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Assembling my new QHY268M, have two questions

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#1 DaveB

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Posted 07 March 2021 - 05:05 PM

For the first time ever, I read an user manual from start to finish twice, which took all of about 2 minutes... Thanks mostly to an online video, I was able to assemble the camera, but I do have two questions:

 

  1. For the few that have received their cameras and are using the OAG and filter wheel, did you bolt the OAG directly to the filter wheel or did you put a spacer in between? I've seen images of both ways. I'm guessing that it won't matter, but I just wanted to check what others have done.
     
  2. The DC cable on the included power supply is way too short to be useful without having to fasten the brick somewhere to the OTA or mount, which I want to avoid. I've found supplies with longer cords online that say they are 12V, but user reviews say that the actual voltage is in the range of 13.8V. I tested the included supply and it does indeed output just above 12V. Does anyone know if the camera can handle 13.8V? Most 12V electronics can handle that voltage fine, but I don't want to find out the hard way that the camera doesn't like it.

Thanks,

Dave

 



#2 OhmEye

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Posted 07 March 2021 - 05:10 PM

I used a spacer between OAG and FW. I used a 10mm spacer and after matching focus with my ASI290MM-mini I found I have 5mm more guidecam space in the OAG for my current prism stalk length so I may be able to use a 5mm spacer and still match focus distance with the 268m. If I bolt the OAG directly to the FW my guide camera bottoms out in the OAG before it achieves focus. I don't know if I can extend the prism 5mm further into the light cone without shadowing the 268m sensor, I may play with that later. I was more interested in just getting first light to the 268m to start with. smile.gif

 

I am running my 268m on my rig 12.6v supply, I haven't tried higher voltage.


Edited by OhmEye, 07 March 2021 - 05:14 PM.


#3 SilverLitz

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Posted 07 March 2021 - 05:14 PM

I have yet to receive my QHY268M, but have had the CFW3-US and OAG-M for a few weeks, and have been measuring everything.  It seems to be clear that you CANNOT attached the OAG directly to the CFW, as the distance to the 268M (directly attached to the CFW) is shorter than it is possible to get your guidecam sensor to the OAG prism.  I think you will have to put some of the spacers in between.  How much will be determined by how far the OAG prism is inserted into the OAG body.  

 

I have heard of someone getting OAG focus using 5mm in between.  My calcs are going to start with about 10mm in between, as I would like the bottom of the prism about 16mm below the inside top of the OAG circle, but I expect I will have to add another 1mm.

 

It would be much easier if QHY provided a M48 OAG Thread Adapter (like the M42 and M54; 3mm thick), this would cut 2mm off the min distance between the scope and OAG, and give you more latitude to add more spacers between the OAG and CFW.


Edited by SilverLitz, 07 March 2021 - 05:19 PM.


#4 DaveB

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Posted 07 March 2021 - 05:32 PM

OK, thanks. The little card that came with the gear suggests to attach the OAG directly to the FW [even the slimmer CFW3M(US)] but their online manual suggests to put a 10mm spacer in between, which I did. 

 

I'm still wondering about the PS. I do have a supply at home that will work except that I'll need to do some wiring assembly, which I was hoping to avoid but in reality isn't a huge deal. I don't want to do any surgery to the included supply.



#5 SilverLitz

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Posted 07 March 2021 - 05:39 PM

Re looking at my exact calcs, instead of memory:

 

At max prism insertion, the bottom of the prism is 20mm below the inside top of the OAG circle, and ~8mm above the light cone centerline.  The short dimension of the 268 is 16mm, so the top of the sensor would be 8mm above the centerline, but at the OAG this would project up higher.

 

With the included adapters/spacers, you should be able to get focus at:

1) 11mm of spacers between the OAG and CFW.

2) 5mm M48/M54 adapter between the scope and OAG

3) for an QHY5L-II-M guidecam w/o nosepiece (11mm sensor depth), extract the OAG prism ~5mm from max insertion, e.g. bottom of the prism ~15mm below the inside top of the OAG circle

4) the OAG helical focuser at its absolute lowest position

 

At this setup, the distance from the middle of the OAG prism and the image sensor and guidecam sensor is ~45.3mm and the distance from the input of the M48/M54 adapter to the sensors is ~55.3mm.

 

Ideally, I would like my calc to show ~1mm helical focuser extension, to give some margin of error for mismeasurement and product and temperature variance.  Things get easier if your guidecam BF distance is shorter.

 

I would prefer to have the prism inserted as much as possible without shadowing the image sensor.


Edited by SilverLitz, 07 March 2021 - 05:41 PM.


#6 bigeastro

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Posted 07 March 2021 - 09:00 PM

Hey guys,

An imager from Alaska has a Youtube Video out that pretty much explains everything.  It is pretty good.  You may want to look at that.   He has a thread on here also.



#7 DaveB

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Posted 07 March 2021 - 10:13 PM

Hey guys,

An imager from Alaska has a Youtube Video out that pretty much explains everything.  It is pretty good.  You may want to look at that.   He has a thread on here also.

I did watch that - it was the online video that I referred to in my original post. However, I didn't read your post about not removing the center screw/post on the filter wheel in time (or I read it once but forgot it)...  foreheadslap.gif  I did remove the outer screws initially, but it was on tight enough that I figured the instructions were wrong. It's back together now and appears no worse for wear, with that being my only mistake (thus far) in assembling it. Now I'm just waiting for an adapter to be able to hook in a power supply with a longer cable. Also waiting on O3 and S2 filters, but I can start imaging with my LRGBHa set in the interim.


Edited by DaveB, 07 March 2021 - 10:15 PM.


#8 2ghouls

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Posted 07 March 2021 - 11:36 PM

I use a 5mm spacer between the filter wheel and the OAG. I'm using an ASI290mm mini as the guide cam.

Sent from my VOG-L29 using Tapatalk
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#9 lucam

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Posted 08 March 2021 - 04:55 AM

I did watch that - it was the online video that I referred to in my original post. However, I didn't read your post about not removing the center screw/post on the filter wheel in time (or I read it once but forgot it)... foreheadslap.gif I did remove the outer screws initially, but it was on tight enough that I figured the instructions were wrong. It's back together now and appears no worse for wear, with that being my only mistake (thus far) in assembling it. Now I'm just waiting for an adapter to be able to hook in a power supply with a longer cable. Also waiting on O3 and S2 filters, but I can start imaging with my LRGBHa set in the interim.


You may want to consider putting a drop of blue thread locker on that brass center screw. If you don’t, in time it will tighten itself to the point that the motor cannot spin the filter wheel.

I also use a 5mm spacer between filter wheel and OAG and can achieve focus with a ZWO ASI290 mini.


Sent from my iPhone using Tapatalk
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#10 SilverLitz

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Posted 08 March 2021 - 04:12 PM

I use a 5mm spacer between the filter wheel and the OAG. I'm using an ASI290mm mini as the guide cam.

Sent from my VOG-L29 using Tapatalk

How far down did you place the bottom of the prism?  

 

What f/ratio of scope?

 

Was your 290 fully illuminated?



#11 2ghouls

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Posted 08 March 2021 - 04:16 PM

How far down did you place the bottom of the prism?  

 

What f/ratio of scope?

 

Was your 290 fully illuminated?

I didn't measure, but pretty far down. I found you could extend it quite a way without any hint of a shadow on the 268 sensor. 

f/5.4.

Yes.


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#12 SilverLitz

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Posted 08 March 2021 - 05:30 PM

What is the 290mini's sensor BF?  Is this without the CS piece?  From websites, it seems 8.5mm w/o the CS, assuming the CS can be removed.

 

My QHY5L-II-M is ~11mm w/ CS.  I need to see if the CS screws off.  If it can be removed, the sensor BF drops to 6mm, and things get much easier.

 

I wish QHY had not put a long "neck" on the OAG.  It looks like the "neck" is there so the OAG can be attached directly to the camera.  But if it was ever attached directly to the camera, no guidecam could ever achieve focus, as the top of the inside OAG circle to the bottom of the helical focuser is >22mm, the prism would have extend a min of 8mm w/ midpoint ~5mm, there are screw heads on the inside of the helical focuser that would push up the guidecam's edge ~1mm, and then the guidecam's sensor BF (absolute 6mm min, maybe more).  So the absolute min distance between the center of the OAG prism to the guidecam sensor (w/ very low BF) would be ~34mm, and the prism might not see much of the light cone.  Compare that to the distance between the OAG prism mid and the image sensor of: 12.5mm (268M) + 5mm (OAG mid point) or 17.5mm total.  The neck would need to be enough to clear the CFW, which would allow it to be a few mm shorter, giving more flexibility.



#13 2ghouls

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Posted 08 March 2021 - 05:48 PM

What is the 290mini's sensor BF?  Is this without the CS piece?  From websites, it seems 8.5mm w/o the CS, assuming the CS can be removed.

It is 8.5mm with the CS adapter, and I'm not sure if the CS adapter is removable. I've never tried.

 

I can't comment on your notes about the OAG design since I've only used this one and the ZWO OAG, and I prefer the QHY since it seems a lot sturdier. (I gave up on the ZWO OAG). I didn't have any real trouble getting it operational. Initially I didn't have the 5mm spacer in there because the QHY diagrams made it seem I wouldn't need it, but after initial testing and surmising in which direction the guide camera had to move to reach focus, it was easy to understand the change that needed to be made. I think I had it all working with about 30 minutes of tests. I work at a very forgiving 1.6"/px so I could easily use a guide scope instead. I moved to OAG with the 268M since I was tired of having about 60 degrees of rotation blocked by a filter wheel / guide scope conflict. Occasionally this limited my framing choices, so I'm happy to have switched.

 

Edit: should also say I use a telescope with an advertised 60mm image circle (Stellarvue SVQ86), and since the corrector is built-in, I don't have to worry so much about particular back-focus requirements as one would with an external field flattener. YMMV if you have a more complex setup than me.


Edited by 2ghouls, 08 March 2021 - 05:53 PM.

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#14 lucam

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Posted 09 March 2021 - 08:11 AM

How far down did you place the bottom of the prism?  

 

What f/ratio of scope?

 

Was your 290 fully illuminated?

Hi Mark,

 

I had the same experience as Nico. The ASI290 Mini is limited in insertion depth by the shoulder but my guess is that it still wins over the longer BF of the QHY guide camera. Before using the ASI290 I was using the same OAG and filter wheel with an SX Ultrastar (no shoulder but 12.5mm BF) and I needed longer spacers between the OAG and filter wheel.

 

I didn't measure how far down the prism is but it clears the APS-C sensor abundantly and there is no shadow of the prism on images. The 290 is a small sensor so yes, it is fully illuminated. The SX sensor is much bigger and you could see the outline of the prism but it was still very usable. This is with a f4 scope after a TV Paracorr (so effective f-ratio 4.6).

 

Luca


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#15 Wilsil

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Posted 02 April 2021 - 11:07 PM

I have the 10mm spacer between the CFW and the OAG. Initially I followed the included diagram,  but I couldn't focus my 120MM mini as it bottomed out as mentioned before.

Now it's all good 



#16 DaveB

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Posted 03 April 2021 - 10:25 PM

This is attempt #2 at adjusting the spacers. From the direction of the light path to the sensor, I went with this configuration:

 

5mm M48 -> 1mm M55 -> OAG -> 3mm M55 -> 3mm M55 -> 3mm M55 -> filter wheel (skinny version).

 

So in summary, there are 6mm of spacers before the OAG and 9mm of spacers between the OAG and the filter wheel. I can't go any less than 6mm in front of the OAG because I have 5mm+ worth of threads on my flattener (with M48 threads) that screws into the spacer. Any less on those spacers would result in the threads running into the prism stalk of the OAG.

 

Here is what it looks like:

 

OAG spacers.jpg

 

I measured the distance between the *bottom* of the prism and the top of the OAG circumference as shown below. I can achieve focus with a ZWO 174 mini, but I am just out of focus with my QHY5L-II guider if I leave the CS (small black screw-on attachment on the bottom) attached. I can achieve focus if I remove it. I plan on moving the prism up 1-2mm - that should provide enough distance to allow the guider to focus with the CS attached.

 

OAG depth.jpg

 


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