Astro-Physics

The filter thickness is 2mm. You find such informations when you scoll down the product page (after you selected the filter size) and then you see a tab "specifications"

We are very sorry, we only offer the filters you see on our website and there is mentioned that we offer these filters only for Canon DSLR. There are no plans to offer filters for Pentax Cameras because we need to manufacturer thousands of filters at once - and the Pentax Cameras are not common among amateur astrophotographers so that it would not make sense.

If the filters are used outside the specified aperture ratios, there is a strong loss of contrast of the photographed object which increases towards the edges of the image.

Thanks for your follow up. You are right, we the female T-2 thread this clamp can be used for T-2 diagonals as you described. However unfortunately it is not possible to reposition the lever here as with other 2" ClickLock clamps. The screw you described is cemented and needed for the ClickLock functionality, it can't be removed.

Making a zoom become waterprove has severe consequences. The designer must decide if he can accept a hard rotation action or not. For use with a spotting scope it "could" have been be made waterproof by fitting O-rings into the rotating mechanics to seal the moving area. However - this does work on a short and relatively lightweight spotter - but the rotation movement of the zoom-action in this case is getting stiff and hard to rotate.

For an astronomical telescope this would be an impossible behaviour because the telescope would wiggle when the zoom-action is so hard to turn - especially in winter.... Also the "Click-function" would become impossible to feel - the whole eyepiece would become "just another zoom".

So - in order to enable an effortless zoom action with the click-stops to be just sightly noticeable (if these are "hard-clicks" likewise astronomers do complain!), we omitted a tight seal in the area relevant for the zoom action. However - as soon as the eyepiece is connected onto a telescope (or spotter), the upper lens parts certainly are O-ring sealed and the eyepiece can justifiedly be called water resistant, because rain will not enter.

At any rate - if you are in need of a completely watertight solution for harsh outdoor use on a spotting scope, this eyepiece may not be a solution for you.