m82 suggestions please

[Christopher Davenport]

Hello,

I am new to AP and would like some advice. (kit in sig)

600D, raw, 4.51um 18mp

Guiding with a sensitive finder guider and PHD.

Choice of

- 80ed, 600 at f7.5

- 80ed, 378 at f4.75

- 127mak, 900 at f7

So going after m82 this weekend, 5 hr predicted weather window on Sun morning.

So practical imaging window of 3hrs with setup and glitches.

Thinking for lights @iso800

Stars - 5x120 subs

Galaxy - 10x300 subs

Luminance - 2x600 subs

This leaves me with down time in case of clouds.

Will do another 10x300 weather permitting.

Will do 5 darks per timing interval (5x120,5x300, etc)

Any suggestions to change the plan or scopes?

[DrRobin]

Hi,

I took a nice picture of M82 last week with a C11 (@F/10 Fl=2700mm) and a Canon 600D.  As I didn't have much time, I used ISO 1600 and exposures of 180 seconds.  I took 11 images before the cloud rolled in and stacked 8 of them.  I took 10 darks at the end of the run.  Over such a short time it was okay to do them at the end.  I didn't take any flats, my C11 is pretty flat or BIAS shots.  I do have a library of these, but didn't bother applying them.  With a small amount of imaging time I wouldn't bother taking darks during the run unless a bit of cloud rolls in.  Much better to use your clear sky to get some lights.

I used a QHY5 on a 50mm guidescope, locked to a nearby star.  Tracking was fine and I could have easily got a longer exposure.

At F/7 your images will be twice as quick as mine (forget the aperture) so you should get 180 seconds @ ISO 800.  Or at F/4.7 you will be 4.5x as faster so you could probably get around 100 second exposures.

At F/10 I really needed 360 - 400 seconds @ ISO 800.  You get a good image scale at this Fl but exposures go right up.  I have a 0.62 FR for this scope, but I haven't tried it yet, that should get me around 150 seconds at ISO 800, next clear spell.

Copy of the pic I took, a little grainy, but not bad for 24 minutes of exposure time.

Robin

[Yoddha]

Hi Christopher,

I would go with the Mak, using ISO 1600. Then make as much as possible 300s subs. Two luminance looks me too few but will give you time for four 300s Also will not loose time for darks - dithering + sigma clip is giving better results for me with much less time

Today saw interesting link in other forum which gives some numbers on the dithering side http://www.christoph-kreher.de/Astro/DC.pdf

[lensman57]

Hello,

I am new to AP and would like some advice. (kit in sig)

600D, raw, 4.51um 18mp

Guiding with a sensitive finder guider and PHD.

Choice of

- 80ed, 600 at f7.5

- 80ed, 378 at f4.75

- 127mak, 900 at f7

So going after m82 this weekend, 5 hr predicted weather window on Sun morning.

So practical imaging window of 3hrs with setup and glitches.

Thinking for lights @iso800

Stars - 5x120 subs

Galaxy - 10x300 subs

Luminance - 2x600 subs

This leaves me with down time in case of clouds.

Will do another 10x300 weather permitting.

Will do 5 darks per timing interval (5x120,5x300, etc)

Any suggestions to change the plan or scopes?

Hi Christopher,

I too have a Mak 127 plus a Meade 0.63 reducer. Have you tried your reducer with the Mak and does it work? I believe I need a back focus of 105mm from the flange. Hope  work out for you with the capture of M82, I have not seen a clear night for nearly 3 weeks now.

Regards,

A.G

[Christopher Davenport]

Hi Christopher,

I would go with the Mak, using ISO 1600. Then make as much as possible 300s subs. Two luminance looks me too few but will give you time for four 300s Also will not loose time for darks - dithering + sigma clip is giving better results for me with much less time

Today saw interesting link in other forum which gives some numbers on the dithering side http://www.christoph-kreher.de/Astro/DC.pdf

Just read that link, very interesting, basically on the 600D at ISO800 at 10C (sensor), only start to suffer from noise after 387 seconds.

The other night my sensor reached 10C, when it was about 1C outside. So in theory I don't need darks in winter unless I push above 380 Sec

Makes me think I should try to devise some kind of peltier when I mod

Question is @iso1600, do I halve these times? 

[Christopher Davenport]

Hi Christopher,

I too have a Mak 127 plus a Meade 0.63 reducer. Have you tried your reducer with the Mak and does it work? I believe I need a back focus of 105mm from the flange. Hope  work out for you with the capture of M82, I have not seen a clear night for nearly 3 weeks now.

Regards,

A.G

Good question, I have used a small 0.5 focal reducer on the moon and achieved focus, but not actually tried my 0.63 yet. 

I do have a extension tube, and a barlow, which with lense removed ive me even more distance.

I will definitely setup in the light and check tho. (Will let you know how I did it.)

[Christopher Davenport]

Hi,

I took a nice picture of M82 last week with a C11 (@F/10 Fl=2700mm) and a Canon 600D.  As I didn't have much time, I used ISO 1600 and exposures of 180 seconds.  I took 11 images before the cloud rolled in and stacked 8 of them.  I took 10 darks at the end of the run.  Over such a short time it was okay to do them at the end.  I didn't take any flats, my C11 is pretty flat or BIAS shots.  I do have a library of these, but didn't bother applying them.  With a small amount of imaging time I wouldn't bother taking darks during the run unless a bit of cloud rolls in.  Much better to use your clear sky to get some lights.

I used a QHY5 on a 50mm guidescope, locked to a nearby star.  Tracking was fine and I could have easily got a longer exposure.

At F/7 your images will be twice as quick as mine (forget the aperture) so you should get 180 seconds @ ISO 800.  Or at F/4.7 you will be 4.5x as faster so you could probably get around 100 second exposures.

At F/10 I really needed 360 - 400 seconds @ ISO 800.  You get a good image scale at this Fl but exposures go right up.  I have a 0.62 FR for this scope, but I haven't tried it yet, that should get me around 150 seconds at ISO 800, next clear spell.

Copy of the pic I took, a little grainy, but not bad for 24 minutes of exposure time.

Robin

At the risk of sounding like a total noob and I know I used to understand this from terrestrial photography.

I am struggle to convert the Fstop to the ISO. I know half iso means twice exposure time, but change in Fstop calc is confusing me.

How did you calc from F10 to F4.7 at x4.5 times? 

(Did search this on google, but can't seem to find an easy formula)

[DrRobin]

Hi,

A doubling of the ISO reduces the exposure time by a half. A doubling of the F/number increases the exposure by 4 times. So if you take the ratio of F/numbers and square the result that is the change in exposure.

I went from F/10 to F/4.7, that is a ratio of 2.12 and then squared it to get 4.5x. Using the F/number ratio is only an approximation, it works quite well for evenly lit frames, but doesn't work well for point sources (stars) as the size of aperture also comes in to play slightly.

But if you use the same scope with and without a focal reducer, you should see the exposure times change by the square of the focal reducer. A 0.7x will give exposures nearly 2x as quick, wilts a 0.5x FR will give exposures 4x as quick.

Use it as a guide, and adjust your exposure from there. I often take 6 to 10 test shots first, getting the exposure/framing set right, you sometimes seem to spend half the night messing on rather than getting imaging.

A Barlow with require more out focus, I.e. your focus tube will be further out. A focal reducer requires in focus. If you could use a 0.5x then a 0.62x will require less in focus, so should be okay. Sensible idea to check it during the day though.

Robin

[ollypenrice]

If your target really is M82, and not what's around it, then you need the maximum number of photons from that source, so you need the largest aperture you have. Using focal reducers will have no effect on the number of M82 photons you collect and will not take you deeper into M82. It will just concentrate them onto fewer pixels and make them look brighter. (To argue otherwise is to fall into the dreaded F ratio myth.) You can have the same effect (or better) by reducing the screen size of the longer FL image.

Exposure time really depends on your skyglow.

Olly

[Christopher Davenport]

Hi,

A doubling of the ISO reduces the exposure time by a half. A doubling of the F/number increases the exposure by 4 times. So if you take the ratio of F/numbers and square the result that is the change in exposure.

I went from F/10 to F/4.7, that is a ratio of 2.12 and then squared it to get 4.5x. Using the F/number ratio is only an approximation, it works quite well for evenly lit frames, but doesn't work well for point sources (stars) as the size of aperture also comes in to play slightly.

But if you use the same scope with and without a focal reducer, you should see the exposure times change by the square of the focal reducer. A 0.7x will give exposures nearly 2x as quick, wilts a 0.5x FR will give exposures 4x as quick.

Use it as a guide, and adjust your exposure from there. I often take 6 to 10 test shots first, getting the exposure/framing set right, you sometimes seem to spend half the night messing on rather than getting imaging.

A Barlow with require more out focus, I.e. your focus tube will be further out. A focal reducer requires in focus. If you could use a 0.5x then a 0.62x will require less in focus, so should be okay. Sensible idea to check it during the day though.

Robin

I knew it was something easy like this, thanks for clarifying, it's the squaring that sometimes ties my brain in knots!

[Christopher Davenport]

If your target really is M82, and not what's around it, then you need the maximum number of photons from that source, so you need the largest aperture you have. Using focal reducers will have no effect on the number of M82 photons you collect and will not take you deeper into M82. It will just concentrate them onto fewer pixels and make them look brighter. (To argue otherwise is to fall into the dreaded F ratio myth.) You can have the same effect (or better) by reducing the screen size of the longer FL image.

Exposure time really depends on your skyglow.

Olly

I appreciate what you mean about aperture, my largest at the moment is a 127mak (with obstruction, so light gathering is actually less), still better than my 80ED.

My current testing on guiding for 300 seconds is stable at 600mm (F7.5), problem is that my Mak 1500 (F11.8) focal length dramatically reduces my exposure times.

@ISO800 for 300 seconds I don't have significant skyglow, but have not tried 600 sec or ISO1600

I have not tried the focal reducer on the Mak, but it should bring the focal length down to 945mm, (F7.4) which widens the FOV and should be okay @ISO800.

This means that I can potentially reduce my exposure times or up the ISO if my guiding suffers.

I have looked at stellarium on the POV and I get this

Nice thing is if I frame correctly I should get both galaxies

[Christopher Davenport]

Hi Christopher,

I too have a Mak 127 plus a Meade 0.63 reducer. Have you tried your reducer with the Mak and does it work? I believe I need a back focus of 105mm from the flange. Hope  work out for you with the capture of M82, I have not seen a clear night for nearly 3 weeks now.

Regards,

A.G

Just got this to focus on Jupiter (On the Mak Clockwise is Infocus and Anticlockwise is Outfocus)

Picture left to right.

0.) EOS->

1.) TRing->

2.) ANTES (2') (CELESTRON ADAPTOR) ->

3.) CELESTRON 6.3 FR (2') ->

4.) CELESTRON BARLOW (1.25') (Lens Removed) ->

5.) MAK EXTENSION ->

6.) SCOPE.

4 and 5 came in the box with 6.

I take it you already have a the equivalent of 1,2,3 (i.e a way to connect the 6.3 FR to your Camera)

So all you have to do is screw the back of the (4.) celestron barlow into (3.) celestron 6.3FR.

(Remove the silver extention tube out of 4 and the Barlow grub screw off 3.)

Hope this helps.

[lensman57]

Just got this to focus on Jupiter (On the Mak Clockwise is Infocus and Anticlockwise is Outfocus)

IMG_20140201_185424.jpg

Picture left to right.

0.) EOS->

1.) TRing->

2.) ANTES (2') (CELESTRON ADAPTOR) ->

3.) CELESTRON 6.3 FR (2') ->

4.) CELESTRON BARLOW (1.25') (Lens Removed) ->

5.) MAK EXTENSION ->

6.) SCOPE.

4 and 5 came in the box with 6.

I take it you already have a the equivalent of 1,2,3 (i.e a way to connect the 6.3 FR to your Camera)

So all you have to do is screw the back of the (4.) celestron barlow into (3.) celestron 6.3FR.

(Remove the silver extention tube out of 4 and the Barlow grub screw off 3.)

Hope this helps.

Hi Christopher,

Many thanks for taking the trouble of posting the set up, mine is pretty similar. Just waiting for a clear night. If this set up works with my CCD too it will be great. Can't wait to see the results your capture.

Regards,

A.G

[Christopher Davenport]

Quite a ordeal last night, with my mount making a clown of me! (Full story http://cassiopeiascat.blogspot.co.uk/)

Anyway only managed to get 3x150sec @ISO1600 (2 Interrupted due to clouds) and 5x30Sec @ISO12800 (stacked separately in DSS, layered in PS5)

No darks due to rain and frustration and this has become experimental anyway

My Cigar!

I am planning to give this a proper go tonight, if the weather permits.

[Christopher Davenport]

Finally managed to get my data captured last night. Did not manage to get my guider to work - Frustrating!

Could not find a star on PHD and just thought, I would up the ISO and drop the exposure times.

Managed to get three hours of data, which after about 25% loss of frames. (stretched stars)

And faffing about with incorrect exposures landed me with about 2hrs of stacked data. (excluding about a hour of darks)

- 27 stacked images (with darks at 15C) at ISO6400 for 120 seconds (Galaxy detail)

- 22 stacked images (with darks at 15C)  at ISO800 for 180 seconds (Stars and bright details)

DSS Stacking and RGB aligning, Photoshop Layers (two images) and curves, and Image noise / saturation cropping and compression.

Well I hope you agree that it was not a complete failure, but I still have a long way to go!

Excuse the cheesy, sig, I need to work on a better way of recording the image details.