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MN 190 First Images - Really puzzled

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#1 JayS_CT

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Posted 06 December 2018 - 10:18 AM

First time out with MN 190..  Canon 5D Mk III (full frame), STC Optics clip filter, no dew cap or light shield.  Similar results with Pleiades image but over head and did not see central obstruction.  To my east, there is an apt. complex with terrible LED based super spots which could have been reflected onto the front corrector plate (again, no central obstruction on the over head image).  The "rectangles" appear after doing an Auto Background Extraction in Pixinsight.  Other than using APS-C format camera (I have 7D Mk II as well)..  I'm really at a loss to explain these reflections and why they appear with ABE in Pixinsight..  Appreciate any ideas..  Focus is good, visual observations excellent.  Suspect something to do with clip filter (which is a rectangle) but never created an issue with other scopes (like Quattro 250).

Jay S.

 
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Album: MN190
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#2 OleCuss

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Posted 06 December 2018 - 11:27 AM

To me it looks like in-camera reflections.  I'd seriously consider putting a dew/light shield on it first.  Ambient light is not your friend.


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#3 MitchAlsup

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Posted 06 December 2018 - 12:59 PM

I see a fairly well focused image hiding behind a bunch of unbaffled stray light.

Since the primary bands of the stray light are straight, this points at the camera.

Once you get the camera baffled properly, you will also find some stray light from the telescope that needs baffled or flocked.


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#4 JayS_CT

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Posted 06 December 2018 - 07:46 PM

I see a fairly well focused image hiding behind a bunch of unbaffled stray light.

Since the primary bands of the stray light are straight, this points at the camera.

Once you get the camera baffled properly, you will also find some stray light from the telescope that needs baffled or flocked.

Agree that the camera is involved, but not sure it's the "cause".  Since the corrector plate is right up front, I have to wonder if there's some cause and effect there (since there is external light sources nearby).  That said, the nearly "overhead" picture of M45 had a similar set of straight lines minus the central obstruction, hence the confusion.  The same camera and filter works fine on standard Newtonian, so I have to assume it's something with extra light coming in and the only difference is the corrector plate..  :-(



#5 OleCuss

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Posted 07 December 2018 - 05:26 AM

Do note that the problem shows up as a roughly rectangular pattern (for the most part).  The dimensions are roughly proportional to that of your sensor.  To me this strongly suggests you have a reflection/scatter problem.

 

Since your meniscus/corrector plate is not buried deep within the telescope tube it can fairly readily pick up ambient/stray light which can be conveyed down to your camera to greater or lesser degrees depending on exactly what light is where.

 

My Mak-Newt (ES Comet Hunter) comes with a dew/light shield to greatly reduce this problem.

 

It is possible you could reduce the problem with flocking, but a good dew/light shield for that OTA is likely to be your most effective solution and will not only reduce your stray light problem but reduce any dewing problem you may have.

 

Some of us believe we should be making/using light shields for even our standard Newtonians.  High Point Scientific sells the Astrozap light shields for Dobsonians/Newtonians:  https://www.highpoin...p/light-shields and it is possible that even something like that would significantly reduce your problem but I think I'd try to find or to craft a full light/dew shield.


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#6 Smug

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Posted 07 December 2018 - 09:25 AM

Yeah I absolutely need a shield with mine, any stray light across the corrector at all results in rainbows refracting all over the pic. I can definitely see that being compounded by the clip in filter. Even if you can't see the light yourself there are sometimes CCTV cameras around with IR and stuff.

 

The scopes are already baffled so I'm not sure how much improvement flocking would give but it certainly won't hurt anything.


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#7 JayS_CT

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Posted 07 December 2018 - 09:48 AM

Do note that the problem shows up as a roughly rectangular pattern (for the most part).  The dimensions are roughly proportional to that of your sensor.  To me this strongly suggests you have a reflection/scatter problem.

 

Since your meniscus/corrector plate is not buried deep within the telescope tube it can fairly readily pick up ambient/stray light which can be conveyed down to your camera to greater or lesser degrees depending on exactly what light is where.

 

My Mak-Newt (ES Comet Hunter) comes with a dew/light shield to greatly reduce this problem.

 

It is possible you could reduce the problem with flocking, but a good dew/light shield for that OTA is likely to be your most effective solution and will not only reduce your stray light problem but reduce any dewing problem you may have.

 

Some of us believe we should be making/using light shields for even our standard Newtonians.  High Point Scientific sells the Astrozap light shields for Dobsonians/Newtonians:  https://www.highpoin...p/light-shields and it is possible that even something like that would significantly reduce your problem but I think I'd try to find or to craft a full light/dew shield.

Thanks.. I have the dew shield from the 8" Celestron and will check out the Astro-Zap..  Wasn't sure about the flexible as I don't know how they do when they become "damp".. any loss of shape?  That said I can't find a rigid manufactured for the 190 and yes, can make one of my own, but not sure I wouldn't spend $39 in parts.  :-)  I'm assuming this one will also fit the Mak-Newt 190 as they advertise it for a Mak..  Have thought about one for my Quattro 250.. more for the secondary than primary.  For now I'll try the simplest solution first.  Baffling is very good in the SW MN190 and if I don't have to remove corrector I'd prefer not to, but can if needed.

https://www.highpoin...90-mm-mak-az146

Thanks..
Jay S.



#8 JayS_CT

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Posted 07 December 2018 - 09:50 AM

Yeah I absolutely need a shield with mine, any stray light across the corrector at all results in rainbows refracting all over the pic. I can definitely see that being compounded by the clip in filter. Even if you can't see the light yourself there are sometimes CCTV cameras around with IR and stuff.

 

The scopes are already baffled so I'm not sure how much improvement flocking would give but it certainly won't hurt anything.

 

You make your own, or pick up an Astro-Zap (or another brand)?

Thanks!
Jay S.



#9 OleCuss

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Posted 07 December 2018 - 11:14 AM

The AstroZap light shields for Dobsonians/Newts are pretty good.  They are designed specifically to reduce the amount of ambient light getting into the focuser.  No matter how damp things get they are not going to be significantly affected.

 

However, I'd really prefer the all-around dew shield because dewing can be a real problem with our Mak-Newts as is the case for the SCTs.

 

I'd be getting a good measure of the outside diameter of the OTA and then check to see if there is anything already made which will fit.  There likely won't be anything made specifically for your MN190.

 

But you could probably go to your local craft store and get some flexible foam sheets and glue/tape something together in a few minutes which might work for this weekend.  That should be relatively inexpensive.

 

I think some people use certain kinds of insulation from their hardware/lumber store and get by OK.  Some kinds are reflective on both sides so you'd have to paint whichever part you made into the inside.

 

Wishing you the best of luck!


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#10 JayS_CT

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Posted 07 December 2018 - 12:38 PM

The AstroZap light shields for Dobsonians/Newts are pretty good.  They are designed specifically to reduce the amount of ambient light getting into the focuser.  No matter how damp things get they are not going to be significantly affected.

 

However, I'd really prefer the all-around dew shield because dewing can be a real problem with our Mak-Newts as is the case for the SCTs.

 

I'd be getting a good measure of the outside diameter of the OTA and then check to see if there is anything already made which will fit.  There likely won't be anything made specifically for your MN190.

 

But you could probably go to your local craft store and get some flexible foam sheets and glue/tape something together in a few minutes which might work for this weekend.  That should be relatively inexpensive.

 

I think some people use certain kinds of insulation from their hardware/lumber store and get by OK.  Some kinds are reflective on both sides so you'd have to paint whichever part you made into the inside.

 

Wishing you the best of luck!

 

Thanks..  Weather window doesn't look too great this weekend so will see if I can "McGuyer" something together.  I have flat black spray paint.  Order the Astro Zap from High Point as they're the closest to me and Amazon didn't have the one for the 190 Mak..  Checked with Isaac at HighPoint who has a SW190MN and that's the one he's using..

Jay S.


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#11 Smug

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Posted 07 December 2018 - 12:54 PM

You make your own, or pick up an Astro-Zap (or another brand)?

Thanks!
Jay S.

I used a rolled up camping mat because that was what I had on hand, but I'd like one with a built in dew heater so I can kill two birds with one stone.


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#12 JayS_CT

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Posted 07 December 2018 - 12:59 PM

I used a rolled up camping mat because that was what I had on hand, but I'd like one with a built in dew heater so I can kill two birds with one stone.

OK, not sure what a camping mat is.  :-)   And just what I need.. another wire cause I don't have enough now!   LOL  ASIAir is looking attractive!!  Of course PrimaLuce Labs Eagles are attractive as well.. just a WHOLE lot more..  :-)

Jay S.


Edited by JayS_CT, 07 December 2018 - 01:00 PM.



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