ASI Microlensing

[spillage]

Hi All,

I have just noticed microlensing from my asi 1600 using baader filters. and my ed80 The thing is that images from my 130pds are not showing this effect. Also as my image train has changed I am not sure if this is due to the scope or a spacing issue within the image train or even from the FF. Has anyone noticed a change in microlensing on this camera when switching around gear.

Cheers,

[souls33k3r]

Yeah i noticed that when i changed from WO Star 71 to SW Esprit 100. I must admit, i need to check using my SCT.

[vlaiv]

So far, I've encountered two schools of thought on this issue.

First one is that it depends only on sensor itself and missing AR coating on sensor cover window (not chamber window, that one is AR coated, but protective glass on sensor itself).

I don't believe this to be the case, and I personally think (second school of thought) is that it depends on other optical components of the system - F/ratio of the scope, any reflective elements before sensor in combination with spacing. Your finding collaborates this view.

Try changing spacing of something in your optical train to see if you can lessen or even remove artifacts. FF/FR distance to sensor is fixed, but position of filter can change in relation to those two.

[RolandKol]

or..

as Baader writes on their website,

try to swap filter sides if you use unmounted ones..

Not a really pleasant procedure... but probably worth a try before changing spacings which may result FF spacing related coma.

I guess, you can even flip the mounted ones, but it becomes even more unpleasant procedure as it is quite fiddly to remove a holding ring... Wooden toothpick probably may help...

[spillage]

Thank for all the replies.

Yes I do use 36mm unmounted baader filters so I will check these are fitted correctly but they have not been moved since using the 130pds.  If I get the time I will go back to the 130 and see how the lights look again.  I am sure that I had removed the camera from the filter wheel so maybe I changed the spacing there?

Cheers,

[RolandKol]

130PDS and 80ED are different.

the text below is from Baader web, 

the main explanation is in the section after the magical word "BUT"

 

Answer:

Always put the more reflective side towards the telescope side. To guide you we already put a small arrow on the filter rim, on those filters were the position matters. This arrow indicates which face of the filter should be directed towards the sky (telescope-sided). All cell-mounted filters are already oriented in a way that the most appropriate filter face is facing the sky when the filter would be mounted directly onto the front end of the nosepiece of a camera.
If you mount your filter the other way, any reflected light would have a short way to the camera sensor, resulting in a higher risk of getting some kind of back-reflections inside the camera field. Many sensors have highly reflective areas near to the light sensitive area, also the area with the bonding contacts is sometimes highly reflective.

But: this is true only for instruments without optical elements near to the focal plane. If you have f.e. a coma corrector, field flattener, focal reducer, focal extender (to a lower degree due to concave surface), or in extreme cases a whole lens group for more complex field corrections a few centimeters in front of the filter it could be useful to flip the filter against the rule from above (thus having the arrow pointing away from the telescope). Cause in such cases the likelihood of reflections from the sensor could be lesser then fort- and back- reflections from such glass-surfaces. If in doubt, it helps to make some test images from a star field with bright stars, using the filter in both ways for comparison.

Should you really have some reflections with both positions it can be more effective to add a spacer between filter and camera, eventually shifting the reflection out of the image field. With focal correctors having curved surfaces changing the filter-lens distance could help also.

[spillage]

Thanks @RolandKol I will check these asap. It would also explain why this has happened whilst changing scopes around. It does make it harder to change though if all the filter also need to be flipped.

[RolandKol]

I doubt it will have any effect on 130PDS + ASI1600,

I tried both filter directions and have not noticed any difference (I use SW CC).

[Adam J]

On 27/03/2019 at 12:07, spillage said:

Hi All,

I have just noticed microlensing from my asi 1600 using baader filters. and my ed80 The thing is that images from my 130pds are not showing this effect. Also as my image train has changed I am not sure if this is due to the scope or a spacing issue within the image train or even from the FF. Has anyone noticed a change in microlensing on this camera when switching around gear.

Cheers,

I have often noted in others images that the faster the F-ratio the less micro lensing you see. The 130PDS is F5 the ED80 is F6.25 assuming its the SW doublet we are talking about. However, having said this on bright stars I do still see micro lensing with my 130PDS.