Skywatcher 190MN or 10"Newt+MPCC ?

[PortableAstronomer]

Hi I know we've had a similar thread to this before ( 190MN or Equinox 120)

I have an EQ6 mount and comparing the following:

Skywatcher 190MN , 190mm dia, f/5.3, OTA weight 12.3kg, cooldown time: slow

vs

Orion SPX250 + Baader MPCC, 250mm dia (73% more area), f/4.8, OTA weight 11kg, cooldown time: probably faster

both come to about the same price and weight.

but you get a lot more aperture for your buck with a 10" newtonian, even if you add the Baader MPCC

What do you think?

I'd be using it with a QHY8 CCD for imaging.

Your opinions much appreciated

Regards

Chris

[Whippy]

Aperture isn't the most important factor (if at all) when it comes to imaging so you can discount that.

I'd go with the SW 190MN as it's a smaller and shorter OTA (less chance of flexture) and got a shorter focal length (more forgiving for imaging). Cooldown isn't an issue, just buy a fan. What you will need though is a dew shield and dew straps/controllers as the corrector plate is a real dew magnet. The OO is going to be a bit of beast to setup and tear down for imaging every night, though the MN isn't excatly a lightweight either! If you had it on a permenent setup though (ie; in an obs), the advantages of the MN are lessened IMO.

Tony..

[PortableAstronomer]

Thanks Tony,

but the 10"/250mm Newtonian is *lighter* than the 190MN

My friend has a 190MN and I am quite impressed, and agree the front plate is a dew magnet but my past scope was an LX200GPS so I'm kitted out with dew controllers & sheilds etc..

"Aperture isn't the most important factor (if at all) when it comes to imaging so you can discount that. "

... Maybe so if you have a permanent setup and can leave the CCD on autopilot all night. But for a grab & go setup, I beg to differ; at the moment I live in an apartment so image 100% in the field, setup & align every time, and more aperture = less sub-exposure times = less critical on accuracy of polar alignment and more photons captured during short nights out. Ok that's a gross simplification. But if you want to capture as much light in a two-hour session before you have to pack up and drive home, then I'm still convinced aperture matters.

Anyway, grateful for your opinion. Clear skies to you!

Regards, Chris

_____________________________________________________

WO Megrez 90, Equinox 80, EQ6, QHY8

see my imaging & processing videos at

http://portableastronomer.blip.tv/posts?view=archive&nsfw=dc

_____________________________________________________

[Whippy]

the 10"/250mm Newtonian is *lighter* than the 190MN

The newt is indeed lighter, but it is bigger and longer which I reckon makes it more prone to flexture.

"Aperture isn't the most important factor (if at all) when it comes to imaging so you can discount that. "

... Maybe so if you have a permanent setup and can leave the CCD on autopilot all night. But for a grab & go setup, I beg to differ; at the moment I live in an apartment so image 100% in the field, setup & align every time, and more aperture = less sub-exposure times = less critical on accuracy of polar alignment and more photons captured during short nights out. Ok that's a gross simplification. But if you want to capture as much light in a two-hour session before you have to pack up and drive home, then I'm still convinced aperture matters.

You're entitled to your opinion but I'll give one very simple thing to think about. If aperture mattered in relation to imaging, then everyone who uses small refractors is wasting valuable time. I use a ZenithStar66 and an FLT98 for imaging and I do just fine. In fact I sold my 110m refractor to buy the smaller 98!

What does matter is focal length and focal ratio. Longer focal lengths are more affected by atmospheric conditions and show up errors in guiding more easily. Focal ratio is the 'speed' of the scope and antyhing f6 and under is quick enough I reckon.

Tony..

[PortableAstronomer]

Thanks again Tony, your comments are appreciated.

I use my Equinox 80 / Megrez 90 for wide field targets, so yes small APOs do have a great purpose, but for items such as planetary nebulae and smaller galaxies then you could do with a longer focal length. When I put the camera into my friends 190MN the longer focal length at same f/ratio (because of the increased aperture), then I never want to put it down. With a 10" newtonian + MPCC I'll get a bit more focal length for the smaller targets, plus an even faster system. That's the attraction for me (or so I think !)

Regards, Chris

[Starflyer]

I image with a 10" f/6.3 newt and it does give a nice image scale, but....

It's hard work getting the balance right

If there's even the slightest breeze you can't image

The longer the fl the better your mount needs to be set up and tweaked to get decent tracking.

Personally I'd go for the 190MN

[narrowbandpaul]

i would go with the MN190....flat field. Plain and simple.

I would wonder whether the MPCC would flatten out to the edges of a large chip such as that in the QHY8.

the MN190 I would think is more imager friendly...as it was designed for imaging and nothing else.

The only!!! thing that counts when imaging is focal ratio...focal length affects how much the seeing affects you, as tony has already said.

aperture is completely irrelevant....

I know it sounds stange, but for an extended source (not point source like a star) the focal ratio determines the number of photons striking each pixel.

i have a mathematical proof, if you want to see it, just ask.

but for me, the 190 wins.

good luck with the choice

Paul

[SteveL]

From someone who also has to set up and strip down for every session, the 190MN is about as large as I would go. That 10" will get blown around a hell of a lot in even the slightest breeze... the 190MN gets moved about a bit too, but maybe the slightly heavier weight of the 190MN helps with that.

Even so, you ask the question, but your comments in this thread seem to imply you really want to find a reason to go for the 10" anyway

[narrowbandpaul]

for the focal ratio-aperture debate see here....

http://stargazerslounge.com/astro-lounge/77512-focal-ratio-vs-aperture-size.html

paul

[PortableAstronomer]

Thanks everyone for your responses. I never expected so much input within just a couple of hours.

Yes I know focal ratio is really the more important items for getting light onto your CCD, and it's the faster focal *ratio* of the fast 10" Newtonians (for the same f.length) compared to the 190MN that was the attraction. I didn't mean to say that more aperture means brighter images in a direct sense; I meant that for the same focal length, more aperture gives you faster f/ratio, so less exposure time.

But like Paul says, a lot has to be said from a scope that's designed from the start for imaging. And 190MN is certainly proven for having flatter fields right to the edges of larger sensors. Plus the larger aperture newtonian will catch the wind more.

I think that's my question well & truly answered ! What a great site :-)

Thanks again

Chris

[narrowbandpaul]

here to serve.....