Bahtinov Focusing Mask Generator Version 0. Input values appropriate for your telescope, and press the Generate! Basic parameters Enter these three values, press Generate! Focal length mm Focal length must be a positive number. The focal length of your scope, in mm. Aperture mm Aperture must be a postive number.
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Better Focus using a Bahtinov Mask February 4, Tutorials 10 Comments A Bahtinov mask can help you achieve a sharp focus for your astrophotography images.
This process is an essential step of any deep-sky astrophotography session. With so much time and effort put into your polar alignment and autoguiding accuracy, it would be a shame to spoil a photo due to poor focus.
In many cases, I did not realize how bad the focus of my image was until I attempted to process the final image. You can avoid this unfortunate circumstance by using a simple tool that effectively confirms that your focus is as sharp as can be, a Bahtinov mask. Related Post: Practical Focusing Tips for Astrophotography Use a Bahtinov mask for better focus No matter which type of camera you use, a Bahtinov mask can help you achieve a higher level of accuracy when focusing your telescope or a camera lens.
The process involves placing the focusing tool on the objective lens of your telescope or camera lens, and observing a bright star. The design itself was created by Russian astronomer, Paul Bahtinov. The mask helps visual observers and digital astrophotographers to achieve a razor-sharp focus in seconds. Other types of focusing masks include the Hartmann mask and Scheiner Disk. Why Focus is Critical for Astrophotography In general, the smaller the stars are in your image, the better.
One of the reasons I love apochromatic refractors , is their ability to capture colorful, pinpoint stars. However, this pleasing characteristic is only present when your focus is spot-on. Refractor telescope owners expect razor-sharp details in their photography, so mastering the art of focusing stars is a must.
An image of the Eastern Veil Nebula with sharp, pin-point stars Different types of telescopes have better ways of achieving a sharp focus than others. For example, a Newtonian reflector creates its own star diffraction spikes by nature of its design. These patterns can be dissected and tweaked to diagnose issues with collimation and find a sharper focus for astrophotography. Automatic and motorized focuser users have the ability to use software that tells them when a star is as sharp as possible.
But if your shooting with a DSLR camera or dedicated astronomy camera and you just want quickly confirm your focus is on — using a Bahtinov mask is one of the easiest ways to do this. The diffraction spikes Bahtinov mask from William Optics is a patented design, and it works exceptionally well. You may have noticed me using this focusing tool in a number of YouTube videos.
The optical acrylic material really helps to create large, intense diffraction spikes that make focusing easy. A nice bonus to this tool is that it also aids in the star alignment process. When the acrylic Bahtinov mask is applied, you will begin to see the elongated star spikes enter the image frame long before the actual star itself.
If I need to make a slight adjustment, and I can easily do so between sub-frames. I enjoy the simplicity and visual nature of diagnosing and correcting the star diffraction spike pattern.
This technique provides instant gratification in real-time, which is rare in this hobby. Bahtinov masks are inexpensive and easy to use. The openings in the mask design create a set of diffraction spikes on the star that will assist in the accuracy of our focus. The diffraction spike pattern from a bright star using a Bahtinov mask As you adjust the focuser of your telescope, the central spike will move in and out of the X-pattern.
I prefer to use a loop of about 4-seconds for a bright image using Astro Photography Tool. The difference is, the image will be much dimmer, as you are essentially looking at a live video feed rather than a short image exposure.
You can also magnify the center of the pattern to get the focus just right. When you are in focus, bright stars in the night sky will appear on the screen. Even a subtle change in focus can be the difference between a star that is in focus, and one that is so far out that you cannot see in on your live view display. Because it is so dark at night, your live-view screen may appear as pure black when looking through your telescope.
These stars are all bright enough to appear on your live-view screen. Slower shutter speeds will dim the star, and we want it as bright as possible for focusing. Adjust the focus knob on your telescope And finally, focus your telescopes draw tube until you see a bright star appear on-screen. You may be way out, so make sure that you check end-to-end. What about using a camera lens?
The same settings apply if you are using a camera lens in place of a telescope. The only extra step you will need to take is to make sure that the lens is set to its fastest aperture. Other Ways to Focus Your Camera If you are not satisfied with your results using a Bahtinov mask, you can improve your focusing accuracy using dedicated astrophotography software like BackyardEOS. BackyardEOS was built to help astro-imagers improve their acquisition process in the field.
This function associates a value on the star you have selected in a target window. Using the live view mode within BackyardEOS will show you a real-time image of a bright star in your field of view. Focus is achieved when you get the lowest value for the same star over time, indicating a tighter star. BackyardEOS implements FWHM by calculating the standard deviation the square root of the variance of all pixel values in a very small selected area. If your camera settings are correct, and your focus is close, you should see a number of stars on screen.
I prefer to choose a medium-sized star within the frame as my target star. Double click the target window around your chosen star. This will show a zoomed-in preview window at the top right of the interface. You will now notice a number below this zoomed star image, and this is the value we will monitor to achieve a high accuracy of focus.
The Zoom box center can zoom in on the star if desired, but I prefer to use the default 3X zoom. Adjust the fine focus knob on your telescope and watch as the number associated with that star changes.
The goal is to get the star as small as possible, with the lowest number. There is no set number to reach, as stars vary in size. On a medium sized star, I usually reach a number as low as 3. Once you have reached the lowest number possible for that star, go ahead and lock your focus into position using the lock screw on your telescope. The photo above is misleading because you will only be adjusting focus and referring to the FWHM number when the mask is off.
The Zoom box is used for an up close look at the star diffraction pattern only. A real reading of the star size can only be obtained when the mask is off. Test Exposures vs.
Live View For my small refractor, the live view image was not bright enough to get a useful star diffraction pattern. Instead, I used short preview exposures the Snap Image button and made adjustments back and forth. After about 3 slight focus adjustments, I was able to produce the ideal star diffraction pattern to indicate that my focus was as sharp as possible.
The nice thing about the Bahtinov focus mask is that the star diffraction pattern provides you with a useful visual aid. Slight changes in focus are evident in the star pattern right away. This telescope upgrade allows me to me micro-adjustments to focus without touching the telescope. Aside from being able to make fine adjustments to the focuser, it also means that I can now adjust the focus remotely from inside the house.
This comes in handy on those cold winter nights with the gear running outside. The Pegasus Astro Stepper Motor Kit installed on my Telescope It now has this ability to focus on its own, although I have not deployed the autofocus features as of yet. The dedicated focuser software reads the star size information and communicates with the motor to make small adjustments to the focuser as needed. A temperature probe reads the ambient temperature outside to decide if a focus tweak is required.
As for the rest of the telescopes I use, the Bahtinov mask makes the focusing routine simple and straight forward. Helpful Resources:.
This is the same method I used to build an aperture solar filter as well. Required tools and materials: Binder made from hard, thin plastic must be non transparent Stanley or a hobby knife and scissors Contact glue Ruler and a marker pen Printer A3 if possible for larger scopes Required materials for a 8" mask First step was to print the mask - you can use the provided templates , or use the original bahtinov mask generator , and then print it any modern browser can open the generated. In my case I had to print the mask on two pages. Then I cut one half of the plastic binder, and attached to it my printed mask. It is important to keep the lines straight and parallel to ensure that diffraction spikes will be bright and thin Then the annoying task - cutting the plastic.
Home Made Bahtinov Focusing Mask & Templates
Although masks have long been used as focusing aids, the distinctive pattern was invented by Russian amateur astrophotographer Pavel Bahtinov Russian : Павел Бахтинов in The mask consists of three separate grids, positioned in such a way that the grids produce three angled diffraction spikes at the focal plane of the instrument for each bright image element. In reality, all three spikes move, but the central spike moves in the opposite direction to the two spikes forming the "X". Optimal focus is achieved when the middle spike is centered between the other two spikes. Small deviations from optimal focus are easily visible. For astrophotography, a digital image can be analyzed by software to locate the alignment of the spikes to sub-pixel resolution.
Make Your Own Bahtinov Focusing Mask
It is named after its inventor Pavel Bahtinov. The Bahtinov Mask is a variation on the Hartmann Mask which uses three separate grids. The grids are aligned in such a way that they produce three angled diffraction spikes on the focal plane of the instrument for each bright star or planet. Optimum focus is achieved when the middle spike is centered on the star and symmetrically positioned between the other two spikes. Small deviations from optimal focus are easily visible. Creation of a Bahtinov Mask is very similar to that of the Hartmann Mask.