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Wide field imaging lens question

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#1 tag1260

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Posted 24 November 2017 - 11:28 AM

First I'll list my equipment, then my question.

 

Canon T5i

50mm f/1.8 nifty fifty lens

28mm f/2.8  prime lens

18-55mm zoom lens

28-80mm zoom

70-300mm zoom lens

 

Ioptron Sky Tracker.

 

 

Anyways, with the lenses that I have available, which will be my best bet to try imagining something easy like M42 ? What settings should I try? 

Any help for the newbie would be appreciated.

 

Thanks

 


Edited by tag1260, 24 November 2017 - 11:44 AM.


#2 oldstargazer

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Posted 24 November 2017 - 01:17 PM

You will want bulb mode and maybe start with 800 iso and say 45 seconds using the 300 zoom at 300. Focus using live view 10x on a fairly bright star for pinpoint focus manually. If you don't have one you will have to get remote shutter release or 5i I guess you can use your phone to control the shutter. Look at the picture you just got the best you can for trails of stars and how much detail you captured of the nebula. If you didn't get much detail you can increase exposure time as long as there were not any trails. If you saw trails you will need to go to next iso 1600 and cut time in half and look again. Great thing about digital is you get instant feedback so you can make corrections without burning a whole roll of film and then starting again.



#3 RedLionNJ

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Posted 24 November 2017 - 02:09 PM

 

Canon T5i

70-300mm zoom lens

 

Ioptron Sky Tracker.

 

 

Which will be my best bet to try imagining something easy like M42 ? What settings should I try? 

Any help for the newbie would be appreciated.

 

Thanks

Make a concerted effort to polar align the iOptron as best you can. That is going to be, by far, the primary aspect in determining how long individual exposures can be before they become trailed.

 

Zoom in the 70-300mm lens to maximum, close it down a stop or two. Then focus on a bright, nearby star using zoomed liveview. Use tape or something to lock the focus in place. Then point toward M42.

 

Initially, you want to see how long an exposure you can take without skyfog dominating, OR trailing becoming obvious. If it's cold out, use ISO1600. Else drop back to ISO800.  You might be able to get 30 seconds, you might be able to get 2 minutes. Experiment. Once you find a setting you like, stick with it.  Take ten or twenty such exposures (always in RAW mode), then stack them together. You'll get even better results if you throw in a few dark frames, too.

 

Once you a stacked and semi-calibrated result, tweak the levels and apply a steep curve to it (maximize the curve's gradient through the highest, densest part of the histogram). You may need to repeat these two steps a few times. Try not to clip the black side or the white side.

 

Ta da - hopefully a pleasant image with little effort.



#4 Kendahl

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Posted 24 November 2017 - 08:37 PM

 My club's observing site lies on the border between dark yellow and bright green. With an f/6.3 optical tube, a good combination for galaxies is ISO 800 for 300 seconds. Cut that in half for star clusters. Use the principle of reciprocity to come up with other combinations. Since your lenses will be faster than f/6.3, you should be able to shorten your duration. A factor of two in focal ratio is worth a factor of four in duration. It wouldn't hurt to bump ISO up to 1600.



#5 Zachricornus

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Posted 24 November 2017 - 08:52 PM

Agree with all above posts.

If you'd like a different perspective, try the 28mm (i'm a fan of Barnard's Loop).

Whichever you choose, try not to blowout the core too much... there's only so much you can do in processing.

Have Fun! grin.gif



#6 17.5Dob

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Posted 24 November 2017 - 10:15 PM

With the SkyTracker, you really want to stick to 100mm or less fl, or you'll be tossing away a lot of our exposure time culling out bad subs . The SkyTracker REALLY starts to suffer beyond 135mm. I consider 200mm barely usable at 1 min, and 300mm limited to 30"

You need to start to think a bit wider field. This is from my Nikon D5300a, from my Red/White zone yard. 85mm,f4, ISO 400, 60" x 210. I had to keep the exposures this slow / short because of my LP. But I've had no problem getting perfect 3 min subs  at 70-100mm.

29682152474_ace54464e9_z.jpg

 

34452091834_80526b0762_z.jpg

 


  • james7ca, Zachricornus and Cajundaddy like this

#7 bobzeq25

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Posted 25 November 2017 - 12:03 AM

First I'll list my equipment, then my question.

 

Canon T5i

50mm f/1.8 nifty fifty lens

28mm f/2.8  prime lens

18-55mm zoom lens

28-80mm zoom

70-300mm zoom lens

 

Ioptron Sky Tracker.

 

 

Anyways, with the lenses that I have available, which will be my best bet to try imagining something easy like M42 ? What settings should I try? 

Any help for the newbie would be appreciated.

 

Thanks

Definitely start with the nifty fifty, it will be the best to learn on.  Which is what you need, you won't be doing great images until you do, so what is "best" for an experienced imager trying to do the best image is not best for you.

 

Stick with fixed focal lengths, no matter what.  Zooms are too geared for terrestrial photography.  Too slow, bad aberrations.

 

Settings.  ISO 800.  Expose until the back of the camera histogram is maybe 1/3 to the right.  30-120 seconds, depending on your skies.

 

Don't omit the camera calibration frames; bias, flats, darks.  That will really mess up your ability to learn processing, which is more than half the game.

 

Did I mention this is all about learning, right now?  <grin>

 

This book will help.

 

http://www.astropix....bgda/index.html


Edited by bobzeq25, 25 November 2017 - 12:04 AM.



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