TheSkySearchers

Being I'm getting older, my eyesight is not as good as it was. Many times I find that I spend lots of time getting things focused to where they look good to me but when I process them I discover that what I thought was focused was not. So I thought I would start this thread to both, ask how others are accomplishing good focus and some of the techniques I have used.

For both photography and visual work the good old "Hartmann mask" https://www.iceinspace.com.au/index.php ... 87,0,0,1,0. I have used my version of this on some of my smaller scopes in the past. It works well and is inexpensive to make. (I used the bottom of an old butter container).
Also there are Bahtinov Masks. These work similar to the Hartmann but I found the Bahtinov is a bit more 'accurate'. These can be purchased from most telescope vendors, and you can even make one yourself!! https://www.deepskywatch.com/Articles/m ... -mask.html

I'm now using electronic focusers on my telescopes so for deepsky I'm using the 'autofocus' tools that most of the capture software provides. Nina is the one I use the most. https://nighttime-imaging.eu/docs/maste ... autofocus/. As mentioned in their article, you can set the autofocus to re-adjust while taking long multiple exposures.

For Solar, Lunar and planetary it's a little more difficult. Sharpcap uses a method to autofocus, but I personally haven't had a lot of luck with it for solar images. The constant in and out of focus because of the atmosphere. The waviness is caused by turbulence in the atmosphere, so there's not much that can be done to combat it. Taking video of the object rather than trying to capture a single shot is one way. Using stacking software like Astrosurface http://astrosurface.com/pageuk.html or AutoStakkert https://www.autostakkert.com/ will allow help you select the best images to stack.

I would like to hear what others are doing.

Gordon

I have used a bahtinov mask for focusing for several years. I have used it both with BackyardEOS and APT tools to do the measurements, as I don't seem to have much luck figuring out the proper position for the "X" when looking by eye. I believe N.I.N.A. has a bathinov tool in the "imaging" tab as well. Someday I get an electronic focuser but for now the manual way with the mask is my go-to.

Bob

I started out using a Bahtinov mask. It is a little bit tricky to use on a Newtonian, because you have to coordinate the spikes from the mask with the spikes from the secondary spider. Without proper coordination, they can interfere with each other and with the focusing process. With careful use, it was very accurate.

Drawbacks of the Bahtinov mask are: forgetting to remove it (you will, I guarantee it!) and having to be out in the cold. As I automated my sessions, I switched to a focus motor and automated focusing. After getting the focuser parameters, especially backlash, dialed in in the software, it has been very reliable.

I haven't done much planetary imaging. When I have, I mostly just focused by eye. For solar imaging, specifically the transits of Venus (2012) and Mercury (2019), I made a Hartmann mask, which was fairly easy to use.

I use a Bahtinov mask for all my scopes that need critical focus.

I used to use a bahtinov mask and found it easy and reliable. I use APT which has a tool for measuring the spike but I never really got on with it.

However, since attaching ZWO EAFs to my scopes I do it automatically using the autofocus tool in APT.

Like David, I use acquisition software for autofocus. Like Gordon, I use N.I.N.A. for autofocus and had good success with it right out of the box.
In fact, I recently installed the N.I.N.A plugin "Hocus Focus" which is superb. Not only does it focus by averaging star HFR in the chosen region of interest, it also rejects stars of insufficient brightness or irregularities such as eccentricity.

Hi Gordon - I used a Bahtinov mask in the beginning and always had good success with it. Once I was able to control my equipment from a laptop in the house I purchased a motorized focuser for the telescope. I continued to use the Bahtinov mask for a while, but, didn't like having to go out and put the mask on for focusing and then go out and take it off after focusing (sometimes forgetting to take it off!). Finally I switched to software auto-focus when it became available on APT. It has always worked well for me.

Steve

Thanks for the info on the Hartmann mask Gordon, I'll have to make one and try it. I'm mostly Solar/Lunar for AP, so a Bahtinov doesn't really work for me.

I'm "building" a portable Solar white light setup; almost finished and probably have spent too much. I'm hoping to do what I did with my C80-HD; that is, lock it into focus on the Moon (pick some prominent craters and go from there) and then you're good to go with the Sun.

Still, it would be nice to use the scope I'm making with this for visual, and the Hartmann mask might be my ticket to "eyepiece to AP", so to speak. Thanks too for the link on the proper way to make one, everything else I've found so far is really a general idea...

Much appreciated!

Hi Gordan,

I'm one of the few hold outs, I don't auto focus even though I have EAFs on both my scopes. I sometimes use the Bahtinov aide in APT, but I normally use a tool called Focus Aid. It measures HFD, I get is at low as I can, usually about .5 on one of the stars closest to the edge oi the FOV.

Clear Skies,
Chris

Like most folks here, I started with a Bahtinov mask and then moved to a Pegasus Autofocus. Getting the backlash dialed in took a bit of work but now that is dialed in it's really convenient. Overall I get much better focus since I went ahead and automated. Also, the autofocuser will automatically refocus when the temperature drops. The autofocuser is also super handy when switching filters using a filter wheel.

I use autofocus in APT and refocus every 1.5 degrees change in temp or on filter change , I was using inverted method in Apt but switched to hfd for now as I can’t seem to get inverted to work properly at the minute since changing camera to atik 490 mm and I use better of two algorithm, if your doing imaging you definitely need to refocus if temperature changing a few degrees during the night imo.