Mysterious internal refections tried to ruin my dark sky trip. Grrr.

[mrflib]

Hello fellow space dudes

 

I am getting some odd refections on my subs when I try to image M45. I was at a dark site and in the end had to switch targets - I did not get these same reflections on M31 or M51. I only tried LUM and RED filters on M45 before switching targets (dark sky time, can't waste it!) and the same refecltion was on both filters. I've never imaged M45 and I've not seen these reflections before.

I've made an album linked below. All targets were taken on the same night.

 

SINGLE FRAME STF STRECHED SUBS HERE

 

I am running:

Sharpstar 94EDPH > 0.8x Matched Sharpstar Reducer > ZWO OAG-L >> ZWO 7x2 Filter Wheel >  ZWO 2600MM

I use Antlia LRGB V-series Pro filters (unmounted, black edge, 36mm) and Antlia 3nm 36mm Ha SII OIII (unmounted, black edge, 36mm).

https://www.365astro...-36mm-unmounted

https://www.365astro...-36mm-unmounted

https://www.365astro...-36mm-unmounted

https://www.365astro...-36mm-unmounted

 

I do have some shadow from the OAG but flats take that out - bottom 2 images in the album show them.

Looking at a wider frame image of M45 on astrobin I can't see any bright stars out of frame that might be causing this? There was no moon.

https://www.astrobin.../full/d8a4jn/0/

I can't see any scratches or marks on any of the spacers / image train. The 94EDPH is flocked with black fabric inside the tube. The OAG is adjusted on the tilt plate for a flat field and black tape is around the outside edge of the whole OAG to stop light.

Any ideas!

 

(I have posted this on CN too)

 

[pipnina]

The only idea I have is to set the telescope up during a cloudy night, point it at a bright torch of some sort (could make a pinhole in a foil sheet to simulate a star maybe), and move the bright light source around the field of view of the scope, even out of field, and see if the reflection pops up.

When you find it, be meticulous in working out where it's coming from. Remove the corrector and see if it's still there, then try the filter wheel, oag, even take the cam off entirely and see if it's also there in an eyepiece.

Looking at where the focal point of that curve would land, way off screen, the only bright object in that area is mars... Does it show up in the field if mars is near by? It's brighter than any star by a long margin so if anything can cause a reflection in an otherwise dark sky that might be it.

[pipnina]

2 hours ago, mrflib said:

Hello fellow space dudes

 

I am getting some odd refections on my subs when I try to image M45. I was at a dark site and in the end had to switch targets - I did not get these same reflections on M31 or M51. I only tried LUM and RED filters on M45 before switching targets (dark sky time, can't waste it!) and the same refecltion was on both filters. I've never imaged M45 and I've not seen these reflections before.

I've made an album linked below. All targets were taken on the same night.

 

SINGLE FRAME STF STRECHED SUBS HERE

 

I am running:

Sharpstar 94EDPH > 0.8x Matched Sharpstar Reducer > ZWO OAG-L >> ZWO 7x2 Filter Wheel >  ZWO 2600MM

I use Antlia LRGB V-series Pro filters (unmounted, black edge, 36mm) and Antlia 3nm 36mm Ha SII OIII (unmounted, black edge, 36mm).

https://www.365astro...-36mm-unmounted

https://www.365astro...-36mm-unmounted

https://www.365astro...-36mm-unmounted

https://www.365astro...-36mm-unmounted

 

I do have some shadow from the OAG but flats take that out - bottom 2 images in the album show them.

Looking at a wider frame image of M45 on astrobin I can't see any bright stars out of frame that might be causing this? There was no moon.

https://www.astrobin.../full/d8a4jn/0/

I can't see any scratches or marks on any of the spacers / image train. The 94EDPH is flocked with black fabric inside the tube. The OAG is adjusted on the tilt plate for a flat field and black tape is around the outside edge of the whole OAG to stop light.

Any ideas!

 

(I have posted this on CN too)

 

Also, you aren't following the topic - heads up

[ollypenrice]

We got comparable arc-like curves when shooting M45 in the RASA. In the case of the RASA there's a lengthy discussion online but stopping down the inner edge of the optics around the central obstruction seems to work for some. This wouldn't be applicable in a reflector but edge blackening or some mild stopping down might help. Sometimes reducers just do this on bright targets. I'd certainly ask the supplier to comment.

Alternatively, the fairly easy fix is to shoot some subs with the image moved in the frame so that you still capture the part under the arc but the new arc will be in a different part of the image. You then use the second image as a patch. You don't need a full set of subs just for an arc. You can get away with a short run and a good dose of noise reduction.

This can also help if you get a shaft of flare from a star out of shot. Steer the scope towards the star and as close to it as you can before shooting the patch panel (which obviously has to cover the flare in question.) These flares often only appear at some distance from the source star.

Olly

[mrflib]

@ollypenrice @pipnina

Guys thank you for the input. I have recreated Stellarium at the date and time and got the following (attached). Not exactly sure how it all lines up, but plausible for sure!

Mars indeed - it has to be it.

When I have the scope back from FLO (they are looking at some pinched optics for me) I will take your suggestions on board and try and nail this down. I have actually pinged an email to Flo to see if that can see anything obvious inside the scope while they have it that would be a warranty repair issue - I'll do the rest when I get it back.

In the event, Ollie,  I just changed targets because dark skies are a treat for me and I'll try and nab M45 when it Mars does not have the audacity to poke its nose in.

[ollypenrice]

Decidedly possible and good news if correct.

Olly