Solving "Blue Bloat" at source.

[DaveS]

My widefield imaging train is afflicted with Blue Bloat. I was using my 180mm f/3.4 Leitz Apo-Telyt-R on a SA with ASI 183 MM and Baader LRGB filters (An early version with quite a deep blue cut off). Last week I was at the Notgrove astro meet and was imaging M31, just an hour in each channel (Not enough, I know)

The result is below.

This isn't the first version, I have been through all kinds of evolutions but none are any better than this unfortunately

Therefore I was thinking of solving the problem at source.

My options appear to be

1) A more modern apo 'scope. The closest is one of the Borg 55FL f/3.6 versions. I have also considered the Tak 60 with reducer, which comes in at a similar price when everything is added up. There are also a couple of Askar offerings of unknown quality.

2) Move to an OSC camera, whose colour response will be closest to the colour film the lens was computed for. A couple of options come to mind, the colour version of the 183, or the ASI 533, just a little concerned about the sampling with such large pixels relative to the FL of the lens. Keep the 183 mono for NB.

3) A different set of filters, with a blue cut-off that isn't so extreme. The Astronomik Deep-Sky set with the L3 IR / UV cut filter might be a possibility.

 

Does anyone have any thoughts on the above? Any other suggestions?

[AstronomyUkraine]

40 minutes ago, DaveS said:

My widefield imaging train is afflicted with Blue Bloat. I was using my 180mm f/3.4 Leitz Apo-Telyt-R on a SA with ASI 183 MM and Baader LRGB filters (An early version with quite a deep blue cut off). Last week I was at the Notgrove astro meet and was imaging M31, just an hour in each channel (Not enough, I know)

The result is below.

This isn't the first version, I have been through all kinds of evolutions but none are any better than this unfortunately

Therefore I was thinking of solving the problem at source.

My options appear to be

1) A more modern apo 'scope. The closest is one of the Borg 55FL f/3.6 versions. I have also considered the Tak 60 with reducer, which comes in at a similar price when everything is added up. There are also a couple of Askar offerings of unknown quality.

2) Move to an OSC camera, whose colour response will be closest to the colour film the lens was computed for. A couple of options come to mind, the colour version of the 183, or the ASI 533, just a little concerned about the sampling with such large pixels relative to the FL of the lens. Keep the 183 mono for NB.

3) A different set of filters, with a blue cut-off that isn't so extreme. The Astronomik Deep-Sky set with the L3 IR / UV cut filter might be a possibility.

 

Does anyone have any thoughts on the above? Any other suggestions?

Looking closely at the blue stars, it looks like you have a collimation or flattener problem. The blue on the r/h stars is on the left, and the blue on the l/h stars is on the right.

[DaveS]

No flattener needed. Possible play in the mounting.

 

Remember, this is a Leitz lens that was designed to be diffraction limited wide open, for scientific use.

[AstronomyUkraine]

10 minutes ago, DaveS said:

No flattener needed. Possible play in the mounting.

 

Remember, this is a Leitz lens that was designed to be diffraction limited wide open, for scientific use.

I would be tempted to go for a new apo. The Borg with the Esatto motorized focuser looks a great deal at 2500 Euro.

[DaveS]

That is a heck of a lot more than I want to spend.

[MarkAR]

See if you can borrow another filter or have a look at the ASKAR offerings, they appear to be really good.

[DaveS]

Will probably get a set of Astronomik RGB filters plus a L3 and H-alpha.