Newbie Question-Focusing

Being a Newbie to CCD Imaging and currently on a huge learning curve I am now tackling the issue of focusing. What method are you experienced imagers using..Software...Hartman Mask...Stellar Technologies Stiletto IV..Flip Mirror??

Thanks in advance for any info

Hello Hans, and welcome to The Dark Side of Imaging... 8)

Focusing is the most critical part of Imaging, and as you mentioned, there are a miriad ways to accomplish this...

I particularly use the Focus IN-OUT method, going several times back & forth until I get what I believe is the tightest focus (on a star).

Imaging software will give you readings that could tell you when you are at the optimal focus, based on some values that it represents on the screen. (Maxim DL will do this, for example)

I'm gonna make a Hartman Mask for my scope, but have not gotten around it yet...



Clear skies! 8)

Hello Hans,

I use software-based focusing (@Focus in CCDSoft, on to Maxim's focusing routines, onwards and upwards to - freeware FocusMax). I started off using a manually-controlled electronic focuser (JMI NGF-S), then moved on up to a computer-controlled focuser (Robofocus).

The difference is night and day. Manually focusing can be a chore - no fun in the cold - so it's easy to get sloppy. Computer-controlled focusing has eased the task so much that if you are so inclined, you can refocus quickly and accurately between exposures.

HTH,
Eric

Hans,
I generally first go to a bright star to get rough focus down visually on screen. Once I get to my target and have filters in place I'll use the focus routines in AstroArt. It is far easier on my small refractor with fine focus knob than on my SCT with image shift! Also, if you are using filters, remember to refocus with each one.
Have fun,
Larry

I use DSLR Focus mostly.

On my newt 10" F4.5 newt, I have a homemade parfocal adapter. I glued a surplus 2" to 1.25" adapter to an appropriate rear lens cap (that had a hole cut in the middle. I use this adapter to locate the object and do the intitial focus. I can then remove it from the t-mount and place the camera on the t-mount already mostly focused.

I then use DSLR Focus. There are other programs that do the same job though. The only two I have is DSLR Focus and Images Plus, and, despite the improvements in IP 2.8, I still like the process better in DSLR Focus.

I also use an electric focuser with a step controller. ON the SCT, I have a stepper motor, and can go back and forth exactly. On the newt, I have a DC focuser, and the steps are not quite repeatable. But at any rate, I would suggest you use an electric focuser so that you can avoid touching the scope while focusing. I also recommend a motor controller with a step in it (sends out a pulse instead of continuing power) so you can control just how much the focuser moves each time you hit the button.

Remember, the depth of focus is less than part of a millimeter--easily enough that just touching the focusing knob can send the focuser right through the critical area and out the other side. So, relying on your hands becomes difficult.

I also have a Stiletto CVF (or whatever it is called). I think it would do a good job, but I have not used it too much at night. (I bought it for eclipse photography.)

I do use a flip mirror on my guiding port--but I would not rely at all on the flip mirror for focusing the main camera body. There is no guarantee that the eyepiece on the flip mirror is in exactly the same place as the camera body. It is sufficient for the ST-4, but not for critical image focusing.

Alex

Thanks all for the info..it's a real help and has given me an idea of what direction I want to head in regarding focusing.