Narrower narrowband?

[Xplode]

1 minute ago, ollypenrice said:

The price is horrendous but exposure times are not longer. I remember reading an account of why this is but can't remember the explanation. However, I find I collect a satisfactory 3nm signal in less time than I need for the 7nm.

Olly

The reason for exposures not being longer is that the Ha emission line is less than 0.5nm so you capture all of the Ha anyway, anything outside that range acts as noise you won't want to capture and which is the reason 3nm is much smoother than 7nm.

 

[ollypenrice]

44 minutes ago, Xplode said:

The reason for exposures not being longer is that the Ha emission line is less than 0.5nm so you capture all of the Ha anyway, anything outside that range acts as noise you won't want to capture and which is the reason 3nm is much smoother than 7nm.

 

This makes sense, although the 5nm also captures the NII line. I've no experience of the 5.

Olly

[Gina]

Only a handful of DSOs emit NII wavelength light so for the most part a 3nm Ha filter will capture as much of the DSO as the 5nm but cut out more background light.  Another point is that the Astrodon filters pass something like 90% of the hydrogen wavelength whereas most other makes only manage around 70% from what I've read of research into this.  I'm afraid you get what you pay for.  Personally I've found money spent on the best filters has proved better value for money than almost anything else.

[Gina]

I have both 5nm and 3nm Ha filters having bought the 5nm first and later upgraded to the 3nm.  The difference is far far greater than you would think from the seemingly small difference in band-pass.  I can unreservedly recommend the Astrodon 3nm Ha filter if you buy none other in the range.  There are superb monochrome images to be got with simple equipment and a 3nm Ha filter with a decent astro camera.  And I recommend the ZWO ASI1600MM-Cool camera for the latter.  High resolution yet with a 4/3" sensor you can use 1.25" filters saving vastly over the cost of bigger filters.

[Thalestris24]

1 hour ago, Gina said:

I have both 5nm and 3nm Ha filters having bought the 5nm first and later upgraded to the 3nm.  The difference is far far greater than you would think from the seemingly small difference in band-pass.  I can unreservedly recommend the Astrodon 3nm Ha filter if you buy none other in the range.  There are superb monochrome images to be got with simple equipment and a 3nm Ha filter with a decent astro camera.  And I recommend the ZWO ASI1600MM-Cool camera for the latter.  High resolution yet with a 4/3" sensor you can use 1.25" filters saving vastly over the cost of bigger filters.

Yes, but you have to fork out the dosh for the ZWO first! (or QHY163). Otherwise it's $995 for a 50mm, 3nm Ha so even with a free trade deal...

[gnomus]

I'm sorry to add to your woes, but have you seen Sara Wager's recent Horsehead?  This comment from her was telling: https://stargazerslounge.com/topic/286368-b33-horsehead-2-pane-mosaic-as-if-it-needed-more-space/?do=findComment&comment=3137794

Like you, I thought the idea of spending hundreds of pounds on small pieces of glass was plain silly and there was no way I was ever going to do that......  I have never heard anyone express any disappointment with the product though. 

[Gina]

If you haven't already bought any Astrodon filters you might find it worthwhile to sell your BIG camera and current filters and buy the ZWO camera and the Astrodon 3nm Ha filter.  For the optics, a vintage SLR lens would do you well and they're very cheap on ebay.  Or if you have a DSLR, the lens off that would be a start.  If the only camera you have ATM is a DSLR with a relatively huge sensor then filters will cost you the earth.  Plus you will suffer all sorts of horrors from lights, the moon and other things.  That is what I found with a DSLR some years ago.

TBH if you want to capture great images, particularly DSO in narrow-band you do really need a proper astro camera.  You could go for a second hand Atik 314L+ or similar to get started or even a 460EX but the latter costs more than the ZWO camera.  You really don't want to spend three grand on a triplet of NB filters.  £500 gets you an Astrodon 3nm Ha filter and about £1300 for the ZWO camera.  A nice cheap ST80 scope will work quite well for NB - I've used them.

[Davey-T]

47 minutes ago, gnomus said:

I'm sorry to add to your woes, but have you seen Sara Wager's recent Horsehead?  This comment from her was telling: https://stargazerslounge.com/topic/286368-b33-horsehead-2-pane-mosaic-as-if-it-needed-more-space/?do=findComment&comment=3137794

Like you, I thought the idea of spending hundreds of pounds on small pieces of glass was plain silly and there was no way I was ever going to do that......  I have never heard anyone express any disappointment with the product though. 

Not silly at all especially in the UK, one 30min sub with Astrodon 3nm HA is quite good enough for a stand alone image.

Dave

[RayD]

Are the Astrodon 3nm available in 2" mounted?  I can't seem to find them.

[Davey-T]

56 minutes ago, RayD said:

Are the Astrodon 3nm available in 2" mounted?  I can't seem to find them.

I think for another 20$ you can get a screw in mounting ring.

Dave

[RayD]

Just now, Davey-T said:

I think for another 20$ you can get a screw in mounting ring.

Dave

Ah ok cheers Dave, just thought it was me missing them.

[Davey-T]

Just now, RayD said:

Ah ok cheers Dave, just thought it was me missing them.

Not sure if they actually fit in anybodys filter wheels though 

Dave

[RayD]

9 minutes ago, Davey-T said:

Not sure if they actually fit in anybodys filter wheels though 

Dave

Well at £1,000 odd I'm not going to take a chance until I know for sure, and that's for sure!

[ollypenrice]

2 hours ago, RayD said:

Are the Astrodon 3nm available in 2" mounted?  I can't seem to find them.

I thought not. Bit of a bugbear for us, too. I wrote to Don G and was told that nobody asked for them but I must follow up the possibility of the screw in thing. It is no small matter since changing the filter wheel carousel means changing all the other filters as well and... at some point you have to say Nooooo!!!!

lly

[RayD]

2 minutes ago, ollypenrice said:

I thought not. Bit of a bugbear for us, too. I wrote to Don G and was told that nobody asked for them but I must follow up the possibility of the screw in thing. It is no small matter since changing the filter wheel carousel means changing all the other filters as well and... at some point you have to say Nooooo!!!!

lly

Precisely.  I have LRGB in a 5 position 2" wheel, so not an option to change.  I'm really surprised.

[ollypenrice]

2 minutes ago, RayD said:

Precisely.  I have LRGB in a 5 position 2" wheel, so not an option to change.  I'm really surprised.

Yup. To be honest, we should never have gone for 2 inch mounted. It is a format that has no business existing, since often the users of 2 inch will be pushing the filter size to its limits with common full frame chips. For all that, we can cure vignetting on full frame at F5 with 2 inch mounted so I think the mighty Astrodon might offer us the chance to give him some dollars.

Olly

[Thalestris24]

6 hours ago, Gina said:

If you haven't already bought any Astrodon filters you might find it worthwhile to sell your BIG camera and current filters and buy the ZWO camera and the Astrodon 3nm Ha filter.  For the optics, a vintage SLR lens would do you well and they're very cheap on ebay.  Or if you have a DSLR, the lens off that would be a start.  If the only camera you have ATM is a DSLR with a relatively huge sensor then filters will cost you the earth.  Plus you will suffer all sorts of horrors from lights, the moon and other things.  That is what I found with a DSLR some years ago.

TBH if you want to capture great images, particularly DSO in narrow-band you do really need a proper astro camera.  You could go for a second hand Atik 314L+ or similar to get started or even a 460EX but the latter costs more than the ZWO camera.  You really don't want to spend three grand on a triplet of NB filters.  £500 gets you an Astrodon 3nm Ha filter and about £1300 for the ZWO camera.  A nice cheap ST80 scope will work quite well for NB - I've used them.

Hi Gina

Well I sortof have a cooled mono 550d but it's been sent back for repair... Assuming I get it returned and it's working ok, it doesn't really have a resale value. I also have a qhy8l which although a osc does pick up Ha quite well. Plus a qhy minicam5s which I guess is an equivalent to an Atik 314l? Yes, I've used my Takumar 200mm quite bit . I have a TS 80mm f6 APO that the minicam5s is currently on, together with a quick change filter drawer. Also just got a TS 115mm APO + reducer. No shortage of equipment... But I don't also have the money for an Astrodon now  I'm all spent out, lol. I did think about getting the QHY163 which Herra and Luis have been showcasing but not enough money for that as well. I think I'll invest some time with PI and see what I can do with it and, especially the DBE. Of course, I only get to image here occasionally anyway on account of the weather...

Louise

[SilverAstro]

On 29/01/2017 at 16:50, ronin said:

Any "narrowing" would be to chance - slight difference in where the peak lies or one just happened to have a width of 6.5nm not 7nm.

Yes, that is why I was wittering on about the specs earlier, if the position of the passband or its width is not exactly controlled then a narrow passband would result. But no one has the spec so it would be an expensive experiment !

However xplode  has said that the Ha is only 0.5 ,  so Baader only need to make sure that the tolerances in manufacture put the pass band of each run somewhere over that 0.5 ( depending how flat the top is !)   So the variation could be large and the resulting combined bandwidth quite small !

All wiffling in the wind as Louise is not about to buy some 1/2 doz. to find out !

 

[Thalestris24]

1 minute ago, SilverAstro said:

Yes, that is why I was wittering on about the specs earlier, if the position of the passband or its width is not exactly controlled then a narrow passband would result. But no one has the spec so it would be an expensive experiment !

However xplode  has said that the Ha is only 0.5 ,  so Baader only need to make sure that the tolerances in manufacture put the pass band of each run somewhere over that 0.5 ( depending how flat the top is !)   So the variation could be large and the resulting combined bandwidth quite small !

All wiffling in the wind as Louise is not about to buy some 1/2 doz. to find out !

 

I'm certainly not!

[SilverAstro]

Just now, Thalestris24 said:

I'm certainly not!

SGL bulk buy ? 

[SilverAstro]

In your first post you say lp 'gradient' but subsequently lp in general terms, if it is the former I am having a (probably wako) thought :-

lp grad. mixed in Ha nebula is difficult to distinguish and get rid of, especially in Gimp ! (but I believe PI is better and IRIS (free) has a similar tool)

what if we could make a 'flat' of the grad ? :-

make a frame of sky nearby with only stars, use Gimp to extract the stars and leave the grad. (that is easy) then apply as you would a flat ?

Ok, blame it on the rain, I'll get my coat ! >>>

 

 

[Thalestris24]

17 minutes ago, SilverAstro said:

In your first post you say lp 'gradient' but subsequently lp in general terms, if it is the former I am having a (probably wako) thought :-

lp grad. mixed in Ha nebula is difficult to distinguish and get rid of, especially in Gimp ! (but I believe PI is better and IRIS (free) has a similar tool)

what if we could make a 'flat' of the grad ? :-

make a frame of sky nearby with only stars, use Gimp to extract the stars and leave the grad. (that is easy) then apply as you would a flat ?

Ok, blame it on the rain, I'll get my coat ! >>>

 

 

It tends to be sort of like a light 'shadow', if you get my drift. Despite having PI for about 18 months I've never yet had a go with dbe. I think it's probably too subtle for artificial flats. It's caused by a nearby yellow streetlamp (probably only a couple of metres away and slightly below me) and it's bright! I can probably deal with it, if only to my own satisfaction. I can't really justify the expense of an Astrodon for what might only be 2 or 3 attempts a year that might be affected. There always plenty of star clusters to do! It's only a hobby after all...

Louise

[SilverAstro]

46 minutes ago, Thalestris24 said:

It's only a hobby after all... 

Couldnt agree more

[Gina]

DBE is an excellent tool and not too difficult to get the hang of.  Use the online tutorials.

[alacant]

12 minutes ago, Gina said:

DBE is an excellent tool

Hi. I think that's wipe in StarTools. Also very good.