Optec Alnitak Flat-Man XL Flat Fielder Panel
The Optec Flat-Man XL is Alnitak's stationary observatory model electroluminescent panel that will accommodate telescopes up to 18" in diameter. This product is revolutionizing the way flats are acquired at observatories around the world. They are used by both professionals and amateurs on several continents.
For the serious observer with large observatory mounted telescopes, there is now a way to guarantee excellent flats on demand. Alnitak's testing shows that the Flat-Man XL provides an exceptionally evenly illuminated field when imaged by a camera mounted to a telescope focused at infinity.
For today’s millimagnitude exoplanet photometry, or for the extensive stretching that is being done with aesthetic astronomical imaging, image flatness is of utmost importance. Generating good flats has been a challenge until now.
This unit is completely controllable from a USB interface using Windows controller software and is also compatible with CCDAutopilot. Here is the relevant information from the CCD Autopilot help page.
Testing the Flat-Man XL
Evaluating the overall evenness of a flat field light source is straightforward:
- Generate a series of images with the telescope pointed to the flat field illumination source.
- Rotate the camera by 90 degrees, and generate another series of images as flats with ADU values in the midrange of your camera’s linear regime.
- Dark subtract each image, then divide each image in the first set of images by a sigma-combined stack of the second flat series.
- Median (or sigma clip) the first stack of images.
If the camera has been evenly illuminated, then the resultant stacked image should show a poisson distribution with very small standard deviation.
Testing Results: Alnitak's tests were carried out at the Galaxy Quest Observatory in Lincolnville, Maine with a 12.5 RCOS Ritchey-Chretien reflector and a SBIG ST-2000 camera with no filters. There was no moon, the roof of the observatory was closed, and the Flat-Man XL was positioned 22" from the secondary ring of the telescope. The telescope was focused on a star immediately prior to the testing. The data can be seen in the images above.
Note the standard deviation of the flatted stack (figure 3) is ~ 8 ADUs. Three standard deviations comprises 99.7% of the pixel value difference, which in this case would be ~24 ADU variation in the image. Since the average pixel value in the image is 31293 ADU, 99.7% of the pixel values are within 2X 24/31293 x 100 = 0.16% of each other! Alnitak was skeptical of this value, so they did another test, this time leaving the camera alone and rotating the entire Flat-Man XL panel. Figure 4 shows that the results were just as good.
You can also see how flat the image is by looking at the line profile shown in figure 5. Again, there is very little variation from one end of the image to the other.
Note that the above analysis relies on combining a number of images as would be done when processing aesthetic images. For those who do time series photometry and are not stacking frames, no flat can match the performance of a stacked set of frames. For single frames, Alnitak finds that the Flat-Man XL is uniform to < 0.75% across the field. That’s a conservative estimate. If you are careful to expose the flats to the upper range of the linear part of your chip, you may be able to get even better uniformity.
Narrowband filters are no problem for the Flat-Man XL. Alnitak did testing through an Astrodon Ha filter with excellent results. Using the same test setup as above, they found that with an ST2000 monochrome camera and the brightness turned up to 255, Alnitak got 30,000 ADU flats in 5 seconds. Figure 6 below summarizes the results. The results: less than 0.4% deviation from even illumination.
Optec Product Number: 19062
- Additional Information
SKU OP-19062 Manufacturer Optec Warranty 1 Year Warranty
- Included Items
- Optec Alnitak Flat-Man XL 18" x 18" Flat Fielder Panel
- Windows Controller Software
- Questions & Answers
Product QuestionsQuestion by: Steve Crouch on Sep 9, 2015 6:18:00 AM
- Support / Downloads