tube between the camera and the lens, can I calculate a new ISO value for the meter that will give me the correct combinations for shutter speed and aperture?

Answer 1

Yes, you can definitely use set the light meter at 400 and figure out what the exposure has to be at 800. It's a one stop difference so if it's saying f/5.6, set your aperture to f/8. Most old lenses will have the markings at one stop intervals. And it's a good idea to memorize the major f stops as well.

With extension tubes, there's usually a compensation value associated with them. Otherwise, I would do a few experiments on non-critical items. Meter the subject, shoot as the meter says, expose one stop higher, expose two stops higher, etc. Then label the tubes accordingly. Expect one to two stops of required added exposure for extension tubes.

Have fun!

Answer 2

If you meter at ISO 400, but are actually using ISO 800 (1 EV), but cannot set ISO 800, just decrease your metered exposure by 1 EV... Close down one f/stop, or double the shutter speed number (like 1/100 goes to 1/200). That would be -1 EV exposure compensation.

Macro work is a different game, because it reduces the actual exposure according to the magnification. Magnification changes the f/stop number, and 1:1 magnification specifically requires 2 EV more exposure than a non-though-the-lens would meter. Less magnification is less increase.

Through the lens metering would solve this. Or Many modern macro lens compute this and will show the new correct f/stop number, but extension tubes will not, you must adjust exposure to be satisfactory. Easy to do with digital, but an issue with film. There are formulas, but which require you to know the magnification and extension (my site shows the formulas for extension tubes at https://www.scantips.com/lights/cropfactor.html#mag ). The easiest rule of thumb is that 1:1 magnification requires 2 EV additional exposure, and remembering past experience results with your gear will be very helpful.