Alpine Astro Baader AstroSolar BDSF 3.8 Digital Solar Filter Review

Important: The "3.8" version of the Alpine Astronomical Baader AstroSolar BDSF Digital Solar Filter is not rated safe for viewing (other densities are available). "This filter is only intended for digital imaging of the sun and is not safe for direct solar viewing or for use on cameras with an optical viewfinder. Only use on cameras with an electronic viewfinder (EVF) or Live-View option. If you do not know what kind of viewfinder your camera has, do not use this filter."

Are you geared up to photograph the sun? As I write this review, numerous sunspots add entertainment to the solar disk, the International Space Station passes in front of the sun routinely, and, huge, is that a total solar eclipse should be visible across a broad swath of North America in April 8, 2024.

Back in 2017, an upcoming solar eclipse generated a solar filter search, and I opted for the Meade Glass White Light Solar Filter. That eclipse was incredible, and I'm now planning to photograph the 2024 total solar eclipse.

While I still have the Meade solar filter and use it on occasion, it had a shortcoming that I want to avoid during the next solar eclipse. Despite the sun's extreme brightness, this filter blocks so much light that exposure durations challenge image sharpness with a long telephoto focal length in use. For example, a 1/125 shutter speed was required to photograph Mercury Transit of the Sun at 1200mm (ISO 100).

This search led to the Alpine Astronomical 120mm Baader AstroSolar BDSF 3.8 White-Light Digital Solar Filter. The "3.8" indicates that this filter blocks less light (vs. the 5.0), and a quick test showed the following exposures to result in approximately equivalent brightness:

Baader: 1/2500 f/8
Meade: 1/80 f/8

That difference is massive, translating directly to sharper images, especially under suboptimal conditions, such as in wind.

Sharpness still matters for solar photography. While the sun appears to lack details, especially sunspots should be rendered sharply. Is the Baader solar filter sharp? Is it also an upgrade to the Meade filter in that regard?

These 100% crop images are the best of 20 optimally captured (solid mount over concrete, 10-second timer, electronic shutter, clear sky, no wind, 1200mm) images using each filter. Remember that the sun is 92.96 million miles away.

Load Comparison Images

Succinctly stated, the Baader filter produces obviously sharper details.

Yes, the sun is a different color in these samples.

Do you want a white sun or an orange sun? Technically, the sun is white, and solar filters that produce an orange sun are filtering certain wavelengths of light stronger than others. The white sun appears harsh, and artistically, I prefer my sun to be orange. Still, I seldom wish to filter specific light colors during image capture.

Fortunately, turning a white sun to orange is easy to accomplish in Photoshop. Here is how to change a Baader solar filter's white sun to orange:

1. Open the white sun image in Photoshop
2. Add a new layer above the sun image layer
3. Change PS's foreground color to #ff9c38
4. Use the paint bucket tool to fill the new layer with the selected orange color
5. Change the orange layer's blending mode to "Multiply"
6. Add a color balance adjustment layer and set the blue slider to +10
7. Add a vibrance adjustment layer and set vibrance to +20 and saturation to +10

This image shows the result of those steps.

The Baader filter provides both sun color options — and many others. Change the layer fill color to create a blue or another color of your choosing sun.

Let's take a closer look at this filter.

Right, the wavy solar film does not mesh with our photographic understanding of high performance optical requirements. We just looked at how well this wavy film performs, and Baader assures us that the wavy design is required (and harmed if stretched flat).

The solar film is mounted in a thin but rigid aluminum ring.

The flat housing needs a means of lens attachment, and the parts kit appears daunting at first.

However, installation is easy (though slightly fiddly).

Basically, three rubberized centering bolts are adjusted and tightened into three slots on the ring, snugly gripping on the outer (or inner) end of the lens. Velcro straps can be used for enhanced retention.

For a wide range of adjustability, 10mm and 20mm diameter centering bolts are provided, and six total ring slots are available. Three slot covers block light through the unused slots, and oval washers block light through the used slots. A slot on the large washers aligns with indexing on the ring, permitting even and repeatable installation.

While the Alpine Astro filter seems adequately constructed, it is not as ruggedly constructed as the strong metal-rimmed glass filters from Meade, Thousand Oaks, Spectrum Telescope, and others. However, the 4.2 oz (118.8g) weight is favorably light, and the unassembled size is considerably thinner.

An inexpensive plastic storage box would be convenient to have, especially for travel.

Solar filters come in a wide range of sizes, and the question "Which lens should I use to photograph the solar eclipse?" needs to be asked before selecting a solar filter. Or, for a much higher frequency opportunity, "Which lens should I use to photograph the sun?" This important and primary question needs asked and answered in part because different lenses require different sizes and possibly different styles of solar filters.

The timing of the 2017 and 2024 solar eclipses means a high sun. With a high sun, it is challenging to incorporate landscape or landmarks in the same frame during the eclipse.

Also, with a solar filter installed, it is hard to get exposures bright enough to even composite a scene together as only the sun is visible and everything else in the frame is totally black. In this case, I can easily create any additional black border desired in Photoshop, so the larger the sun in the frame, the happier I am (as long as image quality remains at least reasonably close to equal between the options). That means the longest focal length available (1200mm is my choice) is going to be the best choice for photographing the sun.

To select a sun photography focal length, it is helpful to view a comparison. These images were captured with the Meade filter on a full frame body with the APS-C/1.6x equivalent angle of view focal length shown in parenthesis.

Load Comparison Images

Note that the 1680mm example was captured using the Canon EF 600mm f/4L IS II USM Lens with both 1.4x and 2x extenders behind it. While that combination delivers a favorable sun disk size, the image quality is ... not so good.

Also, keeping up with the rate of the sun moving through the frame becomes challenging at this narrow angle of view. My recommendation is the 1200mm angle of view. For me, that is a 600mm F4 lens with a 2x extender (teleconverter) behind it.

If you don't have a long telephoto lens, a scheduled solar eclipse is a good reason to get one. Renting is a good option if this lens would have only a one-time use for you (reserve that rental early.

While one might get away with photographing the sun without a solar filter using a wide-angle lens (you've taken or seen landscape images that include the sun), photographing the sun with a longer focal length lens means that a proper solar filter is an absolute requirement.

Improper protection can mean rapid destruction of a camera (I melted a camera simply trying to flare test a 600mm lens) and lens, and if telephoto viewing through an optical viewfinder, eye damage will occur almost immediately. As noted at the beginning of this review, not all filters advertised for solar photography use are suitable for viewing the sun through an optical viewfinder. Put safety first.

So, we've determined that a very long focal length lens is generally desired for photographing the sun. Telephoto lenses tend to be large, and some of these lenses do not have front filter threads.

Which solar Filter should I get for a telephoto lens? Which solar filter should I get for the April 8, 2024 total solar eclipse? The Alpine Astronomical Baader AstroSolar BDSF 3.8 Digital Solar Filter is the answer (for mirrorless cameras only).

This filter ("3.8" version) is available for lenses with 100mm to 240mm front outside diameters. For Canon and Sony 600mm F4 lenses, I opted for the Alpine Astronomical Baader 120 AstroSolar BDSF 3.8 Digital Solar Filter.

The model number, 120, provides 10mm of "aperture" diameter range on both sides of 120mm, 110mm to 130mm. This size translates to 140-180mm outside diameters or 170-210mm inside diameters.

Should I get the solar filter sized to fit the hood or the lens itself? Is there an image quality difference with the filter mounted on the hood, farther away from the lens? I asked that question to Meade, another solar filter company, and B&H. All three promptly gave me the same answer: "No."

During the solar eclipse, the lens will be pointed at the biggest source of lens flare available, the sun. So, the lens hood isn't going to reduce flare. The lens hood provides some physical protection, but this time I opted for sizing the filter to the end of the lens (though it might size up to fit the hood also).

Back to the "Which size filter do I need?" question. You should measure the end of your lens or lens hood. Note that, while we provide accurate measured dimensions in the site's lens specifications and measurements tool, these are max size measurements and may not correlate directly to the end of the lens or lens hood (specifically, the hood's thumbscrew may be included in the measurement).

How do you focus on the sun with a solar filter in place? Select a wide AF area, and the mirrorless camera should autofocus on the sun.

The sun's distance to the earth will not relevantly change during a photo session. Thus, it seems that switching to manual focus would be optimal. Focus, confirm image sharpness, and forget about this aspect, right? Not so fast.

My experience in 2017 was that manual focus did not reliably hold the correct focus distance. If opting for manual focus, constantly monitor image sharpness.

To get the optimal exposure, choose settings that push the brightest channel in the RGB histogram to the right edge of the chart. While red was the brightest channel transmitted by the Meade filter mentioned here, expect blue to be your color to watch when using the Baader filter.

While photographing the sun with a solar filter is not difficult, practice is required to ensure the right gear and procedures are in place.

If using a long lens to photograph the sun, and especially the solar eclipse, a solid, high-performing tripod and head should be used.

I used the ProMediaGear TR424/TR424L Pro-Stix Carbon Fiber Tripod for the images shared in this review, and the Really Right Stuff TVC-34/TVC-34L Carbon Fiber Tripod is another outstanding choice. Both tripods (yes, having two complete setups is highly recommended) perform impressively, including keeping vibrations to a minimum.

What is the best long lens tripod head? I highly recommend using a 2-way tripod head mounted on a level tripod for photographing the solar eclipse, and the tripod and head combination must accommodate shooting at a strong upward angle. A pair of low-vibration gimbal heads are currently my preferred, the Wimberley WH-200-S Sidemount Head and Really Right Stuff PG-02 MK2 Pano-Gimbal Head. The Wimberley WH-200 Gimbal Tripod Head II (full gimbal vs. sidemount) is another great choice.

With the tripod leveled and the lens's tripod ring locked in the horizontal (or vertical) orientation (the sun is round, so orientation makes little difference), these extremely solid, low-vibration gimbal heads provide independent panning and elevation changes without introducing any roll. While a slight change in camera angle may not be noticeable in any single frame, it may become more obvious in composites showing the stages of the eclipse, sunspots, etc. Making one adjustment at a time is beneficial for keeping the sun in the frame at high magnification.

Note that when shooting nearly straight up with a large, heavy lens, the tripod tipping over becomes a potential issue. Ensure that your technique is such that this risk is not realized with options including anchoring the tripod to the ground. Camera clearance can also be an issue when photographing straight up, especially with a battery grip mounted. Prepare for camera clearance while panning through the entire eclipse or another sequence, ideally without tripod repositioning needed. Practice with your gear to ensure it is up to this task.

How much does a solar filter cost? You are probably thinking that a high-quality filter of this size is going to cost a fortune. Originally, I did, and thankfully, it doesn't. In fact, it costs considerably less than many smaller threaded filters I've bought.

At this price, adding an Alpine Astronomical Baader AstroSolar BDSF 3.8 Digital Solar Filter to your kit is a great idea even if there is no solar eclipse. Photographing the sun is always entertaining with sunspots and perhaps some clouds being ever-changing factors.

The reviewed filter was purchased online retail.

Summary

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Important to note is that, if there is a solar eclipse in the forecast for a populated locale (such as most of North America forecasted for the April 8, 2024 total solar eclipse), solar filters will likely become scarce. The moon is going to cause the sun to disappear, and that event will cause solar filters to disappear from retail inventories.

Thus, it makes sense to order your filters now if you have any interest in photographing that event (or any that occur prior to that event). Use the links below to order the Alpine Astronomical Baader AstroSolar BDSF 3.8 Digital Solar Filter or view the entire selection of solar filters at B&H, Adorama, and Amazon.

I intend to photograph the 2024 total solar eclipse with the Alpine Astronomical Baader AstroSolar BDSF 3.8 Digital Solar Filter (perhaps two of them). This filter provides sharp resolution with optimal exposures obtained at a fast shutter speed.