C6/Starizona Corrector II Test : M81 M82
I think i enjoy testing things as much as i do full acquisition finished product. This post is the sort of thing i look for when researching before making a purchase decision, and in so, i hope it's useful to someone. Sort of a crazy story but i was considering purchasing a C11 a few months ago. I preemptively purchased a Starizona Corrector II and then decided against ordering the C11. So...i've been sitting on an expensive SCT corrector II without a home :). After looking at High Points Scientific's price on a C6 ($388), i couldn't pass it up and took receipt of it a week ago. When the Starizona SCT Corrector II is used with the C6, the focal reduction is .69X which equals a FOV of 1035mm / F6.9 with a Full Frame Sensor. I like to do my 'tests' during the moon period, and last night it was bright and full. I attached the corrector and mounted the C6 to the ZEQ25 after leveling. As a note, the C6/Corrector/A7S = just under 11 lbs. The C6 tube by itself ( i weight it) is almost exactly 8 lbs.
So, i wanted to see just how well this combo's field is. If anyone has ever imaged with a standard SCT (or even a standard SCT with the standard Celestron .63x reducer), knows how bad it really is. Every image that i've ever seen captured by a standard SCT (even with the standard reducer), the end product has about half of the image cropped out, and even then, coma and elongation is evident. Only the very center is flat. Starizona's selling point, as it relates to the corrector, or at least the 'buzz' about it, is that it essentially will turn a standard SCT into the same field as the Edge series. Now i have the EdgeHD 8 and i can tell you that it's for real - completely flat from edge to edge on a full frame.
Does the buzz hold water? Not exactly but it's close. I would say that the field is very flat somewhere between a FF-APS-C coverage area but just falls short on full frame coverage. This was my first time imaging with this set up and i do have a few issues. The bottom right quadrant is out of proportion as it relates to the other three quadrants. Most of my issues can be seen in this area and it's either a slight collimation variance or the compression ring holding the corrector in place wasn't even. I hope to later work that out.
However, i'm thrilled with it and i would absolutely recommend it. It's very costly to have a large aperture with a flat field, a decent F stop (F6.9), and light in weight. Here you have a flat APS-C (at least), a little over 1000mm, 11 lbs (total tube/camera/corrector), and 150mm of aperture. Total cost : less than $800 bucks (388 scope / 399 Corrector).
Flat frames are absolutely necessary with this combo and especially when using a full frame sensor.
Single light frame : A7S/C6/Srarizona Corrector II
For the stack, I tried to leave as much of the full frame as i could after the stack but i did have to crop out the stacked edges. Here is the stack of 1hr 45 minutes,during full moon, backyard, hard-stretched to emphasize star shape imperfections, with my standard editing routine.
Let me know what you think in general.
I really like the result from your stack. Yes, that corrector does a good job in helping the SCT's field. But I also enjoyed how you preserved a lot of star colors as well as some nice detail in the galaxies. There are a few very faint background galaxies to be found as well. Overall a very good image of an iconic pair. That 6-inch SCT gives a very useable focal length, particularly with the Starizona corrector. Thanks for sharing your success with the forum!