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  #121  
Old 28-02-2018, 07:24 AM
Stefan Buda
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Thanks Peter, I appreciate your kind words. This little instrument combined with my OSC camera should be good for recording brighter comets, which we lack at the moment. I have to think of a suitable target for the Messier star party. I do not intend to image the usual bright targets where people with mono cameras and fancy filters would leave me for dead, regardless of how good the Honders is. I think we are over due for a half decent comet.
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  #122  
Old 05-03-2018, 05:21 PM
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Lognic04 (Logan)
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I saw this scope in person at yesterday's ASV meeting. A really awesome idea and even cooler scope!!! Cant wait to see what pics you get!

...I want one now
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  #123  
Old 08-03-2018, 08:59 PM
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Thanks Logan,
The way you are going, it won't be long before you can make your own.
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  #124  
Old 08-03-2018, 10:47 PM
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  #125  
Old 11-03-2018, 03:00 PM
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Just back from the Messier star party - the driest and warmest night that I remember at the LMDSS.

The bad news: The astrograph is almost unusable as it is, due to internal reflections.

The good news: It produces perfect stars, corner to corner, and the internal reflection is easy to rectify - so I'm completely happy with it.

I noticed that on 5min exposures, that I stretched severely, faint reflection arcs were visible, that appeared to be produced by off the field bright stars.
In the end I used Jupiter, as the brightest light in the sky, to characterise the problem. With Jupiter in the field I was getting only the expected halo circles, due to faint multipath reflections. When Jupiter was just off the field, I was getting no spurious reflections at all, but as I kept increasing the offset, at some point, perhaps 5 degrees off the field, a bright arc appeared across the chip.
It is quite clear now where I went wrong. When I designed the primary baffle, I concentrated only on cutting out stray light that can enter through the front lens and reflect off the inside of the baffle at a grazing angle.
It turns out that this optical arrangement is trying to produce a much larger image circle, that what can actually fit through the aperture of the small corrector lenses.
So, these partially focused stars that cannot fit through, end up hitting the inside of the baffle tube at an incidence angle that will allow them to reflect onto the chip.
The fix should be as simple as machining out the small ridges from the inside of the baffle tube and applying a strip of self adhesive synthetic velvet to absorb that unwanted photons.
I will post some test images in a few days, when I had time to do some processing.
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  #126  
Old 12-03-2018, 07:20 PM
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Here's a 32 minute exposure (32x1min) stacked and flat/dark corrected in DSS. The only other processing is a stretch in StarTools to reveal the background and all the faint stars.
The first image is a highly compressed postage stamp version of the full frame, and the rest are 100% crops of the corners and centre.
Looks like there is a bit of a sensor tilt in the camera, but I think it may not be worth worrying about.
Also this set does not seem to suffer noticeable reflections from off the field stars, but not only bright stars produce reflections and so the image must have some extra photons adding false background brightness.
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  #127  
Old 12-03-2018, 08:02 PM
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Good images,
Glad things are working out.
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  #128  
Old 13-03-2018, 02:10 PM
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Thanks Troy, the reflection issue will be very easy to fix and even without the fix, it is not too bad.

Here's a StarTools processed version of the same image, slightly cropped to improve the framing and reduced to 33% with high jpeg compression.
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Last edited by Stefan Buda; 13-03-2018 at 04:51 PM.
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  #129  
Old 13-03-2018, 02:43 PM
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Saw this in person again at the MSP! Beautiful pics!
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  #130  
Old 13-03-2018, 03:48 PM
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The telescope looks to perform magnificently!
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  #131  
Old 02-04-2018, 09:27 AM
Stefan Buda
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Thanks Logan and Colin for the feedback.

I used the blue moon a couple of days ago to illuminate the inside of the OTA while visually looking trough the focuser, trying to identify the nasty reflections I noticed during my recent dark sky testing.

It turns out that nothing is wrong with my baffle tube design. The reflections are coming from the two inch bore of the focuser. My camera nose piece is very short and that leaves part of the smooth bore of the focuser exposed to off axis illumination.
I won't even need to pull the OTA apart to fix the problem.

I'll be ready for that, long overdue, half decent comet.
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  #132  
Old 02-04-2018, 10:01 AM
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Quote:
Originally Posted by Stefan Buda View Post
Thanks Logan and Colin for the feedback.

I used the blue moon a couple of days ago to illuminate the inside of the OTA while visually looking trough the focuser, trying to identify the nasty reflections I noticed during my recent dark sky testing.

It turns out that nothing is wrong with my baffle tube design. The reflections are coming from the two inch bore of the focuser. My camera nose piece is very short and that leaves part of the smooth bore of the focuser exposed to off axis illumination.
I won't even need to pull the OTA apart to fix the problem.

I'll be ready for that, long overdue, half decent comet.
Good thing its a quick, easy fix!
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  #133  
Old 09-08-2018, 12:54 PM
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DaveGee (Dave Gault)
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Stefan, I just found this thread. (I should look at IIS more often)...

Bloody hell! What workmanship! What an instrument! What a first-light image! Inspirational. Wow, just Wow!!!
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  #134  
Old 19-08-2018, 10:47 AM
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Wow. this is a true work of passion and looks stunning. Can you estimate how much time this has taken for you to make. And I see two on your mount, did you make 2?
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  #135  
Old 15-09-2018, 10:25 AM
Stefan Buda
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Thanks Dave and Fahim,

Yes I made two. The smaller one was a practice run for the larger one.
Both have the same focal length but the smaller one is f/4.5 having 100mm aperture.

Last weekend, at the Galactic Centre SP, I wanted to test it for any remaining stray reflections, but the weather did not cooperate.
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