View Full Version : focusing with DFK21AU04.AS

January 31, 2011, 20:02:18
I have just purchased a DFK21AU04.AS and i am having difficulty focusing on any star. I have a skywatcher ED80.
Using IC Capture to see the live view, i have focused right in and right out but to no avail. The camera does work because i have tried it on a streetlight and that was visible in IC Capture

Has anyone used the DFK21AU04.AS with the SkywatcherED80, and could give me an idea of the focusing position of this camera.

Thanks in hope someone can help


February 2, 2011, 11:36:00
Focusing is quite difficult and not to be underestimated!!!!

It isn't your camera or scope....both are just fine! However, I'd suggest that you start with the moon. If you can get that to focus then you can be sure that your eyepiece focuser will travel to the correct length to focus on a star. You may need an extension tube, but probably not.

Stars are considerably harder. Start by picking a medium bright star you can find and put up your gain to a point where the image doesn't blow out. Also, pick a reasonably fast shutter speed. If you focus slowly you ought to be able to identify a narrow range of focuser position where you cannot detect a change in the image. This puts you close, but not good enough! Some capture programs, such as K3CCD Tools have a focus program that may help, but I'm not sure if the DBK camera will run with it. What you can do is capture a short video of you almost focused star, then play it back to see how close it is to focus. Then make a small change and repeat until you are as close as you can get. Once you find focus then lock down your focus tube and move carefully to the star/planet you want to photograph

But, really the best way is to invest in one of these types of focus masks: http://www.spike-a.com/?gclid=CN-cvLyu6aYCFQHybwodaRns0w or http://www.kendrickastro.com/astro/kwikfocus.html

I just got one and it is really amazing.

May 3, 2011, 13:04:27
I just got my DFK 21AU04.as and put into the eyepiece holder of my 10" Meade GPS. I looked at Saturn and focussed on the computer screen with no issues. I have a standard Meade supplied manual focus and Meade microfocus controlled by the handbox. I thought the image was great for a first time user. I will probably order the mask mentioned and get more precise.

May 3, 2011, 14:04:06
The Bahtinov Mask (first link above) is probably the best focusing mask most amateurs can use. It works very well on stars. In addition here is a link to FREE software that works with any Bahtinov Mask and will allow you to focus within 0.1 pixel accuracy with any CCD, including the ImagingSource cameras. It is all I use.

The link:


Hope this helps.


May 19, 2011, 13:01:43
This mask seems a good idea, but it looks like you would have to use it for each object. I have to center the object in the eyepiece, then remove the eyepiece and carefuly insert the camera, and then focus with obect on the computer screen. If the object is faint, e.g., M3, then I can't see it all now, so I am wondering if this is practical for dim objects, and just primarily for planetary focussing.

May 19, 2011, 21:27:44
The way to use the Bahtinov mask is to focus on a star.I usually use Polaris because it does not move.I focus the telescope with the mask and then lock the focus and slew the telescope to the object I want to photograph.The purpose of the mask is to get the telescope focussed at infinity.You can try manually focussing on a planet, but unless you have very very good seeing you wont get as sharp a focus as with the mask.
So If I am shooting Jupiter I focus on Polaris,lock the focus and then slew to Jupiter.
You will find centering the object you want to photograph is much easier if you use a flip mirror.The flip mirror allows you to have your camera attached to one of the mirrors ports and an eyepiece to the other port.You center the object with your eyepiece and then flip the mirror so it projects the image onto the camera.
It is very hard to center the object if you are constantly switching out the eyepiece and camera ( I used to do that). The flip mirror makes centering the object you want to photograph very easy.If you like I can post a pic of my setup so you can see how it works.

As far as deep space objects they are much harder photograph.You really need a flip mirror for these since the object weill not likely show up in the live view of the camera because you will need a long exposure for the camera to "see" a dim object.
I center the DSO with my eyepiece (with an illuminated reticle so I can center the object accurately) and then I flip the mirror so the camera receives the image and I set the exposure on the camera to 20-30 seconds.After the camera has exposed you should see the dso in the exposed frame.You can use the histogram feature of the camera to make sure you have captured enough photons to get a good image.
For DSO is like the peak of the histogram to be about 1/3 of the way from the left.For a planet I like the histogram to reach all the way to the right.

October 24, 2011, 22:36:26
Using a ST80 will require an extension tube (like the Orion 1.25" extension tube) in order to achieve focus with the DMK.
You require about an 1" or 2" extension tube.