130-PDS, light leaking rubbish? Or is this a problem with me?

[pipnina]

After Vlaiv and Olly kindly helped me solve my issues with getting flats to behave in DSS, I started realising my flats still weren't right even once they were being handled correctly in software.

Digging into the issue, I realised my 130-PDS was leaking light, and not just by a little, and not just in one place. 10 second exposures in a darkened room (though still daylight, only curtains closed) were enough to reveal notciable patterns of light ingress... AFTER I put two layers of electerical tape over the back of the primary mirror cell!

Several hours later, having taped the seam along the side of the scope, the joint between the rear mirror cell and tube (as well as previous tape over the back of it!), around the join between the focuser and the tube, the joint between the dust cover holder and the tube, and finally between the focuser tube and focuser body, I finally managed to take a 20 minute exposure without noticable light coming through in a bright room. Buit even then, the dust cover turned out to be a major source of light ingress no matter how much I made sure it was on the front securely! I had to cover it up with multiple black t-shirts and fleeces to remove it as a variable...

All in all, my 130-PDS is now more tape than telescope, and I think the images I took on friday during the full moon must have been truly contaminated in a way flats can no longer correct for. Let alone the reduction in ability to focus I now suffer!

This all screams to me that the scope has major quality issues, which I suppose could be expected considering its low price, but many recommend it as a scope for imaging with!

Does anyone else have this problem? Do all newts suffer this problem? How do you guys deal with light ingress during flats/bias/darks? If this is an issue with the scope, (especially the dust cap not sealing light out properly!) i'll be seriously looking at moving to a higher quality optic for my imaging rig : /

[ollypenrice]

I once took some darks on my Tak 106/Atik rig. I had a snug-fitting metal objective cover over the scope, a closed electric filterwheel and, for good measure, put the Ha filter into the lightpath - and shot these darks in the closed observatory. I then compared them with darks taken with the camera off and its metal, o-ring sealed chip cover screwed on.  Set point cooling was running for both. These were 30 minute darks but the off-scope ones were 'darker.' How it did it I do not know, but light got in somehow. Not much, but the difference was measurable and consistent.

However, you should be able to get panel flats if you shoot them in the dark.  I can see twilight flats being a problem and vaguely remember someone else posting about this with a Newt. I'd try a direct question putting '130 PDS Flats' in the title.

Olly

 

Edited March 21, 2022 by ollypenrice
Typo

[vlaiv]

Flats themselves won't be a problem for scope as they are flooded with light and small additional light leak is not going to impact flat itself much (as long as good flat signal is shot in short amount of time - not enough for light leak to build up). Good/strong flat panel solves this.

What is more problematic is:

- darks shot on the scope. Solution here is to do dark library with camera taken off scope and protected from light ingress (cover placed on camera and shielded from IR with something - people use aluminum foil, I just place it face down on wooden desk after putting rubber/plastic cover on).

- Lights. These are shot at night, but there are small sources of light that can find the way into the scope.

Try to do some LP management. If you have laptop next to the scope - make sure it is facing away from telescope. Turn down brightness of the screen if you can. Don't put anything highly reflective next to laptop screen - wear dark clothes if you sit at the laptop during imaging.

Cover any leds that might be shining - like power adapter leds, mount led - whatever creates light next to the scope. If you can - shield yourself from local lights. Like house or street lights.