Strange mark only when using a telescope on a digital camera

[tonyowen]

Not strictly 35mm camera and accessories, but the logic of the problem [and its answer] applies to both film and digital cameras – and using the digital camera gives quick results.

I’m connecting a Nikon camera body via an adaptor to a refractor telescope.

I’m getting a curly mark on the image – see looped areas of mark01.

There is no intervening ‘glass’ between the Nikon body and the objective lens of the telescope.

Image mark01 was taken out doors

Using the Nikon

without the telescope and its adaptor ring, but with a Nikon 85mm lens I get the good images without the curly mark – see mark02.

I used a mobile phone to see if anything was visible – mark03 – but to no avail.

I can see no marks on the outside of the 75mm objective lens

When using a webcam with the telescope I get no indication of a curly mark – perhaps that is to do with the receptor size of the webcam??

I’m assuming that the curly mark is dust on the inside of the objector lens unit. But before dismantling that portion of the telescope I thought I’d ask questions.

 

[MattKing]

Are these all digital images? If so, the post belongs in a digital forum, because the imaged hair is quite likely to be related to the camera's interface with the lens.

 

[tonyowen]

okay how do I move it?

 

[MattKing]

I can move it for you, but before I do, have you tried it with a film camera? If it images on film as well, this is as good as any place for it.

 

[tonyowen]

I only have 35 exp film and no chemicals - using digital seemed the ideal and quick way of proving what did not work rather than exposing a roll and finding out that I had missed a combination etc. No real excuse except I wonder if the problem IS NOT CAMERA RELATED - hence my query where it was and my excuse on the first line.
If it does not fit where it is, please move it.
regards

 

[mshchem]

Is there a hair laying on the sensor. Like a eyelash???

 

[MattKing]

Thread moved to a hybrid area.

 

[MattKing]

Is there a hair laying on the sensor. Like a eyelash???

Or possibly in the light path in the camera body?

 

[tonyowen]

Thread moved to a hybrid area.

Where is the hybrid area? - cannot find it?
regards

Or possibly in the light path in the camera body?

If so why does it not show up when using the 85mm lens [mark02]

 

[MattKing]

It is in the Misc. Hybrid Discussions sub-forum at the bottom of the section seen here:
https://www.photrio.com/forum/#hybrid-workflow-forums.387
Do you have Hybrid ticked at the top of the page here?

As for why the hair doesn't show up with the 85mm lens, perhaps it relates to where the nodal points are with respect to the two different choices - 85mm vs. telescope.

 

[tonyowen]

It is in the Misc. Hybrid Discussions sub-forum at the bottom of the section seen here:
https://www.photrio.com/forum/#hybrid-workflow-forums.387
Do you have Hybrid ticked at the top of the page here?
View attachment 285707
Had not but have now and can see the 'forum'
regards

 

[tonyowen]

'Fired' the camera twice without a lens. Used ps to 'explore' the image - nothing untoward.
I would have thought an eyelash or dust on the sensor would have been thus revealed
regards

 

[MattKing]

Right on the sensor (or actually the protective screen in front) - yes.
But forward of that? That is where the nodal points of the lenses come into play.

 

[tonyowen]

Right on the sensor (or actually the protective screen in front) - yes.
But forward of that? That is where the nodal points of the lenses come into play.

The part that is revealed once the mirror lifts.
Not certain what you mean by 'forward of that'
Are you suggesting a long exposure and 'blasting' with an 'air brush' in the exposed volume'- but away from the mirror when it returns - to see if the eye-lash/debris moves?
regards

 

[Mr Bill]

'Fired' the camera twice without a lens. Used ps to 'explore' the image - nothing untoward.
I would have thought an eyelash or dust on the sensor would have been thus revealed
regards

Probably not, unless you used a very "small" light source. This is because most DSLR-type cameras have a filter package sitting on top of the sensor; it holds dust particles a bit of a distance away from the sensor. So to "see" sensor dust you need a light "source" that appears small to the sensor, such as f/16 on a lens. Or, with lens removed, perhaps a single light bulb from 5 or 10 feet away.. This gives a crisp shadow of the dust particle on the sensor.

Regarding your telescope adapter, are you using the telescope eyepiece? If so, that's probably where the curly dust particle is. Eyepieces generally use (internally) a so-called field lens (or a rough equivalent) to give you a wider field of view. So if the dust particle is sitting on the field lens there's a good likelihood it will appear in the camera image.

 

[tonyowen]

Probably not, unless you used a very "small" light source. This is because most DSLR-type cameras have a filter package sitting on top of the sensor; it holds dust particles a bit of a distance away from the sensor. So to "see" sensor dust you need a light "source" that appears small to the sensor, such as f/16 on a lens. Or, with lens removed, perhaps a single light bulb from 5 or 10 feet away.. This gives a crisp shadow of the dust particle on the sensor.

Regarding your telescope adapter, are you using the telescope eyepiece? If so, that's probably where the curly dust particle is. Eyepieces generally use (internally) a so-called field lens (or a rough equivalent) to give you a wider field of view. So if the dust particle is sitting on the field lens there's a good likelihood it will appear in the camera image.

Will try single light bulb.
No eyepiece fitted - the camera fit directly into the focusing tube
Otherwise I need to remove the objective lens assembly from the telescope to see if the dust particle is on the inside face.
regards

 

[tonyowen]

SOLVED - I hope.
Used Nikon's cleaning low-pass filter routine - a lot of specks on it.
Used blower several times - no visible change BUT when using the telescope there was no curly bit shown!
So, hopefully all sorted - thanks for input
regards

 

[AgX]

Not solved fopr me...

Why did the artefact only appear with that telescope? Or with other words, why was it dependant on angle of incidence? I mean, other lenses also got rays entering rather perperndicular. Was there the effect overwhelmed by the more angled rays??

 

[Nodda Duma]

Telescopes have big volumes of empty space that can trap dust and lint which falls down onto the sensor. It’s not unheard of in the astrophotography world to have this happen.

 

[tonyowen]

Not solved fopr me...

Why did the artefact only appear with that telescope? Or with other words, why was it dependant on angle of incidence? I mean, other lenses also got rays entering rather perperndicular. Was there the effect overwhelmed by the more angled rays??

Only telescope I have.
The suggestions made abut dust, debris, crap on sensor made sense and blowing air on the sensor gave an image without the curly artefact. Ergo, it might not be the primary cause, but the artefact has 'gone' when using the Nikon body plus adaptor plus refractor telescope without eyepiece. When the Nikon body is used with an 85mm Nikon lens no artefact is seen.

 

[tonyowen]

Telescopes have big volumes of empty space that can trap dust and lint which falls down onto the sensor. It’s not unheard of in the astrophotography world to have this happen.

Agreed,
but this telescope is only used in horizontal or slightly inclined attitude.
Also the artefact could have come from another source prior to me using it on the telescope as the Nikon body was purchased second {??] hand

 

[MattKing]

It is at times like this that I like to drive my digitally shooting friends crazy by telling them that with most of my cameras, I use a fresh, new and clean "sensor" with every shot!

 

[tonyowen]

Matt
I'm not certain if that is a touché towards me or a fact of life.
But I have learnt a lot, which is the purpose of this and similar sites
many thanks for the help given me
regards
Tony

 

[MattKing]

Matt
I'm not certain if that is a touché towards me or a fact of life.
But I have learnt a lot, which is the purpose of this and similar sites
many thanks for the help given me
regards
Tony

Neither.
I just like to tease some of those friends, who are often former film photographers who like to evangelize about the joys of digital! Particularly when they start having detailed discussions about screen cleaning methods.
I'm glad that we were able to help. I too have learned from this thread, because although I have some knowledge about the optics issues, I have very little experience with telescopes.