MN190 or Equivalent for Photography

[BlueAstra]

I've seen lots of good reports of the SW MN190 for astrophotography. It has an aperture of 190mm and a focal length of 1000mm, working at F/5.3. The current price is around £940. A focal length of 1000m would be close to ideal resolution with my camera setup. On the other hand, a lot of people would recommend a refractor for photography. I'm not sure what would be an equivalent refractor that gives similar or better performance as the MN190 at about £1k-£1.5K, so my questions are:

Does such a refractor/s exist?

What is it?

Would you choose it over the MN190?

Are there any significant pros and cons for the MN190 v Refractor?

As you might have guessed, I'm considering buying a MN190 for photography, and I want to explore the other possiblities.

[MartinB]

Refractors at this sort of focal length tend to be slower than F5.3. The ED120 is F7.5. You can spend several thousand pounds and get a high end apo with equally high end focal reducer and flattener to bring things down more but you are still likely to be around F6+

I have an ED120 and an MN190. I use my ED120 largely as a quick visual set up on a small Vixen Super Polaris mount. Relatively light so easily mounted, no worries about collimation. Cools down much quicker than an MN190. Also a refractor is much more pleasant and convenient to use that a reflector design for visual.

My MN190 is used in a dome on an EM200 (similar weight capacity to an EQ6). The dome is very sheltered which is a good thing because the MN190 is quite bulky and heavy. This could be an issue when out in the open and there is a breeze. In my opinion it would struggle on anything less weighty than an Eq6

The Mn190 has a very flat field which is great for larger chips. The ED120 reducer apparently works very well but I haven't used it.

For imaging the MN190 will grab your data faster than an ED120 and the optics are certainly up to the job. The main downside is that it is harder (and scarier) work mounting and more susceptible to wind. A fast scope quickly looses it's advantages if you have to dump a lot of subs owing to light gusts of wind! It makes some big demands on it's mounting rings so differential flexion is a potential problem. I am using off axis guiding to avoid this problem, and also to reduce the set up weight.

If I had to choose, purely for imaging, I would go for an MN190 but I would want a small refractor set up as an alternative for those breezy nights.

As a general purpose visual, imaging, convenient, go anywhere scope it would be an ED120.

[BlueAstra]

Thanks for that reply, its very useful to see the differences. I have to set up the EQ6/C8 SCT and tear down each evening, and don't have the wind shielding advantages of a observatory. I was thinking of building a run off shed, but the scope would be exposed to the wind when used. Although I guess I wanted the MN190, its weight and wind susceptability may make it problematic in my situation. I currently lift about 10kg of scope kit (C8+ED80+bits) onto the mount each time, compared with 10-12kg for the MN190 so maybe its not too different. But if the wind picks up it would have a bigger area than my current scope. Perhap a refractor would be a better choice.

Is there any optical/other difference between the Eqinox 120 APO and the Evostar 120ED PRO?

[Whippy]

The Equinox 120 and the ED120 have the same optics. It's worth a mention that I don't use my ED120 when it's windy because of the potential for dropped subs too so maybe that's not such a huge issue.

I occasionally get the urge to swap my 120 for a MN190 but I would also budget in for an OAG which bumps the cost up a bit, I'd also have add in dew straps, a shield and a larger heavy duty dovetail too. It's a tricky one because it's clearly a great scope but it is a bit of a brute which causes it's own issues.

The ED120 weighs nowhere near the same, it balances side by side with a ED80 or ZS66 and as Martin mentions, it's a pretty good all rounder. But it is a fair bit slower so imaging, epecially the fainter targets I've found can be a bit more drawn out. I've yet to try my reducer (WO FFII) on it but it's works well on my ZS66 & ED80 so I'm hoping it'll work just as well on my 120 and cure my urge to spend money!

Tony..

[ollypenrice]

I think Martin's is a definitive reply to this one and also covers the practical charms of the refractor. Physical difficulties apart, the MN190 is clearly a killer telescope.

If you are dead set on about a metre of FL then I can't think of any refractor that can give you that with a fast f ratio.

I now have a TEC140/980 F7 and previously had a Meade 127/950 F7.5. They both gave/give excellent results. On DS objects the TEC has only a small advantage but on the quality of the stellar image it is way ahead, controlling hot blue stars incomparably better. How the Meade compares with the ED120 I don't know.

Catatonia has just switched from ED120 to MN190 so might have useful input.

Personally I wonder why you are so concerned to get the perfect sampling rate. I use our Atik 4000s happily between FLs of 328 and 980mm. Indeed I use them with an 85mm camera lens as well, though just maybe there you would see an improvement from smaller pixels. Of the various focal lengths I have available I feel that a metre is the least productive for me. Too short for most galaxies and too long for many nebulae. It still has plenty of work to do, of course, but if I had to choose a one size fits all FL it would not be a metre but rather less than that.

For me the big issue is, 'What FL do you need to frame your chosen object?' and if that is where you are coming from, then I'm with you.

Olly

[BlueAstra]

Olly, you are perfectly right, I have been fixating a little too much on pixel resolution of my new SX H16. My Meade ED80+FR gives a stunning wide FOV of 2.3deg, but when you zoom in you can see the effects of 4"/pixel, so I was looking for something with a little longer focal length. But I guess its horses for courses for wide field. My C8+FR would be 0.7deg @ 1.2"pixel, so I was looking for a middle ground FOV. 1000mm (MN190)would give me about 0.9deg but its a bit close to the C8 FOV, whereas the SW120+FR would be about 1.1deg. So taking into account a FR, I guess I'd be looking at about 700-800mm focal length to give about 1.5deg FOV.

Its all a bit of a thought experiment at the moment: 'What would be the next scope you would buy if you had the chance'. If the opportunity arose for a bargain (Astrofest?), I'm just trying to work out what it would be.

[Coco]

Ive just changed form a Meade 127 APO 950mm /7.5 to an MN 190

I would assume the 120 Skywatcher would have similar capabilities ..

Advantages of the APO triplet:

Light weight - (Flexure - additional scopes mounted at the same time)

Smaller form factor (width wise)

Faster cool down

Less susceptible to wind

Dew issues almost none!

Reasonably flat field (certainly superb for 314L chip set)

Not having to hand cameras upside down

Advantages of the MN190:

Fast - very fast

Flat Image - Even with DSLR size chip sets

Cant really think of others... someone will jump in no doubt

Would I have kept my triplet?.... yes!

had I not calculated the real size of the MN190 - it doesn't fit my obs ( neither did the triplet) so I'm back outside in the wind and therefore worse off.. Money lost on the sale of the triplet also annoys

If I had a bigger obs I'd be much happier...

[TrickySpot]

I hear lots of people complain about the weight and flexure, but a good losmandy style dovetail top and bottom (400mm+) does wonders for stability. The wind is not my main complaint, my neighbor's spotlights is! Fab scope all in all!!

[perfrej]

190MN is, as stated above, a killer scope. Besides, the images have a distinct refractor feel about them.

You need to tweak it, though, something that you usually do not have to worry about with a refractor.

/per

[Gina]

I love my MN190 - a really superb scope which gives great images. I have a large observatory so it goes in alright though I wouldn't like to accommodate anything bigger Yes, it needs a dew shield and dew heater. I bought the former from FLO and made the latter. And it's certainly heavy at 10KG but I have an electric hoist I use to move scopes and the NEQ6 mount but a reasonably strong man shouldn't need that. I certainly wouldn't class it as portable but is a great astrograph when installed in a big enough observatory.

[reddoss]

As I live in the middle of a city in a new housing development where the LP is terrible, I have no choice but to take my MN 190 out into the country. I have no problems  with portability and setting it up, you get used to it. People say it's heavy at 10 Kg, but that is about the average weight of a 120-130 mm triplet APO OTA. It takes wonderful images and I think it would be very hard to beat the quality for the price. 

I am thinking of getting a triplet APO for imaging as well.  Possibly the WO 132 flt but not sure which make/model is best in my budget of around £4000 which has to include everything, OTA, rings, finder, case and reducer/flattener. 

[laser_jock99]

I hear lots of people complain about the weight and flexure, but a good losmandy style dovetail top and bottom (400mm+) does wonders for stability. The wind is not my main complaint, my neighbor's spotlights is! Fab scope all in all!!

There is a lot to be said for ditching the factory supplied Vixen/SW dovetail bars and 'top & bottom' bracing the tube rings with longer, stronger dovetail bars.

My 300mm Newtonian sits upon a 0.5m custom Losmandy bar (pictured with standard Skywatcher bar for comparison....)

I don't worry about flexure anymore.