The second lens in my triplet has some spots and a smudge on it. Guessing it's risky and not common to correct?

[Trippelforge]

Title kind of says it all but I have been trying to eliminate some dust spots in my chain, and an "odd" area showing up in my photos. So I went ahead and bought a kit and cleaned the sensor, then took some test shots. They were gone from my DSLR, but then when I hooked it up to my scope and took some shots I still had specks. So carefully cleaned the main lens following some directions online and those went away. However I still had a few left and on my images notice a consistent "smudge" in one area. So I shined a light through the scope and inspected things closer. Turns out the second lens also has some spots on it and an actual smudge.....

Ugh.

I am going to assume this happens due to moisture build up over time? It's a newer thing I have noticed and had the scope out in some very large swings in temperatures. Is this something that just "happens" or is something broke, like a seal or something?

Anyhow is there anyway to fix it, or do I just ignore and and try to clear things up in post-processing? 

[AstroKeith]

It's very unlikely that a smudge on the objective will produce a resolvable smudge on the focal plane. What ever is producing the smudge needs to be close to the image plane (sensor), or the object plane (infinity).

One way of imagining how the optics work is, each pixel in your sensor, receives photons that have been through every part of the objective. So any defect in the object is effectively shared over all the sensor  pixels evenly. Hence dirt on theobjective will produce a loss of overall image contrast or blurring, but over the whole image

[Trippelforge]

17 hours ago, AstroKeith said:

It's very unlikely that a smudge on the objective will produce a resolvable smudge on the focal plane. What ever is producing the smudge needs to be close to the image plane (sensor), or the object plane (infinity).

One way of imagining how the optics work is, each pixel in your sensor, receives photons that have been through every part of the objective. So any defect in the object is effectively shared over all the sensor  pixels evenly. Hence dirt on theobjective will produce a loss of overall image contrast or blurring, but over the whole image

Where ever it is coming from is causing me to crop more than I would like. I wonder if there is something wrong with the sensor itself in one area? Could that cause the aberration / smudge, whatever it is? It sensor looks spotless, and nothing shows up when taking flats. Would any sensor damage show up on those? Although a secondary question would be if could the filter have an issue (defect) that wouldn't pick up anything on flats, but might only be in the Ha band?

I mean it is what it is... I did assume objective wise there was nothing really I SHOULD be doing. But it's good to hear that the scope itself wouldn't be contributing to the problem.

Side question; is buildup of random stuff over time in doublets / triplets normal? I wasn't sure if they were supposed to be vac sealed between them. Or if it's inevitable that things like dew form..

Thanks for the help, I appreciate it! 

 

[AstroKeith]

Some images showing the effect might help. 'Smudge' is rather open to interpretation!

Stray light might be the cause? Either coming in a gap, or in the objective (ie the moon or mars etc). Flats are less likely to show most issues. Darks maybe!

It's not usual to see a noticeable build up of stuff inside a doublet or triplet cell. It's not vacuum sealed, but the lenses are held on seats by rings and there isn't really anyway for dust to get past

Fluids can thought. Rain, really bad dew or too much cleaning fluid have been known to get inside. Usually that leaves a fairly obvious residue that 'runs' in from one side.

[Jim L]

You can rotate the camera to see what effect that has on the location of the defect.  If the defect follows the orientation of the camera, the problem is with the camera.  Same with the filter and anything else in your optical system.

Many spotting scopes are sealed, Astro telescopes are not.  Dew and accumulating dust and other debris is inevitable, but you can take steps to minimize their effect.  Dew heaters help, as does keeping the objective caped when not in use and blowing it off after use.  Good luck!

[Trippelforge]

1 minute ago, Jim L said:

You can rotate the camera to see what effect that has on the location of the defect.  If the defect follows the orientation of the camera, the problem is with the camera.  Same with the filter and anything else in your optical system.

Many spotting scopes are sealed, Astro telescopes are not.  Dew and accumulating dust and other debris is inevitable, but you can take steps to minimize their effect.  Dew heaters help, as does keeping the objective caped when not in use and blowing it off after use.  Good luck!

That's a very good suggestion and something I should have thought about... I have a tendency to put the DSLR in the exact same position each time. If it shows up in the same area I will have to share some images... I really hope it's not a defect in the sensor or filter.. I bought this camera used. 

[900SL]

If it's a DSLR you can easily clean the sensor. My D610 looked bad after a few years in Saudi, but an air blower and sensor swab brought it back to perfect

[Adam J]

On 07/02/2023 at 20:52, Trippelforge said:

Title kind of says it all but I have been trying to eliminate some dust spots in my chain, and an "odd" area showing up in my photos. So I went ahead and bought a kit and cleaned the sensor, then took some test shots. They were gone from my DSLR, but then when I hooked it up to my scope and took some shots I still had specks. So carefully cleaned the main lens following some directions online and those went away. However I still had a few left and on my images notice a consistent "smudge" in one area. So I shined a light through the scope and inspected things closer. Turns out the second lens also has some spots on it and an actual smudge.....

Ugh.

I am going to assume this happens due to moisture build up over time? It's a newer thing I have noticed and had the scope out in some very large swings in temperatures. Is this something that just "happens" or is something broke, like a seal or something?

Anyhow is there anyway to fix it, or do I just ignore and and try to clear things up in post-processing? 

Anything on the images will not be from the objective lens those are simply too far from focus to ever show up. Any problems you are seeing on flats are from the the corrector backwards. 

But the most likely location is from the sensor itself. 

If you can post a flat frame and let me know the F-ratio of the scope I can actually work out were they are located mathematically. 

Adam

 

[900SL]

I had to do the sensor swab twice. The first time it left some un-noticable streaks on ther sensor, but when I stretched the next set of images they were clearly evident

 

I did it twice the next time, once with cleaning solution and a second swab with a clean dry swab 

[Trippelforge]

4 hours ago, 900SL said:

If it's a DSLR you can easily clean the sensor. My D610 looked bad after a few years in Saudi, but an air blower and sensor swab brought it back to perfect

I had purchased a kit and did what you mentioned. I noticed some hairs on it, and a few spots that looked like the original owner tried to blow it off (via mouth). The hairs also looked like the ones on those brushes. I was able to clean it up and don't notice anything when shooting flats now. I was SUPER careful, so I don't think I did anything bad too it. However I am curious if filters can ever just be defective? It is Ha modified and this spot seems like it could be related to acquisition (no idea though). Visually it looks perfect. 

1 hour ago, Adam J said:

Anything on the images will not be from the objective lens those are simply too far from focus to ever show up. Any problems you are seeing on flats are from the the corrector backwards. 

But the most likely location is from the sensor itself. 

If you can post a flat frame and let me know the F-ratio of the scope I can actually work out were they are located mathematically. 

Adam

 

I carefully cleaned the sensor and was able to remove many of the spots and seemingly some hairs. I guess the original owner "brushed" the sensor with one of those brushes. It looks perfectly clean now and when I do shoot flats now nothing shows up. When I shoot images I do notice a few spots that I have to crop out though. That's why I assumed it was the lenses. I will for sure snap some, and also share a photo with the problem areas. I am going to be out shooting tonight. 

Thanks for the help, oh and the f-ratio is 7.

[Trippelforge]

2 minutes ago, 900SL said:

I had to do the sensor swab twice. The first time it left some un-noticable streaks on ther sensor, but when I stretched the next set of images they were clearly evident

 

I did it twice the next time, once with cleaning solution and a second swab with a clean dry swab 

Sorry this popped up as I was typing. I only swabbed a few times and did not use a dry one after so maybe that is part of the problem. I will try it again tonight, thanks for the suggestion!

[900SL]

Could well be the H mod, was a replacement sensor glass fitted?

 

[Trippelforge]

43 minutes ago, 900SL said:

Could well be the H mod, was a replacement sensor glass fitted?

 

I am not sure actually, I can shoot the seller over a message. It was done by life pixel, so I don't know if that's standard for them or not. He did share some images and they look good, but of course I can crop it out so who knows. I am going to be shooting tonight, is there anything special I should do to try and check that?