Age old Question of MN190 Vs 10" CF Quatto

[Northernlight]

Hi All,

I'm now residing to the fact that the second hand RC i bought was a lemon, and i need to move on instead of pulling my hear out.  So i'm looking at the Skywatcher MN190 Vs CF Quattro 10" and just wanted to get peoples views on the 2 scopes. I know everone will have their own views and i probably wont get a resourding answer either way, but still interested to get peoples feedback.

Weight is not an issues as i have an EQ8, so weight can be discounted in the argument.  Also cool down is not an issues as it will live permanently in my obs.

 

What i Like about MN190   : Flat field and no need for coma corrector or flattner,  Pretty Fast at F5,   Easy to fit a direct replacement Feather touch Focuser without opening the tube, good optics providing sharp refractor like perfoamance. Good for visual as well as imaging.

What I Like about the 10" Quattro :  Very Fast @ F4 so great for Fickle british weather,  Larger Aperture (10")

 

 

So i guess it comes down how much more detail would the 10" Quatto resolve over the MN190 for a given exposure length, lets say 600 secs.  Is the 10" & F4 optics of the Quattro going to make a huge difference or will it be marginal ?

Also, when itcomes to collimation of the 2, which is likely to holid it collimation better ?   Is the MN190 colllimated in the same way as a normal Netwtonian ?

 

Many Thanks,

Rich.

 

 

                                 

 

 

[billyharris72]

I'm not the best to advise, not having owned either scope, but I've read a few reviews on here and elsewhere and if it were me I'd probably go for the Mak.

On the plus side for the Quattro.

• The faster F ratio of the Quattro is equivalent to gathering about 1.5 times as much light, so you would need about 2/3 the exposure time (relative exposure scales with the square of the ratios between the two F ratios, so 4/5^2)
• The larger aperture means a smaller Dawes limit and theoretically higher resolution. Great if you often image from a mountain in the Atacama desert, probbaly means nothing in the UK.

Against:

• Collimation will be extremely critical, and quite prone to getting out of whack. I get the impression there is a big difference between F5 and F4 in this regard, but others will know better.
• I've read reports about this one being tricky to collimate and not holding it well (though at F4 even the tiniest shift will put you out).

By contrast:

• The Mak-Newt seems to get consistently good reviews
• Collimation should be relatively easy
• Pretty much coma free due to the corrector plate
• No diffraction spikes

I'd go for the Mak personally, but not any kind of expert. Be interested to see what others think.

Billy.

[Northernlight]

thanks Billy,

you just made a very good point about the resolution and the fickle british weather, which i had never even considered. Which i guess renders the extra aperture almost irrelevant. This makes my decision a lot easier.

Deep down in my heart i've always leaned towards to the MN190, as i like the idea of not needing any sort of corrector, which just means extra glass which can potentially fog up, which i have personally experienced.  Going to Give my 8" RC one last try, and if i'm still not happy with it, i'll be dumping the RC and pulling the trriger on the MN190 with an upgraded feather touch focuser as it fit's directly into the skywatcher base plate without needing to open the scope up.

 

Rich.

 

 

[Freddie]

Always been happy with my 190 and no spikes was a real bonus for me. I fitted a Moonlite to mine and opening it up to fit the new base plate was easy. The feathertouch will be a nice unit but I wouldn' restrict your options because some may need you to remove the corrector to fit them.

[Northernlight]

Hi Freddie, 

the feathertouch focuser bolts directly onto the Skywatcher base plate, so no need to open the tube :-) 

guess I'm just worried about mucking up the scope by opening it up.

[Skyline]

The MN190 is a nice imaging scope, the corrector plate shows round stars to the edge even with a APC-S size chip. Hence the reason I never changed to focuser as most of my imaging with the scope was with a dslr.

If I had the cash now and had to choose just one scope over what I have now, it would be another MN190.

[ollypenrice]

You've not had much fun trying to get the RC into collimation. (Neither did I when I was trying to help one of our robotic shed clients with his. We knew the theory and had the Glatter tools but one adjustment always threw another out.) This being so, how keen are you to risk another struggle with the Quattro? F4 does make a big difference to collimation and tilt as compared with F5. (The depth of field is so much shallower.) It really isn't easy to make an F4 system and trying to do it at a budget price is even harder.

I don't think you can expect the Mak Newt to be necessarily plug and play either but it might be less of a trial than the Quattro. Singlin wrote an excellent and detailed account of fettling a Quattro a couple of years back on here. If you can find it I think it would be very instructive.

Not tempted by the 12 inch F5 Newt?

Olly

[Northernlight]

Olly, a 12" newt is just too much of a big beast, the MN190 is the biggest wind sail I would want in my obs.

[ollypenrice]

23 minutes ago, Northernlight said:

Olly, a 12" newt is just too much of a big beast, the MN190 is the biggest wind sail I would want in my obs.

Good answer.

Olly

[Northernlight]

Grrrrrr, so sick of those BBC baboons, once again they forecast clear sky all night, and surprise surprise half way through collimating testing thick cloud cover rolls in. They couldn't get the weather right if their life depended upon it.

 

[Northernlight]

Well Olly,

I gave the RC collimation one last bash last night whilst waiting for the clouds to clear.  I gave my best effort with the Tak Scope, which when adding lots of extra lighting in the room was a lot easier to read.  finally the clouds cleared enough at 2am to do some collimation testing. The conditoins were less than ideal as it was really murky, so i couldn't get the best focus.

This was the best i could get with the Rc last night.  it's not the best, but it's also not the worst and i'm attributing the slightly elongated stars at the edge being down to my AstroPhysics .667 Reducer.   On the next clear night i'll try a test at the Native F8 and see if i still have the elongated stars or not, and if they still persist i'll pull the trigger on the MN190.

Have a look and let me know your thoughts.   Attached image was taken at F5.3 with the AstroPhysiscs .667 reducer and the FL was approx 1050mm.  Please excuse the unprocessed single image taken through thick murky conditions, but at least it still gives an idea on the state of collimation.

Rich.

 

[ollypenrice]

2 hours ago, Northernlight said:

Well Olly,

I gave the RC collimation one last bash last night whilst waiting for the clouds to clear.  I gave my best effort with the Tak Scope, which when adding lots of extra lighting in the room was a lot easier to read.  finally the clouds cleared enough at 2am to do some collimation testing. The conditoins were less than ideal as it was really murky, so i couldn't get the best focus.

This was the best i could get with the Rc last night.  it's not the best, but it's also not the worst and i'm attributing the slightly elongated stars at the edge being down to my AstroPhysics .667 Reducer.   On the next clear night i'll try a test at the Native F8 and see if i still have the elongated stars or not, and if they still persist i'll pull the trigger on the MN190.

Have a look and let me know your thoughts.   Attached image was taken at F5.3 with the AstroPhysiscs .667 reducer and the FL was approx 1050mm.  Please excuse the unprocessed single image taken through thick murky conditions, but at least it still gives an idea on the state of collimation.

Rich.

 

Well that looks pretty darned good to me. I could live with it as is, though I'm not of the pixel peeping mindset. A few dabs with a recorded 'star rounder' action in two of the corners would sort it completely. It might just be the disance to the reducer, anyway.  I'd call that nailed to within a gnat's crotchet, as Humphrey Littleton would have put it.

Olly

[billyharris72]

Not too shabby at all is my opinion; the stars in the centre look quite good to my (albeit uncultured) eye.

I can't see from the image but are the elongated stars at the edge of the image comatic or are they symmetrical around 2 axes? If the later then is this not likely to be the RC itself? I thought that was the point in the RC design, trading off increased (but symmmetrical) astigmatism against coma.

[johnrt]

If you're at approx 1050mm focal length then you're right at the limit of the focal reducer, the CCDT67 is very forgiving up to it's maximum reduction of a spacing (of I think 85mm) from chip to reducer. I would just reduce the spacing and I think you'll find those corners will be just fine. I have mine set to reduce about x0.7 on my 6" RC, just a little under the maximum tolerance.

But like Olly, I'd be happy with that, don't forget you'll lose the edges anyway cropping the RGB channel overlaps.

[Northernlight]

Thanks All,

It's nice to make some progress with the RC as i was ready to throw it out of the window.  One other factor that may have helped was that i completely stripped it down and rebuit it, which may have resolved issues like pinched optics etc.

John, thanks for the heads up on the focal reducer spacing. I set it to exactly 85mm as that was the quoted spacing distance to use on the Teleskop Express website where i bought it from. On the next clear night, i'll reduce the spacing down maybe 5mm and see how i get on with that,whilst it would be slightly slower, i would welcome a little bit of extra focal length.

I'll post another image after i reducing the spacing on the next clear night i get.

 

Cheers,

Rich.

[alan potts]

I have a M.N 190mm and have always been very happy with it, purely for visual use I find it realy does almost offer APO views. I am not sure about your claim that it is easy to change the focuser, I remember reading a sizeable thread on this and then thought I will stick with what I have. I have seen some first class images taken with them too and although I don't know much about AP it does just come into Olly's a meter or less F/L is best quote that he made a long time ago. My AZ EQ 6 handles it with ease, I even had it on a HEQ 5 Pro before but only for visual you understand.

Alan 

[Northernlight]

Hi Alan,

on the MN190 focuser side of things, you can get a feather touch focuser with adapter that fits directly onto the Skywatcher base plate, no opening the tube or removing any base plates, literally swap out the Skywatcher focuser with the feather touch and the associated adapter and it's perfectly aligned, no faffing and no worries about positioning it correctly, just a direct swap.

you can get them directly from FLO

 

Rich.

[Northernlight]

Well i managed to get a 15m break in the clouds so rushed to power up the obs and test RC again. I reduced the recommended 85mm spacing down to 75mm for the AP CCDT 667 reducer, which has added approx 100mm to the focal length. scope has went from approx 1050mm @ F5.3 to  1150mm f/l @ F5.75

so gained a bit of extra focal length and speed still acceptable, but now has now greatly improved the corners and reduced the vignetting significantly.

 

Rich

 

[johnrt]

That looks pretty good now Rich. Glad it's sorted for you.

[Northernlight]

Still not 100% happy as there stars are now slightly elongated to the left side of the image, and looking at CCD inspector i can see that i'm slightly off, so i'll keep plugging away, but at least it show that the image is fairly flat.

 

 

[Northernlight]

The hard bit now it trying to interprate what ccd inspector is showing me. Is that pink area due to primary or secondary, who knows. Guess I'll just have to try with trial and error.