Bahtinov Mask tool

[chongo228]

Not really a "how do I"....more of a can I do it better.

I use the display histo stretch to dial in the bahtinov mask first.....I love this feature. I can focus with narrow band filters with around a second or less exposures.....before I realized the display stretch was there I had to expose 8 to 15 seconds depending on the star.....awesome feature.

Once I get it close with my eye I start up the Bahtinov mask tool. I've found that early in the night when my scope is cooling or the target it low the bars differ a decent amount form one exposure to another as you would expect with bad "seeing". I usually dial it in so that some of the bars are on both sides of the line.....I figure this puts me in the middle of bad "seeing". Once my scope has reached temp after an hour or two I do it again....usually when changing filters....at this point the bars usually don't dance as much.

My questions are this....

Does changing the black point and noise reduction change how Sharpcap reads the lines in the BM tool? Sometimes I adjust these settings and it seems to shift the bars an equal distance one direction. Is there a rule of thumb for setting black point and noise reduction....like you want to see a little of the star blown out around the middle...or go for no blow out? I usually adjust gain, black point, and noise reduction so I get a little blow out from the star and 3 or 4 of the little "dots" in the tail of the diffraction spikes.

Does Sharpcap count the pixels between the lines at a set distance from where the lines intersect? How does it calculate the readings?

My 80mm shoots around 2 arc seconds and my 130mm shoots around .8. When I use my 80 I usually don't scrutinize the BM tool as much as I do with my 130. Figuring that fine detail can't be seen at 2 arc second anyway. I usually spend 2 or 3 times longer trying to nail it with my 130mm. Is this the wrong approach?

I've played with some of the other focus aids and this one seems the best to me.Looking for any pointers or input from others. Great tool....It consistently shows I can get pretty good with my eye....but I've never nailed it with my eye alone....The tool always shows room for improvement.

[BlackWikkett]

I use this BM Focus aid quite a bit. Any changes you make, exposure, gain the noise reduction or black point in the focus tool will change the readings. When ever I make a change to any settings I make sure to click the reset in the focus tool. This allows for a new base line for any changes you've made. Based on the camera and scope I'm using I find settings that will consistently draw the lines in the BM tool. This is where I start the focusing and may have to make slight adjustments based on sky conditions.