Andy Wray:
Alan Brunelle:
But for the IR work I mostly bought this for, I will only be sampling a small area right in the center of the field, so will ditch the coma corrector.
I'm intrigued. What will you be observing in IR and what kind of camera will you be using?
Hi Andy,
Thanks for the question! It gives me a chance to rehash to myself, just what it is I plan on doing and yet explain to someone who is actually interested.
I am interested in observing the light curves of young stellar objects (YSOs) and the like. I have some fool idea that I may actually see transits of such objects such as planets, dust from planetary disks, and nascent planets and star companions. Particularly ones that are more in the formative stage of developing solar systems. In fact, I would find it interesting to just find stars being eclipsed by rather dense dust clouds as well. There are a number of transiting planets that are now well known and fall into the category of "visible to the amateur" that can be followed. I point you to
@sky-watcher (johny) and his posts as someone who is very active at showing the AstroBin community his captures of variable star light curves. And he has also posted on planet transiting light curves.
But rather than just attack objects that have already been reported, I hope to do more of a saturation survey of starfields that the pros have identified as being particularly rich in YSOs. This will also include some well known and not so well know star-forming clouds. I hope to also follow some of the interesting well-known variable nebulae. By taking this approach, I hope to find some objects that have yet to be identified or to better characterize some of those that are already listed. Bu the discovery is the fun stuff for me.
To do this, I plan on imaging in both a visible channel and a NIR channel. This falls within the limitations of my currently planned setup. The camera I plan on using is the QHY5III462c. It is a pretty inexpensive small sized CMOS sensor that has physically deeper silicon elements that extend its sensitivity well into the NIR. Please see
New Toy(s), "First Light", IR camera for my first light with this camera. While the literature for this camera cuts off the performance data at 1,000nm, I found that when I use a strong 950 nm Edge filter (which strongly eliminates any light below 950 nm), I still get good sensitivity. Please also see
IC 1396A: Study Comparing Images from QHY5III462C (IR950 edge filter vs. UV/IR cut "visible"), and RASA QHY268C and
SH2-106, A Study in False Color with Combination of a NIR Channel two examples of imaging I did with this camera and the 950 cut filter using my 5 inch Mak Newt. For sure the hoped-for 12 inch will collect a lot more light.
My design for the 12 inch, f4 is to place a dichroic beam splitter in front of focus. Not unlike the On Axis Guiders used by some here on AstroBin to guide with higher end telescopes. The plan is to have the dichroic splitter do its job of separating the vis image from the NIR image and send them to two identical cameras that I mentioned above. That way, I can image real-time, both the vis and NIR bands I want to use simultaneously. Most variable star studies look at stars that show magnitude variations that have periods of hours, days or longer. I have seen some studies that have shown variation "features" that can change in minutes or less. Certainly, my 12 inch will not be able to see changes of seconds. But I am hoping to try for short as possible. And being able to image IR and vis simultaneously will be a great help in working out seeing issues as well as possibly discriminate between occluding planets and dust. NIR is less affected by dust than say violet of the vis, so such differential responses can say something about the occulting objects. Aside from the hardware challenges, I will need to learn to software processing in order to automate as much as possible the compiling of the data, since I hope to survey a good number of stars at the same time. I am not sure I am up to the task, but it will be fun trying. I would certainly like to reach further into the IR than 950-1100 nm. And there are cameras that work up to 1700 nm or even higher. But these are pricey and I will need to work my chops on the simpler setup first. What I do like about the QHY5III462 is its capability to work at both vis and IR. With identical image frame and pixel dimensions, it makes it really nice to compare the vis and IR data with a simple alignment. But unfortunately, the vis has a Bayer color layer. That limits its vis sensitivity if I work with one color band. So I may have to scrape off the Bayer filter, which is doable.
Probably more than you wanted to read! But you asked! I just got an email from my telescope vendor today. With a couple simple mods to go, the scope should be ready to ship soon!
Edit: I should have stated that I chose to use a Newtonian because the light path is 100% reflective. For the IR work, I wanted no glass between my subject and my sensor. And the filters that I do place between subject and filter, I define and can ensure that I do not lose signal to the wrong kind of glass, or optical coatings. I also was careful to ensure that I got an aluminum coated primary and secondary. Many of the reflective optics are now dielectric coated. And the manufacturers and vendors absolutely will not give you data proving reflectivity/transmissivity across the wide range of wavelengths I needed. In fact, some dielectric coatings have sharp cutoffs just longer than red. Finally, with the aluminum, I can easily strip the coating and do my own silver if I desire. Silver is a truly superior reflector for wide range light work, though it is painfully delicate and does not last long!