Svbony SV231 Color Correction Filter 1.25″ review

The Svbony company continues to delight astronomy lovers with a variety of accessories. I received an interesting filter for testing to  chromatism suppression – Svbony SV231 Color Correction Filter 1.25″.

Svbony SV231
Svbony SV231

Chromatism in an achromatic lens telescope is a aberration that appears as a blue or purple halo around bright objects (planets, moon, stars). Chromatism appears due to the inability of an achromatic telescope to bring all rays in the visible range into focus – usually only red and green rays are brought together. This is especially actual for fast (f5-f6) achromats. Some people, unknowingly, even consider these halos to be the “atmosphere” of stars or planets. In ED telescopes and apochromats, chromatism can be significantly reduced or even completely eliminated compared to conventional achromatic telescopes. However, the cost of ED refractors and apochromats is significantly higher than that of achromats. I would also like to add that people’s tolerance for chromaticism may vary. Some people don’t see chromatism at all, for others it doesn’t bother them, and for others it irritates them. In my opinion, an age factor may also play a role here, since with age the lens in the eye turns yellow and acts as a kind of light filter. Moreover, a person can get used to the yellow image, and thus not notice the chromatism. My left eye is a little yellowish. But children and teenagers are great at noticing chromatic halos thanks to the young transparent lens.

Characteristics declared by the manufacturer:

How to use an optical pole finder?

The pole finder is an accessory for equatorial mounts that allows you to quickly set the mount’s polar axis. When the polar axis is precisely set, an equatorial mount allows you to track an object while rotating along only one axis (right ascension). If the polar axis is not set accurately, the object will gradually “drift” in the field of view and additional correction will be required along two axes at once. Accurate polar axis alignment is especially important for long exposure photography. There are various ways to set the polar axis (drift method, auto-targeting system, electronic pole finders, etc.), however, in my opinion, the optical pole finder is still a simple and fast option, especially for small mounts -trackers, and also if it is not possible to carry a laptop or microcomputer with you.
The optical pole finder is a small lens telescope that consists of a lens, an eyepiece and a special reticle located in the field diaphragm of the eyepiece. The pole finder is designed to simultaneously show Polaris and the reticle clearly in the eyepiece. To adjust the sharpness of the reticle, simply rotate the eyepiece around its axis. The pole finder can also be equipped with a reticle illumination. The image in the finder is upside down, this is normal and has already been taken into account.

QHY5III462C camera review

I have been using specialized astronomical cameras for more than 10 years now and keep an eye on new matrices. During this time, sensors with small pixels, low noise and different diagonals appeared. One of the significant breakthroughs occurred in 2014 with the advent of the Sony IMX224 color sensor, which is characterized by very low read noise and high sensitivity to near-infrared radiation. Moreover, in the visible range, this sensor operates in color mode, and in the near-infrared range, color microfilters “leak” and at a wavelength of 850 nm or more, the matrix begins to operate in full monochrome mode.

How to choose a Barlow lens?

A Barlow lens is an optical accessory that increases the focal length of a telescope. The Barlow lens is mounted on a focuser, visual back, or diagonal mirror. It can be used for both visual observations and astrophotography. The main photographic application is photographing planets, the Moon, the Sun, double stars, and in some cases, photographing small planetary nebulae.
A Barlow lens looks like a tube with glass in the front. It consists of a lens cell (lens in a metal frame), as well as a housing with a clamping screw.

Lacerta Herschel wedge 1.25″ review

Клин Гершеля Lacerta 1.25
Lacerta Herschel wedge 1.25″

The Herschel wedge is a special optical accessory designed for safe observation and capturing of the Sun through a telescope in conjunction with additional neutral density filters. The principle of operation of this device is very simple – sunlight focused by a telescope is partially reflected from a glass wedge, further attenuated using several light filters and then enters the eye or camera, but most of the solar energy passes through the wedge and hits the radiator. That is, an aperture filter is not used – only a Herschel wedge and additional sub-aperture protective filters. This device was first proposed and used around 1830 by astronomer John Herschel (son of William Herschel). Instead of a wedge, a 90° prism or a more complex design can also be used.
What can you see through the Herschel wedge?
Using a Herschel wedge, you can observe and photograph sunspots, flare fields, and granulation. Prominences are not visible – to observe them you need a special chromospheric telescope or a chromospheric attachment.

The Sun observed through the Herschel wedge in white light and with Baader Solar Continuum filter(540 nm)
The Sun observed through the Herschel wedge in white light and with Baader Solar Continuum filter(540 nm)

Of course, when observing the Sun, you should be careful and be extremely attentive, since if you make a mistake, you can instantly damage your vision or equipment. Considering that light falls on the Herschel wedge without preliminary filtering, the Herschel wedge can ONLY be used with lens telescopes, since overheating and damage to the secondary/diagonal mirror and hood are possible in mirror and mirror-lens telescopes. Yes, there is a Triband-SCT mirror-lens telescope with a full-aperture three-band filter for use with a Herschel wedge, but this is the exception to the rule.

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