Is it possible my draw tube is causing this light streak

[Nicola Hannah Butterfield]

As the title says, I did a sequence on M33 the other day L.P. apart I am struggling with the very bright band of light and the darker one to the right of it, the 38 x 120's lights (flats bias and darks about 20 of each) after a little bit of PP work this is what I get.

So could the focus tube extended in to the light path be able cause this.

[michael8554]

What Camera ? Scope ? 

Is it on your Flats ?

Is it on individual Lights ?

Michael

[Nicola Hannah Butterfield]

7 hours ago, michael8554 said:

What Camera ? Scope ? 

Is it on your Flats ?

Is it on individual Lights ?

Michael

Canon 6D Skywatcher 200P, it isn't on the flats. i did think at first it was clouds, but only used the best of the image with as little cloud in the 30 odd lights

Master flat

Single 120's light

AZ/Alt approx 203° 65° left of frame is towards the horizon.

[david_taurus83]

Whats your LP like? I struggled with a newt when I started. I noticed one night that a strange gradient started appearing on my subs. Turned out to be the bathroom light was switched on by one of the kids and even though the scope wasn't pointed directly (more like 45°) in that direction, the extra light still managed to find its way into the tube. I get the same effect now if one of the streetlamps manages to illuminate the inside of the dew shield on my refractor.

A dew sheild may help to keep stray light out on the 200P.

[Nicola Hannah Butterfield]

@david_taurus83I have a home made light shield, as O have a neighbours bathroom light on most of the night, it shines right down on the scope, about the only place in the garden it does, at the time of imaging it would have been greater than 90°there are insecurity lights on two opposing housing, but the scope is hidden from most of those sources by the boundary fence, It is rather a steep hill I live on.

I am just working on a sequence of M51 and no such issuses with this one, taken later the same evening. so it is likely to be a light source of one form or another, I will invest on a better dew shield if the problem persists.

I do actually find shooting NE/east I get better results, as from the SE to SW there is Doncaster about 8 miles away and Barnsley somewhat closer, then Wakefield at about 12 miles to the west. Looking East there is very little between here and the North Sea, Hull/Grimsby about 40 miles away.

[michael8554]

So only on the Lights, so external to the scope and camera setup.

Full Moon ?

Michael

[Nicola Hannah Butterfield]

6 minutes ago, michael8554 said:

So only on the Lights, so external to the scope and camera setup.

Full Moon ?

Michael

Possible the moon was 59° 2.5' away. I will try again next week with no moon, proving there are clear nights. When I did M51 later in the evening, the moon was 84° 32'.

[The Admiral]

Out of interest, what do the darks look like? Depends on how you take them of course, but if you leave the camera on the 'scope and just cover the end of the 'scope, that might reveal a possible light leak.

And just another thought, does the light streak stay the same for all the subs? If it was light leakage then I would have thought it would vary a bit as the 'scope tracks across the sky.

Ian

Edited January 28, 2021 by The Admiral

[tooth_dr]

Light coming into the bottom of the scope would be my suggestion. Do you have a laptop or light shining at the mirror end?

[Nicola Hannah Butterfield]

@The Admiral, @tooth_dr Thanks for your input but as you can see from M51 shot the same night different direction and further from the moon, the moon at this moment seems the likely candidate.

This is a cropped and to me at the moment a finished image of M51 well at least today. I know I need to work on different aspects but, very little time with clear skies since last Sept, and only about 4-5 nights since I got the guide scope in late Sept early Oct.

[CraigT82]

The moon light must be reflecting off of something to give that weird light band though? Else it would just be a general brightening of the image wouldn't it? What are the edges of your secondary like? Also is the focuser drawtube shiny? 

[Nicola Hannah Butterfield]

5 minutes ago, CraigT82 said:

The moon light must be reflecting off of something to give that weird light band though? Else it would just be a general brightening of the image wouldn't it? What are the edges of your secondary like? Also is the focuser drawtube shiny? 

Secondary edges and draw tube  painted mat black as is the base of the primary, plus I was using a homemade light shield from cardboard, ok it's internals are not painted, but just the matt brown cardboard is, so not likely to produce such a bright streak. It might be another light source from the direction the scope was pointing.

Edited January 28, 2021 by Nicola Hannah Butterfield

[Nicola Hannah Butterfield]

I have just had a thought, it could have been the interior shed light, as it was pointing in that general diection, and I was imaging in the shed at the time. M51 was almost 180° in the other direction, and I was imaging from my bedroom via remote excess and the shed light was off.

[discardedastro]

The 200P will absolutely create this sort of artefact if you apply light behind it. I can't find the post on SGL but I blogged on a similar issue - I confirmed and diagnosed with a coat over the scope's various potential light paths but you could do the same thing with your shed light with darks to be sure.

https://www.talkunafraid.co.uk/2019/02/how-to-fail-at-astrophotography/

The fix is to cover the rear - you can do this with fabric and tape or do what I did and drop a black plastic insert over the back, using the locking screws to secure it in place.

If you want to get paranoid on other bits of the scope, chalkboard paint on the drawtube (less the bearing contact surfaces) and flocking will help massively. Flocking is super easy to do - all it involves is popping the primary mirror out to get access (and that's much less daunting than it sounds if you know how to collimate!)

[Nicola Hannah Butterfield]

 

@discardedastroThanks for the input, as I said previously the rear of the primary is painted matt black (black board paint as you say) as is the draw tube and the edge and rear of the secondary. I am pretty sure it was either the moon angle or the shed light, the next clear night I will try again, with the shed light off and the moon will be out of the way for the next two weeks nearly. I am not worried about removing the primary as I had to shorten tubes in the past, I also did darks frames.

 

Edited January 29, 2021 by Nicola Hannah Butterfield

[Nicola Hannah Butterfield]

Cleaned it up a bit, but it will be better reimagined I think.

Edited January 29, 2021 by Nicola Hannah Butterfield

[Nicola Hannah Butterfield]

A little PP work.

[discardedastro]

12 hours ago, Nicola Hannah Butterfield said:

the rear of the primary is painted matt black

Right - but if your 200P is the same construction as mine (open at the back to the back of the primary in cell), the primary doesn't completely cover the rear of the tube and the primary cell has no baffling to the sides. So light can bounce around the primary/cell, enter the tube at an angle, and cause diffuse artefacts in dark frames taken with the front and drawtube covered. Note the coloured "rays" top centre of this image which are a result of mono image stacking causing the light (in my case from a neighbour) leaking into the tube to appear in different places per filter. I'm at a different image scale (2.4um pixels at 0.5"/px) but it's quite a similar effect to what you're seeing I think.

This was fixed with my tube end cap which completely blocks light entering the tube assembly rather than cutting down on reflected light internal to the primary or cell arrangement.

If your dark frame there was shot in total darkness that looks pretty sane - I'd try this experiment. Get some heavy coats or other blackout materials and cover the drawtube and top end of capped scope, so no light can enter - tie them up at the bottom or use a bungee strap to hold the material against the tube. The objective is to only allow light to potentially enter at the bottom. In daylight, or with the rear of the scope diffusely illuminated with a lantern/floodlight, take some dark frames. If your dark frames look identical you're good. If they have cast - there's your culprit.

The two dark frames below were captured with the above set-up in bright daylight; the only difference being a coat wrapped around the end or not (the 183MM's amp glow is the big star on the right, not an artefact of the tube). That's with the stock focuser and drawtube (not even blacked out) in daytime conditions, and a 300s exposure.

You can reverse the experiment, of course, and leave the draw tube exposed instead of the bottom, and see what impact that makes. Flocking the tube across from the drawtube will help direct reflections from light entering from around the drawtube. With my stock focuser in daylight and the bottom of the tube capped, I can take darks that have very little difference to nighttime darks; even better with my current focuser (Baader Steeltrak) which is internally baffled and painted black etc.

[Nicola Hannah Butterfield]

@discardedastroWhat I will do when I get sometime is do a long exposure during the day and try this, the camera/focuser is covered with a lightproof cover, it is possible that some light is getting around the main mirror cell, but I don't think that was the issue in this case, as the M51 exposure later that night, did not show the same issue, nor on my previous attempts of M42/43 and the Horsehead Nebula earlier this month. The mirror cell is usually in the darker part of the area the scope is in, it is just the front the experiences overspill light from neighbours lights, but as we know light just bounces around everywhere these days, not that the nature of light has changed, just so much more of it.

[malc-c]

Is the inside of the tube flocked - or is it stock ?

Applying black flocking to the inside helps stop stray light bouncing around the inside of the OTA.

https://www.firstlightoptics.com/misc/black-velour-telescope-flocking-material.html

However I must say that the images shown are very good...under the condition you have with your neighbours light.  Have you asked why it's always on, or if they could install a blind to help you out ?

Edited January 30, 2021 by malc-c

[Nicola Hannah Butterfield]

@malc cThanks, I will get to flocking eventually, if I stay with this scope as my primary imaging scope, I still need a coma corrector, so I am debating to get a refractor, yes I know it needs a flattener as well. @discardedastro Has pointed out some interesting things of which I have just done a few test shots. These are just single images, but they do highlight a few issues.

This first is with the rear covered with just the normal dust cover on the front all are 300s @f5 prime focus and with the camera covered with extra blackout though a perfect fit with the tube, anything camera wise is cover and tight around the bases or the focuser. Focus and orientation as set the other night. I have done nothing other than a simple jpg export in lightroom

 

This second just front dust cover.

This one front covered with extra material, and rear covered as the first.

This final one just a shot to show the orientation of the camera on the scope, which is roughly 90° to the tube.

I did do a few others in the home position, but the sun was weakly shining through the clouds and was effecting the bottom of the tube.

So the conclusion is yes there is excessive light around the mirror cell and a dark centre which might explain so artefacts I am getting. The first the one with just the extra rear cover is interesting because whilst it does so a similar artefact to M33 it is in a different position.

Below is the one with just the rear cover on the left and both front and rear covered on the right, cr2's stretched in pixinsight.

So my next test will be on a subject with the extra cover on the rear and see where I can go from there, and an extra cover on the front doing the darks.

 

[Nicola Hannah Butterfield]

@discardedastro I finally managed to get out the other night with no moon in the sky, Rear of the scope covered with a dark towel, camera covered with a lightproof bag, home-made light shield (though this can be improved on) This is the full frame from my Canon 6D , a quick stack in DSS and a little stretching and a little editing in pixinsight/photoshop. Thank you for your help.

[discardedastro]

On 18/03/2021 at 10:38, Nicola Hannah Butterfield said:

@discardedastro I finally managed to get out the other night with no moon in the sky, Rear of the scope covered with a dark towel, camera covered with a lightproof bag, home-made light shield (though this can be improved on) This is the full frame from my Canon 6D , a quick stack in DSS and a little stretching and a little editing in pixinsight/photoshop. Thank you for your help.

 

Glad that you've figured out the cause of your woes! The image looks great!

The mod I made to mine - an acrylic cover for the rear - can be had quite cheaply and the SVG file required for laser cutting via RazorLabs/others is available at