D600 and Star Trails

[dave_terry1]

<p>So I've read previous posts about star trails, but they are all 3-4 years old. Since cameras and sensors have greatly improved since then, I want to hear current opinions.</p>

<p>I have my new D600 (so far, no spots). I will be going to Hawaii in a couple of weeks, first Maui the Kauai. I'd really like to do star trail shots on Haleakala, but I don't know if long exposure noise is still an issue on the new sensors. I know that high ISO noise has been greatly reduced, but not sure about long exposures.</p>

<p>Anyone tried this yet on the D600? </p>

<p>I know about photo stacking (in theory), but I've never tried it. What is the field technique? I'll ask about the computer technique at a later time.</p>

<p>Thanks for your insights.</p>

<p>Dave</p>

[tim_eastman]

<p>I have not tried it, but results I have seen are great:<br>

http://www.tawbaware.com/startracer.htm</p>

[thomas_lozinski]

<p>Dave,<br>

Having used many different Nikon DSLRS but not the D600 I have some suggestions. Long exposure noise is an issue. If you're at ISO 200 for 10 minutes and have Long exposure noise reduction on you will be fine. If you're at ISO 800 for 2 hours and don't have long exposure noise reduction on then you're going to have problems. The newer cameras limit exposure sequences to 100 shots. This means that if your'e doing 30s exposures then you're only going to be able to get 50 minutes of trails. For wide angle you need substantially more time than you may imagine (hours). If you don't have much time using a longer focal length will fill the frame with star trails much quicker. Temperature is also a big determining factor for noise. If you're on top of Haleakala then it's going to be really cold and you're going to get much less noise than you would in Death Valley in August. Stacking is the best way to go (startrails.exe is good) although that startracer program looks appealling. The downside is that you loose the ability to do raw processing (<strong>I really wish there was a program that would just add raw images and leave it in raw format, if one exists someone please let me know!!!!) </strong></p>

[Andrew Garrard]

<p>Thomas - what? I can believe that stacking won't leave things in RAW format (you'd get fractional offsets such that the bayer grid doesn't line up, for a start), but DeepSkyStacker can output 16-bit images, which will let you do raw-like processing on the output. I've not tried it yet, but had it recommended to me. (Until you mentioned this, I didn't realise that Registax apparently <i>doesn't</i> let you output in more than 8-bit.) I agree that stacking is the preferred solution. APoD has shown a 24-hour star trail from the South Pole; disappointingly, it's very visibly stacked; I was hoping someone might do it "for real" in a single exposure...</p>

[thomas_lozinski]

<p>Andrew- for star trails stacking the bayer grid would line up because you're not shifting the image. You're correct thought if we were talking about aligning things like in DSS or registax but that's not what this is about. There are a lot of things besides raw that I've become accustomed to besides the bit depth. If you were able to stack the raw images in this case it would just be like having an extra long exposure (I'm not sure how the noise would add up.) </p>

[Andrew Garrard]

<p>Thomas - fair enough, although I think that's a special case for stacking software. I'd generally not trust any mount that I can afford not to shift by a single pixel during a long exposure. But I'd also like to try stacking software as an (iffy) alternative to a driven mount, so I'm quite glad the registration facility is in there. My T-ring and F adaptor only turned up a few days before I had to leave for the US for a week, and I only just got back, so I'll only be able to report on this when I've had the chance to play.<br />

<br />

What RAW features were you after? If you're concerned about what the raw converter can do, can you not apply lens ("lens"?) corrections etc. before you feed the images to the stacking software? I'm sure you could convert from a 16-bit image back to RAW at the potential loss of some information - possibly not noticable with the resolving power of most scopes - but it feels like the wrong approach.</p>

[mike_halliwell]

<p>OK, silly question...?</p>

<p>If you're stacking star trails, what do you infill with when the shutter's closed?</p>

<p>If you take a dark-frame for the evening maybe... but if you're on Long-Exposure Noise Reduction, AFAIK, that takes a Dark-Frame EVERY time the shutter closes.....ie 30 seconds open followed by 30 seconds closed and then there's writing time.?</p>

[thomas_lozinski]

<p>Mike: you have to disable LENR. The 1/5s that the shutter is closed between shots is negligible but can be seen.</p>

[mike_halliwell]

<p>Thomas, I guess that's where my..</p>

 

<blockquote>

<p>If you take a dark-frame for the evening maybe<br>

</p>

</blockquote>

<p>came from...:-) I've done some star-trail shots, but never bothered stacking.<br>

<br>

Perhaps I should have been clearer and said "One Dark-Frame for all subsequent frames that evening".</p>

[mike_halliwell]

<p>Thomas, I guess that's where my..</p>

 

<blockquote>

<p>If you take a dark-frame for the evening maybe<br>

</p>

</blockquote>

<p>came from...:-) I've done some star-trail shots, but never bothered stacking.<br>

<br>

Perhaps I should have been clearer and said "One Dark-Frame for all subsequent frames that evening".</p>

[Andrew Garrard]

<p>Mike - yes, it depends on the size of the star projection compared with the closed aperture time. Something like <a href="http://apod.nasa.gov/apod/image/1208/Startrails24Schwartz.jpg">this</a> looks good at a small size, but you can see the gaps at larger resolutions. I admit it's a bit hard to get a sky dark enough for a really long exposure, especially where I am.</p>

[dave_terry1]

<p>No idea what you guys are talking about. What do you mean by "dark frame"?</p>

<p>I see the advantage of using startracer, but it doesn't look to be available for Mac.</p>

<p>I get the impression from Thomas' first response that I can't shoot raw if I am stacking shots, is that right? </p>

<p>As I said, what is the field technique?</p>

<p>Thanks.</p>

 

[mike_halliwell]

<p>A 'Dark Frame' is a reference image taken with identical characteristics to your star pics but with the lens cap on. As things such as TEMPERATURE, ISO and TIME affect the sensor output uniquely, it's normal to take a frame per shoot for use later. Nikon's own LENR takes a 'dark frame' after every shot, thus extending the time you can't capture the next frame x 2.</p>

<p>It is therefore a record of camera produced 'noise' ie not stars, that can be subtracted from your star pics to leave JUST the stars!</p>

[thomas_lozinski]

<p>Field Technique is simple. Get a rock solid tripod and weigh it down if possible. Try setting your camera for ISO 400 f5.6 30s, use a cable release and just continuously take shots. Do not use exposure delay mode, use highest frame rate to reduce interuptions between shots(make sure you're not blowing any highlights in the foreground, star trails are OK to blow out since there is no detail there anyhow.) Startrails.exe won't use raw files that I recall but you can always convert the raws to jpgs as an intermediate step in post which lets you color balance and adjust exposure much better. The nikons limit you to 100 shots and then you have to reset the cable release. If you don't have a cable release you can pick one up on ebay for $5 or you may be able to use the interval mode if your camera has it (need to set interval to 31s or so (experiment, might need 32s etc.) This might give gaps between the stars trails, cable release is the best bet. Do NOT do long exposure noise reduction between shots. You are going to want to take several dark frames (same exact settings but with lens cap on). The startrails programs will average these dark frames and subtract them accordingly from your image. In terms of time, try for 200 minutes for 20mm or 20 minutes at 200mm (might need to stop down more and raise ISO.) You also could do it in one shot on bulb setting in which case you'd probably want to have long exposure noise reduction on. </p>