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AGO iDK Reducer: Solved!

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#1 Monkeybird747

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Posted 27 September 2021 - 10:00 AM

Happy to report that with the help of rockstarbill I've tested a reducer that works very well with my 12.5" AGO iDK and APS C QHY268M. Enter the Takahashi .73X ReducerCR! The reducer is designed to work with the corrected Mewlon 250 CRS and the FSQ106. Nothing fancy needed to make it work. I threaded it on the NiteCrawler and bam! The 2132mm f6.7 iDK now solves to 1563mm for .733X reduction, and a very pleasing f4.9 focal ratio. This yields a image scale of 1.0" (.99" actually). So now the reduced fov with APS-C is very close to native focal length with a full frame chip. Still a bit smaller, but a nice fov gain for sure. Effectively this added a new telescope to my lineup for $700.

 

Having previously tried the 27TVPH with disappointing results, I'm very satisfied with the field produced by this combo! Pixel-Peepers like myself can find some very slight error in the corners, but IMHO its nothing of concern, and I probably have a small amount of tilt I could work out if so inclined. I'm not sure how well it would hold up to a full frame chip, though. You might get a little extra, but I doubt complete full frame coverage would be in the cards. I imagine, being a reducer and not a flattener, that you can vary the spacing between reducer and chip to vary the amount of reduction. So perhaps by adjusting the spacing to achieve for example .8x reduction, you may improve field coverage for a larger chip.

 

As for me I'm happy as a clam with this combo and have started my first project with it. The out of the box results were great, and the reduction revealed I had a small collimation adjustment to make that I didn't notice before. The post-collimation adjustment 120s red frame I'm uploading is excellent imo. I'm linking a folder with raw data and stacks for your perusal. I do not intend to use bin1x1 with this camera/scope combo because the pixels are so small they resolve small reflections/halos that are (arguably) a result of central obstruction optics, good seeing, and tiny pixel low noise cameras. I think the winning recipe for me is to bin2 and then drizzle if more resolution is desired. I've included a few drizzle integrations to compare to the standard integrations. JFYI guiding was horrid with the fish data. I think the seeing took a dive. Guiding was good for the cygnus data.

 

Full datas here: https://1drv.ms/u/s!...PjUo4Q?e=bYu90d

 

The 120s star frame is red filter bin 2. The Cygnus wall is about 1.5 hours of red data bin 2. The Fish is 2.5 hours of Ha data bin 2. No processing other than calibration of the fish and cygnus data. 120s sub is raw. Look forward to hearing everyone's thoughts. This could prove to be an option for CDK owners that don't need full frame coverage.

 

 

Reducer Red 120s
 
integration
 
Integration Ha
 

 


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#2 Monkeybird747

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Posted 27 September 2021 - 10:07 AM

Abberation Inspector for the red frame above. Pretty darn good!

 

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  • Reducer_Red_120s1_mosaic.png

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#3 Monkeybird747

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Posted 27 September 2021 - 10:10 AM

I think it's a winner.

 

FWHMEccentricity.PNG

 


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#4 whwang

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Posted 27 September 2021 - 10:18 AM

That looks very good!  However, based on the image you showed in #2, I have a hard time believing that the median FWHM is less than 2 pixels.  The stars look many times larger than those hot pixels.  I can be wrong, but I think the number 1.982 is contaminated by the hot pixels, not just stars.

 

Anyway, looking your nice results, now I am hoping that there exists a good reducer for Planewave CDK for FF or at least APSC.

 

Cheers,

Wei-Hao


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#5 Monkeybird747

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Posted 27 September 2021 - 10:24 AM

That looks very good!  However, based on the image you showed in #2, I have a hard time believing that the median FWHM is less than 2 pixels.  The stars look many times larger than those hot pixels.  I can be wrong, but I think the number 1.982 is contaminated by the hot pixels, not just stars.

 

Anyway, looking your nice results, now I am hoping that there exists a good reducer for Planewave CDK for FF or at least APSC.

 

Cheers,

Wei-Hao

The measurement in post #3 is for a single red sub taken on a different night that the stack of red data in the cygnus wall image. There was a collimation adjustment between the cygnus image and the 120s sub. Here are the stats for the cygnus stack. My subs typically range from 1.8" to 2.4", so this seems to be in line with my norm. Not sure what the correlation is between size of hot pixels and star size?

 

This could be a possible fit for a CDK if APS-C coverage is desirable. The iDK and CDK seem more similar that the iDK and Mewlon CRS.

 

 

Capture2.PNG


Edited by Monkeybird747, 27 September 2021 - 10:27 AM.


#6 whwang

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Posted 27 September 2021 - 10:31 AM

Not sure what the correlation is between size of hot pixels and star size?

 

The size of a hot pixel is one pixel.  A FWHM of ~2 pixels means twice the size of a hot pixel.  But the stars look much larger than just two hot pixels.  It doesn't look right to me, according to my experience.  But again, I can be wrong.  One should not completely trust eyes.



#7 Rouzbeh

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Posted 27 September 2021 - 10:38 AM

Very nice work and results. 

At f/5 that is a very attractive f ratio and FOV for the 10 and 12.5 IDKs and APSc chips.

 

Specially now that the f/5 series IDKs are  no longer produced (not sure why).


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#8 Monkeybird747

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Posted 27 September 2021 - 10:38 AM

For comparison here is the FOV for full frame at native, and reducer with APS-C.

 

Capture3.PNG



#9 Rouzbeh

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Posted 27 September 2021 - 10:40 AM

The size of a hot pixel is one pixel.  A FWHM of ~2 pixels means twice the size of a hot pixel.  But the stars look much larger than just two hot pixels.  It doesn't look right to me, according to my experience.  But again, I can be wrong.  One should not completely trust eyes.

 

I got a copy of one of those subs and ran it through cosmetic correction to remove hot pixels. 

 

1.909 pixels

0.38 eccentricity

 

Although at bin2 its a bit different as you said, bin1 does reveal more flaws (if any).


Edited by Rouzbeh, 27 September 2021 - 10:41 AM.

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#10 Monkeybird747

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Posted 27 September 2021 - 10:40 AM

Very nice work and results. 

At f/5 that is a very attractive f ratio and FOV for the 10 and 12.5 IDKs and APSc chips.

 

Specially now that the f/5 series IDKs are  no longer produced (not sure why).

Thanks Rouzbeh. Seems a great option for those scopes.

 

The question now is who if brave enough to pay $$$ for the 645 reducer to test full frame coverage? Not me! grin.gif


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#11 Rouzbeh

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Posted 27 September 2021 - 10:42 AM

For comparison here is the FOV for full frame at native, and reducer with APS-C.

 

attachicon.gifCapture3.PNG

Interesting iwas after the same idea, to get the FF FOV out of the APS-C

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  • cdk f8 FF vs FR APS-C.png


#12 Monkeybird747

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Posted 27 September 2021 - 10:43 AM

I got a copy of one of those subs and ran it through cosmetic correction to remove hot pixels. 

 

1.909 pixels

0.38 eccentricity

Sounds about right. The Ha Fish data wasn't quite as nice. Really weird guiding results last night during that test.

 

I need to adjust the prism height, and possible move the OAG more towards the scope. The Ultrastar wouldn't come to focus, so I had to pop in the 290 mini. The stars in the guider are elongated, but with the exception of last night guiding has not been an issue.



#13 Monkeybird747

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Posted 27 September 2021 - 10:44 AM

Interesting iwas after the same idea, to get the FF FOV out of the APS-C

Yes, it almost seems as if that is what PW had on their minds with choosing the .66x number.



#14 Monkeybird747

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Posted 27 September 2021 - 10:49 AM

Rockstarbill has this same reducer on the way and I'm really looking forward to seeing if his results are similar.


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#15 Rouzbeh

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Posted 27 September 2021 - 10:59 AM

Sounds about right. The Ha Fish data wasn't quite as nice. Really weird guiding results last night during that test.

 

I need to adjust the prism height, and possible move the OAG more towards the scope. The Ultrastar wouldn't come to focus, so I had to pop in the 290 mini. The stars in the guider are elongated, but with the exception of last night guiding has not been an issue.

I cut the threaded nose on my Lodestar with a mini hacksaw, allowed it to go deeper into the OAG when needed. Not pretty but works great.


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#16 rockstarbill

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Posted 27 September 2021 - 10:59 AM

It should arrive tomorrow. I need one more adapter from Tak as well and some weather help though, so I'll probably know more in 6 months. 😭

#17 Monkeybird747

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Posted 27 September 2021 - 11:01 AM

I cut the threaded nose on my Lodestar with a mini hacksaw, allowed it to go deeper into the OAG when needed. Not pretty but works great.


🤣🤣 I was thinking of doing exactly that!

 

Here is the current reducer config.

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  • ACA298BB-554C-49B3-A5FE-9ED48D07E5B1.jpeg

Edited by Monkeybird747, 27 September 2021 - 11:06 AM.

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#18 Rouzbeh

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Posted 27 September 2021 - 11:01 AM

Yes, it almost seems as if that is what PW had on their minds with choosing the .66x number.

Bin2

 

The idk combo is at f/5    0.99" scale right"

The CDK8  x0.66 is 5.3    0.92" scale

CDK14 x 0.66 is f4.7          0.91 scale"

 

Interestingly the cdK!4 and 12 have the same focal length.



#19 rockstarbill

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Posted 27 September 2021 - 11:03 AM

A friend of mine designed a 3D printed front replacement for the lodestar x2 that reduces the backfocus without a hacksaw. Unfortunately it doesn't appear to be on thingieverse.

#20 Rouzbeh

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Posted 27 September 2021 - 11:05 AM

It should arrive tomorrow. I need one more adapter from Tak as well and some weather help though, so I'll probably know more in 6 months.

Given how close we are Im assuming the same weather there too. Night and day have aout the same brightness now!

 

I don't think folks with "normal" weather can really appreciate the need for faster systems. From now it I fear its a few good nights a month.


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#21 rockstarbill

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Posted 27 September 2021 - 11:12 AM

Love this reducer find. The APSC limitation is the reducer itself and not the scope. The scope has a native 60mm corrected field. But for folks that want to speed the iDK and CDK scopes up without breaking the bank it's an excellent option! The other Tak reducers may be worth exploring for those with some extra cash to burn, but I'm pretty happy with this option especially considering how nice the stars are across the field.

#22 Rouzbeh

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Posted 27 September 2021 - 11:24 AM

🤣🤣 I was thinking of doing exactly that!

 

Here is the current reducer config.

I replaced the qhy OAG with the Hercules OAG.

The prism is 12.5x12.5mm, m54  threads. The helical is better. Its thicker but you have the backfocus.

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  • CDK AP reducer CN.jpg


#23 Monkeybird747

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Posted 27 September 2021 - 11:31 AM

That looks nice. I have the Sagitta motorized OAG but didn’t have the adapters on hand to make it work with the reducer. It will require some custom adapters, and I didn’t want to spend for them not knowing if the reducer would work. For the reduced config I think this will work fine. I’ll explore the Sagitta adapters down the road, but for now it will only be for native FL.



#24 rockstarbill

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Posted 27 September 2021 - 11:31 AM

Given how close we are Im assuming the same weather there too. Night and day have aout the same brightness now!

I don't think folks with "normal" weather can really appreciate the need for faster systems. From now it I fear its a few good nights a month.


It will slowly get worse through October then Nov - March are very spotty. One year I had 0 imaging nights from October to March. It's not always that bad though.

#25 Rouzbeh

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Posted 27 September 2021 - 11:39 AM

It will slowly get worse through October then Nov - March are very spotty. One year I had 0 imaging nights from October to March. It's not always that bad though.

I wasted months last winter/spring in the freezing cold trying to get perfect collimation on my previous RC, one night I wanted to throw it down the stairs!

 

My critierra have now become:

 

1-Minimal fiddle time

2-As fast as possible f/ratio

 

I think these CDK/IDK scopes fit the bill perfectly. 

 

For me, the CDK slightly more given the fixed primary (collimate adjusting 2 screws only) and f/4.7 with the dedicated reducer. 




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