Is the Esprit 120 the Best 4" to 5" Telescope for AP ?

[Peter Drew]

The worst case scenario is that you buy the Esprit 120, a proven performer, and it doesn't quite come up to the parameters you aspire to.   There must be a queue of imagers waiting for a 2ndhand Esprit to appear for sale.  You would take only a small financial hit but would have satisfied your current dilemma.     🙂  

[johninderby]

If you buy an Esprit 120 make sure it’s from someone like FLO where it is properly tested and set up by E.S. Reid. Quality control on the Esprit scopes is a bit variable and really need checking and setting up.

[Timebandit]

3 hours ago, Midnight_lightning said:

Absolutely makes sense but this will almost certainly be the last scope I buy (Pension lump sum) so whilst I really like the Esprit I'm still hoping there is something even better if I spend a bit more. My very subjective evidence suggests maybe not but I'm still hoping someone proves me wrong. Also, I focused on Star Shape, some of these other scopes may be more or less sharper and have better/worse contrast.

 

 

 

You can always find something better . But at what cost. If you do not mind paying many many thousands of pounds more for something that maybe a fraction better. Then that is the option with an unlimited budget. But if you are like me and want Tak performance but on sensible money then the Top quality SW scopes like the Esprit really do take some beating. If its the last scope you want to buy then look at a used TEC 140 .

 

 

[Midnight_lightning]

2 hours ago, Skipper Billy said:

You do!  I have noticed that after I changed my budget scope for the Takahashi I do a LOT less in Pixinsight! 

You have a very nice scope there Skipper - and lots of great images

 

[gorann]

I do not think you could go wrong with an Esprit 120. I have two Esprits, 100 and 150, and I love them so I have also contemplated a 120, but then there is this one, slightly bigger and the same price, and it gets great reviews as far as I have seen:

https://www.teleskop-express.de/shop/product_info.php/info/p7717_TS-Optics-PHOTOLINE-130-mm-f-7-FPL53-Triplet-Apo---3-7--Focuser.html

Have a look at these on Pete's Astrobin:

https://www.astrobin.com/users/pete_xl/

 

[Midnight_lightning]

2 hours ago, ollypenrice said:

If you want the best and largest flat field in your approximate budget, with the best controlled stars, buy a used TEC140 with dedicated TEC flattener. You'll also get an FT focuser and the best QC in the business into the bargain. Mine produces tighter stars, especially bright blue ones, than either of the Tak FSQ106 scopes I use here. Indeed much tighter. This is confirmed by a second TEC140 I also use here.

Let me be honest: I put the optics last in the imaging priority list. For me it's mount, camera, optics without any doubt whatever. Now you clearly have a supernaturally good HEQ5 if it's pulling an RMS of about  0.2. arcsecs. You cannot bank on that continuing with a heavier scope and and one with a longer moment. Nor can you bank on your outstanding HEQ5 marching on forever, so you might want to leave some budget for a mount upgrade. Be aware that you're leading a charmed life with that mount! 😁 My Mesus run at around 0.3 arcsecs but they've been doing so for years.

But what would I buy without pushing your initial parameters? An Esprit 120 from FLO.

Olly

Thanks Olly, great advice as always.

I'll take a look at the TEC 140 but where do you pick these things up, I've been looking on SGL and Astro Buy Sell for various scopes fro a while and not seen much?

I can be slow on the uptake   but your "supernaturally good" comment alerted me to a high probability of a cock-up on my part 😮. TBH I'm still at the stage where I know what to do but don't always understand "why" in detail - including guiding so "mia culpa". I thought I had the RMS set to arc" but I'm wondering if I was looking at pixels - sample log attached (see entries 8 through 11 - everything else was calibration and Guide Assistant).  I would be grateful if you would take a look and let me know what you think. Whilst imaging it was showing around 0.21 RMS but I suspect dithering must throw this out (?). The HEQ5 has just come back from Stellar tuning so this is a first run, its not run in yet but hopefully will improve and should last quite a while - I think all the bearings have been replaced. Compared with pre-tuning its massively improved, I can leave it to run for hours whereas before I would be constantly tweaking it.

Thanks again Olly.

 

PHD2_GuideLog_2020-04-11_203434.txt

[gorann]

2 hours ago, johninderby said:

If you buy an Esprit 120 make sure it’s from someone like FLO where it is properly tested and set up by E.S. Reid. Quality control on the Esprit scopes is a bit variable and really need checking and setting up.

I bought both my Esprits from FLO and had them tested by Es, although I was informed by Steve at FLO that this was really not needed for the Esprits since Es never had any issues with them. So John, I would be interested to hear from from where you had the information that "Esprit scopes is a bit variable and really need checking and setting up"?

[Midnight_lightning]

23 minutes ago, gorann said:

Have a look at these on Pete's Astrobin:

There are some very nice images there and generally star shapes are great - although oddly some of them show quite a bit of star stretching in the corners with an ASI1600 - presumably more so if it were full frame. I'm being picky though, I would be please to be imaging at that standard  

[johninderby]

A quote from FLO about testing the new Stellamira scopes and ES reid had said the StellaMira scopes were very consistant and hardly any needed any adjustment but the Esprit scopes needed more attention as they weren’t as consistant.

Edited May 3, 2020 by johninderby

[John]

28 minutes ago, johninderby said:

A quote from FLO about testing the new Stellamira scopes and ES reid had said the StellaMira scopes were very consistant and hardly any needed any adjustment but the Esprit scopes needed more attention as they weren’t as consistant.

 

[ollypenrice]

10 hours ago, Midnight_lightning said:

Thanks Olly, great advice as always.

I'll take a look at the TEC 140 but where do you pick these things up, I've been looking on SGL and Astro Buy Sell for various scopes fro a while and not seen much?

I can be slow on the uptake   but your "supernaturally good" comment alerted me to a high probability of a cock-up on my part 😮. TBH I'm still at the stage where I know what to do but don't always understand "why" in detail - including guiding so "mia culpa". I thought I had the RMS set to arc" but I'm wondering if I was looking at pixels - sample log attached (see entries 8 through 11 - everything else was calibration and Guide Assistant).  I would be grateful if you would take a look and let me know what you think. Whilst imaging it was showing around 0.21 RMS but I suspect dithering must throw this out (?). The HEQ5 has just come back from Stellar tuning so this is a first run, its not run in yet but hopefully will improve and should last quite a while - I think all the bearings have been replaced. Compared with pre-tuning its massively improved, I can leave it to run for hours whereas before I would be constantly tweaking it.

Thanks again Olly.

 

PHD2_GuideLog_2020-04-11_203434.txt 363.53 kB · 2 downloads

Sorry but I'm not up on PHD guide logs so I'm not much use there, and with dual rigs dither is not really possible without inordinate effort so I don't know how it records the trace while dithering.

Getting hold of a TEC is a matter of luck. They do come up, though. I was tipped off by a guest about one but couldn't afford it at the time so he bought it himself! I had another chance later and bought mine. The other one on our dual rig was also second hand so they're rare but not impossible. Too big for an HEQ5 though. The flattener is a big chunk of glass and a long way from the centre of gravity.

Olly

[old_eyes]

11 hours ago, Midnight_lightning said:

Thanks Olly, great advice as always.

I'll take a look at the TEC 140 but where do you pick these things up, I've been looking on SGL and Astro Buy Sell for various scopes fro a while and not seen much?

I can be slow on the uptake   but your "supernaturally good" comment alerted me to a high probability of a cock-up on my part 😮. TBH I'm still at the stage where I know what to do but don't always understand "why" in detail - including guiding so "mia culpa". I thought I had the RMS set to arc" but I'm wondering if I was looking at pixels - sample log attached (see entries 8 through 11 - everything else was calibration and Guide Assistant).  I would be grateful if you would take a look and let me know what you think. Whilst imaging it was showing around 0.21 RMS but I suspect dithering must throw this out (?). The HEQ5 has just come back from Stellar tuning so this is a first run, its not run in yet but hopefully will improve and should last quite a while - I think all the bearings have been replaced. Compared with pre-tuning its massively improved, I can leave it to run for hours whereas before I would be constantly tweaking it.

Thanks again Olly.

 

PHD2_GuideLog_2020-04-11_203434.txt 363.53 kB · 5 downloads

I did a quick check with PHD2 Log Viewer. For those sections 8-11 it gave RA RMS from 0.55" (0.12px) to 0.68" (0.15px) and Dec RMS from 0.43" (0.10px) to 0.54" (0.12px). PA error around 1.5 arcmin. So no, you haven't got px and arcsec mixed up (a mistake I have sadly made several times). The header says that the  guidescope FL is 400mm and the pixel scale on the guide camera 4.43 arcsec/px. That's another setup error I have made before now.

The slightly odd thing is that the Dec axis is drifting steadily followed by a relatively large correction as here:

It is close to, but not actually aligned with the dither shifts.

[Midnight_lightning]

3 minutes ago, old_eyes said:

I did a quick check with PHD2 Log Viewer. For those sections 8-11 it gave RA RMS from 0.55" (0.12px) to 0.68" (0.15px) and Dec RMS from 0.43" (0.10px) to 0.54" (0.12px). PA error around 1.5 arcmin. So no, you haven't got px and arcsec mixed up (a mistake I have sadly made several times). The header says that the  guidescope FL is 400mm and the pixel scale on the guide camera 4.43 arcsec/px. That's another setup error I have made before now.

Thanks for checking it. I'm pretty sure that when I was actually imaging it was showing an RMS of 0.21, I took a screen shot at the time but cant find it - also it may not have been the same night as this log. I use OAG with Lodestar so the guide scope is the esprit. The Dec drift is beyond my understanding, I generally do 20 min exposures for NB without problem, this was just a test when I got the mount back, it's not run in yet so may settle down.

[ollypenrice]

18 minutes ago, old_eyes said:

I did a quick check with PHD2 Log Viewer. For those sections 8-11 it gave RA RMS from 0.55" (0.12px) to 0.68" (0.15px) and Dec RMS from 0.43" (0.10px) to 0.54" (0.12px). PA error around 1.5 arcmin. So no, you haven't got px and arcsec mixed up (a mistake I have sadly made several times). The header says that the  guidescope FL is 400mm and the pixel scale on the guide camera 4.43 arcsec/px. That's another setup error I have made before now.

The slightly odd thing is that the Dec axis is drifting steadily followed by a relatively large correction as here:

It is close to, but not actually aligned with the dither shifts.

Good stuff. So in terms of imaging choices at higher resolution this trace would support a pixel scale of about twice the error - something like 1.3 arcseconds per pixel. The seeing is still likely to be the limiting factor on most nights. 

Olly

Edit. In all honesty a guide trace of 0.21 arcsecs RMS would be very, very exceptional. My Mesus, which I consider ecemplary, run at a third as much again as that. However, this doesn't mean you're wrong.

Edited May 4, 2020 by ollypenrice

[gorann]

I was thinking about this thread from 2018 where FLO praised Esprits, saying

 "A small number have needed tweaking on the bench before they were released but I cannot recall one that was rejected outright for optical reasons. We still occasionally reject one for mechanical/cosmetic reasons, though usually before it is sent to Es Reid. Overall we, ourselves & Es, are very impressed with the Esprit series. I am not aware of any other range of triplet refractors that perform as well, certainly not at the price Esprits sell at. "

 

[Laurin Dave]

I have two ES Reid checked Esprits from FLO a 100 and a 150.. both are great so would recommend an Esprit 120 ..    but, good as it is with 0.8"RMS guiding I think you'll need a bigger mount than your HEQ5 to do it (or indeed an Esprit100) justice (an EQ6 equivalent or better).  When I first got the 150 I ran it on a Stellartuned AZEQ6 in an observatory and had guiding of 0.5" RMS (albeit only achieved with 1" guide exposures).  I now have it on a Mesu with guiding of 0.4" RMS and the stars are much tighter, in fact on resolution the Esprit 100 on the Mesu is as good as the Esprit150 on the AZEQ6..   The point I'm making (or trying to make) is beware of investing in the optics without a mount capable of exploiting them as you'll loose field of view for no increase in resolution..  

[Midnight_lightning]

32 minutes ago, Laurin Dave said:

I have two ES Reid checked Esprits from FLO a 100 and a 150.. both are great so would recommend an Esprit 120 ..    but, good as it is with 0.8"RMS guiding I think you'll need a bigger mount than your HEQ5 to do it (or indeed an Esprit100) justice (an EQ6 equivalent or better).  When I first got the 150 I ran it on a Stellartuned AZEQ6 in an observatory and had guiding of 0.5" RMS (albeit only achieved with 1" guide exposures).  I now have it on a Mesu with guiding of 0.4" RMS and the stars are much tighter, in fact on resolution the Esprit 100 on the Mesu is as good as the Esprit150 on the AZEQ6..   The point I'm making (or trying to make) is beware of investing in the optics without a mount capable of exploiting them as you'll loose field of view for no increase in resolution..  

I am as we speak looking more closely at an Esprit 120 and EQ6R-Pro set up

I haven't looked at mounts recently, does this mount seem like a reasonable  way forwards - just looked at Mesu and they are out of my price range?

From what Olly was saying I'm now thinking the mount doesn't need to be perfect, just better than the seeing.

For info, I would like to continue using EQMOD, PHD2 and SG Pro.    

EDIT - Do you use a reducer on your Esprits, I cant see a dedicated one for the 120, just a flattener? The only issue I have with my esprit is getting back focus - my EFW/OAG/CCD takes 60mm.

 

Edited May 4, 2020 by Midnight_lightning

[andrew s]

10 minutes ago, Midnight_lightning said:

From what Olly was saying I'm now thinking the mount doesn't need to be perfect, just better than the seeing.

The same is of course true for the optics. Very few locations and or nights can deliver diffraction  limited seeing for a 4 or 5" scope.

Regards Andrew 

Edited May 4, 2020 by andrew s

[Midnight_lightning]

1 minute ago, andrew s said:

The same is of course true for the optics. Very few locations and or nights can deliver diffraction  limited seeing for a 4 or 5" scope.

So much to consider  

So, is seeing going to have a much bigger impact with a 120 than an 80 - is it the aperture or focal length that influences it?

Just wondering because the reason I am looking to upgrade is to get more detail in my images (and allow me to get smaller targets).

My pixel scale with existing SX814 and 120 would be 0.91"/px which I think is ok for 2"-4"FWHM seeing.

[old_eyes]

1 hour ago, Midnight_lightning said:

Thanks for checking it. I'm pretty sure that when I was actually imaging it was showing an RMS of 0.21, I took a screen shot at the time but cant find it - also it may not have been the same night as this log. I use OAG with Lodestar so the guide scope is the esprit. The Dec drift is beyond my understanding, I generally do 20 min exposures for NB without problem, this was just a test when I got the mount back, it's not run in yet so may settle down.

From memory PHD2 includes dither moves when it calculates RMS error, so you may be better than that. I think you are going to be seeing limited under most circumstances.

[Adam J]

22 hours ago, Midnight_lightning said:

Having spent weeks of research I am still trying to find my next telescope, something to give me a longer reach and better definition than my excellent Esprit 80/400. 

Good Star shape is especially important all the way into the corners.

I started looking at £2-3K scopes and am now also considering increasing the budget - here are my current candidates:

• Esprit 120
• APM 107/700
• Altair 115 ED
• APM LZOZ 115/805
• WO GT102
• Vixen SD 115 S
• TSA-120

Based on reviews and reading forum posts I expected the TSA-120 and APM LZOS 115 to come out strongly on top.

However having spent a day looking at images on the web taken with each of these scopes I have ranked them in order of teh ones I found had best star shape across the FOV - the results surprised me.

Many of these have good star shape near the centre but, even with a flattener or reducer, show marked stretch into the corners - particularly with full frame cameras. Astigmatism and mis-aligned colours were also noticeable even in the higher end scopes. 

It is highly subjective due to differences in flatteners, guiding, cropping, cameras, processing etc etc but I made notes as I went through the analysis and the Esprit 120 came out top and surprisingly the Tak didn't seem better than the cheaper scopes. In a blind test I would find it difficult to distinguish between most of these scopes although I suspect the Esprit 120 would do better than most.

I was hoping to find a light weight 115 or 120 to go on my HEQ5 but I'm now wondering whether to get the Esprit and use the c. £2500 I save to buy a stellar tuned EQ6 mount.

I would really like to hear your views if you use one of these scopes, and also please post see your images showing sharp round stars across the frame.

I'm happy to be proved wrong, I would rather stay with my HEQ5, and welcome any help in making a decision.

 

Would not currently recommended the AMP 107/700 a friend of mine is having trouble with his, I don't think it's up to the standard of their LZOZ lenses. The esprit 120 seems like the best bet, if your feeling poor the TS version of the 115mm is great, if your feeling rich the LZOZ. 

[old_eyes]

1 minute ago, Midnight_lightning said:

So much to consider  

So, is seeing going to have a much bigger impact with a 120 than an 80 - is it the aperture or focal length that influences it?

Just wondering because the reason I am looking to upgrade is to get more detail in my images (and allow me to get smaller targets).

My pixel scale with existing SX814 and 120 would be 0.91"/px which I think is ok for 2"-4"FWHM seeing.

I think, if I understand it correctly, that seeing is an absolute number for that time/sky condition. If your optical/guiding resolution is better than the seeing, your final result will be dominated by the seeing. So FL rather than aperture is the key feature. Aperture gives number of photons per pixel per unit time.

[andrew s]

9 minutes ago, Midnight_lightning said:

So much to consider  

So, is seeing going to have a much bigger impact with a 120 than an 80 - is it the aperture or focal length that influences it?

Just wondering because the reason I am looking to upgrade is to get more detail in my images (and allow me to get smaller targets).

My pixel scale with existing SX814 and 120 would be 0.91"/px which I think is ok for 2"-4"FWHM seeing.

The diffraction limit it is just under 1 arc sec for a 120mm objective and about 1.45 for 80mm.  

Regards Andrew  

PS aperture determines theoretical diffraction limit. Focal length the image scale.

Edited May 4, 2020 by andrew s

[andrew s]

16 hours ago, Peter Drew said:

The worst case scenario is that you buy the Esprit 120, a proven performer, and it doesn't quite come up to the parameters you aspire to.   There must be a queue of imagers waiting for a 2ndhand Esprit to appear for sale.  You would take only a small financial hit but would have satisfied your current dilemma.     🙂  

This is well worth repeating.  Regards Andrew 

[Midnight_lightning]

2 minutes ago, andrew s said:

The diffraction limit it is just under 1 arc sec for a 120mm objective a d about 1.5 for 80mm.  

Stretching my knowledge now but does that mean if the scopes diffraction limit is less than the seeing limit - as in 1.5" is less than 2" seeing - the seeing dictates what is possible and the scope doesn't have any influence. I will probably also use a reducer so if the diffraction limit is based on focal length it would be less than 1.5" at say 600mm (840mm native)?