notFritzArgelander wrote: ↑Mon Sep 16, 2019 9:39 pm
Jaq1967 wrote: ↑Mon Sep 16, 2019 2:51 pm
I gain nothing then from moving from a 6" f5 (150/750) to a 8" f4 (Quattro, being 200/800) - except for the extra f1 difference?
Seems like a pointless upgrade if going bigger means no massive improvement in image capability?
I think the 190NM isn't going to do anything for me and seeing my HEQ5 Pro isn't up for the extra weight then no point looking at it.
The Skywatcher Quattro 8CF (Carbon) is discontinued. No idea why.
So, the choice is between the 200PDS (f5) and the Quattro 8S (f4) - (Now known as the Quattro 200P). I gain nothing with the 200PDS on my existing 150P. Both are f5. So unless you are doing visual, for AP they offer nothing new? Not to mention lumbering a larger and heavier scope for my mount and essentially more to catch the slightest breeze!
You gain a little in resolving power. The 6" has 0.95 arc seconds resolution, the 8" has 0.71 but you will only see that on nights of above average seeing where the atmosphere allows better than 1 arc second resolution. On average nights of about 2 arc second seeing you won't be able to tell.
Visually you gain in limiting magnitude for stars, point sources. The 6" has a (Baker) limiting magnitude of 12.7 and the 8" has 13.3. I find the Sidgwick limiting magnitudes more useful for which the limits are 14.6 and 15.2 but the human eye is fickle YMMV.
As far as
AP is concerned the figure of merit I use is the square of the
aperture divided by the square of the f ratio.
That's where you'd see a difference. It's a measure of the relative anergy delivered to each pixel of the sensor. By that measure the 8" will give the same signal to noise ratio 2.8 times faster. So you'll get good images much quicker.
Thanks for that... all very technical. A real learning curve this.
We talk a great deal about the lens/scope and its ability to deliver information to whatever it sends this information too. How about the latter? The quality of the receiver, the thing that receives this information? The eye? The Sensor? Camera; be it
CCD,
CMOS sensor, a dedicated Astro camera or
DSLR (modded or un-modded) is of equal, if not greater, consideration when pairing up with the scope? A good camera could afford to work on a less 'fast' and/or smaller scope?
I have an Altair Astro Hypercam 183C Pro TEC. I've yet to have tested this properly in the night sky. It seems to be fairly medium (to high?) in spec. Being dedicated (a reason for purchasing it), I'm kind of guessing it is a better option for
AP than a modded
DSLR? Is it better? What could I get away with (scope-wise) using this type of camera? I used to use an old Pentax KX (un-modded) with fairly good results, considering it isn't really designed for
AP.
Thanks for your advise on this. I'm kind of thinking now maybe I should consider refractors as scope options for
DSO AP now, and not just reflectors? They are lighter and smaller. I dare say more expensive? Evostar: 72ED, 80ED, 100ED and/or 120ED (...range of DS Pro). Hmmm....
Finally, I guess the bottom line is having the tools to hand is what you can do with them and how good you are at using those tools pre and post processing.