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Baader Flip Mirror with two ZWO cameras

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#1 Cey42

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Posted 16 June 2021 - 03:20 PM

I have a ZWO 294MM that I use for galaxies and a ZWO 294MC for nebulae. I have been picking which camera I want to use for the night and sticking with that. I do not like to switch while viewing because that requires capturing new flats. I have a light panel, so doing flats is not that bad but it still takes about 10 minutes to switch cameras, capture flats and focus. Because of this, I only do it once at most.

 

I recently saw the Baader FlipMirror II Star Diagonal and thought about attaching both cameras on that. I attach the camera that I plan to use the most for the night on the straight path. Then the other camera on top. I know that adding more glass to the light path is non-optimal, but this is for EAA so I am not looking for the perfect image. I still can get a backfocus of 105mm.

 

I can capture flats before the night starts and then switch between them. This assumes that the flip mirror position is the same each time for the flats. Now if I wanted to switch cameras, all I need to do is flip the mirror and then focus using my focus motor. I think, this should only take about a minute and would be easy to do. Doing this a couple times a night would not be a big deal. Especially once I have the focus motor position for each camera.

 

Thoughts on this idea?



#2 bips3453

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Posted 16 June 2021 - 03:46 PM

Very interesting idea. A few things that popped up in my mind:

- If using reducer, the back focus distance would need to be carefully setup. That would mean that both cameras should come to focus at the same point on the focuser.

- It will be good to verify that the flip mirror doesn't introduce any internal reflections.

- I hope the focuser doesn't mind the extra weight, seems unlikely. 



#3 Cey42

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Posted 16 June 2021 - 08:38 PM

I am using a 6.3 reducer but I am not worried about the focus because I have a focus motor. Once I have the focus position for each camera, I can quickly switch back and forth.

 

I would not expect any internal reflections on the straight path. As to the angle path, that is one thing I am worried about but it is one of those you won't know until you try it.

 

Why would the extra weight be a problem for the focuser?

 

Thanks,



#4 Noah4x4

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Posted 16 June 2021 - 11:48 PM

How are you saving time? You must still do seperate flats for each camera? You just do them at different times. I rear mount my ASI294 behind a x6.3 reducer and leave it in place when I bolt on Hyperstar/Atik Horizon to the front. Chang8ng from f/6.3 (actually nearer f/5.2 through my diagonal) and f/2 produces a more meaningful switch. I think you will over complicate things with a flip mirror.

#5 bips3453

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Posted 17 June 2021 - 11:09 AM

I am using a 6.3 reducer but I am not worried about the focus because I have a focus motor. Once I have the focus position for each camera, I can quickly switch back and forth.

 

I would not expect any internal reflections on the straight path. As to the angle path, that is one thing I am worried about but it is one of those you won't know until you try it.

 

Why would the extra weight be a problem for the focuser?

 

Thanks,

It's 0.8 lb of additional weight for the flip mirror and camera. But I see now that you might be using an SCT, not a refractor. It should be fine with the weight. 



#6 garyhawkins

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Posted 17 June 2021 - 12:06 PM

That will add approximately 100mm to your optical chain.  Can you accommodate that?



#7 Cey42

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Posted 17 June 2021 - 08:27 PM

Noah4x4, I must not have been clear on the flats. I meant that it saves me imaging time. Right now when I switch cameras in the middle of the night, I need to capture a flat then. Last night I timed how long it took me to switch cameras and capture a new flat. It took 13 minutes. Since I normally spend about 5 minutes per DSO, that is two DSOs that I missed out on.

 

Now in theory with the flip mirror, I attach both cameras and then before I start viewing for the night I capture the flats for both. Then when I switch cameras, I don't need to capture a new flat. I find for me that there is a significant difference between the mono and color cameras that having easy access to both would be great.

 

 

 

garyhawkins, I should be fine for backfocus. F6.3 reducer <==> T-adapter (21mm) <==> Flip Mirror (59mm) <==> Camera (18mm). This gives a total of 98mm. Giving me 7mm of buffer. How are you getting 100mm?



#8 Cey42

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Posted 27 June 2021 - 03:36 PM

I decided to sell some equipment to fund the purchase of the flip mirror. I was so happy that it arrived on the weekend and on a night that would be clear. That rarely happens with a new purchase.

 

 

Installation was easy. It came with the right adapter rings such that I did not need to buy any new ones. I really liked that the telescope side and the rear mount allows for rotational adjustment. Unfortunately, the top mount does not allow for rotational adjustment. But fortunately, the camera almost nearly aligned to have the same orientation as the rear camera.

 

 

My installation was short T-adapter (19mm) <==> 8 mm spacer <==> flip mirror (60mm) <==> camera (18mm) which gives 105mm backfocus. I was able to confirm with astronomy.net that I was getting .63 reduction as expected.

PXL_20210627_201124535.jpg

 

 

One downside of the flip mirror is that it leaks light. So doing flats or darks during the daytime means wrapping it all up. Which I did and the flats came out fine.

 

 

I spent the first part of the night viewing low Messier globular clusters that I had not seen before. Then when I decided to go view planetary nebulae, it only took me 3 minutes to make the full switch. Less than 1 minute to walk outside and flip the mirror. After doing my polar alignment, I had found each camera focus point on the focus motor using the Bahtinov mask on a high altitude star. But going to the low objects had a different focus point. I used SharpCap's FWHM focus feature which took about 2 minutes. As I get better at using the FWHM focusing tool, I would expect to get faster.

 

 

The top camera was my 294MM and images of M107, M80, M4, M9, M14 and M19 all came out pretty good considering that the were low altitude and seeing was poor.

 

 

The next time out, I will image the same object (high altitude), probably M13, with one camera and then flip to the other to compare the images. I want to make sure the top camera does not have any serious image degradation issues because of the mirror. But given last nights performance I don't think this will be the case.

 

 

Pros:
• Can reach backfocus
• Quick and easy to switch cameras. A flip of a switch
• Can attach the two cameras easily
• Can rotationally adjust the telescope side and rear side

 

Cons:
• Cannot rotationally adjust top side
• Light leaks in so need to cover up if doing flats or darks during daytime
• Cannot attach my filter drawer because of backfocus issues

 

 

Overall, I think I will like this setup. I need a couple more observation sessions with it to make my final decision if I will keep it.


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#9 alphatripleplus

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Posted 27 June 2021 - 04:42 PM

Nice mini-review. I'm curious whether the light leaks are bad enough to affect nighttime captures? Do you notice any difference in images at night if you cover the leak areas vs going uncovered?



#10 Cey42

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Posted 28 June 2021 - 06:02 PM

I did not notice any light leaks for my nighttime captures.

 

 

Because I like to capture my flats and darks during the day, I have made a light shield using 2mm foam roll. Using this completely fixed the light leaks. My darks looked perfect with no light leaks. This solution should work fine for me since I don't change my image train often.

 

PXL_20210628_011318021.jpg

PXL_20210628_013341050.jpg


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#11 Cey42

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Posted 24 July 2021 - 07:38 PM

Now that I have a couple sessions in, I can say that this has overall been working well. The other night when I wanted to switch cameras: I walked out to the scope, flipped the mirror, set the focus motor to the previously calculated position (I found the focus position for both cameras after doing polar alignment) and I was good to go. Took 90 seconds.

 

 

Two issues that I must deal with.
1 – The top camera image is flipped, which makes it a little hard mentally when comparing the image to what I see in SkySafari or Stellarium. I will need to create a new set of darks using the flipped setting in SharpCap to get around this issue. Question: Can I simply flip the darks I have already captured using an image program?

 

2 – Given the size of the sensor, it is important that the top camera be aligned. This is a pain because there is no way on the flip mirror to adjust the camera rotation. I had to add shims to get the camera properly aligned. This probably would not be an issue with a smaller sensor.

 

 

The image below is of a flat that I have stretched to make obvious the strange vignetting with the camera not properly aligned.

Flip_Rot.jpg

 

 

This next image is with the camera aligned and the flat stretched again.

Flip_Align.jpg

 

 


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