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Milliways

Astrophotography scopes

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Hey guys and gals. I am goin to attempt an astrophotography rig and am after a cheap'ish scope. The scope that has caught my eye is the WO Megrez 72, but i have also seen the Vixen A80MF Refractor, the vixen looks great and the price is fantastic! So i guess my question is.. Which would be better out of the two? (For DSO's)

thanks all and clear skies!

Dave

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Hi Dave,

Of the two I would definitely, no question, go for the Megrez. The Vixen is very slow for imaging at F11.4 (in general, the lower the F number, the better for imaging - the Megrez is I think about F6), and also, the Vixen is an achromatic refractor, which is cheaper to produce but prone to colour fringing.

I'd really recommend before buying an imaging scope to read the book: Making Every Photon Count, which as well as going through how to take the images, has got advice on which type of gear to buy.

Edited by Luke

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Hi Dave,

I know what I would go for ... Megrez with the x.8 WO flattener but Im a bit bias ... :grin:

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Be careful buying what seems like a bargain refractor for imaging. As well as the speed (f ratio) check the objective lens construction.

An achromat in faster ranges suitable for imaging (these are generally cheapest) split the light and then doesn't resolve it back in the same place, so you get coloured fringes and bloated stars. Especially in shorter lengths of scope where separation is more severe.

A semi APO using glass such as fpl53 will give a good image (not as good as a full APO) but a significant improvement.

A true APO uses 3 (I think) lenses to fully correct but a good one is horrifically expensive. Some use more than 3.

A good price point for an introduction to refractor imaging is a semiAPO. Rather than look at a manufacturer, try looking for the glass used. There appear to be a lot of economic scopes around made of FPL51 glass but these perhaps don't correct as well as FPL53.

I have a very untrendy Revelation semi APO which uses FPL53 glass (same as that in a Skywatcher ED80) and it is fantastic. Makes a big difference, comparing it with the same design of Revelation scope I had previously, which was a achromat.

Typed by me, using fumms...

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There's a Megrez 70 on the bay which should be, as far as I know, an FPL53 semi APO doublet.

I've no idea if it's a good deal but might be of interest.

Typed by me, using fumms...

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The 72 does and, as best I know, the 70 and now 71 all use fpl-51 not fpl-53, if they used fpl-53 WO would advertise it.

They do show some CA on brighter objects. Several have reported it and I think WO say it on their site: it says something like CA is kept to a minimum, meaning it is there, even if not a lot of it.

Still a damn nice scope however.

Never quite understood why they swapped from 72 to 70 as the 72 had a good name and was going to be difficult to follow and better without a significant such as 53 instead of 51 or going to a triplet as in the GT-81.

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This photo taken with a cheap reflector and a DSLR made my jaw drop:

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The 72 does and, as best I know, the 70 and now 71 all use fpl-51 not fpl-53, if they used fpl-53 WO would advertise it.

They do show some CA on brighter objects. Several have reported it and I think WO say it on their site: it says something like CA is kept to a minimum, meaning it is there, even if not a lot of it.

Still a damn nice scope however.

Never quite understood why they swapped from 72 to 70 as the 72 had a good name and was going to be difficult to follow and better without a significant such as 53 instead of 51 or going to a triplet as in the GT-81.

Quite right. The one on the bay is a 72 (my fat fingers on my phone keypad). I think this is FPL53.

Typed by me, using fumms...

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This photo taken with a cheap reflector and a DSLR made my jaw drop:

I suspect the ASA Coma Corrector he used cost an 'arm and a leg' though!

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I'm now running an AA Wave 115 f7 refractor. It's a 'wow' scope for me, but when I look back at a few of my ED80 images, I can't help thinking that in terms of bang per buck, that little scope takes some beating. Easy to carry, easy to guide, a smidge of false colour, but fairly easy to de-fringe in photoshop or similar. I'll be shooting some more DSLR shots with it soon, currently my site shows some pics from an SBIG ST7 coupled to it (which is undersampled really). http://www.alphageek.co.uk/astronomy.html has pictures with the ED80 and ST7 http://www.alphageek.co.uk/page24.html has the wave 115 and DSLR shots. Has to be the ED80 for me in the 300-400 quid bracket (less used), have used a friends WO and it was really good, but neither 'wow', nor a great bargain. Their focus dials or digital readouts just leave me cold - pointless. Love the Altair 115, but the ED80 wIll probably go to someone when I croak, and will still be a good scope then.

Just my two-penneth,

Jack

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This photo taken with a cheap reflector and a DSLR made my jaw drop:

http://stargazerslou...5/#entry1671184

That's a cracking picture, but it's an inexpensive newt with a £700 Astro Systems Austria Reducer Corrector, so it's in the >£1000 category and not £300.

Anton

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Bah, sorry didn't see that laser jock already pointed this out..... /hangs head in shame

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Also getting the refelctor to perform to the book would require some skill. Tomy_H is clearly no slouch! Apos are easier...

Olly

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OK, so it is a fancy coma corrector... but surely you get 80% of the benefit using the skywatcher coma corrector? I mean, with star images tending to a point, the law of diminishing returns has to kick after the first couple of hundred pounds spent?

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It's a reducer too Ags, I think around 0.75 , brings an f/5 Newt down to around f/3.6.

I wanted one, but didn't fancy the idea of collimating a newt that fast, so I bought an apo instead.

Olly's right, tommy_h is doing a great job getting it performing like that.

But I think the point is that it requires money and plenty of skill to get wide field views like that on a newt.

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Ah... I see. tommy_h was doing 20 minute subs in that pic - without the reducer he would have had to shoot 40 minute subs.

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Welcome back Dave, long time no see. Out of curiosity what happened to your old setup, you sure produced some fantastic images with that. I been playing around with the same idea as you, keep me informed of how you go on and what you decide, would be really interested to see how you go on mate.

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I wouldn't say that the A80Mf is really a AP scope.

It's light but:

a) it's an achromat

B) it's f12

c) the focuser is not particularly sturdy and wobbles (well the 1.25" does!)

d) It's not a flat field.

Using the titan on a vixen porta mount a long time ago (now have alot better images form the Titan!):

index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=56915

Edited by NickK

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It's a reducer too Ags, I think around 0.75 , brings an f/5 Newt down to around f/3.6.

I wanted one, but didn't fancy the idea of collimating a newt that fast, so I bought an apo instead.

Olly's right, tommy_h is doing a great job getting it performing like that.

But I think the point is that it requires money and plenty of skill to get wide field views like that on a newt.

The ASA Keller Coma Corrector/Reducer is indeed a nice piece of kit for imaging but could easily cost more than the scope!

http://www.astrosysteme.at/eng/correctors_newton.html

However- it will turn an F4 astrograph Newtonian into a superfast F2.9 but requires a fair amount of tweaking to get the best results (something I have yet to achive), so possibly not for the begginer. On the plus side though you can get very deep exposures in ridiculously short times- if it was easy to get the crispness of an Apo we would all be using them!

How fast is F2.9? A 300s single sub is enough overexpose the Crescent Nebula and capture the field faint background nebulosity through a 7nm Ha filter.

DSIR6089_noels_1024.jpg

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Wow them images are fantastic!.

Hey Carl yeah long time no see! I still have the same setup and can still get pin sharp images from 3-5min subs, but i want to start taking longer exposures to get the finer deltails without any streaking.

I am using my 250px 10" skywatcher as the imaging scope and a 70mm skywatcher for the guide scope, i treated myself to a synguider and had a proper go last night... I was absolutley blown away with the ease and accuracy of the system, i was taking 5min subs and they where perfect every time! This is also on an EQ5 pro, so i am propper chuffed and cant wait to start attacking the galaxies in virgo!

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