Quote:
Originally Posted by rmuhlack
This might muddy the waters further, but now for a practical test: compare the following images of NGC6164:
- Broadband image with Canon 450D @ ISO1600, FL = 650, f-ratio = 5, integration = 12.1 hours
- Narrowband 6nm Ha with ST10XE, FL =1278, f-ratio = 6.4, integration = 4.7 hours
I think the comparison is 'chalk and cheese' (especially in light of the slower scope in (2) ), and quite insightful given the discussion here in this thread. Even reducing the mean QE of the DSLR in the formula to 10% still suggests that the ST10XE is (only) 9.77x more sensitive than the 450D used here. Considering that the ST10XE image is narrowband and taken with a slower telescope, perhaps 10% is still being generous... |
thank you Richard.
At the risk of muddying the waters even further, I found some luminance data of the same region taken with my 250f4 and icx694 system. I tried a few different stacks until reasonably satisfied that the image SNR and depth was roughly comparable to your colour image. That required 36 minutes of data, which is about 1/20 the time needed for the colour image. There is not much science here (how to compare image quality by eye?, sky brightness?), but if the 20x difference in imaging time is anywhere near right, then I would agree with you that 10% is over generous for the average QE of the DSLR (at 10% QE, the model says that the difference should be "only" 6x). Although it is a sidetrack to the thread, this is a real eyeopener - I hadn't fully appreciated the extent (in image terms) of the difference between DSLR and mono.
I assume that the DSLR had been full spectrum modded when this was taken.