Image "Smudge"

Discussion of using SharpCap for Deep Sky Imaging
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brenski
Posts: 82
Joined: Mon Aug 10, 2020 4:01 pm

Image "Smudge"

#1

Post by brenski »

Equipment:
♦ Skywatcher Star Adventurer Pro 2i Wifi ♦ Skywatcher Evostar 72ED DS-Pro [420mm F/5.8] ♦ Zwo ASI 183MC Pro (cooled)

I’m hoping someone with more experience than myself can help identifying this “smudge”.

This has appeared on image stacks recently whether stacked in DSS or Affinity Photo. It appears in the same position in each frame.
Is this likely to be camera or scope glass smudge. Or could it be symptomatic a more sinister fault?
I can’t “see” anything at either camera or scope end.

Image
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oopfan
Posts: 1321
Joined: Sat Jul 08, 2017 2:37 pm
Location: New York
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Re: Image "Smudge"

#2

Post by oopfan »

Yes, possible suspects include a fingerprint or fleck of dust on the sensor window or a filter. Do you use an IR/Cut filter or Light Pollution filter? Generally, we don't worry about these. Capturing "Flats" takes care of it.

Here is a write-up that I made for someone at the Astro Pixel Processor forum. It describes an easy method of using an Electroluminescent panel for taking flats:

"If you are looking for another solution to taking flats, I recommend this 10cm x 10cm EL Panel from Adafruit:

https://www.adafruit.com/product/625

They say it is White but it is stronger in Blue, but fortunately it is panchromatic light. OIII flats will require a shorter exposure than Ha and SII.

I have a scope similar to yours: 71mm f/5.9. My 6nm OIII flats take about 2 seconds whereas my 6nm Ha and SII flats take about 25 seconds. My pixel size is larger than yours (4.65um) but Peak QE is only 54%. I would imagine that your exposure will be similar, possibly a little less.

I have two versions using the same EL Panel. The first is really simple. I don't have a photo of it but I can describe it. Buy a sheet of balsa wood: 12" x 4" x 1/8". Cut it so it measures 4" x 4" x 1/8". Buy an inverter to power the EL Panel. I use this one:

https://www.adafruit.com/product/564

Buy some double-sided sticky tape and affix the inverter to one face of the balsa. Next, buy two large nylon bolts and nuts. Also purchase two large rubber grommets. The diameter of the grommets need to be larger than the head of the bolts. Measure the diameter of your refractor's dew shield. Use a draftsman's compass to draw a circle on the balsa opposite the inverter. Hand-position the two grommets so that their center is outside the circle and their outer diameter is tangent with the circle. Position the grommets so that they subtend a 90 degree arc with the optical axis. Mark with pencil the center of the grommets and drill holes through the balsa just wide enough for the nylon bolt to pass. Next, lay the EL Panel atop the balsa and mark where the bolts need to pass through the EL Panel. Use a simple hole punch purchased from a stationery store to punch two holes in the EL Panel. Assemble. Use double-sided tape to affix the EL Panel to the balsa while keeping the holes aligned. Insert the Nylon bolts, making sure that the grommets are on the EL Panel side. Hand lighted the nuts. Complete the electrical connection between the EL Panel and the Inverter. Insert batteries and test. Note that the rubber grommets are meant to grab the outer circumference of the dew shield with gravity assistance.

Note: To thwart possible splitting of the balsa when drilling the holes for the nylon bolts, I purchased a sheet of 1/16" balsa. I cut two 4" x 4" sheets and laminated them with woodworkers glue. I made sure to rotate the wood grain 90 degrees for strength."
brenski
Posts: 82
Joined: Mon Aug 10, 2020 4:01 pm

Re: Image "Smudge"

#3

Post by brenski »

looks okay now that i've applied a dust blower to it, thanks.
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