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Old 11-03-2019, 10:24 PM
raymo
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DSLR modding question

When a DSLR is modded to be more sensitive to Ha, does the mod move the whole sensitivity "band" along to go further into Ha, or does it stretch the "band" and leave the other end of the "band" where it was. I ask because
modded camera images I see on here don't seem to show the greens and blues as well as unmodded ones do. Is this a fact, or is it just that people who mod their cameras are after more red, and process their images to emphasise the red?
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Old 11-03-2019, 10:53 PM
glend (Glen)
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From my experience, the removal of the filter improves the take up at the red end of the spectrum but it does not affect the other end. Processing is as per normal, they show up as red because it's there. Typically the nebula targets are heavy in Ha anyway, which sits down at that end of the spectrum. There is no need to boost saturation, it was always there, you just could not pick it up before because the LP2 filter blocked it.
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Old 11-03-2019, 11:19 PM
raymo
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Thanks Glen,
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Old 12-03-2019, 07:49 AM
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Quite a lot of studies were done for Canon 400D (not for AP specifically but the results are still valid for us), see here:

Last edited by bojan; 12-03-2019 at 09:32 AM.
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Old 12-03-2019, 09:26 AM
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Modding of DSLRs is not needed anymore with modern cameras.
I have an unmodded 6D and can take nice pictures of even faint red nebulas like Heart Nebula IC1805 and Elephants Trunk IC1396 (when using a UHC filter). Barnards Loop is displayed as well and Eta shows also many reds, in both cases I did not use filters.
Proper postprocessing does the trick.
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Old 12-03-2019, 09:40 AM
glend (Glen)
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Quote:
Originally Posted by skysurfer View Post
Modding of DSLRs is not needed anymore with modern cameras.
I have an unmodded 6D and can take nice pictures of even faint red nebulas like Heart Nebula IC1805 and Elephants Trunk IC1396 (when using a UHC filter). Barnards Loop is displayed as well and Eta shows also many reds, in both cases I did not use filters.
Proper postprocessing does the trick.
Of course Skysurfer's post is off the original topic, but it is important to not let comments like this pass through without remark. I suggest you read this, particularly Jon Rista's post #7:

https://www.cloudynights.com/topic/5...transmittance/

"
Most DSLRs attenuate the reds such that they gradually fall off into IR (750nm) where transmittance is 1% or less. At the H-alpha line, transmittance is rarely more than 20% tops, and as little as 10%. For the 6D, given what I've seen with John Hayes can do with one, Ha transmission is probably around 20%. This limitation is ultimately imposed by the IR cutoff filter.*
For an unmodded DSLR, you then have 25% of the pixels passing 20% of he light. So its .25*.20, or a mere 5% Ha transmission. Throw in the quantum efficiency on top of that, which according to sensorgen is 47% (although that is for green, which is usually a bit higher than red or blue...but let's go ahead and use it), you then have .05*.47, or 2.35% actual sensitivity.

If you remove the IR cutoff filter, then you get significantly greater transmission. It's not perfect, but lets say it's 90%. So now you have 0.25*0.9*0.47, or 10.6% sensitivity.*

In comparison to a mono CCD camera, which is going to have no filtration at all and thus its entire Q.E.: For a KAF-8300 ~49% sensitivity; For a KAF-16200 ~55% sensitivity, for a Sony ICX834 ~70% sensitivity.*

No amount of post-processing mumbo jumbo is going to improve a 2,35% Ha sensitivity for an un-modded 6D.
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Old 13-03-2019, 11:55 PM
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Raymo, if an image from a mono camera looks too pink, it probably is

Colour correction needs to be tackled more critically with modded cameras because the spectral response is now outside what our eye is used to in the natural world.

Some newer camera donít block as much Ha as the old faithfuls, but the end result should be more or less the same if correctly colour balanced. All youíre doing with modding is letting more Ha through which improves the signal to noise ratio for the red channel.
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Old 14-03-2019, 12:20 AM
raymo
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Thanks everyone.
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Old 14-03-2019, 08:36 AM
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By accident, I discovered one more thing that may improve the camera handling when used with telescopes ...
When trying to use LP filter in adapter I made (3D print) with my (un-modded) 60D, I "managed" to lose the focus screen.
I noticed since than that I can see much fainter objects in the view finder, but I became really aware of the cause for this when trying to take terrestrial images in Snake Valley - first, it became immediately obvious that the screen is missing, view was limited to centre of the frame only (I was using 18mm lens).
And of course, all pics were over-exposed.
I removed the screen from my moded 450D but it did not fit into 60D of course, so I ordered the replacement on ebay (not original - it is $45 + post!).
Now I started thinking of 60D full modification - without screen the camera is useless for terrestrial photography, but on telescope or longer it is easier to use viewfinder as it is now.
And I have un-modded 450 for everyday use.
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Old 14-03-2019, 10:44 AM
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A bit more on focusing screens you can find here.
And here.


It would be nice to find clear lens of appropriate size and FL.... maybe to use suitable lens from reading glasses

Last edited by bojan; 14-03-2019 at 11:27 AM.
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Old 14-03-2019, 05:05 PM
raymo
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Cheers Bojan, I'll have a look.
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