How important is flat fielding?
That depends on what you are imaging. For small bright targets like globular clusters where you aren’t doing a lot of stretching of the image and will be keeping the background dark, not so important. For dim nebulosity that requires lots of stretching and digital development, critical.
For photometry, flat fielding is important for accuracy. Since it is impossible to keep the target on exactly the same set of pixels over a photometry run even with the best autoguiding and mount performance, any inconsistencies in pixel response have to be characterized and removed. That’s what the flat does. I have used the Flip-Flat on my NP-101 to get millimagnitude accuracy for exoplanet transits. Try that without a flat field!
How much better is a flat frame from your products than a dome flat or twilight flat?
What Alnitak Astrosystems products offer are stable, repeatable, and extremely uniform flat field images, with uniformity which deviates less than 1% from a mean value. See the results of our tests here and on the Flat-Man XL page.
Your alternatives are twilight flats or dome flats. Twilight flats can give good results when the telescope is pointed to a null point in the sky, but just where that null point is depends on lots of variables, some of which are changing from moment to moment.
In addition, since you are using the light of the sun below the horizon to illuminate the sky, the brightness is always changing, so your flat durations have to constantly change. While there are automated solutions out there, CCD Autopilot being one of the best, you still are racing with the clock to get enough flats (say five to ten in each filter) for good noise statistics.
As your camera/telescope field of view gets wider, it becomes harder and harder to avoid some gradient across the image when using twilight flats. Any gradient in the flat field images will ADD a gradient to your flatted images, just what you are trying to avoid!
Dome flats can be a good alternative to twilight flats, but they have their own set of problems, chief amongst them being uneven scatter off the white surface that has been illuminated by an off-axis light source. Open tube telescopes will suffer most from this scattering. We have seen good dome flats, but none with less than 0.5% deviation from uniformity, and usually with some sort of radial gradient.
What about spectral flatness? Don’t I need to use a uniform light source that has the same spectral signature as the night sky?
Ideally, yes, but I challenge you to find such a light source. Twilight flats come close, but you loose the spatial uniformity. The rule of thumb is that as long as you use the same filter for flatting as you do for imaging, the spectral response won’t be an issue.
For critical scientific photometry, professional observatories often combine dome flats (rarely less than 1% deviation from uniformity) with high quality sky flats to combine the best of spatial and spectral flatness.
A sky flat is a median combine of hundreds (or thousands) of images of a star free section of the night sky, free of light pollution gradients. It is virtually impossible for amateurs to make a master sky flat since it would take many evenings of imaging to do so, and who of us has gradient free skies?
What about narrowband filters?
Our products are perfect for narrowband filters. The broad spectral output of the electroluminescent panels means that there is plenty of light at each of the three major narrowbands (Ha,OIII, S2) to reach ADU counts of 20,000 to 30,000 in 5-20 seconds, depending on the quantum efficiency of your detector. Here is the spectral output of the panels.
Will your products remove the dust donuts on my images?
Yes, but only if your filter wheel positions the filters in EXACTLY the same place as they were when you imaged the target through them. We recommend taking flats between filter changes. This is easy to do when you have on-demand uniform light sources as provided by our products. Try that with twilight flats!
Can I control your products from a terminal window in the Mac OS?
Yes. See our generic serial commands reference document.
When I am using other FTDI-based USB devices, the Alnitak application cannot find the Alnitak device or cannot connect to the Alnitak device. The status is “Invalid Handle” or “OK”. How do I fix that?
Download and install version 1.1.6 or later of the Alnitak Astrosystems Controller from our website. This version fixed a problem with not connecting when other USB/Serial devices that use the FTDI chip are connected.
When I run the Alnitak Astrosystems Controller my QSI camera starts beeping and may stop responding. How do I fix that?
Download and install the latest software from our website. You may need to do a one time update of your Alnitak hardware. Read the “Please Read this First” document found at the Downloads page and follow the instructions for update.
Download the latest camera drivers for Maxim and CCDsoft from QSI.
Do the Alnitak software applications work in Windows 7?
Our appications were designed in a 32 bit XP environment but Windows 7 will treat them as such an run fine. If you need to view the device or update the FTDI driver you can open Device Manager which looks very similar to XP’s Device Manager. To open it click Start, then Control Panel, then System & Security, then System, then Device Manager. From the list, click Ports (COM & LPT) and find the Alnitak device by selecting the device named USB Serial Port (COMx) where x is the comport that your computer assigned to it when you installed it. Some customers with Win 7 have been unable to connect to their Alnitak device. We have found that if you uninstall the FTDI driver (see below) and then reinstall it from our folder the problem is fixed.
How do I update the FTDI drivers for the Alnitak device?
Plug in the device. Open the Device Manager. In XP you find it by clicking Start and then select Control Panel then System then Device Manager. In Win 7 you click Start/Control Panel/System and Security/System/Device Manager. Then click on Ports(COM & LPT). Using the COMx port number that you see when running our application, double click the “USB Serial Port COMx” device (where x is the port number). Then click the Driver tab. The latest driver at this time is 2.8.2.0. If you want it to check for later drivers click Update Driver. If you are not connected to the web you will first need to go to the Alnitak folder in the Program Files folder and expand the file called CDM20802 to a new folder you should call “CDM20802”. If you are connected to the web you can check “Yes, this time only” then “Install the software automatically”. It will go find the latest Windows drivers (two of them). If you are not connected to the web you can click “Install from a list or specific location” and navigate to the i386 folder in the CDM20802 folder.
What do I do if the application will not connect to the device and gives an IO_ERROR?
Uninstall the driver as described below then re-install the driver as described above.
How do I remove the FTDI driver from my PC?
Disconnect the Alnitak device(s) from the PC. Open the Alnitak Astrosystems Controller folder in the Programs folder and unzip the file called “CDMUninstaller_v1.4.zip”. Open the resulting folder and double-click the file called “CDMUninstallerGUI_v1.4.exe”. Leave the VID and PID at the default values and click the Add button then the Remove Devices button. If you later reconnect the Alnitak Device(s) you will have to allow the PC to search for the drivers on the web and let it reinstall them.
How do I change the COM port that the Windows assigns to the device?
Plug in the device. Open the Device Manager. In XP you find it by clicking Start and then select Control Panel then System then Device Manager. In Win 7 you click Start/Control Panel/System and Security/System/Device Manager. Then click on Ports(COM & LPT). Using the COMx port number that you see when running our application, double click the “USB Serial Port COMx” device (where x is the port number). Click the Port Settings Tab. Click the Advanced button. In the COM Port Number window select the COM port you want. Note, COM ports may be declared (In Use) even though they are not. That means that a device was assigned that port when it was connected and Windows remembers that. Be careful to select a port you know is not being used. Click OK and you will get a warning. Click Yes if you are sure you want to continue. From this point on, whenever the device is connected it will use the new COM port unless you have manually assigned another device to the port.
How do I delete Phantom Devices from the Ports(COM and LPT) list in Device Manager?
Open this document and go to section 7.2 Phantom Devices. This will allow Windows to show all hidden devices that may have been previously connected to Ports in the past.
You may then delete any that you know are not going to be used. If you delete a USB Serial device that is later reconnected to the PC you will have to go through the driver installation again and a new COM port number will be assigned starting at the lowest available number.