Baader contrast booster

[vlaiv]

14 minutes ago, Louis D said:

If you want information overload, take a look at this spectrograph of multiple violet reduction filters:

Hahaha, this is great.

Without looking at the legend to see which filter is which, and just by looking at the graphs - I said to myself: "I'd prefer the green one ... "

 

[Don Pensack]

The advantage of the CB on Mars is that the minus violet filtration also eliminates a lot of atmospheric light scatter and doesn't appreciably change the color balance on Mars.

So it yields a sharper image and augments surface detail.  The last apparition, it was shocking how good the image of mars was.

[badhex]

On 05/08/2023 at 15:40, Louis D said:

If you want information overload, take a look at this spectrograph of multiple violet reduction filters:

I have the Hirsch 12A and find it just about the best compromise of the purely yellow violet-cut filters.  There's still a tiny bit of violet fringe, but it is hardly noticeable.  There is also very little yellow cast introduced.  It also doesn't cut into the Hβ line much, so it could be left on with nebula within bright open clusters.  The problem is, it isn't made anymore.  The closest modern equivalent are some of the generic yellow filters coming out of China (which I have).  The problem with them is that they tend to scatter more light than the older US, Japan, and newer Taiwanese filters like Meade, Hirsch, and GSO.

The modern #8 Light Yellows are similar to the Meade #8 above (which I also have).  It cuts a little bit of the far violet, but not enough to be effective.  On the plus side, there's little to no yellow cast.

The older, true Wratten #8 (Yellow K2) is very similar to the modern Baader 495 Longpass.  However, the yellow cast is strong.  It's not as strong as the modern GSO #12 Yellow, but still strong.  I tried the GSO #12 first of all my yellow filters, and find it the least usable because it cuts all blue and some green, which is massive overkill.  The Yellow K2/#8 filters are still available as new old stock 48mm (2") filters on ebay for under $20 if you want to try one.  It cuts into the Hβ line, so not appropriate for those nebula that strongly emit it.

The Baader Contrast Booster and Semi APO filters simply add a Neodymium glass base that cuts some of the yellow and yellow-orange part of the spectrum to compensate for the loss of violet.  The CB is basically a #8/K2 Yellow or 495 Longpass combined with the Neodymium glass.  The SA is somewhere between the Meade #8 and Hirsch #12A in cutting violet as you can see from the graph, and then adds the Neodymium glass.  In my experience, the SA gets rid of enough of the violet fringe without adding a nasty yellow cast.  My poor man's CB still shows some yellow cast and no violet fringe at all.  The Baader filters add violet cutting coatings to the Neodymium glass to get higher transmission.  However, this doesn't really matter all that much on the bright objects that display violet fringing the most.

There's no violet-cut benefit to the Neodymium's suppression of teal-blue to green wavelengths just above 500nm.  However, when combined with the yellow/yellow-orange cut, the Neodymium filters increase contrast by separating blue from green from red with bandgaps.  Eyeglasses for the color blind work in a similar manner to cut notches between the colors they can't separate with their retinas.

Here's some of my yellow filters run through my spectroscope.  It also includes some Rosco yellows and my attempt to photograph an artificial star through my ST80 with some of these filters.

Yikes, that first graphic is busy! 

It seems to the layperson that on paper the CB and Wratten #12 are not dramatically dissimilar at the blue end of the spectrum and your images and experience confirms that. Shame you don't have a contrast booster to run through your spectrograph for a side by side with the #12!

 

 

[badhex]

On 05/08/2023 at 15:43, Don Pensack said:

Given the results from the Fringe killer, this scope didn't have the most severe CA I've seen in doublet refractors.

But looking at the bottom edge of the coupler on the right, only the contrast booster eliminated the violet.

Of course the Moon & Sky Glow filter did not eliminate any violet--it has no violet filtration at all.

It tends to create a "cold" image of Jupiter as well, which is one of the reasons it enhances the banding, like a #82 light blue, only without the red filtration of the blue filter.

Overall I definitely prefer the image taken through the CB from a CA reduction perspective, just a bit of a shame the sky is also quite green! 

[Louis D]

4 hours ago, badhex said:

Yikes, that first graphic is busy! 

It seems to the layperson that on paper the CB and Wratten #12 are not dramatically dissimilar at the blue end of the spectrum and your images and experience confirms that. Shame you don't have a contrast booster to run through your spectrograph for a side by side with the #12!

The only reason I have the Baader Semi APO is because it came with an achromat.  It actually does quite well visually.  The previous owner said he left it on his diagonal continuously when using that scope.

4 hours ago, badhex said:

It seems to the layperson that on paper the CB and Wratten #12 are not dramatically dissimilar at the blue end of the spectrum and your images and experience confirms that. Shame you don't have a contrast booster to run through your spectrograph for a side by side with the #12!

Make that #12A.  I also have the #12 (GSO version), and it is quite aggressive at cutting out all blue as you can see from the lower right sub-image in my spectrogram composite image.  It was my second attempt to cut violet.  My first was over 20 years ago when I bought a "Minus Violet" filter, which, as you can see from the second sub-image down in the left column, is a very weak yellow filter.  Any violet reduction it might technically accomplish is not detectable to my eyes.

I then tried the #12 and found that it completely cuts all violet while imparting a very strong yellow cast to everything.  So, I set off on my journey to find the Goldilocks of yellow/minus violet filters.  The #12A and K2/Wratten #8 come closest.  The former leaves a bit of violet without adding an undue yellow cast while the latter cuts all violet while leaving a pale yellow cast that I can tolerate while picking out fine details.  For some reason, the #12A is not available in new production today, and the latter is only available in the 2"/48mm photographic size as new old stock.

The current #8 Yellows are much closer to the 1990s Minus Violet I mentioned above as you can see from the third sub-image down in the left column.  As I've said before, some of the cheap Chinese made "Yellow" filters from ebay are actually very close to the #12A as you can see from the fourth and fifth images in the left column.  However, the one I have does induce some light scatter as is visible in that artificial star image to the right of the fourth image.  Even the polyester film Rosco filters have less scatter (see R### yellows in that composite image).

Of the Rosco filters, the R312 Canary was my favorite.  It cut all visible violet while imparting only a mild yellow cast.  It turns out it is nearly identical to the K2/Wratten #8 photographic filter as is obvious from the second and third images in the right column.

[Louis D]

Based on all of my "research" I really wish all companies would do like Baader and publish spectrographs/grams of each of their filters so we'd know what we're actually getting, not what we're supposed to be getting.  The #8 Yellow is a major case in point.

[Mark2022]

I noticed nobody has mentioned the Baader 495 longpass filter in this thread. I've been reading a lot about this filter and it all sounds good (except trying to find one and at a decent price). So many  are  saying that while it imparts just a shade of yellow - but apparently not too strong - it completely eliminates CA. Some have put it ahead of the Contrast Booster in fact. 

One of my scopes is the StarTravel 120 and it's that one I'm thinking of using the most for EAA when I get my entire setup up and running. I'd love to try out both, the CB and the 495 LP before deciding which I'd prefer. I'd want the 2 inch version to be 'always on' my 2 inch diagonal. Do you think someone like FLO would allow the buying of both and returning the one I didn't prefer? My bank account really doesn't like me.

[Franklin]

Baader 495 longpass cuts CA very well but it does add more than just a hint of yellow, it's a very strong yellow, which would be fine if you plan on using a monochrome camera for your EAA set up. If using a OSC camera I'd go for the CB filter.

[Louis D]

59 minutes ago, Mark2022 said:

I noticed nobody has mentioned the Baader 495 longpass filter in this thread. I've been reading a lot about this filter and it all sounds good (except trying to find one and at a decent price). So many  are  saying that while it imparts just a shade of yellow - but apparently not too strong - it completely eliminates CA. Some have put it ahead of the Contrast Booster in fact. 

One of my scopes is the StarTravel 120 and it's that one I'm thinking of using the most for EAA when I get my entire setup up and running. I'd love to try out both, the CB and the 495 LP before deciding which I'd prefer. I'd want the 2 inch version to be 'always on' my 2 inch diagonal. Do you think someone like FLO would allow the buying of both and returning the one I didn't prefer? My bank account really doesn't like me.

If you can find a new old stock 48mm Yellow K2/#8 photographic filter local to the UK, it will have roughly the same bandpass characteristics as the Baader 495 Longpass for a lot less.  I have the Rokunar version, and it works very well with a distinct yellow cast, but not nearly as strong as a GSO Yellow #12 filter.  The 48mm photographic threads are an exact match for astronomy 2" filter threads.

[Mark2022]

1 hour ago, Franklin said:

Baader 495 longpass cuts CA very well but it does add more than just a hint of yellow, it's a very strong yellow, which would be fine if you plan on using a monochrome camera for your EAA set up. If using a OSC camera I'd go for the CB filter.

Have you tried both yourself?

[Mark2022]

14 minutes ago, Louis D said:

If you can find a new old stock 48mm Yellow K2/#8 photographic filter local to the UK, it will have roughly the same bandpass characteristics as the Baader 495 Longpass for a lot less.  I have the Rokunar version, and it works very well with a distinct yellow cast, but not nearly as strong as a GSO Yellow #12 filter.  The 48mm photographic threads are an exact match for astronomy 2" filter threads.

Sounds good, I'll have a look. Thanks.

[Mark2022]

1 minute ago, Mark2022 said:

Sounds good, I'll have a look. Thanks.

Actually, I wasn't thinking when I first posted. I won't need a 2 inch because I won't be using the diagonal for EAA. A 1.25 inch would do attached to the screw thread of the camera. Do these filters come in 1.25 inch?

[Mark2022]

1 hour ago, Franklin said:

Baader 495 longpass cuts CA very well but it does add more than just a hint of yellow, it's a very strong yellow, which would be fine if you plan on using a monochrome camera for your EAA set up. If using a OSC camera I'd go for the CB filter.

Also, Franklin, it will be OSC not mono.

[Franklin]

1 minute ago, Mark2022 said:

Have you tried both yourself?

Yes, I've tried Contrast Booster, Semi-Apo, 495 longpass, Wratten #8 and others and various other minus violet filters. They all work to a varying degree but the best way to combat CA is to use a reflecting telescope or an Apo refractor. Out of all of them, for visual, I thought the Contrast Booster gave the best performance.

[Mark2022]

Isn't it possible to adjust white balance to balance out the yellow hue caused by the 495 longpass?

[Franklin]

1 minute ago, Mark2022 said:

Do these filters come in 1.25 inch?

FLO do the CB and 495 in 1.25" and they come up on the used market every so often.

 

[Mark2022]

Just now, Franklin said:

FLO do the CB and 495 in 1.25" and they come up on the used market every so often.

 

FLO never seem to have them in stock. I'll check again. However, to repeat my previous question since I just mentioned the longpass - Isn't it possible with a OSC and in Sharpcap, to balance out the effect of  the change of hue by any of these filters using white balance?

[Don Pensack]

11 hours ago, badhex said:

Yikes, that first graphic is busy! 

It seems to the layperson that on paper the CB and Wratten #12 are not dramatically dissimilar at the blue end of the spectrum and your images and experience confirms that. Shame you don't have a contrast booster to run through your spectrograph for a side by side with the #12!

 

 

A #12 is a longpass filter.

The Baader Contrast Booster is very different.

Here is the spectrum on my own personal CB filter:

 

[Louis D]

The Contrast Booster filter is basically a 495 Longpass combined with a Neodymium glass subtrate.  You can get roughly the same results with a Yellow K2 filter stacked with a generic Moon & Skyglow filter.  Transmission might be a bit lower than the CB.

[Louis D]

7 hours ago, Mark2022 said:

Isn't it possible to adjust white balance to balance out the yellow hue caused by the 495 longpass?

I was wondering a similar thought last Thursday except I was wondering if adding a Zhumell Moon & Skyglow (Urban Skyglow) filter or a Tiffen CC50B color compensating photographic filter to various yellow filters would yield a more neutral color balance when combined with my DSLR's automatic white balance setting.  The CC50B filter has just about the same density and color appearance (purplish) as a M&S filter despite not having that notch at yellow-orange.  Basically, cutting yellow (M&S or purple CC filter) somewhat compensates for cutting violet (yellow longpass filter).

Here are the results below:

The Baader Semi APO is fairly neutral all by itself.  It does a semi-decent job of cutting violet at night.

The M&S plus either the Hirsch #12A or cheap Chinese Yellow yields a result very similar to the Semi APO and also does a decent job cutting violet at night.  The vignetting in the cheap Yellow image is because I was using a 1.25" filter instead of 2" filter in this one case in front of the taking lens.

The M&S plus Rokunar K2/#8 Yellow looks very similar to the daylight Contrast Booster images I've seen with that weird greenish sky.  At night, it cuts all violet.

The Tiffen CC50B plus Rokunar K2/#8 Yellow is very similar in color balance to the M&S/K2 combo as I expected.  I don't recall trying this combo at night.  Something to remember to try out next time.

The M&S plus Meade #8 Light Yellow is closest to the original color balance, but doesn't do much to reduce violet.  Again, I don't recall trying this combo at night, but I doubt I'll try it since the Meade #8 Light Yellow doesn't cut any violet that I can see.

Overall, even a DSLR with sophisticated color balance algorithms couldn't correct out the weird color casts completely.

[badhex]

12 hours ago, Don Pensack said:

A #12 is a longpass filter.

The Baader Contrast Booster is very different.

Here is the spectrum on my own personal CB filter:

 

Ah apologies, I understand the difference, I actually meant that the Hirsch 12A—not the Wratten as I originally wrote—and the CB are quite similar up to about 480nm. Nice to see the real world example though, thanks!