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My Measly Attempt at M81/M82 With a Mere 500mm Lens.


StuartJPP

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I haven't been out capturing photons for ages but managed to get out this last Saturday. I decided to capture some more data on M81/M82 to put that target to rest. Sky conditions were pretty good and guiding and acquisition was also good (no dropped subs in 4 hours). The problem is image processing and not doing any for ~3 months starts to show how quickly you, or at least I, forget things, especially the important subtleties.

I started with just a small cropped section of just M81 and M82 and managed to get something I was quite happy with. The problem is that the PC crashed and I didn't have the history of what I did to get to this stage for this image to apply it to the whole FOV. My subsequent attempts have been pretty dire in comparison. So I am giving it a break for a few nights and hope I can get back into the zone...hopefully I can get the full FOV with a bit more IFN visible, though I am not holding my breath.


Baader modified Canon 6D @ ISO400.
Canon 500mm f/4 L IS @ f/4.
Avalon Instruments M-Zero.
PHD2 for guiding using QHY5L-II-M and QHYCCD miniGuideScope.
APT for image acquisition, plate solving and dithering.

2016-04-10 14x5 minute subs
2016-05-01 38x5 minute subs
2016-11-06 20x5 minute subs
2017-03-25 61x5 minute subs
A total of ~120 x 5 minute subs totalling ~10 hours.

 

This is a 100% (1:1) crop from roughly the centre of the image.
33342391410_cf07d6e698_o.png
M81/Bode's Nebula,  M82/Cigar Galaxy With New Data, 100% Crop by Stuart, on Flickr

 

Thanks for looking, comments and criticisms welcome...

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Amazing image!

PS. but a "mere" 500 mm lens? If we talk aperture that is a 5" f/4 full-APS size flat field apo refractor you have got with 16 lenses in 12 groups, so I understand the price tag. Don't think any of the regular telescope produces make anything close to a 5" f/4.

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Thanks again everyone...

 

3 hours ago, frugal said:

Your camera lens has only got a 10mm shorter focal length than my ED80 telescope ;)

That is 100% true once you have a reducer/flattener fitted.

 

3 hours ago, gorann said:

Amazing image!

PS. but a "mere" 500 mm lens? If we talk aperture that is a 5" f/4 full-APS size flat field apo refractor you have got with 16 lenses in 12 groups, so I understand the price tag. Don't think any of the regular telescope produces make anything close to a 5" f/4.

Ah, but think of all that light loss through those 16 lens elements :wink2:
Luckily some of those lens elements are the "telephoto" lens group which physically shortens the lens to less than 500mm (and still keeping all wavelengths focused) which makes daytime use much more manageable.

I actually used "mere" because there has been a few stonking images of M82 recently with ~1.2 meter focal length...they make mine look...well...inadequate :)

 

14 hours ago, carastro said:

Wow, amazing for a DSLR camera lens image, and even showing some IFN. 

It looks like some Ha has been added, but I can't see anything to that effect in your specs.

Carole 

 

Carole, the only Hα that is present in the image is what was captured from the modified Canon 6D. Here is the image after stacking with a quite heavy stretch before any processing has started. The Hα regions are quite visible dotted in red on M81 and the burst on M82, but obviously very much lacking in contrast and colour, much like the rest of the image.

Like most people, I only enhance what is there, I don't add anything. This is one of the reasons I advocate modifying a DSLR if it is going to be used for astro work...there is currently a theory going around that DSLRs don't need to be modified but I disagree (though it depends on the camera). If people want dual use then fine but if it is dedicated to astro why throw up to 70% of the Hα away?

 

RGB_Start_crop.thumb.png.ddcc9ad8a3029ceafdf55deab9c97ffb.png

 

And here is what a single stretched sub looks like:
L_0021_ISO400_300s__13C.thumb.png.d2eb2de7f54763a86c9b33e0e96a6feb.png

 

And if you want some IFN, here's a preview but I am still busy with it. I don't like to make the IFN as bright as or brighter than the actual galaxies, because I don't believe that is representative...but trying to show it on a dynamic range limited monitor is tricky.
RGB_2_MERGED2.thumb.png.d791dc5818b6c62d862dd74b8e5b7c40.png

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