Light pollution filters

[ianpwilliams]

I need to buy an LP filter as my guided subs are being limited by my light pollution. So I've looked on FLO:

 

http://www.firstlightoptics.com/light-pollution-reduction-imaging.html

 

But I'm not sure which one I should be going for (I believe I need the 2" version, but that's all I know).

 

Also, there seems to be some sort of adaptor on FLO which says that "no tools would be required":

 

http://www.firstlightoptics.com/light-pollution-reduction-imaging/idas-mfa-filter-adapter-kit-for-canon-eos.html

 

What does that mean, and what tools would I need if I didn't buy that adaptor? And where does the filter go?

 

Also, I have a coma corrector between by camera  scope, will that cause issues?

 

I've attached a light-polluted 5-minute sub to show my light pollution.

 

IMG_2041.CR2

[MarkyD]

The MFA one fits into the camera body.  The others screw onto your barlow/eyepiece/extender etc. You don't need both.   That's as far as I can tell and I'm sure someone with far more experience will come along and explian better than me

--

Mark

 

[Leveye]

They are a bit on the pricey side but I'm saving up for a Hutech IDAS lps D1 or P2. After looking at the results from using it it will also take care of a bit of my scopes CA as well so two birds with one stone there. Check them out.

[ianpwilliams]

Ok, so I guess I would screw the non-MFA one onto the end of the various adaptors (coma corrector, DSLR adaptor etc) and then the whole lot would slot into the scope's eyepiece holder, like it does now, but with the LP filter on the end. If that is the case then I wonder if I will still be able to put the cap on the end of the camera adaptor once the LP filter was attached, as I tend to to remove the camera from the scope and put the cap on to take Darks while I'm packing up (that is until I can get dithering to work).

 

Looking at the FLO page for the MFA one, like you say it goes right next to the camera body, and then presumably the various adaptors can then be attached as normal. Given the choice I think I would prefer the other option, as this looks more inconvenient should I wish to remove it for daytime photography etc.

 

I have noticed some people complaining that the IDAS ones cause reflections though, and that you can see reflections of the inside of the scope around the brighter stars, which doesn't sound good:

 

" On my Skywatcher Exploer 150PDS however, my images produce a reflection of the internal optics around very bright stars on long exposures. Hutech assures however that this is not always the case so I guess it depends on your telescope! It does by no means destroy your image but is worth mentioning. "

 

Then there's also the Baadar Neodymium Filter, which is only £81, but there must be a reason why it is a lot cheaper.

 

[Davesellars]

If you're going to go for the IDAS I'd go for the 2" over the MFA for the very reason you mention plus it's cheaper.  It depends a bit on what you want to image but for the DSLR the newer D1 is supposed to give better colour balance.   I bought the IDAS LPS-V4 which is primarily for nebulae with my modded DSLR and use the cheap and cheerful 2" Skywatcher LP filter for everything else (seems to do the job and only £27).   The effectiveness of any of these will really depend on the type of your light pollution.

[wxsatuser]

Get an Astronomik CLS clip, it's cheaper and is on a par with the Hutech ones.

I have both and nearly always use the clip filter.

The CLS non IR is £104 fron Bern at Modern Astronomy

[ianpwilliams]

How do I find out what kind of light pollution I have, and which filter would suit it?

[Davesellars]

All LP filters are dependent on the LP source not covering the entire wavelength spectrum light in the case of white light LED lamps.  I'd guess that Edinburgh though still has the old sodium style ones (orange/yellow) glow - these types are cut very well by LP filters.  Obviously the more expensive you get the better/accurate coverage of LP wavelengths as what your're interested in is generally quite a narrow part of the spectrum.  Check out the wavelength response graph for the various LP filters (a quick search on Google).

[ianpwilliams]

This is a JPEG of one of my 5 minute subs. Would you agree that the light pollution looks like the orange/yellow type?

 

I did wonder if there was a way of getting a graph which represented the light pollution in this image, so that maybe I could compare it with graphs relating to the LP filters. 

[geordie85]

4 hours ago, ianpwilliams said:

This is a JPEG of one of my 5 minute subs. Would you agree that the light pollution looks like the orange/yellow type?

 

Are you sure that this is a 5 minute sub? I'd have imagined a 5 min sub without a light pollution filter would be a lot more washed out and you can still see the trapezium perfectly fine. It does look like your imaging under the sodium street lights as your image has an orange hue to it so a light pollution filter would help.

I have an Astronomik CLS CCD clip in light pollution filter and a 2 inch IDAS LPS-2 light pollution filter and they both work perfectly fine although I find the colour balance of the IDAS a lot more pleasing.

Here is a single 5 min sub I took of M42 through my IDAS 2 inch light pollution filter

[wxsatuser]

8 hours ago, ianpwilliams said:

This is a JPEG of one of my 5 minute subs. Would you agree that the light pollution looks like the orange/yellow type?

 

I did wonder if there was a way of getting a graph which represented the light pollution in this image, so that maybe I could compare it with graphs relating to the LP filters. 

Yes mainly sodium but in there as well could be mercury which is green.
Would'nt worry about graphs, all you want to do is get rid of the two most obvious LP forms.
The very best LP filters will have sharp cuts at sodium and mercury.
IMO, don't skimp on the LP filter, try to afford the best.
 

3 hours ago, geordie85 said:

Are you sure that this is a 5 minute sub? I'd have imagined a 5 min sub without a light pollution filter would be a lot more washed out and you can still see the trapezium perfectly fine. It does look like your imaging under the sodium street lights as your image has an orange hue to it so a light pollution filter would help.

I have an Astronomik CLS CCD clip in light pollution filter and a 2 inch IDAS LPS-2 light pollution filter and they both work perfectly fine although I find the colour balance of the IDAS a lot more pleasing.

Here is a single 5 min sub I took of M42 through my IDAS 2 inch light pollution filter

Ian's could be a 5minute exposure, depends on the ISO and f ratio used in both images.
Agreed! the IDAS filters do have a slightly better colour balance but I would'nt worry to much about that.

[geordie85]

Good point, I forgot about ISO setting. F ratio wouldn't make a difference since the camera is connected to the scope so it'll be 00 anyways.

I only ever image at ISO 800 so I never really think about it 

[wxsatuser]

18 hours ago, geordie85 said:

Good point, I forgot about ISO setting. F ratio wouldn't make a difference since the camera is connected to the scope so it'll be 00 anyways.

I only ever image at ISO 800 so I never really think about it 

Why do you think the f ratio is zero?

[MarkyD]

22 hours ago, geordie85 said:

Good point, I forgot about ISO setting. F ratio wouldn't make a difference since the camera is connected to the scope so it'll be 00 anyways.

I only ever image at ISO 800 so I never really think about it 

Your F ratio is f5 for the 130P-DS.  The camera will report back as zero because there is no lens attached to it

 

--

Mark

[ianpwilliams]

Yes it is 5 mins, but I kept lowering the ISO when I increased the sub length, because I was worried about saturation. I'll just keep it at 800ISO in future.

 

So assuming I go for the IDAS filter, should I go for the P2 or the D1, both of which are £155? And I take it I need the 2" version for my 130P-DS?

[Ken82]

I've been using an Idas d1 filter and I find it doubles my exposure without the effects of light pollution . Before I purchased this I did a little research and some people were having issues with reflection although I've had no such issues with a canon 6d and 70d . I also purchased a neodymium filter for visuals but I've also found it to be exceptionally good for photography ! 

[ianpwilliams]

Yes I've decided to go with the D1. Looking forward to it!

[ianpwilliams]

I've received my D1, but as is often the way with these things, there are no instructions. Would anyone happen to have a link to a page which shows you how to fit it? Or should it just screw onto the end of may various camera adaptors (t ring, coma corrector etc)?

[ianpwilliams]

Never mind it just literally screwed onto the end of my camera adaptors, so it looks like I'm good to go.

[Guest]

You can always make and subtract fake flat frame... This is your photo, I processed it like this:

1. Duplicate the layer

 

2. Noise -> Dust and scratches (Radius - 200, threshold - 0)

3. Blur -> Gaussian Blur (Radius - 1000)

4. Blending mode -> Subtract

5. Flatten the image

6. Adjust color, contrast and brightness

[Stub Mandrel]

I bought a cheap moon & skyglow filter. I didn't expect a lot although I could see it dimmed sodium lights more than other types.

The difference is astounding, before every image I took had a big gradient across it and I needed to use GradientExterminator. My first two images with the new filter haven't had any gradient at all, even when stretched.

Now in about three weeks they are changing the street lighting to LED...