Reflections when using MPCC and NB filters?

[RAC]

Ok i've just started using my new Atik 383 mono camera with my skywatcher f5 newtonian so of cause i need to use a coma corrector but have come into a bit of a problem. When using this same setup with lenses right down to f2.8 there is no problems but the problems comes when i try and use my MPCC in the newtonian.

Here are some examples and i think what it shows is some form of relection between the filter and MPCC. The filter is a baader 1.25in 7nm HA.

This is a flat with filter and no MPCC.

This is with no filter and with MPCC.

This is with filter and with MPCC.

Shifting the mpcc away makes it better, moving it close makes it alot worse but thats making other problems so it must stay where it is. Maybe when people shell out trillions for 2in filters they don't think there is a reflection there as they just don't see it?

And why has there not been any first lights of the new Baader mk111 MPCC yet? I see the new one looks to have more anti reflective coatings everywhere. If i could confirm that it would fix my problem i would get one.

I also see a few people on the net with the same problem but i havn't seen a fix for it yet.

Thanks Raymond.

[RAC]

Well baader seem to think i have a camera/filter reflection problem. Its srange that this setup without mpcc on lenses works great from f5.6 - f2.8. Even if the camera was a smaller sensor 460 i would still have the same problem unless the front glass in the 383 is to fault somehow?

[RobinW]

You need to put the info tool over the image. I'm guessing these are from maxim using screen stretch. You need to realise that these images are like an excel spreadsheet, A document full of numbers. If you stretch them on the screen they can look wrong but when you look at the numbers there may only be a few digits difference across the entire image. Use them and see if they work.

[RAC]

I can clearly see this ring when taking lights. Flats dont clear it up well at all.

[RAC]

Baader seem to think there is no other way to use an mpcc other than using 2in filters in front of it. Well thats a pain in the but!

I have some lrgb filters on there way so i hope these will work as they dont have that shiny reflective coating. I can borrow a set of 2in nb filters if i have to. I wont be buying a full set anytime soon.

[RAC]

I downloaded a trial of ccd inspector.

Whats your thougts on this?

This is with an ha filter and no MPCC.

This is with filter and with MPCC.

[RAC]

Well i can thankfully say that this problem does not happen with baader 1.25in LRGB filters. The results are as good as perefect. But is does mean using narrow band with my scope will be a pain in the but untill i can solve this.

I am VERY surprised this problem has not come up on here before. I see a thread on CN forum about the same problem inculding the reflections when using FR's or FF's with narrow band filters but it went nowhere sadly!

[rnobleeddy]

On 04/03/2013 at 05:40, RAC said:

Well i can thankfully say that this problem does not happen with baader 1.25in LRGB filters. The results are as good as perefect. But is does mean using narrow band with my scope will be a pain in the but untill i can solve this.

I am VERY surprised this problem has not come up on here before. I see a thread on CN forum about the same problem inculding the reflections when using FR's or FF's with narrow band filters but it went nowhere sadly!

No idea if you're still here but I've run in to exactly the same problem so wondering if you ever found a solution? 

[tooth_dr]

7 hours ago, rnobleeddy said:

No idea if you're still here but I've run in to exactly the same problem so wondering if you ever found a solution? 

Not much help to you but I use the 383L+ with the MPCC and 1.25” filters at F4.7 and I don’t recall this issue but I’ll check back through my older data from last year to see if it’s present and I didn’t notice. 

[rnobleeddy]

2 hours ago, tooth_dr said:

Not much help to you but I use the 383L+ with the MPCC and 1.25” filters at F4.7 and I don’t recall this issue but I’ll check back through my older data from last year to see if it’s present and I didn’t notice. 

Thanks and sorry, should have been more specific! I'm running in to the strange circle on flats issue that is visible above. Not using a 383 but the same sized sensor, with 36mm unmounted filters 

Based on research it looks like it's probably an issue with the older baader mpcc 2 lacking a reflective coating, but only shows up when using it with narrowband filters.  There's a couple of other threads on the internet that seem to have the same issue, but no resolution. 

 

It's probably easieat if I try to either change the filters or the cc.

[tooth_dr]

25 minutes ago, rnobleeddy said:

Based on research it looks like it's probably an issue with the older baader mpcc 2 lacking a reflective coating

I’m using a Mark I MPCC 

[rnobleeddy]

1 hour ago, tooth_dr said:

I’m using a Mark I MPCC 

Interesting! I can barely find documentation on the mark ii. 

Either way, once the scope is outside I'll refocus without the cc and see if the reflection dissaappears. It's only present on Ha/S filters and calibrated out fine on the Ha data, so presumably could be very setup dependent. 

 

There's a thread on another popular forum where similar kit produced the same odd circle.

The only thing I really have control over is the filter direction - apparently some baader filters are intended to be used in a specific direction and it can be worth flipping them to see if reflections improve.

 

[rnobleeddy]

Just in case any one ends up here in the future - baader state (https://www.baader-planetarium.com/en/filters/filter-sets/baader-full-frame-ccd-narrowband-filterset-i-(h-alpha-7--oiii--sii).html?___SID=U)

Quote

 

We have this in our FAQ:
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.

 

The filters I have do have the directional arrow on them, but with them swapped, the flats still look like this. Albeit they're stretched - the difference is not as big as it looks, but the abrupt nature of the circle does lead to issues processing as whilst this does largely calibrate out, it's not perfect.

 

 

Anyway, mainly to help the next person who has this issue, I have 3 possible things to try next:

- change the CCD to filter spacing - I can do this by a few mm by changing the way the camera mounts to the filterwheel, but I'll need another adapter to get the right backfocus, so I'll try the others first

 

- try changing filter/coma corrector

 

- make a small mask to cover the filter edge - https://www.cloudynights.com/topic/582053-problem-with-narrow-band-filter-reflections/

 

Edit - the paper mask did not fix the issue!

Edited January 20, 2021 by rnobleeddy

[rnobleeddy]

Just so when the next person comes here in a few years time and wonders what happened....

 

I decided that the easiest/most cost effective/most likely to work option was to change coma corrector. Due to covid/brexit, availability wasn't great and I wasn't keen on spending a massive amount of money. I ended up getting a MPCC mark iii as I was happy with the MPCC mark ii in terms it's ability to correct coma. The mark iii is supposed to have better anti-reflective properties but otherwise appears to be similar.

The good news is that the issue is much reduced. The bad news is that because I know to look for it, I think it's still there, just much less intense. Or maybe it's just my eyes. Either way, this almost calibrated out before the change, so I'm not too worried about it impacting the final result now.

Below are side by side comparisons of single flats taken with exactly the same settings, except for swapping coma corrector, keeping the exact same spacing.

Not saying that changing the coma corrector was the only way to fix this - but it has certainly helped.

 

Ha - left mark 3, right mark 2

S - left mark 3, right mark 2

 

[tooth_dr]

On 30/01/2021 at 12:31, rnobleeddy said:

Just so when the next person comes here in a few years time and wonders what happened....

 

I decided that the easiest/most cost effective/most likely to work option was to change coma corrector. Due to covid/brexit, availability wasn't great and I wasn't keen on spending a massive amount of money. I ended up getting a MPCC mark iii as I was happy with the MPCC mark ii in terms it's ability to correct coma. The mark iii is supposed to have better anti-reflective properties but otherwise appears to be similar.

The good news is that the issue is much reduced. The bad news is that because I know to look for it, I think it's still there, just much less intense. Or maybe it's just my eyes. Either way, this almost calibrated out before the change, so I'm not too worried about it impacting the final result now.

Below are side by side comparisons of single flats taken with exactly the same settings, except for swapping coma corrector, keeping the exact same spacing.

Not saying that changing the coma corrector was the only way to fix this - but it has certainly helped.

 

Ha - left mark 3, right mark 2

S - left mark 3, right mark 2

 

That is really interesting. I’m sure your results will help anyone who searches the web 👍🏼👍🏻

[tooth_dr]

@rnobleeddy First night using narrownband with my QHY268, and low and behold, a big bright circle in the middle.  It immediately got me thinking about this thread, so many thanks for coming back and providing your solution.  I havent had a chance to take flats yet as I was only imaging late last night.

Here are my images from last night, 7nm Ha filter, and MPCC (mark i or possibly ii, it's about 12-14 years old, not sure when the mark ii came out)

Integration:

 

Sub: 

 

Sub:

 

 

[rnobleeddy]

7 hours ago, tooth_dr said:

@rnobleeddy First night using narrownband with my QHY268, and low and behold, a big bright circle in the middle.  It immediately got me thinking about this thread, so many thanks for coming back and providing your solution.  I havent had a chance to take flats yet as I was only imaging late last night.

Here are my images from last night, 7nm Ha filter, and MPCC (mark i or possibly ii, it's about 12-14 years old, not sure when the mark ii came out)

Integration:

 

Sub: 

 

Sub:

 

 

 

Looks very similar. Not sure if you're also using a QHY filter wheel, but if so, we have very similar setups¬ I've not seen anything similar show up on any images since I swapped to the mark iii.

 

[tooth_dr]

25 minutes ago, rnobleeddy said:

 

Looks very similar. Not sure if you're also using a QHY filter wheel, but if so, we have very similar setups¬ I've not seen anything similar show up on any images since I swapped to the mark iii.

 

No filterwheel, just a drawer.  Trying to find a new MPCC now 

[tooth_dr]

Not a slightly hazy photo of a blank solar disk but an h- alpha flat with an MPCC 🤪

[tooth_dr]

On 26/02/2013 at 23:14, RAC said:

Well baader seem to think i have a camera/filter reflection problem.

I have been in touch with Baader.  They replied and said they havent see this issue before.  I suspect it's going to be the same answer as you got.

Edited April 29, 2021 by tooth_dr

[Jan S]

I am having the same issue with Baader MPCC mark III. But only with my new QHY294, I believe because of spacer and back focus set to 55mm. I've never had any issues like this on my DSLR with the same corrector. I am thinking to reduce the back focus to 44mm as it was with DSLR.

Do you, guys, have other solutions to get a rid of that? I am using 200/1000 newt, btw.

[tooth_dr]

11 minutes ago, Jan S said:

I am thinking to reduce the back focus to 44mm as it was with DSLR.

I think the back focus would (or least should) have been 55mm with DSLR anyway.   44mm is the distance between the sensor and the flange and then you’d have an adapter to join to the MPCC. What filter where you using?

[Jan S]

43 minutes ago, tooth_dr said:

I think the back focus would (or least should) have been 55mm with DSLR anyway.   44mm is the distance between the sensor and the flange and then you’d have an adapter to join to the MPCC. What filter where you using?

I was getting decent images even with 44mm (including adapter), but without any reflections, so I thought to give it a try. But for sure you are right.

I am using Optolong L-Pro, also used it on DSLR, btw...

[tooth_dr]

11 minutes ago, Jan S said:

I was getting decent images even with 44mm (including adapter), but without any reflections, so I thought to give it a try. But for sure you are right.

I am using Optolong L-Pro, also used it on DSLR, btw...

Hi Jan

Can you drop Baader an email and show them the photo?  I have been in touch with them about the same problem and  I think it would be great if more of us show them the same problem and hopefully get something done.  I am using a 250/1200 newt, so a similar scope.

support@baader-planetarium.de

[Jan S]

2 hours ago, tooth_dr said:

Hi Jan

Can you drop Baader an email and show them the photo?  I have been in touch with them about the same problem and  I think it would be great if more of us show them the same problem and hopefully get something done.  I am using a 250/1200 newt, so a similar scope.

support@baader-planetarium.de

Hi

sure, will write them, let's see what their response gonna be...

Will let you know

Cheers!