Drop-in filters + IDAS filters for widefield astrophoto

[BFR]

Hello everyone,

here I share a review where I show my thoughs about the drop-in filter system for conventional mirrorless cameras + some idas filters for widefield astro. You have some images that hope they help for you. I will be pleased to answer any question. Cheers.

Introduction
Astronomical filters are a fascinating tool for landscape astrophotography using conventional cameras. Although they come in different formats and systems, clip-in filters (sensor filters) are the most well-known. While they perform excellently, they have some drawbacks due to their nature: they are difficult to install and remove, complicating the workflow when creating panoramas, increasing the risk of scratching the sensor or getting dust on it during installation, and they are prone to vignetting and aberrations. For all these reasons, drop-in filters have been gaining popularity lately.

What is a Drop-in System?
Drop-in systems are, in essence, filter holders placed between the lens and the camera. They mimic the filter drawers commonly used in deep-sky astrophotography and allow filters to be used without having to detach the lens from the camera. As a result, we achieve better alignment between filtered and unfiltered photos (which also facilitates panoramic workflows), reduce the risk of sensor scratches or dust, and produce fewer aberrations and less vignetting in the corners. The "downside" of these systems, in the case of conventional cameras, is that they only work with Canon EF lenses in combination with mirrorless cameras (Canon EOS, Sony E, or Nikon Z). That's because EF lenses have a large flange distance, which allows space for the drop-in filter holder between the rear of the lens and the camera mount without affecting focus. Therefore, drop-in systems are (and must be) adapters between these lenses and Canon, Nikon, or Sony mirrorless bodies.

Drop in filter system

 

Example of a Drop-in System: the Meike MK-EFT
The most popular drop-in filter holder currently is the Meike MK-EFT, but there are others (Canon and Kolari, as far as I know, eventhough they are only available for Canon EF to Canon EOS R). The Meike drop-in is available for Canon EOS R, Nikon Z, and Sony E mounts. It is made of high-quality metal and plastic, includes weather sealing, and has fully functional electronic contacts, allowing autofocus with compatible lenses. This holder supports many native Meike filters (NDs, polarizers, mist filters, etc.), as well as other 2" circular astronomical filters with a compatible drop-in frame-such as those from IDAS, available with frames from either Meike (DRE or DRT) or Kolari.

Meike Drop-in filter system Canon EF to Sony E

 

MK-EFT mounted on TT artisans 11mm 2.8 EF lens

 

IDAS Astronomical Filters
IDAS filters are well-known in the astrophotography community for their excellent quality and durability. The brand offers a wide range of filters specifically designed for the MK-EFT drop-in system, including both broadband and narrowband options. The filters are sold with integrated resin frames (DRE or DRT models) that perfectly fit the Meike drop-in holder, clicking securely into place. Additionally, Kolari also produces compatible metal-framed versions. I've personally tested three of them: the NBZ II DRE, the GNB DRE, and the HEUIB II with the Kolari frame. All are narrowband filters, with the NBZ II being the most restrictive and the HEUIB II the least.

Drop in filters. From left to right, and up to down: Meike clear filter, HEUIB II (with a Kolari frame), GNB DRE and NBZ II DRE

 

Meike drop-in filter adapter + IDAS astro filter mounted on the TT artisand lens and a Sony a7s

 

HEUIB II
The HEUIB II filter is designed to block ultraviolet (UV) and infrared (IR) light. It enhances night sky detail while preserving natural colors, resulting in an RGB-style image. Unlike some other UV/IR blocking filters, this one performs well even with fast optics (from f/1.7). It allows H-alpha light to pass, which helps emphasize emission nebulae and other celestial objects, improving contrast and separating the sky background from the main structures. The resulting images have very natural colors, with improved sharpness, contrast, and saturation-making it a great choice for RGB shots or more natural-looking images that don't require filter stacking.

IDAS GNB
The IDAS GNB filter captures H-alpha and OIII, plus a small portion of the visible spectrum. It is designed to target a wide variety of celestial objects such as galaxies and nebulae, and in landscape astrophotography, it is excellent for enhancing H-alpha. According to the manufacturer, it performs well from f/1.4, and although some haloing is theoretically possible, I have not experienced it. This filter yields rich H-alpha reds along with greenish, bluish, and yellowish hues. Though it is relatively selective, it is highly usable for enhancing winter Milky Way reds without the need to blend with RGB shots.

IDAS NBZ II
The IDAS NBZ II is a very selective dual-band filter that captures only OIII and H-alpha wavelengths. It has very narrow bandpasses (8 nm and 9.5 nm) and a very high transmission rate (close to 96%), making it highly efficient for H-alpha imaging. It is designed to avoid halos and works well with fast lenses while maintaining high transmission. The resulting images are almost two-tone (red and greenish), with a strong H-alpha presence, so combining them with RGB shots is necessary. Because of all this, the NBZ II is one of the best filters for boosting reds with fast lenses, even under heavy light pollution.

Histogram comparison of the filters used on this article.

 

Comparison between different photos (only one shot - no stacking) using the Meike clear filter (15s), the Heuib II (30s), the GNB (100s) and the NBZ II (100s)

View: original size

Same photos than before with the WB corrected

View: original size

Conclusions
In my opinion, the drop-in system is currently the best solution for using astronomical filters with mirrorless cameras. The Meike version is of very high quality. It is well build, safe to use, does not produce vignetting or aberrations, makes aligning filtered and unfiltered shots easier (especially useful for panoramas that combine both), and supports a wide range of high-quality filters. The only drawback is that it can only be used with Canon EF lenses, which I admit can be frustrating. However, once we understand that this system is actually a way to use a wide array of astro filters with conventional cameras-not a limitation on lens choice-we will start enjoying all its benefits, which are far superior to those offered by clip-in filters. As for IDAS filters, their quality is top-notch. The NBZ II easily captures H-alpha even under severe light pollution, and its results rival those of any high-end H-alpha filter, with the added benefits of dual-band imaging (easier integration, better image quality, etc.). The GNB, though less restrictive than the NBZ II, performs very well under dark skies without needing RGB stacking-especially in winter. Lastly, the HEUIB II is excellent for RGB-style imaging, providing beautiful colors, reducing light pollution, and enhancing H-alpha. It is a great option on its own or in combination with the NBZ II or GNB for more impactful results.

Panorama done with the NBZ II with no RGB images combined (only one shot of 100s for the sky, with the GNB)

 

Panorama done with the NBZ II in combination with RGB images. Only one shot of 100s with the NBZII for the sky combined with one RGB shot of 20s)