Hello,
I hope it's the right place to post this thread.
So, I'm a person interested in observing exoplanets. I started in 2016 and for now I have 4 succesful detections. Could be many more, but it wasn't possible because of clouds. My first setup was Canon EOS 60D and Pentacon 4/200 on EQ5 mount. I got a very satisfying results, but the problem was a limiting magnitude. I was able to measure up to 10th magnitude, so only a few (6-7) planets were within range.
So I decided to upgrade my setup a little. Now I use ASI178MM-cooled camera and Canon FD 300mm f/4 lens, which gave me new possibilities. My photometric tests have shown that I'm able to observe up to 12.5-13.0 magnitude with a decent accuracy at 9-11 mag. Unfortunately, this lens has large chromatic aberration, but I don't use any filters (just AR coated window). But as I see, it doesn't affect that much (and I found the same thing in other topics). For a 10.6 star, I got +/- 0.028 mag for 10 second exposures. Stacking to 6 images (to get a 1-minute integration) gives me an error of +/- 0.012 mag for every measurement during my observation.
If there was a question about using a yellow filter. I used it once and I got quite OK results. But another day I tested without this and I had a little better measurements. Maybe the conditions were different or made a mistake in camera settings, so I should try again.
So, here are my questions regarding to situation. I plan to still upgrade my set and I'm not sure where should I go next. At this step, I'm thinking about placing 4x Sky-Watcher 120/600 achromatic refractors on NEQ6 mount + one smaller scope for guiding. It's 2.56x more light than currently for one telescope, so it gives +1 magnitude for limits. It's all about getting as much data as possible, so typically 4x more measurements allow to compare/average etc to get a 2x smaller magnitude error. I don't think that exposures longer than 60s are needed, probably never tried to do that because of tracking problems (at this moment, I don't have guiding). Mostly because of ampglow thing. I'm pretty sure it would take a few years to finish, but at this moment I would know what I think wrong or if there are any other solutions.
1) I'm very happy about the current ASI178MM-c photometric accuracy. Do CCD cameras in the same price allow me to get similar or better photometric results? And the limiting magnitude? My knowledge about that limits to Google graphic images for phrase "Atik 314L+ photometry light curve". There actually isn't much! I don't have any CCD experience yet, just DSLR and curent CMOS camera. Personally, if the results are similar, I would choose ZWO cameras, because later I can use it for other purposes (like occultations, which require me to record in high FPS). I also don't plan to find new exoplanets, only observe the currently known. Why this question is important for me? Because I don't know if I should buy 4x ASI178MM-c cameras or (for example) 4x Atik 314L+'s.
I'm nearly sure I will get answers like "it's 14-bit, and CCD is 16-bit!", "look at the full well, it's so low!". Only practical tests interest me. This is a little example what I'm trying to do:
http://var2.astro.cz/tresca/transit-detail.php?id=1494701725
David used a camera that costs 6.000$. For the same money I would buy 5 ASI178MM-c (or nearly 5) cameras. He got +/- 0.003 mag accuracy on 180-sec exposures using his 8" scope. His telescope collects 7.326 more light than my lens, so if the star has 12.26 magnitude, the same exposure setting he would use with 75mm lens to measure a 2.16 mag brighter star, so 10.10 mag. For a 10.10 mag star, my accuracy is +/- 0.021 mag for 10s exposure times. Because in 180s I can get 18 shots, typically it reduces the error by 4.25x, making it +/- 0.005 mag. David wins, beacuse he got +/- 0.003 mag. But I still could use 5 cameras at once, making 5x more measurements giving me ~2.24x smaller error (giving me finally +/- 0.0022). But the thing is, if he got a CCD camera 5x more expensive, would (for example) Atik 314L+ with similar price beat ASI178MM-c camera?
Sometimes I think if these calculations actually make sense, so I hope to get more direct tests from AAVSO community.
2) Is the idea about 4x achromatic refractors good? What are your opinions about that? Is there a requirement about the distance between telescopes, so seeing won't interfere? This is an example why I even think about this idea: http://bialystok.ptma.pl/wp-content/uploads/2017/04/Tranzyt_56.png (yes, all 4 telescopes would be aligned to track the same object). Or, just focus about one large telescope (like 10" f/5) and one more expensive camera, in total price of 4x 178's and 4x 120/600's.
Regards,
Gabriel