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Old 29-06-2018, 12:20 PM
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thegableguy (Chris)
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Reverting from reflector to refractor

Hi all, would love some advice on which direction from here.

I started about 3 years ago with a little Orion ED80 on an NEQ6 mount, imaging with a cheap crop sensor Nikon. I got reasonably good results reasonably quickly so upgraded straight away to an 8" f/5 Newt. I don't think I was ready for the learning curve. Couldn't get autoguiding to work (probably because I was using the ED80 as a guidescope and it was simply too sensitive); got frustrated night after night. Since then my Newt has sat collecting dust for a year or so, as has the mount.

I put both the Newt and the ED80 on the mount the other night to make sure all works, and yep all is fine... but I was simply delighted with the ED80. Made me wonder why I'd ever moved on. Razor sharp, super light & easy to use, no collimation required, no coma correctors & fiddling with spacing, doesn't get dust inside. In practice the f ratio makes absolutely no difference. Literally! Even though the f/5 tubes should allow for much shorter exposures than the flattened ED80 (down to f/6.4), same exposure results in identical brightness. I know the secondary mirror takes up some of the light, but didn't expect that much. In practice my ED80 is no "slower" than my f/5 Newt.

In short, reflectors (at least the cheap ones I've been using) seem inferior to refractors in every way except focal length. So I'm thinking I'll sell my reflectors and go back to the ED80, with the aim of eventually upgrading to an ED100 / ED120.

Has anyone gone in this direction, ie from reflector to refractor? Did you regret it? How much did you miss the focal length? Any major benefits?

Also interested to know experiences in comparing APO vs ACHRO. Achro is vastly cheaper, which appeals, but I don't want to buy something that frustrates me. I'd be very interested to hear from anyone who's imaged with an achro.

Thanks for reading!!
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Old 29-06-2018, 12:50 PM
glend (Glen)
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I have imaged with an achromat but only in narrowband, where CA is not a limiting factor (and you must re-focus for each filter).

I have a nice 10" f5 newt, which I simply do not use much anymore. Most of my imaging is now done with my refractors (APOs from 60mm, 80mm, and 115mm) and my wonderful MN190 f5.3 Mak-Newt. I prefer them as there are no diffraction spikes, they do not have coma issues to correct, they are easy to heat, no star bloat, and great contrast.

IMHO It's not unusual to move from reflectors to refractors. Many people start out with reflectors, often due to cost when compared to a good refractor.
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Old 29-06-2018, 02:15 PM
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Chris

I am the same - started with a good 8" newt on an EQ5. Then moved to a Williams Optics Megrez90 on an EQ6 and never looked back. I also don't use the 8" much anymore. I probably only get it for the kids to use and look at the planets once every 2 or 3 years.

The reflector was a good place to start and learn. I may have been lucky, but everything translated well to the refractors for me. My cameras were able to focus; the guiding worked well; good practice at balancing and polar aligning.

No regrets with any of it - time or money spent.

Do I miss the focal length? Nope. I quite like wide fields. I prefer the quality of the view. I am much more into imaging now so light gathering is not an issue (200mm comapred to 90mm), I just do longer subs.

Darrell
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Old 29-06-2018, 02:20 PM
Imme (Jon)
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I', the same....started with a newt and then bought another because I thought the poor quality of the first was what was causing my imaging issues.....didn't help.

Spent a small fortune on a triplet refractor but I haven't looked back. So much easier to deal with, reflector has been 'retired'.
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Old 29-06-2018, 03:09 PM
raymo
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Chris, Your 8" Newt was undermounted on an EQ5, need at least an HEQ5.
If your cameras wouldn't focus, you hadn't done your research, and had bought a Newt optimised for visual.[which is to say, most Newts].
You can't beat the laws of Physics, the 200mm has 5x the light gathering power of a 90mm. The secondary reduces light gathering by around 6%,
negligible. Your images may well be as bright, but will not show as much
nebulosity or colour, [for the same length sub],and on objects full of detail such as the moon will not show as fine a detail. Resolution is a function of
aperture, so the finest optics known to man will not allow a 90mm scope to
resolve detail as small as a 200mm will. Horses for courses.
raymo
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Old 29-06-2018, 04:18 PM
Imme (Jon)
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Quote:
Originally Posted by raymo View Post
Chris, Your 8" Newt was undermounted on an EQ5, need at least an HEQ5.
If your cameras wouldn't focus, you hadn't done your research, and had bought a Newt optimised for visual.[which is to say, most Newts].
You can't beat the laws of Physics, the 200mm has 5x the light gathering power of a 90mm. The secondary reduces light gathering by around 6%,
negligible. Your images may well be as bright, but will not show as much
nebulosity or colour, [for the same length sub],and on objects full of detail such as the moon will not show as fine a detail. Resolution is a function of
aperture, so the finest optics known to man will not allow a 90mm scope to
resolve detail as small as a 200mm will. Horses for courses.
raymo

Can't argue with the laws of physics.......as long as colimation is always spot on. If its off your 200mm gathering capacity goes out the window because your image won't be great.
So unless you like to tinker....and tinker often with a cheap scope then maybe the refractor isabetter option. Was for me
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Old 29-06-2018, 05:17 PM
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thegableguy (Chris)
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Quote:
Originally Posted by raymo View Post
Chris, Your 8" Newt was undermounted on an EQ5, need at least an HEQ5.
If your cameras wouldn't focus, you hadn't done your research, and had bought a Newt optimised for visual.[which is to say, most Newts].
You can't beat the laws of Physics, the 200mm has 5x the light gathering power of a 90mm. The secondary reduces light gathering by around 6%,
negligible. Your images may well be as bright, but will not show as much
nebulosity or colour, [for the same length sub],and on objects full of detail such as the moon will not show as fine a detail. Resolution is a function of
aperture, so the finest optics known to man will not allow a 90mm scope to
resolve detail as small as a 200mm will. Horses for courses.
raymo
Hi Ray, it's been a while.

Firstly, like I said, it was on a NEQ6. The mount was never the issue.

Secondly, totally agree that the larger aperture and faster ratio SHOULD by all accounts - and laws of physics - make for a better exposed image. No argument there. I've been a photographer for years and understand the principles very well. All I'm saying is that in practice it absolutely does not.

Thirdly, both my reflector OTAs are imaging OTAs. One was a brand new GSO, and the other was in fact your very own blue Skywatcher with the motorised focuser. I did indeed do my research - quite a lot of it.

All good. I'm very glad to hear I'm not the only one who decided that refractors are the better option! I now know what my ideal rig is. Time to start saving again...!

Thanks all, appreciate your help.
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Old 29-06-2018, 05:45 PM
raymo
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Excuse my mix up, it was Darrellx who was using the EQ5, but I'm still
wondering why you had focusing problems.
raymo
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Old 29-06-2018, 05:54 PM
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thegableguy (Chris)
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Quote:
Originally Posted by Imme View Post
I', the same....started with a newt and then bought another because I thought the poor quality of the first was what was causing my imaging issues.....didn't help.

Spent a small fortune on a triplet refractor but I haven't looked back. So much easier to deal with, reflector has been 'retired'.
Yep - exactly the same here. Bought a second hand newt then bought a brand new one. Similar issues and frustrations with both. My coma correctors don't get rid of the blurred corners no matter what spacing I use, collimation is a pain (and my newer scope seems to be incapable of lining up perfectly)... Yeah nah. I might revisit reflectors another time but right now I'd rather do any number of things instead of the constant fiddling and maintenance they require.

What sort of triplet did you get, what sort of targets are you imaging?
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Old 29-06-2018, 06:01 PM
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thegableguy (Chris)
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Quote:
Originally Posted by raymo View Post
Excuse my mix up, it was Darrellx who was using the EQ5, but I'm still
wondering why you had focusing problems.
raymo
Never had focusing problems mate. Had issues with coma correction & collimation, had major frustrations with guiding, and the focuser on your old OTA broke a bearing, but both OTAs worked more or less like they're supposed to.

When I said that the refractor was razor sharp, I meant to say across the whole field rather than just in the middle. Neither my Baader nor my GSO coma correctors seemed to sort that out for me. Dunno why. I'm guessing the spacing was off but I tried a lot of variations after reading dozens of forums - still no luck.
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Old 29-06-2018, 08:49 PM
Imme (Jon)
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Quote:
Originally Posted by thegableguy View Post
Yep - exactly the same here. Bought a second hand newt then bought a brand new one. Similar issues and frustrations with both. My coma correctors don't get rid of the blurred corners no matter what spacing I use, collimation is a pain (and my newer scope seems to be incapable of lining up perfectly)... Yeah nah. I might revisit reflectors another time but right now I'd rather do any number of things instead of the constant fiddling and maintenance they require.

What sort of triplet did you get, what sort of targets are you imaging?
Wo Flt 132......very happy with it.

Have only had it out in anger once so far as it is fairly new to me. Its an absolute joy though.
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Old 29-06-2018, 09:20 PM
raymo
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Chris,Its a bit late now the horse has bolted, but you should have got the
SW f/5 coma corrector, its designed specifically for their f/5 Newts no spacers are required, and beautiful stars to the edge of the field with the scope you got from me. I've just passed it on to another member. My poor old octogenarian brain is a bit of a mess, on looking back I discovered it was also Darrellx who had trouble getting his cameras to focus, so I apologise for the confusion..
The larger scope won't give you a better exposed image, but it will give
you a deeper one. A couple of years ago I posted a series of single frame
images, and numerous members expressed their surprise at what an 8"
can do in 30 or 40 seconds.
raymo
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Old 29-06-2018, 10:42 PM
Startrek (Martin)
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My 6Ē newt at f6 on a HEQ5 mount is a great scope both for visual and Astro work and with my unmodded Canon 600D has produced some great single images of planets , moon and many DSOís

I posted one on Bintelís photo site last month ( Eta Carinae - itís still there to view )

I am looking at upgrading next year to an 8Ē SW f5 newt

I concur with Raymo

Cheers
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Old 30-06-2018, 09:13 PM
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Okay. I've attached some quick & dirty (and pretty awful) photos here to show what I mean about there being no visible benefit to the larger aperture of the 200mm reflector over the 80mm refractor.

Each target was taken within about a minute of each other with the two different scopes (as in I changed back and forth between OTAs for each target). Same camera, same ISO & exposure settings for each target. Imported straight into the computer, cropped for comparison and exported without any editing whatsoever.

Surely I'm not alone in thinking that there should be a lot more difference than this, yeah? The flattener on the ED80 takes the ratio down to f/6.4, but that's still more than half a stop below the Newt. It should be two thirds as bright, but somehow they're within 5% of each other.

(Apologies for the quality of the shots, they're awful! I didn't align at all, just plonked down the mount in an approximation of south and crossed my fingers. Actually had to move the thing halfway through because a tree got in the way of Mars. Enough to get the idea though.)

Might post these in a new thread and see if anyone can explain why this should be.
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Old 01-07-2018, 12:06 PM
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Larger aperture scopes are more about higher resolution, extra light gathering is a bonus. I can defiantly notice the difference between my smaller scopes and larger ones.

Here is a 5 sec single sub at iso 6400 with a 10" f5 newt and canon 1100d. And now added, a 10sec iso 6400 with a 120mm f5 achro and canon 1100d, this is from the archives so not the best comparison to use.
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Old 01-07-2018, 04:23 PM
Wavytone (Nick)
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Quote:
Originally Posted by thegableguy View Post
Has anyone gone in this direction, ie from reflector to refractor? Did you regret it? How much did you miss the focal length? Any major benefits?

... APO vs ACHRO.
Chris...

First question is whether you are interested in wide field photography, or are a visual observer (i'm a visual observer, no AP whatsoever). For AP focal ratio is the first priority where "average" image quality over a wide field will do, but visual observations of close double stars, lunar & planetary - these are all about image quality (resolution) on-axis.

A few years ago I sold all my gear and, succumbing to a bout of refractoritis, I bought a TS 130mm f/7 triplet APO to see what all the fuss was about. A significant aspect in my case is that my first "real telescope" was a superb refractor - a Thomas Cooke 4.25" f/15 on a beautiful bronze clockwork mount. Not only a beautiful antique, but one that works superbly. The TS 130mm refractor was very nice, optically everything you would expect.

However... one night I did a side-by-side comparison with a C5 and an old-school 15cm f/8 newtonian. Sorry refactor guys, stop reading here. At the same magnification the refractor and the C5 were indistinguishable... it's true. However the refractor didn't fare so well compared to the 15cm Newtonian - which had perfect optics and slayed the refractor on Jupiter at high power.

A few months later a Skywatcher 180mm f/15 Mak was advertised here on IIS which was optically 9/10 and cost ⅓ the price of the refractor. Side-by-side with the 130mm refractor, the Mak killed it on every object, bar none. Bang-per-buck, the mak was a clear winner. Always.

At X2 per mm (260X) on double stars the refractor was good. On the trapezium in Orion, E and F stood out in the mak but the refractor struggled.

Ultimately, in 2016... an acquaintance in the US decided to part with a rare scope - a Santel MK91. I had met the owner and the scope many years ago and when he decided to sell it I leapt at it.. However not cheap and I sold all my gear - the refractor, SW Mak, mount and eyepieces to fund this, AND mount a new mount to put it on.

No regrets... optically this scope kills Questar 7's, 10" and 11" SCTs.

In retrospect IMHO the SW 180mm Maks are a bargain - optical quality appears to be consistently better than 20cm SCTs, and its a perfect size and weight for a portable scope.

Stepping up to a 9" or larger scope is problematic - the weight and focal length are both significant and pose challenges that may be beyond some owners.

As for a 9" refractor ... that is way beyond portable.

Last edited by Wavytone; 02-07-2018 at 02:36 PM.
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Old 02-07-2018, 02:34 PM
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Quote:
Originally Posted by doppler View Post
Larger aperture scopes are more about higher resolution, extra light gathering is a bonus. I can defiantly notice the difference between my smaller scopes and larger ones.

Here is a 5 sec single sub at iso 6400 with a 10" f5 newt and canon 1100d.
Lovely shot. I usually avoid ISO 6400 with my cheapo Nikon, gets very noisy, but might give it a shot to see how it compares to your shot here. I'll also need to align it a bit better than the other night, to see the difference in resolution. If the clouds ever bugger off I'll report back...
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Old 02-07-2018, 02:44 PM
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Originally Posted by Wavytone View Post
Chris...

First question is whether you are interested in wide field photography, or are a visual observer (i'm a visual observer, no AP whatsoever). For AP focal ratio is the first priority where "average" image quality over a wide field will do, but visual observations of close double stars, lunar & planetary - these are all about image quality (resolution) on-axis.

A few years ago I sold all my gear and, in a bout of refractoritis, I bought a TS 130mm f/7 triplet APO to see what all the fuss was about. A significant aspect in my case is that my first "real telescope" was a superb refractor - a Thomas Cooke 4.25" f/15 on a beautiful bronze clockwork mount. Not only a beautiful antique, but one that works superbly. The TS 130mm refractor was very nice, optically everything you would expect.

However... one night I did a side-by-side comparison with a C5 and an old-school 15cm f/8 newtonian. Sorry refactor guys, stop reading here. At the same magnification the refractor and the C5 were indistinguishable... it's true. However the refractor didn't fare so well compared to the 15cm Newtonian - which had perfect optics and slayed the refractor on Jupiter at high power.

A few months later a Skywatcher 180mm f/15 Mak was advertised here on IIS which was optically 9/10 and cost ⅓ the price of the refractor. Side-by-side with the 130mm refractor, the Mak killed it on every object, bar none. Bang-per-buck, the mak was a clear winner. Always.

At X2 per mm (260X) on double stars the refractor was good. On the trapezium in Orion, E and F stood out in the mak but the refractor struggled.

Ultimately, in 2016... an acquaintance in the US decided to part with a rare scope - a Santel MK91. I had met the owner and the scope many years ago and when he decided to sell it I leapt at it.. However not cheap and I sold all my gear - the refractor, SW Mak, mount and eyepieces to fund this, AND mount a new mount to put it on.

No regrets... optically this scope kills Questar 7's, 10" and 11" SCTs.

In retrospect IMHO the SW 180mm Maks are a bargain - optical quality appears to be consistently better than 20cm SCTs, and its a perfect size and weight for a portable scope.

Stepping up to a 9" or larger scope is problematic - the weight and focal length are both significant and pose challenges that may be beyond some owners.

As for a 9" refractor ... that is way beyond portable.
Ha! 9" refractor. I hit the gym fairly often, but even so... yeah nah.

Thanks for the stories, sounds like you've spent a lot of time looking through the different types. I've never attended a star party so the only scopes I've ever looked through are those I've owned. Would love a chance to experience something other than mine, particularly something that cost real money, just to see what the differences are.

I'm curious, though. When it comes to visual observing, aren't all telescopes basically limited by seeing conditions? I mean, wouldn't it take truly exceptional conditions to experience a significant benefit of one over another? Isn't sharpness very strongly affected by atmospheric blurring, isn't contrast affected by light pollution? Are the differences only really visible under perfect conditions?

Personally, I'm mainly interested in AP, which is why I got the Newts in the first place - they're supposed to be the best bang for an AP's buck. I was just surprised to learn that the bigger, heavier, faster Newt was actually only bigger and heavier - without actually being faster at all!

Having said that, I've got a 5-yr-old little girl who LOVES looking at the planets, so maybe there will be increased visual use in years to come.
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Old 02-07-2018, 07:37 PM
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Lovely shot. I usually avoid ISO 6400 with my cheapo Nikon, gets very noisy, but might give it a shot to see how it compares to your shot here. I'll also need to align it a bit better than the other night, to see the difference in resolution. If the clouds ever bugger off I'll report back...

I found a shot taken last year with my 5" f5 achro and added it to my earlier post for comparison. I'm sure an ED would do a much better job but resolution is about resolving finer detail and that's where aperture comes into play.
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Old 02-07-2018, 09:11 PM
Wavytone (Nick)
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When it comes to visual observing, aren't all telescopes basically limited by seeing conditions?
For 40 years I also thought all scopes would be equally affected by seeing, however a recent occasion proved otherwise.

A few weeks ago Alex and I put my Santel (228mm f/13 Rumak with exquisite optics, a small central obstruction and strehl 96.5%) side-by-side with a Meade 20cm SCT, which is known to have very good optics by SCT standards.

Our original intention was to compare planetary eyepieces, with Jupiter and Saturn as the primary targets. However... we very quickly noticed something else - the SCT was affected very badly by seeing, whereas the Santel was not so badly affected.

In the SCT, when the seeing settled for a moment Jupiter was a fine sight with detailed swirls, but when seeing deteriorated it was just a confused mess, just like a kid stirring a pot of multi coloured paints. The Santel continued to show an image with fine details - although shaking like jelly.

Next - Saturn. The Santel showed the crepe ring nicely and a whole retinue of little moonlets, whereas in the SCT the crepe ring was not visible nor were the moonlets.

IMHO what this shows is that in average seeing a scope that can put ALL THE PHOTONS exactly where they should be will easily outperform an average scope, even though the latter may meet the quarter wavelength criterion.

For the same reason at high magnification a good APO outperforms an achromatic doublet of the same focal ratio.

This is also why some pay the $$$ and patiently wait for a mirror from Messrs Zambuto or Royce, as compared to buying a cheap and fast mirror from the likes of Skywatcher or GSO.

There is the legendary Questar 90mm maksutov, despite their puny aperture these are ostensibly perfect and produce remarkable resolution for which many will pay the price.

And similarly, some shell out 12,000 euros for a 10" Maksutov from Matthias Wirth, rather than settling for a rather pedestrian C11 or C14.

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