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Telephoto Lens Tips

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#1 GSqwid

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Posted 14 November 2019 - 09:30 PM

I've had some luck with my 5DIII attached to my C8, but would like to try imaging with something shorter and faster.  I'd like to experiment a bit before investing in another scope, so for now I'm thinking of using my Sigma 150-600C lens.  I know a fast refractor (or even a better lens) would be a better choice, but I'm thinking it should be suitable for some basic trial and error.  

 

Is there anyone who has experience with that lens, or long telephotos in general, that has suggestions on how best to image?  I'm also curious what targets are best to start with?  My camera is unmodded, I don't have any filters for the Sigma, and I'll be shooting from suburban to urban skies.  Therefore I don't want to go after something really dim or that wouldn't show up well with my "conventional" setup.  Eventually I plan to either mod my 5DIII when I upgrade (or get a CCD) but for now it does double duty.

 

Thanks for any advice!



#2 JDShoots

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Posted 15 November 2019 - 07:36 PM

Sometimes I think you are better not knowing what you can't do.   The more I read, the more I hear that I shouldn't bother with my 500mm on an un-mod'ed camera without guiding.   I would say use what you have and see what you get.  You can only loose three or four hours of time on a target or on the flip side, maybe you will like the results.  I just started learning about astrophotography 3 months ago because I bought an old 500mm f4 manual focus lens for wildlife photography.  I figured I could shoot the moon and then learned it's not a bad focal length for DSOs too.   So then I got a German equatorial mount for this.  I also have a 300 f4 that's a beautiful lens and tried that too.   One day with the right target I'll take out the 180 f2.8.  You have a sigma zoom, you could have better glass, but this is what you can take out back today, do it.  

I don't know where you are to say what you should shoot, but I am starting with the big and the bright from my vantage point and in the last three months despite the moon and the clouds, I've take a half dozen images.   Get out and try it, I figure a few extra hours on the target will hide some of the limitations of the setup.   

I'd also recommend a dew heater, and a Bahtinov Focusing Mask, maybe a rain sleeve and another dovetail to attach it all too your mount.  

 

These are generally about 2 - 3 hours of total integration time for each image and the subs are 60 seconds each f5 or 5.6 @ an ISO of 200-400.

of course 60" @ 500mm will require adequate polar alignment and tracking or a guided mount.  

 

M31 with the 300, my first.  

original.jpg

 

 

M33 with the 500

original.jpg

 

M45 with the 500

original.jpg

 

M31 with the 500

original.jpg

 

The Heart Nebula with the 300

original.jpg

 

And an honorable mention, my M101 w/NGC 5474 and NGC 5422

I think I ended up in the trees after only an hour and a half on this one.  

original.jpg

 


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#3 Kendahl

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Posted 15 November 2019 - 07:48 PM

.... the subs are 60 seconds each f5 or 5.6 @ an ISO of 200-400.

With an f/5.6 lens and 60 second subexposures, I find I need an ISO of 6400 to get the histogram off the bottom end of the range.



#4 JDShoots

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Posted 15 November 2019 - 07:54 PM

With an f/5.6 lens and 60 second subexposures, I find I need an ISO of 6400 to get the histogram off the bottom end of the range.

Yeah you probably would if you planned on going up to 25 - 30% from the left.   But I haven't really bothered with that since my first M31 up top.   That was ISO 2000.   Since then I leave it at 400 except for the Plieades, that I dropped to 200 because those stars were so bright.  



#5 GSqwid

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Posted 15 November 2019 - 09:42 PM

Sometimes I think you are better not knowing what you can't do.   The more I read, the more I hear that I shouldn't bother with my 500mm on an un-mod'ed camera without guiding.   I would say use what you have and see what you get.  You can only loose three or four hours of time on a target or on the flip side, maybe you will like the results.  I just started learning about astrophotography 3 months ago because I bought an old 500mm f4 manual focus lens for wildlife photography.  I figured I could shoot the moon and then learned it's not a bad focal length for DSOs too.   So then I got a German equatorial mount for this.  I also have a 300 f4 that's a beautiful lens and tried that too.   One day with the right target I'll take out the 180 f2.8.  You have a sigma zoom, you could have better glass, but this is what you can take out back today, do it.  

I don't know where you are to say what you should shoot, but I am starting with the big and the bright from my vantage point and in the last three months despite the moon and the clouds, I've take a half dozen images.   Get out and try it, I figure a few extra hours on the target will hide some of the limitations of the setup.   

I'd also recommend a dew heater, and a Bahtinov Focusing Mask, maybe a rain sleeve and another dovetail to attach it all too your mount.  

 

These are generally about 2 - 3 hours of total integration time for each image and the subs are 60 seconds each f5 or 5.6 @ an ISO of 200-400.

of course 60" @ 500mm will require adequate polar alignment and tracking or a guided mount.  

 

M31 with the 300, my first.  

 

 

 

M33 with the 500

 

 

M45 with the 500

 

 

M31 with the 500

 

 

The Heart Nebula with the 300

 

 

And an honorable mention, my M101 w/NGC 5474 and NGC 5422

I think I ended up in the trees after only an hour and a half on this one.  

 

 

I understand what you are saying; I think some folks make assumptions about minimum acceptable quality levels, willingness to experiment and tweak, etc., and offer some strongly worded suggestions that don't take into account a person's specific situation.  I'm well aware that by conventional wisdom my SCT is too long and too slow and my mount is old and buggy.  And people who say that aren't necessarily wrong.  But I accept the limitations and know that there will be trade-offs in quality and headaches until I get different equipment, more experience, or both.  And, lets face it, I could drop months of full-time practice and tens of thousands of dollars and still be a novice!  In short: I agree with you, but I figure it doesn't hurt to ask for some advice to help decide where to start.  Just don't get discouraged by things that may seem a bit dismissive (for lack of a better term) of what you are trying to do.

 

I do have a dew heater that will fit the lens; may need to figure out a focusing mask.  I have one for the SCT and it made a big difference.

 

 

With an f/5.6 lens and 60 second subexposures, I find I need an ISO of 6400 to get the histogram off the bottom end of the range.

Because my SCT has such a long focal length and I have yet to invest in guiding, I have been limited to 20 to 30 second subs.  I'm hoping to double that with the lens.  Even at those short subs, though, I rarely go much above 2000 ISO.  It just seems to bring out too much noise when I process.  In my limited experimentation lower ISO has seemed to produce better results than optimizing the histogram, but I haven't done enough imaging yet to consider my results "conclusive".  



#6 JDShoots

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Posted 16 November 2019 - 01:49 AM

.........

I do have a dew heater that will fit the lens; may need to figure out a focusing mask.  I have one for the SCT and it made a big difference.

 

Because my SCT has such a long focal length and I have yet to invest in guiding, I have been limited to 20 to 30 second subs.  I'm hoping to double that with the lens.  Even at those short subs, though, I rarely go much above 2000 ISO.  It just seems to bring out too much noise when I process.  In my limited experimentation lower ISO has seemed to produce better results than optimizing the histogram, but I haven't done enough imaging yet to consider my results "conclusive".  

This one may work, or the next size up.

https://www.amazon.c...73886130&sr=8-2

 

Yes I have been keeping the ISO low 400 ± a stop, more Dynamic range and less noise.   My Nikon seems to do well there.  I figured I am already stretching the hell out of the image, what's another stop or two, I caught the proton.  

 

Is your mount a tracking mount?

edit:

Oh and what are you being dismissive of?  


Edited by JDShoots, 16 November 2019 - 01:52 AM.


#7 NGC 2419

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Posted 16 November 2019 - 12:34 PM

Sometimes I think you are better not knowing what you can't do. The more I read, the more I hear that I shouldn't bother with my 500mm on an un-mod'ed camera without guiding. I would say use what you have and see what you get. You can only loose three or four hours of time on a target or on the flip side, maybe you will like the results...


I think this is the best advice I've ever seen here. Too many times, the resident "experts" do nothing but discourage people by telling them what they "can't" do with the equipment they already have.

I'd say take whatever equipment you have outside and take some pictures! You'll probably be amazed by the results.

As to which targets to shoot, I put my sensor info and some lenses into Stellarium and use that to frame my target.

Clear skies!
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#8 GSqwid

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Posted 16 November 2019 - 11:35 PM

This one may work, or the next size up.

https://www.amazon.c...73886130&sr=8-2

 

Yes I have been keeping the ISO low 400 ± a stop, more Dynamic range and less noise.   My Nikon seems to do well there.  I figured I am already stretching the hell out of the image, what's another stop or two, I caught the proton.  

 

Is your mount a tracking mount?

edit:

Oh and what are you being dismissive of?  

 

And I intended to say that some folks on here, while well-intended, can be dismissive of people who aren't following the path they feel is best.  Apparently I needed to reread that before posting!  And that kind of goes into your question about the mount.  After some rather blunt unsolicited opinions regarding what I have, I tend not to bring up much of my equipment unless it is relevant.  I have a CG5-GT advanced, which seems to strike-up some strong pro/con arguments on here.  It may not be perfect, but it seems to work and I'd rather experiment with it now rather than waiting to get a "true" astrophotography mount.

 

How do you all typically polar align using a DSLR and lens?  I can't see Polaris from my viewing location, and I'm not sure if the view through the DSLR is going to be sufficient to do an All Star Polar Align.  I could align using the SCT and swap it out, but I'd probably knock something out of place that way!



#9 JDShoots

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Posted 17 November 2019 - 01:05 AM

And I intended to say that some folks on here, while well-intended, can be dismissive of people who aren't following the path they feel is best.  Apparently I needed to reread that before posting!  And that kind of goes into your question about the mount.  After some rather blunt unsolicited opinions regarding what I have, I tend not to bring up much of my equipment unless it is relevant.  I have a CG5-GT advanced, which seems to strike-up some strong pro/con arguments on here.  It may not be perfect, but it seems to work and I'd rather experiment with it now rather than waiting to get a "true" astrophotography mount.

 

How do you all typically polar align using a DSLR and lens?  I can't see Polaris from my viewing location, and I'm not sure if the view through the DSLR is going to be sufficient to do an All Star Polar Align.  I could align using the SCT and swap it out, but I'd probably knock something out of place that way!

I get ya. Sounds like a good mount to me, and it can carry some payload:)  Probably could carry the SCT and the DSLR+Sigma:)  

So, I can't help you at all with the polar issues of a guiding and polar alignment.  I just have a polar scope in my GEM and I make sure to get on it.   For the first time since I've lived here I have actually thought of cutting some trees down:)  You can barrow my chainsaw:)  I won't but I hear you about getting on Polaris, sometime I have to carry all this stuff further out then I intended to get both my target and a good alignment.  



#10 GSqwid

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Posted 18 November 2019 - 05:28 PM

I get ya. Sounds like a good mount to me, and it can carry some payload:)  Probably could carry the SCT and the DSLR+Sigma:)  

So, I can't help you at all with the polar issues of a guiding and polar alignment.  I just have a polar scope in my GEM and I make sure to get on it.   For the first time since I've lived here I have actually thought of cutting some trees down:)  You can barrow my chainsaw:)  I won't but I hear you about getting on Polaris, sometime I have to carry all this stuff further out then I intended to get both my target and a good alignment.  

 

Well, if it can handle my 18" refractor it should be good ;).  

 

I've considered cutting some trees, but being the required ones are not on my property I'm concerned the respective property owners might be unhappy.  I think I just need to learn how to drift align...



#11 okiedrifter

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Posted 20 November 2019 - 10:45 AM

I used my Tamzooka (150-600mm) lens for quite a while for imaging. I stopped it down to f8, but pulled some pretty good images out of it.

I even had it mounted on my skytracker at first and could get good one minute exposures.



#12 Alex McConahay

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Posted 20 November 2019 - 11:14 AM

When stopping down a lens, you sometimes get funny diffraction spikes. Instead stop the aperture using filter adapter rings. They are round all the way around and do not leave spikes. 

 

See:

 

 https://www.amazon.c...la-447286125255

 

 

A whole set for $20. 

 

Alex




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