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Planning A Go at M51 - But Which Scope ???


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Tonight’s predicted to be clear for the first time in a while so even though it’s going to be cold (18 F) and a little windy (10 – 15 mph) - I’m considering having a go at M51 and it looks like I have two options regarding my setup. I’ll be using the G3 mono CCD with astronomik LRGB filters either way - but my question is which scope. I’ve checked Stellarium and the ES 80 mm refractor with 2.5x Powermate will fill about 2/3’s of the frame with the galaxy while the Celestron 8” SCT at native focal length will have the object completely filling the frame with a small portion of the outer most regions falling outside.

The moon is in its 1’st quarter and will cross the S meridian at 20:40 (sunset is at 20:09) at an altitude of 67 deg. while at the same time M51 will be in the NE at an altitude of 30 deg. However, by 02:20 - M51 will have reached 81 deg. when it crosses the N meridian while the moon will set at 03:47 followed by sunrise at 07:42.

Since I only have one EQ mount (AVX) and piggybacking isn’t an option - whichever scope I mount will dictate any alternate targets I might try before M51 reaches an altitude suitable to start the imaging run. Since I really don’t want to be switching out scopes after I get aligned, an alternate target for the refractor might be M101 - which reaches 45 deg. around 22:40 in the NE or - if I mount the SCT, Jupiter will be crossing the S meridian at 21:50 at an altitude of 70 deg. however, the moon’s position will likely make capturing decent subs problematic. I’m hoping if set up goes well, there might be some time to try for one of these – or some other target - before M51 is in the right position however, I want to use the best setup for M51 and let that dictate any other targets I might try for.

I realize good PA is essential and I’ll be auto guiding as well, so in terms of capturing the best image of M51 possible – with the primary goal of at least coming away with some data worth processing - would I be better off going with the 80mm refractor and 2.5x Powermate or the 8” SCT at native focal length? Also, any general tips on imaging M51 (length of subs and how many subs of each type - LRGB) would be very much appreciated as well as any suggestions on when to start the imaging run in terms of M51’s altitude and position of the moon.

About to begin loading the gear, food and warm clothes I’ll need for another long awaited, all-nighter at my reasonably dark sky site - but will be watching out for any advice someone might be willing to offer this newbie astro-imager...  :smiley:

Regards,

Scorpius

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Personally I would go with the ES80 because it is F6 but I would not use the 2.5X powermate as this will give you F15 which is high for imaging. You would need some really long exposures. In this respect the C8 would be better at F10 but that's still more than you really want for shortish exposures. The Moon may pose problems with its illumination and long exposures so the conditions are not ideal.

Good luck.

Peter

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Personally I would go with the ES80 because it is F6 but I would not use the 2.5X powermate as this will give you F15 which is high for imaging. You would need some really long exposures. In this respect the C8 would be better at F10 but that's still more than you really want for shortish exposures. The Moon may pose problems with its illumination and long exposures so the conditions are not ideal.

Good luck.

Peter

Thanks Peter and I was petty sure it wouldn't be the best conditions due to the good 'ole man in the moon  :smiley: But it's the first decent night in a long time so I've got to try for something. If not M51 - any suggestons? If I try M51 what do you consider shortish exposures? What length subs should I go for?

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If (and I stress the if bit) you have had previously good results auto-guiding the Celestron without a focal reducer, then that will be the most challenging option (and so the one I would choose!) - however guiding at a focal length of 2m will be a test if you're not well set up for it and I think a more sane approach would be to add the f/6.3 focal reducer to both lower the exposure time and make the guiding a little less critical.

M51 is fairly bright, so you can get away with short subs which puts less stress on the guiding and polar aligning - for example my first attempt at M51 with a similarish setup (LX90 on AZEQ6 with ST-8E) used just 15 x 30 second exposures unguided and whilst it's a bit rubbish, you can see that it is M51. 

post-41448-0-68423000-1425460696_thumb.j

At the end of the day, your sub length is determined by the accuracy of your guiding and assuming you don't want field rotation, the accuracy of your polar alignment. If you can guide up to 10 min subs that's likely to give you some pretty decent data and if you can bin your CCD, you could shoot the RGB 2x2 binned to save some imaging time - you will get the detail from the L at full resolution.

Other more experienced imagers are likely to have a better idea of the number of subs for each of LRGB that make sense.

Enjoy the night whatever scope you choose and do share the images when you get back!

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If (and I stress the if bit) you have had previously good results auto-guiding the Celestron without a focal reducer, then that will be the most challenging option (and so the one I would choose!) - however guiding at a focal length of 2m will be a test if you're not well set up for it and I think a more sane approach would be to add the f/6.3 focal reducer to both lower the exposure time and make the guiding a little less critical.

M51 is fairly bright, so you can get away with short subs which puts less stress on the guiding and polar aligning - for example my first attempt at M51 with a similarish setup (LX90 on AZEQ6 with ST-8E) used just 15 x 30 second exposures unguided and whilst it's a bit rubbish, you can see that it is M51. 

At the end of the day, your sub length is determined by the accuracy of your guiding and assuming you don't want field rotation, the accuracy of your polar alignment. If you can guide up to 10 min subs that's likely to give you some pretty decent data and if you can bin your CCD, you could shoot the RGB 2x2 binned to save some imaging time - you will get the detail from the L at full resolution.

Other more experienced imagers are likely to have a better idea of the number of subs for each of LRGB that make sense.

Enjoy the night whatever scope you choose and do share the images when you get back!

Thank you! This is just the kind of advice I was looking for. Unfortunately, not only have I not tried guiding with the SCT (with or without focal reducer) I've never had time to get the focal reducer spacing set correctly either (really shows my inexperience huh?) But after reading your advice, I may just use the lead time to see if I can get decent tracking results with the SCT at native focal length since it sounds like that would yield the best results. But if I can't get it, I'll go ahead and change scopes (will probably have to realign :sad: ) in order to take the "safer route"  (80 mm refractor) resulting in a much smaller, less detailed image.

If M51 reaches it's highest altitude at 02:20 what time would you begin the imaging run and how many L subs would you consider to be a bare minimum?

If I get anything at all, I will definitely post the results however, if no images ever turn up, you'll know the whole thing was a bust...   :smiley:

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Thanks :) I'm looking at the field of view you'll get with the Celestron and G3 and I think that would be tough to do at f10 - I'd suggest adding the focal reducer or switching to the ES80 without the powermate.

Exposure wise, I'd say start short to check your guiding and then ramp up as you have confidence in the setup. If they're looking good at 60", try 120" and then 300" and check your stars are still round - if you can get nice round stars at 5 minute subs you'll get great results when you stack them. 

As for when to start - it depends if you want to shoot a few things in the same night, or want to spend all your efforts on M51. I'd maybe do 1 hour L (12 x 5 mins subs) and if you can bin the camera 3x3, you should be able to get away with 20 mins each R G B. If binning 2x2 you would need longer R G B, around 45mins each as well (given the filters) and that means you're looking at a 3 1/4 hour session - I'd likely be more concerned about when I would sleep rather than the height of the object and generally I would do L first so that if anything goes wrong later in the night, I still have a good mono shot to process.

Strong disclaimer - I'm not remotely expert at this!

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Thanks :) I'm looking at the field of view you'll get with the Celestron and G3 and I think that would be tough to do at f10 - I'd suggest adding the focal reducer or switching to the ES80 without the powermate.

 

Exposure wise, I'd say start short to check your guiding and then ramp up as you have confidence in the setup. If they're looking good at 60", try 120" and then 300" and check your stars are still round - if you can get nice round stars at 5 minute subs you'll get great results when you stack them. 

 

As for when to start - it depends if you want to shoot a few things in the same night, or want to spend all your efforts on M51. I'd maybe do 1 hour L (12 x 5 mins subs) and if you can bin the camera 3x3, you should be able to get away with 20 mins each R G B. If binning 2x2 you would need longer R G B, around 45mins each as well (given the filters) and that means you're looking at a 3 1/4 hour session - I'd likely be more concerned about when I would sleep rather than the height of the object and generally I would do L first so that if anything goes wrong later in the night, I still have a good mono shot to process.

 

Strong disclaimer - I'm not remotely expert at this!

All of this makes sense and your points are well taken – thanks! Unless I can get the FR properly spaced and everything setup & ready to go before dark, I’ll probably just go with the refractor this time and save trying to guide the SCT for another night. Plan to spend most of the time trying for M51 since I’ve fallen far short of getting enough subs to stack in my few attempts at imaging DSO’s so far.

Regarding sleep, and provided the skies remain clear, they’ll be none of that until the sun comes up. I have a cabin (4 season gazebo) at my remote observing site which has almost all the comforts of home (bunk, wood stove, cook stove, solar power, etc.) and although it’s not that far from home – once I load everything up and get over there, I want to take advantage of the whole night. It’s going to be cold and I’m somewhat concerned about the wind (another good reason for the refractor) but I have a pop-up tent for shelter during the night so shouldn’t be any worse than the last time I was out when it was about 16 F if I recall.

Anyway, I’m usually spent by sunrise but depending on the weather can usually just cover the scope, then sleep til mid afternoon and pack up the gear later that evening. It’s also nice to have a small fire going in the gazebo during the night so I can run in and get warmed up while I’m fixing myself a hot cup of coffee in between subs... :)

Below is a pic of the gazebo which is nice to have waiting whenever it’s time to go imaging or even when it’s just time to get away from the house (spouse?) every once in a while... :)

Well - better get moving or this will end up being all talk and no action but thanks again for all the pointers and clear skies!

post-37916-0-50862100-1427568257_thumb.j

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If (and I stress the if bit) you have had previously good results auto-guiding the Celestron without a focal reducer, then that will be the most challenging option (and so the one I would choose!) - however guiding at a focal length of 2m will be a test if you're not well set up for it and I think a more sane approach would be to add the f/6.3 focal reducer to both lower the exposure time and make the guiding a little less critical.

M51 is fairly bright, so you can get away with short subs which puts less stress on the guiding and polar aligning - for example my first attempt at M51 with a similarish setup (LX90 on AZEQ6 with ST-8E) used just 15 x 30 second exposures unguided and whilst it's a bit rubbish, you can see that it is M51. 

At the end of the day, your sub length is determined by the accuracy of your guiding and assuming you don't want field rotation, the accuracy of your polar alignment. If you can guide up to 10 min subs that's likely to give you some pretty decent data and if you can bin your CCD, you could shoot the RGB 2x2 binned to save some imaging time - you will get the detail from the L at full resolution.

Other more experienced imagers are likely to have a better idea of the number of subs for each of LRGB that make sense.

Enjoy the night whatever scope you choose and do share the images when you get back!

Well – had issues with Orion capture software as usual and tracking wasn’t great which meant I didn’t even have time to get any RGB subs but did manage 12 (200 sec.) L subs and came up with the image below following a quick attempt at processing. I took darks, flats and bias as well but don’t know much about calibrating subs so maybe I can get a little more detail out of it once I learn what I’m doing. The Orion software has been real finicky when trying to stack these subs - giving me multiple error messages - so may try downloading Deep Sky Stacker when I get home to see if that helps. Can DSS process Fits files as that’s the only format Orion Camera Studio outputs unless you export to Tiff or JPG.

Anyway, guess it’s ok for my first attempt and was wondering – is that another faint galaxy in the lower left corner? First thought it was a star trail but the rest of the stars seem fairly round if not a little over-sharpened...  :)

post-37916-0-80075400-1427667639.jpg

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