Help Me Pick the Right Lens for a 4/3 Bellows System

Leo

I've been stumbling around trying to find the right combination of lenses / extension tubes to take pics of coins with my Olympus E-420 4/3 DSLR.

My prelim setup was magnifying filters.



I attach this to my tripod and am able to take decent pics of coins:

with 4x multiplying filter



with 10x filter:




I tried an EX-25 digital extension tube, but the focusing distance was too short. Just unworkable.




So I'm thinking about an Olympus bellows with an enlarging lens.

With the 4/3 system and its "strange" sensor size, I thought I'd ask ya'll for some advice re the enlarging lens for the bellows system. I want to maintain a distance between the front of the lens and the coin of 4 in to 6 in. I suspect a 75MM enlarging lens will put me too close to the coin. Perhaps a 135mm. Not sure.

Can ya'll advise?

:wave

dbd

Leo wrote: »

I've been stumbling around trying to find the right combination of lenses / extension tubes to take pics of coins with my Olympus E-420 4/3 DSLR.
...
With the 4/3 system and its "strange" sensor size, I thought I'd ask ya'll for some advice re the enlarging lens for the bellows system. I want to maintain a distance between the front of the lens and the coin of 4 in to 6 in. I suspect a 75MM enlarging lens will put me too close to the coin. Perhaps a 135mm. Not sure.

Can ya'll advise?

The OM system included 80mm, f4 and 135mm, f4.5 short body lenses for use on bellows and other extenders.

Dale B. Dalrymple

Leo

dbd wrote: »

The OM system included 80mm, f4 and 135mm, f4.5 short body lenses for use on bellows and other extenders.

Dale B. Dalrymple

Thanks.

Any idea which lens would give me the desired distance from front of lens to subject?

I don't know the math, and I just don't feel like doing it empirically and buying too much stuff that doesn't work and I won't use.

ziggy53

I'm not sure if you really need a bellows solution.

Your Olympus E-420 has an image sensor size of 17.3mm wide by 13 mm tall. Assuming that your smallest coin is not more than 13mm in diameter, a true macro lens that is capable of 1:1 magnification will fill the vertical component of the frame with a 13mm object at closest focus. Larger objects will simply require a longer working distance.

Since you already have the 25mm extension tube you could even achieve a little better than 1:1 magnification (at the expense of working distance).

Unless you have something much less than the 13mm diameter (or height) to shoot, a true macro lens is probably the best recommendation for this application.

The longer the lens' focal length, the greater your working distance. A macro lens of around 100mm focal length is a very nice length to own.

Leo

Thanks, Ziggy.

Yeah, I realize that I can make a regular macro lens work. In fact, I've got something in this area on the way.

I'm believe a bellows system might give me more control for the many different sizes of coins I need to take pics of. For example, a 3 cent silver is only 14 mm wide (tiny), while a $1 Eisenhower is 38 mm. Not to mention that I sometimes need to get pretty close to a coin to identify mint errors.

Most folks are using 75MM lens off darkroom enlargers for their typical Nikon / Canon bellows setup. But with the 4/3 system on my Olympus, I suspect I'll need a larger lens. Perhaps a 135mm, maybe a 150mm.

Perhaps something like this.

Yet I can't do the math to confirm that the lens will maintain some decent (5 inches or so) distance from the coin, so I can light it well.