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Which OAG for ASI290MM (Non Mini) ?

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#1 TheSheriff

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Posted 24 July 2021 - 07:56 PM

So i'm putting together a new refractor imaging rig using a ZWO 2600mm and EFW.  I have always used a guide scope with a SSAG and more recently a ZWO 290mm planetary camera.  For this setup, I thought I would like to try an OAG, but the ZWO M68 OAG and OAG-L appear to only work with mini cameras.  I asked in this thread https://www.cloudyni...86-new-zwo-oag/

 

I'm not willing to replace this camera anytime soon and will just stick with my guide scope if there is no quality option.  Any ideas? 

 

It appears the original ZWO OAG would work, but....  I read some stuff from 2016-18 that was fairly positive.  Read more recent stuff saying they were poorly machined junk.  I would likely use this one if I knew I wouldn't be fighting it endlessly.  If they are lacking in quality, did they improve at all toward the end of production?

 

I would be open to any other reasonably priced brand, but once I move away from ZWO, it gets a bit confusing with compatibility and spacing.

 

And I do have a message in to ZWO if they know of any way to make my camera fit the new OAG, but I don't expect helpful answer.



#2 rgsalinger

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Posted 24 July 2021 - 09:46 PM

I've got the original ZWO with a 290 mini on it right now out at my observatory with a QHY268C sittting in front of it. I don't "fight" with anything. I am careful to make sure that everything is nice and tight. Before the advent of the current crop of cameras, if you were using a mono (say) SBIG rig you'd be putting several pounds in back of the OAG. Perhaps people had trouble with that amount of weight. Anyway, I've had this OAG since I got my ZWO1600 about 5 years ago and it worked well then and it works well now. 

Rgrds-Ross 


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#3 arbit

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Posted 24 July 2021 - 11:05 PM

I have the original OAG48 with a 385 on it. It works fine, once it is set up properly. The initial sync of focus with imaging camera took some time, but after that have never needed to touch it again.

It has 2 adjustments possible - stalk position to ensure prism doesn't cast a shadow, and distance from prism to camera, for fine focus adjustment.

If you are looking at the OAG-L yes the specs say it works only with the minis, which means the helical focuser is not detachable. Its an odd design choice, but can wait for ZWO to confirm.

Other option could be to use a 1.25 inch nose piece on the planetary to insert in the helical. That will move the sensor away from the prism and so you might need to shift the OAG much further towards the scope.

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#4 TheSheriff

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Posted 25 July 2021 - 12:19 AM

I have the original OAG48 with a 385 on it. It works fine, once it is set up properly. The initial sync of focus with imaging camera took some time, but after that have never needed to touch it again.

It has 2 adjustments possible - stalk position to ensure prism doesn't cast a shadow, and distance from prism to camera, for fine focus adjustment.

If you are looking at the OAG-L yes the specs say it works only with the minis, which means the helical focuser is not detachable. Its an odd design choice, but can wait for ZWO to confirm.

Other option could be to use a 1.25 inch nose piece on the planetary to insert in the helical. That will move the sensor away from the prism and so you might need to shift the OAG much further towards the scope.

Sent from my SM-N960F using Tapatalk

DId you mean the M68 OAG?   I'm not actually looking at the OAG-L since I don't think my sensor would benefit from the larger prism.   I was looking at the older M68 or the newer "L" model only because I had read quality concerns on the original.

 

Your idea of moving the OAG closer sounds interesting, but a bit above my current knowledge level.  I would prefer to get something I know will work from the start.  Sounds like Ross has had good luck with his original.



#5 arbit

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Posted 25 July 2021 - 12:27 AM

I meant the "normal" OAG, which has M48 threads scope side and M42 camera side. That takes both the mini as well as planetary cams like 385.

I think the OAG68 has been discontinued and replaced with the OAG-L.

Even though I suggested the nosepiece option, not sure its a good one in your case :-).

It will also involve further adjustments to the imaging train if you have say a flattener as the 55mm distance to the imaging camera will change.

If you are just starting out and don't want to change your guide camera, might be best to stick to the guidescope. Unless the OAG48 works with your scope and camera.

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#6 TheSheriff

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Posted 25 July 2021 - 12:47 AM

I meant the "normal" OAG, which has M48 threads scope side and M42 camera side. That takes both the mini as well as planetary cams like 385.

I think the OAG68 has been discontinued and replaced with the OAG-L.

Even though I suggested the nosepiece option, not sure its a good one in your case :-).

It will also involve further adjustments to the imaging train if you have say a flattener as the 55mm distance to the imaging camera will change.

If you are just starting out and don't want to change your guide camera, might be best to stick to the guidescope. Unless the OAG48 works with your scope and camera.

Sent from my SM-N960F using Tapatalk

Thanks for the clarification... I should have guessed you meant the original based on the camera you mentioned, my bad.

 

I'm not new, but it's a new scope and never used a mono camera or OAG.  I have 75mm of back focus from the flattener, and from everything I've read,  the original OAG should work.

 

Thanks for your help!



#7 Der_Pit

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Posted 30 July 2021 - 12:27 PM

A bit late maybe, still some comments:

There had been quality issues with the first versions of the ZWO OAG, that were actually design flaws.  They added more/better fixation screws, and with that the OAG (IMO) was rock solid.  I've used it with my Stowaway and the ASI1600 for 1.5-2 years.

 

I doubt however that the old one can be properly used with the large new EFW and the 2600, definitely not with a non-mini camera.  You can "fix" this by moving the OAG further away from the EFW using a spacer in between (at least if you have more than 55mm BF requirement).  But then the focal plane also gets (far) away from the hole in the prism stalk, and you will get (very) strong vignetting.  Also not desirable.

 

The M68 OAGs helical indeed cannot be removed, so no real way to attach the non-mini cameras, unless far away from the prism.  Again, this could be compensated by moving the OAG further away from the camera.  Maybe the vignetting would be less severe with the larger prism of the OAG-L....



#8 TheSheriff

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Posted 31 July 2021 - 05:12 PM

A bit late maybe, still some comments:

There had been quality issues with the first versions of the ZWO OAG, that were actually design flaws.  They added more/better fixation screws, and with that the OAG (IMO) was rock solid.  I've used it with my Stowaway and the ASI1600 for 1.5-2 years.

 

I doubt however that the old one can be properly used with the large new EFW and the 2600, definitely not with a non-mini camera.  You can "fix" this by moving the OAG further away from the EFW using a spacer in between (at least if you have more than 55mm BF requirement).  But then the focal plane also gets (far) away from the hole in the prism stalk, and you will get (very) strong vignetting.  Also not desirable.

 

The M68 OAGs helical indeed cannot be removed, so no real way to attach the non-mini cameras, unless far away from the prism.  Again, this could be compensated by moving the OAG further away from the camera.  Maybe the vignetting would be less severe with the larger prism of the OAG-L....

Your comment regarding the revised original version is exactly the information I was looking for in my initial post.  I had read a good many negative comments, but even though I suspected it, I didn't find any direct reference to a older and newer version.  I did not want to build my new image train around an OAG I was going to have problems with.

 

After posting and digging even deeper, I found the info on the revised version and ordered one.  As you can see, the full size 290MM fits just fine with the 2600MM and new 36mm EFW.  Of course the OAG position needs to be fine tuned to the EFW, or clearance disappears rapidly!   And for disclosure, I have not yet focused both camera's... plan to later today when it cools down.

 

Build quality seems very good.  Other than the small prism hole, which is odd, the 3 lock down screws could be longer so you could get a good finger hold on at least 2 that would then extend beyond the FW.   Also, on the scope side, the M48 threads go all the way through to the stem without a hard stop, so your adapter's threads may be longer than the space available. In this pic, the flattner bottoms out on the shoulder of the flattner.  On my 120mm scope, the threads on its flattner are longer, so it bottoms out by hitting the prism stem.  This resulted in using up an additional 1.5mm of backfocus (OAG edge to flattner shoulder) which I did not anticipate on paper.  So that is something to keep in mind.

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#9 Palmito

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Posted 18 August 2021 - 11:27 AM

So i'm putting together a new refractor imaging rig using a ZWO 2600mm and EFW.  I have always used a guide scope with a SSAG and more recently a ZWO 290mm planetary camera.  For this setup, I thought I would like to try an OAG, but the ZWO M68 OAG and OAG-L appear to only work with mini cameras.  I asked in this thread https://www.cloudyni...86-new-zwo-oag/

 

I'm not willing to replace this camera anytime soon and will just stick with my guide scope if there is no quality option.  Any ideas? 

 

It appears the original ZWO OAG would work, but....  I read some stuff from 2016-18 that was fairly positive.  Read more recent stuff saying they were poorly machined junk.  I would likely use this one if I knew I wouldn't be fighting it endlessly.  If they are lacking in quality, did they improve at all toward the end of production?

 

I would be open to any other reasonably priced brand, but once I move away from ZWO, it gets a bit confusing with compatibility and spacing.

 

And I do have a message in to ZWO if they know of any way to make my camera fit the new OAG, but I don't expect helpful answer.

 

I am currently looking into the possibility of removing the helical focuser on OAG-L and replacing it with a custom machined adapter, for a non mini ZWO camera.

 

Waiting for some information from ZWO, but looks like it is feasible with a female M34 (or M36) to male M42 adapter.



#10 Palmito

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Posted 19 August 2021 - 04:40 AM

I am currently looking into the possibility of removing the helical focuser on OAG-L and replacing it with a custom machined adapter, for a non mini ZWO camera.

 

Waiting for some information from ZWO, but looks like it is feasible with a female M34 (or M36) to male M42 adapter.

 

Well, it seems even easier than I anticipated as the thread for the focuser is M42 as per ZWO answer:

 

The focuser can be removed by loosing the four screws, the screw thread is M2.


#11 Palmito

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Posted 24 August 2021 - 05:43 AM

Well, it seems even easier than I anticipated as the thread for the focuser is M42 as per ZWO answer:

Please disregard my previous message as ZWO has provided false information. You can remove the focuser, but all together with the red plate, you're left with a "square connection" and four M2 screws.

 

Also ZWO said the prism tube did not protrude beyond the red plate, when placed at extreme position for full frame. It does protrude about 1 cm.

 

This makes me sick, I hope nobody else bought one thinking it was possible.

 

Edit: I have designed a replacement part, once machined and tested, I'll be happy to share the design if anyone is interested:

 

OAG-L_nfrp_top.jpg OAG-L_nfrp_bottom.jpg


Edited by Palmito, 24 August 2021 - 07:34 AM.


#12 rgsalinger

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Posted 24 August 2021 - 10:18 AM

I've been using the original version for years. I've used it on an AP155, a TV127is and right now on a WO71. Never had a problem with it but I do use the "mini" cameras. I think that it does need to be set up carefully - everything really tight and with the bigger camera that the OP has, maybe the grub screw just can't be tightened down enough.

Rgrds-Ross



#13 Palmito

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Posted 24 August 2021 - 12:28 PM

I've been using the original version for years. I've used it on an AP155, a TV127is and right now on a WO71. Never had a problem with it but I do use the "mini" cameras. I think that it does need to be set up carefully - everything really tight and with the bigger camera that the OP has, maybe the grub screw just can't be tightened down enough.

Rgrds-Ross

Well the issue is that it is made for mini camera.

 

A "non-mini" camera has to be screwed on the T2 thread at the end of the focuser, that will pull it away ~40mm, plus sensor being 9mm further away.

That makes it impossible to achieve backfocus as the OAG is screwed (4 screws) directly onto EFW, even adding an additional 5mm tilt plate between camera and EFW.

 

I don't get the link between grub screw and bigger sensor, what did you mean ?

 

With a full frame sensor it has exactly the space for fitting the prism inside a 44mm image circle without casting a shadow onto the sensor.

 

Here it is with a 3D printed "fullframe guide" threaded onto the M48 tilt plate:

20210824_191548.jpg



#14 rgsalinger

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Posted 24 August 2021 - 05:17 PM

I get it now. You're using a full frame sensor! I've been using APS-C sensors, so I have a bit more room to play with. Should have noticed that.

 

My point about the grub screw goes back a couple of years when it was loose one night when I was testing a flattener for my AP155. When I got it home I had to "really crank down" on the grub screw to get rid of some play. 

 

I'm not sure that I follow the problem with just screwing the camera onto the and then putting a spacer between the OAG and the camera which I often do. Maybe with a reducer at 55mm you just run out of back focus.

 

Rgrds-Ross



#15 Palmito

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Posted 25 August 2021 - 02:06 AM

Ah yes, I have had many grub screw related flexure too with my current OAG. The new ZWO OAG-L seems much better and more sturdy.

 

The issue is that contrary to the older model (the black one), the new OAG doesn't have a thread that would allow the use of a spacer.

Instead it is attached directly to the camera body (or filter wheel) using four screws. If you look at my previous picture you can see the four holes and no thread.

 

PS: On the telescope side of the OAG, you may have a M48, M54 or M68 thread, depending on which tilt plate is installed.



#16 rgsalinger

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Posted 25 August 2021 - 10:58 AM

That's the same way that my QHY OAG's work - bolt to the camera. What I did was buy a "family" of M54 spacers from Cyclops Optics when I first encountered the problem. Then I bought a bunch of longer M3 screws so that I could add the spacers to the rig to get the spacing I wanted. That would not work with a 55mm backfocus flattener but it does work nicely with the 86.5mm backfocus of the only flattener that I have these days.

 

On the telescope side I cheated and had a custom adapter made for each my two larger scopes. That also meant that I could save some backfocus. Anyway, thanks for the interesting thread. 

 

Rgrds-Ross


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#17 Palmito

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Posted 25 August 2021 - 12:34 PM

Thanks to you Ross for your very useful feedback and inputs!

I will keep in mind this longer screws options, if I still can't reach backfocus (still might be missing a few millimeters lol.gif )

 

Also thanks to OP for opening this thread with common interest.

 

I have opened a new thread about the custom adapter if anyone is interested: https://www.cloudyni...on-mini-cameras

 

Cheers and clear skies!



#18 TheSheriff

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Posted 26 August 2021 - 03:20 AM

Thanks to you Ross for your very useful feedback and inputs!

I will keep in mind this longer screws options, if I still can't reach backfocus (still might be missing a few millimeters lol.gif )

 

Also thanks to OP for opening this thread with common interest.

 

I have opened a new thread about the custom adapter if anyone is interested: https://www.cloudyni...on-mini-cameras

 

Cheers and clear skies!

Though my "original, second edition" ZWO OAG is working great with my scope(s) / 2600 / full size 290, I am following your new thread with interest.  Very impressive Sir.


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