Advice needed re spots on image

[BrendanC]

Hi all,

I bought a SkyWatcher 130p Synscan end of last year.

 

I've started taking stacked photos using the Bresser HD Mikrokular camera - all very basic I know, but these are my first steps.

 

The first shots I took were great. However, the last time I noticed there were dark specks on the image.

 

I've checked the camera, eyepieces and secondary mirror and they all seem fine. However, when I shone my mobile phone torch into the scope, I could see what looked like little dust particles on the primary.

 

So, I took the (for me) big step of removing, cleaning and collimating it. 

 

I think everything went ok. However, I can still see the specks on the primary, and unfortunately the image from the camera still has spots on it.

 

Here's what I'm seeing:
 

 

This is with just pointing the scope at the (very grey) sky so that I can see any spots that appear against a blank background.

 

I think the mirror is fine for viewing, but as you can see, not at all suitable for photography. This is especially going to be a problem if I want to start solar imaging, which was my intention in the near future, for sunspots.

 

I need to know whether it is indeed the primary mirror, if so what I can do to fix it, or even whether I can buy a replacement if something has gone terribly wrong with it. I was very careful to clean it properly as per videos I found on YouTube (warm water, touch of detergent, distilled water rinse). I don't know what the marks are - pollen?

 

Any ideas? Any/all advice appreciated.

 

Thanks

Brendan

 

[paul mc c]

Its not the sensor on the camera is it.......you wouldnt really see specs on the mirror showing up in a pic taken through a camera.

[tooth_dr]

Hi Brendan

Firstly I would say that those spots arent on the primary, and that the primary mirror has nothing to do with it.  This is dust on the glass covering the sensor of the camera.  The good news is that these are found on everyones kit, and that they are easily removed in processing.  Obviously you will want to gentle use a blower to clean the camera glass, and then if you take calibration images called flats, this will 'remove' them from any future images.

[BrendanC]

Hey, thanks for such quick advice, both of you. You beat the Astronomy Shed hands down.

I'll take another look at the camera - and I take your point about post-processing, that's how I got around the problem at first before deciding to address it properly.

Cheers, Brendan

[BrendanC]

Hi, just as a check, I've tried cleaning the camera (can't get to the sensor unfortunately) and one thing that I've noticed is that, when I rotate the camera in the eyepiece holder, the image rotates in SharpCap - but the spots do not. Would this be the case if the dust was on the sensor? Surely the spots would rotate with the image? I have to say even trying to imagine this, even drawing diagrams of 'this bit rotates so this bit doesn't', with the interactions between the primary, secondary, camera and 'real world' is hurting my brain. If it makes sense that the spots would stay in place if it's the camera, then do you think it's acceptable that it could get so dirty so quickly? I've used it, what, ten times and been careful to protect it in storage etc. 

[upahill]

9 minutes ago, BrendanC said:

Hi, just as a check, I've tried cleaning the camera (can't get to the sensor unfortunately) and one thing that I've noticed is that, when I rotate the camera in the eyepiece holder, the image rotates in SharpCap - but the spots do not. Would this be the case if the dust was on the sensor? Surely the spots would rotate with the image? I have to say even trying to imagine this, even drawing diagrams of 'this bit rotates so this bit doesn't', with the interactions between the primary, secondary, camera and 'real world' is hurting my brain. If it makes sense that the spots would stay in place if it's the camera, then do you think it's acceptable that it could get so dirty so quickly? I've used it, what, ten times and been careful to protect it in storage etc. 

If its on the sensor then a spot in the bottom left will always be in the bottom left, regardless of how you rotate the camera in the scope as this will just rotate the image in the frame..... I think, im doubting myself now too.

Removing them in processing may be your only option if you cannot get to the sensor for cleaning. I was painstakingly trying to remove all dust from my gear last year, then I just resigned to the idea of taking calibration frames and forgetting about it - short of being in a clean room lab I dont think its even possible to keep gear dust free.

 

[BrendanC]

Hmmm, I think you're right - the spots should stay in the same place because they're on the sensor, everything else should move. 

Thanks for the help again. I think I'm going to contact the vendor of the camera because I'm not particularly happy that it should get like this so quickly. But, as you say, perhaps that's just our lot in our dirty, dirty world.

[Peter Drew]

The dust specks will be microscopic and almost invisible until a photo is taken of an even white background, such as a wall. sheet on a line, or the Sun!    😀

[BrendanC]

Well, that was partly what bothered me - if I'm going to want to view sunspots (which I will), then how will I know what's a sunspot, and what's a, well, spot?!

I think the answer is that they'll look quite radically different, plus I can start looking into flats to help subtract out the dust spots, and post-processing of the image too.

I'm still contacting the vendor to ascertain whether they think it's a problem with my particular camera. In the meantime I must admit I do feel a hell of a lot better about it all after the advice here. I've been on forums before for other stuff, mainly computer tech sorts of things, and they're such great resources for this sort of thing. Thanks all for your advice, it's been really helpful.

[BrendanC]

Vendor reply: sadly this is very common on all astro cameras no matter how well kept.

Seems to be the case! OK, well, onward and upward as they say...

Thanks, Brendan

 

[Stub Mandrel]

Dust is ubiquitous, definitly not a fault in any unsealed camera unit.

You need one of these, the only way I have found to get a sensor clean without major frustration :

https://www.ebay.co.uk/itm/Sensor-Gel-Stick-Jelly-Camera-CCD-CMOS-Sensor-Cleaning-Kit-for-DSLR-Red/153136678365?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

But in practice, using flats will get rid of them.

[BrendanC]

Thanks! I think the sensor is sealed into the unit on my (very cheap) camera  - see https://www.bresseruk.com/bresser-mikrokular-full-hd-eyepiece-camera.html) but it's definitely something to bear in mind if/when I upgrade.