Rokinon 135mm Lens issue

Hello,

In order to rule out light leakage you could put the lens cap on and do a long exposure light frame while pointing some lights at the image train from different angles. But make sure no light is entering from the front as the lens cap does not seal the lens perfectly. If you happen to notice that light is infact leaking try to narrow down from where it is coming. 

Does this occur on the individual light frames as well? Try stacking without flat frames and see if this issue also comes up. If not this might be a problem with the flat frames. This has actually happened to me once using the Samyang and by simply retaking the flat frames the issue was resolved. (I never figured out why the first batch of flat frames was bad).

Good luck!

Hi Alan,

Thanks, and I also seem to see an octagonal shape as well.  The blades were where I kind of thought of right away.  Lens was new back in October.  I can trying changing the F stop up and down to see if anything changes or not.  Thanks for the input on this, and I'm hoping to get it figured out.  It is pretty much impossible to see it when a single sub is finished even when stretched.  The stars have to be removed to find it, and obviously the more images that sack the more it becomes obvious. 

Chris.

The F-stop remained the same for flats, and I re-took some sky-flats even to try something different than the flat master flats.   So I'm still scratching my head on it if it is flats not doing their job or something else.

It appears to be in individual frames after a very heavy stretch.  I have stacked without flats and that didn't seem to change the outcome.  I have also re-taken new flats from both a flatmaster and sky flats and that also did not remove it.

Chris.

What does a heavy stretch of your flats look like?  Or the master flat?  In theory it should not be there since it fails to remove the ring, but if it was inherent to your setup, then it really ought to be seen in the flats.  

If you can't see any sign of it in the flats, then that might be a tool to help solve the mystery.  

Dumb question, but I assume you did not move focus before taking your flats?

Also, try taking an image during daytime of some rather bland object to see if is seen then.  Say the side of a bland cloud. It kind of a flat, but.  

During a daylight image session, wile you have live frames coming in to you computer monitor the image as you rack the focuser in and out.  Try at different f-stops and see if you can reproduce the effect.  Shoot a distant bland wall.  If you can see anything, then try to see if you can block them to find where they are.

Alan Brunelle:
What does a heavy stretch of your flats look like? Or the master flat? In theory it should not be there since it fails to remove the ring, but if it was inherent to your setup, then it really ought to be seen in the flats.

If you can't see any sign of it in the flats, then that might be a tool to help solve the mystery.

Dumb question, but I assume you did not move focus before taking your flats?

I can't see it in the flats from what I can tell.  The focus point remained the same as where the last autofocus point would have been during the lights.

Chris Parfett:

Alan Brunelle:
What does a heavy stretch of your flats look like? Or the master flat? In theory it should not be there since it fails to remove the ring, but if it was inherent to your setup, then it really ought to be seen in the flats.

If you can't see any sign of it in the flats, then that might be a tool to help solve the mystery.

Dumb question, but I assume you did not move focus before taking your flats?

I can't see it in the flats from what I can tell.  The focus point remained the same as where the last autofocus point would have been during the lights.

Ok.  I think what @andrea tasselli said is spot on.  But the question remains as to what is illuminating that.  It may be poor blackening or light leakage, but you would think that you would see it in the sort of flats you have done.  Stop down all the way and look in the front and back of your lens.  It should be obvious if the blades are not blackened.  Also in a dark room, blast a bright LED light at the outside of the lens near the f-stops ring and all the joints down there and between the camera.  Shield your eyes from the external light.  Leave only the camera off and look into the back to see if light is getting through. 

If you cannot immediately resolve this and cannot return the lens, then I would not use the built-in f-stop.  Get an aperture stop down ring and use that.  In any case, you should quickly learn what your typical f-stop setting is and that should not change. Buying an aperture stop-down ring at that f-stop and using it should be the preferable way to image anyway.  Unless you like the multipoint diffraction spikes on your stars.  

I'm afraid I have not helped you and not sure I have anything more I can add.

@Alan Brunelle ​​@andrea tasselli 

After some further investigation the ZWO lens adapter does have an exposed aluminum flange that does face the camera sensor.  Could this possible be the problem that is maybe causing an internal refection?

I did run a fairly bright flashlight at the joints and couldn't see anything that made it through.  I'm going to paint that up and re-test.  The pictures are not the best to show the full aluminum ring edge, but it does have a similar shape to the artifact in the image.

HI Cesar,

Thanks for the reply.  The closest artificial light is about 500 yards +/- away.  When I was shooting the M81 area just recently with no moon, the lens was pointing directly away from the closest light.  I'm in a rural area with no ultra close neighbours and zero street lights.   The ability for me at this time of the year to travel to a dark location isn't ideal until the spring.

Observatório Astrográfico do Boqueirão:
I think you’re using heating bands also, right?
Im saying that because, dew can be also the culprit.

I am using a dew heating strap, and I check the lens after every run when it comes back to home for any sign of dew before I cap it.  I also use the anti dew feature of the camera as well.  I attempted to run a bright flashlight around the joints of the drawer and couldn't detect any light getting in, but wrapping it could be another step to figure things out.

Hi there!


Let me start by introducing myself. My name is OSC Neon Palette, and I use a Nikon D5600 as an amateur astrophotographer from Panama. I'm sorry to everyone for my writing; I'm not native to English .


This reply to @Chris Parfett. I recently encountered internal reflections with my Sigma 70-300mm f/4.0-5.6 APO DG Macro Lens for Nikon, however the circumstances were different. I've been using this lens for more than two years without experiencing any issues, thus this issue drove me insane (i.e., an unprocessed photo between 2023 and 2024). The biggest distinction is that, in 2024, I relocated from the rural Bortle 4 area to a Bortle 7 city.
Initially, I thought it might be my filter (Baader Neodymium Moon & Skyglow 2") or my adapter. However, I obtained the same result with and without the filter. I even tried using another Optolong L-Quad Quadband filter and borrowed an SVBony Duo-Band OSC from a colleague, but the result remained unchanged. I also considered the possibility of flat frames; I stacked images with flat frames (using panel, sky, and manual) and without flat frames, but unfortunately, the result was the same.After reading various posts and responses from other colleagues, I realized that lenses for DSLRs struggle to capture optimal photos at F8 or lower in Bortle 7 conditions. I conducted various tests with many exposure (i.e., 30, 60, 120, 180, 240, 300) in different scenarios with both full moon and new moon phases. Another issue I encountered was that, currently, I can only capture photos from my balcony starting at 40 degrees elevation. To test this theory, I took a comparison shot at F11 versus F8 (both at ISO 800, 40 degrees elevation, 300mm focal length, without filters, and without calibration), and this resolved the issue. I experimented with different focal lengths (70, 100, 135, 200, 250, 300), and F11 consistently produced optimal results.
On another hand, I had around 2 hours of data with this issue, but yesterday Pixinsight released a new version with gradient correction, as neither DBE or GrapXert could resolve the aggressive gradient and donuts. After conducting various tests with my data, this issue was resolved using this new feature.


I used the following settings: everything in default, except High Threshold set to 0.40, Scale set to 2.20, Smoothness set to 0.12 with automatic convergence, and Structure Protection disabled for this issue and data.



I hope this response can help others who are experiencing or have experienced the same issue with their DSLRs. Everyone can take this response to perform different tests or improve the English wording . It doesn't bother me at all.

Clear Skies,

OSC Neon Palette:
I hope this response can help others who are experiencing or have experienced the same issue with their DSLRs. Everyone can take this response to perform different tests or improve the English wording . It doesn't bother me at all.

Hi OSC, thanks for the detailed write up!

Nice results from the new PI process on your data.  I have also used it with a few different settings and it is not able to remove the artifact.  I will continue to use the new process with different setting, but initially it doesn't look like this will be able to be removed. 

Chris.