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AstroZap - AstroCaps - Bahtinov Focusing Caps

SKU AZ-402


Getting perfect focus with the telescope when making astrophotographs can be very difficult to do, and serious astrophotographers have long used various tools such as Hartmann Masks, or knife-edge focusers. In 2005, Russian astrophotographer Pavel Bahtinov created a mask that fits over the front aperture of a telescope to solve this problem with high accuracy.

The Bahtinov 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. As the instrument's focus is changed the central spike appears to flipåÊfrom one side of the star to the other. Actually all three spikes move but the central spike moves in the opposite direction to the two spikes forming the 'X'. Best focus is reached when the middle spike is centered between the other two spikes.

In digital astrophotography it is relatively easy to examine the stars for tiny deviations in focus with images made with theåÊBahtinov Mask with image processing software. Once you gain experience with this device you can even understand which way to turn the focus knob to achieve sharpest focus.åÊThe Bahtinov Mask is truly a must have device for almost any astrophotographer.


The image below shows a simulation of the Bahtinov mask diffraction pattern as the image is brought from out of focus to focused to out of focus again. Image souce: Wikipedia.

We carry the full range of Bahtinov Mask devices from Astrozap. They are made from lightweight aluminum, finished in a durable textured black powder coat finish. This series have three subapertures that open for focusing, and can close to serve as a focusing device and a front dust cover cap that attaches to the front of the telescope, giving double duty for focusing and protection. Of course the mask is removed when making astrophotographs or for visual observations when the most perfect focus is desired.

Astrozap makes these Focusing Caps with the Bahtinov Mask to fit telescopes with apertures ranging from 90mm to 405mm. They are held in place with three thumbscrews to to outer edge of telescopes's front cell or dew shield.

★ Reviews

Let customers speak for us

19 reviews
Exceptional Mount

A couple of years ago, I wanted to replace my old VMA200 mount with something more modern.
While visiting the Paris Astronomy show (RCE 2012) I noticed the Nova120. At that time, it was a brand new offering that I have not seen before, hence my hesitation to purchase
I wanted to purchase a E.U product to guarantee the quality and ease of access to support in my own language. I checked the forums and heard nothing but good things about the Nova120 so I decided to purchase it.

I have used enough astronomical instruments in the last 30 years to know what great quality is. The Nova120 coupled with the PRISM v10 and a CDK20 (508 mm) helped me pull off 900s unguided images with great ease. (Raw FITS File here). Payload of this setup is about 80 kg (160 lb).

The dizzying slew speeds, excellent accuracy and painless tracking makes this hobby easy and enjoyable again.
After using this setup for a year and a half, the only problem I had was rebalacing the gear after changing scopes. The superb electronics and software included make this tasks even more easier that just eyeballing the scope for movement due to unbalance.

You can very easily watch the motor consumption and know where the unbalance is....that easy. I have so much data that it is becoming difficult yo keep up.
I have absolutely zero regrets, this purchase has made everything easier: No summer/winter worm-gear adjustments, no guiding... just start imaging night after night after night.

Eric Barbotin

Imaging Made Easy

Prism is my GoTo program for observatory control and imaging. Prism's many features make imaging taking a breeze.

I was concerned about giving Prism a try , especially as its quite expensive. So far Im very impressed and glad of my decision.
Im a beginner at all this so haven't tried other more recommended software, Prism appealed as it seems to do everything instead of using several programs 👍🏻

Great lightweight guide scope

This guide scope replaces a 400/80 that was waaay too heavy for what it did. The smaller 60mm scope does a great job guiding and I can RA balance with just one counter weight now - much better - and it looks like something Ferrari designed

Still learning Prism using Wireless links...

I have much of your software working at this time... I have it parked on my main computer, and a notebook... My main computer is a OverClock computer with 32 Gigs of RAM Clocking presently at 4400MHz with software parked on SSD drives... The rotation dome by NexDome is still not working... Most problems like this have to do with ASCOM Drivers... There is not very much detail information on how to use this software... I have to feel my way to a total operational staus... Second issue... The rain in the San Francisco Bay Area this year has limited my access to my larger telescope (12 inch SCT)... This rain has been so significant, I was force to weatherize my observatory... My goal here is,,, I am trying to remotely control my observatory totally. I have used Netgear Powerline 2000 to handle camera images and discover controlling rules to do that... High speed is vital for images with cameras over 3 Megs... I have both 12 Mega sensors and 24 Mega sensors... I am also using Netgear Nighthawk router and its mating extender to increase control signals to my observatory that is about 100 feet on the side of hill... I am also using Virtual Here software on a Raspberry Pi inside the observatory to solve the USB interface requirements... I started out using Model B and B+ on level 3 raspberry Pi's... I have moved to Level 4 Raspberry Pi to gain access to USB 3.0 technology... Big difference! I hope by early spring to have everything working... Bob Ritter MicTechS