Proper "rule" for pinpoint stars with M43

Giiba wrote:

boxerman wrote:

OutsideTheMatrix wrote:

I just noticed something really curious. 13 seconds is acceptable if you're talking about stars near the center of the field. But when those same stars drift towards the edge of the field, the star trails appear to blend close stars together. I wonder if stars trailing more near the edge of the field could be caused by lens distortion or perhaps a lower resolution near the edge of the lens?

That sounds right to me. I have read that lens coma, which gives you elongated images for points, is especially critical for astrophotography. So, that's a thing to look for. I don't think it's just lack of resolution, but maybe that contributes, too.

Lack of coma distortions is one of the key things to look for in a lens for shooting stars. Some lenses smear points across 20 or more pixels just from this imperfection. The only place I know of that tests this is Lenstip reviews.

Thanks for the tip I bet Olympus primes like the 75 1.8 are really good in this regard (much better than conventional telescopes like SCTs.)

Would you say that even Olympus zooms are better than SCTs in this regard?

Here is an image taken with an E-PL6 that I found on astrorobin:

http://www.astrobin.com/271196

that is with the 75mm 1.8 lens

I certainly cannot speak to lens vs telescope but m4/3 has a good selection of primes with terrific image quality wide open. Coma performance standouts I know of are the Oly 8/1.8 and Pany 42.5/1.2.

http://www.lenstip.com/461.7-Lens_review-Olympus_M.Zuiko_Digital_8_mm_f_1.8_ED_PRO_Fisheye_Coma__astigmatism_and_bokeh.html

http://www.lenstip.com/394.7-Lens_review-Panasonic_Leica_DG_Nocticron_42.5_mm_f_1.2_Asph._P.O.I.S._Coma__astigmatism_and_bokeh.html

The 75/1.8 is also very good.

http://www.lenstip.com/351.7-Lens_review-Olympus_M.Zuiko_Digital_75_mm_f_1.8_ED_Coma__astigmatism_and_bokeh.html

For zooms, the 40-150/2.8 is the strongest.

http://www.lenstip.com/479.7-Lens_review-Olympus_M.Zuiko_Digital_40-150_mm_f_2.8_ED_PRO_Coma__astigmatism_and_bokeh.html

Giiba wrote:

I certainly cannot speak to lens vs telescope but m4/3 has a good selection of primes with terrific image quality wide open. Coma performance standouts I know of are the Oly 8/1.8 and Pany 42.5/1.2.

http://www.lenstip.com/461.7-Lens_review-Olympus_M.Zuiko_Digital_8_mm_f_1.8_ED_PRO_Fisheye_Coma__astigmatism_and_bokeh.html

http://www.lenstip.com/394.7-Lens_review-Panasonic_Leica_DG_Nocticron_42.5_mm_f_1.2_Asph._P.O.I.S._Coma__astigmatism_and_bokeh.html

Thanks, what do you suggest for M13, M31 and M42?

Just wanted to file an update- I am back to using 10 sec exposures at 14mm, the colors at 10 sec seem to be much better than the ones at 13 sec, I'm not sure why.  I recently did a test of exposures between 6 sec and 13 sec and 10 sec came in first, followed by 8 sec and then 13 sec, 6 sec came in last.  Also since I am stacking, 10 sec exposures much easier to determine total exposure for than 13 sec exposures are

As an aside, what is the degree separation between Bellatrix (in Orion) and Sirius? I want to find the right focal length that gives me the tightest view of this area.

OutsideTheMatrix wrote:

Just wanted to file an update- I am back to using 10 sec exposures at 14mm, the colors at 10 sec seem to be much better than the ones at 13 sec, I'm not sure why. I recently did a test of exposures between 6 sec and 13 sec and 10 sec came in first, followed by 8 sec and then 13 sec, 6 sec came in last. Also since I am stacking, 10 sec exposures much easier to determine total exposure for than 13 sec exposures are

You don't say f-stop or ISO, so I'm uncertain what your exposure actually was. Here's what I know from experience. With brilliantly clear skies (Kalahari desert), the following exposure will JUST about reach saturation for the brightest stars.

f/ 2.0, ISO 200, T = 30 secs.

If you expose more than that, you're into blowing out starts. That's not a big issue most cases, but if you want the colors of stars, you'd best stay below that. On the other hand, if you're photographing astro structure other than stars (nebulae, etc.), then you can go with a much greater exposure. There's no hope to have the same exposure cover both stars and other astronomical structure.

What software are you using for stacking?

As an aside, what is the degree separation between Bellatrix (in Orion) and Sirius? I want to find the right focal length that gives me the tightest view of this area.

I'm sure you can figure this out from a star chart. I've never done this, so it'd take me a while to figure out. Surprisingly, I googled "angular separation between Bellatrix and Sirius" and got some hits! This one seems to say it's about 7 1/2 degrees, but I did not read carefully enough to be sure:

https://books.google.com/books?id=EVdLAAAAMAAJ&pg=PA26&lpg=PA26&dq=Bellatrix+to+sirius+angular+separation&source=bl&ots=ukT6ESCwFQ&sig=ehofH3Lpk4dbIZuAtZYlfD6LNOM&hl=en&sa=X&ved=0ahUKEwjRip7hsLjQAhVFxmMKHZqSD4AQ6AEIJjAB#v=onepage&q=Bellatrix%20to%20sirius%20angular%20separation&f=false

offtheback wrote:

Great shot!

Thanks. We had to work pretty hard to get a good print of that shot. Screens are just very different for this kind of shot compared to paper. Glowing stars are much more visible on the screen. With paper, your top end brightness is very limited. Our final print, 24" wide, looks pretty good, but the stars are still not as prominent as with a screen.

boxerman wrote:

OutsideTheMatrix wrote:

Just wanted to file an update- I am back to using 10 sec exposures at 14mm, the colors at 10 sec seem to be much better than the ones at 13 sec, I'm not sure why. I recently did a test of exposures between 6 sec and 13 sec and 10 sec came in first, followed by 8 sec and then 13 sec, 6 sec came in last. Also since I am stacking, 10 sec exposures much easier to determine total exposure for than 13 sec exposures are

You don't say f-stop or ISO, so I'm uncertain what your exposure actually was. Here's what I know from experience. With brilliantly clear skies (Kalahari desert), the following exposure will JUST about reach saturation for the brightest stars.

f/ 2.0, ISO 200, T = 30 secs.

If you expose more than that, you're into blowing out starts. That's not a big issue most cases, but if you want the colors of stars, you'd best stay below that. On the other hand, if you're photographing astro structure other than stars (nebulae, etc.), then you can go with a much greater exposure. There's no hope to have the same exposure cover both stars and other astronomical structure.

What software are you using for stacking?

I came up with f/3.5 ISO 1000 and 10 seconds shutter speed (that's just about exactly 1 stop below your values when summed and compared. Then again I am also dealing with light pollution here.) Regardless of the other numbers, reduced DR above that ISO rears its ugly head in paler stars. It's still fine up to ISO 1600 (and you can still see some star colors at ISO 3200) but star colors peak at ISO 1000.

I'm using Deep Sky Stacker for stacking and a program called Sequator to enhance dim stars above the noise floor. Both are free.

One other thing I noted is that when the moon is +/- 3 days from full its light overpowers the stars and they all appear to be white regardless of the settings used. That might also be because I was using Auto WB.  Once you're 4 days away from a full moon or more then the star colors come back (this translates to a moon that is 3 hours or less after moonrise or 3 hours or less before moonset.)

Question- to expose for both star colors and faint nebulae can I just use exposure bracketing and blend multiple exposures into the same frame? I wonder if stacking is good for that or if I need to use a different type of blending- perhaps HDR blending? I see that option in Sequator.

As an aside, what is the degree separation between Bellatrix (in Orion) and Sirius? I want to find the right focal length that gives me the tightest view of this area.

I'm sure you can figure this out from a star chart. I've never done this, so it'd take me a while to figure out. Surprisingly, I googled "angular separation between Bellatrix and Sirius" and got some hits! This one seems to say it's about 7 1/2 degrees, but I did not read carefully enough to be sure:

https://books.google.com/books?id=EVdLAAAAMAAJ&pg=PA26&lpg=PA26&dq=Bellatrix+to+sirius+angular+separation&source=bl&ots=ukT6ESCwFQ&sig=ehofH3Lpk4dbIZuAtZYlfD6LNOM&hl=en&sa=X&ved=0ahUKEwjRip7hsLjQAhVFxmMKHZqSD4AQ6AEIJjAB#v=onepage&q=Bellatrix%20to%20sirius%20angular%20separation&f=false

-- hide signature --

The BoxerMan

I loaded up Starry Night and got a radically different result- 30.4 degrees angular separation and then ran that in a focal length calculator and came up with 20mm as the appropriate M43 focal length to use.

Oh that explains it- the link you presented states that the distance between Betelgeuse and Bellatrix is 7.5 degrees.

boxerman wrote:

offtheback wrote:

Great shot!

Thanks. We had to work pretty hard to get a good print of that shot. Screens are just very different for this kind of shot compared to paper. Glowing stars are much more visible on the screen. With paper, your top end brightness is very limited. Our final print, 24" wide, looks pretty good, but the stars are still not as prominent as with a screen.

I was wondering about prints!  Is there a best type of paper to use for this kind of work?

OutsideTheMatrix wrote:

boxerman wrote:

offtheback wrote:

Great shot!

Thanks. We had to work pretty hard to get a good print of that shot. Screens are just very different for this kind of shot compared to paper. Glowing stars are much more visible on the screen. With paper, your top end brightness is very limited. Our final print, 24" wide, looks pretty good, but the stars are still not as prominent as with a screen.

I was wondering about prints! Is there a best type of paper to use for this kind of work?

I've done 24x18 prints that looked good on standard print shop paper, prefer the matte finish. Haven't done anything fancy, though I'm curious about prints on metal and canvas to see how they turn out.

I experimented the other night (my first seeing stars in months) with my 40-150/2.8 and found that 3.2sec was the max I could shoot without trailing @150mm when looking ENE. I have adjusted the formula on the spreadsheet to account for my findings. I am now reasonably happy with the max exposure time ouput as it gives a rough idea that can be used as a starting point for untracked exposures; increased when facing the pole, and decreased facing the equator. I have now tested 8mm (fisheye), 12mm, 15mm, 17mm, 150mm. Going to do some shots at 40mm'ish next chance I get.

OutsideTheMatrix wrote:

I was wondering about prints! Is there a best type of paper to use for this kind of work?

Well, my wife used to run a graphic arts company, so we do printing "right" (aka expensive) for our favorite few shots. The night shot of Mt. Cook was done professionally, at a local printer, on Hahnemuhle (umlaut on the u), rag, satin finish. As it was, the first trial print (smallish part of the original) was too dark, and we had to change the overall brightness. Got some good advice from the printer.

Like Giiba, I've wondered about metal prints, but have not tried them, yet. They might do well with the highlights (stars) since you're getting reflective light, there (not 100% sure). But, my intuition is also that you don't want to print on metal with anything less than tack sharp original.

OutsideTheMatrix wrote:

boxerman wrote:

OutsideTheMatrix wrote:

Just wanted to file an update- I am back to using 10 sec exposures at 14mm, the colors at 10 sec seem to be much better than the ones at 13 sec, I'm not sure why. I recently did a test of exposures between 6 sec and 13 sec and 10 sec came in first, followed by 8 sec and then 13 sec, 6 sec came in last. Also since I am stacking, 10 sec exposures much easier to determine total exposure for than 13 sec exposures are

You don't say f-stop or ISO, so I'm uncertain what your exposure actually was. Here's what I know from experience. With brilliantly clear skies (Kalahari desert), the following exposure will JUST about reach saturation for the brightest stars.

f/ 2.0, ISO 200, T = 30 secs.

If you expose more than that, you're into blowing out starts. That's not a big issue most cases, but if you want the colors of stars, you'd best stay below that. On the other hand, if you're photographing astro structure other than stars (nebulae, etc.), then you can go with a much greater exposure. There's no hope to have the same exposure cover both stars and other astronomical structure.

What software are you using for stacking?

I came up with f/3.5 ISO 1000 and 10 seconds shutter speed (that's just about exactly 1 stop below your values when summed and compared. Then again I am also dealing with light pollution here.) Regardless of the other numbers, reduced DR above that ISO rears its ugly head in paler stars. It's still fine up to ISO 1600 (and you can still see some star colors at ISO 3200) but star colors peak at ISO 1000.

I'm using Deep Sky Stacker for stacking and a program called Sequator to enhance dim stars above the noise floor. Both are free.

I'll keep a note on these, to try when I get back to astrophotography.

One other thing I noted is that when the moon is +/- 3 days from full its light overpowers the stars and they all appear to be white regardless of the settings used. That might also be because I was using Auto WB. Once you're 4 days away from a full moon or more then the star colors come back (this translates to a moon that is 3 hours or less after moonrise or 3 hours or less before moonset.)

Question- to expose for both star colors and faint nebulae can I just use exposure bracketing and blend multiple exposures into the same frame? I wonder if stacking is good for that or if I need to use a different type of blending- perhaps HDR blending? I see that option in Sequator.

I just don't know. From terrestrial shooting, I'd think that combining with HDR might do it. But, do you really need color in the stars if you're shooting nebulae and the like? People expect stars to be white (because their eye technology is not up to seeing the color), so wouldn't be surprised.

As an aside, what is the degree separation between Bellatrix (in Orion) and Sirius? I want to find the right focal length that gives me the tightest view of this area.

I'm sure you can figure this out from a star chart. I've never done this, so it'd take me a while to figure out. Surprisingly, I googled "angular separation between Bellatrix and Sirius" and got some hits! This one seems to say it's about 7 1/2 degrees, but I did not read carefully enough to be sure:

https://books.google.com/books?id=EVdLAAAAMAAJ&pg=PA26&lpg=PA26&dq=Bellatrix+to+sirius+angular+separation&source=bl&ots=ukT6ESCwFQ&sig=ehofH3Lpk4dbIZuAtZYlfD6LNOM&hl=en&sa=X&ved=0ahUKEwjRip7hsLjQAhVFxmMKHZqSD4AQ6AEIJjAB#v=onepage&q=Bellatrix%20to%20sirius%20angular%20separation&f=false

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The BoxerMan

I loaded up Starry Night and got a radically different result- 30.4 degrees angular separation and then ran that in a focal length calculator and came up with 20mm as the appropriate M43 focal length to use.

Oh that explains it- the link you presented states that the distance between Betelgeuse and Bellatrix is 7.5 degrees.

Sorry.  Searched for what you wanted, but then did not check the source Google responded with well enough.

Nice chatting again... best of luck.

Giiba wrote:

OutsideTheMatrix wrote:

boxerman wrote:

offtheback wrote:

Great shot!

Thanks. We had to work pretty hard to get a good print of that shot. Screens are just very different for this kind of shot compared to paper. Glowing stars are much more visible on the screen. With paper, your top end brightness is very limited. Our final print, 24" wide, looks pretty good, but the stars are still not as prominent as with a screen.

I was wondering about prints! Is there a best type of paper to use for this kind of work?

I've done 24x18 prints that looked good on standard print shop paper, prefer the matte finish. Haven't done anything fancy, though I'm curious about prints on metal and canvas to see how they turn out.

I experimented the other night (my first seeing stars in months) with my 40-150/2.8 and found that 3.2sec was the max I could shoot without trailing @150mm when looking ENE. I have adjusted the formula on the spreadsheet to account for my findings. I am now reasonably happy with the max exposure time ouput as it gives a rough idea that can be used as a starting point for untracked exposures; increased when facing the pole, and decreased facing the equator. I have now tested 8mm (fisheye), 12mm, 15mm, 17mm, 150mm. Going to do some shots at 40mm'ish next chance I get.

How does that fit in with our findings of 10 sec at 14mm?

I saw this formula somewhere- what do you think?

Recently, I ran across this equation:

time = 240 / (lens fl * cos dec)

where dec is the declination of the star closest to the celestial equator. This over estimates the time so I've now modified it to the following:

time = 150 / (lens fl * cos dec)

boxerman wrote:

OutsideTheMatrix wrote:

boxerman wrote:

OutsideTheMatrix wrote:

Just wanted to file an update- I am back to using 10 sec exposures at 14mm, the colors at 10 sec seem to be much better than the ones at 13 sec, I'm not sure why. I recently did a test of exposures between 6 sec and 13 sec and 10 sec came in first, followed by 8 sec and then 13 sec, 6 sec came in last. Also since I am stacking, 10 sec exposures much easier to determine total exposure for than 13 sec exposures are

You don't say f-stop or ISO, so I'm uncertain what your exposure actually was. Here's what I know from experience. With brilliantly clear skies (Kalahari desert), the following exposure will JUST about reach saturation for the brightest stars.

f/ 2.0, ISO 200, T = 30 secs.

If you expose more than that, you're into blowing out starts. That's not a big issue most cases, but if you want the colors of stars, you'd best stay below that. On the other hand, if you're photographing astro structure other than stars (nebulae, etc.), then you can go with a much greater exposure. There's no hope to have the same exposure cover both stars and other astronomical structure.

What software are you using for stacking?

I came up with f/3.5 ISO 1000 and 10 seconds shutter speed (that's just about exactly 1 stop below your values when summed and compared. Then again I am also dealing with light pollution here.) Regardless of the other numbers, reduced DR above that ISO rears its ugly head in paler stars. It's still fine up to ISO 1600 (and you can still see some star colors at ISO 3200) but star colors peak at ISO 1000.

I'm using Deep Sky Stacker for stacking and a program called Sequator to enhance dim stars above the noise floor. Both are free.

I'll keep a note on these, to try when I get back to astrophotography.

One other thing I noted is that when the moon is +/- 3 days from full its light overpowers the stars and they all appear to be white regardless of the settings used. That might also be because I was using Auto WB. Once you're 4 days away from a full moon or more then the star colors come back (this translates to a moon that is 3 hours or less after moonrise or 3 hours or less before moonset.)

Question- to expose for both star colors and faint nebulae can I just use exposure bracketing and blend multiple exposures into the same frame? I wonder if stacking is good for that or if I need to use a different type of blending- perhaps HDR blending? I see that option in Sequator.

I just don't know. From terrestrial shooting, I'd think that combining with HDR might do it. But, do you really need color in the stars if you're shooting nebulae and the like? People expect stars to be white (because their eye technology is not up to seeing the color), so wouldn't be surprised.

As an aside, what is the degree separation between Bellatrix (in Orion) and Sirius? I want to find the right focal length that gives me the tightest view of this area.

I'm sure you can figure this out from a star chart. I've never done this, so it'd take me a while to figure out. Surprisingly, I googled "angular separation between Bellatrix and Sirius" and got some hits! This one seems to say it's about 7 1/2 degrees, but I did not read carefully enough to be sure:

https://books.google.com/books?id=EVdLAAAAMAAJ&pg=PA26&lpg=PA26&dq=Bellatrix+to+sirius+angular+separation&source=bl&ots=ukT6ESCwFQ&sig=ehofH3Lpk4dbIZuAtZYlfD6LNOM&hl=en&sa=X&ved=0ahUKEwjRip7hsLjQAhVFxmMKHZqSD4AQ6AEIJjAB#v=onepage&q=Bellatrix%20to%20sirius%20angular%20separation&f=false

I loaded up Starry Night and got a radically different result- 30.4 degrees angular separation and then ran that in a focal length calculator and came up with 20mm as the appropriate M43 focal length to use.

Oh that explains it- the link you presented states that the distance between Betelgeuse and Bellatrix is 7.5 degrees.

Sorry. Searched for what you wanted, but then did not check the source Google responded with well enough.

Nice chatting again... best of luck.

I wanted to pass on this equation I found:

Recently, I ran across this equation:

time = 240 / (lens fl * cos dec)

where dec is the declination of the star closest to the celestial equator. This over estimates the time so I've now modified it to the following:

time = 150 / (lens fl * cos dec)

Also, I wanted to ask when you used the settings you mentioned what were the dimmest magnitude stars you captured?  I am trying to separate dim stars from the light pollution floor and wondering if lowering contrast to -1 or -2 would help or would that be counterproductive in making dim stars easier to spot in the background sky?  Maybe I should increase contrast instead?

OutsideTheMatrix wrote:

Giiba wrote:

...

I experimented the other night (my first seeing stars in months) with my 40-150/2.8 and found that 3.2sec was the max I could shoot without trailing @150mm when looking ENE. I have adjusted the formula on the spreadsheet to account for my findings. I am now reasonably happy with the max exposure time ouput as it gives a rough idea that can be used as a starting point for untracked exposures; increased when facing the pole, and decreased facing the equator. I have now tested 8mm (fisheye), 12mm, 15mm, 17mm, 150mm. Going to do some shots at 40mm'ish next chance I get.

How does that fit in with our findings of 10 sec at 14mm?

It doesn't. At 150 mm, the formula gives 1 second. But, as I suggested, people have different display requirements and tolerance. Maybe Giiba can comment.

I saw this formula somewhere- what do you think?

Recently, I ran across this equation:

time = 240 / (lens fl * cos dec)

Yes, correct. The formula we worked on was maximum trailing, which is in the equatorial plane. For wide-angle shots, you'll usually get some at that declination, so it's sensible. But, if you're doing a narrower field (like 150 mm), you can get a better estimate by including the declination.

where dec is the declination of the star closest to the celestial equator. This over estimates the time so I've now modified it to the following:

time = 150 / (lens fl * cos dec)

boxerman wrote:

OutsideTheMatrix wrote:

Giiba wrote:

...

I experimented the other night (my first seeing stars in months) with my 40-150/2.8 and found that 3.2sec was the max I could shoot without trailing @150mm when looking ENE. I have adjusted the formula on the spreadsheet to account for my findings. I am now reasonably happy with the max exposure time ouput as it gives a rough idea that can be used as a starting point for untracked exposures; increased when facing the pole, and decreased facing the equator. I have now tested 8mm (fisheye), 12mm, 15mm, 17mm, 150mm. Going to do some shots at 40mm'ish next chance I get.

How does that fit in with our findings of 10 sec at 14mm?

It doesn't. At 150 mm, the formula gives 1 second. But, as I suggested, people have different display requirements and tolerance. Maybe Giiba can comment.

I wonder what it will be at 40mm?  That is a good middle ground to test- not wide angle but not quite telephoto either.

I saw this formula somewhere- what do you think?

Recently, I ran across this equation:

time = 240 / (lens fl * cos dec)

Yes, correct. The formula we worked on was maximum trailing, which is in the equatorial plane. For wide-angle shots, you'll usually get some at that declination, so it's sensible. But, if you're doing a narrower field (like 150 mm), you can get a better estimate by including the declination.

Yes that makes sense since you need a "finer" result with a narrower field.

where dec is the declination of the star closest to the celestial equator. This over estimates the time so I've now modified it to the following:

time = 150 / (lens fl * cos dec)

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The BoxerMan

By the way I was inspecting my photographs 1:1 on a large monitor and I noticed something curious- there are some stars I can see at 8 sec and 13 sec exposures but can't see them at 10 sec exposures.  And there are other stars I can find in my 10 second exposures that are nowhere to be found in the 8 sec and 13 sec exposures.  The funny thing is the 8 and 13 sec exposures look more alike than either does to the 10 sec exposures.  I wonder why this is?

I also found that pictures I took after around 2 am showed star colors a lot better than pictures taken at, say, 11 PM.  Not only that but the sky was a lot darker at 2 AM and a lot "redder" at 11 PM.  That must be the effects of more light pollution earlier in the evening rearing its ugly head.