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

[Midnight_lightning]

7 minutes ago, andrew s said:

This is well worth repeating.  Regards Andrew 

The thing is (aargh!) the HEQ5 limitation severely restricted the scopes I could use - now I'm considering an EQ6 I have even more options  

That said I do think the Esprit 120 would be good, I'm so pleased with my 80. As I mentioned above, the only issue with the 80 was the short back focus on the flattener so I'm trying to see if its the same with the 120. I would REALLY like a manual camera rotator in the image chain but no chance with the 80. I know you can rotate from the focuser but it changes the balance and unless the FW was vertically up or down it would never balance the same on both sides of the pier. I notice it more since the Stellar tune as the mount now rotates so freely the slightest misbalance is noticeable.

Edited May 4, 2020 by Midnight_lightning

[Adam J]

1 hour 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..  

Yes a HEQ5pro can't guide an esprit 100 unless your camera has big pixels like a 8300. The newer CMOS cameras with smaller pixels show guide errors. I am speaking from personal experience here. I had to upgrade to an AZ EQ6 GT. 

[johnturley]

1 hour ago, gorann said:

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. "

 

One interesting, but probably less well known fact is that the Esprit 150 currently sells for about the same price in real terms as the early Astro Physics 6in Refractors, which sold for $1,295 in 1987.

Although these early AP scopes represented quite good value for what was available at the time, however contrary to what some reports state, having owned both scopes, I can say that the early AP scopes were not that marvellous both in terms of colour correction and build quality, compared to the Esprit. For example the focusing mounts were rough (I think that most people who kept them subsequently upgraded the focuser), and the lens cells were not collimatable. I should stress though that the later  Starfire models were of  a much higher standard, and also much more expensive. Nevertheless you sometimes see, mainly in the USA, these early 6in AP scopes up for sale at around $4,000 or more.

John 

Edited May 4, 2020 by johnturley

[andrew s]

32 minutes ago, Midnight_lightning said:

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)?

Yes, seeing dominates if it is larger than the diffraction of the lens. The diffraction limit is not based on focal length but a reducer will have an effect. It may flatten the field making things better or add aberration making it worse.!

Regards Andrew 

Edited May 4, 2020 by andrew s

[Midnight_lightning]

1 hour 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 

Based on the 100 and 150 do you think the 120 will go on an EQ6R-Pro without crashing the tripod legs - just read a post that suggested this combination may prevent meridian flips and zenith imaging?

 

[gorann]

1 hour ago, Midnight_lightning said:

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)?

Not sure why you worry about seeing. Since you say that you have your current mount guiding at 0.21" RMS, which is almost unbelievably good, that must mean that you have very good seeing at you location (that kind of super guiding would be impossible with even slightly bad seeing), so an Esprit 120 would have no problems catching more details than an Esprit 80 if you have it on a mount that can handle it, like one of the EQ6 varieties.

PS. I assume you have put in the correct focal length of your guide scope into PHD2 (or the RMS value would be wrong).

Edited May 4, 2020 by gorann

[andrew s]

6 minutes ago, gorann said:

Not sure why you worry about seeing. Since you say that you have your current mount guiding at 0.21" RMS, which is almost unbelievably good, that must mean that you have very good seeing at you location (that kind of super guiding would be impossible with even slightly bad seeing), so an Esprit 120 would have no problems catching more details than an Esprit 80 if you have it on a mount that can handle it, like one of the EQ6 varieties.

PS. I assume you have put in the correct focal length of your guide scope into PHD2 (or the RMS value would be wrong).

Seeing and guiding accuracy are not the same thing. Your guiding needs to be better than the seeing otherwise you will be guiding limited not seeing limited.

You guiding could be very good but still have poor seeing. Yes poor seeing can  if you are not careful,  reduce your guiding accuracy but only if badly set up.

Regards Andrew 

[Midnight_lightning]

22 minutes ago, gorann said:

Not sure why you worry about seeing. Since you say that you have your current mount guiding at 0.21" RMS, which is almost unbelievably good, that must mean that you have very good seeing at you location (that kind of super guiding would be impossible with even slightly bad seeing), so an Esprit 120 would have no problems catching more details than an Esprit 80 if you have it on a mount that can handle it, like one of the EQ6 varieties.

Just trying to understand where the limitations are.

For example if the guiding isn't limited by the seeing it may be worth me buying a Stellar Tuned EQ6 from the outset rather than an out of the factory one and then maybe later wanting to get it tuned? 

I need to check that RMS figure, I'm sure that's what I was seeing but it does sound too good.

[Laurin Dave]

1 hour ago, Midnight_lightning said:

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.

 

I'd think the EQ6R-Pro would be ok or its Ioptron or Avalon equivalent, are you setting up each time?  If so you don't want something too heavy or fiddly to balance.  

I have the flatteners on both Esprits  @gorann has a reducer so maybe he can comment..  I've used the 150 with a D750 and once you've cropped out the shutter box shadow it's pretty flat.   The 120 has loads of room for backfocus 90mm or so, it comes with a spacer to which you need to add 55mm,  my setup required a rather expensive spacer ..  also were you aware that SX have just brought out a new FW with inbuilt OAG which gives 55mm backfocus .. 

 

[Laurin Dave]

40 minutes ago, Midnight_lightning said:

Based on the 100 and 150 do you think the 120 will go on an EQ6R-Pro without crashing the tripod legs - just read a post that suggested this combination may prevent meridian flips and zenith imaging?

 

Skywatcher do a pillar mount on wheels which will get around this potential issue

[Midnight_lightning]

16 minutes ago, Laurin Dave said:

I'd think the EQ6R-Pro would be ok or its Ioptron or Avalon equivalent, are you setting up each time?  If so you don't want something too heavy or fiddly to balance.  

 

I leave the rig set up but have to move it outside each session. I'm thinking of having 3 x 3 wheels "coasters", one under each leg so I can wheel it out and then one leg at a time remove the coasters. Also looking at full dolly's but they are expensive and its something else to wobble

19 minutes ago, Laurin Dave said:

The 120 has loads of room for backfocus 90mm or so, it comes with a spacer to which you need to add 55mm,  my setup required a rather expensive spacer ..  also were you aware that SX have just brought out a new FW with inbuilt OAG which gives 55mm backfocus .. 

I think the backfocus issue comes from the flattener used, the straight SW flattener gives 75mm which is fine.

I haven't identified a reducer yet, seen people discuss Riccardi, Hotech etc but the ones I looked at so far only have 55mm BF so looks like they are aimed at DSLR users. 

[Midnight_lightning]

21 minutes ago, Laurin Dave said:

Skywatcher do a pillar mount on wheels which will get around this potential issue

I looked at the SW pillar mount last year, for a different reason but got warned off by a few people who reckoned the tripod was a much firmer base.

Always hard to know with these things without trying or getting good references.

[gorann]

57 minutes ago, andrew s said:

Seeing and guiding accuracy are not the same thing. Your guiding needs to be better than the seeing otherwise you will be guiding limited not seeing limited.

You guiding could be very good but still have poor seeing. Yes poor seeing can  if you are not careful,  reduce your guiding accuracy but only if badly set up.

Regards Andrew 

I know that you should use guide-exposure times that are long enough not to chase the seeing (around 5 s), but in my experience I can never get really good guiding on nights with poor seeing and to get guiding at 0.21 "/pixel RMS would at least be impossible for me at a night with poor seeing (I am happy when I get 0.4" with my Mesu and that only happens with good seeing).

[gorann]

37 minutes ago, Laurin Dave said:

I'd think the EQ6R-Pro would be ok or its Ioptron or Avalon equivalent, are you setting up each time?  If so you don't want something too heavy or fiddly to balance.  

I have the flatteners on both Esprits  @gorann has a reducer so maybe he can comment..  I've used the 150 with a D750 and once you've cropped out the shutter box shadow it's pretty flat.   The 120 has loads of room for backfocus 90mm or so, it comes with a spacer to which you need to add 55mm,  my setup required a rather expensive spacer ..  also were you aware that SX have just brought out a new FW with inbuilt OAG which gives 55mm backfocus .. 

 

Unfortunately SW does not make dedicated reducers for the Esprits (those for the Evostars do not work for Esprits), and the ones that people have got to work are two from TS (TSRED379, TSAPORED075) and the Riccardi reducer. With the TS reducers you need only one adapter ring while you need a whole costly bunch for the Riccardi. I have a TSRED379 and after much testing with distances I kind of got it to work with my Esprits, but for an APS-C ship I still get some annoying star elongation and chromatic abberation in the corners. It may be that with the newer and slightly more expensive TSAPORED075 you could get better results. It may also be that you need to be lucky with the particular sample you get.

[Midnight_lightning]

20 minutes ago, gorann said:

Unfortunately SW does not make dedicated reducers for the Esprits (those for the Evostars do not work for Esprits), and the ones that people have got to work are two from TS (TSRED379, TSAPORED075) and the Riccardi reducer. With the TS reducers you need only one adapter ring while you need a whole costly bunch for the Riccardi. I have a TSRED379 and after much testing with distances I kind of got it to work with my Esprits, but for an APS-C ship I still get some annoying star elongation and chromatic abberation in the corners. It may be that with the newer and slightly more expensive TSAPORED075 you could get better results. It may also be that you need to be lucky with the particular sample you get.

I assumed that if you got good focus using a mask that the backfocus must be ok. From what you are saying it sounds like you also need to adjust backfocus within the "in-focus" range. Is that correct? 

Presumably you are talking fine adjustment with Delrin spacers  or similar?

[Filroden]

Deleted post - misread the original

Edited May 4, 2020 by Filroden

[RayD]

Post no longer relevant.

Edited May 4, 2020 by RayD

[Laurin Dave]

56 minutes ago, Midnight_lightning said:

I looked at the SW pillar mount last year, for a different reason but got warned off by a few people who reckoned the tripod was a much firmer base.

Always hard to know with these things without trying or getting good references.

Indeed.. I was looking at one but will reconsider..  thanks.. 

[gorann]

31 minutes ago, Midnight_lightning said:

I assumed that if you got good focus using a mask that the backfocus must be ok. From what you are saying it sounds like you also need to adjust backfocus within the "in-focus" range. Is that correct? 

Presumably you are talking fine adjustment with Delrin spacers  or similar?

The stars are not out of focus - they are elongated in the corners of the image (like you get with the wrong distance between reducer and chip). I have tried with thin spacer rings in 0.5 mm steps. Unfortunately TS just says that it has to be tested out and could not give me the correct distance. There is this thread on CN where they at the end seemed to get it to work with the TSAPORED075:

https://www.cloudynights.com/topic/659716-sw-esprit-100ed-focal-reducer/

This is what a simply stretched image looks like when I use a 52.5 mm distance between reducer (TSRED379) and chip, and it is the best I got so far. I also include the finally processed one where I used a few tricks in PS to kind of fix the stars.

 

 

Edited May 4, 2020 by gorann

[Midnight_lightning]

8 minutes ago, gorann said:

This is what a simply stretched image showing what it looks like when I use a 52.5 mm distance between reducer (TSRED379) and chip, and it is the best I got so far. I also include the finally processed one where I used a few tricks in PS to kind of fix the stars.

Nice image, the PS tricks worked well

Unfortunately, I need 60mm back focus + the width of an adapter and with no dedicated reducer I'm wondering if the Esprit 120 is going to do the job. 

[gorann]

5 minutes ago, Midnight_lightning said:

Nice image, the PS tricks worked well

Unfortunately, I need 60mm back focus + the width of an adapter and with no dedicated reducer I'm wondering if the Esprit 120 is going to do the job. 

Then you need to go for the Riccardi - it has a longer distance:

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p11122_Riccardi-0-75x-APO-Reducer-and-Flattener-with-M63x1-Thread.html

But I am not sure why you need that camera rotator.

[gorann]

PS. APM even sells it with a Riccardi as a set:

https://www.apm-telescopes.de/en/telescopes/refracting-telescopes-ota/apochromates/skywatcher-esprit-120ed-triplet-apo-refractor-120-mm-f-5.25-corrector-apm-riccardi-apo-reducer-set.html

[Midnight_lightning]

12 minutes ago, gorann said:

PS. APM even sells it with a Riccardi as a set:

That's interesting  

15 minutes ago, gorann said:

But I am not sure why you need that camera rotator.

If I rotate from the focuser for framing the weight of the filter wheel being offset from vertical throws the mount out of balance. 

I suspect I'm also going to have an issue with the FW or Lodestar (they stick out on opposite sides) colliding with the mount when used with the 120.  I may be able to reduce the risk by adjusting the orientation - but again throwing the balance out - choices!

If I could just rotate the camera it would be easier to frame targets and allow better balance. 

[gorann]

2 minutes ago, Midnight_lightning said:

That's interesting  

If I rotate from the focuser for framing the weight of the filter wheel being offset from vertical throws the mount out of balance. 

I suspect I'm also going to have an issue with the FW or Lodestar (they stick out on opposite sides) colliding with the mount when used with the 120.  I may be able to reduce the risk by adjusting the orientation - but again throwing the balance out - choices!

If I could just rotate the camera it would be easier to frame targets and allow better balance. 

That suggest that you are really running near the limits of your mount - maybe that would not be a problem with a bigger mount. Also, I still do not really understand how rotating the filter wheel could change the balance. You do not change the weight on each side of the center of gravity of your telescope. If that was the case - would you not be in trouble after a meridean flip?

[Midnight_lightning]

13 minutes ago, gorann said:

That suggest that you are really running near the limits of your mount - maybe that would not be a problem with a bigger mount. Also, I still do not really understand how rotating the filter wheel could change the balance. You do not change the weight on each side of the center of gravity of your telescope. If that was the case - would you not be in trouble after a meridean flip?

The mounts fine, its me wanting perfect balance. Since I had the stellar tune done the mount rotates very freely - with the clutch off you could gently spin the RA and it will just keep spinning for quite a while. 

When balancing it with the EFW anywhere other than vertically up of down (home position) I can only get balance on one side of the pier or the other. So balance it one side and I can let go in any position and it just stays. Move to the other side and its not balanced. Took me a while to work it out but its because the CoG isn't symmetrical without the EFW vertical - it only affects Dec balance.

I'm sure the mount could handle the mis-balance, before the tuning I wouldn't have even being able to detect it due to stiction, but I put so much time, effort and money into this hobby I am looking to get the best out of everything