Lots of talk lately about various adapters, so I thought I would add two that I have found useful. Possibly some others will as well. These go from T-mount to M42 and just the opposite... M42 to T-mount. (These mounts are both 42mm but the T-mount has a 0.75mm pitch and the M42 has a 1mm pitch)
Here in the US I got them from Hutech Corp in Torrance, CA. These are Borg/Oasis/Tomytec branded, and marketed by firms dealing with telescopes and other astronomical products. No.7855 is the (female) T-mount thread to (male) M42; No.7856 is the (female) M42 to (male) T-mount. (Occasionally I've seen similar adapters on ebay.) These are very nicely made (Japan) and cost $23 each.
We've talked a great deal about microscope objectives lately but it's been a long time since we hashed over flare issues. One thing to remember is that many of these objectives have bright metal or chromed outside barrels. In our bellows adapters with straight through holes this presents a bright ring inside the bellows. (A microscope nosepiece blocks the outer edge, so it's not an issue there). This can really create a flare problem in some shots. (I first realized this when I tested a Nikon objective some time ago. I thought the objectives was damaged or defective since the images looked so bad. Once the bright ring was covered all was well.) This can be blacked out on the objective itself, or masked out on the adapter (as I have done with the black flocking material shown here.)
Have questions about the equipment used for macro- or micro- photography? Post those questions in this forum.