There are two common methods of defining and measuring hyperfocal distance, leading to values that differ only slightly. All original images copyright Brian Ventrudo. This critical object distance "h" is known as the Hyperfocal Distance. The confusion arises because amateur astronomers often mean different things when it comes to back focus. It weights only 230g and measures only 71mm from front to back, but this is an autofocus lens, not manual. Thanks,,it was so beautiful and amazing pictures I have seen. InternetSales@optcorp.com. I told him my concerns, and he agreed with most of my reasons why I shouldn't buy another 4". @Damien where are you seeing that the ASI1600 specifies 55mm backfocus? Then there's the wide field views. Astrophotography, also known as astronomical imaging, is the photography or imaging of astronomical objects, celestial events, or areas of the night sky.The first photograph of an astronomical object (the Moon) was taken in 1840, but it was not until the late 19th century that advances in technology allowed for detailed stellar photography.Besides being able to record Now if you go with a longer focal length lens, your exposure time will get shorter using the same math, so keep that in mind when photographing the Milky Way. The other hardware is very nice, too. Please may I ask what lens you recommend and a link to the lens if possible (UK based). Focus Merge is straightforward and easy to use. Bigger telescopes are most of the time not great with DSO imaging. The Gov is awsome compared to other scooes of the like. I am truly amazed by this scope. I have one of the original versions of this telescope when it sold for much more. Read more about Nasim here. / This criterion is the largest acceptable spot size diameter that an infinitesimal point is allowed to spread out to on the imaging medium (film, digital sensor, etc.). Such scopes as the ASKAR FRA series would be prime examples of this. I already had a 4" (Meade Infinity), would this really show anything different? The problem is that the lenses wont get to infinity; just a tad short. As mentioned above, 55mm is an industry standard for back focus length. Equatorial & Altazimuth Accessories & Adapters, Personal Planetariums / Electronic Sky Guides, Rechargeable Batteries And Power Supplies, Astronomics Used, Demo, Closeout, Spring Cleaning Page, Various Closeouts Meade, Kendrick, Bob's Knobs, JMI and others, Explore Scientific APO Triplet Carbon Fiber, Explore Scientific APO Triplet FCD100 Carbon Fiber, Explore Scientific APO Triplet FCD100 Series, Explore Scientific APO Triplets Essential Series, Sky-Watcher Truss Tube Collapsible Dobsonian, Astro-Tech AT102ED 4" f/7 ED Refractor OTA, Astro-Tech 1.25" 99% Reflectivity dielectric mirror diagonal, Astro-Tech Dedicated 0.8x reducer/field flattener for the Astro-Tech AT102ED refractor, Astro-Tech 2" 99% Reflectivity Dielectric Mirror Diagonal For Refractors, Astro-Tech Illuminated multiple reticle finder. Lets turn to that subject now. Aim the telescope at the moon and move the focuser out until the moons image comes to focus on the paper. There are many other benefits to shooting RAW see my RAW vs JPEG article for more details on why you should stay away from JPEG for night photography. When Affinity stops, you get a final image, with a single pixel layer. When paired with a Baader T-2 Prism 32mm clear-aperture diagonal, for example, the optical length increases to 148mm. The question I have , how can I add a non-clipping filter (CLS-CCD OR any other filter) to the system, without affecting the focus not the length. I have owned the AT80mm F7 ED for several years now and was so impressed that I had to try the 102 version glad I did, this is an awesome scope and for the price is amazing. Start Chat In some cases, apochromatic designs without anomalous dispersion glasses are possible. Of course, knowing the optical path length of your accessories and how it relates to the back focus of your telescope is only useful if you know the available back focus of your telescope. The Best Dedicated Astronomy Cameras for Beginners, Astronomik OIII 12nm CCD Filter - T-Threads, Pegasus Astro Dual Motor Focus Controller, 10 Micron 12kg (26.45lbs) Stainless Steel Counterweight- GM 2000. 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. His 0.41 should obviously be 0.40. If it is out and it is not too bright, you could use it to your advantage to illuminate foreground elements, or perhaps make it part of your final image. In every lens there is, corresponding to a given apertal ratio (that is, the ratio of the diameter of the stop to the focal length), a certain distance of a near object from it, between which and infinity all objects are in equally good focus. The 102 sits on a manual GEM and works wonderfully for easily pulling out for shorter viewing sessions, or for lower magnification / wide field viewing. In addition, the dovetail plate can be unbolted from the split rings to allow you to mount the rings directly on other equatorial mounts for example on the D-plate used on Losmandy mounts something that is difficult to do with the short mounting foot on competitive clamshell rings. The Moon was spectacular and this instrument even took 223X on the Moon without a shred of CA. We offer Meade telescopes, binoculars, spotting scopes and Meade telescope accessories. All you need to do then is click the purple fringing in the image, and Lightroom will automatically desaturate all the edges in the photo of that color. So, this usually isnt the main cause of purple fringing in your photos. So, if anything in your photo is very high in contrast, as well as being slightly in front of the focus point, purple fringes are going to appear with most lenses. The distinction between the two meanings is rarely made, since they have almost identical values. The whole scene was illuminated just by moonlight! For practical purposes, there is little difference between the first and second definitions. The Infinity 70mm Alt-azimuth telescope features a slow-motion control rod that allows for easy tracking of objects in the night sky. {\displaystyle D_{1}} But it all relates to making sure that the optical accessories you use focal reducers, field flatteners, and coma correctors are positioned in the optical path at a location where they work as their designers intended. What I would do first, is start out by determining the length of exposure. And tall ones at that. The finely-machined Astro-Tech AT102ED comes with both 2" and 1.25" eyepiece holders using non-marring brass compression rings that wont scratch your star diagonal or eyepiece barrels. 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). It strongly depends on the image, but Ive found that highlight recovery is one of the more common adjustments that can exaggerate purple fringing and make it more saturated. For example, the Baader MaxBright II binoviewers have a straight-through path length of 110mm. After stacking 150 images of two minutes exposures, the photo came out very flat with no vignetting or anything. Sean, the article was pretty old with some outdated info, so we put more information and added some extra pictures. The benefit of making this adjustment in Photoshop is that you can apply it to selective parts of the image, thanks to layer masking. {\displaystyle N} / If you see blurry stars when zoomed in to 100%, then you know that you need to rotate the focus ring a tad to get better focus. If the limit of confusion of half of the disc (i.e. Almost everything, from filter wheels to cameras to off-axis guiders, has an optical length associated with it that needs to be accounted for, since it takes up part of the limited budget of a telescopes overall back focus (see Figure 6). The dovetail plate also has a 1/4"-20 thread mounting hole that allows it to be installed on any suitable heavy-duty camera tripod that has a standard 1/4"-20 thread mounting bolt. Buy your Meade digital telescope products online from High Point Scientific! In an SCT, turning the focuser moves the primary mirror, which changes the focal ratio of the telescope changes slightly. False color is barely noticeable in focus. Newtonian reflectors have a more limited back focus compared to refractors and catadioptric scopes. Move the focus ring until you can clearly see the defined shape of the moon and simply turn off Live View you are done. Use the Dark Sky Finder website to find the best locations with minimal light pollution. = 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. " I have Meade infinity 80mm and I have problem Focusing with T-ring and T-adapter on my Canon 60D. Back focus, in its simplest definition, is the measurement between the last optical component, such as a corrector or reducer, of your telescope and the focal plane. I can even split binaries near the Dawes Limit. Click here to watch the video now. For a camera focused on this distance, While the back focus of a telescope is an important concept, most manufacturers of refractors and Newtonians do not publish this specification. I never use AF in astrophotography and I do use iOptrons Sky Guider Pro mount. Its interesting to know how fringing can be a symptom of improper focus when shooting the stars. is measured from a point that is one focal length in front of the front principal plane. I was skeptical then it came up for sale for 499. If I wanted to keep the length of the exposure the same and used a slower lens, say f/2.8 (two stops slower), I would have to increase my camera ISO from 1600 to 6400, which is a big difference. If you like our content, you can subscribe to our newsletter to receive weekly email updates using the link below: 1. Keep in mind that having the moon out while shooting the night sky is not particularly desirable, as it might spill too much light into the sky and make it difficult to photograph all the details of the Milky Way. The Meade Instruments Infinity 102mm AZ Refractor telescope has a four-inch aperture with a focal length of 600 mm and a focal ratio of f/5.9. A system with a shorter focal length bends the rays more sharply, bringing them to a focus in a Many Newts have a very limited back focus and may not have sufficient inward focuser travel to even accommodate the additional 55mm optical path of a DSLR. Yea it's there. I prefer If they get past infinity so I could focus back to infinity. h Finally, purple fringing can be exaggerated by digital processing. Based on his formulae, and on the notion that the aperture ratio should be kept fixed in comparisons across formats, Abney says: It can be shown that an enlargement from a small negative is better than a picture of the same size taken direct as regards sharpness of detail. = John Hodges discusses depth of field without formulas but with some of these relationships:[6]. Awesome article by the way. The scope now comes with a retractable dew shield. I'm always amazed by the crisp views of clusters & binaries. I got the scope out with good conditions and Jupiter high in the sky. For the best experience on our site, be sure to turn on Javascript in your browser. Best of all are the optics! Had the scope out twice so far, first time I imaged with it, the 2nd time I used it visually. This is my first refractor; until now I've only used a classic 8" SCT. {\displaystyle D_{2}=h/2} The optics are better than I expected and so is the focuser even though there is some focus shift. Piper (1901) calls this phenomenon "consecutive depths of field" and shows how to test the idea easily. I do see stars being elongated on one side and not the other when imaging at F7, but not when imaging at F10. Color correction is quite good but the scope will show faint violet on bright targets at high power (Vega for example). 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. And lastly, if nothing works out, you can try using the infinity mark on top of the lens and take sample shots to see if focus is properly acquired or not. Camera mode for star photos. Another way to get purple fringing is to use a lens with strong longitudinal chromatic aberrations (AKA green and purple color fringes in out-of-focus areas). (Unfortunately, as discussed earlier, low-level chromatic aberrations that are normally invisible can be the primary cause of purple fringing.). If you use any of the below telescopes, then make sure your back focus spacing is accurate. To make this easier, many astronomy camera manufacturers (such as ZWO) include the correct spacers to reach 55mm back focus. For clarity, half the aperture and circle of confusion are indicated.[3]. , this gives the equation for the first definition above. 800-483-6287 telescopes) and microscopy than in photography. Its also a problem when using binoviewers because light travels a much longer path than in a diagonal. I had high expectations coming from a well built William Optics triplet and I must say that this scope has met those expectations. He was not wrong. While many lenses particularly fast and poorly corrected designs will produce a small amount of purple fringing by default, post-processing can make it particularly noticeable. However, some manufacturers do specify a camera back focus distance, and many comments on astronomy forums refer to the back focus of a camera. Is it minimum length or depends on what we set as 20 or 25 or 30? Thank you. The 105mm back focus (using a 0.7 reducer) is the sweet spot and I can achieve that using the electrical focuser that I use by pushing the imaging equipment in and out until I have good focus. This scope is incredible, and at $599, its a steal! However, with some tricks, it is possible to get the P900 to focus and expose stars and planets correctly. There is a point, however, beyond which everything will be in pictorially good definition, but the longer the focus of the lens used, the further will the point beyond which everything is in sharp focus be removed from the camera. 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. The scope weighs 9.1 lbs with mounting rings attached. This back focus spacing guide is sized to be saved on your phone for easy reference. Now that I see many good reviews on this scope. I use it for DSO and occasionally for moon and planets. Apochromatic lenses are designed to bring three colors into focus in the same plane typically red (~0.620m), green (~0.530m), and blue (~0.465m). Thanks for the confirmation. $600 for the AT102ED is a crazy good price. For example, in astrophotography, its very common to get purple fringes around stars if youve focused a bit too far. I wanted to follow up my review. Right now I have about 40mm spacers attached to the end of the OTA, then the OAG, and finally my ASI2600MC-P and through plate-solving I am getting 2438mm focal length. I wasnt sure of adding or removing. If you do not know how to photograph the night sky and the Milky Way, this guide might help you in understanding the basics.

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