By Inside the window is a crosshair, move the window so that the crosshair lines up with the centre of a stars diffraction pattern, see left image below. This shows as a blue halo around bright stars and as a yellow and blue colour cast to the opposite edges of the Moon and planets. For this article, Edited by Kevin_A, 30 October 2020 - 11:08 AM. The stars at centre are round but not at the corners and they differ at each corner. The methods I have described here are easy to grasp and require little or no additional equipment, so I hope you can incorporate some of the ideas here into your routine. I will often run the focusing back-and-forth through the focal point a few times to help me get a feel for when the spike hits the exact centre point. The autoguiding is done through the ST-237 guide chip of SBIG ST2000XM. and this is a video of the 40 fits frames where you can see the problem with elongated stars in some frames. In both images the stars were pretty round. The above setup is loaded on Skywatcher HEQ5 mount. Optical, Tracking, and Diffraction. We also set additional cookies that help us improve your experience, perform analytics, and serve relevant ads. To access the Bahtinov Aid in APT, select the Tools tab on the right-hand side of the main display and select it from the list. I have a flattener/reducer that produces similar stars radiating away from the center, and my understanding was that indicated more spacing was necessary between the flattener and sensor. [PS - I've hidden the duplicated thread in the other section ]. Bianca Andreescu breezes past second French Open hurdle | The Star Credit: Astronomy: Roen Kelly Entering the second week of June, Venus approaches the Beehive Cluster, arriving within 1.1 of these stars on June 12 and standing 0.8 north of M44 on the 13th. Something like M44 or M67, depending on your FOV. Any comment on these M51 images will be welcomed. Does substituting electrons with muons change the atomic shell configuration? rev2023.6.2.43474. Which advice is correct? It may involve a bit more trial and error; however, with some patience and a deft touch, you can still easily achieve sharp star focus. I'm waiting on delivery of a zero-length t-adapter to test reduced spacing, but I can say with confidence that I don't know what is going on here. Distortion in star images that is caused by distortion Here is your typical chart for spacing but in some instances your flattener may not be able to correct enough for the amount of edge elongation vs the sensor size you are using and that I think comes down to the cost of equipment. The longer the total exposure time, the further around the sky the stars will create a light streak. The effect can be minimised in scopes that use two glass elements made from different types of glass (historically crown and flint glass). Coma is an aberration that occurs predominately in reflectors and manifests itself in the appearance of comet-shaped stars with their brightest portion pointing towards the centre of the field of view. The New Orleans Pelicans brought him in on Thursday. NOTE: Using another one or two! The additional piece of filter glass refracts the light at its front and rear surfaces pushing the focal point away from your objective by a small amount. Asking for help, clarification, or responding to other answers. Star Focusing using the Cameras Live View, Astrophotography Focusing Aid The Bahtinov Mask, live view focusing sequence outlined above, For outer tube diameters from 105mm-150mm, For outer tube diameters from 125mm-180mm, For outer tube diameters from 195mm-240mm, For outer tube diameters from 215mm-260mm, Astrophotography Focusing: How to get Sharp Stars, Widefield Astrophotography with the Samyang 135mm f/2 Lens, Get Ready for the 2020 Perseid Meteor Shower. They are generally worse out on the edges. HOWEVER, you must now Learn more about Stack Overflow the company, and our products. We hope these tips can help you get the most out of your setup and lead to some stunning images. ChrisIS Second A quick and simple tutorial on how to round off oblong stars. This proves that my mount has no mechanical problem. Many of the standard Bahtinov Masks available allow you to adjust the size by moving adjustable pins along a slot. I wouldn't get too concerned unless the ratio of bad subs to good was high. One final thing about DSLR lenses is there is often no focus lock. Third November 24, 2014 in Imaging - Deep Sky. Thanks in advance cell made of something other than glass will often cause it to warp as This ensures a secure fit around your telescope tube, simply find the size that fits your telescope. severe coma, stars appear distinctly comet-shaped. your optics are Images with beautiful detail in galaxies, great capture of faint outer regions of planetary nebulas and great capture of h-alpha in emission nebulas often simply get 'destroyed' by harsh, clipped, bloated and too prominent stars. At least that's my experience with reducer/flattener vs flattener only. Looks for small variations. Increasing the ISO will increase the camera sensors signal gain, making the image brighter, which is ideal for low light images. My limited experience is that a backfocus issues would not affect stars in the center of the image, nor would a bf issue produce a prominent flare as I see? Coma can be removed by the use of a coma corrector. Therefore if you havent already, I recommend using a bright star to help make things easier. Step 3 If you use a DSLR lens with an adjustable aperture, you will want to set this to at least f/4.0 or wider. rather than "Gaudeamus igitur, *dum iuvenes* sumus!"? Just something like a 10-second exposure, then really critically assess the stars in all corners/edges and the center. Now remove the Bahtinov mask and, if possible, lock your focuser. Basically I am scratching my head as to what the problem is and any help would be much appreciated. Stack Exchange network consists of 181 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. Also have a look atimage1.JPG, this is the PHD lab output after inserting the PHD logs, point the telescope to Zenith - target star Mizar. Step 8 Move your mount or tripod to find and centre a bright star. I'm not sure the Baader MPCC Mk III is capable of coma correction for full frame. There are two main types of primary mirrors used in Newtonian telescopes: lower cost spherical mirrors, which form part of a sphere and are supplied with low-budget telescopes, and the more popular parabolic mirrors, which are sculpted into the shape of a parabola. During the astrophotography session, the telescope was pointing to the East and there's was no problem noticed with PHD guiding. That, in turn, means that you should expect about a 2-3 pixel tangential smearing with exposures in the range you're working at. I think there were 15 in a plastic package. I have been looking into backspacing and from Kevin's charts it could be the camera is too close to the coma reducer, though Baader specify the correct distance and that is what I have used. Short focal length telescopes especially Newtonian reflectors exacerbate this problem, but field curvature is present in most telescopes to some extent. So, really what I am saying is first check collimation to rule it out, then when imaging, look at your target and make sure it is in perfect focus and not just round stars in the center because, stars can be out of focus slightly and still be round which will amplify the corner star issues further and then adjust back focus to get rid of any elongation and what is left is maybe some residual coma or a perfectly flat image. How to figure out what is wrong with your telescope when ), or, if the error's periodic(?) Goofy looking stars - they are not round. While not being a perfect fix for all problems you may find this removes any issues you are facing. Fourth When light from a star passes through a grating of regularly spaced lines, it creates a very pronounced diffraction spike perpendicular to the direction of the grating lines. A Guide To Untracked Astrophotography | Light Stalking Invented by Pavel Bahtinov as recently as 2005, the Bahtinov focusing mask consists of three gratings: one with horizontal slits, one with slits angled about +25from horizontal, and one with slits angled about -25from the horizontal. The very fine details of the nebula are softened and begin to be lost in this image; it now lacks the same punch that the in-focus image delivers. Fifth condition: Put your coma corrector back in the focuser A second pair of Ontario eyes might not help here: to me the stars are either very fine in the center or fine enough that if you can achieve the same roundness across the field, edge to edge, you will probably be very satisfied :-) Regardless, your path to happiness (in the short term ;-) is to get round stars near to the edges. Try popping your DSLR on and see if you still get the same star distortion (better to simplify when hunting for issues). You need to be a member in order to leave a comment. A good amount of detail is shown in the nebula, with lots of fine structure and contrast visible. November 30, 2022 There are times when you might want to consider doing astrophotography without tracking. Your scope could be centered exactly at the NCP, and if it were then Polaris would not be there. After that, I pointed the telescope low to the East and took two exposures of 15 and 25 minutes of Deneb. Your picture does not meet the optical because the issues are even across the field. Thank you for your analysis about my problem. Image via Chris Grant. power you are using - if it is fairly low, the distortion may be coming The technical storage or access that is used exclusively for statistical purposes. Centre the star as best you can. high-quality eyepiece, move the star This means aligning the right-ascension axis parallel to the Earth's axis of rotation. Such a star will show an enlarged Airy disc and close examination on either side of correct focus can reveal much about the quality of the optics by noting the formation of the concentric rings formed in the image. You will need to make sure that the focusing mask fits correctly over the end of your lens or telescope. One of the easiest ways to focus is to use the cameras live view feature, standard on many DSRL cameras. This one used PHD2. What is the 500 Rule? Its the telescope opticians job to minimise these aberrations as far as possible to produce a bright, high-fidelity view. If the image is still faint using these settings, you can increase the exposure length. Guide to Astrophotography + 8 PRO Night Sky Tips As you adjust the focus of your lens or telescope, the central diffraction spike will move from side to side between the two X shaped diffraction spikes. 2023 nPAE Southern Hemisphere Astrophotography competition, "Sun-geometer", a new type of solar finder, This is not recommended for shared computers, Back to DSLR, Mirrorless & General-Purpose Digital Camera DSO Imaging, Ha first light image with the Mewlon 250 / May 28, Networking: Windows VNC viewer to ubuntu mini-pc hotspot, AT90CFT First Light - NGC 7000, M97 and M13, June 3, 2023 WLHa drawing, Ha image AR3323. Note: the steps outlined below are available on all DSLR or fully manual cameras. astrophotography - Am I experiencing field distortion while astro astigmatism. I have never found this to be an issue with half-decent lenses, and unless you knock the focuser, it will remain in position. Heres a few tips and tricks that should help you round up your stars. CEO Update: Paving the road forward with AI and community at the center, Building a safer community: Announcing our new Code of Conduct, AI/ML Tool examples part 3 - Title-Drafting Assistant, We are graduating the updated button styling for vote arrows. Despite this, it demonstrates the importance of being in focus. We can all look up and appreciate an exceptionally bright moon or a surprisingly clear night. (Or perhaps I mistakenly interpreted the advice, but I don't think so.). 1. your head. Round Star Tips By Jacob on February 6th, 2018 Astrophotography can be particularly challenging at times, with so many variables and potential problems to consider. what do you mean by this? Astrophotography: Removing Purple Star Halos - Sky & Telescope The problem must be backlash in the motor gears of HEQ5 mount. APT will now display an overlay over the diffraction pattern and let you know how close you are to being in focus. My primary lense I use is Sigma 70-200mm F2.8 APO with Nikon D7100 and Sigma 2X TC. focuser, here are some other mechanical tips. This last test will provide the answer if mispolar alignment was the reason for getting elongated stars http://myastroimages.com/Polar_FinderScope_by_Jason_Dale/, Sensor centrality problem bugging me (is it even a problem? Any suggestion for troubleshooting the problem. By using this site, you agree to our Terms of Use. A lot of astrophotography setups can be very demanding. Equipment: Mount HEQ5 Pro Telescope - Orion 6" f/4 Camera - ASI178MM Baader Planetarium MPCC Coma Corrector Subs - 50 x 10 sec (PHD2 multistar Each method produces a range of aberrations, although some are common to both types. I have gotten rid of the coma by making the A 3-4 steps bigger ie from 5.6 --> 9.0. I have offset the mount even more than usual but the problem persists. NGC7822 in Cepheus, with increasing defocus from left to right, by Mike Soulby stellardiscovery.com. Our dedicated support team are always available to offer in-depth advice and if your looking for more tips and tricks weve got some for colourful stars here and guiding tips here. The technical storage or access that is used exclusively for anonymous statistical purposes. where a star will appear round even with no coma corrector being used) Please re-enable javascript to access full functionality. This way, you get to see exactly what your camera sensor sees, plus it is quick, simple, and doesnt require any additional equipment or software. The Flaming Star Nebula in Auriga has some fascinating structure, by Mike Soulby stellardiscovery.com. the cell shrinks by a different amount and pulls on the mirror, Several functions may not work. The Bahtinov mask will reduce the brightness of the star you are trying to focus on as it diffracts and spreads the light from a single point into three diffraction spikes. Barring miracles, can anything in principle ever establish the existence of the supernatural? Failure to get this very fine adjustment correctly set at the factory can result in the mirror being slightly deformed resulting in the optics being pinched. Focus is adjusted using a focusing ring around the lens housing.
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