Rectagular pattern found in Flats - Forums

Topic starter

Aug 29, 2023

Please check out the attached streched master flat in Ha: masterFlat_BIN_1_4212x2850_FILTER_Ha_mono_FILTER_Ha_DATE_20230812_integration_stretched.jpg
All the subs were similar in nature. (20 -20second subs)
OTA: Sky-Watcher 120mm ESPRIT
Camera: QHY294M
FW: QHCFW3m-US
OAG: QHYOAG-M
Filters: Baader Planetarium: H-alpha; Item no. 2459431; BW: 7nm; 36mm diameter ; unmounted

Can someone explain this rectagular pattern?
Is there anything to worry about?
Is this natural?

or, can someone point me to a previous post or related post here or other website?

I know I'm asking alot!

Thank you!

Joe Linington

Aug 29, 2023

An actual explanation, no. But I can assure you that is perfectly normal. I have 2 QHY 294m Pro’s and they both look like that. Freaked me out at first too.

Joe Linington

Aug 29, 2023

Although on second look, the steep, vertical lines on the left and right don’t look quite normal. But if it calibrâtes your lights then don’t be to concerned.

Rob Foster

Aug 30, 2023

Curious about What light source are you using for your flats, how wide is it compared to diameter of scope, and how far away from scope when you aquire flats? Rob

Pierre Fleurant

Topic starter

Aug 30, 2023

Source is an electrolumince light panel covering the whole diameter of aperture. It rests on the dew shield while scope pointing at zenith. It is about 30cm x 30cm square. OTA is a 120mm.

Sean Mc

Aug 30, 2023

Almost looks like internal reflections? ¯\_(ツ)_/¯

Rob Foster

Aug 30, 2023

I agree with Sean Mc - though in looking at your incredible images, Pierre, not sure why you are now seeing this with your master flat. Is that particular panel new? I might try to diffuse the light with lucite or opaque cellophane paper to diffuse any internal (light-specific) source of artifact.

Pierre Fleurant

Topic starter

Sep 5, 2023

The following is directly from the QHYCCD web site, and may explain the situation:

Beginning September 1, 2023, QHY will provide Filter Masks free as standard accessories for the QHYCFW3-M, QHYCFW3-L and QHYCFW3-XL filter wheels to replace the small round fixers previously provided to hold unmounted filters in the carousel. These filter masks make installation easier and, more importantly, they help eliminate stray light from passing around unmounted 50mm filters in the carousel filter slots.

Well Written Helpful Concise

Padraig Farrell

Sep 5, 2023

Just wondering …

if you put you light source a couple of feet away from your OTA and defuse the light with a tee shirt or something on the front of the OTA to see if you get the same result ?

It might point you towards what’s causing the issue

Concise