35 replies to this topic

[melodasi]

Hi,

 

I am struggling to capture some nebulosity from the Pleiades using my Rasa 8, ASI533 and a light pollution filter.

My last session I had about 700 lights of 60 seconds but I barely see any nebulosity after stacking and stretching.

Any advice?

 

Marcelo

[matt_astro_tx]

Can you post the image?  With 11.6 hours of data from an F/2 system are you sure the image wasn't just totally clipped with saturation?  

[sbharrat]

Hi,

 

I am struggling to capture some nebulosity from the Pleiades using my Rasa 8, ASI533 and a light pollution filter.

My last session I had about 700 lights of 60 seconds but I barely see any nebulosity after stacking and stretching.

Any advice?

 

Marcelo

Maybe the light pollution filter? bobzeq has his favorite RASA picture of M45 but I believe his is with just UV/IR and with 10s exposures.

[Jim Waters]

Need more info.  How much light pollution?  What type of filter?  Where was the histogram on your images?  What were you using for image acquisition and processing?

 

Bortle 8 site without a light pollution filter.

https://flic.kr/p/2k9R6M7

 

 

Post an image...

[gcardona]

I've used an IDAS LPS-V4 with good effect on the Pleiades from my bortle 9 back yard and my Hyperstar (F/2). The LPS-V4 has a similar response to the Optlong L-enhace. You need to make sure your filter passes the blue-ish band between 460-600nm or so.

[bobzeq25]

Maybe the light pollution filter? bobzeq has his favorite RASA picture of M45 but I believe his is with just UV/IR and with 10s exposures.

Well, the light pollution filter certainly hurts significantly, not helps.   You're correct that I didn't use one, on a reflection nebula (broadband source) they make no sense.  These so-called "light pollution" filters don't magically filter out light pollution, they just whack out chunks of the spectrum.  That doesn't work well on broadband targets, it does on narrowband sources, mostly emission nebulae.  I often use one for those.

 

But, _no_ nebulae seen?  That too does not make any sense.  60 second exposures are very long for a RASA.  My M45 (below) was 665X10 (ten) seconds (Bortle 7).

 

My recommendations to the OP, both are important.  Give us more information about the setup.  Exactly what filter?  Upload the unstretched stack (not the subs) to something like Dropbox, and let people here look at it.  It's hard to say what's wrong without the data.  I suspect it's something pretty major.

 

Edited by bobzeq25, 29 November 2021 - 12:26 PM.

[melodasi]

Thanks guys for all the response.

Here is the quick stretched file.

The filter I used was the Orion  SkyGlow Ultrablock.

 

Here is the stacked file.

 

https://drive.google...iew?usp=sharing

Attached Thumbnails

• 

Edited by melodasi, 29 November 2021 - 01:33 PM.

[melodasi]

Can you post the image?  With 11.6 hours of data from an F/2 system are you sure the image wasn't just totally clipped with saturation?  

Maybe

[melodasi]

Need more info.  How much light pollution?  What type of filter?  Where was the histogram on your images?  What were you using for image acquisition and processing?

 

Bortle 8 site without a light pollution filter.

https://flic.kr/p/2k9R6M7

 

 

Post an image...

I live in a Bortle 5 zone, so I guess not a lot of light pollution, Image acquisition SGPro and processing with Photoshop.

Yep great picture in the link

Edited by melodasi, 29 November 2021 - 01:39 PM.

[pedxing]

I think that filter is designed for visual, not AP - you're getting some crazy reflections from it.

 

I would remove the filter and deal with the LP some other way.

[melodasi]

I think that filter is designed for visual, not AP - you're getting some crazy reflections from it.

 

I would remove the filter and deal with the LP some other way.

Yeah, I am just looking at some marketing paper about the filter and it doesn´t mention astrophotography.

[Aquawind]

As a rookie I have had a couple of sessions with useless results. Now I always watch the images and even stretch sometimes to make sure my data is usable. It also let's me scrutinize and delete some files to avoid corruption. It really saves time in the long run. I am fortunate that I can do it remotely. I had good luck last weekend with the ZWO UV/IR cut filter only. My second night using the filter and first reflective nebulae. Next time it will be without the filter. Constant experimentation. 

[HubSky]

Looking at the transmission graph for the Orion Ultrablock, it is primarily an Oiii filter with about a 30-50nM bandpass (hard to tell) and the description for it says "increases contrast of emission and planetary nebulas".  So it will not work well with a reflection nebula such as M45. 

[bobzeq25]

Thanks for the stack, cleared up questions I had.

 

Really bad filter for this.

 

You desperately need flats, and bias, necessary for flats to work well.  Math.

 

When you shoot without a filter, you'll need very short exposure to somewhat reduce blowing out the bright stars.

 

The principal tool to use to reduce the effects of light pollution (especially on broadband targets) is gradient reduction in processing.  Astro Pixel Processor has an excellent tool.  I highly recommend it.

 

Duo or triband filters work well on emission nebulae.  Only.  The Celestron LP filter for the RASA works some on emission nebulae, but is nowhere near as good as this.

 

https://astrohutech....t/idas-nbz-uhs/

 

Edited by bobzeq25, 29 November 2021 - 02:26 PM.

[jonnybravo0311]

First: lose the filter. It is absolutely killing your subs.

Second: take and use calibration frames (flats, darks, biases)

 

As Bob showed in his edit, there's definitely some nebulosity hiding in your data, but the filter is absolutely destroying it. Take it out... use it for anything OTHER than astrophotography going forward

[17.5Dob]

The filter I used was the Orion  SkyGlow Ultrablock.

That is a visual filter strictly to isolate the Oiii line. It's useless as an LP filter.

[melodasi]

Looking at the transmission graph for the Orion Ultrablock, it is primarily an Oiii filter with about a 30-50nM bandpass (hard to tell) and the description for it says "increases contrast of emission and planetary nebulas".  So it will not work well with a reflection nebula such as M45. 

Thanks. Yep luckily this filter came together with some user gear I bought in the past and I assumed wrongly how to use it.

[melodasi]

First: lose the filter. It is absolutely killing your subs.

Second: take and use calibration frames (flats, darks, biases)

 

As Bob showed in his edit, there's definitely some nebulosity hiding in your data, but the filter is absolutely destroying it. Take it out... use it for anything OTHER than astrophotography going forward

Hehe, yep you are right. Thanks.

[melodasi]

Thanks for the stack, cleared up questions I had.

 

Really bad filter for this.

 

You desperately need flats, and bias, necessary for flats to work well.  Math.

 

When you shoot without a filter, you'll need very short exposure to somewhat reduce blowing out the bright stars.

 

The principal tool to use to reduce the effects of light pollution (especially on broadband targets) is gradient reduction in processing.  Astro Pixel Processor has an excellent tool.  I highly recommend it.

 

Duo or triband filters work well on emission nebulae.  Only.  The Celestron LP filter for the RASA works some on emission nebulae, but is nowhere near as good as this.

 

https://astrohutech....t/idas-nbz-uhs/

 

anothers M45.jpg

Thanks, I will definitely buy the proper filter.

[lakeorion]

There is nebulosity showing, but it's overwhelmed by the reflections.

[Fegato]

In Bortle 5 you can probably dispense with anything other than a UV/IR filter. Shoot with no moon, and you should be able to pick up the nebulosity in no time at all. 

 

Below is 37 minutes (74 x 30s) with RASA 11, but Bortle 3.  Some would say too bright, but it's what I went with, no work on reducing stars. And yes - flats, bias, darks.

 

[melodasi]

In Bortle 5 you can probably dispense with anything other than a UV/IR filter. Shoot with no moon, and you should be able to pick up the nebulosity in no time at all. 

 

Below is 37 minutes (74 x 30s) with RASA 11, but Bortle 3.  Some would say too bright, but it's what I went with, no work on reducing stars. And yes - flats, bias, darks.

 

Great pi

Great picture. Yes, I am right now just waiting for the weather.

[bobzeq25]

In Bortle 5 you can probably dispense with anything other than a UV/IR filter. Shoot with no moon, and you should be able to pick up the nebulosity in no time at all. 

 

Below is 37 minutes (74 x 30s) with RASA 11, but Bortle 3.  Some would say too bright, but it's what I went with, no work on reducing stars. And yes - flats, bias, darks.

 

Does the RASA 11 need a UV/IR block?  An advantage of the RASA 8 is an unusually apochromatic response, which focuses a wide range of wavelengths at the same point.  So, a UV/IR block will likely just reduce signal.

 

"Performs over a wider spectral range than most telescopes, from 400nm – 800nm, so more of the light passing through the astrograph is in sharp focus."

 

Outside 400-800nm is usually a low response region for CMOS sensors.

 

Bottom line.  I never use a UV/IR block.  I sometimes use a Baader neodymium to reduce light pollution.  Bortle 7.

[Fegato]

Does the RASA 11 need a UV/IR block?  An advantage of the RASA 8 is an unusually apochromatic response, which focuses a wide range of wavelengths at the same point.  So, a UV/IR block will likely just reduce signal.

 

"Performs over a wider spectral range than most telescopes, from 400nm – 800nm, so more of the light passing through the astrograph is in sharp focus."

 

Outside 400-800nm is usually a low response region for CMOS sensors.

 

Bottom line.  I never use a UV/IR block.  I sometimes use a Baader neodymium to reduce light pollution.  Bortle 7.

Ah, interesting question. Always learning in this game, so I've had a quick look at the RASA white paper. It does indeed say an IR cut filter "should not be required" for the RASA 8 (thus potentially allowing more detail to be caught). And it quotes 390nm - 800nm.  Not sure if this would affect colour balance, although maybe that's a minor point?

 

However, the RASA 11 range is 400nm - 700nm, so I think the IR cut is probably sensible. In any case, my ASI2400MC Pro has a UV/IR Cut window built in (although I guess it could be replaced with an AR one if there was any advantage to that).

[unimatrix0]

 

 

 but the filter is absolutely destroying it. Take it out... use it for anything OTHER than astrophotography going forward

I have a couple of these filters myself.  While mine was actually saying astrophotography compatible, they are completely useless after testing them. 

 

They could make a good DIY John Lennon style sunglasses though...