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Space Oddities

Photographing 46P/Wirtanen: what's the optimal setup?

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Hello everyone!

I've never photographed a comet before, and since 46P/Wirtanen is around, I'd like to give it a try. Unfortunately, I haven't seen a clear sky for weeks now, and the weather forecasts are only predicting despair and frustration... 😕

So, since I will most likely have only one small chance to photograph 46P, between two clouds, I won't have the time to try out different setups, and I want to be prepared.

Considering I'm using an APS-C camera, and imaging from a Bortle 6/7 area, what would be the optimal focal length / shutter speed? I have no idea how big and fast the comet actually is.

After seeing the great pictures posted on SGL, my initial thought was that the total exposure time should be rather short, to avoid trailing after stacking. And if I'm lucky, the comet might be close to the Pleiades, so a 135mm lens around f/2.8 would make an interesting composition. Or perhaps the 200mm f/4 if the timing is good. But at these focal length, could there be visible trailing? 

What do you guys think?🤔

Thanks for your support!

Pierre

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The 300mm F/4 might be a bit tight, 200 sounds more like it, the 135 should easily allow you to capture the comet with e.g. the Pleiades in one FOV. I see you have a tracking mount, which should work well with telephoto lenses. I used a simple EQ3-2 mount and could track readily for 60 s without trailing at 384 mm focal length. Under good conditions with my Canon 550D I go for 60s and ISO 800 with this F/4.8 set-up, but last time I shot the comet I opted for 30s at ISO 1600. Should skies clear tomorrow or over the weekend, I will probably use my 200mm F/2.8, with step-down ring to F/3.5, but might go for a dual set-up with my EOS 550D and 80mm F/6 scope+ 0.8x reducer combo, twinned with the 200 mm F/2.8 on the EOS 80D. The latter has very high dynamic range, and might well work a treat with lower ISO settings.

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Thanks a lot Michael for your feedback, that's a great starting point. 60s should be plenty enough, especially under my light polluted skies. 

Let's hope for clear skies!

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I took quite a few last night with my Canon 450D and 135mm on the star adventurer. 30 seconds at F2.8 ISO400. It was very visible in the subs, histogram was about 1/3 from the left. I haven't processed them but had a quick look at the raw files after I downloaded them from the camera and there didn't seem to be any comet trailing. I also took a few 1 minute exposures but the histogram was in the middle and they were looking a bit washed out. i took them from about 10.30pm so it was quite high but I have quite a bit of light poloution, could really only make out the brightest two stars in Ursa Minor naked eye.

Hope this helps and you get a chance to image it. I was quite pleased to find it with the camera :) 

Edit here's a couple of subs as processed by the camera for a guide, 30 seconds and 1 minute. I think your skies might be better than mine though. 

IMG_1733a.thumb.JPG.68aef76ad87c2a16640b2793b64e68be.JPGIMG_1726a.thumb.JPG.167c8cc380430c4f1a933eece33656da.JPG

Edited by Scooot
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Maybe a silly question but how do you find out about which comets are passing? I'm guessing the answer is research but I often use the website dso-browser.com but this doens't mention about comets, only DSO's and planets.

I wasn't aware of this comet and have never taken an image of one yet either but if it's currently around the Pleiades region, that's an ideal location from my back garden at the moment. Thanks.

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2 hours ago, mikeonnet said:

Maybe a silly question but how do you find out about which comets are passing? I'm guessing the answer is research but I often use the website dso-browser.com but this doens't mention about comets, only DSO's and planets.

I wasn't aware of this comet and have never taken an image of one yet either but if it's currently around the Pleiades region, that's an ideal location from my back garden at the moment. Thanks.

I just follow the comet sections on SGL. Observing & imaging, and you’ll soon pick up the current nearby target. Sky Safari also shows them as I’m sure other planetarium apps do as well. Hope you manage to see it. :) 

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On 13/12/2018 at 14:50, Space Oddities said:

Interesting, thank you very much! Indeed, it looks quite light polluted :( 

You can see how it turned out here.  Better than I thought after seeing the subs :) 

 

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On 13/12/2018 at 18:54, mikeonnet said:

Maybe a silly question but how do you find out about which comets are passing? I'm guessing the answer is research but I often use the website dso-browser.com but this doens't mention about comets, only DSO's and planets.

I wasn't aware of this comet and have never taken an image of one yet either but if it's currently around the Pleiades region, that's an ideal location from my back garden at the moment. Thanks.

I use Cartes du Ciel.  It gives the expected magnititude, speed and direction as well as the precise location.   This works really well and makes finding comets really easy.

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On 13/12/2018 at 19:54, mikeonnet said:

Maybe a silly question but how do you find out about which comets are passing? I'm guessing the answer is research but I often use the website dso-browser.com but this doens't mention about comets, only DSO's and planets.

I wasn't aware of this comet and have never taken an image of one yet either but if it's currently around the Pleiades region, that's an ideal location from my back garden at the moment. Thanks.

Not silly at all! 

I use this website to know about astronomical events: https://www.timeanddate.com/astronomy/sights-to-see.html

It's a great tool, especially for eclipses, because it shows you what the eclipse will look like (depending on your location). Then, I just add the event to my personal agenda. There's also a page dedicated to planets, to help you know when they are visible.

Basically, check out the "Sun & Moon" menu at the top, it's full of interesting tools!

Regarding comets specifically, there's also this dedicated website: http://www.cometwatch.co.uk/bright-comets-of-2018/

Edited by Space Oddities

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Thank you all for your replies. I now have the comets database imported and thank you too Pierre, very useful website links (sorry I didn;t mean to hijack this thread).

I had a quick go last night on a static tripod with a 200mm lens on my DSLR with 30 second exposures and I can see 46P but even at those short exposures, there is a lot of star trailing. I will try next time on the Goto mount but the forecast is not looking good for a while now but at least I managed to image a greenish fuzzy blur as my first comet image 😀. Thanks again everyone.

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My pleasure! :) 

I also had a go at it yesterday evening, and did a quick and dirty stacking in DSS, but it's not so great 😕 I'll have to study comet stacking!

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I worked on a quick timelapse of 46P flying near the Pleiades, I'm rather happy with the result :) Even though the lens I use has heavy vignetting, and some kind of white ring is showing. I don't know where this comes from, as it's not on all the frames. Perhaps a flare of some kind?

647335032_46P-WirtanenTimelapseWide.gif.43478fe9388ffb92d26d496f14cea4c6.gif

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I'm so pleased to bag my first comet on 16-Dec-2018.  Here is my single frame shot 30s, f/5 54mm ISO 1600 with AP_C camera. at 00:55.
I just used the kit lens (18-55) that came with the camera
The camera was fixed to the side of my Bresser 102 and I used the tracking motor on the EXOS-2 mount - which worked fabulously at keeping the subject in the frame.
My focus went a bit off (must have jogged the focus ring in my excitement). I did try a few other focal lengths and exposure times ( and I even tried some stacking) but this single frame came out best.
I have a remote camera app on my phone which helped keep things stable.


It absolutely poured down all day and I was surprised to see anything that night.
The air was very humid and anything closer than about 30deg to the horizon just get lost in the 'fug' of streetlights, Christmas lights, neighbours security lights etc.

Comet - DSC00506.jpg

Edited by Fraunhoffer
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19 hours ago, Fraunhoffer said:

I like that time lapse - over what duration was it taken ?

 

Thanks a lot! It's ~60x30s, so half about an hour!

Nice pic by the way. Not always easy to have a perfect focus, especially in the cold and sometimes in exotic body positions :D 

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On 13/12/2018 at 12:02, Space Oddities said:

optimal focal length / shutter speed?

Hi. I used a Takumar 135mm lens, Canon 700d and 60s frames. I tried one stack for the stars and another for the comet.

The result is here.

HTH and happy comet hunting:)

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The thing with comets is they are traveling fast if you push the exposure length too long you get an oblong comet. 30 seconds appears a popular exposure length used across many of the images posted of this comet.

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Thank you alacant! Your photograph looks great! Is that a dark nebula near the comet?

Sadly, no more comet hunting for me! Clouds are back, and I'll be flying back to a Bortle 999 location soon for Christmas :(  But I had a chance to photograph 46P, and here is the result :) 

And indeed, 30 seconds seems to work well for comets!

Thanks everyone for your suggestions! :) 

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