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Andromeda Widefield with the Astrotrac


iksose7
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This is my first go at M31, taken with the EF200L and an unmodded Canon 1100D on a Astrotrac. I quite enjoy this wider FOV for Andromeda, its a nice change to see it floating in space rather than squeezed diagonally into frame :grin:hopefully this time next year i will have a scope and i myself will be doing the squeezing.

Exposure details:

1 hour of 120 second subs, f4, ISO 800

4 hours of 180 second subs, f4, ISO 1600

Calibration frames

200mm FL

gallery_26473_2565_127348.jpg

Clear skies!

Callum

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That's very pretty, isn't it! I bet you're pleased.

I don't know much about the Astrotrac. How easy is it to polar align? And how consistent is the removal of star trailing shot to shot? It's not guided is it?

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What produces the 8 nice diffraction spikes on the bright stars in a lens like that?

The apeture blades.... which is why I prefer to use them wide open using a thirds focusing point rather than a central one....

If you neen to stop them down then your better off using a front aperture mask...

Peter...

Sent from my GT-P7300 using Tapatalk 4

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Yes, I see. My first thought was that it was the aperture blades, but I assumed it was being used with the aperture wide open. I didn't notice the f/4 in the exposure details.

I assume, iksose, you have traded light gathering for sharpness. It's worked anyway.

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That is a splendid shot and very nice to see M31 (with M32 & M110) in this frame/context. It's perhaps impossible to comprehend the sheer scale of this as an object (the combined light of 1 trillion stars at 2.5 million ligh years from us - or at least the miniscule portion of these photons sucked in by your EF200L), but no doubting the beauty.

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I don't have anything original to say about this, but I'll repeat the sentiment from above: this is absolutely stunning and a great result from the astrotrac. Even with 3 minute subs you must have had the polar alignment spot on. This is an absolutely dandy...

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Thanks all for the very nice feedback :)

I don't know much about the Astrotrac. How easy is it to polar align? And how consistent is the removal of star trailing shot to shot? It's not guided is it?

This is unguided. The Astrotrac is very easy to polar align, although i have never used any other mount so i have nothing to compare it to! You can be up and imaging in 5-10 minutes. If you have the polar scope collimated accurately, star trailing is non existent. The only downfall i experience with the Astrotrac is the limited exposure times. And yes, i traded light gathering for sharpness :)

If you neen to stop them down then your better off using a front aperture mask...

Hi Peter, thanks for your kind compliment :) do you know of any guides to build a mask for this lens or somewhere to buy one? With M45 right around the corner, i wouldnt mind getting one as starspikes would ruin the image in my opinion. Or are you saying that using your 3rd point focusing technique on the lens wide open will eliminate the spikes?

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Hi Peter, thanks for your kind compliment :) do you know of any guides to build a mask for this lens or somewhere to buy one? With M45 right around the corner, i wouldnt mind getting one as starspikes would ruin the image in my opinion. Or are you saying that using your 3rd point focusing technique on the lens wide open will eliminate the spikes?

I use just about all my "quality" lenses wide open by using the thirds focusing technique... Focusing becomes even more critical "wide open" but is fine if you something like the excellent FWHM "autofocus" in APT or BackyardEOS and yest it elliminates the diffraction spikes caused by stopping a lens down plus you are gainign a stop on the exposure - twice the light inthe same time or same in half which helps with tracking - although you don't seem to have any issues there :)

I have convinced quite a few people to try it even on their scope and CCD setups - Most notably Olly Penrice and Steve Richards...

For a front aperture mask all you need is a circle cut in a piece of black card - although plastic is better as it is damp proof.. use a cutting compass to get a clean circle and rememebr to cut the OD first then the ID to give a "Ring"... you can calculate the ID by using ID= FL / Focal Ratio... so 50mm for f4 on the 200/2.8L

I had a mate laser cut me a load of disks for the 200/2.8L in 0.25 f-stop increments to do some testing but then came across the 1/3rd's focusing method and stopped using them...

Peter...

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That is a beautiful image. I too like the fact that it isn't squashed into the corners of the frame.

Out of interest, what has caused the defraction spikes on the brighter stars? I understand the normal four defraction spikes in shots are caused by the secondary mirror support vanes, but a camera lens doesn't have these. Are they caused by where the individual leaves of the diaphragm meet causing a 'kink' in the apertures edge?

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That is a beautiful image. I too like the fact that it isn't squashed into the corners of the frame.

Out of interest, what has caused the defraction spikes on the brighter stars? I understand the normal four defraction spikes in shots are caused by the secondary mirror support vanes, but a camera lens doesn't have these. Are they caused by where the individual leaves of the diaphragm meet causing a 'kink' in the apertures edge?

Or is it the edges of the blades...... Hmmm

Sent from my GT-P7300 using Tapatalk 4

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I use just about all my "quality" lenses wide open by using the thirds focusing technique...

I think I must understand something different by the "thirds focusing technique", by which I mean the way to find the hyperfocal position in a 'deep' image like a landscape. How does your method work for something at infinity?

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