Drop-in Bahtinov mask. The one that sits on filter threads can be used with different lenses of the same filter thread size.

What are the special characteristics of these mask?

• The Bahtinov pattern has been specially calculated and adapted for focal lengths of photographic lenses. Various other masks are actually designed for large telescopes with very large focal lengths even if they are offered in a small diameter
• The mask fits and was tested with focal lengths from 100 mm to 600 mm
• The same mask can be used with your other lenses with the same filter diameter
• The mask is installed by putting it into filter thread ring of the lens. If a filter has the same outside diameter as its thread, the mask can be used on the filter as well. A protective ring makes sure that the mask does not touch the lens surface
• I always use such a mask myself, because it works well and I still use a few photo lenses for astrophotography
• The mask comes in a storage box. The box is labeled with the size of the selected filter thread, e.g. "77mm"

Please select the right filter thread size in options selection list.

Attention: the minimal supported focal length is 100mm. The mask works with shorter focal lengths, but you will need large magnification on the display or an external monitor to see the defraction effect needed for focusing.

Please note that these masks are not screwed into the thread. They just sit there and will fall out if the lens looks down. Well, this should not be a problem when pointing towards stars... 😉

Please note that the material of the mask is heat-sensitive and starts deforming at 50˚C and hotter. Thus, the mask should be not left in the sun, for example.