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Forum: Pentax K-5 & K-5 II
08-26-2018, 03:12 PM
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Until you decide what to do, here is a slightly different approach. You can stack any number of images, which would combine all the captured light together. Just aim the camera to the sky and take multiple images. It would be better to have the mirror up and just put the body in burst mode. I would probably go with 10 second exposures to keep the star trails at a minimum.Then use a program like sequator (free download), to align the images together and then stack them.
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Forum: Pentax K-5 & K-5 II
12-06-2015, 02:19 PM
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I am certainly not mikeSF - not nearly as talented, but in the two years (well two Milky Way seasons - Feb to Oct) I have been using the GPS unit, I have found (through trial and error - a lot of error), that time (shutter) is a critical parameter in all of this. Initially, I thought that 5 minutes (300 seconds) - go for the max, was the way to go. Optimize / maximize you exposure time to light (collect as much as possible). Then I started to see the stars trailing around the edges of the frame. Initially, I thought that it was coma, but the lens I was using - the FA 31Ltd and Sigma 18-35 are noted for their lack of coma. At the same time, I was also experimenting with ISO - and have settled on no higher than 1600. [note - changing two items, shutter time and ISO, just prolonged the agony of discovery.]
Anyway, back to time. I also considered just abandoning the GPS unit and just going for a single image containing both the landscape element and the sky (MW). The 500 rule (500/focal length) was being pushed a lot on the web. Another poster over on Reddit (RClark - who does some really magnificent MW shots and processing) made an off hand remark (working through the math on the pixel level) that to eliminate trailing a good approximation is the 200 rule (200/focal length). This got me thinking earlier this year, and I backed off of 5 minutes to 4 minutes and was able to capture a really nice shot, but I still was capturing some trailing - essentially "sensor shift is off-axis in respect to the earth axis", as you described it.So, now my rule of thumb is no more than 2 minutes (120 seconds) with the GPS unit, and when not using GPS tracking 10 seconds (the 200 rule with an 18mm lens). Unfortunately, earlier this year, I kept missing opportunities - with business travel back east, and then later in the year, the MW rotated a bit too high over the landscape elements. So, I missed it - there is always next year!
In terms of stitching, one evening after being kicked out of the state park (upon closing) - I went up to a slightly different area with a poorer view of the landscape and did some stitching - with just the body and lens - no GPS. Even using 20 seconds and doing about 50% overlap, I did not get any real trailing (center of the lens and center of the sensor). This was essentially a throwaway shot at the last minute, before heading home.So, this year has been filled with the frustration of discovery (the hard way), missed opportunities, and just plain making stupid mistakes. But I have learned quite a bit overall. Then, there is this unity discussion over on the Astrophotography group here on PF - that a number of you are also on....The main thrust is that there is an ISO level that is optimum in terms of capturing light photons - and anything over this ISO is just adding noise. So, for my K5IIs it appears to be either 800 or 1600. Reading the posts after recovering from surgery has not done a lot for my full understanding - I need to go back and re-read them. My question is now 800 or 1600?
So, my take away is that ...- in terms of both shutter speed and ISO - less is more. Somewhat counter intuitive.
- in terms of stitching, you can get away with more with a lot of overlapping - which essentially forces the use of both the center of the lens (and sensor). This I really did not expect until I really looked at that stitched image I was going to toss.
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Forum: Pentax K-5 & K-5 II
07-24-2015, 04:23 PM
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Take a look at LonelySpec. He has a scoring criteria for comparing various lenses...Ian has reduced it to a spreadsheet...It looks like the best lens available for Pentax is the Sigma 18-35/f1.8 One note. He is suggesting that a 20 second exposure is possible. I think that 10 seconds at 18mm is probably the tops. I have a bunch of 15 second exposures that show star trailing.
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Forum: Pentax K-5 & K-5 II
06-08-2015, 06:19 PM
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I have not upgraded yet, but have read about it. The LR6 thread here on the forum was lukewarm about the update. Also, I need a new printer, so was sort of waiting for another package deal....
Actually it's the same rockpile from slightly different perspectives. The rockpile is called Superstition Mountain, and it's located about a hour east of downtown Phoenix (which is off to the right of both images).The second image was taken about a mile behind and two miles to the left of the photographer (the idiot behind the camera) of the first image. The best view - the first image is from the picnic area of the Lost Dutchman State Park. The Dutchman about a 100 years ago came into town with a load of very rich gold ore from his mine up on the mountain, then died. Folks have been searching for it since - which is now illegal, because the US Forest Service is tired of going out and rescuing folks off the mountain, who have been out searching for it.
Anyway, this was a test on stitching the MW, plus I wanted to try out my new lens and needed some new raw shots to try out some ideas.
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Forum: Pentax K-5 & K-5 II
06-07-2015, 08:16 PM
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I went out last night - forgetting to check the battery in my GPS (which turned up to be somewhat gone - to the point that I could not get the unit to calibrate) so I winged it. I stitched using 15 second exposures (20 seconds started to trail) at ISO 4000 using the Sigma 18-35 at 18. The area closed before the Milky Way really was able to get up in the sky, so my son and I found another spot - not as good, and made the best of it.
The first image was about 9.45pm and the second was about an hour later. We left just as the moon was coming up. What I was really going after was the first image's landscape paired with the second image's sky and MW.
Post processing for what ever reason is difficult for me in astro. I'v got it down to a workflow, especially with stitching. Microsoft ICE I have found, does not lend its results to good post processing, so I have post processed one of the panels in LR, then copy pasted the workflow to the other panels, exported in TIFF, stitched and then brought the result into LR for just minor adjustments - cropping, etc. It's not the best, but so far this is the best that I have been able to go. I have to learn Mike's approach.
I also think that I need a darker location.
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Forum: Pentax K-5 & K-5 II
05-07-2015, 08:57 PM
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You might want to take a look at this series of e-books for Pentax DSLRs. The Pentax manuals describe each of the controls, but really does not tell you how and why they might be used. You can download the e-book immediately. Some of them have sample chapters available to read.
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Forum: Pentax K-5 & K-5 II
12-11-2014, 07:51 PM
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I think I have some answers for you. Its not your tripod nor the calibration of the GPS unit. It is your geographic location that are the root of your problems. Let me explain. The GPS satellite constellation flies in orbits that oscillates between 60 degrees North and 60 degrees South around the Earth. You are located near Helsinki Finland, if I am not mistaken, which is at 59 degrees North. So the GPS satellites fly up from the south, and essentially turn overhead and head back south again.
What does that mean to you. Well GPS is a distance triangulated system. The GPS receiver essentially gets information from 4 satellites (latitude, longitude, elevation and time) that is converted in to a distance from the known position of each satellite. If all the satellites are clustered in a single area in reference to your location, you are going to get poor fixes. You need a good spatial dispersion of the satellites for perfect fixes. A perfect spatial dispersion would be about 120 degrees apart around you with one overhead. However all of your birds are to the south of you - i.e., at best half the optimal coverage. You will get location fixes, but their quality will be somewhat wanting.
The O-GPS unit in order to do astro tracking, will want a good fix, with a good heading (direction in which the camera is pointed), with the smallest error possible, with good consistent uniform updates. You are probably getting good updates, with a random set of bad geometry (the satellites cluster more tightly from time to time, which will reduce the quality of the fix). This is probably leading to your needing to re-calibrate more often. Also, with a location and a larger than normal error component, coupled with a long focal length which is going to have a very narrow field to track in, you are going to be subject to a perfect storm of events, which leads to abbreviated tracking opportunities.
Here is a link discussing GPS location and navigation in the polar regions.
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Forum: Pentax K-5 & K-5 II
11-01-2014, 10:04 AM
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Morning Tomster,
You certainly will not be able to get 4.5 minutes of tracking with a 300mm. 60 seconds is about as long as you are really going to be able to get. The limit for the longer focal lengths is caused by the angle of view of the lens (the longer the focal length the shorter the tracking time), along with the amount of movement the sensor is allowed. If you want longer tracking times, you can take successive shots each at 60 seconds each and then stack them. That will help a bit with the accumulation of sensor noise and built up heat.
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Forum: Pentax K-5 & K-5 II
08-09-2014, 10:24 PM
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Good Evening - These are wonderful images and the detail is excellent. I am in the process of doing the same types of shots are you. I picked up a GPS unit a couple of months ago and have been combining it in with my shooting - more on that a bit later.
I see that you are using f2.8 lenses in each of the images. Plus one image appears to be 10 seconds while the other is 30 seconds. Night landscapes with the Milky Way essentially pushes you to the extremes across all fronts. Faster glass helps a lot - but Pentax is limited (Sigma has come out with their new 18-25/f1.8 which is suppose to be extraordinary). Higher ISO works really well, but the higher you go, the more noise you acquire during shooting. The whole crux of the situation is the shutter speed. The longer the shutter speed, you enhance your landscape but at the cost of star trails - so 30 seconds is about the maximum using wide angle lenses.
GPS - solves some of these problems but in doing so, exacerbates others. With the GPS attached and in the star tracking mode, you can get shutter speeds up to about 5 minutes (actually about 4.5 minutes - beyond this, you start to get star trails in the corners of the frame). This is wonderful - and is due to the sensor inversely tracking the movement of the stars. This (solution) is also the problem - since the camera's sensor is tracking the stars (to make them appear to be static), the static landscape elements - now appear to be moving. I have found that you can get about 40 seconds of shutter time before you really start to see the landscape elements degrade in sharpness (they take on some of the qualities of a painting). I have been adding to a link here that has been some what of a notebook in my trials and tribulations in this approach (unfortunately, it out to about 3 pages now [~40 posts], a real wall of words).One approach is to divide the problem in half. Take a long exposure with a very low ISO (ISO80) image at f8 for the landscape element. Then boost the ISO to 1600 or 3200, open the aperture wide open and then with the GPS unit in star tracking mode, run a 2 to 4 minute exposure for the stars. Then in post processing, put the two images together using something like Topaz remask with photoshop elements.
You asked about very high ISO levels. Out in the dark, I have used ISO 51200 to take images in pitch black darkness, to see how I am framed and what I am pointing at. These have turned out VERY well, a bit grainey - but very interesting. I have some of these in the link above. Which brings us back to the problem with the landscape element. With the high ISO and noise, you start to loose the detail and the qualities that you want in the landscape. Actually, I took a vertical stitch of the landscape and the Milky Way - but for the landscape, I forgot to lower the ISO. The whole process has become somewhat long and is prone to error. In working through this, one of the problem areas is that when you are in the GPS set of menu items, you are unable to modify the ISO value. So you wind up with a lot of button pushes via the rear panel menu system.
ISO 1600 is a good balance for the single frame shots of the type that you are taking. Increased sensitivity to record as much starlight as possible, while still remaining at a relatively low noise ISO range to record excellent detail in the landscape.
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Forum: Pentax K-5 & K-5 II
07-10-2014, 08:11 AM
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You would want a nice smooth pumping action - not one that pulses, since that too would cause a shutter to be induced through the fluid column.
Actually, I believe that there are some pumping systems that are based around the thermal fluid expansion within the heat sink, that moves the fluid column along. That should be the smoothest of all.
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Forum: Pentax K-5 & K-5 II
07-10-2014, 06:26 AM
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Is that a muffin fan attached to the heat sink? If that is the case, wouldn't this be a possible trade of thermal noise for mechanical vibration?
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