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ZWO spacing for guide camera

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#1 telfish

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Posted 17 May 2019 - 11:26 PM

I just changed my QHY 5L ii for a ZWO ASI290MINI   guide camera. I have a ZWO thin OAG in front of my ZWO 071 camera with a 15 mm spacer between. The QHY just reached focus nearly at the bottom of the tube.

 

I find I cant each focus with the ASI290 no matter where I put it in the tube and suspect I may need more spacers between the camera and the filter wheel to enable focus higher in the tube, does that sound right?

 

Anyone have this working and if so what spacer are you using so I can order if necessary. 

 

Edit. Looks like I need a 20 mm spacer so I am 5 mm short of focus right now. Can anyone confirm this.


Edited by telfish, 17 May 2019 - 11:39 PM.


#2 stephanedore

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Posted 18 May 2019 - 12:53 PM

Did you play with the adjustment distance of the prism and guide camera holder?    There are small hexagonal head scews to loosen that portion of the Zwo OAG, plus the locking screws that you tighten/ untighten manually.  See the Zwo documentation about it: OAG Manual EN.pdf, page 6 is especially clear about focusing the guide camera.

 

Hope that helps.

 

Clear skies.



#3 telfish

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Posted 18 May 2019 - 01:57 PM

Did you play with the adjustment distance of the prism and guide camera holder?    There are small hexagonal head scews to loosen that portion of the Zwo OAG, plus the locking screws that you tighten/ untighten manually.  See the Zwo documentation about it: OAG Manual EN.pdf, page 6 is especially clear about focusing the guide camera.

 

Hope that helps.

 

Clear skies.

Yep all-adjusted now. I increased the spacing from camera to OAG by 5 mm and put the stalk at it's lowest position to get into the light cone went to all 48 mm fittings to reduce any vignetting. It looks fine now on distant objects I need to check it out under the stars now for intrusion and final focusing between the cameras.


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#4 ThatsMyCoffee

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Posted 20 May 2019 - 03:38 PM

I've just set mine up as well.  I was able to achieve focus (after HOURS of playing with every adapter I've got), but to my surprise...the OAG image is a different axis than the OTA.  I thought it would be in the middle of the main camera's area.

 

Does this mean that the prism isn't lowered enough?

 

This is on my refractor.  Perhaps the Newt would be different...


Edited by ThatsMyCoffee, 20 May 2019 - 03:39 PM.


#5 telfish

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Posted 20 May 2019 - 03:50 PM

The prism should be just in the light path but not encroaching over the camera sensor.You can look down toward the sensor and adjust the stalk to  be just off it's edge. It helps if you can orientate the camera so the prism is in line with the long edge of the sensor, then you can get the stalk lower. 


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#6 ThatsMyCoffee

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Posted 21 May 2019 - 02:48 AM

The prism should be just in the light path but not encroaching over the camera sensor.You can look down toward the sensor and adjust the stalk to  be just off it's edge. It helps if you can orientate the camera so the prism is in line with the long edge of the sensor, then you can get the stalk lower. 

I've aligned it with the sensor, like you say, and then lowered it until the prism is *just* clear of the ring (none of the prism is hidden.)  Considering what it 'sees' is outside of the sensor's field of view, I think I can safely say it's not blocking anything.

 

I just don't know if it's "normal" this way.  [Update:  Yes, it's normal.  Found a diagram here that shows what I mean:  http://solo.dc3.com/...lp/oag-fovi.htm ]

 

Focused both of them on a daylight target, but at night the OAG stars were blurry.  I was happy to see multiple stars that I could have guided with, but PHD2 kept losing the guide star.  Will have to try again, hopefully on a night when I have more time and can nail the focus.


Edited by ThatsMyCoffee, 21 May 2019 - 02:50 AM.


#7 telfish

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Posted 21 May 2019 - 06:11 AM

The focus zone is pretty small depending on your F ratio of the scope. So daylight focusing will get you in the ballpark. I use a one and a half inch ring on the barrel of the guide cam so I can lock it in position when perfect focus is reached, then it's repeatable if I need to dissemble the imaging train for any reason.

 

I am looking to change the existing barrel for a non rotating helical focuser to fine tune things as pulling and pushing on the guide cam it's a bit hard to tel if you have passed the focus point. That might be overkill as perfect focus is not required.But with my fast newt it's best to get as close as possible as edge stars even with a Coma corrector are not really great.



#8 ThatsMyCoffee

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Posted 22 May 2019 - 03:09 PM

The focus zone is pretty small depending on your F ratio of the scope. So daylight focusing will get you in the ballpark. I use a one and a half inch ring on the barrel of the guide cam so I can lock it in position when perfect focus is reached, then it's repeatable if I need to dissemble the imaging train for any reason.

 

I am looking to change the existing barrel for a non rotating helical focuser to fine tune things as pulling and pushing on the guide cam it's a bit hard to tel if you have passed the focus point. That might be overkill as perfect focus is not required.But with my fast newt it's best to get as close as possible as edge stars even with a Coma corrector are not really great.

I haven't found the focus yet, but my guidescope is already very low.  I did not use the 5mm spacer ZWO supplied, so I doubt I'd have room for that helical focuser.  Too bad, I'd like to try it!  This OAG's hex screw to lock it in place doesn't inspire confidence.  I bet it will slip, and frequently.



#9 ChrisWhite

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Posted 23 May 2019 - 06:59 AM

If you have a 1.25in camera and connect with a barrel clamp there is really no need for a helical focuser. If you adjust focus after you have calibrated PhD you will need to repeat calibration, but once you get focus you will not need to touch it again unless your system changes.

#10 ThatsMyCoffee

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Posted 23 May 2019 - 07:02 AM

If you have a 1.25in camera and connect with a barrel clamp there is really no need for a helical focuser. If you adjust focus after you have calibrated PhD you will need to repeat calibration, but once you get focus you will not need to touch it again unless your system changes.

Who said I "need" it?   ;)

 

Gear accumulation is an addiction, right?  I admit I have the problem.


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#11 ChrisWhite

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Posted 23 May 2019 - 01:34 PM

Who said I "need" it? ;)

Gear accumulation is an addiction, right? I admit I have the problem.


Touche.

If you need any spacers between the Oag and scope to achieve correct spacing for your imaging camera, you could swap the oag with that spacer to allow for more room on the guidecam base. That might give you enough room for a helical focuser.

Also, depending on the focuser, you could still probably insert the guidecam just as far as you could without it... Unless of course the focuser is too tall and the shoulder on the camera prevents you from being able to get it close enough. This actually is a problem for me with my 290mini and my kiss focuser for my qsi wsg. One design flaw of the 290 over a lodestar, but not enough for me to spend hundreds of dollars to be able to use my kiss.

#12 ThatsMyCoffee

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Posted 23 May 2019 - 02:43 PM

Touche.

If you need any spacers between the Oag and scope to achieve correct spacing for your imaging camera, you could swap the oag with that spacer to allow for more room on the guidecam base. That might give you enough room for a helical focuser.

Also, depending on the focuser, you could still probably insert the guidecam just as far as you could without it... Unless of course the focuser is too tall and the shoulder on the camera prevents you from being able to get it close enough. This actually is a problem for me with my 290mini and my kiss focuser for my qsi wsg. One design flaw of the 290 over a lodestar, but not enough for me to spend hundreds of dollars to be able to use my kiss.

I've got a 2" x 2" extension tube between the focuser and OAG.  If I remove it, it's going to be too much, I think.

 

Better off just nailing the guidecam focus and never touching it again.




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