Red vs Blue, what's going on???

[davedownsouth]

A couple of nights ago I had my first outing with my new scope, and although I could not get the focusing sorted out properly, I took a few short shots (2 minutes) of M81 binned 2 x 2 in Red, green and blue.  I only managed 3 shots in each colour and the order of taking the shots was Red, green, blue, repeated 3 times.  Now, the Red and green shots all looked fine, and attached is a quick stretch of what the Red looked like (green was similar):-

My problem was with the Blue shots, all of which were showed the same problem and attacked is a quick stretch of the intergrated image of the three shots:-

Does anyone know what is causing this effect?  I have never seen this before when using the camera on my other scope, so what could be causing it?

Cheers,

Dave

[ollypenrice]

Looks as if your filterwheel has a problem and is not centering the filter. I can't see it being anything else. Just look down the OTA or, if the camera's off the scope, fire it up and look from the scope side.

Olly

[davedownsouth]

Thanks. I have taken the blue filter out of the camera and put it back it, next clear night  , I will give it another bash .  

NB.  Problems with the blue shots aside, I am please with how round the stars are at the corners with the red shots

[ollypenrice]

The filterwheel uses an optical signal to tell it when the filter carousel has reached the right place. It looks as if, for some reason, yours is stopping in the wrong place for the slot you are giving to blue. This has nothing to do with the filter per se, only with the rotation of the carousel, and you can test it any time. You don't need a clear night. Just look at the filterwheel when you've sent it to blue. Is the filter centred over the chip? It's easy to tell but I don't think this problem will go away without action on your part. I wonder if dust or contamination inside might be blinding the optical sensor?

Olly

[davedownsouth]

I assumed that a filter wheel would just turn it round a set amount. Will check if it is stopping in the correct place later.

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[ollypenrice]

I assumed that a filter wheel would just turn it round a set amount. Will check if it is stopping in the correct place later. Sent from my iPhone using Tapatalk

It doesn't turn by a set amount, it turns till an optical signal tells it to stop. This signal seems not to be working properly. (A system whch said, 'rotate by x degrees' would gradually develop an increasing error. Filterwheels therefore use a technology which operates on an ever-fresh basis sayng, each time, 'stop here.' But like any other technology it can fall on its bum!

Olly

[davedownsouth]

Wired that it just fails on the blue filter? Will check out tomorrow went I am not drunk

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[davedownsouth]

Just had a manual play with the filter wheel (which is an integral part of the Atik One 6), and from just eye balling it, it looks like each of the five filters are going to the same position.  Think I need to try it out again with the scope to see if I was just unlucky last time, or if it repeats the pattern again with the blue filter.  If it does this, I will then swap over the filter position to see if it is the Blue filter or position five which is causing the problem.  Hoping it was just a one off glitch

[ollypenrice]

This is good news. Some minor contaminant on the carousel may have been confusing the signal at the position you gave to blue. The Atik wheels have a reputaion for reliability. I have two here and they're very dependable.

Olly

[davedownsouth]

Finally got to take the scope out last night, conditions not brilliant, and clouds came in after just 2 hours, but I managed a quick 7 x 180 minutes RGB 2x2 binned on the Whale Galaxy.  Good news, there was no funny effects seen with the blue filter this time round .  Attached is a quick processing of the data in PI, look forward to seeing what this will come out like if I manage to get any Luminance to go with it........

[ollypenrice]

Good. You need flats to sort that bunny but good.

Olly

[davedownsouth]

Yes, that is a real pain.  The one problem I have got with my new set-up is the flattener and CCD camera all need to be screwed together, and doing this is causing bit of 'grit / dust' to get dislodged which then fall onto the lens / sensor .  As at this point it is screwed together and is effectively a sealed system, I can not blow these bits of dust away  .  

Basically I need a better way of attaching the camera / flattener to the scope so that this problem is avoided ; I do not want to have to start doing flats.  Also, the sensor is the wrong distance from the flattener, so I need to get this sorted out as well.

[davedownsouth]

Did the whale again on Sunday; this time with Flats

[johnrt]

I do not want to have to start doing flats

Why on earth not? I'm afraid every imager taking their craft seriously takes flats. They are a part and parcel of the process.

Which OTA is this with, it looks to have very good blue colour control on the stars (the sign of a quality imaging instrument), very nice image too by the way.

[davedownsouth]

Flats at this time of the year are fine, as it is easy to set up while there is still a bit of light about. When it gets to later in the year, this is not going to be possible for me as I can not usually set up till 7:30 pm, and that is pushing it. Will have to work out a different way of doing it, no doubt this will end up being a bit more expensive that a white t-shirt / elastic band .

NB. The photo was taken with the 120ED. Like this scope a lot, very easy to set up with the Lakeside focuser

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[michael.h.f.wilkinson]

Glad the filter glitch got sorted out. Nice result on the whale with the flats.