sensor tilt (?)

[alacant]

Hi everyone. I'm getting vignetting along one edge of my modified Canon 700d. Here's an Av shot with nothing attached to the camera pointing at an evenly lit white wall. Could I conclude that the vignetting may be caused by a sensor which is not properly square to the light path? Is there anything I -a non optical specialist- I could do to fix it? Attached snap stretched in APT. TIA, Merry Xmas and clear skies.

[cjdawson]

It could be sensor tilt.  It could also be that the sensor is not in central in the optical light path, so the defraction.  There is software that can measure this stuff, not something that I know much about.  I'm sure someone will be along with more information in that regard.

[ollypenrice]

Tilt can have various sources. I wonder, here, if either the lens cell is not directing the light cone down the true axis of the tube or if the focuser body itself, or draw tube, are not parallel with the main tube. Tilt in the chip itself, in a Canon camera, is probably not very likely. If you have any push fit components then be suspeicious of those, first.

If you have an accurate laser collimator you could put it in the draw tube and see where the beam lands on the objective. It should be central. You'd put a circle of translucent paper with a centre dot over the lens to do this.

Olly

[ChrisLX200]

38 minutes ago, alacant said:

Hi everyone. I'm getting vignetting along one edge of my modified Canon 700d. Here's an Av shot with nothing attached to the camera pointing at an evenly lit white wall. Could I conclude that the vignetting may be caused by a sensor which is not properly square to the light path? Is there anything I -a non optical specialist- I could do to fix it? Attached snap stretched in APT. TIA, Merry Xmas and clear skies.

You don't say what scope was used (refractor?) or how the connection was made between camera and focusser (2" push-fit rather than screw fittings?) but I would suggest the camera is sagging under its own weight pulling it off axis. This will be most noticeable with the OTA horizontal pointing at a wall..

ChrisH

[geordie85]

11 minutes ago, ChrisLX200 said:

You don't say what scope was used (refractor?) or how the connection was made between camera and focusser (2" push-fit rather than screw fittings?) but I would suggest the camera is sagging under its own weight pulling it off axis. This will be most noticeable with the OTA horizontal pointing at a wall..

ChrisH

Judging from the original post he didn't have a scope or lens connected. 

 

11 minutes ago, ChrisLX200 said:

Here's an Av shot with nothing attached to the camera pointing at an evenly lit white wall

By the sounds of it, I'd say whoever modified it didn't put the sensor back in perfectly. 

Or could it just be that the wall wasn't evenly illuminated? do you get the same vignetting in your subs?

[alacant]

15 minutes ago, ChrisLX200 said:

how the connection was made between camera and focusser

 

35 minutes ago, ollypenrice said:

either the lens cell is not directing the light cone down the true axis of the tube or if the focuser body itself, or draw tube, are not parallel with the main tube.

Hi everyone. There is no telescope or focuser or lens attached. It is just the camera pointed at a wall. Nothing is attached. TIA.

[Oddsocks]

You can not measure sensor tilt or vignetting with no lens or telescope attached since light is entering the detector chamber from all different angles, you would need to at least attach a standard lens assembly to the camera and then make the vignetting test.

[alacant]

 

16 minutes ago, Oddsocks said:

You can not measure sensor tilt or vignetting with no lens

Hi. The vignetting is the same no matter what is attached. I performed this test as a final can't-blame-it-on what's-attached scenario. Here we are with a lens attached, but it wouldn't matter. It's the same no matter what is attached no matter where or what angle it's pointed, nor where it's focused. TIA.

[ollypenrice]

Sorry, I didn't read the original post correctly. I guess Geordie is probably right, in that case. The chip may not be properly located.

Olly

[Oddsocks]

Looking at the latest image with the lens attached I agree with Ollie and Geordie, the sensor, or possibly the anti aliasing filter, has not been located properly in the camera body.

[alacant]

3 minutes ago, Oddsocks said:

anti aliasing filter, has not been located properly in the camera body

OK, thanks. Is there a quick fix for that for a non-optical-engineer user? Cheers.

[Oddsocks]

30 minutes ago, alacant said:

Is there a quick fix for that for a non-optical-engineer user?

It is not something I would recommend, work around the sensor area needs some experience and, in theory, clean-room working conditions else you risk damaging the sensor.

[Waldemar]

I would send it back to the one who modified it... this should not happen. If this is not a warranty case, please let us know where it was done to prevent future customers getting the same problem.

[Astrosurf]

If you fail with your returning the camera to the one who modded it, contact Juan here. He's excellent.

http://cheapastrophotography.vpweb.co.uk/

Good luck!

Alexxx

[sharkmelley]

I think this methodology for determining sensor tilt is flawed:

Mark

[StuartJPP]

Wouldn't an actual star test indicate the orthogonality of the sensor rather than looking at vignetting?

The raised mirror can cause vignetting and it is something that flats help with.

I have found it nearly impossible to measure flat fieldness myself on the ground as everything has the be perfectly square (and I am useless at it). Pointing towards the heavens is so much easier.