Spotty images

[Coastliner]

Hi all,

My Nexstar 4 SE looks as though it has debris on one of the mirrors, I get the spots on images from webcam or dslr. The front of the corrector plate is clean, the flippable mirror is clean and the dirt is not on an eyepiece.

Can the mirrors be cleaned diy? Is the ota easy to take apart? I was condidering filling the ota from the back with a mixture of washing up liquid and water and giving it a good shake ( joke!).

Serously, any advice anyone?

Neil.

[JB80]

It could be dust bunnies on the sensor of the cameras, it kind of sounds like it.

I would investigate that first before taking the mirrors out as its a much simpler task cleaning the sensors.

[Peter Drew]

Definitely dust on the sensor, dust or spots on the mirrors are not in focus so can't normally be seen. 

[JB80]

Depending on what cleaning equipment you have if any the best way to remove it would be to use an air blower of some type, never be tempted to just blow on it with your mouth as it can create more spots on the sensor.

If the air blower doesn't work then it's worth purchasing a small cleaning kit with a fluid.

[ronin]

It will not be anything on the mirrors, they are not at the object plane so nothing on them would form an image.

That brings it back to the sensors or anything that is very close to the sensors.

You mention an eyepiece - do you have a filter fitted in that, have you checked it is totally dust/dirt free?

Why have you an eyepiece?

The most common option chosen is prime focus without the use of an eyepiece.

[Coastliner]

What is confusing me is the fact that I get the same pattern of dots whether I am using my dslr or my webcam, therefore two different sensors. They are more prominent on the webcam, there are no eyepieces involved now. If I have an image produced by the webcam I can rotate the webcam in the eyepiece by 180 degrees, the image turns upside down, but the dots are in exactly the same place on the screen, at the bottom of the image. There is nothing in the way, the sensors are at prime focus.

I admit that I am relatively new to this and am still experimenting, but this has me stumped. It is dark here now, but if I can capture an image from each sensor tomorrow I will post them here.

[Coastliner]

Gentlemen,

I offer the humblest of apologies tinged with a bucketload of embarrassment.

1) Getting the same pattern of dots on two different sensors was a lie, caused by me being totally disorganised in filing/naming my images.

2) My assertion that the dots on the screen image (using Sharpcap here) would rotate  and keep pace with the image rotation when the camera was rotated was an obvious mistake, once I got my head around it.  Altering the orientation of the sensor, i.e rotating it relative to a fixed object, will rotate the object relative to the sensor and therefore alter its angular position on the screen.  It will not alter the position of the dots, as the image pane does not rotate with the sensor.

Lesson learnt!  And now I understand the reasoning behind your certainty that it had to be the sensor, as any dirt on mirrors etc would not be on the focal plane.

That's me a couple of points higher up the learning curve - now I'm off to look for a sensor cleaning kit!

Regards,

A red-faced Neil.

[Peter Drew]

Been there, done that myself!     Glad it's sorted. 

[Owmuchonomy]

Make sure you take flat frames too and then use them to stack/process out your dust.