Extreme overcorrection

I'll try a download and see if I can identify the issue. Looks definitely like a data issue, also an iPad may not be the best source of light (I don't think that's the problem here, but in any case), a good flat panel needs a full spectrum light source that's very even. The iPad may not be full spectrum.

I'll come back with my findings.

Also consider the possibility that it is condensation.

@oopfan this is constant issue over few times now, I have noticed no condensation yet. but overall could be reason ofcourse

Looking at the mono lights, you need to expose way longer, I'd say at least 5-10 min per sub. The signal of this nebula can be much more pronounced in single light frames even. Seems like you have something going on with the bias signal in the flats versus that in the darks and lights, but I'm not sure. How are you taking the darks and darkflats?

@vincent-mod Flats with ipad on top of telescope with white fabric.I used AAP autoflats, was around 24k, 10sec exposure, if I don't remember wrong, but I tried also 14k with with 5sec exposure and got same result

Darks and darkflats with cap on and covered with tripod bag, same settings

Mm, seems ok, I'm not seeing exactly why it would do this so I'll ask Mabula to have a look as well. I'm pretty sure it has to do with the bias signal somewhere, either in the lights or in the darks something is off I think. We're investigating..

@vincent-mod Ok, Thanks!

Mikko,

I agree with Vincent that you can expose a lot longer. I've got a 7nm Ha filter with Bortle 5 skies. I like to expose for at least 10min. My rule of thumb is for the background to come in at "1000 ADU over Bias". For example, my Bias level is 215 ADU, so I try to shoot for the background to come in at 1250 ADU. That's for my noisy CCD. You've got a CMOS camera, so you can get away with "300 ADU over Bias". It doesn't need to be precise, just in the "ballpark".

Brian

@mikko,

Thank you for sharing your issue and your data. I have looked at your data and something seems to be wrong definitely with your data.

I suspect that you have some form of light leakage in your optical train, which is causing this severe problem.

If you look at the MasterDark and it's histogram, you can quickly tell that something is fishy here...

The histogram should not look like that for a masterdark with only dark current and no amp-glow like in your case.... the right side of the histogram should continue to drop..., but instead it rises in values.

Now if you zoom in a bit on the masterdark, it seems that we can even see stars in there...:

The median and average value of your masterdark however don't indicate a like leak however, since these are almost identical to the values in the MasterDarkFlat... looks very weird though to me.

Have you always had this issue with this setup? Or what did you change with your setup before this issue started happening?

Mabula

@mabula-admin thank you for your reply!

this is new setup for me, first cooled camera. Asi2600mm bolted to filter wheel and to fra400 scope with adapter. 

i’ve imaged around 5times only with it, so it is very new system for me. I have done until now darks after every session outside, but i’ve been careful to have no light leaks.

i will do some darks in the fridge next and see how they come out. I will keep you posted.

Thanks!

Posted by: @mikko

Asi2600mm bolted to filter wheel and to fra400 scope with adapter. 

The bolts between the ASI2600MM and filter wheel unfortunately do not prevent light leakage. Is there a way you can screw the camera to the EFW using and M54 adapter (at least, I think that's the size of the thread on the ASI2600MM side. Could be M48)?

@oopfan thanks for tip, i'm new with narrowband imaging, so I've been still experimenting.. But 3nm ha is extremely powerful filter, that I have to say and I've tested 5min exposures and no problem

I assigned new darks 45x180sec

I cannot see no change, results are the same

https://drive.google.com/drive/folders/17X-_oeJX_p-GYn2HgH8zmu4r1tjvoXj3?usp=sharing

Can you check, like Mabula did, if you have the same issue in the darks? Did you take these darks in a different way?

1. @vincent-mod i took them in dark room, same gain and cooling setup. 
   they look the same as previous when stretched

Hi Mikko,

Yes indeed, this looks rather identical.

Perhaps you need to try a different light source for your flats? Have you tried that?

Looking at the vignetting of your flats compared to the lights, the flats clearly show much more vignetting than the lights, so that might be the cause. It could be that the ipad screen is just not up for the task? (i have never used an ipad/tablet for making flats myself but I can imagine that they will not produce uniform broadband light.) Have you created well working flats before with the ipad?

Mabula

@mabula-admin Hello, i have used ipad before, but with dsrl and wideangle, not in a very precise manner. But i do remember having some issues with clip on narrowband filter. At that time i was thinking it is filter issue and not lightsource issue. But i wil try another lightsource and ordered flat panel already. We will see the results later.

What comes to star shaped artifacts, i found topic on CN and there is reports on exactly similar artifacts. But as reading the topics, they should be calibrated out with no problem according to some owners

https://www.cloudynights.com/topic/772185-help-understanding-asi2600mm-dark-artifacts/

but i will do imaging again on weekend and pay attention on calibration frames and let you know

thanks!

@mabula-admin As i was trying other software too, I got same results. I ran flats thru blink, clearly see variation 

https://drive.google.com/file/d/1B4Fs9iCXv420afn4zbGmzkuuZ02uVGR6/view?usp=sharing

Hi Mikko,

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.

Brian

Well, good news 🙂

 Used different light source, taped all the holes, drove to bottle 4 skies, and exposed longer. Worked flawlessly! Cannot say exactly what was the exact issue, but at least frustration is gone now 🙂 thank you!

I never realized it before but there is a cat's face in the Rosette Nebula!

Congratulations Mikko. Very nice image!

Awesome!