Getting a sharp focus

[pbyrne]

Hi all

Tonight I got out with my new zwo 120mc a attached to my 127mm Maksutov on the moon.  When the camera was attached to the computer the image on the screen was not sharp, no matter how well I tried, maks can be difficult to focus.  I could not get it into perfect focus, is this normal?  If not, how can I achieve better focus?

I have not processed the images yet, will they sharpen with processing?

Thanks

Paul

[Whistlin Bob]

You might be able to sharpen a bit with processing, but it's unlikely to completely solve the problem. The best way to achieve focus is to make/buy a Bahtinov mask (I made mine from cardboard) and focus on a bright star first, then aim at the moon.

 

This site may help you: http://www.deepskywatch.com/Articles/make-bahtinov-mask.html

[JamesF]

If the seeing isn't great then it can be a huge problem focusing, but on a good day there are a few options that may be worth trying.

One common mod to help with focusing is to make the focuser knob larger thereby allowing finer control, often by modifying something like the lid of a Marmite jar to fit over the top.  Do be aware that you'll need the appropriate hazardous waste disposal licences if you don't intend to eat the Marmite first however

An alternative that I've used myself on the 127 Mak is to put a clothes peg (the type with a spring that closes the jaws) over the focuser knob.  This means you can move the focuser with just a finger and hopefully avoid any shaking of the OTA whilst doing so.

Then there are electric focuser mods and secondary focusers, but perhaps that's going a bit far right now.

If you search the site in the DIY section you'll probably find quite a few examples of mods along these lines.

Something else worth being aware of is that it's not uncommon for the mirrors of Maks to "rock" a little on the bearings when the focuser changes direction, meaning the focus point isn't necessarily in the same place depending on the direction you approach it from, so you may find you need to make allowances for that.

James

[Cosmic Geoff]

The seeing could have been bad.  The images should sharpen with processing, but you won't know how much till you try it.   You may also need to allow the Mak a bit of time to cool down.

I always focus my 127mm Mak & ASI120MC on a star rather than on the Moon or planet, and just adjust for the most point-like image.  This also gives a feel for how bad the seeing is. 

[pbyrne]

Got to processing the images and these are the results.  I still need to work on my focusing and improve my post processing techniques.  Still, I am quite pleased with my initial efforts.  Any tips or critiques are most welcome.