5" Apo or a Mn190 for 80% imaging 20% Visual

[Davey]

Hi Guys, I've not long moved to Oz from North Wales ( just over a year)where I reluctantly let most of my Astro kit go. Mistake!

I'm now living in country Vic and hope to get started soon and want opinions regarding buying a 5" Apo or another MN 190 ( I used to own one back in the Uk, see attached images).

My Mn 190 was in a permanent setup under a roll off roof obs, here I'm going to have to set up and tear down each night .

My scope use will be approx 80% imaging and 20% visual

My biggest worry with this equipment dilemma is ,

Will I miss the higher resolution and light grasp of the Mn 190 if I buy a quality 5"Apo refractor.? Having never owned one you see.

I should also add that I already have a Ed80 in the stable and a QSi 583 with all filters. I'm being swayed at the moment by the convenience of a refractor setup though.

I'd especially like to be pointed in the direction of deep sky images others have taken using a 5" Apo.
Thanks Guys

Dave Moulton

[glend]

Welcome Dave. I have a similiar setup to your old one: a roll off roof observatory with a pier mounted CGX mount. My scopes are: MN190, a TS Photoline 115mm f7 APO, with reducer to f5 when required. I also have a 10" f5 imaging newt and an Edge HD8 for long focal length and planetary imaging. I am pretty much all imaging due to age related eye problems. My cameras are the ASI1600MM-C and a cold finger cooled full spectrum Canon 450D.
I do prefer the MN190 for most of my imaging, for the reasons you mentioned. But it is heavy to move back and forth. The Photoline APO is a great lighter weight package that gives wider field capability. I see a place for both. Have a look at my Astrobin gallery link at the bottom here, and you will see examples from both scopes, and the 10" newt. I don't claim to be a very good imager, so don't judge the quality, rather look at the field coverage.

[Atmos]

http://www.astrobin.com/users/AtmosFearIC/

Only ever used a 5" APO or DSLR lens' for wide field.

[Wavytone]

Hi Dave,

I have a very nice 130 triplet ED APO and a 180mm mak and if you have to pick just one, the 190MN is definitely the one to go for, it will beat a 5" APO on every score.

For Astrophotography the MN will be far superior being a bigger light bucket and faster f/ratio.

The only niggle to watch for is the size of the central obstruction - apparently skywatcher recently decided to use a bigger secondary in theirs to reduce vignetting for photography, but it's not as ideal as the smaller previous version was for high-magnification visual observing.

But I'm not parting with my APO as I do find it useful to have the two in a side by side setup for visual.

[Davey]

Thanks Glen for both the welcome and the detailed reply.
Tired old eyes here too mate :)
I'll try and find you on Astro bin, I'm there too. I think the link was missing from your post.
Regading the refractor I had in mind by coincidence it's also a TS scope the 130 Apo triplet. Similar F/L to the MN 190
Cheers,

Dave

[Davey]

Thanks for the this , I was aware the latest model was due to feature a larger secondary. The version with the 51mm secondary was the scope I would buy it's big enough for my ccd.
Great input
Cheers for that

Dave

[Slawomir]

Hi Dave,

Since MN190 has a rather small 22mm fully illuminated circle (according to Orion/SW), I would go for a quality refractor. My 105mm refractor has a 44mm fully illuminated and corrected circle, and a 130mm refractor will most likely have a 55mm fully corrected circle. Having said that, a 22mm illuminated circle should be sufficient for KAF8300.

I believe a refractor would be more versatile, because you could image for a greater detail with just a flattener, and one day invest in a quality reducer and have a wider field with a faster f-ratio. I'm not sure if a reducer can used with MN190:question:

MN190 and 130mm f/7 refractor when combined with KAF8300 will both have very similar image scale.

One more thing, I'm not sure how cooling times and backfocus compare for both designs.

[glend]

The MN190, with the small secondary, is fine for sensors up to APS-C size. No vignetting with my Canon 450D (APS-C).
I considered upgrading to the TS Photoline 130mm, as it uses the same focuser and reducer (3" Photoline) as my 115mm, but could not justify the cost differential at that time, now its cheaper. Consider that the MN190 gives you 1000mm fl, the TS 130 would be 910mm at native f7 (reduced to 719mm, f5.53 with the Photoline 0,79x reducer). I see they have reduced the price of the TS 130mm APO with the R&P focuser, it looks a pretty good deal for only 300 euro more than the 115mm - i am tempted as all my gear will fit.
Don't forget to consider the cost of buying the reducer. I have both the 0,79x reducer corrector and the f7 flattener.
You would probably need to replace the MN190 focuser with the new Moonlight one. The new adaptor suits the MN190 much better than the original adaptor, which did not allow focuser centering exactly over the secondary.

And Dave, the Astrobin link is my signature line below here.

[Davey]

Thanks for your thoughts. A tick in the box for refractors, I doubt very much that I'd enjoy gathering photons at native F7 though.

With a reducer yeah it's much more doable.

No the Mn 190 can't be used with a reducer but it's fast enough anyway. This scope choice will probably come down to ease of use as my future rig will be portable. Having owned one ,I've seen first hand what a Mn190 can deliver , so finding it difficult to switch to a frac, but they would be an easier option for a portable rig.

[RickS]

A f/7 scope with a sensor with big pixels could be faster overall than a f/5 scope with a sensor with small pixels. You should think about the whole system, not just the scope. You might also want to give some thought to the type of objects you plan to chase and what sort of FOV is going to work.

Cheers,
Rick.

[Davey]

It's a Bargain price that scope right now Glen, I've been reading about it all week. I doubt I would have the time and patience to get enough data at the native F7. The reducer flattener makes it a different proposition. Flateners and reducers are another minefield. I've a televue 2008 but it's suited to a faster refractor so probably of no use.

I'm guessing there are no baffles in your TS115 , not found a reference in the advertising.

I'm following you on Astrobin mate. Thanks, nice work

[Slawomir]

What about a 4inch f/5 flatfield APO then?

Here is an interesting one: http://www.teleskop-express.de/shop/product_info.php/info/p7331_TS-Optics-Imaging-Star-102-mm-f-5-1---6-element-Flatfield-APO-Telescope.html

Theoretically a plug n play, fast, and TS guys could for sure make an adapter for your QSI. Nice wide field with KAF8300, and resolution can be easily increased with drizzle integration to about 1arcsec pp if needed.

[Davey]

Rick I already have a widefield rig, plus the camera I am looking for a longer focal length scope mainly for Nebs

[glend]

Dave my TS 115mm APO is baffled, it has four progressively deeper baffles from the objective back, they look to be properly staggered based on ray tracing. The 3" Photoline 0,79x reducer/corrector is a very nice unit and easy to use, requires standard 55mm backfocus so is compatible with DSLRs and works with my ASI1600MM-C and QHY filter wheel with a small T2 spacer. I keep it configured with the reducer/corrector so it images at f5.5 which is nice an quick. I have rarely used it at f7 because it is getting to close to the MN190 fl.

[RickS]

Depends what sort of nebs you mean, Davey. For small planetaries and galaxies you need focal length, or more correctly small image scale, but a lot of nebs are very large and a wide field set up is more appropriate. The small stuff will take a lot of imaging time for any affordable set up.

Cheers,
Rick.

[Davey]

That's a lovely scope for sure but too close a fl to my ed80.

[traveller]

Hi Dave,
First of all, welcome to IIS and Australia.
Second, envious of your country location and dark skies.
As others have said, different scopes will be suited to different targets. I am a refractor fan, having learnt the craft with an ED80 and now on a FLT 110, which I really enjoy using.
I haven't imaged with reflectors. But refractors have good colour correction (esp triplets) and easy to maintain (no collimation etc). Flatteners and reducers will shorten the expsoure time as well.
Quite a number of large nebs in the southern hemisphere, so a refractor in the 700-900 FL range may do the trick.
Bo

[Davey]

Thanks Rick, you're correct I agree. I have to confess to not spending much time on small Nebs. However I do like getting in a bit tighter and seeing more detail within the Neb than a widefield view affords, see attached an image I took with an MN 190.
I've had a look at your Narrowband Eastern Veil segment which shows great wealth of fine detail, very impressive. I'd go so far as to say it's the best I've seen.
That image scale is my aim, all be it with more modest equipment
Cheers,

Dave

[Davey]

Hi Bo, Thanks for the welcome, I see where you are coming from as I still own a Ed80 and once owned a WO 110. Most of my imaging back in North Wales was Narrowband due to LP which was off the scale.
Thanks fir your input,

Dave

[RickS]

Thanks for the kind comment, Dave :)

Of course, the answer to the conundrum is that you need at least 3 or 4 scopes of varying aperture and focal length and a couple of cameras, and ... :lol: