Quote:
Originally Posted by Mickoid
These look great. I'm amazed at how consistently good your shots turn out. They're better than I get with my 8 inch scope so I'm wondering if shooting at f25 is actually reducing the resolution I can achieve with the 8 inch. Either that, or your ADC really makes that much a difference and I need to buy one of these! I always do a RGB align in Registax. I might try some shots at around f15 and see if I can get better detail.  |
Thanks Michael.
We have done a lot of experimenting and optimising of our optical set up and processing just trying to get the best results possible. So this is some of the things that we do which we are sure you most likely already know, but there just might be something of use.
The ADC is not a silver bullet and only fixes atmospheric dispersion and that's it. Attached are the only images we kept from a with and without experiment of the ADC on Venus in April. Venus does show AD very well. Having said this, we would always use the ADC on planets.
You might have noticed we quote our barlow magnification as 1.8. It's recommended to be at >F10 when using an ADC. This is so the beam is not too convergent and therefore introducing other aberrations. We therefore use the barlow first, then the ADC, then the camera. This introduced some other issues as the magnification of common barlows change with the focal distance between the barlow elements and the sensor, so adding the ADC in there increases the magnification significantly. You can change the barlow magnification a little by varying this length but it does introduce spherical aberration. Telecentric barlows like the Powermates overcome this but the only one suitable for us is 2.5x which is pushing the magnification of the scope and would require excellent seeing. So we removed the barlow element from a x2 barlow, and screw it directly to the nose tube of the ADC which we had shortened by 15mm in a lathe. We then take the nose tube off the camera and the draw tube off the front of the ADC and then use a 42mm male to male thread adapter to attach the camera directly to the front of the ADC. This gives a focal length slightly shorter than the actual barlow body, which was what we were trying to achieve. It calculates to be roughly 1.8 times however, in measurements it is probably closer to 1.9x. This is because the camera sensor is already further back than the focal point using an eyepiece in the barlow body.
Having said all this, a person we know has experimented with using the barlow after the ADC (so the ADC is at F10) and reports that it works OK. This would solve the added focal length with a barlow. We haven't tried this so can't comment ourselves.
Increasing magnification with barlows does require better and better seeing. Also as you increase your focal ratio, for a given camera, you are increasing oversampling. We have tried F25 and F20 and definitely get better results at F18 for our set up.
We use AutoStakkert (AS!3) to stack the images and the RGB align in AutoStakkert. We have tried to use RGB align in Registax with unsatisfactory results. According to the Planetary Imaging book, AS!3 is the way to go for the stacking and then go to Registax for the wavelet sharpening which is what we do and have found to give the best results for us.
