Look like I damage secondary mirror ?

[Shashi pal]

I had notice few dust particle , look like they enter by eye piece , may be eye piece fell down on ground during observation and when I put them back on telescope , dust fell down inside ,

I saw lots of vedio on YouTube , I also phone few companies but they charge a lot , new telescope similar one I have is around 300 pound and they charging around 270 pound including postage , sounds crazy 

Cut to long story short , when I do focus on secondary mirror I can see patches like cotton thread , primary mirror so far look ok to me , 

i clean my primary and secondary mirror lots of time , but these patches are at same spot and same shape , look like they are scratches , 

If we zoom this picture, it’s look terrible 

I do not know what can I do now , 

[JOC]

Is it affecting the view?  I've seen loads of threads on SGL about people with mirrors with dust etc. on them, but  what has been constant in those reports was actually how little the 'contamination' of the mirror actually affected the view.  When you think how you can close the aperture on something like a larger Reflector and still get a good view a small area of deterioration on the mirror might not make a huge difference to what you see in the sky.  Have you had a look?

Edited September 18 by JOC

[Shashi pal]

Thanks for reply , vedio was i can see few patches but not that bad , but when i take pictures of stars , on long exposure timing , it’s really look terrible 

last night I did shoot moon vedio and i could see few patches but not much 

 

[Elp]

You've mentioned three things here:

1. Eyepiece,

2. Primary mirror,

3. Secondary mirror.

Have you actually approached this practically to determine which one it is. You'll know if it's the eyepiece if you look through it and rotate the eyepiece and see if the dust rotates with it.

How have you cleaned the mirrors, have you used a bulb blower and lint free microfibre cloth? These are basic cheap tools for cleaning optics.

[Elp]

Also if you're focused at infinity you shouldn't see the dust on the mirrors, a dusty eyepiece however you will see the dust within the eyepiece.

[RobertI]

3 hours ago, Elp said:

Also if you're focused at infinity you shouldn't see the dust on the mirrors, a dusty eyepiece however you will see the dust within the eyepiece.

Agreed, small particles of dust and hairs on the mirrors will not show as dots and lines when viewing through the eyepiece or taking images. In fact they are very unlikely to degrade the images at all. If you are seeing dust and hairs then it’s either contamination in the eyepiece lenses or contamination on/near the sensor. 

[Shashi pal]

i took few picture of saturn in RAW format , it look terible , but moon pictures are much better . may be for moon i have to low the ISO not sure . i cleaned the mirror as much as i could , i have no idea where these patches comes from , they are not from camera lens as i did took picture from camera , i do not use any eye piece . and when i saw by bare eyes , i do not see these marks on any of the mirror , i had cleaned the mirror lots of time , when i put my camera on telescope and i zoom in , i can see  these patches , but when i do focus adjustment on the telescope , these patches do not have any effect , so look like these are not from primary mirror , otherwise i could see some impact while doing adjustment , not sure i am not professional , i am looking for help . i tried to clean as much as i could . 

i use sky watcher 127 , new of this telescope cost around 300 pound and companies are charging like 270 pound to get this correct . its insane  ,so i have no option to get it correct some how on my own , i will be very very thankful for any suggestion and guidance 

kind regards 

 

[Elp]

They could be on the camera sensor.

[Padraic M]

That definitely looks like dust on the camera sensor. That's the only place where dust will be perfectly in focus. If the dust is any further into the optical train, even on secondary or primary mirrors, it will be out of focus and will look like big donuts.

What camera are you using?

There is a tool here https://astronomy.tools/calculators/dust_reflection_calculator that can tell you where the dust is, given the radius of the donut (in pixels) but as you can see, if you enter the width of your dust marks as <10 pixels, you will see that the dust is less than 1mm from the camera sensor - i.e. on the sensor!

[Padraic M]

Just a few more thoughts:

It's not a good idea to clean your primary and secondary mirrors, unless they are really really dirty. Normal dust and dirt on mirrors has very little impact on the final image. Just like your moon shot above, it's perfect. You're likely to scratch the mirrors and make them worse.

Don't clean your camera sensor either! Maybe just very carefully use a blower brush, and don't let the brush touch the sensor. And definitely don't use compressed air. Better to bring it to a camera shop and get them to do it for you.

 

I'm not sure what went wrong with Saturn, but to me it just looks overexposed and possibly out of focus. It's hard to believe that Saturn and the Moon pictures came from the same camera.

 

[wimvb]

To check if dust is on the sensor or the mirror is easy. Take an image without anything attached to the camera. Make sure the image isn't overexposed. Any dust or scratches visible must be on the sensor.

You can also rotate the camera when attached to the scope. If dust stays in the same place in the image, it's on the sensor. If you attach just a camera body to your reflector telescope, you can never focus on any of the mirrors, simply because there's nothing to focus the light between the mirrors and the sensor.

what camera do you use, and how do you attach it to your telescope?

Edited September 19 by wimvb

[GasGiant]

I had similar.

At night I wear (dont laugh) a poncho but its made from that harsh wool fibre. For convenience, I was putting eyepieces in the large pocket at the front of the poncho. Loose wool found its way on the lenses and I got exactly what this looks like.  Lesson learned. 

 

Edited September 19 by GasGiant

[Shashi pal]

Thanks a lot guys , finally found it , it’s the camera sensor , I use cannon 2000d dslr 

Now I am checking how to clean that 

 

[TiffsAndAstro]

1 hour ago, Shashi pal said:

Thanks a lot guys , finally found it , it’s the camera sensor , I use cannon 2000d dslr 

Now I am checking how to clean that 

 

Very very carefully 

[Padraic M]

3 hours ago, TiffsAndAstro said:

Very very carefully

This ^^^

You can permanently damage your sensor if you touch it with anything. Also, don't blow on it with your breath as you can get moisture droplets on it which can stick the dust in place.

Your best bet is to use an air blower and gently try to blow the dust away. If the dust is already stuck to the sensor you could be in trouble 😞

 

[TiffsAndAstro]

I tried to clean my 1.25" uvir cut filter once.

Won't do that again

[PhilB61]

Best bet to clean the sensor on a DSLR is with a cleaning kit that includes fluid and single use swabs, its not that difficult or time consuming once you've done it a few times. For DSLR users who swap lenses frequently its just something you have to learn to do. The sensor part that you actually clean is a glass cover/filter and is much more robust that the reflective coating on telescope mirrors.

[Martyn87]

On the canon, it will have a sensor clean function which may be enough to shake some debris loose. Other than that, stick to the tried and true "least contact to most contact" method. Use a rocket blower to remove as much loose debris and possible, followed by a soft brush, then move on to the single use swabs as mentioned above. 

Remember on a DSLR, unless it's been modified, you're not cleaning the actual sensor, but the filter stack in front of it. 

[900SL]

17 hours ago, Martyn87 said:

On the canon, it will have a sensor clean function which may be enough to shake some debris loose. Other than that, stick to the tried and true "least contact to most contact" method. Use a rocket blower to remove as much loose debris and possible, followed by a soft brush, then move on to the single use swabs as mentioned above. 

Remember on a DSLR, unless it's been modified, you're not cleaning the actual sensor, but the filter stack in front of it. 

Yep. I had to do this on a regular basis on my FF Nikon in Saudi. It might take a couple of swabs to avoid streaks, but it leaves the sensor spotless. 

[Gfamily]

If you lock up the mirror, and remove the lens, looking under a decent light may well show you the dust on the sensor.

If you get a rocket blower you should be able to blow most of them away (hold the camera so that the sensor is facing downwards, and puff with the blower).

Don't use canned compressed air, as the propellant can land on the sensor instead.

I probably wouldn't recommend it, but I had one piece of dust that wouldn't move, but I made a 'stick' of bluetack and touched it to the dust and removed it that way. 

Edited September 20 by Gfamily