Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Newtonian Upgraded Focuser Issues (Hole Alignment)

  • Please log in to reply
16 replies to this topic

#1 jimgerrr

jimgerrr

    Lift Off

  • -----
  • topic starter
  • Posts: 16
  • Joined: 03 Mar 2021

Posted 09 December 2021 - 08:28 AM

Hello!

 

I just purchased a Bresser BR-N20839, however it came with a serial plate labeled as Explore Scientific PN210 (but that's besides the point). I bought this telescope strictly for astrophotography, I did lots of research and realized I will likely have to upgrade the focuser to hold my AP gear without slipping (OAG, Filter Wheel, ASI294MM Pro). I am using ASIAIR for my imaging, so I needed a focuser that supports the EAF. I settled on a JMI Event Horizon EVRZ-N. Upon installing last night, I noticed that the focuser holes will not line up on the optical tube, the holes on the tube are approximately 74mm apart, while the focuser is 70mm apart. See attached for a picture.

 

Are there any baseplates that I can buy to get this focuser to fit? If not can anyone recommend a focuser that will fit, and support an EAF?

 

Worst case scenario, am I able to drill holes to make it fit? This is definitely an option but I'm nervous drilling holes in a brand new Newtonian. Would I have to drill 4 new holes, or put 2 screws in, and drill 2 new holes (shifting the focuser 4mm)?

 

Thank you!

Attached Thumbnails

  • PXL_20211209_120718616.jpg


#2 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 97,185
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 09 December 2021 - 08:47 AM

- Does the new focuser have the correct curvature to fit the tube?

 

- Have you tested the scope with the current focuser to be confident it's the scope you want?

 

- My intuition is that it's unlikely that you can find an adapter.

 

- When I was confident that I was going to keep the scope and confident the center to center spzcing difference was 4.0 mm for all the holes, it'd carefully drill out all 4 existing holes with a 4 mm oversize drill. I think that works.

 

Jon



#3 jimgerrr

jimgerrr

    Lift Off

  • -----
  • topic starter
  • Posts: 16
  • Joined: 03 Mar 2021

Posted 09 December 2021 - 08:59 AM

Thanks for the reply Jon.

 

- The curvature seems to be identical. The focuser sits in the hole just fine, mounting holes just don't line up.

 

- Unfortunately not yet, I've had many cloudy nights since I received everything. I have the original focuser back on there now, so I plan on trying it over the weekend.

 

- ****! 

 

- I will verify the spacing but 99% sure its only 4mm. I can expand each hole by 2mm and should ensure that everything fits. I will just need to add small washers to compensate for the larger holes.

 

If I'm unable to use this scope for AP, I will use it for visual. So modifying it isn't too big of a deal



#4 jimgerrr

jimgerrr

    Lift Off

  • -----
  • topic starter
  • Posts: 16
  • Joined: 03 Mar 2021

Posted 09 December 2021 - 10:25 AM

Thats reassuring! I'll try enlarging the screw holes this weekend. 



#5 SteveG

SteveG

    Voyager 1

  • *****
  • Posts: 10,779
  • Joined: 27 Sep 2006
  • Loc: Seattle, WA

Posted 09 December 2021 - 07:16 PM

Thats reassuring! I'll try enlarging the screw holes this weekend. 

Make sure you purchase a new bit for drilling in steel. I would prefer new holes that align with the new focuser, over enlarging the existing holes - unless they are that close or overlapping.



#6 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 97,185
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 10 December 2021 - 06:40 AM

Make sure you purchase a new bit for drilling in steel. I would prefer new holes that align with the new focuser, over enlarging the existing holes - unless they are that close or overlapping.

The holes are 4mm apart.. The screws are certainly larger than 2mm.  The holes would be overlapping.  

 

But a little wiggle room in the mounting of a focuser can be a good thing and once tightened down, it will not move.  

 

But the reason I would drill the existing holes oversize:  Centering a drill on a curved steel tube is not so easy.  With the holes already there, the drill is automatically centered. 

 

Jon


  • SteveG likes this

#7 jimgerrr

jimgerrr

    Lift Off

  • -----
  • topic starter
  • Posts: 16
  • Joined: 03 Mar 2021

Posted 10 December 2021 - 09:48 AM

I think what I'm going to end up doing is elongating each hole inwards by 2mm using a Dremel and 1/8" metal cutting bit. I felt uncomfortable drilling it just in case the bit grabs, and pulls. Also if I end up wanting to put the old focuser in, there will be some slop in the alignment. I have attached a few more pictures with measurements as well. 

 

The new focuser is flat on the bottom, and not curved, unlike the existing focuser. I noticed with it sitting on my tube last night that there might be some light leakage inside the tube with it. Should I fill the gaps with foam to prevent light leakage? 

 

Finally, I was doing a lot of reading about drawtubes. I'm hoping I can reach infinity focus with the stock JMI drawtube. If I can't, are they universal, or do I have to purchase a longer JMI drawtube?

 

https://photos.app.g...6aa3bbRuaD7zKc7

 

Thanks for the replies everyone, you guys are giving me the confidence in getting this thing right.



#8 SteveG

SteveG

    Voyager 1

  • *****
  • Posts: 10,779
  • Joined: 27 Sep 2006
  • Loc: Seattle, WA

Posted 10 December 2021 - 03:24 PM

I think what I'm going to end up doing is elongating each hole inwards by 2mm using a Dremel and 1/8" metal cutting bit. I felt uncomfortable drilling it just in case the bit grabs, and pulls. Also if I end up wanting to put the old focuser in, there will be some slop in the alignment. I have attached a few more pictures with measurements as well. 

 

The new focuser is flat on the bottom, and not curved, unlike the existing focuser. I noticed with it sitting on my tube last night that there might be some light leakage inside the tube with it. Should I fill the gaps with foam to prevent light leakage? 

 

Finally, I was doing a lot of reading about drawtubes. I'm hoping I can reach infinity focus with the stock JMI drawtube. If I can't, are they universal, or do I have to purchase a longer JMI drawtube?

 

https://photos.app.g...6aa3bbRuaD7zKc7

 

Thanks for the replies everyone, you guys are giving me the confidence in getting this thing right.

It's a shame they don't offer curved bases. Can we see a pic of the base profile on the new focuser?



#9 jimgerrr

jimgerrr

    Lift Off

  • -----
  • topic starter
  • Posts: 16
  • Joined: 03 Mar 2021

Posted 10 December 2021 - 03:50 PM

See attached. I went into buying this Newtonian fully expecting to have to modify and tinker with it to be happy with it. Just want to make sure I'm doing it right!

Attached Thumbnails

  • PXL_20211210_204437736.jpg
  • PXL_20211210_204322290.jpg


#10 MitchAlsup

MitchAlsup

    Fly Me to the Moon

  • -----
  • Posts: 6,066
  • Joined: 31 Aug 2009

Posted 10 December 2021 - 08:17 PM

In my opinion, elongated (or enlarged) holes will work just fine when backed up with suitable washers to spread the load.

 

When I do things like this, on a 1/4" thread, I use 6mm washer at the bolt head, and a 1/4" washer under the 6mm washer. {And there is no reason to go all the way to aircraft washers and fitments.}


  • Jon Isaacs likes this

#11 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 97,185
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 11 December 2021 - 05:04 AM

I think what I'm going to end up doing is elongating each hole inwards by 2mm using a Dremel and 1/8" metal cutting bit. I felt uncomfortable drilling it just in case the bit grabs, and pulls. Also if I end up wanting to put the old focuser in, there will be some slop in the alignment. I have attached a few more pictures with measurements as well. 

 

The new focuser is flat on the bottom, and not curved, unlike the existing focuser. I noticed with it sitting on my tube last night that there might be some light leakage inside the tube with it. Should I fill the gaps with foam to prevent light leakage? 

 

Finally, I was doing a lot of reading about drawtubes. I'm hoping I can reach infinity focus with the stock JMI drawtube. If I can't, are they universal, or do I have to purchase a longer JMI drawtube?

 

https://photos.app.g...6aa3bbRuaD7zKc7

 

Thanks for the replies everyone, you guys are giving me the confidence in getting this thing right.

 

The base isn't really flat, it's designed to fit a wide range of radii.  I wouldn't worry about light leakage.  

 

Since you are doing astrophotography, I assume you will be using a coma corrector.  If you don't have enough outward focuser travel, you can just slide the coma corrector out somewhat.  Or you can by a short extension tube.

 

Jon



#12 bobharley

bobharley

    Lift Off

  • *****
  • Posts: 14
  • Joined: 23 Oct 2021
  • Loc: Oglesby, Il

Posted 12 December 2021 - 07:14 PM

When I drilled 4 holes in my ota, I put 2 magnets inside near the drilling area, and taped my shop vac hose to the front, ran the shop vac while drilling. After drilling pull the magnets out to remove 90% of the filings, and then shop vacced the rest out. Do drilling with the tube horizontal.

#13 jimgerrr

jimgerrr

    Lift Off

  • -----
  • topic starter
  • Posts: 16
  • Joined: 03 Mar 2021

Posted 13 December 2021 - 08:50 AM

I used the dremel to elongate the holes last night with success! I did a few tests last night and I was able to collimate and hit focus. I will either need a much larger drawtube (4.6"), or just mark my focus with painters tape on my coma corrector. 

 

This scope has 3 collimation knobs, and 3 set screws for each one (see attached for the picture). How do I properly collimate this scope? Last night using a laser, I adjusted the knobs, then slowly tightened the set screws to prevent my secondary from moving. As I tightened them, it shifted the collimation but I just adjusted the set screws until everything was aligned and tight. Is this the correct way to collimate it? 

 

I also noticed there was a slight vignette, or tilt in my picture. Bottom right of the image consistently had it. Where should I look into adjusting to fix that? OAG, Focuser Base? 

Attached Thumbnails

  • PXL_20211213_121428897.PORTRAIT.jpg
  • PXL_20211213_121534478.PORTRAIT.jpg

  • Jon Isaacs and George N like this

#14 SteveG

SteveG

    Voyager 1

  • *****
  • Posts: 10,779
  • Joined: 27 Sep 2006
  • Loc: Seattle, WA

Posted 14 December 2021 - 02:06 AM

See attached. I went into buying this Newtonian fully expecting to have to modify and tinker with it to be happy with it. Just want to make sure I'm doing it right!

That’s a nice base. That focuser should work well for you.



#15 SteveG

SteveG

    Voyager 1

  • *****
  • Posts: 10,779
  • Joined: 27 Sep 2006
  • Loc: Seattle, WA

Posted 14 December 2021 - 02:09 AM

I used the dremel to elongate the holes last night with success! I did a few tests last night and I was able to collimate and hit focus. I will either need a much larger drawtube (4.6"), or just mark my focus with painters tape on my coma corrector. 

 

This scope has 3 collimation knobs, and 3 set screws for each one (see attached for the picture). How do I properly collimate this scope? Last night using a laser, I adjusted the knobs, then slowly tightened the set screws to prevent my secondary from moving. As I tightened them, it shifted the collimation but I just adjusted the set screws until everything was aligned and tight. Is this the correct way to collimate it? 

 

I also noticed there was a slight vignette, or tilt in my picture. Bottom right of the image consistently had it. Where should I look into adjusting to fix that? OAG, Focuser Base? 

Could you take another picture of the open end of the tube, showing the secondary and vanes as well as the tube.

 

Is your only tool the laser? Which model do you have?



#16 jimgerrr

jimgerrr

    Lift Off

  • -----
  • topic starter
  • Posts: 16
  • Joined: 03 Mar 2021

Posted 14 December 2021 - 12:27 PM

Could you take another picture of the open end of the tube, showing the secondary and vanes as well as the tube.

 

Is your only tool the laser? Which model do you have?

I only have a laser, it is the Hotech SCA-2. 

 

See below for more pictures, let me know if these are good enough, or do you want a picture from where the focuser point of view?

https://photos.app.g...SL9stRdoFEb6LB7



#17 SteveG

SteveG

    Voyager 1

  • *****
  • Posts: 10,779
  • Joined: 27 Sep 2006
  • Loc: Seattle, WA

Posted 14 December 2021 - 02:47 PM

I only have a laser, it is the Hotech SCA-2. 

 

See below for more pictures, let me know if these are good enough, or do you want a picture from where the focuser point of view?

https://photos.app.g...SL9stRdoFEb6LB7

That is a very different hub than any I've seen. In this picture, it looks like the three tilt screws are spring loaded, but I only see one setscrew pushing against the hub. The spring-loaded screws would behave more like a typical hub, which has 1 spring-loaded center screw (pull), and 3 tilt screws (push).

 

PXL_20211214_121941268.jpg




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics