Sharpstar 140 - to buy or not to buy??

[petevasey]

Hi, folks,

Some of you may have seen my agonising over whether to get an Esprit 150.  Great scope and fine on my Obsy mount, but will my EQ6 Pro 'star party' mount carry it successfully for astrophotography?  I'm beginning to think not 😐  so I've been looking at the Sharpstar 140 (140mm aperture, 910 mm fl), which IS light enough for that mount.  I came across this review by Alan Dyer which is very favourable.  I contacted him and he kindly sent me one of his test images of M3.  You will see in his review that he mentions 'near textbook-perfect Airy disks'.  Presumably the proverbial 'good thing'.

But I show below a centre crop from the full size image.  And as you can see the Airy patterns are very obvious on brighter stars, something I've never seen before in images.  So is it after all a 'good thing'?  Maybe he had superbly steady sky, so the stars were not twinkling which tends to blur the edges even with good guiding.  The original image is with a full frame camera, unflattened so edge stars are well stretched, but I will be mainly using my QSI683 with a flattener, so not worried there.

What do you think, people?

Cheers,

Peter

Edited July 21, 2022 by petevasey

[catburglar]

I’m not sure what you’re seeing, but can’t see the airy pattern…if I look at the bright star towards the bottom and just left of centre in your cropped view then I think it shows a ring artefact - probably as a result of sharpening or deconvolution algorithm. Are you looking at something else?

[Adam J]

58 minutes ago, petevasey said:

Hi, folks,

Some of you may have seen my agonising over whether to get an Esprit 150.  Great scope and fine on my Obsy mount, but will my EQ6 Pro 'star party' mount carry it successfully for astrophotography?  I'm beginning to think not 😐  so I've been looking at the Sharpstar 140 (140mm aperture, 910 mm fl), which IS light enough for that mount.  I came across this review by Alan Dyer which is very favourable.  I contacted him and he kindly sent me one of his test images of M3.  You will see in his review that he mentions 'near textbook-perfect Airy disks'.  Presumably the proverbial 'good thing'.

But I show below a centre crop from the full size image.  And as you can see the Airy patterns are very obvious on brighter stars, something I've never seen before in images.  So is it after all a 'good thing'?  Maybe he had superbly steady sky, so the stars were not twinkling which tends to blur the edges even with good guiding.  The original image is with a full frame camera, unflattened so edge stars are well stretched, but I will be mainly using my QSI683 with a flattener, so not worried there.

What do you think, people?

Cheers,

Peter

Looks like a processing artefact to me.  You should not see an Airy disk in prime focus imaging so long as you are in good focus, seeing / guiding errors would normally blur out the first diffraction ring in any case in long exposures. You would normally have to use eyepiece projection to image it.  

Adam

 

Edited July 21, 2022 by Adam J

[scotty38]

I think folk have used an Esprit 150 on an EQ6 with no issues so if it's just a worry for the odd star party why not just get the scope you want and "suffer" when you're out and about but know you have what you really, really want when in your observatory?

[Space Hopper]

Yikes : never realised the Esprit 150 was 17kg with rings, dovetail etc.

That is a hefty old beast.

 

[Richie092]

I have the 140, have only set it up on the Gem45 and had a test run under less than ideal skies but it seemed to guide ok but you can see on the graph when it gets a bit breezy.

It is heavy. I think the GEM45 or equivalent is the minimum mount for it. My plan is to buy a 70 for it or wait to see how the new Pegasus mount performs.

Build quality is excellent, I haven't tried the flattener or reducer yet as I think the native FL is really useful. The focuser is silky smooth and it does come in a lovely case that you will never use once you put your EAF on 🙂

[petevasey]

4 hours ago, Space Hopper said:

Yikes : never realised the Esprit 150 was 17kg with rings, dovetail etc.

That is a hefty old beast.

 

Well, I'm not so sure about that.  Elsewhere on this forum it's mentioned that the Esprit 150 weighs 12.7 kg, with the focuser attached, but no tube rings.  So Skywatcher's quoted weight of 14.5 kg is probably with tube rings etc..  Then of course add the camera.  So we are up to around 16 Kg, but that's with everything.  I've seen the EQ6, mine is the earlier Pro version, quoted at 18 Kg for imaging.  So the 150 just squeezes in.  No problem with the Sharpstar 140, 11.7Kg with rings & dovetail according to First Light Optics.  I've had substantial weight on my EQ6 - image below.  The RC10 truss is around 17Kg with focuser, then add the camera.  As can be seen it needed lots of balance weights.  The Celestron tripod foot dampers made a big difference to the stability, but I've never imaged with that setup.  Regarding the strange looking stars, maybe not Airy patterns.  I certainly haven't seen anything like that in any of my own refractor images.   I'd be VERY VERY interested if Richie could comment on the quality of his own 140 - any sign of chromatic aberration on bright stars, coloured fringe on the Moon etc.

Scotty, you say people have used a 150 on an EQ6 without problems.   Can you be any more specific?  And the rest of your comment is making the 150 even more tempting, you devil 👹

Cheers,

Peter

Edited July 21, 2022 by petevasey

[scotty38]

@petevasey regarding an Esprit 150 on an EQ6 then it was @StuartT that had this combo before he bought his EQ8 and I'm pretty sure he had decent results so if you  just want to use that combo for star parties I'm sure he'd give you the thumbs up....

[StuartT]

morning all.

As @scotty38 says, I have an Esprit 150 and I love it. It's given me some really super images. I use the field flattener/reducer too which takes it down to f/5.4.

I had it riding on a EQ6R Pro for about a year. I would say the total mass of the scope, flattener, camera, pegasus powerbox etc was pushing 20kg and that is right at the very upper limit of what the EQ6R can manage for photography. Having said that, I wasn't getting bad guiding numbers - they just weren't all that good. So I mostly kept to short exposures. The main problem wasn't the guiding but the slewing. I'd polar align in NINA and then when I slewed the scope across the sky to my chosen target the plate solve would be a fair way off (I'm talking degrees here, not minutes). I put this down to moment of intertia issues, as the Esprit 150 is a long scope

So ultimately, I decided to upgrade to a EQ8.

In summary, you can get decent results with the Esprit 150 on a EQ6, but you are working within constraints and it does feel like you are at the upper limit of your gear. Is it essential to get a EQ8? No. But it is desirable.

Edited July 22, 2022 by StuartT

[petevasey]

15 minutes ago, StuartT said:

morning all.

As @scotty38 says, I have an Esprit 150 and I love it. It's given me some really super images. I use the field flattener/reducer too which takes it down to f/5.6.

I had it riding on a EQ6R Pro for about a year. I would say the total mass of the scope, flattener, camera, pegasus powerbox etc was pushing 20kg and that is right at the very upper limit of what the EQ6R can manage for photography. Having said that, I wasn't getting bad guiding numbers - they just weren't all that good. So I mostly kept to short exposures. The main problem wasn't the guiding but the slewing. I'd polar align in NINA and then when I slewed the scope across the sky to my chosen target the plate solve would be a fair way off (I'm talking degrees here, not minutes). I put this down to moment of intertia issues, as the Esprit 150 is a long scope

So ultimately, I decided to upgrade to a EQ8.

In summary, you can get decent results with the Esprit 150 on a EQ6, but you are working within constraints and it does feel like you are at the upper limit of your gear. Is it essential to get a EQ8? No. But it is desirable.

Hi, Stuart, many thanks for responding.  I understand the EQ6R Pro has a slightly higher payload capacity, about 2Kg more than my original EQ6 Pro.  It would appear that most of the changes related to the drive system, belts etc.  Maybe strengthwise there is little to choose between them, and mine is a particularly good one - very smooth and quiet.  I'm puzzled about your slewing problems.  Stepper motors aren't supposed to lose position, when they do slip it sounds like gears grating horribly - could you hear them falling out of sync?

As far as guiding goes, you can see my Starlight  Xpress  AO unit in front of my camera in the photo above.  No guide scope and powerbox, but a heavier camera setup than yours.  Nevertheless the AO unit means that almost all the guiding is done without altering the speed of the mount, and even when mount adjustments are necessary the tip tilt plate keeps working, generally with a decent guide star at least 2 or 3 corrections per second, so the inertia of the system is less of an issue.  It's only for the few days a year at star parties that it would be riding on the EQ6.  Most of the time it would be on my Gemini G41 Observatory mount which carries that sort of weight easily.

Decisions decisions!

Cheers,

Peter

[newbie alert]

Looks like a processing artifact, to see the airy disc you need to slightly defocus 

[StuartT]

11 hours ago, petevasey said:

Hi, Stuart, many thanks for responding.  I understand the EQ6R Pro has a slightly higher payload capacity, about 2Kg more than my original EQ6 Pro.  It would appear that most of the changes related to the drive system, belts etc. 

I believe this is correct. In terms of naming, the "pro" part is redundant, by the way. It doesn't mean anything. The EQ6 and EQ6 Pro are the same mount (as are the EQ6R and EQ6R-Pro). But you probably know that.

11 hours ago, petevasey said:

I'm puzzled about your slewing problems.  Stepper motors aren't supposed to lose position, when they do slip it sounds like gears grating horribly - could you hear them falling out of sync?

I'm never near my scope when it's slewing, I'm indoors. So I couldn't tell you. However, I don't have this problem with the EQ8. It slews right across the sky and lands with pinpoint accuracy.

But whatever the mount, the Esprit 150 is a joy

Edited July 22, 2022 by StuartT

[petevasey]

5 minutes ago, StuartT said:

I believe this is correct. In terms of naming, the "pro" part is redundant, by the way. It doesn't mean anything. The EQ6 and EQ6 Pro are the same mount (as are the EQ6R and EQ6R-Pro). But you probably know that.

I'm never near my scope when it's slewing, I'm indoors. So I couldn't tell you. However, I don't have this problem with the EQ8. It slews right across the sky and lands with pinpoint accuracy.

But whatever the mount, the Esprit 150 is a joy

Hi again, Stuart,

Yep, undoubtedly the 150 is an excellent telescope.  But I'm coming to realise that it's just too heavy for my EQ6 mount.  I've done some checking, my camera assembly weighs 2.5 Kg, so takes the whole thing right up to the limit.  Lots of balance weight needed, and probably marginal for successful imaging.  I've been looking at a secondhand one (not physically, unfortunately the seller lives 290 miles away!) but the seller has a similar sized mount to mine and says it's marginal for him, so he's downsizing.  I've realised that this year I'll have spent 21 nights at star parties, and hope to continue at that level for a few years anyway, so would like a quality scope to replace my Meade 127 and do the trips away.  I guess it's going to be the Sharpstar.  Still a fair weight, but well within the limits of the mount.   I'll certainly keep my RC10 for now.  Maybe as time increases personal decrepitude I'll eventually downsize my 'big gun' to something more manageable, perhaps even a 150!

Cheers,

Peter

[StuartT]

On 21/07/2022 at 10:23, petevasey said:

Great scope and fine on my Obsy mount, but will my EQ6 Pro 'star party' mount carry it successfully for astrophotography? 

reading your original post again, I think I may have misunderstood.

I've never been to a star party, so I don't really know what's involved. But I always assumed it is an event where more serious amateurs congregate somewhere to allow beginners to look through their scopes. So why would you be needing an astrophotography level mount for that? Presumably a visual grade mount is all you need for visual?

By the sound of it, you already have a higher spec mount (Obsy mount) so why can't you use that for astrophotography?

Edited July 23, 2022 by StuartT

[petevasey]

Hi, Stuart,

As you would have seen above, this year I'll have been away from home for 21 nights in dark places - which for me are a mixture of Kelling Heath, Kielder and Galloway.  Yes indeed one does wander round looking at and through other people's equipment.  And if members of the general public are there, they are always made welcome.  But certainly the ones I attend are mainly peopled by the astronomy fraternity.

In cloudy old UK, an astrophotographer can't afford to let a clear dark night pass without doing some imaging.  The star parties I go to include both visual and imaging attendees, and are primarily for their benefit, often renewing acquaintances you might only see once or twice a year.  Outreach occasions aimed more for the general public are usually short lived affairs, one, perhaps two evenings for a few hours, often with the Moon in the sky - always an ooh aah target for newcomers, unlike star parties which are generally organised for moonless nights where you might stay up from dusk to dawn.

The biggest star party of the year is in the Autumn at Kelling Heath, Norfolk, organised by Loughton Astronomical Society.  People travel there from all over the country.  Details here.

Cheers,

Peter

Edited July 24, 2022 by petevasey

[petevasey]

Hi, guys,

Well I took the plunge!  Had to wait a little while for the telescope - I bought it from First Light Optics, and they were awaiting one.  But it came near the end of August, was duly checked by Es Reid and pronounced good.  And arrived with me on 31st August.  Full description here, hope to complete it after first light.

Cheers,

Peter