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GSO RC 8'' - Baffle tube reduction/shade

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#1 Epox75

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Posted 08 April 2021 - 07:25 AM

Hello, 

 

since I've collimated my RC and threaded the imaging train to the focuser ( I use an AP CDD 0.67x reducer). I've started noticing an increase in reflections of the brighters stars and a faint donut shape at the center of my flats. The impact on the final image is not big but still it doesn't allow me to stretch the image as I would like.

 

Here's a flat as example, as you can see there's this darker circle and then the flat gets bright again at the center.  

 

Flat.jpg

 

I've looked around and I think that my problem matches what is reported on this thread on Astrobin: https://www.astrobin...on-10-rc-truss/

 

Teleskop Service even started selling baffle tube reductions for 10'' RC and above : https://www.teleskop...Telescopes.html

 

My questions are: does anyone know a shop selling such reduction for the 8'' RC? If I am to build a DIY shade, how do I calculate how much reduction I should apply? 

 

Clear Skies, 

 

Andrea



#2 Hawkdl2

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Posted 08 April 2021 - 08:52 AM

I had the same problem with light leaks into the baffle of my RC 10".  I 3D printed a simple extension to the baffle that extends its length 1.5" and completely eliminates the light leaks.  I tested various lengths before settling on 1.5" as the minimum effective length.   My existing baffle happens to have a small  exterior shoulder about 1" from the end, so I made the extension to slide over the end of the existing baffle and rest at that shoulder.   I used gaffer's tape to line the portion that forms the 1.5" extension to eliminate any reflections off the PLA (the plastic used by the 3D printer) and to keep the I.D. the same as the original baffle. 

 

The TS device accomplishes the same thing, but both effectively slightly reduce the cone of light entering the baffle from the secondary mirror, but only very slightly. I cannot detect a difference in image field or corner vignetting with and without my extension. 

 

Both approaches would be easy to 3D print.  However, I suspect the PLA version is lighter than the aluminum TS device. 


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#3 Epox75

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Posted 08 April 2021 - 03:09 PM

I had the same problem with light leaks into the baffle of my RC 10".  I 3D printed a simple extension to the baffle that extends its length 1.5" and completely eliminates the light leaks.  I tested various lengths before settling on 1.5" as the minimum effective length.   My existing baffle happens to have a small  exterior shoulder about 1" from the end, so I made the extension to slide over the end of the existing baffle and rest at that shoulder.   I used gaffer's tape to line the portion that forms the 1.5" extension to eliminate any reflections off the PLA (the plastic used by the 3D printer) and to keep the I.D. the same as the original baffle. 

 

The TS device accomplishes the same thing, but both effectively slightly reduce the cone of light entering the baffle from the secondary mirror, but only very slightly. I cannot detect a difference in image field or corner vignetting with and without my extension. 

 

Both approaches would be easy to 3D print.  However, I suspect the PLA version is lighter than the aluminum TS device. 

Thanks for the tips Larry. An extension would be indeed much easier to apply. I assume that having the 8'' version with the closed tube needs different measurements. I am thinking to buy some thin dark foam to place inside the baffle tube and try at which lenght an extension would work better and who knows, maybe with just some tape I may find a temporary solution.



#4 Hawkdl2

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Posted 08 April 2021 - 06:40 PM

I imagine the extension length will be different.  In any case,  I tested length with rolled up black craft paper - worked just fine.  Then printed the final version.   I suspect any reasonably dark paper, like a paper bag, would work well enough to assess  whether this or the TS device will solve your problem.



#5 Kzoech

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Posted 09 April 2021 - 10:05 PM

I have had similar on my lights after stacking, I run the same set up as yourself, I run the reducer at 0.67ish to get a focal length of 1057mm. The only thing i changed really was getting the ASI071MC, on my process of Running Chicken (IC2944) I don't have that issue. 

I would be interested in any insights too.

 

Karl




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