Baader UV/IR Cut vs Baader Semi Apo for Achromat Imaging - Lunar Test

[Chris]

This is more of a practical review/test rather than a write up. The Baader Semi Apo cuts the IR region of the spectrum just like the Baader UV/IR Cut filter, therefore this is mainly showing the importance of using some kind of IR cut when imaging with at least an achromat refractor (*Unless you're specifically targeting IR wavelengths with an IR pass filter).

 

[vlaiv]

It is always worth adding simple wratten #8 filter to these comparisons as it is by far the cheapest option for dealing with blue fringing in achromat scopes.

[Chris]

10 minutes ago, vlaiv said:

It is always worth adding simple wratten #8 filter to these comparisons as it is by far the cheapest option for dealing with blue fringing in achromat scopes.

I'll add one to my next order Vlaiv, it will be good to compare. 

[bosun21]

I’m still preferring the Baader contrast booster filter being slightly better than the semi apo for cutting down the fringing. I am not alone in this assumption. 
PS:

I’ll be trying a wratten No 8 

Edited April 18, 2022 by bosun21

[bosun21]

https://www.firstlightoptics.com/reviews/baader-contrast-filters_US-ATT_review_0414.pdf
Here is a comparison between the Semi Apo, Fringe Killer and the Contrast Booster 

 

[Chris]

1 hour ago, bosun21 said:

https://www.firstlightoptics.com/reviews/baader-contrast-filters_US-ATT_review_0414.pdf
Here is a comparison between the Semi Apo, Fringe Killer and the Contrast Booster 

 

 A good read that, thanks for sharing  I prefer filters with minimal colour cast so side with the author with regards to favouring the Semi Apo. I confess I didn't keep the contrast booster long when I had one but wouldn't rule out giving it a second go purely for the imaging side of things as you can play with the colour balance in post. The fringe killer is one I'm yet to test!  

[bosun21]

The color hew that he showed on the contrast booster isn’t really present to the degree shown when visually observing. It seems more prevalent with a camera 

[Ratlet]

The image seemed sharper with the semi apo than with no filter.  Do you think that is an effect of the filter or improved seeing?

[Chris]

2 hours ago, Ratlet said:

The image seemed sharper with the semi apo than with no filter.  Do you think that is an effect of the filter or improved seeing?

Hi, I suspect it's more the filter because the semi apo filter cuts UV/IR wavelengths as well as cutting chromatic aberration. 

In hindsight it was a bit pointless stacking the Semi Apo with the UV/IR cut filter because I was forgetting that the Semi Apo already does the job of the UV/IR cut filter!

[Ratlet]

43 minutes ago, Chris said:

Hi, I suspect it's more the filter because the semi apo filter cuts UV/IR wavelengths as well as cutting chromatic aberration. 

In hindsight it was a bit pointless stacking the Semi Apo with the UV/IR cut filter because I was forgetting that the Semi Apo already does the job of the UV/IR cut filter!

I guarantee that someone just starting out is going to Google stacking those filters.  Might seem pointless, but I'll be my house that you'll have saved someone some cash at some point.

[Louis D]

I hope this isn't a stupid question, but why does the no filter image have the most color shift of the four images (I see it as pink on my monitor)?  Did you use a weird color balance on your camera for all four images, and it balances out the color shift of the filters on the other three but ruins it for the no-filter one?  It just seems counter intuitive that the filtered images are more neutral than the unfiltered image.

[vlaiv]

4 minutes ago, Louis D said:

I hope this isn't a stupid question, but why does the no filter image have the most color shift of the four images (I see it as pink on my monitor)?  Did you use a weird color balance on your camera for all four images, and it balances out the color shift of the filters on the other three but ruins it for the no-filter one?  It just seems counter intuitive that the filtered images are more neutral than the unfiltered image.

Without any filter - there will be a lot of IR photons hitting the sensor.

There are a few camera models that have strong red and IR response and that will make everything looking pink.

see for example ASI485mc model - above 700nm it has much stronger red response.

Any IR light will be registered as predominantly red and will be added to the image as reddish hue.

[Chris]

1 hour ago, Louis D said:

I hope this isn't a stupid question, but why does the no filter image have the most color shift of the four images (I see it as pink on my monitor)?  Did you use a weird color balance on your camera for all four images, and it balances out the color shift of the filters on the other three but ruins it for the no-filter one?  It just seems counter intuitive that the filtered images are more neutral than the unfiltered image.

Sounds like an excellent question to me  Exactly what Vlaiv said, I'm using the ZWO ASI462mc which has a very strong red and IR response. The filters are doing a good job of cutting this out

 

 

 

[Louis D]

Thanks guys.  Makes total sense.  I forgot about the lack of IR filtering and high IR sensitivity on those cameras.

I have an old Olympus C-2000 that I use with an R72 filter for poor man's IR photography.  It was the last (or nearly so) Olympus digital camera without an IR-cut filter ahead of the sensor.  It's so sensitive to IR, I can use normal shutter speeds to photograph objects and people without motion blur.