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Old 10-12-2015, 12:25 AM
Carl
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Flair Issue. At the end of my tether.

Before i ring Canon and ask them what's going on could someone take a look and make a comment please.
Attached are 2 images of the Flame nebula. Both taken through my 120ed refractor, both 8min exposure, both 800iso. Images taken 15 minutes apart.
Image 500d.jpg is taken with my Full spectrum Canon 500d
Image 6D.jpg is taken with my unmodified Canon 6D.

What is causing the big flair on the images taken with my 6D? I had the same flair issue 2 months ago when shooting ngc253 and I've noticed some flaring when doing nightscapes.

Anyone shooting with a 6D and having the same issue.

Regards
A frustrated Carl
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Old 10-12-2015, 07:45 AM
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Merlin66 (Ken)
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Carl,
On the assumption these are both full frame images....
The plate scale shows the different chip sizes (500D = 22.3 x 14.9mm, 6D = 35.8 x 23.9mm) and it could be that the larger chip is picking up an internal reflection from inside the telescope.
What happens when you rotate the camera body - does the reflection move with the body??
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Old 10-12-2015, 08:02 AM
glend (Glen)
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Carl have you taped over the viewfinder port on the 6D? Given that there is a prism breakdown of the light it suggests that it is passing through glass somewhere on its way to the sensor surface at an angle. Even if it is hitting the sensor coverglass at an angle (Canon stock coverglass is known to reflect as it is not multicoated) this might cause it. The smaller sensor of the 500D probably still has a coverglass over the sensor but less area overall. Is the viewfinder port covered over on the 500D? I had a light leak on my 450D earlier this year, only apparent on long exposures like your eight minute ones, turned out to be a coming in through a gap in the collimation ring and reflecting in the tube to the sensor - a bit of black tape stopped it.
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Old 10-12-2015, 12:31 PM
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rustigsmed (Russell)
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in line with glen below, I got reflections / light leak if I had live view on. turning it off when capturing fixed the issue.
could be worth a try ... and i'd also be interested to see the nightscape shots.
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Old 10-12-2015, 01:21 PM
glend (Glen)
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Thanks Russell, I forgot to mention that I image with Liveview off. You can set it up and frame it etc with Liveview if you must but turn the screen off before you start the run.
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Old 10-12-2015, 04:19 PM
Carl
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Thanks for the replies. Answers to the above
1. light coming in from the rear viewfinder.
Both the 500d and 6D images were taken in a pitch black observatory. No chance what soever of light coming in from viewfinder, otherwise it would be on both images.
2. Rotation experiement.
Last month captured ngc253, Moonlite focuser was rotated to a different angle. There was still a flair but in a different location.

A mate has suggested that because the 6D is full frame i could be getting reflection of the scope or focuser barrel. My moonlite focuser is 2" and he suggested i may need 3"

Anyone care to comment and is anyone else out there shooting using a full frame DSLR on a 120ed refractor.

Carl
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Old 11-12-2015, 12:05 AM
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rustigsmed (Russell)
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Quote:
Originally Posted by Carl View Post
Thanks for the replies. Answers to the above
1. light coming in from the rear viewfinder.
Both the 500d and 6D images were taken in a pitch black observatory. No chance what soever of light coming in from viewfinder, otherwise it would be on both images.
2. Rotation experiement.
Last month captured ngc253, Moonlite focuser was rotated to a different angle. There was still a flair but in a different location.

A mate has suggested that because the 6D is full frame i could be getting reflection of the scope or focuser barrel. My moonlite focuser is 2" and he suggested i may need 3"

Anyone care to comment and is anyone else out there shooting using a full frame DSLR on a 120ed refractor.

Carl
1. Are you using liveview? Try it without. What about your nightscape shots that you mentioned ?

2. Try the rotation on the same subject .. that will confirm if the light source is a star outside of view.

I thought your obsy was pitch black why would full frame vs crop make a difference, and if its in your nightscape shots? The suggestions/ tests listed by people will help us help you identify the problem.

Last edited by rustigsmed; 11-12-2015 at 08:17 AM.
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Old 11-12-2015, 08:33 AM
ericwbenson (Eric)
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Hi Carl,
Looks like a glancing reflection off anodized Al (or perhaps other metal) somewhere in the camera body or OTA. I had a similar problem with my OTA a few years ago.

See this post from 2013, it shows the diffraction spectra caused by a bright star outside the FOV:
http://www.iceinspace.com.au/forum/s...2&postcount=31

Regards,
EB
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Old 11-12-2015, 11:38 AM
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Octane (Humayun)
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That part of the sky is notorious for internal reflections. There's a bunch of bright stars with Mintaka, Alnitak and Alnilam all contributing to the mess.

Do other areas of the sky cause the 6D to flare?

H
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Old 11-12-2015, 04:46 PM
Carl
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Hi all
Eric, checked your link and that's exactly my problem, very annoying. I dont get the same issue with the cropped sensor camera, only the full frame 6D.
I'll do a test and rotate the camera and see what it does. However how on earth do you stop it, it almost renders a full frame camera useless anywhere near bright stars.

Carl
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Old 12-12-2015, 03:09 PM
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Can't help with the flare besides what has been said, but you also have a protrusion into the light cone - note the dark diffraction "spikes". Usually a foil lens spacer, screw head, asymmetric dewshield, damaged baffle, flex in the drawtube or even a spider web.

I always covered the viewfinder on my Canon 5DMkII (usually with the slide over cover that is part of the Canon strap) regardless of how dark it was - a long exposure can pick up the most minute of light.
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Old 13-12-2015, 12:42 AM
ericwbenson (Eric)
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Quote:
Originally Posted by Carl View Post
Hi all
I'll do a test and rotate the camera and see what it does. However how on earth do you stop it, it almost renders a full frame camera useless anywhere near bright stars.
Hi Carl,
Flocking and baffling are the only way to combat this. It might be something in the OTA/focuser/adapters that is causing the diffraction and the larger sensor picks it up, or there is a shiny bit in the 6D body to reflect the diffracted light back onto the sensor. (Unless...do you use different adapters for the two cameras?)
This may take some detective work to sort out, but is totally feasible. I did it with an artificial star indoors (lightbulb with 1 mm aperture) and an observation screen near the focal plane (see attachment) or just plain-old looking thru the OTA for rainbows coming off at glancing angles. Remember some black anodized Al can be very reflective at shallow angles.

Best,
EB
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Old 17-12-2015, 03:58 PM
Carl
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Yep. It's the problem all-right. only appears when using the 6D.

looks like few few more wasted nights doing tests.

Thanks so far for all the input. Shall report back when tests are done.

Regards Carl
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