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#26 nofxrx

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Posted 14 December 2012 - 05:15 PM


Aboy, you in NO WAY wasted your money. You actually did something that makes perfect sense...problem was that you didnt know what you were doing when you did it lol :D
But, you will be fine!!
Since you have it, install the Astronomik filter...
But, seeing your recent posts about the camera not working the first time, then after you went back in and did something it worked again, and IS working now...I would just leave it as is...
but that is just my opinion...
Yes it means that you paid $ for the filter and didnt use it..but so what..sell it! you might make back some or most of that $..

Or, if you do install it, just be careful and take your time and use the tutorials available and I think you will be fine.

Your AF is going to be way off now that both filters have been removed..so even installing the Astronomik is not going to bring that back to PERFECT calibration, it will be close, but still not accurate enough for daytime use.


Thanks for the post and help me to clear some question.. I'm really glad that you people takes time and answer my question.

Also:

1: jajajajaja yes, I did mod my camera with no much knowledge about it how to mod it.. But everyone do the same the first time. We learn with the practice XD


2. Believe me... I'll.

3. I don't care about the AF. I want my camera for astrophography. If I want to shoot some day time pictures, I'll use manual focus.. :)

Also I'll practice hard in order to learn how to takes good pictures.

Thanks again. :bow:


Anytime! :)

Yea, everyone has to start somewhere..I did..my first camera took me like 5 hours to do and I was a nervous wreck the entire time..now I can do them in my sleep..LOL

But, that is what is so great about CN, you have a ton of people on here that have most likely been through the same situation(s) as you/I/anyone, and we can all help each other figure this out as we go! :grouphug: lol

#27 mmalik

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Posted 14 December 2012 - 05:59 PM

Brent, thanks for the great write-up; this is really helpful in understanding the concept. Please see if you can help clarify some terminology confusion:

One of your fellow professional DSLR modifier offers these mod options:

•Option 1 - IR Filter Removal Only
•Option 2 - IR Filter Replacement with Clear Glass
•Option 3A - IR Filter Replacement with Astrodon UV/IR block filter
•Option 3B - IR Filter Replacement with Baader UV/IR block filter

Does ‘IR Filter’ above refer to LPF-2 (WB filter)? If yes, why there is so much disparity in referring to same components among professionals? My concern being it adds more confusion than clarity for something that is really 'simple' if terminology was standard. After all we are talking two layers/filters, how complicated could it be; would you agree? Sorry, just little frustrated at terminology jargon, nothing against you or anyone else.

Wouldn't following make more sense?

•Option 1 - LPF-2 Filter Removal Only
•Option 2 - LPF-2 Filter Replacement with Clear Glass
•Option 3A - LPF-2 Filter Replacement with Astrodon UV/IR block filter
•Option 3B - LPF-2 Filter Replacement with Baader UV/IR block filter

Thx

#28 nofxrx

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Posted 14 December 2012 - 07:52 PM

Brent, thanks for the great write-up; this is really helpful in understanding the concept. Please see if you can help clarify some terminology confusion:

One of your fellow professional DSLR modifier offers these mod options:

•Option 1 - IR Filter Removal Only
•Option 2 - IR Filter Replacement with Clear Glass
•Option 3A - IR Filter Replacement with Astrodon UV/IR block filter
•Option 3B - IR Filter Replacement with Baader UV/IR block filter

Does ‘IR Filter’ above refer to LPF-2 (WB filter)? If yes, why there is so much disparity in referring to same components among professionals? My concern being it adds more confusion than clarity for something that is really 'simple' if terminology was standard. After all we are talking two layers/filters, how complicated could it be; would you agree? Sorry, just little frustrated at terminology jargon, nothing against you or anyone else.

Wouldn't following make more sense?

•Option 1 - LPF-2 Filter Removal Only
•Option 2 - LPF-2 Filter Replacement with Clear Glass
•Option 3A - LPF-2 Filter Replacement with Astrodon UV/IR block filter
•Option 3B - LPF-2 Filter Replacement with Baader UV/IR block filter

Thx


Yep!! this is one of the reasons for a lot of the confusion!

However, Hap's pricing models there show the options for ALL models, including the older models that DO require an IR Filter replacement, mainly the 20D/30D/300D/350D/etc...so, as to not confuse his customers, I would think that this is why he words things this way...****AFAIK! I cannot speak for him/anyone else!****

There is always confusion in terminology when something is first 'discovered'/brought to attention/debated,etc..
But, with only a VERY small group of guys doing this, and having it split right down the middle(AFAIK, there are several international modification companies that share my exact opinions/ideas..Hap and Gary are the only two, AFAIK, that still hold to the OLD truths that WERE relevant to older models!)
Maybe it is an age thing...? I am "only" 30, so perhaps I am not as set in my ways and unwilling to change as "others" lol (I AM NOT laughing at anyone, or poking fun, or saying ANYthing negative about anyone! atleast not intentionally!)


If you were to ask "them" if you needed an AstroDon or Baader filter to replace LPF-2, they would undoubtedly say YES!
Again..my points are still valid. whether people, or even 'them', believe me or not.
I will not even go into the "proven test" performed by one of those guys that shows LPF-1 does not block enough IR for "proper" astro images. THat test is so flawed it really isnt even funny, and a LOT of people use that as definitive "proof" that one needs an IR replacement for LPF-2.

Things like this prove otherwise!
This is a ***REAL*** test!
REALLY look at the sets of images, particularly the top row of images. Look at the Stock 1000D image, this shows a stock camera not allowing ANY IR data through..the images next to it, the ones of a Baader filter and an LPF-1 only system, guess what? THEY ARE IDENTICAL(to each other, not compared to the stock 1000D image)!!!!

So...since BOTH the Baader AND LPF-1 only images show the exact same amount of IR data in the image, what does this mean?
It means that NO MATTER WHAT MOD you do, assuming an IR Block is LEFT INTACT and LPF-2 is removed, you will have the EXACT same performance.
My guess is that the small amount of IR data(compared to the Full Spectrum 350D image and the stock 1000D image) that still transmits through is of no consequence to our pursuits..

Also, if you look at the images below those that show the remote's IR LED, you will see that by just adding a WB filter(in this exact case the X-Nite CC1 filter from MaxMax), there is ZERO IR data passed....which means, YES, LPF-2 or any WB filter DOES block some IR, which is a result of their spectral curve modification/restrictions..the return a camera back to stock..they remove all deep red(Ha) data....But the point/my main point is, and always has been, that the "bad" filter, LPF-2 has to be removed (this is universal no matter who you ask), whether you use ONLY LPF-1 or an expensive alternative, you get the EXACT same performance!!
That is my whole point. Why waste the $ on an expensive filter if LPF-1 does the EXACT same job/amount of "work" as the expensive filters..?

All of my tests are DIRECTLY in line with this test above, and NOT Gary's!!
Though I have only tested on TRUE IR light sources, not flashlights(like Gary), or a stove burner(like the one above)..
Only with REAL IR sources can you judge a modified system's performance..
And there is very little to debate..
I need to make a write-up very soon to help squash some of this confusion..
I cannot wait til I have some time to finish my website, I would hope that it would help a lot of people see what is going on inside these cameras, and how we can manipulate things to get the desired output..
If I only had SOME spare time! :tonofbricks:


And yes, a lot of confusion would be gone if we could all agree on the same terminology..
I will be the first to admit if/when I am wrong..so all anyone has to do is prove to me that I am, I will change my opinions/advice..
But from everything I have ever seen online, and from ALL of my experience, everything I have said reads 100% true in my head..AND MANY, MANY customer's as well! ;) :shrug:

#29 mmalik

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Posted 15 December 2012 - 03:44 AM

Brent, thanks for the great write-up; this is really helpful in understanding the concept. Please see if you can help clarify some terminology confusion:

One of your fellow professional DSLR modifier offers these mod options:

•Option 1 - IR Filter Removal Only
•Option 2 - IR Filter Replacement with Clear Glass
•Option 3A - IR Filter Replacement with Astrodon UV/IR block filter
•Option 3B - IR Filter Replacement with Baader UV/IR block filter

Does ‘IR Filter’ above refer to LPF-2 (WB filter)? If yes, why there is so much disparity in referring to same components among professionals? My concern being it adds more confusion than clarity for something that is really 'simple' if terminology was standard. After all we are talking two layers/filters, how complicated could it be; would you agree? Sorry, just little frustrated at terminology jargon, nothing against you or anyone else.

Wouldn't following make more sense?

•Option 1 - LPF-2 Filter Removal Only
•Option 2 - LPF-2 Filter Replacement with Clear Glass
•Option 3A - LPF-2 Filter Replacement with Astrodon UV/IR block filter
•Option 3B - LPF-2 Filter Replacement with Baader UV/IR block filter

Thx


Yep!! this is one of the reasons for a lot of the confusion!

However, Hap's pricing models there show the options for ALL models, including the older models that DO require an IR Filter replacement, mainly the 20D/30D/300D/350D/etc...so, as to not confuse his customers, I would think that this is why he words things this way...****AFAIK! I cannot speak for him/anyone else!****

There is always confusion in terminology when something is first 'discovered'/brought to attention/debated,etc..
But, with only a VERY small group of guys doing this, and having it split right down the middle(AFAIK, there are several international modification companies that share my exact opinions/ideas..Hap and Gary are the only two, AFAIK, that still hold to the OLD truths that WERE relevant to older models!)
Maybe it is an age thing...? I am "only" 30, so perhaps I am not as set in my ways and unwilling to change as "others" lol (I AM NOT laughing at anyone, or poking fun, or saying ANYthing negative about anyone! atleast not intentionally!)


If you were to ask "them" if you needed an AstroDon or Baader filter to replace LPF-2, they would undoubtedly say YES!
Again..my points are still valid. whether people, or even 'them', believe me or not.
I will not even go into the "proven test" performed by one of those guys that shows LPF-1 does not block enough IR for "proper" astro images. THat test is so flawed it really isnt even funny, and a LOT of people use that as definitive "proof" that one needs an IR replacement for LPF-2.

Things like this prove otherwise!
This is a ***REAL*** test!
REALLY look at the sets of images, particularly the top row of images. Look at the Stock 1000D image, this shows a stock camera not allowing ANY IR data through..the images next to it, the ones of a Baader filter and an LPF-1 only system, guess what? THEY ARE IDENTICAL(to each other, not compared to the stock 1000D image)!!!!

So...since BOTH the Baader AND LPF-1 only images show the exact same amount of IR data in the image, what does this mean?
It means that NO MATTER WHAT MOD you do, assuming an IR Block is LEFT INTACT and LPF-2 is removed, you will have the EXACT same performance.
My guess is that the small amount of IR data(compared to the Full Spectrum 350D image and the stock 1000D image) that still transmits through is of no consequence to our pursuits..

Also, if you look at the images below those that show the remote's IR LED, you will see that by just adding a WB filter(in this exact case the X-Nite CC1 filter from MaxMax), there is ZERO IR data passed....which means, YES, LPF-2 or any WB filter DOES block some IR, which is a result of their spectral curve modification/restrictions..the return a camera back to stock..they remove all deep red(Ha) data....But the point/my main point is, and always has been, that the "bad" filter, LPF-2 has to be removed (this is universal no matter who you ask), whether you use ONLY LPF-1 or an expensive alternative, you get the EXACT same performance!!
That is my whole point. Why waste the $ on an expensive filter if LPF-1 does the EXACT same job/amount of "work" as the expensive filters..?

All of my tests are DIRECTLY in line with this test above, and NOT Gary's!!
Though I have only tested on TRUE IR light sources, not flashlights(like Gary), or a stove burner(like the one above)..
Only with REAL IR sources can you judge a modified system's performance..
And there is very little to debate..
I need to make a write-up very soon to help squash some of this confusion..
I cannot wait til I have some time to finish my website, I would hope that it would help a lot of people see what is going on inside these cameras, and how we can manipulate things to get the desired output..
If I only had SOME spare time! :tonofbricks:


And yes, a lot of confusion would be gone if we could all agree on the same terminology..
I will be the first to admit if/when I am wrong..so all anyone has to do is prove to me that I am, I will change my opinions/advice..
But from everything I have ever seen online, and from ALL of my experience, everything I have said reads 100% true in my head..AND MANY, MANY customer's as well! ;) :shrug:


Thanks Brent for your understanding and elaborating. Would be great if Hap and Gary could chime in and once for all get following sorted out:

1. Type of mods being offered; if replacing LPF-2 with expensive alternatives is just waste of $, then let's just NOT promote it anymore.

2. Using standard terminology (i.e., LPF-1 & LPF-2, etc., and NOT using confusing terms like ‘IR Filter Replacement’, etc.) so all could speak and comprehend the same language.

3. Last but not least, resolve OLD (single [IR] filter systems) vs. NEW (two [LPF-1, LPF-2] filter systems) confusion; if old truths don't hold true any longer, why not make contemporary (two filter systems) the norm and old (single filter systems) an exception, be it terminology or solutions offered?

#30 nofxrx

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Posted 15 December 2012 - 05:13 AM

All VERY good points, and I agree completely!

But...I really dont see your first point actually happening...
I just dont think anyone is going to stop promoting filters that add more $ to their pockets..
I tell people everything about filters and some people still prefer to have the "name brand" filters installed..to each their own..
So, unless everyone(impossible) became more knowledgeable about the issues, there will always be demand for these filters...
atleast, imho..

And I dont think anyone actively "promotes" the expensive filters, I just think most will let people think what they want and just give them what they want..whether or not they "need" that option or not..
Is that my business motto? not even close.. ;)

#31 microstar

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Posted 15 December 2012 - 09:57 AM

Interesting thread, but with my Baader BCF in the mail for my mod I have no regrets and would make the same choice. I want to also be able to use my 450D with my 100mm Macro lens for nature photography with the custom WB and AF. Best of both worlds hopefully for not much additional cost (compared to what I spend on this hobby).
...Keith

#32 JustinLT

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Posted 15 December 2012 - 01:25 PM

Brent,

after reading this thread, I found out, that I would have made the same mistake and would have been replaced my 1000D LFP-2 filter with Baader IR/UV cut filter (basically 2x UV/IR filters in the camera). Now I know that clear glass is perfectly fine (to get the autofocus). But I still have 2 questions:

1. Is daylight photography still possible with custom wb, if I use a clear glass?
2. I just got an interesting idea into my head: if I could make a plastic plate, that would fit beyond the bayonet mount (same shape as astronomic clip), also if I could remove the without damaging the LPF-2 filter and get it shaped to fit into the plastic plate, would it be possible to use it as a WB filter? Basically everything the same as in basic camera, only different position of LPF-2 filter and one more clear glass in it's place. This way the only expenses would be the clear glass and we could have a very versatile camera for daylight photography (the LPF-2 filter clipped in) and for astrophotography with h-alpha passing (LPF-2 filter removed). Anyway the astronomik or other WB filter are quite expensive (150-190$).

#33 Aboy

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Posted 15 December 2012 - 08:37 PM

Up to I know u can use a costom white balance in order to shoot at day time. Also u can use a filter infrin of the lense.
About your idea I was thinking the same thing... But in my case I'll use the camera just for astrophotography.. I'll get a Nikon Canon lense adapter to shoot some infrared or some night sky shoot.

#34 Hap Griffin

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Posted 15 December 2012 - 09:43 PM

I will chime in here. Brent's assertion that the LPF#1 blocks IR is correct. But the question is, is it enough by itself? Gary's test with IR LED's (and it is indeed a proper practical test) does conclusively show that it lets through a considerable amount of IR light when used by itself, which is greatly reduced when used in concert with a Baader or Astrodon replacement for LPF#2. All astronomical instruments that are refractive in nature (virtually all but a true Newtonian telescope with ONLY mirror elements) will benefit from having IR blocked as completely as possible because of chromatic abberation inherent in all refractive optical systems. Any IR light getting through a lens will come to focus at a different point than visible light because of its longer wavelength...resulting in bloated star images. Star images can be bloated a lot, or just a little. If you are looking for the tightest possible star images, then complete and thorough IR rejection should be a priority. Replacing LPF#2 with nothing results in a camera unable to focus to infinity with normal lenses, inaccurate autofocus, and less IR rejection than the stock camera had. Replacing it with clear glass can fix the focus problem IF it is of the correct thickness (which is very critical) or the sensor platform position adjusted to compensate (which, again, is very critical), but the glass has to be coated with a good quality anti-reflection coating or halos around bright stars will result. Clear glass does nothing for the loss of IR rejection. Replacing LFP#2 with an astronomical UV/IR blocker such as the Baader or Astrodon takes care of both issues. Astrodon filters are widely used in high-end CCD cameras and highly respected for their exceptional anti-reflective coatings. The DSLR replacement filter has that same coating.

If one is content to do with less than optimal IR rejection and is willing to give up imaging with lenses due to the focus issues, then the simple removal of LPF#2 may be all that you need. Personally, I am a bit more critical than that and I think that my astrophotography shows it. LPF#2 is more than just a color balance filter...it has very significant IR rejection that is required in a stock camera to allow the autofocus system to not be fooled by IR light getting through and coming to focus at a different position from chromatic abberation. Canon didn't raise the cost of their cameras in a competitive market by putting in an expensive filter for nothing. By replacing LPF#2 with a true astronomical filter, IR rejection is maximized ensuring the tightest possible star images, the proper back focus is retained, and high quality anti-reflective coatings are in place...at a price not significantly above an inexpensive clear glass substitute when the entire modification cost is taken into consideration.

#35 Hap Griffin

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Posted 15 December 2012 - 10:36 PM

Brent's test page shows on his tests of the 1000D how much IR blocking the combination of LPF#1 and LPF#2 provides in that the hot stove eye is completely invisible. However, with LPF#2 removed and only LPF#1 in place, the IR from the stove eye is coming through clearly. LPF#2 is obviously providing a huge amount of IR blocking.

#36 nofxrx

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Posted 16 December 2012 - 01:40 AM

Brent's test page shows on his tests of the 1000D how much IR blocking the combination of LPF#1 and LPF#2 provides in that the hot stove eye is completely invisible. However, with LPF#2 removed and only LPF#1 in place, the IR from the stove eye is coming through clearly. LPF#2 is obviously providing a huge amount of IR blocking.


First, sorry for the confusion, that is NOT my test/images.etc..just a link I supplied..not my work.. :)

Now. back OT..

No it doesnt..the images clearly show:
1) system with both LPF-1 and LPF-2(stock camera) clearly block 100% IR
2) both *LPF-1 only* -AND- *Baader only* setups block about the same amount of IR, ~90% IR, when compared to the UNfiltered image.

The ****POINT**** (my point) in (linking to) that test was to show that with JUST the Baader filter, there is still an IDENTICAL amount of IR data that passes vs an LPF-1 only system...
Look at the image of the Baader only system, and then the one with only LPF-1...looks like the same image. same amount of IR is being passed.
SO..why use the Baader if LPF-1 does the EXACT same amount of blocking? that's it..

Also, why does things like the attached image show up every once and a while showing that LPF-1 performs NEARLY/identical to a Baader+LPF-1 setup or an AstroDon+LPF-1 setup???


I just do not understand...



cheers..

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#37 JustinLT

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Posted 16 December 2012 - 08:41 AM

According to this graph Baader IR/UV filter does not change anything at all. Astrodon filter cuts a very slight amount of green and also a small amount of IR, actually in the same wavelenght as stock filter. I don't think it can be noticed in the picture (but who knows).
Now the issue is only with the clear glass, which is also very expensive and not too much cheaper than IR/UV filter.

Now my conclusion would be following: best option if you want to get top results for a budget price is to buy a canon 350d (it will be quite cheaper than 450d or you can buy even a faulty one without autofocus or with broken lcd screen)and modify it with Baader BCF IR/UV filter. It would be even worthy to make a cooling case as Gary Honis has done as in this camera there is no live view, so basically you can do everything via laptop. With 450d it would be a pitty to lose live view, as it is really useful.
Of course this is only my opinion. Maybe some people will prefer the larger megapixel amount in 450d.

#38 Mike C

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Posted 16 December 2012 - 12:26 PM

I've found this a very interesting thread, as I've just had a Canon 600D modified here in the UK. Although I cannot contribute to the technical discussion, I can relate my experience.

The camera has the LPF-2 filter removed, not replaced with anything. I did not expect any problems with infra-red, but my experience has been different - at least when there are bright stars in the field.

Below is a test frame of the Pleiades, with minimum processing. I did not continue taking subs due to the red disks around the stars, which I took to be out-of-focus infrared. I was using an apo. refractor.

I've since bought a 2-inch Baader UV/IR block filter, which I'm hoping will make a difference and improve my results when there are bright stars. Having read this thread, I am not so sure! The Baader packaging says it blocks infrared above 680 nm, which sounds more effective than the internal Baader the posted graph refers to. The next clear night, whenever that may be, will tell! :fingerscrossed:

Regards,

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#39 JustinLT

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Posted 16 December 2012 - 12:55 PM

Mike,

your image causes even more confusion now, but it is a really great proof. But again, it gives only few more questions:

1) Is the filter system in canon 600D the same as in 450d, 1000d, etc.
2) If so, is there a possibility, that LPF-1 filter was removed as well? Maybe it is a full spectrum mod?

If the answers would be yes and no, then I suppose Hap Griffin was right and LPF-1 filter still passes some amount of unwanted infra-red. Well, according to the graph, the stock camera cuts IR light exactly at 700 nm and LPF-1 cuts IR light at approx 720 nm, so at least 0.05% of it comes thorugh. I don't know if it is possible, that it would cause red disks around the start. But in this case, only astrodon filter would work, Baaded filter cuts the light at same wavelenght as LPF-1 filter.
This is really interesting topic and more tests are needed for sure.

#40 Hap Griffin

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Posted 16 December 2012 - 01:50 PM

Remember that in the stock system, or one with LPF#1 still in place and LPF#2 replaced with a Baader or Astrodon filter that the IR attenuation of both filters is in play...if as the graph shows, LPF#1 is down to about 1% transmission at 700 nm, then with LPF#2 replaced with a Baader or Astrodon which are down to 1% with the Baader and less than 1% with the Astrodon, that the equivalent IR rejection is the product of the two...0.01 x 0.01 = 0.0001. In other words, without replacing LPF#2 with another IR reject filter, you have around 100 times more IR getting through...which as shown in Mike's image above is sufficient to cause bloated stars from the chromatic abberation inherent in refractive systems...even in very high quality APO scopes that are not corrected for IR light. If one wants to take the inexpensive route and not replace LPF#2 with anything, or with clear glass, then that is their perogative...but as shown in Mike's image above, image quality will suffer. As for me, imaging time under a dark sky is valuable and I want the best chance of having a positive outcome from the time I get to spend imaging.

#41 Hap Griffin

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Posted 16 December 2012 - 01:59 PM

Mike, your image is a good example of IR star bloating. May I use it in my talks on the subject, of course with credit being given to you?

#42 Mike C

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Posted 16 December 2012 - 06:10 PM

Justin and Hap, thanks for your responses.

Just to clarify, I did order a modification with Baader replacement from the UK vendor. However, the mod was taking longer than I wanted and a subsequent conversation led to me settling for a straight removal of the main filter, leaving the other in place. I can only assume that this is what was done, as I have not discussed the IR issue with the vendor. I am pleased with the modification overall, and am hopeful that the Baader IR/UV-cut filter I've purchased will solve the IR problem.

Hap, for this reason, although you are welcome to use my Pleiades image to illustrate the problem of IR not being filtered adequately, I'd prefer not to be credited!

Regards,

#43 Hap Griffin

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Posted 16 December 2012 - 06:11 PM

I understand. Thanks!

#44 nofxrx

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Posted 16 December 2012 - 07:50 PM

Mike, your image shows a LOT of IR star bloat.
I have never seen an LPF-1 only system show that much star bloat..even on bright stars, like in the HH and Flame FOV...

I dont think something is right here...but that is just imho..

I will be interested to see what happens with the external IR Block..

Hap..dont you think you should figure out exactly what is going on in this guys camera before using it as "proof" that an LPF-1 only system does not reject enough IR???

Also..so are you telling us that LPF-1 and a Baader/AstroDon is 100x better at blocking IR than an LPF-1 only system?
Really? 0.01% vs 0.0001%?
yep. LPF-1 only is absolutely dreadful and no one should use it. ;)

#45 austin.grant

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Posted 16 December 2012 - 08:06 PM

Before this gets locked, I'd like to add that that does seem like an extraordinary amount of bloat. My LPF-1 only 1000d never showed any symptoms of star bloat with refractive optics.

#46 nofxrx

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Posted 16 December 2012 - 08:11 PM

Before this gets locked, I'd like to add that that does seem like an extraordinary amount of bloat. My LPF-1 only 1000d never showed any symptoms of star bloat with refractive optics.


I am so glad someone else thought so...I was beginning to think I am crazy..
wait. nope. still crazy :lol:

Why would the thread get locked?

#47 Hap Griffin

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Posted 16 December 2012 - 08:29 PM

Brent, when you put two filters in series, each with a transmission of, let's say, 1% at a particular IR wavelength...then, yes, the two together will pass 1% of 1%, which is 100 times more attenuation than through a single filter. Your detailed picture of the stove eye through an LPF#1 only mod on a 1000D shows clearly that a very significant amount of IR gets through it, as does Gary's test with IR LED's.

Filters in series act similarly to RF attenuators in series (for all the hams and RF engineers out there). A 10 dB attenuator drops the power at its input down to 10% of its value at its output. Putting two 10dB attenuators in series gives 20 dB total attenuation of the power, or 1/100th of the input power. In other words, putting two filters in series doesn't just double the attenuation...the equivalent attenuation is the mathematical product of the two attenuations.

As for Mike's image, I can only go on what he says was done to his camera. In any case, it is an obvious demonstration of IR caused star bloating.

#48 Hap Griffin

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Posted 16 December 2012 - 08:45 PM

The Pleiades (M45) is a great test for both star bloat and reflection halos...it has relatively bright stars which stress the IR attenuation of filters and the anti-reflection coatings. M45 is the target that clearly showed a faulty AR coating on one of my CCD filters once. And the blue stars will expose IR bloat as red (as in Mike's image) since IR shows up mainly in the red channel.

#49 nofxrx

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Posted 16 December 2012 - 09:29 PM

Okay, that makes a lot more sense..seriously.

But, I still do not see that amount of difference in transmission makes images like Mike's...but, I could be wrong.

Again, I go back to the facts that I know, that MANY people who use an LPF-1 only system experience little or NO IR star bloat..


I too have had many issues with reflections on objects like M45..maybe this is also attributing to Mike's issue..? :shrug:

#50 Hap Griffin

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Posted 16 December 2012 - 10:12 PM

That's why I chose Astrodon LRGB filters for my CCD. Unlike other brands, they do not exhibit reflections on M45 or other bright stars. Looking at images of M45 across the web, you can see that other lines of filters do commonly exhibit reflections. Your reflection problems make me wonder what type of coating the Edmunds clear glass has.

As for star bloat, I'd like to see some examples of LPF-1 only cameras with bright stars in the field. As I said before, you can have a lot of star bloat due to IR leakage, or just a little, depending on the brightness of the star, its IR signature and the amount of IR rejection in the system. Personally, I want to ensure that I have the most IR rejection possible so that I know that I'm not allowing my star images to be any larger than they are naturally.


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