OIII filter problem/query

[Z3roCool]

Hi all, I currently have a 1600MM which I use with an adapter for my Canon 400mm lens (5.6). I get great images in Ha and SII using the standard 1.25" ZWO filters that come with the 1600MM package.

I have noticed that OIII data is always bloated and looks out of focus. I have double checked focus with a Bhatinov Mask and nailed it but still the images are bloated looking.

Is this a known issue with OIII filters, should I get a narrower filter Baader 4.5nm etc? Want to make sure it will help before spending £200 on a filter. It is really holding back my NB imaging as currently feel I can only use Ha and SII.

Many thanks for any input.

Tommy.

[dodgerroger]

Yes I think they can give bloated stars, what make of filter are you using? 

[Z3roCool]

2 hours ago, dodgerroger said:

Yes I think they can give bloated stars, what make of filter are you using? 

Hi there, it is the ZWO filter Standard one that comes with the bundle. Was looking at the Baader 4.5 Ultra filter. Cannot push to a Chroma or Astrodon

[Adam J]

27 minutes ago, Z3roCool said:

Hi there, it is the ZWO filter Standard one that comes with the bundle. Was looking at the Baader 4.5 Ultra filter. Cannot push to a Chroma or Astrodon

I really think you need to post an example of each channel, unprocessed equal stretch. The tendency is to stretch oiii data more as it's weaker resulting in larger stars. 

[Z3roCool]

13 hours ago, Adam J said:

I really think you need to post an example of each channel, unprocessed equal stretch. The tendency is to stretch oiii data more as it's weaker resulting in larger stars. 

Hi there, here you go. I have stacked both Ha & OIII with same amount of sub time. Added Ha & OIII with moderate stretch and then the same in Ha. I think you may have a good point with the stretch causing the problem. Think the stars are larger in OIII even in the moderate stretch but not as much as I was seeing. Think I may have been stretching too much. Still wonder how much the Canon camera lens (400mm 5.6L) may be not helping.

Ha (Moderate)

OIII (Moderate)

Ha (Pushed)

OIII (Pushed)

 

Cheers Tommy.

 

 

 

[Tommohawk]

Be aware there are 2 versions of zwo NB filters. The later version is better.

https://astronomy-imaging-camera.com/product/zwo-new-narrowband-31mm-filter

Shows difference. 

Edited November 26, 2020 by Tommohawk

[Z3roCool]

41 minutes ago, Tommohawk said:

Be aware there are 2 versions of zwo NB filters. The later version is better.

https://astronomy-imaging-camera.com/product/zwo-new-narrowband-31mm-filter

Shows difference. 

Very interesting! Will have to check which mine are. Got a feeling they are the new ones. Thanks for info

[Adam J]

14 hours ago, Z3roCool said:

Very interesting! Will have to check which mine are. Got a feeling they are the new ones. Thanks for info

If within the last two years they are likely the new ones. I think it's probably just your lense though now the filters. I think you need to get a telescope if you want good stars.