10 replies to this topic

[rj144]

I'm using a Nikon D750 and a Sigma 150-600 mm zoom lens now.  It's all I have for imaging.  I have a fairly nasty ring from reflections.  Since it's a zoom lens, I can't really look internally.  I have put black cardboard paper at the end of the lens that extends about a foot away from the glass.  I also, put a black towel in front of the lens to also make sure most of the lens is blacked out and I still have it fairly bad.

 

Here's an example after it was run through Startools:

 

 

 

You can cleary see the the more fuzzy, greyish area to the left of the Rosette and in the upper corner on the right side.  It's a complete circle if it wasn't cropped.  It makes it a pain to edit and I have to severely clip that area.  It's a huge problem when faint data is in the ring.  

 

This was my edit after:

 

 

I mean I don't think it's that bad considering, but I'm missing data in the final edit.

 

Does anyone have a lens (not telescope) and know how to minimize this when collecting data or any postprocessing tricks?

Edited by rj144, 17 January 2022 - 01:06 AM.

[Tangerman]

I'm no imager, but...have you applied flats?

[rj144]

I'm no imager, but...have you applied flats?

Yup... this image was fully calibrated with 40 darks, 70 bias, and 45 flats.

Edited by rj144, 17 January 2022 - 01:07 AM.

[Tapio]

Could there be moon affacting ?

Maybe just avoid moon too near your targets (or light pollution?)

 

Some Photoshopping (or PI) tricks could be applied but I'm not the person to tell this

[Mike in Rancho]

Presuming it is in fact the moonlight causing ringing reflections, is your black paper shield all the way around or just on the moon side, like the bill of a cap?

 

At times I have fashioned a shield to stop moonlight from angling into the top of a dewshield.  From there it just bounces on in and can cause a number of strange gradients.  So the shield can't just be an extension of the telescope's (or lens) own shield or the same thing can happen when the far side lights up.  Thus, my moon blockers end up more like a half-shield, only blocking the moon side.

[Tapio]

Presuming it is in fact the moonlight causing ringing reflections, is your black paper shield all the way around or just on the moon side, like the bill of a cap?

 

At times I have fashioned a shield to stop moonlight from angling into the top of a dewshield.  From there it just bounces on in and can cause a number of strange gradients.  So the shield can't just be an extension of the telescope's (or lens) own shield or the same thing can happen when the far side lights up.  Thus, my moon blockers end up more like a half-shield, only blocking the moon side.

True this.

And cardboard can be sowhat reflective too.

Best would be some matt paint, or black velvet.

[rj144]

Presuming it is in fact the moonlight causing ringing reflections, is your black paper shield all the way around or just on the moon side, like the bill of a cap?

 

At times I have fashioned a shield to stop moonlight from angling into the top of a dewshield.  From there it just bounces on in and can cause a number of strange gradients.  So the shield can't just be an extension of the telescope's (or lens) own shield or the same thing can happen when the far side lights up.  Thus, my moon blockers end up more like a half-shield, only blocking the moon side.

Thanks... it's not for the moon, it's for other random lights around me.  It is all the way around, but I'll try to make it halfway around.

[Mike in Rancho]

Thanks... it's not for the moon, it's for other random lights around me.  It is all the way around, but I'll try to make it halfway around.

Well, those can make things difficult.  For street level lights I try to use blockers - one is a swing canopy flipped up, and the other a tarp spanning two poles.  I drove some PVC pipe into the ground by a wall so I can just slip the poles right in when I need to image.  The "cap" for the telescopes is just for the moon, because it's coming from so high there's no other way.

 

On your D750 I presume you are using 14-bit RAW with lossless compression chosen?  If you use the lossy compression, say for more manageable file sizes, this might start running into the known ringing problem.

[DivisionByZero]

It's always better to eliminate problems in the data as opposed to post-processing.  I'd +1 the suggestions for better flocking (i.e. velvet).  Given it's a DSLR lens, I think you might be stuck with what you get.  There are so many elements in those things for such a broad spectral range it'd be hard to eliminate all of the internal reflections.

[rj144]

Well, those can make things difficult.  For street level lights I try to use blockers - one is a swing canopy flipped up, and the other a tarp spanning two poles.  I drove some PVC pipe into the ground by a wall so I can just slip the poles right in when I need to image.  The "cap" for the telescopes is just for the moon, because it's coming from so high there's no other way.

 

On your D750 I presume you are using 14-bit RAW with lossless compression chosen?  If you use the lossy compression, say for more manageable file sizes, this might start running into the known ringing problem.

Thanks.  Yes, it's 14 bit RAW.

 

I ordered some velvet to start.  I'm going to put it inside my lens hood to see if that absorbs some photons on the way to the lens.  I'll still use the black construction paper too in order to minimize it some too.  I'll see how that goes.

 

If that doesn't work, I Googled light absorbing material:

 

https://www.edmundop...material/11682/

 

I'll use that somehow as the next step.  But, I'll see how the velvet works first.

 

Thanks guys.

[jonnybravo0311]

Some lenses have light leaks between the lens hood and the lens. Got some old black compression/tube socks you don't mind sacrificing? Cut a ring out of the sock and stretch it over where the lens hood connects to the lens itself. Double or triple it up if you can to try and prevent as much light as possible from getting through. Maybe that'll help? At worst, you've lost a pair of socks .