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ESPRIT 100 + RICCARDI 0.75 REDUCER BACKFOCUS ADJUSTMENT. CRAZIEST!

Sky-Watcher Esprit 100ED ZWO ASI2600MC Pro Reducer Help Needed
Jandro.rmAstroStewRob KieferChristian KollSilverLitz
•42 replies•1.4k views
Jandro.rm avatar
Jandro.rm avatar
Hi
i´m a owner of esprit 100 with sw flattener and i love this combo . In last  week i get the riccardi 0.75 x reducer but I'm trying to adjust the backfocus. I've seen in the documentation that for this reducer, the distance for this scope varies between 75–78 mm, but it's nowhere near correct, as I'm getting considerable star distortion in the corners. I have an EFW and a ZWO 2600 MC Pro. I've tried various distances, even using 0.1, 0.2, and 0.3 mm spacers, and I still can't get it right. Anyone with this same setup who can give me some guidance?
Rob Kiefer avatar
Rob Kiefer avatar
Hello Jandro,
I have a similar setup (but using QHY), however, I have not used it for quite some time now. Checking my notes, I came close to 80mm. 
Good luck,
Rob
Well Written
Jandro.rm avatar
Jandro.rm avatar
yes..these last nights the distance was between 80-81 but i can´t get it yet….
Christopher Dietz avatar
Christopher Dietz avatar
I had this reducer for my E100/2600MC and it was nothing but trouble (this was before StarXterminator existed). I did everything I could and still couldn't make it work. Sold it.
Ultimately, I went back to the 1x SW flattener at f5.5 and have just accepted it. It is still pretty fast at f5.5 for the extremely good correction at the native setup. Just embrace longer integration times (and a smaller field) and you will find inner peace. If you can get good results, more power to you.
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SilverLitz avatar
SilverLitz avatar
It looks like you have significant tilt to remove before dialing in the BF.
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Rob Kiefer avatar
Rob Kiefer avatar
I just checked some of my raw images and I need to add, that my stars were not perfect as well. BXT corrected most of the  stars reasonable well. So Christopher´s advice it not bad to just stick to the flattener (if perfect stars are important to you).
Jandro.rm avatar
Jandro.rm avatar
Tonight I'm doing tests; tomorrow I'm moving it to a hosting service, and I don't want to deal with these issues. If I can't get it adjusted today, I'll set up the SW one on native Focal
Nico Gärtner avatar
Nico Gärtner avatar
Hi All,

I am using this combo and I am quite happy with it, but I have to admit that I purchased it together with the correct spacers from Lacerta (see the article description - in german ;-) )

https://lacerta-optics.com/RicRed075-63

Fine tuning with sub mm spacers took me some nights, but in the meantime i get pleasing results.
Examples:
https://www.astrobin.com/v49gag/
https://www.astrobin.com/5w0zhq/

Best Regards,

Nico
Tommi Liinalampi avatar
Tommi Liinalampi avatar
Hi!

I have the same combination and I have never got perfect stars even using smaller sensor (ASI294MM), but maybe just decent stars. My backfocus is about 79 mm I think.

Best regards,

Tommi
Jandro.rm avatar
Jandro.rm avatar
thanks for your responses. I will try this night to try to get it. I have the adapters (no lacerta) but the apm adapters to introduce in the focuser tube.
Brian Puhl avatar
Brian Puhl avatar
The 0.75 is just too much for the Esprit IMO.    I've seen competent folks put this combo together and the results never appealed to me.   I don't know if it's the combination of optics or the Riccardi just isn't that good, but the corners are always jacked up.
Tommi Liinalampi avatar
Tommi Liinalampi avatar
Fast optics come with their weaknesses, and you can't have everything at once. Although the stars near the edges are far from perfect, I'm still satisfied with what can be achieved with this combination. It's also important to understand that when stars are really sharp, any flaws in shape become more apparent. Now that star correction works quite well with BlurXTerminator, many of the weaknesses of fast optics can be corrected.

I have a separate manual rotator installed on the Esprit scope, but whenever I touch it, I have to check the sensor tilt. That's life with this combination, but results are very nice!
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Kelvin Hennessy avatar
Kelvin Hennessy avatar
Wow where to begin with an answer !  I battled with this when I first bought it a year ago  (my supplier totally got it wrong, not realising the reducer needed to be recessed inside the focusser tube).  I eventually got all the correct adapters and spacers out of them and got it dialled in very nicely.

Now after several months of cloud I've dusted it all off and tried connecting it up again and had a great deal of trouble with the back focus.  I re-studied all my old information I'd acquired and did some more.  

According to Riccardi the sensor should be 80mm from the very end of the thread.  (one very thorough researcher found his to be 78.5mm - mine would be about the same). 

Assuming you have the Teleskop Service M68 & M63 to M48 adapter (which allows for mandatory insertion of the reducer into the drawtube) then this adapter nominally consumes 6.2 mm out of your 78.5mm backfocus.  Mine measures at 6.0mm so lets go with that.   78.5mm - 6mm leaves  72.5mm back focus.
The 2600MC has 17.5mm of Flange Focal Distance (from the face of the tilt plate to the sensor).    72.5mm backfocus - 17.5mm flange focal distance leaves  55mm distance you have to fill with "something".

Fortunately ZWO make that 55mm easy to fill up.  A separate CTU  (Camera Tilt Unit or tilt adjuster) is in my opinion and many others essential,  I see you are using an EFW - so there's about 20mm gone - and if you are removing the useless tilt plate on the front of the 2600MC  then there's 5mm you have to fill up again.   

So I'd say in your case  you have 72.5mm (from the reducer's adapter front face)  - 12.5mm camera Flange Focal Distance - 20mm EFW = 40mm worth of spacers & adapters you need.   

Oh and you also need to allow for  for the 0.6mm the the filters add to the back focus but that's part of the fine tuning with fixed or variable spacers - I wouldnt be  concerned about including that in your calculations because of the error in the 78 to 80mm estimation of total back focus.

Please let me know your current configuration of adapters and spacers and your calculations.

Cheers, Kelvin
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SilverLitz avatar
SilverLitz avatar
0.75x is not too much for the Esprit 100.  I used the 2019 version of the TSAPORED075 with my Esprit 100 for 4 years, and it was nearly perfect out to my QHY268M (APS-C).  The original TSAPORED075 was supposedly based on the Riccardi, but TS changed it in 2020 (but kept the same part #, why?).  The new version will not work with the Esprit 100, as it does not have enough inward focus.   I found the TSAPORED075 to be better than its native FF, and after I got it, it never came off my Esprit.  It was my most used OTA for more than 3 years, but I sold it as I got lucky with the A-P 110GTX lottery.

Here is my CN thread on my 2019 FR journey.  
 https://www.cloudynights.com/topic/659716-sw-esprit-100ed-focal-reducer/
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Joan Riu avatar
Joan Riu avatar
Hello, I've the same rig configuration with 80mm backfocus. All is ok.
Jandro.rm avatar
Jandro.rm avatar
Kelvin Hennessy:
Wow where to begin with an answer !  I battled with this when I first bought it a year ago  (my supplier totally got it wrong, not realising the reducer needed to be recessed inside the focusser tube).  I eventually got all the correct adapters and spacers out of them and got it dialled in very nicely.

Now after several months of cloud I've dusted it all off and tried connecting it up again and had a great deal of trouble with the back focus.  I re-studied all my old information I'd acquired and did some more.  

According to Riccardi the sensor should be 80mm from the very end of the thread.  (one very thorough researcher found his to be 78.5mm - mine would be about the same). 

Assuming you have the Teleskop Service M68 & M63 to M48 adapter (which allows for mandatory insertion of the reducer into the drawtube) then this adapter nominally consumes 6.2 mm out of your 78.5mm backfocus.  Mine measures at 6.0mm so lets go with that.   78.5mm - 6mm leaves  72.5mm back focus.
The 2600MC has 17.5mm of Flange Focal Distance (from the face of the tilt plate to the sensor).    72.5mm backfocus - 17.5mm flange focal distance leaves  55mm distance you have to fill with "something".

Fortunately ZWO make that 55mm easy to fill up.  A separate CTU  (Camera Tilt Unit or tilt adjuster) is in my opinion and many others essential,  I see you are using an EFW - so there's about 20mm gone - and if you are removing the useless tilt plate on the front of the 2600MC  then there's 5mm you have to fill up again.   

So I'd say in your case  you have 72.5mm (from the reducer's adapter front face)  - 12.5mm camera Flange Focal Distance - 20mm EFW = 40mm worth of spacers & adapters you need.   

Oh and you also need to allow for  for the 0.6mm the the filters add to the back focus but that's part of the fine tuning with fixed or variable spacers - I wouldnt be  concerned about including that in your calculations because of the error in the 78 to 80mm estimation of total back focus.

Please let me know your current configuration of adapters and spacers and your calculations.

Cheers, Kelvin

thanks for your response 
My rig is 2600 without tilt plate, efw and zwo caa (all is 56,5 mm) and i tried very different distances between 78-81 mm and never got puntual stars on the conrners...all the BEST was this

And this is my rig with adapters

Toni Fabiani avatar
Toni Fabiani avatar
Hi
i´m a owner of esprit 100 with sw flattener and i love this combo . In last  week i get the riccardi 0.75 x reducer but I'm trying to adjust the backfocus. I've seen in the documentation that for this reducer, the distance for this scope varies between 75–78 mm, but it's nowhere near correct, as I'm getting considerable star distortion in the corners. I have an EFW and a ZWO 2600 MC Pro. I've tried various distances, even using 0.1, 0.2, and 0.3 mm spacers, and I still can't get it right. Anyone with this same setup who can give me some guidance?

Hi Jandro, I've been using this setup for years. I got a 77.8mm backfocus lens. I used a ZWO183M, and everything worked fine for a while. I decided to change the setup and add a rotator, and a QHY268M, but when I added more weight, I had a lot of problems due to the added weight. I struggled with the backfocus lens for months. I ended up changing the Esprit's stock focuser. Either you change it, or you adjust it yourself, since they tend to be a bit "loose" when changing the focuser and rotator. All these problems are gone. You can see my images; I have round stars even before BlurSterminator. I hope I've helped.
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Kelvin Hennessy avatar
Kelvin Hennessy avatar
@Jandro.rm  here is mine.  Your spacing looks similar but you have extreme tilt.   I did have a 48mm 15-18mm variable spacer in there until last week but it got stuck to my Gerd Neumann tilt adapter and the only way to get it off was with a vice and breaking it .  Luckily I had the right combination of 48mm spacers to replace it and get close enough.  The tilt adapter made a big difference, though my tilt was nowhere as bad as yours. My Espirit focusser is at 47mm.

Here is a PI aberration inspection of one of my subs

At a guess I'd say the combined weight of your camera, EFW and CAA is too much for the draw tube.    

Jandro.rm avatar
Jandro.rm avatar
Hi again
I've been testing backfocus these days but haven't been able to get it right. It's incredibly sensitive to 0.1 mm rings. I'm currently at 77.5 mm and it's the best I've gotten (pinpoint stars in one corner, since I have tilt, which I'll fix later), but it's very difficult to fine-tune. I've used Astap and Hocus Focus, and sometimes they contradict each other. When Hocus Focus tells me I have to move closer to the sensor, however, elongated stars still appear visually in the corners.
Jandro.rm avatar
Jandro.rm avatar
To check in astap. whats is the best HFD Value to check backfocus in this setup? i can´t down to 3,5
Jandro.rm avatar
Jandro.rm avatar
Finally i get it. Stars round on edges and no tilt at 74,5 mm
Rob Kiefer avatar
Rob Kiefer avatar
Finally i get it. Stars round on edges and no tilt at 74,5 mm

Just for clarification - measured from where? From the Riccardi Reducer or from the M63M68M48 Adapter? 
Rob
Jandro.rm avatar
Jandro.rm avatar
Rob Kiefer:
Finally i get it. Stars round on edges and no tilt at 74,5 mm

Just for clarification - measured from where? From the Riccardi Reducer or from the M63M68M48 Adapter? 
Rob

Hi Rob
From riccardi reducer. I  measured from there with a caliper to the 2600 camera and then added 6.5 since I don't have a tilter.
Jandro.rm avatar
Jandro.rm avatar
I adjusted using Hocus Focus and Astap. It was 4-5 hours adding and removing < 1 mm rings. Maybe to complete perfect backfocus need 0.01 mm rings…it´s very sensitive
Dumitru Irizan avatar
Dumitru Irizan avatar
Hi,
I still had problems with the original focuser and changed to another one and since then I haven't had any problems. Of course, I have to mention that I received a lot of advice from @Toni Fabiani . On my telescope the backfocus is 78.2mm. After adjusting the backfocus I encountered the severe tilt problem and I didn't know how to solve it, but it didn't take long and I purchased that ETA from Wanderer astro. That's how I solved the tilt problem and the possibility of controlling and adjusting it remotely (I plan to control the observatory remotely).