where would you suspect the dirt

[iwols]

hi all just wondered where would you suspect the dirt thanks lens filter ccd

Edited February 6, 2020 by iwols

[Alien 13]

Looks in focus to me so it will be on the sensor surface..

Alan

[JonCarleton]

My SVBONY SV105 came complete with a small dead bug stuck to the chip.  I may still have an image of that somewhere.  Fortunately, a blast from an air can eliminated the problem, but I had to void the waranty and take the thing apart to do the deed.

Your problem looks to be on the glass/plastic above the sensor.  But it could be the sensor as well.

 

Edited February 6, 2020 by JonCarleton

[Ships and Stars]

Sensor. I bought a Giotto rocket blower, £12 I think. Try one on the sensor before you clean it with swabs. I use mine on lenses, eyepieces, everything. Does a great job and saves any unnecessary physical contact with lens/sensor surfaces.

Edited February 6, 2020 by Ships and Stars

[Xplode]

Looks like a hair on the sensor

[vlaiv]

Maybe try this for a hint of where it might be:

http://www.wilmslowastro.com/software/formulae.htm#Dust

It'll ask you for diameter of dust shadow, but since this is clearly hair - go with thickness of it as diameter.

[Frank the Troll]

31 minutes ago, Xplode said:

Looks like a hair on the sensor

Thats what I thought, either that or he has  tapeworms

[MarcusH]

If it's in the same spot on every image regardless of filter used -> sensor.

[vlaiv]

1 minute ago, MarcusH said:

If it's in the same spot on every image regardless of filter used -> sensor.

Or flattener / coma corrector (depending on scope type) - or hair caught in adapter thread - or something else ...

Best way to guess where it is would be to calculate likely distance - that will tell you element where it could be. On the other hand - if one is going to disassemble optical train to clear it - does it really matter where it is? Just take apart everything and use blow bulb on optical surfaces and clean everything else with good cloth and cleaning fluid (alcohol).

[Guest]

1 hour ago, Xplode said:

Looks like a hair on the sensor

May not be a hare, but a rabbit?🤔😜  I'll get my coat...

[MarcusH]

40 minutes ago, vlaiv said:

Or flattener / coma corrector (depending on scope type) - or hair caught in adapter thread - or something else ...

Your absolutely right, making assumptions without enough knowledge of used equipment is sketchy at best....

My assumption was the 414Ex paired to a filter wheel and the Imaging Star at F/5.8. Anything beyond the filter wheel would be too much out of focus to be that pronounced in the image.

[vlaiv]

11 minutes ago, MarcusH said:

Your absolutely right, making assumptions without enough knowledge of used equipment is sketchy at best....

My assumption was the 414Ex paired to a filter wheel and the Imaging Star at F/5.8. Anything beyond the filter wheel would be too much out of focus to be that pronounced in the image.

Above formula gives distance to sensor of 1.4mm for F/5.8 system. For F/10 system that distance would be around 2.5mm

Since camera itself has something like 13mm of optical back focus from the front - I doubt it is related to filters:

If desiccant was recently replaced and there was issue with filter - could be the contamination of chamber.

[JamesF]

I'm surprised you didn't plate solve the image to find the exact focal ratio, vlaiv

I've not seen that formula before, and the images from my 314L+ currently appear to have a noticeable dust bunny, so thanks for posting the link.  I shall check it out.  Hopefully if I try to remember it as being "focal length x size of dust image in mm" it might stick in my brain.

James

[vlaiv]

3 minutes ago, JamesF said:

I'm surprised you didn't plate solve the image to find the exact focal ratio, vlaiv

I've not seen that formula before, and the images from my 314L+ currently appear to have a noticeable dust bunny, so thanks for posting the link.  I shall check it out.  Hopefully if I try to remember it as being "focal length x size of dust image in mm" it might stick in my brain.

James

It's really basic math and should be easy to remember - shadow diameter / dust distance = aperture / focal length - same ratio because angles are the same - or even simpler dust distance / shadow diameter = F/ratio. This is of course for very small objects, otherwise it will be approximately this:

(shadow_diameter - object_diameter) / distance = aperture / focal length.

 

[JamesF]

11 minutes ago, vlaiv said:

dust distance / shadow diameter = F/ratio

Now that makes even more sense

James

[iwols]

if i turn my ccd 90 deg and take another image will that tell me if its the ccd or my filter/telescope?

[vlaiv]

5 minutes ago, iwols said:

if i turn my ccd 90 deg and take another image will that tell me if its the ccd or my filter/telescope?

It should - if it stays at the same place with respect to image - it is somewhere in the gear you rotated. If it stays "with the stars" - it is in gear that did not rotate.

[iwols]

only show when pointing in direction of moon,which i usually dont do

Edited February 7, 2020 by iwols

[iwols]

will the dots be dust?

[Davey-T]

1 hour ago, iwols said:

only show when pointing in direction of moon,which i usually dont do

Because the Moon puts more light through them, they should show up on images if you stretch them

1 hour ago, iwols said:

will the dots be dust?

Yes, bunnies and hares, a veritable warren 😂

Dave

[iwols]

Well gave ccd cover a quick wipe and still same will try turning ccd 90 deg tomorrow and see results