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Question about canon modification.

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#51 Hap Griffin

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Posted 16 December 2012 - 10:23 PM

Also, you mention that some people experience little star bloat and that the difference of a few percent may not be noticeable. Bare in mind that we're talking about transmission numbers that determine the photons picked up by the sensor and becoming image data prior to contrast stretching. We often use curves and DDP in processing our images that will take an initial few percent difference in brightness in different areas of an image and stretch it into a much larger range so as to make it visible. So even if we only have a few ADU of star bloat in the RAW, by the time we stretch the histogram to a final presentation level, it can become very visible. So the appearance of IR effects is dependent on processing style and extent of histogram stretching.

#52 nofxrx

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Posted 17 December 2012 - 12:06 AM

So even if we only have a few ADU of star bloat in the RAW, by the time we stretch the histogram to a final presentation level, it can become very visible. So the appearance of IR effects is dependent on processing style and extent of histogram stretching.


Actually, this makes a lot of sense to me! Good point :)

#53 gdd

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Posted 17 December 2012 - 12:13 AM

Also, you mention that some people experience little star bloat and that the difference of a few percent may not be noticeable.



Is it also possible some refractive OTA's are better corrected in the IR than others?

Gale

#54 mmalik

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Posted 17 December 2012 - 02:02 AM

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.


Hap, we are talking science and Mike's image is an uncontrolled test and/or for that matter an uncontrolled mod. I am for using empirical evidence before hastening to the point of citing it. To be fair, at this point I don’t think we have countered Brent’s point of replacing LPF-2 with expensive alternatives being wasteful science, if not the money. Regards

#55 LeCarl

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Posted 17 December 2012 - 02:05 AM

To nofxrx

I'm totally agree (about the LPF-1) and...
I know, I know, (yes I learn something haha! )
But Primary! just want to keep this simple... :p
(I have experiences with peoples/material that don't want astrophotography complicated,
perfect sky balance at each shot, this is why we
choose the Happ's astrodon or baader filter, we found that full spectrum with filter is risky,
and mess a lot of nights, time, money... this is why we choose the DSLR... :grin:
(full spectrum for a first camera?...)

Just to say to don't forget about the distance for focusing on focusing,
Aboy wants to use his nikons lens with an adapter... full spectrum, (no glass/LPF-1) will not work, focussing distance will not be good
:foreheadslap:

The cost/bill of material is near the same full spectrum or not... :roflmao:
(if done by yourself, because not complicated...)

#56 Aboy

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Posted 17 December 2012 - 07:18 AM

Just to say to don't forget about the distance for focusing on focusing,
Aboy wants to use his nikons lens with an adapter... full spectrum, (no glass/LPF-1) will not work, focussing distance will not be good
:foreheadslap:



Yes. I'll use an adapter.. But up to I know it's possible to use it manual, that is in theory.. But I'll find out in real life soon. :smirk:

Ps. I am learning a lot with this thread :grin:

#57 Hap Griffin

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Posted 17 December 2012 - 10:45 AM

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.


Hap, we are talking science and Mike's image is an uncontrolled test and/or for that matter an uncontrolled mod. I am for using empirical evidence before hastening to the point of citing it. To be fair, at this point I don’t think we have countered Brent’s point of replacing LPF-2 with expensive alternatives being wasteful science, if not the money. Regards


Agreed. I'd like to see more images taken with LPF#1 only modified cameras through refractive systems with bright stars in them. As for the money, as I said before, the difference between a clear glass mod and a Baader or Astrodon mod is minimal when compared to the entire cost of the modification and shipping and the value of your imaging time if you find, as Mike did, that you have IR induced star bloat (which is what his image really looks like). Like I stated before, we spend lots of time and money on our scopes, mounts, observatories, travelling to dark sky sites, etc. If we want the absolute most pinpoint star images that our optics are capable of, we need to minimize IR leakage. The stock Canon's have two layers of IR rejection. By removing one of them, you are leaving the camera with less IR rejection than it had in stock condition. Brent's test image of a stove eye that is invisible with both LPF#1 and LPF#2 in place, yet is clearly visible with only LPF#1 in place shows that IR light definitely goes through LPF#1 in amounts sufficent to make a clear photograph. Do you want to have that amount of IR reaching your sensor? It's up to you.

#58 Mike C

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Posted 17 December 2012 - 03:00 PM

Sorry my post was not as informative as I had hoped! I am told that the main filter was to be removed, and not the second (LPF-1 in the terminology used here); however I cannot prove what was done.

Regarding Brent's suggestion that reflections could be partly to blame, I'm hopeful this is not the case. I have imaged the Pleiades with the same 'scope and CLS filter previously, though with a different (and unmodded) camera, with no internal reflection issues.

I'm looking forward to trying out the 2" Baader IR/UV-cut, but alas there is no clear sky on the radar at the moment.

Regards,

#59 mmalik

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Posted 17 December 2012 - 07:19 PM

I am told that the main filter was to be removed, and not the second (LPF-1 in the terminology used here)


Mike, sorry, but you are repeating the ambiguity most of us are trying to avoid. There is no such thing as "main filter" and your sentence is confusing at best as to which one was removed, LPF-1 or LPF-2?

Please confirm with a statement, e.g., “LPF-2 was removed, although you are doubtful”. Thx

#60 Hap Griffin

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Posted 17 December 2012 - 07:47 PM

One way to tell if LPF#1 is installed is to see if the camera is doing a dust cleaning when you turn it off. If it is and isn't throwing an error code, then LPF#1 is probably in place. If the "front filter", otherwise known as LPF#1, is not in place and the camera is set to do automatic dust cleanings, it should generate an error code ( I know it does with some models).

You can tell if LPF#2 has been removed by setting the automatic white balance to daylight and shooting a JPEG of an outdoor scene. If the overall tint is reddish, then LPF#2 is missing.

Mike, please do these tests and let us know the outcomes and we will have a better idea of the actual status of your camera.

#61 Mike C

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Posted 18 December 2012 - 08:20 AM

mmalik: LPF-2 removed; LPF-1 still in place. Hope that makes more sense :)

Hap: I do have the overall red tinge to daylight shots, and am getting good results with emission nebulae imaging, e.g
http://www.flickr.co.../in/photostream
http://www.flickr.co...in/photostream/
Note that both of these display the red disks around the bright stars that I believe to be due to IR.

The self-cleaning routine on the camera works when I switch it on and off (or at least it does not display an error message).

Regards,

#62 Hap Griffin

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Posted 18 December 2012 - 12:15 PM

OK, that sounds pretty definitively that you have LPF#1 still in place and LPF#2 removed. So, evidently LPF#1 by itself is not providing sufficient IR attenuation to prevent star bloating.

Thank you for the additional images with the bright stars. The fact that the bloating is in the red channel is pretty conclusive that the issue is IR related.

#63 vmsguy

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Posted 18 December 2012 - 05:03 PM


Hi,
I'm the "Brent" that did the stovetop tests.

My T1i and another T1i I modded for my friend Jeff Ball, don't show star bloat. Both are the LPF#1 only mod (LPF#1 filter left in camera, LPF#2 removed with no replacement filter)

I can only speak from my experience, but using my relatively low-end imaging gear (Nikkor lenses), I don't see adverse affects of IR related star bloat. Maybe the Nikkors are well corrected for IR.

Now Jeff, on the otherhand has high-end APO gear that probably corrects well for IR, and his images don't show IR bloat issues either.

So, what does this mean. For me, I'm replacing my T1i with a T3i that I will be modding soon. I will remove LPF#2 and
leave only the LPF#1 in place, but before doing so, I will try to perform additional test of before and after to add more "data" to this discussion.

I may repeat the "stovetop" test, and throw in some additional IR remotes that may be transmitting at different wavelengths. I also have a B+W 486 IR filter, A Baader IR 1.25" filter, and an original Baader BCF filter that I will use in the tests to see what results I get using different IR filters.

I will also take series of star images with the T3i before mod
and repeat using the same setup after mod to see if star bloat is apparent.

For other users with different optical systems, the results may be different, so take that into consideration when I post the results.

#64 mikotoy

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Posted 18 December 2012 - 06:53 PM

I'm presuming that it is entirely possible to remove LPF2 and if the star bloat is experienced to go back and install a secondary filter (Astronomik, Baader, Asrtrodon ...etc) at a later time without affecting the camera further?

#65 mmalik

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Posted 18 December 2012 - 07:10 PM

I'm presuming that it is entirely possible to remove LPF2 and if the star bloat is experienced to go back and install a secondary filter (Astronomik, Baader, Asrtrodon ...etc) at a later time without affecting the camera further?


Yes, that's one school of thought per discussion thus far. Thx

#66 Hap Griffin

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Posted 18 December 2012 - 10:25 PM

Note as stated before, the amount of star bloat will be magnified by contrast stretching that is the standard processing procedure in astrophotography. So any A/B test will have to have the processing carefully duplicated so that the final results will have the SAME amount of histogram stretching. I'm suspecting that this may be at least some of the difference why some people are experiencing it and others don't see it...differences in processing. I see many imagers, especially those just starting out, with the low end of the histogram crushed...that is, the dark areas are crushed into a black background. If star bloat is present, it may not come through in these images. In Mike's images, he has processed to preserve the faint detail which will also bring out low level IR related artifacts.

#67 Gary Honis

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Posted 19 December 2012 - 01:25 AM

I agree with Hap's comments. When I first started imaging with a Full Spectrum modified 300D in 2004, I wasn't using a UV/IR cut filter when imaging with a ShortTube 80 refractor. I was very happy with my images until someone commented that my stars seemed bloated. I added a 2" Baader UV/IR cut filter and I got tighter stars. I don't know how much I was loosing in image detail.

I have done many tests over time showing that the original Canon front filter of the newer two-filter models by itself does not fully block infrared. A still image test comparing the front filter only of a 1000D (XS)camera to a Baader BCF-1 DSLR replacement filter is HERE.

Today, I posted a YouTube video using a Full Spectrum modified camera to demonstrate how much more infrared light the original front filter passes than in a Baader (or Astrodon) modified camera. The YouTube video is HERE.

The front filter does not have a sharp cutoff at 700nm like the Baader or Astrodon filters. Baader has the transmission curve of the Baader BCF filter posted HERE. In the FILES section of DSLRmodifications there is a spectral curve by Ken Harrison that shows the front filter of a 1000D (XS) passes infrared above 700nm.

If you are imaging with a reflector, SCT or RC at prime and using a "front filter only" modified camera you should not have star bloat. Once you add a lens such as a reducer or barlow you will and would need to add an IR blocking filter.

#68 Hap Griffin

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Posted 19 December 2012 - 09:35 AM

Thanks for the input, Gary.

Those of us who are offering filter modifications are not trying to sell an extra filter that customers don't need (except in very special cases) but a solution to the IR problem that has been demonstrated clearly by the test images shown in this thread. If you feel that the Canon LPF#1 by itself provides all the IR blocking that you need, that's fine and it's your choice. In my experienced opinion after having worked with television camera optics for 34 years, performing over 800 Canon DSLR modifications and having my DSLR astro images published in books and magazines, I feel that the most versatile modification that will ensure that your Canon DSLR can be used with any telescope you will ever get without resorting to external filters, is one that replaces LPF#2 with a true astronomical UV/IR filter.

#69 Hap Griffin

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Posted 19 December 2012 - 09:42 AM

Actually, Gary, my experience with imaging through a Schmidt-Cassagrain (Meade 10" LX-200) is that the front corrector plate being refractive in nature does indeed cause star bloat without effective IR filtering.

#70 Gary Honis

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Posted 19 December 2012 - 10:28 AM

Thanks Hap,

I have been telling my customers that even though SCTs have a corrector lens up front, it is a weak lens and does a good job of focusing both infrared and visible (RGB) light to the same point. Also, that the Celestron SCTs are especially good in this regard since their correctors are a little thinner than those of Meade SCTs. Samir Kharusi on this page:

http://www.samirkhar...ectrograph.html

..says this...

"Another common remark is that refractive optics need to be used with a UV/IR Blocker; true, but the corollary that SCTs also do because of their corrector plates is not true. The corrector plates are very weak "lenses" and in actual usage resolution is not impaired to any noticeable extent. In fact I got sharper images in planetary webcamming with no UV/IR blocker than with. Ditto with trying to image the 6 stars in the Trapezium or the zillions in M13 using the modded 20D. Do your own testing. The IR does allow you to use very short exposures, important in hi-res imaging, and you should not throw it away by blindly following weighty pronouncements by the Wise."

I have a 10" Meade LX200, so I could do some testing, but I haven't imaged with it in a very long time. Many have been buying the new HD versions of SCTs and with their extra lens elements, I would expect an IR blocking filter is needed. I'd rather be imaging than testing.

#71 Hap Griffin

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Posted 19 December 2012 - 11:21 AM

That's how I found out way back in 2003 what IR bloat was...by imaging with a 300D with the filter removed through my LX-200 and seeing red rings around all the brighter stars. Adding in a Baader UV/IR filter cured it. I can only attribute it to the corrector plate since no other refractive elements were in the system.

#72 LeCarl

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Posted 19 December 2012 - 02:43 PM

Just to say to don't forget about the distance for focusing on focusing,
Aboy wants to use his nikons lens with an adapter... full spectrum, (no glass/LPF-1) will not work, focussing distance will not be good
:foreheadslap:




Yes. I'll use an adapter.. But up to I know it's possible to use it manual, that is in theory.. But I'll find out in real life soon. :smirk:

Ps. I am learning a lot with this thread :grin:


Aboy, I think you get your post stolen, :grin:

yes you will see that with lenses, focal distance without glass/filter is important
(don't be surprised if you can't focus) HAHA!

(someone disagree with that???) :grin:

Sadly, the people with so much experiences can give you a little advices? :lol:

Just received my nikkor 180mm ED F2.8 with canon adapter wow! focus like a charm! woooooo! :bow:

#73 Gary Honis

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Posted 19 December 2012 - 09:23 PM

LeCarl,

I do image with a Nikkor 180mm ED F2.8 camera lens using the Nikon to Canon EOS adapter. Some images with the Nikkor lens can be seen HERE. The lens has no problem reaching focus with my Full Spectrum and Baader Modified cameras. My Full Spectrum cameras use an Astronomik MC DSLR clear glass replacement so focus is not an issue. My guess is that if the Full Spectrum modification is one in which both original filters were removed and replaced with nothing, the lens will not reach focus at infinity for stars.

I'm sure you'll enjoy your new lens.

#74 Gary Honis

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Posted 19 December 2012 - 11:31 PM

[quote name="nofxrx"][quote]

Here is an image showing the dual filter system used in 90% of newer models(ALL Canon from the 400D and newer, and most Nikons)
[/quote]

That image does not represent the "dual filter system used in 90% of newer models(ALL Canon from the 400D and newer".

That image shows the frontmost filter as the Infrared Absorption Glass which may be true in the Canon EOS 1D model but that is not the case in the Canon models 400D (Xti), 450D (XSi), 500D (T1i), 550D (T2i), 600D (T3i), 650D (T3i), 1000D (XS), 1100D (T3), 40D, 50D, 60D and 5D Mark II. In those models it is the second filter that is labeled by Canon as the "Infrared Absorption Glass". A list of Canon Filter Diagrams for various Canon models with the correct labels by Canon is HERE.

#75 mmalik

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Posted 20 December 2012 - 06:34 AM

If you are imaging with a reflector, SCT or RC at prime and using a "front filter only" modified camera you should not have star bloat.


Gary, are you implying that there will be star bloat with a refractor at prime focus and using "LPF-1 only" modified camera?


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