Focusing Aids

On this page, I report on several focusing aids that I bought or which were delivered together with tlescopes that I bought.

Overview

Both with my Atik Infinity camera and when photographing with the projection method, I had problems with focusing the telescope reliably. I therefore bought two focusing aids on the AME2018 astronomy fair in Villingen-Schwennigen, Germany, for my Sky-Watcher 6" Newton (Explorer 150PDS): a Bahtinov mask from Lacerta and an "easy-sharp" focusing mask from noctutec.

Note: I cannot report any experiences here, because I never used these masks in practice and sold them together with the Explorer 150PDS in early 2020.

However, with the eVscope that I received at the end of January 2020, I got another Bahtinov mask, which is inserted into the tube cap for storage; the same was true for the eVscope 2 that I purchased thereafter.

Note: Both eVscopes were sold in the meantime; I therefore cannot report any further experiences here.

And in May 2021, I purchased a Bahtinov mask for my PS 72/432 refractor from TS-Optics, because I was having trouble focusing the images with the newly acquired ASI224MC camera.

I have successfully used both the Bahtinov masks for my eVscopes and those for the PS 72/432.

Bahtinov Mask

Photo: Bahtinov mask (Lacerta, for 150 mm aperture), delivered with 3 clamps

From the product description (from Astrogarten, translated):

Focusing aid for exact focusing of a camera within a few seconds
Just set a symmetrical image
For attaching to the telescopic opening

How to use the mask (from Astrogarten, translated):

No more guesswork, whether the stars are in focus or not. You simply place a Bahtinov mask on the front of the telescope and look at the resulting diffraction pattern of a star.
Three so-called "spikes" (of a a total of six) are created on each side of the star, with the middle spike being movable. Now focus the telescope to place this spike symmetrically in the middle. On closer inspection, a weaker "star" becomes visible between the spikes and the main star. This star must also be set/resolved symmetrically for all spikes: That's it!
Using this procedure, you can focus an image to 100% sharpness in just a few seconds.

A photo of what a correct setting looks like can be found on the product page on the Astrogarten Website (author: Nils Kloth).

At my first attempt with this mask I saw the "spikes", although not always evenly bright. The focusing with the Bahtinov mask seems to have worked to some extent. But this was just a short test on the eyepiece. The "easy-sharp" mask, which I also tested, seemed to be more "stable" and easier to adjust.

Note: I cannot report any experiences with the mask, because I never used it in practice and sold it together with the Explorer 150PDS in early 2020.

"easy-sharp" Focusing Mask

Photo: "easy-sharp" mask (noctutec, for 150 mm aperture)

Description (from noctutec, translated):

The noctutec focusing mask "easy-sharp" guarantees ideal sharpness for astrophotos.
Suitable for all GSO and many Sky-Watcher-based systems with 6", 8", 10" and 12" aperture. The mask is easy to use, and quickly produces perfect results.
Do not be annoyed any longer by hard to be judged, wriggling diffraction lines, as they are known from other masks on sparkling stars, or from moderate a horizon seeing. With "easy-sharp" the result gets simply sharp.

Procedure (from noctutec, translated):

If you point the telescope with the noctutec focusing mask "easy-sharp" at a star, you will see three stars with three 120° offset spikes in life view or on your laptop.
The closer you get to the focus, the more the stars move towards each other.
Once you have reached the ideal focus, the stars superimpose each other and six very fine spikes become visible. The focus is now ideally adjusted. Thanks to the large apertures, this works very well even for fainter stars.

Photos of how to approach a correct focus can be found on the product page of the noctutec Website (provided by the Volkssternwarte Köln).

At a first attempt with this mask, I saw the above-mentioned three stars offset by 120°, and also how they superimposed. Focusing with the "easy-sharp" mask seems to have worked. But I cannot remember the 6 spikes anymore... Anyway, this was just a short test on the eyepiece. The "easy-sharp" mask seemed to be more "stable" and easier to adjust than the Bahtinov mask, which I also tested. That is what the advertising claims!

By the way, the mask was too tight to fit into the tube of my Explorer 150PDS. That is why I temporarily held it by hand. This was announced to me by the dealer when I bough the mask.

Note: I cannot report any experiences with the mask, because I never used it in practice and sold it together with the Explorer 150PDS in early 2020.

Bahtinov Mask for the eVscope (2)

Below, I present some photos of the Bahtinov mask for the eVscope (2). For storage it can be inserted into the tube cap. When in use, it is inserted into the tube alone.


Bahtinov mask inserted in the telescope lid		Bahtinov mask next to the telescope lid

Ditto, other side		Bahtinov mask put on the eVscope tube

I have become accustomed to focusing the eVscope with the Bahtinov mask before observation sessions and sometimes even in the course of them. It is too easy to touch the focus control during set-up and misadjust the focus. And due to temperature changes or because hit the focus control while observing, the focus can also change during an observing session. Adjusting focus with the Bahtinov mask* takes a little time and effort, but it is too bad if all you get from a session are blurry photos!

*) To do this, move the telescope to a bright star and make the pattern created by the Bahtinov mask symmetrical. Here are examples of sharp and fuzzy settings when using the Bahtinov mask (brighter star accessed, Live View mode):


Blurry		Blurry

In focus		In foucs, enlarged (tap on the screen 2x)

Update: I sold my eVscope in Spring 2022 and I bougth an eVscope 2 with the same type of focusing aid. I sold the latter at the end of 2023. I therefore cannot report any further experiences with this Bahtinov mask here.

Bahtinov Mask for the PS 72/432

In April 2021, I first borrowed an ASI224MC camera from a starfriend and later bought it from him, which I also wanted to use at my PS 72/432 refractor. However, first tests showed that focusing a camera is even more tedious than focusing visually. I therefore was looking for an approach that provides a clear criterion for optimal focus. This is offered by the two masks described above, but since only the Bahtinov mask was available in the required size, I ordered and received a TS-Optics Bahtinov mask (mid-May 2021). First tests with the mask at the PS 72/432 looked promising!