I see that Agena Astro has the new QHY miniCam8m with a built in filter wheel and a set of Sloan photometric filters, for $1099. It has an 8 position filter wheel with u’, g’, r’, i’, z’ sloan filter set pre-installed. The camera is a cooled monochrome IMX585 sensor, 12 bit, 2.9μm pixel size, 60% QE in infrared, 92% in visible.
Sensor Size: 11.2 mm x 6.3 mm, 12.85 mm diagonal
Effective Pixels: 8 MP
Full Well Capacity: 54ke-
I’m tempted, as I could stop using my main astrophotography rig for photometry and dedicate a rig just for photometry. Also I’ve been choking on the price of a set of photometry filters, and here’s a camera that includes a set.
My questions are:
What are the downsides of this camera/filter setup? It’s a QHY product so won’t work with a ZWO ASIAIR. I’d have to use a mini-PC instead. It’s 12 bit, so doesn’t have the dynamic range of a 16 bit camera. Sensor size is small, but not the smallest. What else for downsides?
Are the Sloan filters a weakness? Rather than Johnson-Cousins filters?
What telescope would be a good fit for this camera specifically for photometry? I’m thinking moderate size refractor is all that would be needed. Wouldn’t even need to be an APO, since you’re shooting through filters all the time.
I am also considering a second setup and was considering this as an option. In Canada the camera would cost $859 Can (no filters) and the Sloan set of 5 would cost $560 Can. To get a 585 ProM, filter wheel and Baader B,V, and I filters would total about $2000 Can. The concern I have is that I would be tied into the QHY mini format for all future filters, which being a real niche product, may be hard or expensive to obtain. Also, if the Minicam unit goes on me, I have nothing, whereas a modular approach allows me to replace individual bits. (In my own case, I already have a QHY 533M, FW, and Baader B and V filters. I am wondering if a OSC camera might be useful for TG photometry might be a better alternative.)
So a modular approach is more expensive, as long as the minicam combo does not fail, but may be more flexible for other purposes (maybe). I hope someone with actual experience with the unit will tell us of their experience.
Rick
Someone on CloudyNights says the AAVSO was gifted two of these cameras at NEAF in April. I’m eager to hear a report on how well they work for photometry.
I’d love to hear more about this as well. I saw it at NEAF and was very intrigued by it.
I would particularly like to hear expert opinions about the Sloan filters. Are they a real disadvantage for submitting to the AAVSO, where the vast majority of electronic photometric data is Johnson-Cousins? If you do use Sloan filters is the best practice to submit the data directly or transform it to Johnson-Cousins V, R, B, etc.?
The AAVSO received two QHY MiniCam 8’s with their (custom) Sloan filter sets for testing earlier this year. The camera is quite interesting because it includes an additional readout mode that uses both 12-bit A/D converters in tandem to simulate something that has a greater bit depth. Unfortunately, due to an unseasonably wet summer in the south-west USA, we have yet to begin our evaluation of the units.
In regard to transformation from one photometric system to the other, you should always report your data in the native photometric system. Sloan filters should be reported as Sloan. Johnson-Cousins should be reported as Johnson-Cousins. Transforming between systems leads to increased uncertainty regarding effective bandpasses which can be very important for certain astrophysical processes.
What do you think just in general of using native Sloan filters (like the QHY MiniCam8) for submitting data to the AAVSO? Is the data less useful in any way because of the fact that the great majority of the data already there is in Johnson-Cousins filters?
I wouldn’t be too concerned about the quantity of data in any given photometric filter. Professional astronomers are well-versed in applying photometric transformations between systems. They know when and how to apply them, while avoiding the edge cases where transformations fail. In addition, most modern modeling software can simulate observations in any filter, allowing professionals to combine data from a variety of photometric systems to support their analysis.
My advice is to remain in the native system of your instrument. In your case, with Sloan-like filters, you should transform your measurements onto the Sloan system and submit them as Sloan data.
Please also keep in mind that each time you change systems, you must propagate the corresponding uncertainties. Many amateur astronomers overlook this step, which can make their data appear more precise than they actually are.