[jdou]

I was recently trying to take some pictures of the stars at night using a Pentax 150-450mm lens using a B setting but am not satisfied with the results especially using an exposure of 40s at 400mm since I am getting a streaking effects on the pictures (IMGP 4018 and 4020). Photos were taking on a solid tripod and camera was calibrated before shooting. I've also noticed that I am getting a limit for the possible exposure being used. Pictures were taken using remote control switch. Can anyone indicate what am I doing wrong. I got a better result at 250mm (IMGP 4021). Any help would be appreciated.

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[CristiC]

The 500 rule: to determine the optimal length of exposure, you take 500 (the number) and divide it by the effective focal length of the lens (Exposure time = 500/[crop-factor × focal length]). Thus, the shorter the focal length the longer the shutter speed, and the better images you'll get. (explanation on the lonelyspec website here)

While the K1 Mk II camera has some functionality to shift the sensor, in order to "track" stars, it has some limits. Tele lenses reach those limits much faster than wide angle lenses. Better use a motorized star tracker between tripod and camera.

Another aspect: Declination
The closer the camera is pointed to the celestial equator, the more that star trailing will be apparent at the pixel level. Declination is the angular distance measurement of a point north or south of the celestial equator. (The point where we’re pointing our camera.) The farther from the celestial equator, the less star trailing that will be apparent at the pixel level. (source link here)

[biz-engineer]

I was recently trying to take some pictures of the stars at night using a Pentax 150-450mm lens using a B setting but am not satisfied with the results especially using an exposure of 40s at 400mm since I am getting a streaking effects on the pictures

The main problem is that the sensor can't get out of the camera to keep tracking stars with a 400mm lens and even if the sensor could get out of its location it may fall out of the image circle if the lens remains fixed. Solution is to move the sensor and the lens (and eventually move the camera as well) so that stars can be tracked with any focal length.

[interested_observer]

I do a fair amount of astro, but mainly wide-field (the Milky Way over large things - mountains, valleys, etc.). There are several aspects that you need to be aware of.

• The longer the lens' focal length, the narrower the field of view, so that with the earth's rotation the starfield will rotate out of the lens' field of view pretty rapidly. That's why the Pentax AstroTracer is a bit better with wide field rather than deep space objects. A traditional polar-aligned tracker is better than the astrotracer approach, since the polar aligned tracker actually moves the camera's body to track the stars across the sky. With the astrotracer approach, every few shots, you are going to need to re-position the pointing of the camera in order to keep whatever you were pointing at within your lens' field of view. The astrotracer approach is excellent for wide-field astro, since the exposures times are substantially longer with the wide angle lenses (wider field of view).

• Even with the polar aligned trackers, you are going to need to capture hours worth of light, so stacking of images (taking multiple images) is necessary. There are lots of stacking utilities available pretty much for free - see Sequator for example --- https://improvephotography.com/50102/stack-astrophotos-reduce-noise-sequator/

• With deep-space astro, post processing becomes extremely important, in terms of stacking individual images together, in order to increase the amount of light captured, and to reduce the noise acquired. Even after stacking, there is a lot of involved post processing to bring out the shadows and highlights of the nebula and star clusters.

• There is an astro group here on the forum that is pretty much focused on deep sky - they are EXTRAORDINARILY good. There is a lot of expertise in the group, in terms of capturing the frames, as well as both stacking and post-processing the resulting images --- Astrophotography - PentaxForums.com

[photoptimist]

Here are four of the leading causes of astrotracer problems with their characteristic appearance, causes, and their solutions:

1: Comet streak (bright dot with a straight faint tail): Cause: Astrotracer has hit the limit of sensor travel for that focal length and declination. Solution: shorter shutter times.

2. Nearly uniformly elongated or elliptical stars: Cause: Astrotracer is not perfectly calibrated or the magnetic environment of the camera and lens is different from the calibration conditions. Solution: better calibration and avoiding any changes in the amounts and locations of ferrous metals or magnets around the camera. Shorter shutter times can also help.

3. Squiggles, blebs, and commas: Cause: camera shake due to wind, tripod sag, springy ground (and heavy photographers stomping around). Solution: wind-free conditions, remote triggering, harder ground, stiffer tripods, and longer settling times for the equipment.

4. Corner trailing (only with wide-angle lenses): Cause: unavoidable tracking error due to discrepancies between the rectilinear geometry of the sensor and the spherical geometry of the celestial sphere. Solution: longer focal lengths (and tiling to be a wide FoV), shorter shutting times (and stacking to get the desired total integration time), or getting a true tracking mount.

P.S. The examples in this thread look like cause #2. Even a 1° calibration or measurement error in the camera's compass reading can create up to 10 pixels of elongation of the stars.

[jdou]

The 500 rule: to determine the optimal length of exposure, you take 500 (the number) and divide it by the effective focal length of the lens (Exposure time = 500/[crop-factor × focal length]). Thus, the shorter the focal length the longer the shutter speed, and the better images you'll get. (explanation on the lonelyspec website here)

While the K1 Mk II camera has some functionality to shift the sensor, in order to "track" stars, it has some limits. Tele lenses reach those limits much faster than wide angle lenses. Better use a motorized star tracker between tripod and camera.

Another aspect: Declination
The closer the camera is pointed to the celestial equator, the more that star trailing will be apparent at the pixel level. Declination is the angular distance measurement of a point north or south of the celestial equator. (The point where we’re pointing our camera.) The farther from the celestial equator, the less star trailing that will be apparent at the pixel level. (source link here)

Thanks for your feedback

---------- Post added 01-07-22 at 02:13 AM ----------

The main problem is that the sensor can't get out of the camera to keep tracking stars with a 400mm lens and even if the sensor could get out of its location it may fall out of the image circle if the lens remains fixed. Solution is to move the sensor and the lens (and eventually move the camera as well) so that stars can be tracked with any focal length.

Thanks for your feedback

---------- Post added 01-07-22 at 02:21 AM ----------

I do a fair amount of astro, but mainly wide-field (the Milky Way over large things - mountains, valleys, etc.). There are several aspects that you need to be aware of.

• The longer the lens' focal length, the narrower the field of view, so that with the earth's rotation the starfield will rotate out of the lens' field of view pretty rapidly. That's why the Pentax AstroTracer is a bit better with wide field rather than deep space objects. A traditional polar-aligned tracker is better than the astrotracer approach, since the polar aligned tracker actually moves the camera's body to track the stars across the sky. With the astrotracer approach, every few shots, you are going to need to re-position the pointing of the camera in order to keep whatever you were pointing at within your lens' field of view. The astrotracer approach is excellent for wide-field astro, since the exposures times are substantially longer with the wide angle lenses (wider field of view).

• Even with the polar aligned trackers, you are going to need to capture hours worth of light, so stacking of images (taking multiple images) is necessary. There are lots of stacking utilities available pretty much for free - see Sequator for example --- https://improvephotography.com/50102/stack-astrophotos-reduce-noise-sequator/

• With deep-space astro, post processing becomes extremely important, in terms of stacking individual images together, in order to increase the amount of light captured, and to reduce the noise acquired. Even after stacking, there is a lot of involved post processing to bring out the shadows and highlights of the nebula and star clusters.

• There is an astro group here on the forum that is pretty much focused on deep sky - they are EXTRAORDINARILY good. There is a lot of expertise in the group, in terms of capturing the frames, as well as both stacking and post-processing the resulting images --- Astrophotography - PentaxForums.com

Thanks for your feedback however I am still confused of how one can get pictures of comets or even bright stars using wide angle lens and not telephotos. The universe is enormous so one needs to focus on an area to find what he is looking for. So how can one do that witha shorter focal length?

---------- Post added 01-07-22 at 02:22 AM ----------

Here are four of the leading causes of astrotracer problems with their characteristic appearance, causes, and their solutions:

1: Comet streak (bright dot with a straight faint tail): Cause: Astrotracer has hit the limit of sensor travel for that focal length and declination. Solution: shorter shutter times.

2. Nearly uniformly elongated or elliptical stars: Cause: Astrotracer is not perfectly calibrated or the magnetic environment of the camera and lens is different from the calibration conditions. Solution: better calibration and avoiding any changes in the amounts and locations of ferrous metals or magnets around the camera. Shorter shutter times can also help.

3. Squiggles, blebs, and commas: Cause: camera shake due to wind, tripod sag, springy ground (and heavy photographers stomping around). Solution: wind-free conditions, remote triggering, harder ground, stiffer tripods, and longer settling times for the equipment.

4. Corner trailing (only with wide-angle lenses): Cause: unavoidable tracking error due to discrepancies between the rectilinear geometry of the sensor and the spherical geometry of the celestial sphere. Solution: longer focal lengths (and tiling to be a wide FoV), shorter shutting times (and stacking to get the desired total integration time), or getting a true tracking mount.

P.S. The examples in this thread look like cause #2. Even a 1° calibration or measurement error in the camera's compass reading can create up to 10 pixels of elongation of the stars.

Thanks for your feedback however I had calibrated the astrotracer a few hours before using the lens used for the photos

[interested_observer]

Thanks for your feedback however I am still confused of how one can get pictures of comets or even bright stars using a wide-angle lens and not telephotos. The universe is enormous so one needs to focus on an area to find what he is looking for. So how can one do that with a shorter focal length?

The answer is in two parts - stars and comets

Stars - For stars you are not photographing a single star, especially using a wide-angle lens. You are shooting a grouping of stars. Earth is in the Milky Way galaxy which is a spiral galaxy, we view it from the inside looking out. From Feb through November of each year the Milky Way can be seen in the night sky. We look at it edge on, so it appears as a band of stars across the sky. Astronomers estimate there are about 100 thousand million stars in the Milky Way alone. The core of the Milky Way is 25,000 light years away, and the Milky Way is about 100,000 light years across (edge to edge). So this band of stars across the sky are all of these points of light. That is what is being photographed. Using a wide angle lens provides a bit of context to the image.

Here is an image of mine - it's 3 stitched vertical frames - each shot at 15mm, side by side.

Comets - There is not a one size fit all answer that will cover all cases. Comets come in from the outer solar system, then loop around the sun and fly back out to where they came in an elliptical orbit. Yes, you are correct that a telephoto lens is needed to shoot a comet most of the time. However, for each comet's trajectory, there are two CPAs or 2 closest points of approach to earth - one as it flies in, and the other as it flys out after it goes around the Sun. That's the point where there is a potential for using a wide-angle lens, depending on the CPA distance. The smaller the CPA, or the closer the comet is to earth, the larger the comet will appear. Also, it depends on how much ice and dirt flys off the core of the comet which forms the comet's tail. The more debris it loses, the longer the tail and the better it can be photographed.

• Comet Photography Tips & Camera Settings | Nikon | Nikon

Here is a video by PhotoPills on how to shoot the Comet Leonard using a wide angle lens at time 7:19 into the video.

You Tube

You Tube

Hope that helps....

[jdou]

that's excellent! Thanks a million.

[Class A]

Thanks for your feedback however I had calibrated the astrotracer a few hours before using the lens used for the photos

It is definitely worth trying to calibrate the camera again, if results are not as expected.

Photoptimist has mentioned the very tight tolerances and measuring the orientation with an electronic compass is notoriously difficult.

Make sure to perform the calibration at the exact position you are going to use the camera.

The 500-rule is of no use here since the sensor is doing the movement.

Turn off your phone, it may disturb. Recalibrate, sometimes several times is needed, the exact calibration that is. Calibration has to be done everytime you move the camera position, i.e if you move the tripod. Also lessen the exposure time. If it says 3 minutes is possible, try 1.5 minutes. Also try shifting the part of the sky you are photographing.

One important thing I have found is that you have to make sure the LCD is in its home position when calibrating and taking the shoot. So compose and set focus with the LCD pulled out but when shooting, put it back in.

The following is from a Swedish instruction that I here google translated: (The instruction has images but those is not included here...)

Norrköping 2016-12-05 Rev C
Pentax AstroTracer
This letter applies to the Pentax AstroTracer, both the built-in and the separate O-GPS1.
Regarding O-GPS1, I recommend that you buy Lithium batteries or rechargeable
the Eneloop brand. I have tested a couple of rechargeable variants and since it is usually cold outside
when shooting stars, it is important that the batteries last a long time.
When you get to the place you intend to take photos of, I recommend that you show up
his tripod, aligns the camera and composes his image while turning on the GPS
with the button at the top right of the K-1's body. How the GPS indication is displayed applies to both
built-in and O-GPS1, set in the camera's menu system. Recommends that you ask
them on off or as weak as possible.
Turn on the Astrotracer in Camera Menu 3, see the picture above, or if you have it in
the context menu which I think is a good idea. Also set the camera in Bulb, B.
The green button works in Bulb as a switch between traditional Bulb and the new Bulb timer.
With the GPS and Astrotracer running, the function switches between AstroTracer instead
and Bulb.
On the K-1, I now recommend the following:
Make sure you have a Green satellite symbol, ie good reception. See the right image above.
Make sure the LCD is in its home position. This is to minimize the risk of external disturbances.
Make sure the mobile phone is some distance away from the camera. The mobile is a powerful radio transmitter
which in all probability disturbs the following. Sometimes I have not noticed any effect though
why risk the image being destroyed?
Now grab the camera stably and press the Exposure Compensation button
which in this mode turns on the exact calibration. Or start the calibration in the Camera menu
3, at the bottom.
Now turn the camera around its own axis as shown by the symbol on the LCD, see the picture
above, be sure to turn a little further than just 180 degrees. Turn right, left, up, down, around to
left, round to the right and then start again until the symbol says ok. At the end of the pdf there is one
link to a youtube clip that shows how to do.
NOTE !!! Determined movements, but make sure not to drop the camera on the ground.
Now put the camera back on the tripod, zoom in and focus with the LCD in it
angle you want.
The camera will now let you shoot for up to 5 minutes depending on the inclination, focal length and
direction.
Set the camera to the shutter speed you want. It can be easy to choose 5 minutes but dependent
on latitude and longitude, the camera may fail to follow for that long. I usually start with
half the time I am allowed to set.
Now fold the LCD back to its home position !!! The compass is affected by the angle and when the compass
affected, the AstroTracer tracks nothing further. We calibrated with the LCD in the home mode of just
that reason.
It is important that when you press, make sure to select either Live View and 2 seconds
delay with wire release or mirror folding and 2s. The small vibration in the beginning can
make all stars look like commas. Stable stand is A and O. I have a hook in
the middle pillar of my stand on which I hang my heavy backpack to make it more stable.
I taped the hook. So that the bag does not hang and throw, I also attach it to one
or more of the legs. If you change the location of the stand, you should / must do a new exact calibration.
Likewise, if the pictures get star tracks even though you set a very short shutter speed.
If you have noise reduction for long shutter speeds running, the camera will be locked underneath
the same time you just exposed the starry sky so a 5 minute exposure will be a full 10
minutes before you can take a new picture.
Up to 4-5 minutes, this noise reduction is not needed in my opinion. You get
experimenting but something I discovered is that 3 minutes a dark night alone far
from the city's light pollution can feel like an eternity ...
Do not forget to bring binoculars into the night. Then you have something to do while the camera
working to follow stars. It can also be good to have to find things in heaven.
When you get started and take pictures, you will notice that some lenses more than others
have star lines in the corners or even more while the stars in the middle are completely round. This is because
partly because the sensor moves while the camera / lens is stationary and when the optics are not clear
distortion, these phenomena occur. Another phenomenon is called coma.
The lightest lens to start with is the Fish-eye, closely followed by fixed wide angles. Telephoto is one
real challenge as it can be difficult to find among all the stars and planets. The firmament
moves rapidly through long focal lengths…
Below you will find a couple of links to a little more to read and to a video that shows how to
calibrates. Look around among the tabs on the page below as it contains very useful food.
GPS UNIT O-GPS1 | RICOH IMAGING
Calibration | GPS UNIT O-GPS1 | RICOH IMAGING

You Tube

You Tube

///Thomas