Does F10 Matter in CaK?

[sullij1]

Here are a couple of pics as a reminder:

[brianb11213]

Mark, thanks, perhaps a person may be able to achieve a minimal amount of tilt using that method but the set screws are for spacing and retaining the filter in the barrel.
Minimal is the word, mine is quite a tight fit.

The actual filter element in the objective facing front element in my B1200 is tilted very slightly in its mount ... so when pointed accurately at the sun, the bright patch on the objective illuminated by the mirrored surface is off centre (but wholly within the free aperture of the objective). I suspect it's better to have the reflected heat passing through the glass rather than heating one side of the tube / objective cell which would be likely to cause tube currents and/or distortion of the objective by differential expansion.

If there is a contrast reduction caused by reflection off the mirror surface & back off the objective, this will probably depend critically on the curvature of the elements in the objective as well as the efficiency of the anti-reflective coatings on the objective at 393 nm. The only thing I can say here is that, from practical experience, my B1200 CaK module seems to deliver slightly more contrast with my f/7 FLT 110 than it does with the (supposedly CaK optimised) Lunt 60mm f/8 scope it came with. There's not much in it but I'm convinced the effect is real.

[marktownley]

Looking at the pictures looks like you could also alter the tilt of the filters in the cells they are mounted by pulling off the 'gobs' of silicone seal that seem to locate them in place and resealing them in place again, maybe... You don't need much tilt, the sun is only half a degree across and you only want to throw the reflection by slightly more than this.

[sullij1]

Honestly, when doing full disc and close-up in active regions etc. It is not much of an issue. The only time it is a hassle is when trying to grab CaK proms. Then it becomes frustrating trying to keep the reflection out of the close-up prom image.

[Pedro]

I agree, capturing CaK proms is not easy. I've tried lots of times without success. I guess that the DMKs are not good cameras for this kind of work (low blue sensitivity). I've seen great prom images with PGR cameras though.

Pedro

[marktownley]

I guess that the DMKs are not good cameras for this kind of work (low blue sensitivity). I've seen great prom images with PGR cameras though.

Pedro

I've never thought about it this way before Pedro, but I think is a very good point...

[Derek Klepp]

This tilt issue is prominent when it comes to prom capture in CaK I find that my success is dependant on where the prom is in relation to the module set up and that I had best sucess using a 2.4ext on my camera. I am still experimenting here.

[swisswalter]

This tilt issue is prominent when it comes to prom capture in CaK I find that my success is dependant on where the prom is in relation to the module set up and that I had best sucess using a 2.4ext on my camera. I am still experimenting here.


hi Derek

very interesting addition

[sullij1]

Hi Derek, It just dawned on me after a month, of what you were trying to say about te extension helping with the proms. Can you show a pic of how you set up the extension? I am interested in getting better CaK prom in my images.

[sullij1]

:woohoo: >2000 views! Guess there was some interest here. Ya think!