Review of the Askar 72mm f/5.6 Quintuplet Petzval Flat-Field Astrograph and Askar 0.7x Reducer

Many vendors offer premium small triplet refractors for visual use and astrophotography. An ED or apochromatic objective, a relatively fast focal ratio around f/6, and a rotatable two-speed focuser are standard fare, and an optional field flattener facilitates imaging with larger APS-C and full-frame sensors. The new ASKAR FRA400 72mm f/5.6 astrograph builds on the basic idea of a compact triplet, adding two additional elements to achieve a five-element f/5.6 Petzval configuration with two ED elements. With an optional 0.7x focal reducer, the FRA400 delivers a very fast f/3.9 with a flat field across a full 44mm image circle. This makes this little astrograph ideal for capturing wide-field images of the deep sky with large-sensor cameras, and a great premium travel-friendly telescope for wide-field visual observation. This review takes this compact astrograph out for a spin, with and without its focal reducer, to see how it performs on a few wide-field targets in the northern summer sky.

Out of the box the ASKAR FRA400 "Flatfield Refractive Astrograph" looks like a well-crafted instrument with clean design and a visually appealing look and feel. As delivered, the setup weighs in at just under 7 pounds (including the aluminum rings, Vixen-style dovetail, and carrying handle). It's heavier than it looks, not surprising given the quality of the components and five glass elements inside. In my set-up, once I added a camera and other accessories, the whole rig crept into the 15-pound range. The mounting rings include areas on both sides and on the carrying handle to mount additional equipment.

The ASKAR FRA400 includes a large 3" rack-and-pinion dual-speed focuser that's fully rotatable through 360 degrees. This worked out great for framing images, and the rotation worked smoothly and did not move the mount or telescope. The rotator is also fitted with a red anodized lock-down screw. The focus knobs are easily removed with an Allen wrench to add a focus motor control (Figure 2).

Figure 2 – A close-up of the focuser of the ASKAR FRA400 showing the microfocuser knob removed to accommodate a motorized focuser.

The focuser tube terminates with an M68x1 thread for direct camera attachment and it comes with an M68-M48 adapter. It also includes a 2" adapter ring and 1.25"-2" adapter for use with diagonals, eyepieces, or smaller cameras. A star diagonal is not included. The ASKAR FRA400 also has a collapsible dew shield that extends outward by approximately 1 ⅜ inches.

The following equipment was used for testing the imaging capacity of the ASKAR FRA400 and associated focal reducer:

• Celestron CGEM-DX equatorial mount (pier mounted)
• Stock Canon 6D full-frame camera
• ZWO ASI290MC (guide camera)
• Orion 60mm Guide Scope
• Anker Model A7515 7-Port USB 3.0 Data Hub.
• iOptron ZEQ25GT equatorial mount
• ZWO 2" UV/IR cut filter
• Optolong 2" L-eNhance filter
• Daystar Quark Chromosphere (for solar imaging)
• Canon EOS M48 adapter

The initial image testing was done at 400mm and the native focal ratio of f/5.6 with a Canon 6D (stock) full-frame camera. Sixty-second exposures were used to check for any optical aberrations in the image. The software package Backyard EOS was used to capture each image taken for this article. Using the ability to "live view" with the Canon 6D, I was able to achieve focus without using a focus mask. The fine focus knob on this scope was instrumental in obtaining a precise focus.

Figure 3 – A layout of the imaging train for all images captured with the FRA at a focal length of 400mm and native focal ratio of f/5.6. From left to right, the ASKAR telescope, M68-M48 adapter (included in scope package), Canon EOS M48 adapter, and Canon 6D DSLR.

If you are new to astrophotography with a Canon 6D stock camera, you will need the Canon EOS M48 adapter that can be purchased here or here .

Figure 4 – Center (standard size) and corner images (doubled in size) of the area around Messier 29 captured with the Canon 6D and ASKAR FRA400 at a native focal ratio of f/5.6. Taken from a 60-second test frame with no calibration frames applied.

The first test image was on the open cluster Messier 29 in the constellation Cygnus (Figure 4). This 60-second image of Messier 29 showed good optical performance into the corners of the image. Note these 60-second test images were not processed with darks, bias, or flats frames. Each square is a 360 x 360 pixel clip, with the corner clips doubled in size to show star details.

Figure 5 – A wide-field view of the M29 area in a 10-minute stacked and processed imagewith the FRA400 at f/5.6 and Canon 6D camera. Click image to enlarge.

Figure 5 shows a 10-minute stacked and processed image of the Messier 29 area, uncropped, full-frame view at f/5.6 The image shows good details and star image to the edge of the frame.

Image details from Astrometry.net:

Center (RA, hms): 20h 24m 38.501s
Center (Dec, dms): +38° 33' 20.270"
Size: 5.1 x 3.4 deg
Radius: 3.066 deg
Pixel scale: 3.36 arcsec/pixel

Figure 6 – Center (standard size) and corner images (doubled in size) of the area around Messier 57 (the Ring Nebula) captured with the Canon 6D and ASKAR FRA400 at a native focal ratio of f/5.6. Taken from a 60-second test frame with no calibration frames applied.

The second test image at 400mm f/5.6 was the Messier 57 area (the Ring Nebula). Again, the 60-second image of Messier 57 showed good optical performance into the corners of the image with no aberrations detected.

Figure 7 – A wide-field view of the M29 area in a 10-minute stacked and processed image with the FRA400 at f/5.6 and Canon 6D camera. Click image to enlarge.

A 5-minute stacked and processed image (Figure 7) shows the uncropped, full-frame view around M57. The image shows good and sharp detail to the frame edge.

Image details from Astrometry.net:

Center (RA, hms): 18h 53m 30.249s
Center (Dec, dms): +32° 58' 53.064"
Size: 5.12 x 3.42 deg
Radius: 3.081 deg
Pixel scale: 3.36 arcsec/pixel

While the fast f/5.6 focal ratio is ideal for deep-sky imaging, ASKAR also makes an optional 0.7x FRA72RD focal reducer for the FRA400 scope to bring the focal ratio to f/3.9 and a focal length of 280mm while still supporting full-frame imaging. This reducer offers a 2x increase in image brightness. The next series of tests examined the effect of the reducer on image quality. The same Canon 6D (stock) full-frame camera was used for this testing (see Figure 8). The back portion of the focal reducer unscrews to easily enable the addition of a two-inch M48x0.75 threaded filter of your choice.

Figure 8 - Imaging train for 280mm f/3.9 images. Askar telescope, Askar FRA72RD 0.7x Reducer for Askar FRA400 72mm Astrograph (reducer is not included with the telescope but can be purchased separately), Canon EOS M48 adapter, Canon 6D.

As with the tests of the FRA400 at the native focal ratio, sixty-second exposures were used to check for any optical aberrations in the image. The first test image was on the Vega star field.

Figure 9 - Center (standard size) and corner images (doubled in size) of the area around the star Vega captured with the Canon 6D and ASKAR FRA400 at a focal ratio of f/3.9 with the FRA72RD reducer. Taken from a 60-second test frame with no calibration frames applied. Click image to enlarge.

The 60-second test image of Vega showed good optical performance in the center of the image but did show some minor field curvature in the corners and around the far edges of the frame (Figure 9). While not immediately visible when looking at the full frame image, when zoomed to 100% the field curvature becomes more evident. No false color was evident around Vega itself.

Figure 10 – A wide-field view of the area around Vega in a 10-minute stacked and processed image taken with the FRA400 and FRA72RD 0.7x focal reducer (for an overall focal ratio of f/3.9 and a focal length of 280mm) and Canon 6D camera. Click image to enlarge.

Image details from Astrometry.net:

• Center (RA, hms): 18h 36m 25.725s
• Center (Dec, dms): +38° 46' 06.265"
• Size: 7.34 x 4.9 deg
• Radius: 4.415 deg
• Pixel scale: 4.81 arcsec/pixel

Figure 11 - Center (standard size) and corner images (doubled in size) of the area around the globular cluster M13 captured with the Canon 6D and ASKAR FRA400 at a focal ratio of f/3.9 with the FRA72RD reducer. Taken from a 60-second test frame with no calibration frames applied.

The second test image at 280mm f/3.9 was the Messier 13 area (Hercules Cluster). The 60-second image of Messier 13 showed good optical performance in the center of the image, but as in the image of Vega, it does show some minor field curvature in the corners and around the far edges of the frame (see Figure 11). Figure 12 shows a 15-minute stacked and processed image of Messier 13, uncropped, full-frame view.

Figure 12 – A wide-field view of the area around M13 in a 15-minute stacked and processed, taken with the FRA400 and FRA72RD 0.7x focal reducer (for an overall focal ratio of f/3.9 and a focal length of 280mm) and Canon 6D camera. Click image to enlarge.

Image details from Astrometry.net:

• Center (RA, hms): 16h 41m 04.428s
• Center (Dec, dms): +36° 19' 44.683"
• Size: 7.34 x 4.9 deg
• Radius: 4.410 deg
• Pixel scale: 4.8 arcsec/pixel

Since many amateur astronomers will be using the ASKAR FRA400 72mm Petzval astrograph for wide-field astrophotography, I tested it on the North America Nebula and Veil Nebula regions using the Optolong L-eNhance Dual Bandpass Light Pollution Reduction Imaging Filter. The 2" L-eNhance filter threads directly into the imaging train on the back side of the reducer in the order shown in Figure 13.

Figure 13 - Imaging train for 280mm f/3.9 Optolong images. Askar telescope, Askar 0.7x FRA72RD Reducer (not included but can be purchased separately), Optolong L-eNhance 2" filter, Canon EOS M48 adapter, Canon 6D.

The resulting images of the North America Nebula and Veil Nebula are shown in Figures 14 and 15 respectively. Again, the quality of these two full-frame images is impressive, especially given they are captured with a narrowband filter and an unmodified DSLR. This is where the fast f/3.9 focal ratio is a great benefit. Pixel peepers will see some aberrations when zooming in at the corners, but this is the trade off for enjoying a very fast focal ratio. These are impressive results, especially in a telescope in this price range.

Figure 14 - North America Nebula and the Pelican Nebula - 30 x 300 second exposures, 10 bias, 5 dark, and 10 flat frames. For this image, the Canon 6D (stock) camera was used with the FRA400 with FRA72RD 0.7x focal reducer at a focal ratio of f/3.9 and focal length of 280nm. Click to enlarge.

Image details from Astrometry.net:

• Center (RA, hms): 20h 56m 31.088s
• Center (Dec, dms): +44° 27' 43.654"
• Size: 4.89 x 7.32 deg
• Radius: 4.400 deg
• Pixel scale: 4.79 arcsec/pixel

Figure 15 - Veil Nebula complex - 8 x 300 second exposures, 10 bias, 5 dark, and 10 flat frames. For this image, the Canon 6D (stock) camera was used with the FRA400 with FRA72RD 0.7x focal reducer at a focal ratio of f/3.9 and focal length of 280nm. Click to enlarge.

Image details from Astrometry.net:

• Center (RA, hms): 20h 50m 50.013s
• Center (Dec, dms): +31° 05' 08.694"
• Size: 7.32 x 4.89 deg
• Radius: 4.403 deg
• Pixel scale: 4.8 arcsec/pixel

Figure 16 shows a deep-sky image of the Lagoon and Trifid Nebulae, this one captured with a dedicated astronomy camera, the ZWO ASI071MC-Pro. This images was captured with the FRA400 scope and the FRA72RD 0.7x focal reducer for an effective focal ratio of f/3.9 and a focal length of 280mm.Click to enlarge.

6. Solar Imaging at f/3.9

While not an obvious choice for a solar/lunar/planetary scope, especially with the focal reducer, I decided to try out the ASKAR FRA400 for a few solar images since my refractors always pull double duty in the observatory. I tried a few images using a UV/IR block filter, the Daystar Quark Chromosphere, and the ZWO ASI290MC camera. The image train is shown in Figure 17.

Figure 17 - Imaging train for 280mm f/3.9 solar images. Askar FRA400 telescope, Askar 0.7x Reducer for Askar FRA400 (not included with telescope but can be purchased separately), ZWO 2" UV/IR filter, extension tube, Daystar Quark Chromosphere, ZWO ASI290MC.

The ASKAR FRA400 performed admirably on the Sun in H-alpha, revealing fine surface and limb detail even at this short focal length. This suggests this little 72mm astrograph would serve well as a travel scope for eclipse chasers who might also want to do a little visual night time observing and imaging. A good all-around package!

Figure 18 - Active Region 2765 imaged on June 13, 2020. This is the best 25% of 2,000 images processed by Autostakkert and Registax.

Figure 19 - Solar flares, negative image, taken on June 13, 2020. This is the best 25% of 2,000 images processed by Autostakkert and Registax.

About the Author

Tom Wildoner is a retired Environmental Specialist for the U.S. Army who now operates a personal backyard observatory in mountains of northeastern Pennsylvania that focuses primarily on astrophotography. His images have been shared on EarthSky.org, Sky & Telescope, Universe Today, and other outlets. When he's not in the observatory you’ll find him hiking or biking the local trails or visiting one of our great National Parks with his wife Jane.