M42x1 adapter

[Marci Hess]

When would one use a cone shape and when would one use a flat shape?

Many thanks!
Marci

[enricosavazzi]

When would one use a cone shape and when would one use a flat shape?

Many thanks!
Marci

Do you mean M42 to microscope objective adapter? In this case, a conical adapter increases the distance between objective and M42 mount, so at a given magnification on the sensor you will need shorter bellows or set of extension tubes between camera and adapter. This also means that, with a given bellows and lens, you can reach higher magnifications with a conical adapter (as long as the objective still performs well at these magnifications).

A conical adapter makes it easier to place bulky light sources close to the axis of the objective. This is an advantage if a flat adapter forces you to place the light sources at an excessively high angle to the objective axis. With long working distance objectives, there is little difference between conical and flat adapters in this respect.

A flat adapter can be advantageous when you use photomicrographic lenses in RMS mounts and want to achieve a low magnification. In these cases, a conical adapter may force too high a magnification with objectives of short focal lengths (e.g. the Canon 35 mm).

Other than this, there are no fundamental differences between conical and flat adapters. Since they are usually cheap, if you do a lot of photomacrography the best solution is probably to get both and use whichever is most practical for a given situation. If you are starting out in photomacrography, which one is best depends mainly on the rest of the equipment (lens and bellows/tubes) you have or are planning to get, and the magnification you are aiming for.

[Pau]

Another point: Cone shapped adapters are prone to induce flare from internal reflections, you likely will need to flock its interior or to make a flare cut stop.