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Regarding ir-cut filter

EAA
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#1 makeitso

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Posted 20 February 2019 - 07:16 PM

So, I went out the last two days and did some EAA. I got some results but nothing to spectacular. I have other questions but in this thread I want to know if an ir-cut filter would help at all.

 

I am using two cameras, an asi224 and an unmodified canon t3.

 

Would an ir-cut filter half with either one for these cameras?

 

Next question. Which one do you all recommend? I see where I can get an svbony for $15 on Amazon or, I could go with the Baader option for $73, both are 1 1/4”. Is there that much difference? I suppose the Baader is more likely to be a good one.

 

Thanks, Jack



#2 mistateo

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Posted 20 February 2019 - 07:44 PM

The t3i should have one built in.  The ASI224 does not.  The ZWO L filter is uv/ir cut, and will do fine, not quite as cheap as the total no name brands, and not as expensive as the baader.


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#3 selfo

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Posted 20 February 2019 - 09:18 PM

The IR cut filter is particularly useful if you have light polluted skies. It will help remove some of the star bloat as well. You should be aware that Galaxies do emit IR so you may lose some light with the filter installed. Your mileage may vary.

Lastly I would suggest you get a UVIR cut filter instead. The Baader UVIR cut filter works so well from me I usually leave it on all the time.

Edited by selfo, 20 February 2019 - 09:21 PM.

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#4 makeitso

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Posted 21 February 2019 - 09:45 AM

Thanks for the replies,

 

I did some research and apparently, the zwo filter blocks uv and ir. I don’t see any reason to spend more than three times as much on the Baader filter. Since my t3 has one built in, I think I’ll stick with the 1 1/4”. 

 

Thanks, Jack



#5 DSO_Viewer

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Posted 21 February 2019 - 12:06 PM

Thanks for the replies,

 

I did some research and apparently, the zwo filter blocks uv and ir. I don’t see any reason to spend more than three times as much on the Baader filter. Since my t3 has one built in, I think I’ll stick with the 1 1/4”. 

 

Thanks, Jack

Where did you find the information that ZWO has a built-in window with uv/ir coatings? I though all this time that their camera do not block out uv/ir. Can you provide a link to so us where it states this?

 

Steve



#6 jimthompson

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Posted 21 February 2019 - 01:28 PM

Hi Jack,

 

A UV/IR cut filter can be helpful when doing EAA, but only under certain circumstances:

 

1.  If you are using an achromatic refractor or camera lens, then you will see a large benefit in the sharpness of your image using a UV/IR cut filter.  The reason for this is that achromatic telescopes and lenses are designed to give a well focused image of visible light only.  Cameras used for EAA are also able to effectively "see" UV and IR light, so on achromats and lenses you get a fuzzy out of focus image.

2.  When viewing emission type nebulae (H-II regions, planetary nebulae, supernova remnants), adding a UV/IR cut filter will improve contrast by removing light pollution in the IR band.  This is true for any light pollution level.  Adding a UV/IR cut filter when viewing emission nebulae also helps to highlight the nebulosity by reducing the visibility of stars.  It is beneficial to stack a UV/IR cut filter with an LP filter for this application.

3.  When viewing galaxies under dark sky conditions only (Vm +6 or better), adding a UV/IR cut filter can help improve the image contrast by a small amount.  If there is any light pollution it is better to not use any UV/IR cut to view galaxies.

4.  When viewing solar system objects (Sun, Moon, planets), adding a UV/IR cut filter can help to reduce the appearance of atmospheric turbulence (seeing), making it easier to achieve a good focus and providing a steadier image.

 

If you can afford it, I recommend getting a good performing UV/IR cut filter.  The best I have tested is the Baader Planetarium version.  It has measurably superior performance to all the others I have encountered.  Cheaper brands are available, but those brands don't give the same high in-band transmission, and don't come with anti-reflective coatings to eliminate halos and other contrast affecting issues.

 

Regards,

 

Jim T.


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#7 makeitso

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Posted 21 February 2019 - 02:28 PM

Where did you find the information that ZWO has a built-in window with uv/ir coatings? I though all this time that their camera do not block out uv/ir. Can you provide a link to so us where it states this?

 

Steve

I did say the camera has a built in filter. I said the zwo filter blocks both. You would have to purchase it separately.

 

Jack


Edited by makeitso, 21 February 2019 - 02:35 PM.


#8 makeitso

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Posted 21 February 2019 - 02:34 PM

Jim, 

 

Thanks for the information, that clears a lot up for me. Have you tested the zwo ir cut filter? If yes, how did it perform? It less than a third of the price of the Baader filter. I am using a Celestron C6 right now but I have an achromat I’m planning on trying out at some point. I may just wait until I can get the Baader.

 

Once again, thanks, Jack



#9 jimthompson

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Posted 21 February 2019 - 02:41 PM

Jim, 

 

Thanks for the information, that clears a lot up for me. Have you tested the zwo ir cut filter? If yes, how did it perform? It less than a third of the price of the Baader filter. I am using a Celestron C6 right now but I have an achromat I’m planning on trying out at some point. I may just wait until I can get the Baader.

 

Once again, thanks, Jack

Hi Jack,

 

I have not tested the ZWO brand filter, so I can't comment on its performance.  I have tested the Optolong brand filter however, which is cheaper than the Baader one.  It performs pretty well in comparison to the Baader, having similar in-band tranmission, but a slightly wider band pass so more UV and IR are getting through (see test report in link below).  The Optolong filters also don't have anti-reflective coatings so halos can be an issue.  I suspect the ZWO filter would be similar in that respect.

 

http://karmalimbo.co...t_26Aug2015.pdf

 

Cheers,

 

Jim T.


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#10 makeitso

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Posted 21 February 2019 - 05:37 PM

Thanks Jim,

 

I think I’ll go with the Baader filter. The next question is should I get the 1 1/4” or the 2”. I don’t know for sure but sometime in the not to distant future , I can see me getting a larger sensor or eve a modified dslr. I’m sure the 2” inch would be a better choice but more money. I guess I could get the 1 1/4” and get the two later and either sell or use both. If I end up not needing the 2” I could save some money.

 

I know that’s something I have to decide for my self though.

 

Thanks, Jack



#11 ccs_hello

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Posted 21 February 2019 - 06:06 PM

There ought be better terms on those filters.  Not by brand name (a manufacturer can make so many type of filters), nor by overly generalized name.

 

Case in point, in UV/IR-cut filters, there are two most popular types:

1. HVS-type (Human visual system) which will cut off/drastically attenuate wavelength above 630 nm.

2. Astro-type (will let H-alpha 656 nm pass through) which will cut off/drastically attenuate wavelength above 680 nm.

 

The first type almost almost come with the commercial cameras (DSLR, mirrorless, P&S, webcams, and most of the CCTV security surveillance cameras.)

The goal is to mimic the spectrum response of what human eyes'/brain (i.e., HVS) can see about color.  That is, matching the color experience a person can see.  You don't want the green leaves/vegetation look pinkish under the high noon Sun.

 

The second type is to let the common emitted Hydrogen-alpha from astro objects to come through to be captured by image sensor in which the first type has fairly low transmission curve (about 15% or less.)


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#12 makeitso

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Posted 21 February 2019 - 08:05 PM

css_hello,

 

This is somewhat of a curve ball, I am only interested in how it would affect the image a camera would see. I didn’t know there were different types. I’m not going to be using it during the day time at all, only to do eaa of celestial objects at night. I will assume the Baader filter I’m looking at is for this purpose and will be suitable for me to do this. If no one chimes in and says different at least.

 

Anyone reading this has any input on this I’m all ears.

 

Thanks, Jack



#13 tmaestro

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Posted 21 February 2019 - 09:57 PM

I was mislead by the copy on Agena's website.  "A clear IR-cut glass window protects the sensor and helps keep images sharp."  Is in the 4th paragraph under "Product Details"  Thinking I had IR covered, I bought a CLS filter instead of a CLS-CCD.

 

https://agenaastro.c...ing-camera.html



#14 ccs_hello

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Posted 21 February 2019 - 10:34 PM

css_hello,

 

This is somewhat of a curve ball, I am only interested in how it would affect the image a camera would see. I didn’t know there were different types. I’m not going to be using it during the day time at all, only to do eaa of celestial objects at night. I will assume the Baader filter I’m looking at is for this purpose and will be suitable for me to do this. If no one chimes in and says different at least.

 

Anyone reading this has any input on this I’m all ears.

 

Thanks, Jack

Baader UV/IR-cut is the astro type.

See https://agenaastro.c...cut-filter.html

click the third picture to see 656 nm H-alpha is allowed to pass thru (anything above 700 is cut.)


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#15 makeitso

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Posted 21 February 2019 - 11:43 PM

Baader UV/IR-cut is the astro type.

See https://agenaastro.c...cut-filter.html

click the third picture to see 656 nm H-alpha is allowed to pass thru (anything above 700 is cut.)

 

Thanks for that. Good I formation.

 

Okay, that clears it up for me.

 

Thanks, Jack



#16 jimthompson

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Posted 21 February 2019 - 11:56 PM

Hi Jack,

 

What ccs_hello is talking about when he says HVS-type is the filter that comes standard on all commercially available point-and-shoot or DSLR cameras.  Some people call those IR cut filters but I believe they are more accurately referred to as Colour Correction filters.  Their purpose is not strictly to cut out UV and IR, but to force the spectral response of the camera sensor to be more like the human eye.  That way it is easier to get images from the camera that look like what we see with our eyes, an important attribute for a camera...but not when you want to take images of the night sky!

 

Stick with the Baader UV/IR Cut and you will be golden.

 

Cheers,

 

Jim T.


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#17 ccs_hello

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Posted 22 February 2019 - 08:57 AM

"Color correction filter" has multiple contextual meanings depending on what's in the design for various purposes.

Color correction UV/IR-cut filter is a very precise term but rather wordy.


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#18 jimthompson

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Posted 22 February 2019 - 09:42 AM

"Color correction filter" has multiple contextual meanings depending on what's in the design for various purposes.

Color correction UV/IR-cut filter is a very precise term but rather wordy.

Indeed there is a whole family of "colour correction" filters available to adjust the white balance of a photographer's image, accounting for different lighting (sunlight vs. incandescent vs. fluorescent) and other such artistic desires of the photographer (add warmth to image, etc.).  Much of the need for such physical filters has gone away however with the advent of CCD/CMOS based cameras and image processing software.  Nonetheless the cameras we buy even today for terrestrial use by default have a filter installed who's purpose is to "correct" the white balance of the scene to look more like what our eye sees.  That includes not just UV and IR bands but also some of the visible red band, which is why they are undesirable for astronomy.  See the plot below for comparison.  In my plot the green curve (Camera IR/Colour Correction Type 1) is the filter that is most commonly installed in the everyday cameras we buy today.  The Type 2 is an option that some camera manufacturers have available.  The B+W filter is a commonly available aftermarket UV/IR cut used by terrestrial photographers.  You may note that the shape of the two colour correction filters is different than the other two, all smooth with gently sloping sides.  That is because those filters are simple absorption type, like a colour filter.

 

Cheers,

 

Jim T.

Attached Thumbnails

  • cameraIRcutcompare_Feb2019.png

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#19 makeitso

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Posted 22 February 2019 - 09:57 AM

Thanks,

 

I learn something everyday I come on this forum. I think I’ll stick with the Baader. Now I want to get my camera modified to. More money to spend. I don’t think that ever ends, does it?

 

Thanks, Jack




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