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OAG + FW + Camera

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#1 Gregory2012

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Posted 06 April 2019 - 01:48 PM

Hi,

 

I am trying to piece together a OAG, Filter Wheel and CCD camera. All items are ZWO.

 

All I need to know, is there a specific order in these items? From the scope end, OAG first, then FW and then the camera?

 

Thank you and have fun out there.

Gregory Gig Harbor, WA.



#2 Noobulosity

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Posted 06 April 2019 - 02:16 PM

My understanding of this -and I'm no expert, by any means- is that the filter/filter wheel goes between the camera sensor and OAG, not between the OAG and scope or flattener.

The reason for this is the filters often significantly dim the image, so you want the guide cam to see unfiltered (i.e. brighter) stars so you can better choose one for guiding. If you only have dimmer stars to choose from in your composition, the filtered guide scope may have trouble picking any stars up because they're too dim to see or track reliably.

#3 rms40

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Posted 06 April 2019 - 02:17 PM

Yep, OAG attaches to scope side of filter wheel. Flat side of prism faces down the scope. You can look down the top of the oag - where the guide camera goes - and you should see a clear image through it. It helps to get close to something well lit. Camera should thread onto other side of filter wheel. You need a few millimeters of space between the camera and filter wheel so that you can get both the imaging camera and and guide camera focused (parfocal).

 

It is a bit difficult to get really good focus with the the ZWO OAG without a focuser on it. I try and get the guide camera so it will just slide up and down a bit by tightening the set screw down until it just touches. Than move it up and down until it focuses. If you have a retaining ring on the guide camera, that helps so it won't slide all the way down and hit the prism.

 

Randall



#4 rms40

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Posted 06 April 2019 - 02:39 PM

Here are some pics. Notice the spacer/adapter between ASI1600mm camera and EFW. I could have used a longer spacer. The guide camera is low in the OAG. It does come to focus this way. I also have a 2" round adapter on the front of the OAG so I can slide it into my scope eyepiece adapter and tighten down the whole setup. I usually like to have this threaded on but not on this scope.

 

Attached Thumbnails

  • zwo efw 1.jpg
  • zwo 2.jpg


#5 rms40

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Posted 06 April 2019 - 02:40 PM

one more showing OAG prism direction.

 

 

Attached Thumbnails

  • zwo prism.jpg


#6 Robby9newbie

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Posted 06 April 2019 - 02:43 PM

ZWO has put up a good tutorial on how to use their OAG and what connectors are required 

https://astronomy-im...tions-55mm.html

Robin



#7 Gregory2012

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Posted 07 April 2019 - 12:50 PM

Thanks everyone.

 

Part of my problems are that nothing lines up. In my photos, the chip does not line up with the pick off mirror on the OAG. The filter wheel is off as well. Also, it has been my understanding, the filter wheel, according to ZWO, should be as close as possible to the camera. No gap is the best gap. In the first image you can see the camera chip is not straight up and down. I have struggled with this since it's arrival two days ago.

 

Again thanks everyone, and have fun out there,

Gregory Gig Harbor, WA.

 

 

 

 

Attached Thumbnails

  • 20190407_002856.jpg
  • 20190407_003515.jpg


#8 Noobulosity

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Posted 07 April 2019 - 02:06 PM

I'm guessing it needs a thin spacer to get things lined up?

#9 rms40

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Posted 07 April 2019 - 09:23 PM

To get the pick off mirror where I wanted it so it wouldn't cast a shadow on the sensor, I used some thin paper spacers. I used a couple so the prism would be positioned right when the imaging camera got tight. I don't know where I got those. Must have come with one of my cameras or filter wheels. If anyone knows where to get those, please post.

 

There shouldn't be any issue with the EFW being lined up. It has a sensor for each filter location and will go to where you tell it on power up with EFW software. You need to remember or note which filter is at which position (1,2,3 etc). Most EFW software lets you assign a name  - like R - to a position so then you just go to the LRGB and other filters with software.

 

Randall



#10 Gregory2012

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Posted 10 April 2019 - 01:09 PM

Hi,

 

Well, I added one piece that has enabled me to align things up finally. I had to use a 1/25in ep holder in the train to enable me to align the guide scope with the camera. So, unless that additional 1/25in ep holder is causing some kind of issues visually, then it appears this is going to be the route I take until further use suggests otherwise.

 

 

Attached Thumbnails

  • 20190409_225035.jpg


#11 rms40

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Posted 10 April 2019 - 02:30 PM

Greg, That spacer sounds like a good idea as long as it gets tight where you need it. I use 36mm filters so that spacer I used on the nose of the camera worked ok. With 31mm or 1.25", it probably would have vignetted. You did it right. I really should have put the spacer between the EFW and OAG like you did.

 

I just replaced my ZWO OAG with a QHY one I have. It has a focuser on it. I really don't like trying to focus the guider in the OAG with just pulling it up or down. I had some issues with guiding because the guider focus wasn't very good. I see that ZWO also has a new OAG with a helical focuser on it.

 

I still can't find any of those paper spacers. I found a post that some hot rod places have 42mm ones for their axles (may not be paper). Paper works well because it does compress a bit especially with a few put together. I may have to cut some out of paper. I just really am bad at arts and crafts!

 

Randall



#12 Gregory2012

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Posted 12 April 2019 - 01:15 PM

Well I just gave up on my second attempt at using a ZWO OAG. There is simply no aligning the OAG, EFW and CCD, all ZWO. I thought, maybe I gave up to soon with my first OAG. So I bought a second to give it my supreme efforts at aligning the OAG with the camera chip. I have spent some 6 days trying to get alignment with the OAG and camera chip and failed.

 

Apparently I don't have any supreme efforts.

 

I'm a guy that believes in spacers, adapters and mounting rails of all kinds. I have some 30 items serving that purpose only. Not one of them helped. I managed to come up with one exception by using a 2in - 1.25in adapter which allowed me to turn the OAG and achieve alignment. But that was a 1.25mm opening not a two inch. Also, it was mounted using a very thin adapter ring. So my confidence that would work faded quickly. Just did not seem substantial enough for the job.

 

I bought an 80mm guidescope and that has decreased the guide camera mounting stress considerably. For now, this is my preferred way of mounting the guide camera. Will sell this second OAG on CNs and wash my hands of the OAG craze. When mounted correctly, there isn't any flexure in guidescopes.

 

Have fun out there,

Gregory Gig Harbor, WA.



#13 StephenW

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Posted 12 April 2019 - 02:13 PM

So even when using the ZWO recommend connectors it still doesn't line up?

 

https://astronomy-im...AG-solution.jpg

 

That's definitely disappointing - I was considering ZWO as a second imaging train, but not if their own components don't work well together.



#14 Gregory2012

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Posted 12 April 2019 - 02:53 PM

Thanks,

 

I would suggest they are compatible, just confusing. The included rings and adapters do not line up the OAG with the chip.

 

Everything is screwed on. So when tightening the item it ends up to the left or right of the camera but not dead center. They provide these very thin paper and plastic spacers that are amazingly thin. My assumption is these are to be placed between the EFW and the Camera. These supposedly are for adjusting the tightness to allow the aligment when screwing things down. My thinking is they also act as a buffers between the EFW and camera so the body surfaces don't mar one another.

 

If you look at one image depicting the installation of the OAG, there is one part they do not explain. See https://astronomy-im...G Manual EN.pdf

 

You can see, right at the very end of the OTA, there is a silver knurled ring in the back of the OTA. The OAG attaches to that and is shown tight and aligned. I don't know what the adapter ring is, who makes it and how does the OAG align itself perfectly?

 

Thanks,

Gregory Gig Harbor, WA.



#15 OldManSky

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Posted 12 April 2019 - 03:29 PM

I don't have the OAG, but...

Don't the three knurled screws around the OAG body let you loosen them up to rotate the OAG around the optical axis?

Can't you loosen them and rotate the prism to the correct place?



#16 WadeH237

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Posted 13 April 2019 - 09:09 AM

Gregory,

 

You should take a look at the Baader T2 Quick Changer.  If you use one of these as part of spacing between the EFW and the OAG, then you can easily rotate the OAG into any position that you like.

 

I actually have two of them, one between the EFW and the OAG, and one between the OAG and the telescope.  This allows me to rotate the whole camera package with respect to the telescope, or to rotate the OAG with respect to the camera. I've attached a picture of the setup.

 

Here are a few other notes:

 

Because of the way that the EFW attaches to the camera, it is nearly impossible to get them to line up rotationally with each other.  You can use shims (I like these) to change the angle where the threads get tight, but it won't be accurate enough to satisfy any OCD tendencies.  The good news is that the rotational angle of the OAG to the camera does not matter in terms of function.

 

Finally, you if you look closely at my picture, you may notice that the quick changer between the EFW and OAG is not using the stock dovetail that comes with the changer.  I had Precise Parts make one with the minimum back focus because I move this camera package between scopes, and my refractor has a 55mm back space requirement.  It took some thinking, but I got my entire camera, EFW and OAG to fit inside of that 55mm.

 

I hope that this helps,

-Wade

 

 

Attached Thumbnails

  • IMG_0694.jpg


#17 Gregory2012

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Posted 13 April 2019 - 11:52 AM

Thanks Wade.

 

Are you saying the OAG does not have to be in line with the CCD chip to work?

 

Thanks?

Gregory Gig Harbor, WA.



#18 WadeH237

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Posted 13 April 2019 - 12:21 PM

Are you saying the OAG does not have to be in line with the CCD chip to work?

I'm not sure that I understand the question.

 

In order to work, the OAG's pick-off prism needs to be somewhere in the optical path where there is sufficient illumination and the stars are not too badly aberrated.  Also, the guide camera sensor needs to be parfocal with the main camera sensor.  This latter thing often results in some fiddling with the spacing between the filter wheel and the OAG.

 

Rotationally, the OAG doesn't care about the main imaging sensor at all.  It can be at any which angle, and as long as you calibrate your guide software in that orientation, it will work fine.  The main sensor might care about the OAG, though.  Specifically, if the pick-off prism gets in between the main sensor and the scope, then the pick-off prism's shadow will be evident in the main image.

 

Often times, people will orient the OAG so that the pick-off prism sticks into the light path at the long edge of the main sensor.  This lets you get the pick-off prism into the light path as far as possible without obstructing the main sensor.  If you have a telescope with an imaging circle that is much wider than the main camera sensor, then you can have the OAG's pick-off further off axis.  In that case, you can rotate the OAG independent of the main camera.  This can be advantageous for scopes with a slow focal ratio, where you might need to position the OAG so that a bright enough star lands on the guide sensor.

 

I hope that this makes sense,

-Wade



#19 Stelios

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Posted 13 April 2019 - 01:34 PM

You most definitely can get a ZWO OAG, ZWO camera + FW and ZWO guidecam to focus.

 

I think the analysis attempts are confusing things, so I'll just focus on what WORKS. 

 

The first thing is to raise the pickoff prism by its stalk to the very top (allowing full illumination but only *just*), and just lock it there. (With some very fast systems and large sensor cameras you may have to raise the prism a bit further to avoid obstructing the optical path, but that's unlikely.) From this point on, all adjustments will be on either the lock position of the guidecam holder (GH) on the prism stalk or the position of the guidecam (GC) in the GH. 

 

Then one has to realize the following about the geometry: Assume the following (correct) arrangement:

 

[Imaging camera] => [Filter Wheel] => [optional spacer 1] => OAG => [optional additional spacers]

 

The *smaller* the width of [optional spacer 1], the *lower* the guide cam will have to be. If it is flush (no spacer) you probably will not be able to lower the guide cam enough to bring it to focus. If the spacer is too large, then you may need to raise the GC and/or GH to where it's barely clinging. I have found 5-6mm to be an ideal value for [optional spacer 1].

 

This *works*. 



#20 rms40

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Posted 14 April 2019 - 08:33 AM

Wade, Thanks for pointing out the Baader rings. I thought they were much thicker when I looked at them before. Looks just about right. Those should help Greg. Now, if they will just make some 48mm and 54mm.

 

Greg, The prism needs to get light coming down the scope tube. You don't want it in front of the sensor. That is the problem I had. It cast a shadow on my images. The scope light cone is usually much wider than the sensor. You want it to catch the light off to the side of the sensor. Any position will work.

 

The other thing that can be a pain is getting the imaging camera at the same distance as the pick-off prism to the guider. Those lengths need to be about the same - Up to the guide camera and back to the imaging camera. You have to get this close so you can focus.

 

Randall



#21 pgandy

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Posted 14 April 2019 - 09:41 AM

I have a similar setup....all ZWO, OAG, filter wheel, 1600 pro, and 290 mini. Using the provided spacers from ZWO everything worked out distance wise however, alignment to keep the prism squarely above the long side of the imaging chip didnt fall into place.  A pack of Baader Delrin spacers solved it nicely. $17/pack. Go big and get two packs just in case you need more of a thinner size. Now everything lines up and is snug.

 

Paul

 

https://optcorp.com/...g-set-ba-t2ring


Edited by pgandy, 14 April 2019 - 09:43 AM.


#22 Gregory2012

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Posted 14 April 2019 - 01:00 PM

Thanks everyone.

 

I was just about to give up on the second OAG and go back to my trusted guider scope arrangement. But Paul's suggestion for the Baader Spacers seems like a good idea so I purchased a couple of sets. My one concern is if you stack a number of these things together, they don't introduce any flexure or rotational movement?

 

Thanks,

Gregory Gig Harbor, WA.



#23 WadeH237

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Posted 14 April 2019 - 05:16 PM

I use the Baader spacers when I want to change the rotation angle where two threaded components become tight. I also use them if I need to chance a spacing by 1mm or less.  If I need a bigger spacer, then a traditional spacer ring is probably better.

 

And if you haven't seen them, Baader also makes variable length T extensions.  I use them, along with the other stuff mentioned in this thread, and they work well:

 

https://www.baader-p...-part-25y).html

https://www.baader-p...-part-25v).html



#24 rms40

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Posted 30 April 2019 - 06:45 PM

I got the Baader spacers. Perfect for T2, 42mm connections. They seem to be a heavy duty plastic. I don't think these are anymore likely to cause tilt than any other adapter, connector or focuser for that matter. My philosophy is to use a large imaging chip and crop if necessary. Most scopes are more likely to have aberrations from the optics at the edges than sensor tilt issues.

 

Now, If they would only make some 48 and 54 mm wide 1mm spacers....

 

Randall




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