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

Getting an ETX70 to focus with a .5 focal reducer

  • Please log in to reply
14 replies to this topic

#1 tomwall

tomwall

    Ranger 4

  • *****
  • topic starter
  • Posts: 361
  • Joined: 01 Nov 2009
  • Loc: Arizona, USA

Posted 06 December 2018 - 12:40 PM

I'm using an ASI224 camera on my ETX70. I want to use my .5 focal reducer to image at f2.5, rather than f5. It won't come to focus through the standard diagonal. So, I tried the rear photo port. I still couldn't get it to focus. Any advice? Thanks!

 

Tom,

Tucson



#2 sg6

sg6

    Skylab

  • *****
  • Posts: 4424
  • Joined: 14 Feb 2010
  • Loc: Norfolk, UK.

Posted 06 December 2018 - 12:59 PM

There is not a lot to play with on an ETX-70, and I simply guess that the lens cannot be drawn/wound back sufficently for the reduced image to fall far enough out so it coincides with the sensor.


  • tomwall likes this

#3 denny-o

denny-o

    Messenger

  • -----
  • Posts: 466
  • Joined: 10 Aug 2015
  • Loc: hemlock, mi

Posted 06 December 2018 - 02:36 PM

Yup. Gonna need a spacer to reach prime focus (forget about using the diagonal) I'm guessing something in the low 20's mm range of spacer depending on how far back the .5 reducer throws it's focus point..


  • tomwall likes this

#4 tomwall

tomwall

    Ranger 4

  • *****
  • topic starter
  • Posts: 361
  • Joined: 01 Nov 2009
  • Loc: Arizona, USA

Posted 06 December 2018 - 03:13 PM

Denny,

I'll give my Barlow without the lens element.

 

Thanks,

Tom



#5 mikenoname

mikenoname

    Ranger 4

  • *****
  • Posts: 303
  • Joined: 29 Jan 2015
  • Loc: Death Valley

Posted 10 December 2018 - 08:06 PM

I'm fairly certain you guys are going the wrong way. Insufficient back focus is the issue. The EP port is too long to allow the camera with FR to reach focus.

 

https://www.cloudyni...and-the-etx-70/


Edited by mikenoname, 10 December 2018 - 08:11 PM.

  • Jon Isaacs, tomwall and Messierthanwhat like this

#6 tomwall

tomwall

    Ranger 4

  • *****
  • topic starter
  • Posts: 361
  • Joined: 01 Nov 2009
  • Loc: Arizona, USA

Posted 14 December 2018 - 05:51 PM

Mike,

The clouds have set in, so I have some time to do some daytime experiments. I'll try the asi224 in the main eyepiece port first. I know that works. Next, I'll try using the reducer in the main eyepiece port. I'm pretty sure that won't work. It didn't when I was star gazing. After that, I'll use the rear photo port without the reducer. That did work before. Finally, I'll put in the reducer. I'll try it with and without the diagonal and empty barlow as a spacer. Basically... I'll try everything. Why not???

 

As long as I'm socket in with clouds, I'll do the same thing with my Meade etx90. This set of trials should answer the .5 reducer question for both the short focal length ETXs (60, 70, ?) and the longer focus length ETXs (90, 125,?).

 

Thanks guys for all your help with all this. I'll report back.

 

Tom,

Tucson



#7 tomwall

tomwall

    Ranger 4

  • *****
  • topic starter
  • Posts: 361
  • Joined: 01 Nov 2009
  • Loc: Arizona, USA

Posted 09 February 2019 - 12:11 PM

Just another followup:

Two nights ago I took the ETX70 out using the camera at f5 (no focal reducer used). I found that the GOTO accuracy was easily good enough to find my targets in the camera field of view. Either I got lucky or I've gotten better at my alignments. At any rate... this is good enough.

 

Tom



#8 mikenoname

mikenoname

    Ranger 4

  • *****
  • Posts: 303
  • Joined: 29 Jan 2015
  • Loc: Death Valley

Posted 09 February 2019 - 11:48 PM

Tom,

 

Glad to hear you are having a great time with your 70. I am having just the opposite luck.

 

After tearing mine down a couple of weeks ago to completely degrease and clean mine up and regrease with fresh lithium grease I have used mine on several observing sessions and it has performed flawlessly. But last night I was not able to even align it, even after struggling with it for an hour.

 

After putting it in the home position, when it slews to the first alignment star it is WAY off. I have no idea why. This came out of nowhere. I even got desperate enough to do a reset, calibrate motors and train drives, but that did not change anything. Still way off.

 

Going to try some daylight testing tomorrow and perhaps even tear it down again in an attempt to find out what's wrong, but right now I'm very bummed.



#9 HeathM98

HeathM98

    Vostok 1

  • -----
  • Posts: 112
  • Joined: 21 Nov 2018
  • Loc: St. Augustine, FL

Posted 10 February 2019 - 07:39 AM

Tom,

 

Glad to hear you are having a great time with your 70. I am having just the opposite luck.

 

After tearing mine down a couple of weeks ago to completely degrease and clean mine up and regrease with fresh lithium grease I have used mine on several observing sessions and it has performed flawlessly. But last night I was not able to even align it, even after struggling with it for an hour.

 

After putting it in the home position, when it slews to the first alignment star it is WAY off. I have no idea why. This came out of nowhere. I even got desperate enough to do a reset, calibrate motors and train drives, but that did not change anything. Still way off.

 

Going to try some daylight testing tomorrow and perhaps even tear it down again in an attempt to find out what's wrong, but right now I'm very bummed.

Usually when the slew to the alignment star is way off, its a problem with something entered in the Autostar, not a mechanical issue. I often read of quirks with the time zone being -8 instead of +8 or the likes. If you’re getting an intial slew that’s way off, check the current time, lat, and long, and make sure that the box correctly knows where it is and what time it is.


  • Jon Isaacs, tomwall and mikenoname like this

#10 tomwall

tomwall

    Ranger 4

  • *****
  • topic starter
  • Posts: 361
  • Joined: 01 Nov 2009
  • Loc: Arizona, USA

Posted 10 February 2019 - 11:03 AM

Mike,

I think Heath has something there. That's certainly the first thing to check.

 

Another thing that has given me that some problem is a slipping clutch. It's happened on different mounts. Is it slipping in alt or az or both. For alt, just tighten the side knob a bit. For az, you might need to remove the handle and reposition it. I can find a link for you, if needed.

 

BTW: Are you sure you didn't get grease on the clutch surfaces? If it worked before, it should work again... maybe. ;-)

 

I enjoyed you photo gallery and all your DIY projects. Here is a link to my FB photo of my DIY ETX mount. I'm really lazy! :-)

 

Good Luck.

Post back about your progress.

 

Tom

 

https://www.facebook...&type=3


  • mikenoname likes this

#11 mikenoname

mikenoname

    Ranger 4

  • *****
  • Posts: 303
  • Joined: 29 Jan 2015
  • Loc: Death Valley

Posted 10 February 2019 - 05:44 PM

Thanks to both of you for your input.

 

I have just run through some daylight testing using the access to the internal encoder positions in the handbox and confirmed that in both Alt and Az the encoders seem to be reporting exactly correct movement. A 360 degree rotation around the base and a 90 degree rise from ~20 degrees below the horizon to almost zenith (using the settings circles on the side of the fork) reports dead-on movement amounts. So it looks like the encoders are working perfectly and my fear that a glob of grease from my maintenance a couple of weeks ago might have caused an issue, is unfounded.

 

I guess the next thing to try is doublechecking all the settings, though I don't know how they would have gotten mangled by themselves the other night. Will keep you posted.

 

Tom - I LOVE the ETX mount. Does that thing come with a polar align scope?????  lol.gif

 

Thanks again guys!


  • HeathM98 likes this

#12 HeathM98

HeathM98

    Vostok 1

  • -----
  • Posts: 112
  • Joined: 21 Nov 2018
  • Loc: St. Augustine, FL

Posted 10 February 2019 - 05:52 PM

No worries. Yeah, usually if an encoder is blocked you’ll get a drive error and it won’t even move it. 

 

Sometimes the autostar gets wonky and will just change a setting. One dude was on here reporting that one day his worked fine and the next day it was pointing at the floor for an alignment star. He checked the time and it showed +6 instead of -6 for his time setting, even though his city was correct. 

 

Mine was slewing wierd the other day and started “rubber banding,” moving back after I’d slewed the opposite direction, a problem that was supposed to have been solved in previous firmware updates. Mines on the latest version. I just reset it and then calibrated and trained the drives again and now it’s fine. I’ve read about that stuff happening on here and on Weasner’s site. But it was the first time that’s happened to me ever. 

 

So maybe just do a reset, calibrate, and train and see what happens?

 

Heath



#13 mikenoname

mikenoname

    Ranger 4

  • *****
  • Posts: 303
  • Joined: 29 Jan 2015
  • Loc: Death Valley

Posted 10 February 2019 - 06:32 PM

Heath,

 

As my post from last night stated, I tried the reset, calibrate and train right on the spot and that didn't fix it. So then I thought the encoders might be off. But today's testing proves they seem fine. I also can't find any settings that are off, including site and time zone etc.

 

I'm stumped.



#14 HeathM98

HeathM98

    Vostok 1

  • -----
  • Posts: 112
  • Joined: 21 Nov 2018
  • Loc: St. Augustine, FL

Posted 11 February 2019 - 01:34 AM

That is wierd. Guess it just needed a timeout to think about what it had done! lol.gif



#15 mikenoname

mikenoname

    Ranger 4

  • *****
  • Posts: 303
  • Joined: 29 Jan 2015
  • Loc: Death Valley

Posted 15 February 2019 - 12:57 PM

Problem resolved. It was so obvious that I missed it every time. The scope thought it was still January. Have no idea how the month got changed because I used it successfully in February at least once. confused1.gif

 

Was so busy looking for a more complex problem that I blazed right by the date every time. I always check to make sure the day is right but don't bother looking at the month and year since I have already used the scope in that month.

 

Oh well. My 'Little Blue' is humming along great again.

 

Thanks again everyone for your help!


  • tomwall and HeathM98 like this


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