{"id":18052,"date":"2026-09-28T11:16:11","date_gmt":"2026-09-28T09:16:11","guid":{"rendered":"https:\/\/deep-space-astronomy.ch\/?p=18052"},"modified":"2026-09-28T14:07:34","modified_gmt":"2026-09-28T12:07:34","slug":"choisir-camera-barlow-planetaire-sans-acheter-au-pif-2026","status":"publish","type":"post","link":"https:\/\/deep-space-astronomy.ch\/en\/choisir-camera-barlow-planetaire-sans-acheter-au-pif-2026\/","title":{"rendered":"Choosing a Camera and a Barlow Lens for Planetary Photography, Without Buying Blind (2026)"},"content":{"rendered":"

When I\u2019m looking at a camera or a Barlow lens for planetary photography, what I really want to know is whether the setup will actually work with my telescope. I don\u2019t want to pay for high-quality optics only to end up with a huge, dark planet and a hassle to adjust the settings as soon as the sky moves even a little.<\/p>\n

I\u2019ll use a specific example: a 406-mm f\/4 Dobsonian, a monochrome camera with an IMX585 sensor, an ADC, and a Baader MPCC 1\u00d7 coma corrector. This is a good example because it forces you to consider everything together: pixel size, focal length, filters, exposure, and tracking. But the method remains the same whether you\u2019re using a 200 mm telescope or a Schmidt-Cassegrain.<\/p>\n

To set this up properly, I'm relying on Christophe Pellier's articles, Christophe de la Chapelle's explanations, and the Tele Vue documentation.<\/p>\n

Color or black-and-white<\/h2>\n

When choosing a camera, I\u2019d start by thinking about what I want to photograph and how I want to spend my evenings. A color camera lets you capture red, green, and blue information in the same video. That\u2019s really handy on Jupiter when the seeing changes quickly. You keep the acquisition process simple and avoid having to take three successive sequences just to get the color.<\/p>\n

A monochrome camera offers more flexibility with filters. To create an RGB image, you shoot separately through red, green, and blue filters, then combine the three images. Each pixel contributes to the image in the selected band, without a Bayer filter array. You can also work in red, infrared, or other bands, provided the sensor and the entire optical system transmit these wavelengths effectively enough.<\/p>\n

The trade-off is the equipment and the work involved: filters, changing filters or the filter wheel, checking focus, stacking images, and managing the planet\u2019s rotation as the sequence gets longer. A single image can be excellent, but you have to be willing to do all that. A modern color camera can already produce some very beautiful images. Christophe Pellier discusses the possibilities and limitations of these approaches in his presentation, \u201cPhotographing Planets with a Color Camera\u201d<\/a>.<\/p>\n

If I were starting from scratch to photograph Jupiter and Saturn in color, I would seriously consider a color camera. Since a monochrome IMX585 is already available, I would instead build a solid setup around it. There\u2019s no reason to switch cameras before figuring out what\u2019s actually limiting the image quality.<\/p>\n

The video by Christophe de la Chapelle, Which Planetary Camera Should You Choose? Criteria, Pitfalls, and Recommendations<\/a>, is a resource for understanding the selection criteria. It\u2019s a bit older: I\u2019d use it as a starting point, then check the specifications of current models on the manufacturers\u2019 websites.<\/p>\n

Pixel size<\/h2>\n

The first number I look at next is the pixel size. Together with the focal length, it determines the portion of the sky captured by each pixel. This is called sampling. The total size of the sensor, on the other hand, determines the field of view you can frame.<\/p>\n

The formula is quite simple:<\/p>\n

Sampling in arcseconds per pixel = 206.265 \u00d7 pixel size in \u00b5m \u00f7 focal length in mm.<\/strong><\/p>\n

The longer the focal length, the more pixels a given planet occupies. The smaller the pixels, the more pixels it also occupies at the same focal length. But once the accessible details have been properly recorded, continuing to spread them out does not create any new resolution.<\/p>\n

Let's look at three examples that illustrate different needs:<\/p>\n

| Camera | Sensor and Pixels | What I'd Look at First |
\n|\u2014|\u2014|\u2014|
\n| ZWO ASI662MC<\/a> | IMX662 color, 2.9 \u00b5m, 1,920 \u00d7 1,080 | A camera for framing planets, with a narrower field of view |
\n| ZWO ASI678MC<\/a> | IMX678 color, 2 \u00b5m, 3,840 \u00d7 2,160 | Smaller pixels, which require a shorter focal length for the same sampling |
\n| Player One Uranus-M<\/a> | IMX585 mono, 2.9 \u00b5m, 3,856 \u00d7 2,180 | Flexible filters and a sensor large enough to make framing easier |<\/p>\n

At the same focal length, the two cameras with 2.9 \u00b5m pixels produce the same geometric size of Jupiter in pixels. The differences in color, sensitivity, and processing are very real, but the larger sensor does not make the planet appear any larger. It simply leaves more space around it.<\/p>\n

On a Dobsonian telescope, this feature can be useful for locating the planet and keeping it in the field of view. It\u2019s also useful for the Moon or for including satellites. However, capturing several million pixels of dark sky in each image quickly fills up the hard drive.<\/p>\n

The pace<\/h2>\n

Frame rate deserves just as much attention as the sensor. In planetary photography, you typically record videos, then select, align, and stack the images. You need to evaluate the camera\u2019s performance at the actual image size you\u2019ll be using.<\/p>\n

An ROI is a smaller area of the sensor that you choose to read out. It does not change the pixel size and does not replace a Barlow lens. It can significantly increase the frame rate while reducing file sizes. On the Uranus-M, for example, Player One claims 47 frames per second at 3,840 \u00d7 2,160 and 187 frames per second at 1,920 \u00d7 1,080 in its fast RAW8 mode via USB 3. The manufacturer also notes that the storage drive may limit recording. These figures apply to this specific camera, not all IMX585 sensors. Player One Specifications and Frame Rates<\/a><\/p>\n

There\u2019s still one very simple limitation: with a 10-millisecond exposure, you can\u2019t exceed 100 frames per second; with a 5-millisecond exposure, the exposure-related limit is 200. Sensor readout and data transfer can further reduce these values. So a camera advertised as capable of 300 frames per second won\u2019t actually deliver that rate if the planet requires a 15-millisecond exposure.<\/p>\n

I would also check compatibility with the capture software, the drivers, the frame rates depending on the playback modes, and performance in the bands that interest me. Maximum quantum efficiency alone doesn\u2019t tell the whole story about what\u2019s happening in the blue spectrum or at 850 nm. And RAW16 describes an output format\u2014it doesn\u2019t guarantee that the signal will be converted to 16 bits.<\/p>\n

For high-light acquisitions lasting just a few milliseconds, active cooling would be way down on my list of priorities. A cooled camera can be useful\u2014especially if you already have one\u2014but I wouldn't pay the extra cost just to film Jupiter. The situation may be different for lower-intensity applications or longer exposures.<\/p>\n

Sizing the Barlow Lens<\/h2>\n

To determine the size of the Barlow lens, I would start with the final F\/D ratio. A commonly used guideline is:<\/p>\n

Target final F\/D \u2248 5 \u00d7 pixel size in \u00b5m.<\/strong><\/p>\n

Christophe Pellier describes it in his guide as an ideal average ratio, to be adjusted according to conditions and the target. With 2.9 \u00b5m pixels, that works out to f\/14.5. With 2 \u00b5m pixels, the ratio drops to around f\/10. It\u2019s already clear why systematically recommending a 2\u00d7 Barlow lens to everyone doesn\u2019t make much sense. How to Take Great Planetary Photos: Tip 7<\/a><\/p>\n

| Pixel size | F\/D reference | Corresponding magnification from f\/4 |
\n|\u2014|\u2014|\u2014|
\n| 2 \u00b5m | f\/10 | 2.5\u00d7 |
\n| 2.9 \u00b5m | f\/14.5 | 3.63\u00d7 |
\n| 3.75 \u00b5m | f\/18.75 | 4.69\u00d7 |
\n| 5.86 \u00b5m | f\/29.3 | 7.33\u00d7 |<\/p>\n

These are rough estimates for the visible spectrum\u2014not a list of amplifiers to buy. Diameter isn\u2019t included in this formula because it affects both the telescope\u2019s resolution and its focal length when considering a given F\/D ratio. A 400 mm and a 200 mm at f\/15 obviously do not have the same focal length or the same achievable resolution.<\/p>\n

I would certainly not treat the factor of 5 as a dividing line between a good image and a bad one. Filter bandwidth, seeing, the planet\u2019s brightness, and the sensor\u2019s response all affect the trade-off. Christophe de la Chapelle also points out that his sampling guidelines serve as a starting point, which can be exceeded with very good optics and the right conditions. His post on Webastro, by CDLC<\/a><\/p>\n

With a monochrome sensor, I wouldn\u2019t automatically multiply the focal length by an additional factor just to improve image quality. With a color sensor, I wouldn\u2019t double the focal length to \u00abcompensate for the Bayer pattern\u00bb either. You have to evaluate the resulting image and the recorded color channels\u2014not apply a blanket penalty.<\/p>\n

From the visible to the infrared<\/h2>\n

The choice changes when we move from the visible to the infrared. For the same diameter, the diffraction-imposed limit is less fine at longer wavelengths. On the other hand, turbulence and certain optical defects may have less of a negative impact. An IR image may therefore appear better on a given night, even though infrared does not give the telescope a higher theoretical resolving power. Christophe Pellier, Wavelength and Resolution<\/a><\/p>\n

In such cases, it\u2019s often best to reduce the focal length. For a monochrome camera with 2.9 \u00b5m pixels\u2014used primarily for IR imaging\u2014f\/10 is a very good starting point; the filter and shooting conditions can then be adjusted to fine-tune the results. Pellier discusses this adaptation in his article on infrared settings for the IMX462<\/a>. The reasoning regarding sampling can be applied to another sensor with the same pitch, without necessarily attributing the same spectral performance to it.<\/p>\n

That\u2019s why, for the 406 at f\/4 with the IMX585, I\u2019d consider a 4\u00d7 filter for RGB and a 2.5\u00d7 filter for primarily IR use. If I have to buy just one and my focus remains on Jupiter and Saturn in RGB, I\u2019d go with the 4\u00d7.<\/p>\n

Tele Vue: Barlow or Powermate?<\/h2>\n

At Tele Vue, it\u2019s important to distinguish between classic Barlow lenses and Powermates. A good Barlow lens can work perfectly well for planetary observation. The higher price of a Powermate is not enough to prove that it will reveal more detail in every setup. Tele Vue explains the difference in design: the Powermate combines a diverging lens group with a group that corrects the position of the pupils. Concept Overview by Tele Vue<\/a><\/p>\n

The classic Barlow lens has a very practical benefit: you can increase its magnification by moving the sensor farther away. This is useful if you want to adjust your sampling. However, the ADC, filter wheel, and connectors all contribute to this distance; the factor engraved on the body no longer necessarily describes the completed setup.<\/p>\n

The official curve shows, for example, that the Tele Vue 3\u00d7 Barlow reaches approximately 4\u00d7 when the sensor is positioned about 45\u201350 mm behind the top of its eyepiece holder. At about 100 mm, it approaches 5\u00d7. These are approximate readings from the graph, based on its own origin: measurements are not taken from just any lens or adapter. Tele Vue Barlow Lens Magnification Curve<\/a><\/p>\n

For anyone willing to adjust their setup, the 31.75 mm Tele Vue 3\u00d7 Barlow lens is therefore a serious alternative to a Powermate 4\u00d7: it can reach the desired field of view with the appropriate focal length. You simply need to calculate and measure the actual magnification. The 31.75 mm Tele Vue 2\u00d7 Barlow lens is also worth considering for telescopes with smaller apertures, or when you\u2019re looking for lower magnification. I would choose between them based on the complete setup.<\/p>\n

Powermates often simplify this issue, but not all of them are drag-free. The Tele Vue documentation describes four different behaviors:<\/p>\n

| Powermate | Smooth | When the sensor is moved away |
\n|\u2014|\u2014|\u2014|
\n| 2\u00d7 | 50.8 mm | The factor varies very little |
\n| 2.5\u00d7 | 31.75 mm | The factor decreases slightly |
\n| 4\u00d7 | 50.8 mm | The factor increases moderately |
\n| 5\u00d7 | 31.75 mm | The factor increases significantly |<\/p>\n

On the graph, 100 mm behind the top of the original eyepiece holder, the magnification reads approximately 4.4\u00d7 for the 4\u00d7 and 7.7\u00d7 for the 5\u00d7. The latter can therefore project an image much farther than expected. Photo adapters that replace the eyepiece holder alter the mechanical reference point; the original curve must be preserved. Applications and Performance Curves for Powermate and Tele Vue<\/a><\/p>\n

A 50.8-mm diameter does not in itself guarantee better resolution than a 31.75-mm setup. This is notably the size in which the Powermate 4\u00d7 is available. I would also consider the weight, the rigidity of the connections, and the eyepiece holder\u2019s ability to hold the assembly without flexing.<\/p>\n

Specifications for the 406 mm f\/4 lens<\/h2>\n

With the 406 mm f\/4 lens, we can now quantify the choice. The native focal length is 406 \u00d7 4 = 1,624 mm.<\/p>\n

With 2.9 \u00b5m pixels and a 1\u00d7 MPCC, here are the values at the nominal gain levels:<\/p>\n

| Assumed Actual Magnification | Focal Length | F\/D | Sampling |
\n|\u2014|\u2014|\u2014|\u2014|
\n| 2\u00d7 | 3,248 mm | f\/8 | 0.184\u2033\/pixel |
\n| 2.5\u00d7 | 4,060 mm | f\/10 | 0.147\u2033\/pixel |
\n| 3\u00d7 | 4,872 mm | f\/12 | 0.123\u2033\/pixel |
\n| 4\u00d7 | 6,496 mm | f\/16 | 0.092\u2033\/pixel |
\n| 5\u00d7 | 8,120 mm | f\/20 | 0.074\u2033\/pixel |<\/p>\n

At 4\u00d7 magnification, a planet 45 arcseconds in diameter would occupy about 489 pixels. This is an example of apparent diameter, not Jupiter\u2019s actual size. It demonstrates that you don\u2019t need to fill all 3,840 pixels of the sensor to capture a detailed image.<\/p>\n

When switching from 4\u00d7 to 5\u00d7, the same image covers 1.56 times the area. With the same transmission and exposure, each pixel receives approximately 36 % less light. To maintain the same number of photons per pixel, the exposure time would need to be increased by approximately 56 %. Increasing the gain can brighten the display, but it does not replace the missing photons. These figures are simply calculated based on the square of the ratio of the focal lengths.<\/p>\n

A 5\u00d7 magnification might make sense with different pixels, a different F\/D ratio, or under specific conditions. For this 406 and this camera, it wouldn\u2019t be my first choice. The 4\u00d7 already provides a comfortable margin for high-resolution RGB imaging, with amplification that\u2019s less sensitive to accessories than a conventional Barlow lens.<\/p>\n

The ADC, the filters, and the coma corrector<\/h2>\n

ADC remains useful with a monochrome camera. Even through a blue filter, a range of wavelengths is recorded, and the atmosphere does not scatter them all in the same way. Realigning the red, green, and blue layers during processing does not correct the blurriness that exists within a single layer. Pellier demonstrates this, in particular, using a monochrome camera and a blue filter in his article on the atmospheric dispersion corrector<\/a>.<\/p>\n

Amplification is generally placed before the ADC so that it operates within a narrower beam. The distance between the prisms and the sensor also affects its correction capability. Pierro-Astro details these requirements in its practical assembly guide<\/a>. Its recommended distances are not a rule that should be blindly applied to all ADCs.<\/p>\n

For visible RGB, I would also check to make sure that infrared light is properly blocked, either by the camera lens or by the filters used. With a monochrome camera and RGB filters that block infrared light effectively, an additional IR-cut filter isn't necessarily required. The issue is clearly explained in Pellier's article on the IR-cut filter<\/a> : IR contamination cannot always be corrected with a simple color balance.<\/p>\n

The coma corrector requires its own adjustment, even when used with a Powermate. The Baader MPCC does not nominally change the focal length. The Mark III manual specifies a distance of 55 mm from the T2 flange to the sensor when used in a direct photographic mount. You must also take into account the adapter used, as the T2 and M48 mechanical specifications are not identical. Baader MPCC Mark III Manual<\/a><\/p>\n

If a Powermate is inserted between the corrector and the camera, those 55 mm do not constitute a total mechanical length that can be copied as-is. And Tele Vue\u2019s recommendation for a Paracorr does not automatically apply to the same setup with an MPCC. For this specific setup, I wouldn\u2019t just give a random list of adaptor rings: you need to know the ADC model, the camera housing, and whether or not there\u2019s a filter wheel.<\/p>\n

That\u2019s the downside of thinking, \u00abI\u2019ll just get a Powermate so I don\u2019t have to mess around with the exposure.\u00bb It makes it easier to choose the magnification, but the other factors still have their limitations. Buying the right power and setting up the right configuration are two interconnected steps.<\/p>\n

Measuring Actual Sampling<\/h2>\n

Once everything is set up, I\u2019ll measure the actual sampling. All you need to do is determine the apparent diameter of the planet on the date of capture, then measure the same diameter on a raw image\u2014before resizing or drizzling. Be sure to use the correct measurement: equatorial diameter for Jupiter, and the globe or clearly defined rings for Saturn.<\/p>\n

Divide the apparent diameter in arcseconds by the diameter measured in pixels. For example, 45\u2033 divided by 500 pixels equals 0.090\u2033\/pixel. With 2.9 \u00b5m pixels, this corresponds to a focal length of approximately 6,646 mm, or a total magnification of about 4.09\u00d7 on the 406 at f\/4. This provides a more accurate representation of the setup than the \u00ab4\u00d7\u00bb label alone. Measurement Method Explained by Christophe Pellier<\/a><\/p>\n

Follow-up<\/h2>\n

And then there's tracking. A large sensor helps locate the planet, but as soon as you reduce the ROI, the planet needs to stay within the frame with some margin to spare. Before deciding whether you can work comfortably at f\/16, I would therefore check what the motorization or equatorial mount\u2014if the Dobsonian has one\u2014is actually capable of. Collimation, the mirror\u2019s thermal equilibrium, focusing, and sky stability deserve at least as much attention as the Barlow lens\u2019s reference.<\/p>\n

The Final Choice<\/h2>\n

For my example, I would stick with the IMX585 mono and choose the Tele Vue Powermate 4\u00d7 in 50.8 mm for RGB, along with the ADC and a verified mechanical setup. If my setup were to focus primarily on IR, the 2.5\u00d7 Powermate would be my first choice. And if I wanted to fine-tune the magnification\u2014even if that meant making a few adjustments\u2014the Tele Vue 3\u00d7 Barlow lens would still be a very good option.<\/p>\n

The result I'd be looking for in the field is an image with usable details, sufficiently short exposure times, and enough signal to process cleanly. If the setup consistently delivers that, it's a good choice.<\/p>\n

Sources : Christophe Pellier \u2013 Planetary Astronomy and Imaging<\/a> ; Christophe de la Chapelle \u2013 Webastro (CDLC)<\/a> ; Tele Vue \u2013 Barlow and Powermate<\/a> ; Player One Astronomy \u2013 Uranus-M<\/a> ; Baader Planetarium \u2013 MPCC Mark III<\/a><\/em><\/p>\n

See also on Deep Space Astronomy: Barlow and Back Focus: Why You Can't Get the Image in Focus<\/a> ; Player One Astronomy: Why This Brand Has Won Over Astrophotographers<\/a><\/em><\/p>\n

Signature: CBurkhalter<\/em><\/p>\n<\/div><\/div>","protected":false},"excerpt":{"rendered":"

A practical guide to choosing a camera and Barlow lens for planetary photography: pixel size, sampling, final F\/D ratio, frame rate, ROI, ADC, and coma corrector. Includes a real-world example using a 406 mm f\/4 telescope and a monochrome IMX585 sensor. Tele Vue Barlow vs. Powermate, calculation tables, sources: Christophe Pellier and Christophe de la Chapelle.<\/p>","protected":false},"author":187,"featured_media":18051,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[949],"tags":[],"class_list":["post-18052","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-matos"],"_links":{"self":[{"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/posts\/18052","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/users\/187"}],"replies":[{"embeddable":true,"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/comments?post=18052"}],"version-history":[{"count":2,"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/posts\/18052\/revisions"}],"predecessor-version":[{"id":18055,"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/posts\/18052\/revisions\/18055"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/media\/18051"}],"wp:attachment":[{"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/media?parent=18052"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/categories?post=18052"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/tags?post=18052"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}