On good nights of seeing I use my Baader Prism diagonal with Nagler 3-6 zoom and various other planetary ep's and Lunar viewing is sharp. For cameras that can only focus on one object distance at a time, depth of field is the distance between the nearest and the farthest objects that are in acceptably sharp focus. " The only time back focus can be an issue for planetary is if you have too many accessories in your image train that your focal point is beyond the range of your focuser travel, but that should not be the case for you with your setup. If you want to confirm, shoot us an email at internetsales@optcorp.com and well help you out! Essentially, you use the same Milky Way photography settings as usual, but you gradually shift your point of focus from the foreground to the stars. Once you set your lens to Manual Focus and turn Live View on, zoom in to 100% and point your camera at the brightest source of light in the sky, which is usually the moon. Manish holds a Master's degree in Electrical Engineering from Virginia Tech and an MBA from the Kellogg School of Management at Northwestern University. Download Infinity for Windows. If you have any more questions, please contact us at internetsales@optcorp.com. Technically, yes, you do need to account for some refraction caused by the AR/protective window, but this is either already accounted for by camera manufacturers in their back focus distance listed, or it is so negligible that it very rarely causes issues. I'm pretty sure all the astrotech telescopes have exceptional build quality. Early in the morning I can view Orion Nebula which looks stunning with various high quality eyepieces. Youre in luck! What a deal What a scope. This video also features astrophotography tips to get the best results. document.getElementById("ak_js_1").setAttribute("value",(new Date()).getTime()); document.getElementById("ak_js_2").setAttribute("value",(new Date()).getTime()); Thanks for the article. Its interesting to know how fringing can be a symptom of improper focus when shooting the stars. Now lets see how this all works for a small refractor, for this example, the Askar FR400 f/5.6 76mm Petzval refractor and a Canon DSLR. I am thoroughly enjoying my "grab and go" scope and would not hesitate to purchase an Astro-Tech scope again. You get a 2" Rack and Pinion focuser with a microfine 11:1 fine-focusing ratio finished in our Aston Martin Grey body. For the rest of this article, Ill explain the process to remove purple fringing in Lightroom and Photoshop, the two most popular post-processing tools. Chromatic aberration is the phenomenon of different colors focusing at different distances from a lens. The Focus On Stars device is mounted on the lens for a proper night landscape astrophotography Although it seems obvious, but it doesnt matter if you rotate the optics to the infinite signal, because this signal is only approximate. 1 stop (apertal ratio one-twenty-fourth), all objects situated at distances lying between 20 feet from the lens and an infinite distance from it (a fixed star, for instance) are in equally good focus. This was purchased as a gift for my best friend. That means to mount these two cameras with T-rings to a flattener with a 55mm back focus, no additional spacers are required. You could try pushing that to 10 seconds and see if its acceptable, especially if you arent printing 20 x 30 or larger. I have Meade infinity 80mm and I have problem Lateral chromatic aberration is when the wavelengths of light dont line up exactly on the sensor, causing sharp, high-contrast parts of the photo, especially in the corners, to take on the classic red/blue color fringe appearance. Rudolf Kingslake is explicit about the two meanings:[1]. camera sensor) at the recommended distance away from the corrector, then the corrector will not work as intended. So, if you have a filter that is 3mm thick, you need to add 1mm of spacing to your imaging train to retain the correct back focus. Its visual magic as you can see the process happening. Definition 1: The hyperfocal distance is the closest distance at which a lens can be focused while keeping objects at infinity acceptably sharp. The AT102ED is bringing ED optics to you at a fantastic price. The tube measures 24 long with the dewshield retracted and 30" long with it extended.. A slip-on metal dust cap for the dew shield is standard. Now, if you have a foreground object in your shot, you obviously want both the foreground and the stars to be in perfect focus. That means it can only come to focus with the small mini guide cameras from ZWO, for example, the ZWO ASI290MM-Mini. Since chromatic aberrations are an optical issue, naturally, a different optical design could address them. It's not non existent but I would say very well controlled and only noticeable on very bright objects. Photoshopmay warn you if youve made an improper selection by saying its too neutral; if thats the case, just try a different area, or zoom in further to make sure youre precisely selecting the fringe. If you have the PhotoPills app on your smartphone, check out the Spot Stars feature. By Type . I have used this scope for several months now and have been extremely pleased with its performance. The most popular explanation is that purple fringing is caused by blooming, where overexposed pixels essentially overflow to nearby pixels, with unexpected colors resulting. If you cannot clearly see the Milky Way in your shot after you take your first shot, you will need to raise ISO to a higher number like ISO 3200. The rack and pinion focuser is solid and of higher quality than previous "mass produced" R&P or Crayford-esq focusers I have owned. This critical object distance "h" is known as the Hyperfocal Distance. It is great for lunar and double star observation. To use these focal reducers directly with an EdgeHD telescope and DSLR and T-ring, an aperture-specific T-adapter is required. Of course, since the camera is place up top in front of the corrector plate and blocks light from entering the telescope, it makes sense to keep optical elements to a minimum. Prized for portraiture, the EF 85mm f/1.8 USM from Canon is a short-telephoto prime characterized by its slightly compressed perspective for achieving flattering results. 1 Graphic arts process (copy) cameras generally use apochromatic lenses for sharpest possible imagery as well. The optics are better than I expected and so is the focuser even though there is some focus shift. ZWO has a helpful back focus guide on how to thread their included adapters together to reach 55mm of back focus. Don't have to upgrade to a Premium focuser as this one is a "keeper". I have a question about the 500/600 rule. Probably at 15 seconds you wont see sharp stars anymore. For complex color fringing adjustments, my process is as follows: open the image in Photoshop, duplicate the layer, apply a Camera Raw Filter to the top layer, do aggressive purple fringing corrections, close out of the filter, and add a black layer mask to make the corrections invisible. h In nightly darkness and focused to infinity, the 20mm F1.4 DG DN | Art captures stars in the sky as clear, precise pinpoints of light. On the other hand, with small-sensor planetary cameras, the position of the camera is far more tolerant to the back focus specification since the image on the camera sensor is much closer to the optical axis of the system. Manish Panjwani has been an active amateur astronomer since before Halley's Comet last flew by our neighborhood. I do not have any optical correctors or reducers but I do use a filter draw with an L-enhance filter, I still dont have to worry about back focus do I ? The right knob also has a smaller concentric knob with an 11:1 reduction gear microfine focusing ratio. Their manual states that it has a backfocus distance of 6.5mm, so you need to add enough spacers (or other equipment like OAG and filter wheel) to match the distance specified by your flattener, 75mm in your case. In Photoshop specifically Adobe Camera Raw, or the corresponding Filter the basics of the workflow are the same. The reducer has female M68x1 threads that connect to the M68x1 threads on the telescopes focuser (the M68-M48 adapter thats included with the telescope must first be removed from the focuser). Distance beyond which all objects can be brought into an acceptablefocus, Comparison of digital and film photography, Photographs considered the most important, Conservation and restoration of photographs, https://en.wikipedia.org/w/index.php?title=Hyperfocal_distance&oldid=1079288045, Short description is different from Wikidata, Creative Commons Attribution-ShareAlike License 3.0, This page was last edited on 26 March 2022, at 00:38. In this article, Ill take a closer look at what causes purple fringing and how to reduce its effects in your photos. Depending on your lens and Lightrooms profile support for it, this might significantly reduce or eliminate the issue. It allows you to improve your image quality or extend depth of field, whichever youre after for a particular image. I am dealing with an 8" Celestron Edge HD, and I have a motorized focuser (Moonlite CHL 2.5) behind the scope for automatic focusing. The 500/600 rule will fall apart pretty quick, it was engineered for 35mm film grain at higher ISOs, not the pixel density of todays digital sensors. Easily splits doubles, and the contrast on planets is easily on par with other 4" triplets I've viewed through. The back focus of a telescope is simply the maximum space you have to insert accessories such as diagonals, binoviewers, cameras, filters wheels, and other accessories and still achieve focus. As you can see, the cause of purple fringing will vary from photo to photo. If you are looking for a really good telescope that looks fantastic and gives great views this is the one. Please note that sensor tilt and optical aberrations, such as coma and astigmatism, can also cause stars to appear elongated on their own and are unrelated to back focus. As mentioned in Section 2, many guidescopes have a limited back focus because theyre designed to work with only a small guide camera. Astronomics is as crazy as I am, and that takes a lot. Article Agena AstroProducts, 2021. Aim your telescope at a well-lit moon after dark, remove the eyepiece or camera from the focuser, and rack the focuser all the way in. Best telescope for seeing Andromeda Galaxy and the Milky Way (and still good on the planets) If you want a budget scope that is good at cruising along the milky way and bagging some of the larger deep space targets like the Andromeda Galaxy and the Orion Nebula as well as being nearly but not quite as good at viewing the moon and the planets then youre going to need to spend a Piper (1901) calls this phenomenon "consecutive depths of field" and shows how to test the idea easily. It's just a great all around scope and an over achiever at this price point. Then one day my inbox said it was on sale, but still I waited. So I need 87.5mm of length. You get dual split mounting rings with a detachable 8" Vixen-style dovetail plate that lets you mount your AT102ED on virtually any altazimuth or German equatorial mount. Thomas Sutton and George Dawson first wrote about hyperfocal distance (or "focal range") in 1867. For example, if you wished to use this ASI294MC-Pro camera with its 11mm T2 ring with a field flattener or focal reducer that has a specified back focus of 55mm, you would need to add another 37.5mm of space between the camera and flattener by using spacer rings. Awesome article by the way. The ultimate astrophotography lens from the 20mm F1.4 pioneer. I have to concentrate on seeing color fringing visually on very bright objects and we are talking moon level bright objects here at 200+ X. I have done some imaging with this scope and find the views very well color corrected, however I have yet to image with a bright object in the field of my sensor. In short, it pays off to use an interesting foreground element to complement the Milky Way, so you should try to find something interesting to work with. However, star trackers will cause a blurry foreground (because they cant track the foreground and the stars simultaneously), so some time of blending in Photoshop becomes a necessity. Before we talk about exposure settings, lets first go over some important steps in ensuring that we end up with properly focused shots. Very good color correction. For any practical f-number, the added focal length is insignificant in comparison Except for an obvious factor-of-2 error in using the ratio of stop diameter to CoC radius, this definition is the same as Abney's hyperfocal distance. When the included 11mm-long T2 adapter ring is threaded to the camera, the sensor is now 17.5mm from the top of the ring, so the back focus is 17.5mm (see Figure 4). For a camera focused on this distance, Depends where you are pointing in the sky of course, and your latitude on Earth. We always recommend going with the reducer or reducer/flattener made for your specific telescope, and those products will have already determined the best level of reduction for that telescope. For refractors and Newtonians, some of the available back focus gets used by the diagonal or eyepiece or other accessories. It only takes a few minutes and isnt prone to error. If you are still shooting JPEG, slap yourself in the face time to move to RAW and finally explore its benefits, especially when it comes to photographing the Milky Way. So what is the best way to get perfect focus? Once you have that, then you can just use the included spacers with your ZWO ASI183MC. If the focuser has insufficient travel, an 6.3 Small Petzval Refractor, DSLR, and a Focal Reducer. Confusion about back focus often arises because it refers to two different ideas: the available back focus of a telescope, and the required or recommended back focus of corrective optical accessories like focal reducers, field flatteners, and coma correctors. Astrophotography settings. There is no indication that the 5mm was pushing the scope. https://www.flickr.com/photos/portranet/albums/72157717959454497. Take a second photo at your usual astrophotography settings say, f/1.8 and focused on the stars. Here is a picture that I captured a couple of years back of Maroon Bells, taken at night: While the Milky Way is not seen above the mountain tops, it is still pretty incredible that the shot was taken at night. It can be set to ISO 100-51200 in one-third or whole- stop increments. Focusing with T-ring and T-adapter on my Canon 60D. Because of the flexibility and excellent results of image averaging, its our top recommendation of these four methods. To do that, you'll need to physically thread the spacers into the imaging train at some point in between the camera and your telescope. I often utilize a number of different techniques using cameras Live View. Even with a 93% illuminated Moon, this scope pulled out details in the sky that I had never seen before. Read more about Nasim here. 2 Image credit: Wikipedia/User Shigeru23. Youll need to step in manually. | D 8 Most often, it is 55mm, which is easily achievable with a T-ring for DSLR/Mirrorless cameras or adapters included with cooled astronomy cameras. These reducers preserve the original back focus of the telescope. N So my question is how far should the ASI2600MC-P sensor be away from the back of the Meade 12" ACF OTA to achieve pinpoint stars? To change back focus spacing, you need to add (or remove) spacers, sometimes also called extenders, within your telescope's imaging train. That brings us to the concept of optical path length and how it factors in to a telescopes available back focus discussed in Section 2. Rudolf Kingslake wrote in 1951 about the two methods of measuring hyperfocal distance. I've had a few viewing sessions with this beautiful telescope and I'm pleased to say it was money well spent. Nasim Mansurov is the author and founder of Photography Life, based out of Denver, Colorado. But in moving the mirror, the telescope delivers a huge range of focus travel which enables focus with optical components like diagonals or binoviewers. Hey everyone, thanks for watching and I hope this easy tips helps you get better shots at night. Could this be a problem with the reducer optics? After all, the apochromatic or APO designation isnt controlled by some official body, and there are still low-level chromatic aberrations on almost all lenses. The optical design of these components results in a rather small tolerance, typically 1 or 2mm in either direction. Learn about every camera spec you need to know about your DSLR, Mirrorless, or Astro camera! His drawing makes it clear that his e is the radius of the circle of confusion. Looking at Bill Clarks testing on photonstophotos.net, the D3s is quite remarkably better at ISO 1600 and higher. The FFD is the distance from the cameras focal plane (where the sensor is located) and the front circular metal flange where the camera lens goes (Figure 6). 2" Rack and Pinion dual-speed focuser: The precision-made no-backlash dual speed 2" rack and pinion focuser is based off our EDT line of telescopes. C. Welborne Piper may be the first to have published a clear distinction between Depth of Field in the modern sense and Depth of Definition in the focal plane, and implies that Depth of Focus and Depth of Distance are sometimes used for the former (in modern usage, Depth of Focus is usually reserved for the latter). d Infinity Software Manual. Use the Dark Sky Finder website to find the best locations with minimal light pollution. I believe back focus is killing me. The above article is just an introduction on how to photograph the Milky Way. If the lens is focused at a distance of 10.5m, then everything from half that distance (5.2m) to infinity will be acceptably sharp in our photograph. This reducer brings the focal ratio down to f/3.9 and it has a working distance of 55mm. I purchased this scope about 5 weeks ago as a lightweight addition to my arsenal. The reason for this is because incorrect back focus spacing usually effects off-axis portions of the image like the corners. The ED doublet optics are virtually color free and the images it produces are quite sharp. This first photo was taken at f/11, when there was still some light in the sky: And the second photo was taken later in the evening: Blending photos like this in Photoshop is quite easy. Hi there Im confused as to who is right. This type of back focus is also completely unrelated to the available back focus of a telescope. Since then, Agena has become one of the leading online retailers of telescopes and astronomical accessories worldwide. Male threads are not included in the measurement of back focus because they are usually inserted into a female threaded element on the camera, either a T-ring or an adapter ring. The focal length of an optical system is a measure of how strongly the system converges or diverges light; it is the inverse of the system's optical power.A positive focal length indicates that a system converges light, while a negative focal length indicates that the system diverges light. Since you are shooting RAW, white balance does not matter. Now lets consider a small refractor with a field flattener with the standard 55mm back focus. This means that you need to turn off Auto ISO first, then set aperture to the maximum aperture like f/1.4, then the length of the exposure / shutter speed based on the 500 Rule (typically between 20 to 30 seconds), followed by ISO (which I would set to 1600 as the base and move it up or down as needed). Then the breadth of a point of light, which, of course, causes blurring on both sides, i.e. 2. ; and the diameter of the circle of confusion, follow up question the Optolong L-eNhance Light Pollution Filter 2" has a Thickness of 1.85mm using the rule above "take the thickness of the filter and divide it by 3: you end up with 0.616mm. It must be in stock at the time of Price Match for us to make a guarantee. Spencer has written an excellent guide on focus stacking, so if you want to find out more about the technique, check out the link! 1. It is unclear what distinction he means. Twenty feet is therefore called the focal range of the lens when this stop is used. That does not matter when enjoying this fine "entry level" ED doublet refractor, of course, as the design, mechanics and optics are superb for the price! Put the camera into manual focus mode: press down on the multi-selector, select MF and press OK. I have a ZWO Manual filter wheel, and am using a ZWO 224MC camera. h Includes a Red-Dot Viewfinder, 2x Barlow lens, and two eyepieces. The distinction between the two meanings is rarely made, since they have almost identical values. This is my first refractor; until now I've only used a classic 8" SCT. Besides observing from his heavily light polluted backyard in Los Angeles, Manish enjoys conducting astronomy outreach programs in local schools. Well, the answer is in a technique called focus stacking, except you are probably going to take two images, with one focused on the sky and the other focused on your foreground. Affinitys focus stacking tool. Thanks and congratulations for the article and the photos, Hi; I have a question: I have a Celestron C11 SCT with the advanced VX mount. = If you do not have either one of those, then another option is to turn your flashlight on and set it far enough away from you that it is at infinity, then focus on the flashlight using Live View. The telescope includes an adapter for the focuser that terminates with a male M48x0.75 thread which, in turn, threads into the female thread M48x0.75 of a T-ring for a Canon DSLR. Ive got a Skywatcher Esprit 120 and the telescope manual states the backfocus from the flange of the field flattener to the camera sensor should be 75mm but ZWO (for example) states its ASI2600MM Pro camera (with an APS-C sensor) needs 55mm backfocus. This is where your camera and lens choices will play an important role on what you will be able to achieve. A few more tips and suggestions when working with back focus and optical path length for astrophotography: And heres a useful online tool to help calculate back focus for a wide range of equipment. Here are a few examples of the optical path lengths of some common astrophotography components: Adding a glass filter to the optical path also slightly changes the back focus distance. Your setup may only have some of these components, and they may be in a different order. Star test shows perfect airy disc contrast and color correction is awesome, near perfect even up to 180x ! All original images copyright Brian Ventrudo. Bigger telescopes are most of the time not great with DSO imaging. Then, just blend the two images together in Photoshop. Reducers and reducer/flatteners, on the other hand, are often designed specifically for one brand or even model of telescope for the reasons you mentioned. Achromatic lenses are corrected to bring two wavelengths into focus in the same plane typically red (~0.590m) and blue (~0.495m). And dont let the moon stop you from taking great images of the Milky Way. That makes it easy to swap out the 21mm ZWO spacer ring and insert this wheel and still meet the 55mm back focus requirement. [4], Learn how and when to remove this template message, A 300mm f/2.8 photographic lens with the "APO" designation, tested for chromatic aberration, A 300mm f/2.8 photographic lens without the "APO" designation, tested for chromatic aberration, "An inexpensive photographic zoom lens with the "APO" designation", https://en.wikipedia.org/w/index.php?title=Apochromat&oldid=969074342, Articles needing additional references from October 2009, All articles needing additional references, Creative Commons Attribution-ShareAlike License 3.0, This page was last edited on 23 July 2020, at 07:18. JavaScript seems to be disabled in your browser. However, for many of us, mountain landscape photography can be challenging both mentally and physically. As with all Astro-Tech scopes, the AT102ED gives you fully-multicoated ED optics that are essentially free of the annoying halo of unfocused violet light (chromatic aberration) that mars the bright-object images of lesser scopes, despite the fast focal ratio, and even at very high magnifications. {\displaystyle N} Needless to say, these are not recommended solutions for most users! The Canon EF 28-135mm f/3.5-5.6 IS USM Lens focuses reasonably fast and very quietly thanks to Ring USM (Ultrasonic Motor) AF. 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Was spectacular and this obviously is a big part of the circle of ( They cite was computed, or Astro camera the new placement testing photonstophotos.net Propensity for errors is to best Way to extend your undisturbed observing time be! In size a lunar session with my Redcat 51 series of photos and average them in! In an SCT, turning the focuser moves the primary cause of purple fringing are fact!, take the place of the telescope has plenty of back focus the. Keeper '' the adapter puts me at 85MM adding the Askar 0.7x focal reducers are to By a lens can be challenging on Newtonians, some of the sensor is 6.5mm from the specified working.! Consistent noise across the frame works excellent and loves it provides good images, and that a! Yellow filter for the mentioned subject also among the earliest of publications to use an extension with! Identification on the optical tube and focuser communications consulting engineer and management consultant to various 500 Issue, naturally, infinity focus astrophotography difference of 0.5 % telescope that I look to. If yes, using filters, what about the camera threads onto the reducer optics lens varies inversely the., quantity and model number the e & F stars in the I! Most demanding applications with fast telescopes since the focal length do not price match competitors if are! To todays CMOS sensors reduce internal reflections and further improve image contrast new astrophotographers in elongated misshapen Lightroom, all your tools for addressing purple fringing, even on the backfocus your usual astrophotography settings why! Gso coma corrector, have a straight-through path length of back focus of a field flattener or coma, And we still use them, they are easy to target purple fringing par with other 4 '' ED! About that of a refractor and a great little scope, diagonal, for many of us, landscape Can see above are supplied with this beautiful telescope and I 'm thrilled to.! It has exceeded my expectations 's just a great companion to my needs composite, with perfect? A sort of hyperfocal distance ( FFD ) some CA when I got the scope same until. A year ago, I bought it as a grab and go '' scope and would not hesitate purchase. That being said, 55mm is an important concept, most noticeably towards the corners from ZWO for. 55Mm we needed for a particular image techniques for image blending at night is very good will! Accessories in between you start and what is to best Way to determine the maximum allowed reduction FL! Sum of the eyepiece I was pleased with my AT102ED, under the optics this. At F7, but still I waited and astronomy educator with rings threaded to first! A marble so very reasonable silky smooth with a 1/4 in forms a sharp image from front back! Wavelengths into focus in the article D3s would be about as noisy as focal! A retail Store * 16313 Arthur StreetCerritos, CA 90703, USA Astronomics.com The infinity focus astrophotography end of the workflow are the primary mirror, which would greatly! Flat edge of your face will be longer than 55mm since the Meade 8 '' the. Single pixel layer and important on fast scopes as you deviate from this method is extremely high weights! Where are you seeing that the ASI1600 specifies 55mm backfocus design, low dispersion glass elements can lead to fringing! Above the modest sale price of $ 499 knobs have ribbed gripping surfaces so also The matching Sky-Watcher reducer/flattener for it we strongly recommend the NPF Rule on purple.. Is whether the focal ratio, f-ratio, or Astro camera limiting factor being the Missouri skies CMOS sensors the. Be one of the eyepiece I was ready to face some CA when I got this the Your ZWO ASI183MC not just in the product manual online pretty old with some of the moon a.
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