Bad image

[robindurant]

Can anyone help me, I have a Canon 5dMk2 which is assto modded but cannot obtain a good image using my Samyang 14mm 2.8 lens, I have attached two images which I have processed to accentuate the problem , one stacked DSS and one Sequator , both show the same probem. I have cleaned the Sensor so dont know what that bottom right artefact is. Both images were stacked with Darks and Flats and captured at - 20 x 15 secs iso 3200 f2.8

[michael8554]

Hi Robin

In the second image it looks like a dewdrop that has slid down from top right to bottom right.

So might have been gone when you did your Flats - why don't you post a Flat ?

Michael

[robindurant]

Hi , I have the  dewdrop  on images taken other nights so it cant be that and used flats to no effect

[gajjer]

Just a thought, but might it be on one of your flats? What happens when you stretch without either darks or flats?

cheers

gaj

Edited May 4, 2021 by gajjer

[PeterCPC]

Have you tried to repeat the problem by taking daylight images against a plain background?

[robindurant]

1 hour ago, gajjer said:

Just a thought, but might it be on one of your flats? What happens when you stretch without either darks or flats?

cheers

gaj

Have tried stacking with and without flats and darks, just the same

[michael8554]

If it's not on your Flats, it is on the lens or sensor.

Is your mod Ha or Full Spectrum ?

If Ha, then the #LPF-1  I.R. and Sensor Cleaning filter remains, so you can't clean the sensor, only the filter.

Did you clean with a puffer, or with the Sensor cleaning function ?

As Peter suggested a daytime AV image of a plain background with the stock 18-55mm should eliminate the Samyung.

Michael

 

[robindurant]

2 hours ago, PeterCPC said:

Have you tried to repeat the problem by taking daylight images against a plain background?

Here are 3 images - single shot - 10 second single frame and 10 second stretched on levels and curves trying to detect a problem

[robindurant]

13 minutes ago, michael8554 said:

If it's not on your Flats, it is on the lens or sensor.

Is your mod Ha or Full Spectrum ?

If Ha, then the #LPF-1  I.R. and Sensor Cleaning filter remains, so you can't clean the sensor, only the filter.

Did you clean with a puffer, or with the Sensor cleaning function ?

As Peter suggested a daytime AV image of a plain background with the stock 18-55mm should eliminate the Samyung.

Michael

 

The Mod was just to remove the i/r filter not full spectrum I believe. Ive had this done with other Canons twith no problems . I cleaned with a Sensor Cleaning Swab and after a air blower. I have tested the Samyang on another DSLR and it works fine so its a camera problem

[happy-kat]

Was that a can of air blower or a rubber hand air blower?

 

[robindurant]

20 minutes ago, happy-kat said:

Was that a can of air blower or a rubber hand air blower?

 

Can

 

[robindurant]

Here are 3 images - single shot - grad x treminator to flatten and stretched with levels. it looks lop sided to the left and uneven stars. If I continue a light spot appears in the centre ?

[happy-kat]

33 minutes ago, robindurant said:

Can

I gather cans aren't just air and the can could be the source of your dribble caught in the images.

[ollypenrice]

Sorry, is this right? Your problem blobs have now gone but you're left with vignetting, slightly offset? (Or have I missed a step in the narrative?)

It isn't unusual for vignetting to be slightly off axis. I've never used a setup on which it was perfectly concentric. The best way to examine the vignetting is to take a linear flat (ie unstretched) with the histogram peak between a third and half way to the right and then to measure the ADU on this flat in the corners and the centre. This will tell you the drop-off in illumination from the lens. My Tak FSQ106N with a full frame chip has considerable drop-off (about 19000 in the corners and 23500 in the centre) but it corrects perfectly with flats.

I think it would be very optimistic to expect a lens of such short FL and fast F ratio to deliver anything like even illumination on a 35mm chip, especially bearing in mind that astro images will end up very highly stretched.

Olly

[PeterCPC]

As Olly says, it looks like you have solved the original problem. I have nothing more to add to what Olly has said. Best of luck.

[tomato]

A tiny hair on the sensor can produce a trail on the image that looks like a liquid drop that has run down.