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ASi 1600MM-C + New ZWO LRGB Filters

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#1 rockstarbill

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Posted 19 August 2016 - 04:18 PM

​Hello all,

 

Quick post on my experience last night testing these filters out on the ZWO EFW-Mini. With my Tak and its associated 130-R reducer I confirmed the level of focus I would need to exert between filter changes, and via testing with a Bahtinov Mask, I confirmed that the filters had the same focus throughout and focusing (at least for my needs) would not be required. I am sure that a electronically assisted focuser solution may find some slight amount of focus changes needed, but to my eye (20/20 vision) and my mask, they were spot on.

 

Now comes the slightly unfortunate part. When testing for vignetting, I did find that there is an ever-so-slight amount of it in the very corners of images. You can see what I mean here:

 

http://astrob.in/260550/0/

 

Sorry for not using the "Forum" format for the image, the Astrobin site seems to not be generating those tags properly on the machine I am using at the moment. The image is a 20 sec L sub, Bin 2x2, Unity Gain preset.

 

On the topic of this filter vignetting, anyone have some tips for how I may be able to eliminate this? My filter wheel has a 5th and open position, and I have confirmed that no vignetting is present when I image using that blank position, so its got to be something with the filters.

 

Here is how I have the camera connected:

 

SCOPE > REDUCER > TRING > Filter Wheel > 1mm T2-to-T2 adapter > ASI 1600

 

Any tips, tricks, or suggestions would be appreciated.


Edited by rockstarbill, 19 August 2016 - 04:21 PM.


#2 FiremanDan

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Posted 19 August 2016 - 04:34 PM

Does the camera not thread right into the FW? That's what I do for my starlight and I only get a small amount in one corner. I am concerned why it's only in one corner, but one train wreck at a time! 

Glad to hear they are (at least near) parafocal. I got the old set, I wonder how they compare. I haven't had a chance to try any LRGB data yet. What f ratio is your set up? 


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#3 mikefulb

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Posted 19 August 2016 - 04:35 PM

Can you put a FITS file up somewhere unstretched?  Hard to tell how severe the vignetting is in a stretched image.

 

But almost all the time a flat will solve this problem.

 

My 6 inch f/4 had severe vignetting and it flat fielded out fine (see attached).

 

Attached Thumbnails

  • Clipboard-4.jpg


#4 rockstarbill

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Posted 19 August 2016 - 05:01 PM

Does the camera not thread right into the FW? That's what I do for my starlight and I only get a small amount in one corner. I am concerned why it's only in one corner, but one train wreck at a time! 

Glad to hear they are (at least near) parafocal. I got the old set, I wonder how they compare. I haven't had a chance to try any LRGB data yet. What f ratio is your set up? 

 

No, it does not. There is a 1mm T2 to T2 adapter you use to connect the camera to the Filter Wheel. In terms being parfocal, I tried to find any difference in terms of the focus and spent a good 15 minutes switching filters and evaluating with a mask and I could not see anything different about the focus at all.

 

F Ratio with the reducer is F/5.77.

 

Can you put a FITS file up somewhere unstretched?  Hard to tell how severe the vignetting is in a stretched image.

 

But almost all the time a flat will solve this problem.

 

My 6 inch f/4 had severe vignetting and it flat fielded out fine (see attached).

 

Yeah sorry about that. The FITS are at home and I am in the office. I forgot to save the images on my OneDrive so I do not have access for a few more hours. I am not worried about flats solving the problem at all, as the vignetting is so minor. If it is possible to eliminate it all together that would be great.


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#5 rockstarbill

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Posted 19 August 2016 - 07:23 PM

Here is a FIT file:

 

https://1drv.ms/u/s!...XL60FkNfUAppv9Q



#6 tolgagumus

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Posted 19 August 2016 - 07:29 PM

It would be helpful if you posted an image of the camera and the filter wheel

#7 rockstarbill

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Posted 19 August 2016 - 07:33 PM

It would be helpful if you posted an image of the camera and the filter wheel

Sure thing, let me get them hooked up and I will post one.
 

Here is the image:

https://1drv.ms/i/s!...bah_9exiV1sd41g


Edited by rockstarbill, 19 August 2016 - 07:45 PM.


#8 NyxAither

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Posted 19 August 2016 - 08:00 PM

Edit: Good news! I looked at your image and you didn't do it right. You're going to be so happy once you do it correctly! Just unscrew that black extension and then screw the red camera body directly into the filter wheel. This gets the sensor only ~10 mm from the filters. If you still need to use spacers or something you'll want them before the filter wheel. Get those filters as close to the sensor as you possibly can!

 

 

Uhh...I have the EFW mini and the ASI1600 and mine are screwed directly together. Maybe yours is a newer version? The camera came with the 11mm M42 extender on the front, so I unscrewed that and this is what I have.

 

asi1600front.PNG

 

That red M42 extension then screwed directly into my EFW mini. 

 

Is that what you did?


Edited by NyxAither, 19 August 2016 - 08:10 PM.


#9 NyxAither

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Posted 19 August 2016 - 08:08 PM

Here's a picture of mine to show how it should look. Sorry I'm a bad hand model!

asi1600front2.PNG

 

There really needs to be a PSA or something about this. None of the angles on the website show the proper connection. The only reason I got it right was because Sam posted a picture of his setup on ZWO's facebook page and I zoomed way in on it to see what it should look like.



#10 rockstarbill

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Posted 19 August 2016 - 08:10 PM

Edit: Good news! I looked at your image and you didn't do it right. You're going to be so happy once you do it correctly! Just unscrew that black extension and then screw the red camera body directly into the filter wheel. This gets the sensor only ~10 mm from the filters. If you still need to use spacers or something you'll want them before the filter wheel. Get those filters as close to the sensor as you possibly can!

 

 

Uhh...I have the EFW mini and the ASI1600 and mine are screwed directly together. Maybe yours is a newer version? The camera came with the 11mm M42 extender on the front, so I unscrewed that and this is what I have.

 

attachicon.gifasi1600front.PNG

 

That red M42 extension then screwed directly into my EFW mini. 

 

Is that what you did?

 

Oh nice! I will give that a try tonight. Thanks for the info. I assumed that spacer was needed since it came with it already installed on the camera.


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#11 ChrisWhite

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Posted 19 August 2016 - 08:13 PM

Well, this settles one of the concerns I had with my first night out last night! I left the 11mm extension between the camera and the EFW and had the same nasty vignetting that the OP had.  I was thinking about eliminating it, but glad to see this is actually the right thing to do.  :grin:



#12 NyxAither

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Posted 19 August 2016 - 08:14 PM

I'm going to send Sam a DM letting him know they need a better angle on their website or people will be disappointed with vignetting.



#13 tolgagumus

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Posted 19 August 2016 - 08:18 PM

That's what I thought. The camera goes right on the FW without the black part. This throws the chip too far back behind the filter. 


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#14 rockstarbill

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Posted 19 August 2016 - 08:19 PM

Here's a picture of mine to show how it should look. Sorry I'm a bad hand model!

attachicon.gifasi1600front2.PNG

 

There really needs to be a PSA or something about this. None of the angles on the website show the proper connection. The only reason I got it right was because Sam posted a picture of his setup on ZWO's facebook page and I zoomed way in on it to see what it should look like.

 

Yeah, I will test this tonight, but I am sure that the outcome will be positive.

 

 

I'm going to send Sam a DM letting him know they need a better angle on their website or people will be disappointed with vignetting.

 

Yeah, they really should make this clear to folks, especially since that spacer is already installed on the camera when it arrives.



#15 NyxAither

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Posted 19 August 2016 - 08:24 PM

Here is what my flat frame looks like at f/3.94 (with a proper connection between EFW and camera). I clearly have some issues with my optical train to produce such a lopsided flat, but you can see that once I get that fixed the whole image will be above 85%, with a large portion of the center above 95%.
 
Capture.PNG

 



#16 rockstarbill

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Posted 19 August 2016 - 08:30 PM

Very cool. What is causing that lopsidedness?



#17 NyxAither

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Posted 19 August 2016 - 08:50 PM

What is causing that lopsidedness?

 

¯\_(ツ)_/¯

 

I think my secondary isn't positioned right, though laser collimation is spot on and it looks centered enough through a collimating eyepiece. You'd think it was flex in the focuser (or in the tube, due to the weight of the camera/focuser) but I've tried forcing the focuser around with no change. It isn't the filter wheel. Everything is perfectly lined up when I look down the train towards the sensor, and the filters switch perfectly.


Edited by NyxAither, 19 August 2016 - 08:55 PM.


#18 ChrisWhite

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Posted 19 August 2016 - 09:44 PM

 

What is causing that lopsidedness?

 

¯\_(ツ)_/¯

 

I think my secondary isn't positioned right, though laser collimation is spot on and it looks centered enough through a collimating eyepiece. You'd think it was flex in the focuser (or in the tube, due to the weight of the camera/focuser) but I've tried forcing the focuser around with no change. It isn't the filter wheel. Everything is perfectly lined up when I look down the train towards the sensor, and the filters switch perfectly.

 

 

Have you tried nudging the filter wheel a hair to the side to see if that centers it?  It might look perfectly centered, but perhaps it is off by a smidge? 



#19 NyxAither

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Posted 19 August 2016 - 09:54 PM

 That's a good thought, but it doesn't appear to have an impact until it's noticeably off-center.



#20 rockstarbill

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Posted 19 August 2016 - 10:00 PM

Have a shop look at the mirrors?

#21 NyxAither

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Posted 19 August 2016 - 10:05 PM

Interesting...I just rotated my imaging train (MPCC MkIII, Orion TOAG, 15 mm spacer, EFW Mini, ASI1600mm-c) by 90 degrees and it's significantly better. I can also make it significantly more lopsided through rotation. I believe that means something in the imaging train itself is a bit lopsided.

 

ImprovedFlat.JPG


Edited by NyxAither, 19 August 2016 - 10:14 PM.


#22 rockstarbill

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Posted 19 August 2016 - 10:13 PM

Well that's a good sign. I don't know much about Newts so I'm not much help. :)

#23 NyxAither

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Posted 19 August 2016 - 10:39 PM

The plot thickens...

This was a much shorter exposure taken with the brightness on my panel turned all the way up. Now the dark corners are at the opposite side of the frame.

 

-It's not light leak. I covered the imaging train with a black cloth to shield it from the light from the flat panel with no change.

-It's not uneven illumination from the flat panel. I tried rotating the flat panel, both when bright and dim with no change. (rotated dim panel stayed bright at bottom, rotated bright panel stayed bright at top of frame)

 

I think it's some weird reflection going on inside the tube?

 

I'm really puzzled now!

 

ImprovedFlat2.JPG


Edited by NyxAither, 19 August 2016 - 10:41 PM.


#24 NyxAither

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Posted 19 August 2016 - 10:46 PM

The good news in all this mystery is that I just figured out that with the brightness all the way up on my flat panel the duty cycle is high enough that I don't get any horizontal banding!

This is going to make my flats go much faster since now I can take 0.1s flats with brightness all the way up rather than 5s flats with brightness all the way down  :).



#25 rockstarbill

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Posted 20 August 2016 - 01:50 AM

Just to confirm, the change of connecting the camera directly solved the vignetting entirely.


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