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RC6 - can see a shadow of the secondary mirror in my images, but focus is good

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Hi All,

new user here and proud new owner of an RC6 telescope :)

Im am trying for a couple of days to get the new scope working correctly and I think I’m close. My biggest issue is collimating, witch I managed to get close yesterday while looking at a defocused star.

My problem is that I can see a “shadow” of the secondary mirror in my images even though I have good focus.

Can someone help me Figur this out?

i also added o picture of my focus on a bright star and a picture where the spider veins of the secondary are visible.


Thanks for the support and clear skies!



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Not really enough information, but a few pointers...

We think it's local light pollution casting a shadow. Do you use a light shade/dew shield?

Our guess is that whilst flat frames will cure the dust and vignetting, they will not cure the secondary shadow.

But you won't be processing anywhere near as aggressively anyway, so not to worry.


Edited by alacant
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There is simply no way that spider be in focus with main optic elements.

It is probably due to something else in optical train.

Do you use any sort of focal reducer? Why do you have such severe vignetting?

When you adjusted collimation of your telescope, did you take care not to change primary / secondary distance?

How close is camera to back end of the telescope? That RC scope has something like 160mm of back focus distance. Changing mirror spacing will change this as well. Using focal reducer will change this distance and make it smaller.

When you position sensor closer to focuser - you can start "bypassing" installed baffles of the telescope and you can start having direct line of sight between the sky and the sensor - see this as example:


This is taken from collimation video made by TS ( https://www.youtube.com/watch?v=aLwTkyJZM1Y)

If you put camera very close - there will be gap in the baffle system even on optical axis (it will be even larger if you move eye to the side - away from optical axis).

However - this alone will not cause spider to be visible on sensor as it is not focused light (it is like taking sensor without lens and expecting to see something on it).

What can happen is that you have some sort of lens element - like focal reducer that strangely focuses light from spiders onto sensor.

- try flats first

- see if you have spacing between primary and secondary right (if you fiddled too much with collimation - focus should be around 160mm away from 2" end of focuser)

- if you have focal reducer - try changing distance between it and sensor to more sensible distance. Looking at vignetting - if you are using one - it is probably at high reduction factor


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  • 2 weeks later...

Hi All,

Sorry for the late response but did not have any clear skies to play around with the scope.

In the end i decided that the RC6 was not the scope for my location (Bortle 9 middle of the city with limited time on 2-3hours per night) so i sent it back.

now i am trying to figure out what a good scope would be for my location.


Thanks for all the responses.


Clear Skies!

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