324 replies to this topic

[mmalik]

EDIT: Title update to include previously missed D1...

There seems bit of dilemma around subtle differences in spectrum in various iterations of IDAS Light Pollution Suppression (LPS) Filters , i.e., D1, P2 and V4. I would like to have a discussion primarily around LPS spectrum plots. Once we have sorted out LPS plots, I think then we can delve into IDAS H-alpha Enhanced UV/IR Blocking Filters (HEUIBII) and how they compare to, for example, V4.


In short, let's keep this discussion focused primarily on P2 and V4, and once we have fully understood the subtleties then we can go a step further and bring HEUIBII into the mix. HEUIBII is NOT an LPS but its H-alpha properties for example might be closer to V4.


Much of what I am talking about does NOT directly relate to any LPS tests folks may have conducted in the past because I would like to focus this discussion more on reading the plots, and application of such filters for given objects and/or DSLR setups.


To kick off this discussion, following are three plots in order:

EDIT: List edited to include D1...

1. LPS-D1
2. LPS-P2
3. LPS-V4
4. HEUIBII


2. LPS-P2:

Link...

[mmalik]

3. LPS-V4

Link...

[mmalik]

4. HEUIBII

Link...

[mmalik]

Reference:

•Infrared (IR).............................0.74 micrometers (µm) to 300 µm
•Hydrogen-alpha (H-alpha).........656.28 nanometers (nm)
•Oxygen III (OIII)......................500.7 nm
•Hydrogen-beta (H-beta)............486.1 nm
•Ultraviolet (UV)........................10 nm to 400 nm

[microstar]

You might also want to include the successor to the P2, the LPS-D1.

I image with the LPS-D1 and the LPS-V4. For imaging, the HEU is designed for modified DSLR cameras imaging under dark skies; the LPS-P2 has notches at several light pollution sources but is designed for slightly light-polluted skies; the LPS-D2 is the P2 with a sharper peak in the red including Ha but still intended for lower levels of light pollution; the LPS-V4 is a different beast altogether and is an attempt at a tri-band NB imaging filter for OSCs/modded DSLRs that works in moderately light-polluted areas. It's pretty good in the Ha (but still, at 18nm, much broader than a NB Ha filter). The blue-green band is too broad in my opinion to be much use for isolating the OIII and Hb and images require quite a bit of color processing to get rid of the blue-green cast.

I expect others will have opinions, but that's my take on these filters.
...Keith

[Samir Kharusi]

The ideal light pollution cutting filter for use on emission nebulae would have a narrow passband around OIII (501nm) and another one around Ha (656nm), say, less than 10nm wide for each passband. This would be equivalent to shooting both an OIII narrowband image and an Ha image simultaneously. All other filters are compromises because of either difficulties/expense of achieving this duo-tone ideal, or, rather foolishly IMHO, chasing white balance. Modern, broad spectrum, light pollution is getting to be near impossible to filter out effectively and still pass useful amounts of white-light spectrum from galaxies to reach pleasant galaxy imaging from a heavily light polluted site. Older street lights, if that is what you have in your area (mercury lights, low-pressure sodium) are good candidates to be tackled by the broader, white-balancing, filters, such as the LPS2. The nearest filters I own to my ideal duo-tone is to use the Astronomic UHC in combination to the usual rectangular passband IR-blocker. It's easy to see what happens:

The upper set uses a tungsten bulb, the broadest, most annoying light pollution there is. That bottom set uses a current technology energy-saver light bulb, easier to handle than the tungsten, but still very bad. I have not measured the spectrum of an LED street lamp, but I suspect it may be very broad, hence near-impossible to filter out effectively. The LPSV4 and similar are basically less nice versions (broader passbands) of what you can do with the Astronomic UHC. Nevertheless most of us probably have street lights from 20 years back, hence mercury lamps or sodium. A few decades back low pressure sodium (easy to filter out) slowly gave way to high pressure sodium (near impossible to filter out). So basically it all comes down to your own local light pollution. Most of the time it's a mixture and to see how various filters handle it, I suggest a deliberate strategy of measuring the amount of your light pollution, then a read on how the various filters affect your imaging, and finally how to choose between the Astronomik CLS and the LPS2 types. Ideally one would like to take the spectrum of the annoying street lights or supermarket parking lot types to determine whether selective-blocking of the spectral lines is even worth chasing (LPS2 type) or whether one should go straight for the selective-pass type of filter (LPSV4 type). But frankly, if your light pollution is high enough, do not waste your money. Just go narrowband (i.e. selective-pass). Unfortunately even the selective-pass are sort of half hearted compared to true narrowband filters. The nearest I have found is the Astronomik UHC (+ an IR-block). Basically your choice is simply between selective-block (like the LPS2) or selective-pass (like the LPSV4, CLS, UHC, etc). If your light pollution is rather modest, then a selective-block like the LPS2 can work well and still give a nice white balance. Otherwise, with high light pollution, the more aggressively you can get to true narrowband, the better. Half-hearted compromises of trying to retain some semblance of white balance are just that, half-hearted, but can still work well with modest light pollution, outer suburbs. For inner suburbs of large cities just go narrow band and be happy. If you are using a mirror scope the Astronomik UHC (+IR-block) is a good choice, but you may sometimes get annoying donuts around your stars if you are using a refracting OTA (camera lens or an APO that's not been designed all the way to cater for the deep red Ha). Nevertheless there are techniques for handling the donuts in post processing...

[mmalik]

You might also want to include the successor to the P2, the LPS-D1.

I image with the LPS-D1 and the LPS-V4. For imaging, the HEU is designed for modified DSLR cameras imaging under dark skies; the LPS-P2 has notches at several light pollution sources but is designed for slightly light-polluted skies; the LPS-D2 is the P2 with a sharper peak in the red including Ha but still intended for lower levels of light pollution; the LPS-V4 is a different beast altogether and is an attempt at a tri-band NB imaging filter for OSCs/modded DSLRs that works in moderately light-polluted areas. It's pretty good in the Ha (but still, at 18nm, much broader than a NB Ha filter). The blue-green band is too broad in my opinion to be much use for isolating the OIII and Hb and images require quite a bit of color processing to get rid of the blue-green cast.

Keith, you provide some very useful information and bring up some good points; I have updated my list above in light of this information and for the sake of completion. Note: You mention D2 but I don't see it listed on IDAS website...?


All, here is the sum up thus far if all agree [updates/corrections welcome; D2 was omitted since it wasn't listed on the site]? Regards


1. LPS-D1 [New LPS filter]
2. LPS-P2 [Old LPS filter]
3. LPS-V4 [Tri-band nebular filter for OSCs/modded DSLRs/moderately dark skies]
4. HEUIBII [H-alpha enhanced filter for modded DSLRs/dark skies]

[mmalik]

The upper set uses a tungsten bulb, the broadest, most annoying light pollution there is. That bottom set uses a current technology energy-saver light bulb, easier to handle than the tungsten, but still very bad.

Thanks Samir for the detailed write-up; if you don't mind I have splitted your plot into two:


Older Tungsten bulb pollution:

Attached Thumbnails

• 

[mmalik]

Newer energy-saver bulb pollution:

Attached Thumbnails

• 

[mmalik]

Also Sameer what's missing from your plots is newer filters under discussion in this thread; would be great if they could be accommodated.


What I also see, by looking at IDAS's plots (links above) is that they don't use the same scale (from plot to plot) to further confuse the matter; what I am puzzled about... is IDAS really helping or hurting the 'filter' cause by producing such an array of filters? For example, I see V4 and HEU as subtleties on the same theme. Regards

[microstar]

[quote name="mmalik"][quote]You mention D2 but I don't see it listed on IDAS website...?


All, here is the sum up thus far if all agree [updates/corrections welcome; D2 was omitted since it wasn't listed on the site]? Regards


1. LPS-D1 [New LPS filter]
2. LPS-P2 [Old LPS filter]
3. LPS-V4 [Tri-band nebular filter for OSCs/modded DSLRs/moderately dark skies]
4. HEUIBII [H-alpha enhanced filter for modded DSLRs/dark skies] [/quote]

D2 was a typo - I meant the LPS-D1.
...Keith

[Astronewb]

Very interesting thread. I can only highly praise the HEUIB-II filter for AP with a modified camera. It totally aligns the LRGB and eliminates the red skies from raw images when used.

Here's a link to a astro image taken with a HEUIB-II on a modified Nikon D5100:
https://flic.kr/p/h6oziN

The other side of the coin, is how the HEUIB-II can be used for normal photography with a modded camera. That's something I was never able to do successfully, even with a custom white balance setting.

All you have to do is set your modded camera to Auto White Balance and you can take fine daytime images with it.

Here is a link to a set of images I took this afternoon with the modded D5100 and the HEUIB-II installed on a 40mm Nikon lens via a step down adapter (52 to 48mm):
https://www.flickr.c...57643974701613/

This may be helpful to someone who is hesitating to modify his/her camera for astro work because daytime photography would be affected? The HEUIB-II is definitely the way to go in this instance.

Clear skies...Paul

[mmalik]

Thanks Paul for the feedback; proud grandpa you are!


Here is the tally of filter uses thus far; corrections/updates welcome.

1. LPS-D1 [New LPS filter]
2. LPS-P2 [Old LPS filter]
3. LPS-V4 [Tri-band nebular filter for modded DSLRs-moderately dark skies]
4. HEUIBII [H-alpha enhanced filter for modded DSLRs-dark skies; daytime photography with modded DSLRs]

[mmalik]

LPS-V4... installed; will post results as I test it. Regards

Note: There is a body-mounted V4 option for select cameras; I tend to like this one.

Attached Thumbnails

• 

[mmalik]

My dialog with Paul in another thread... regarding my dilemma with HEUIBII; thought I'll post it here since quite relevant to the discussion. Regards

Let me ask you about your D5100 and HEUIBII; is your D5100 full spectrum mod? I never really understood HEUIBII purpose; is it really intended for a full spectrum mod? I know you have mentioned in the past that HEUIBII can be used for daytime work/auto white balance, etc., but I am mainly interested in knowing 'proper' astro use of HEUIBII? If I were to say, HEUIBII is intended for full spectrum modded camera used for astro work, would that be a correct statement? Regards

My D5100 is full-spectrum modified. The HEUIB-II filter is indeed intended for modified cameras. According to Hutech, it also enhances Ha a bit.

The nicest aspect, when using it for AP, is that if you set your camera white balance to 'auto', your RAW images look just like they were imaged with a non-modded camera, absolutely no red caste.

I also find it helpful when taking flats, I use iPad flats, using the gray screen from Digital Gray Kard (free) and the color channels are perfectly aligned there also.

It just makes processing a bit easier since you don't have to constantly pull down all the red sky overtones.

Here's a link to Hutechs Digi Borg blog, if you enter HEUIB in the search box, it will give you access to all the posted articles and images of the usefulness of the filter.

http://digiborg.wordpress.com/?s=heuib

The HEUIB-II filter is indeed intended for modified cameras.

Paul, I meant to say that HEUIBII is intended for full-spectrum mods ONLY, NOT standard mods, would that be correct? My understanding is that standard mod would leave native IR/UV filter "in" the camera and that pretty much overlaps/negates HEUIBII purpose (for nighttime/astro work). Is that correct?

Hi Mike, I don't think so. If you read through the various blog posts in the link I posted, you will see an example image of a modded Canon 6dh with the normal UV/IR filter in place, along with example images of various external filters
installed.

It's post #4 > http://digiborg.word...ib-ii-filter-4/

Hope that helps. Although the HEUIB-II is not designed as a LPS filter, I have been having great results with it under heavily moonlit nights as long as I'm not imaging in the same area as the moon, ie; with the moon at my back.

[mmalik]

LPS-V4... installed; will post results as I test it.

Here are few tests conducted with LPS-P2, LPS-V4 and other filter combinations.


Note: These tests were conducted with 6D full-spectrum mod...


Each image is 5min ISO1600 taken out of discrete 'Multiple LENRs...' sequences of Crescent Nebula. I used Canon Digital Photo Professional (DPP) for the mosaic instead of developing since developing introduces other variables/biases. For 100% zoom of the images as seen in DPP, click here...

[mmalik]

Following are LPS-V4 test conducted with 6D 'Full-Spectrum' and 'Removed LPF-2' mods...


Each image is 5min ISO1600 LENR. For 100% zoom of the images as seen in DPP, click here...

Attached Thumbnails

• 

[mmalik]

I DO see... sharpness advantage in Full-Spectrum mod (i.e., stock LPF-1 being gone along with its AA characteristics). Regards

[mmalik]

Next inline is HEUIB-II [H-alpha enhanced filter for modded DSLRs-dark skies; daytime photography with modded DSLRs]


HEUIB-II... installed; will post results as I test it. Regards

[Astronewb]

HEUIB-II... installed; will post results as I test it. Regards

Very informative tests Mike, thanks. Looking forward to your HEUIB-II testing.

Cheers...Paul

[Jon Rista]

Are any more test results forthcoming? 

[mmalik]

Sorry for the very delayed update; here are the results of HEUIB-II with full-spectrum 6D.

 

Note: Image is single 5min ISO1600 LENR of Crescent nebula, full-frame in Canon DPP

Attached Thumbnails

• 

Edited by mmalik, 24 November 2014 - 05:07 PM.

[mmalik]

Here is side by side comparison:

 

Note: Each image is single 5min ISO1600 LENR of Crescent nebula, 100% zoom in Canon DPP

Attached Thumbnails

• 

[mmalik]

Here is another montage of various filter results along with histograms.

 

Note: I intentionally stuck with ISO1600/5min for all these samples for comparison sake and reducing the number of variables.

 

Note: Each image is single 5min ISO1600 LENR of Crescent nebula, as seen in Canon DPP; read left-right top row, left-right bottom row...

 

 

• 100-0035-‘Removed LPF-2’ + LPS-V4
• 100-0100-‘Full-Spectrum’ + Astronomik L + LPS-V4
• 100-0103-‘Full-Spectrum’ + Astronomik L
• 100-0106-‘Full-Spectrum’ + Astronomik L + LPS-P2
• 100-0109-‘Full-Spectrum’ + LPS-V4
• 100-0112-‘Full-Spectrum’ + HEUIB-II

 

 

 

 

Edited by mmalik, 24 November 2014 - 05:15 PM.

[mmalik]

I ended up putting back the LPF-1 on the 6D to make it a removed LPF-2 mod. This one image speaks for itself about the filter and the mod type, the best combination I have come across thus far and would highly recommend it. Regards
 

•25x5min, ISO 1600, Multiple LENR
•125min integration, guided
•Removed LPF-2 6D
•IDAS HEUIB-II
•Minor cropped frame

High Resolution...

Attached Thumbnails

• 

Edited by mmalik, 25 November 2014 - 02:45 AM.