CCD Dust Spots

[Grumman]

I just bought my first CCD camera (2nd hand out of eBay) and it is an Altair Hypercam IMX178C

I have received the camera and it looks OK without any signs of wear.

I have tried to take some flat frames with it and it seems there are some dust spots in the frame.

I have cleared the scope, field flattener as well as the CCD IR window and I am still getting those...

When my DSLR is connected, I can't see any of these in the flat frames...

Any idea where these might be coming from?

[Merlin66]

Looks like they may be on the sensor cover plate....

Dust Bunnies

Distance from chip surface (mm) = (P x Fr x d)/1000

where

P = Pixel size (micron)

Fr = Focal ratio of telescope/ lens

d= Diameter of Dust Bunny (in pixels)

 

 

[Grumman]

Thank you @Merlin66 for the helpful info!

I managed to track them down and they are on the actual sensor.

Because I use a SW 72ED and the wonky SW 0.85x flattener, i have to screw the camera to the flattener using the T2 to 2" adaptor that the camera comes with.

This does not give me any room to mount any filters as the combination of FF/Telescope gives no room for focusing so distances are tight...

I had an "Idea" to remove the protective window from the camera which is held in place by a C-Mount screw and screw there a C-Mount to 1.25" adapter and mount my UV/IR Cut filter on top. Then the T2 to 2" adapter can be mounted on the camera and attached to the SW FF and all the rest onto the focuser...

I was very careful when doing that but i definitely introduced dust in the sensor thus the issue I was having...

Thanks for all your help!

Thanasis

 

 

 

[Adam J]

I would have thought that a filter wheel would fit between the camera and the reducer? I dont see why using spacers instead of the wheel would change that.

[sloz1664]

I agree with Adam. You have around 55mm from the S/W focal reducer to the camera chip. Invest in low profile adaptors and the Baader T2 Delrin Spacer Ring Set and you will be able to add the filter wheel and get the exact spacing to obtain a lovely flat field.

Steve

[Grumman]

Thank you @Adam J and @sloz1664 for you replies.

A filter wheel does fit between the FF and the Camera but I am not keen buying one yet, as the CCD is a color one and I only need a Light Pollution filter to be honest...

I might invest in one in the near future...

 

[sloz1664]

12 minutes ago, Grumman said:

Thank you @Adam J and @sloz1664 for you replies.

A filter wheel does fit between the FF and the Camera but I am not keen buying one yet, as the CCD is a color one and I only need a Light Pollution filter to be honest...

I might invest in one in the near future...

 

Sorry, my mistake. I thought it was a mono camera

Steve

[Adam J]

1 hour ago, Grumman said:

Thank you @Adam J and @sloz1664 for you replies.

A filter wheel does fit between the FF and the Camera but I am not keen buying one yet, as the CCD is a color one and I only need a Light Pollution filter to be honest...

I might invest in one in the near future...

 

I see your point if you want to use 1.25 inch filters, but opening that sensor window comes at a cost as you discovered.

A filter wheel is a good idea even on an OSC (unless you use 2 inch filters) as at a minimum I might want the following filters: Light pollution filter for galaxies, a stronger UHC like the astronomic for emission nebula and a Ha filter for adding Ha luminance.

You should be able to get shut of the dust with a blower of by using a very soft and new paint brush. If you use the blower on the bristles before use it will attract the dust to the brush, just take great care to only touch the sensor window itself with it. 

I have done that on my guide camera before now. 

Adam