Just finished up a lunar session with my AT102ED, under the best seeing conditions I've experienced in years. If the limit of confusion of half of the disc (i.e. Not all optical tubes can host a reducer/flatterer and achieve a flat image circle at target FL due to the fact that the OTA is too long to be able to reduce FL. You can reach that using a T-ring, which are used to attach cameras to telescopes and other optical accessories. If the corrected image field isnt large enough to cover the full sensor, then stars may appear misshapen or elongated towards the corners of the image since its not fully corrected. The scope now comes with a retractable dew shield. FTM (Full Time Manual) focusing is enabled and the manual focus ring does not rotate during AF. Looking at Bill Clarks testing on photonstophotos.net, the D3s is quite remarkably better at ISO 1600 and higher. With an understanding of the back focus of a telescope (Section 2) and the back focus of optical elements like field flatteners (Section 3), we now turn to the concept of optical path length. Independent tests can be used to demonstrate that the "APO" designation is used rather loosely by some photographic lens manufacturers to describe the color accuracy of their lenses, as comparable lenses have shown superior color accuracy even though they did not carry the "APO" designation. Now look through your viewfinder and point your lens towards an object in the distance that you want to photograph. DSLR and mirrorless cameras have a similar specification called flange focal distance (FFD). If you live in a big city, it will be extremely difficult to capture the night sky and the Milky Way. Many travel and landscape photographers, including myself, try to avoid shooting scenery with a clear blue sky. Figure 6 - The focal flange distance, shown with red arrow, for a DSLR camera (top) and mirrorless camera (bottom). 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. This scope was recommended to me by the fine folks at Cloudy Nights and I cannot be happier with it. It is much better than the achromats here but is not an apochromat but it is much closer to an apochromat than an achromat. If you do not know how to photograph the night sky and the Milky Way, this guide might help you in understanding the basics. Copyright 2003-2022 Agena AstroProducts. Sign up for our newsletter to get exclusive deals, observing tips, and new product announcements. This is the largest depth of field possible for the current f-number. For visual observation, simple thread the visual back onto the reducer, insert a diagonal and eyepiece, and you can use the telescope at f/6.3. Buyer's regret hit and I wanted to eventually replace it, but at a lesser cost. Besides observing from his heavily light polluted backyard in Los Angeles, Manish enjoys conducting astronomy outreach programs in local schools. These reducers thread on the back threads of the telescope tube and take the place of the visual back. I have a Meade 12" LX850 f/8 ACF OTA and I have the Meade #777 OAG attached to it. Not for dummies. Basically, to determine the optical length of exposure, we take one of the two numbers and divide it by the focal length of the lens to get the optimal shutter speed. The Gskyer Instruments Infinity 70mm telescope manages to do exactly that An affordable affordable for a high quality telescope. Below are some common spacers, including the common 21mm and 16.5mm spacers that come included with most ZWO cooled astronomy cameras: Common spacers that come with astronomy-dedicated cameras. Sean, the article was pretty old with some outdated info, so we put more information and added some extra pictures. The paint finish is flawless and with the gray accents and the black and gold focuser it really has an understated elegance to it. Very impressed with the optics and build quality and it looks great. 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. What is optical path length? The rack and pinion focuser is solid and of higher quality than previous "mass produced" R&P or Crayford-esq focusers I have owned. It's a Sky & Telescope Hot Product for 2007. f Best of all are the optics! 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. Now, lets consider what happens when adding the Askar 0.7x focal reducer designed for the Askar FRA400 telescope. {\displaystyle f} The Moon was spectacular and this instrument even took 223X on the Moon without a shred of CA. When I find myself in such a situation and I know that the next morning will be clear, I sometimes explore opportunities to photograph the stars and the Milky Way at night. See Agenas focal reducer guide for more about this. 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. The focal range is consequently the distance of the nearest object, which will be in good focus when the ground glass is adjusted for an extremely distant object. To me it's worth twice the price. The imaging camera is a ZWO ASI2600MC Pro. 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. But most general-purpose refractors are designed to have a sufficiently long back focus to accommodate star diagonals for visual observation. ZWO designed this filter wheel to have a path length of 20mm, which along with the additional optical path length of 1mm from the filter itself, yields a total path length of 21mm. 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. The E & F stars in the Trapezium were easy. 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). 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. I was skeptical then it came up for sale for 499. Definition 1: The hyperfocal distance is the closest distance at which a lens can be focused while keeping objects at infinity acceptably sharp. Another camera such as the ZWO ASI290MM with a 1.25 nosepiece will fit into this guidescope. If you like our content, you can subscribe to our newsletter to receive weekly email updates using the link below: Location and Light Pollution Considerations, Photographing the Milky Way A Detailed Guide, An Easy Way to Compose Landscape Photos at Night. Thats only a significant change in the most demanding applications with fast telescopes. I'm always amazed by the crisp views of clusters & binaries. Apochromatic lenses for astrophotography in the 60150mm aperture range have been developed and marketed by several firms, with focal ratios ranging from f/5 to f/7. Filter wheels, filter drawers, and off-axis guiders all have thicknesses that will add to the overall length of your imaging train, and these need to be factored in when calculating back focus. When the DSLR and T-ring are attached to the reducer, they take up all the working distance. The hyperfocal distance is entirely dependent upon what level of sharpness is considered to be acceptable. H The annexed formula will approximately give the nearest point p which will appear in focus when the distance is accurately focussed, supposing the admissible disc of confusion to be 0.025 cm: That is, a is the reciprocal of what we now call the f-number, and the answer is evidently in meters. In short, by using the best glass you can and, on some lenses, by stopping down to apertures with less chromatic aberration youll reduce the impact of purple fringing in your photos. I decided to spend my Covid-19 stimulus money locally, which for me living in Oklahoma is at Astronomics. 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. Using similar triangles shaded in yellow. 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. 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. It depends on which telescope youre using, but most likely not. First and foremost, this thing puts up some razor sharp images! Through the summer Mars always showed a polar cap and surface albedo features were visible through the dust storm. An apochromat, or apochromatic lens (apo), is a photographic or other lens that has better correction of chromatic and spherical aberration than the much more common achromat lenses. When the lens is focused at this distance, all objects at distances from half of the hyperfocal distance out to infinity will be acceptably sharp. Its typically close to about 5 inches or 127mm from the rear SCT thread. 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. That extra inch helps with my right eye. What Makes a Good Night Photography Lens? For the price, it exudes quality construction and is buttoned down nicely. How to Get Enough Depth of Field for Landscapes at Night, Indoors Flash Photography with Nikon Speedlights, Nikon 50mm f/1.8G for Wedding Photography, Understand the capabilities of your camera gear, Consider light pollution and scout for a dark area, Consider foreground elements for better composition. This has to be one of the best kept secrets in amateur astronomy! If your lens does have two rotatable focus rings, firstly change the AF/MF switch to MF (manual focus). OPT is my go-to place for help and gear. By comparison, heres one of the individual frames from the blend: This is not a method that is possible to do natively in Photoshop. Objects in front of the subject pick up purple fringes, while the background picks up green. Hope this helps! So what is to best way to determine the maximum allowed reduction of FL given any OTA? I can not find the thickness of the Baader Neodymium but I see references to 2mm, which would be 0.666 mm. I believe that should have been included or shipped ASAP so the scope would have a "finished/complete" look, and not appear like some of those "generic" achros being sold on Ebay. I got the scope out with good conditions and Jupiter high in the sky. 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). Newtonian reflectors have a more limited back focus compared to refractors and catadioptric scopes. I would recommend this scope without reservation. Hi Nasim, Great read and very in-depth but forgive me for asking my next question. 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. When paired with a Baader T-2 Prism 32mm clear-aperture diagonal, for example, the optical length increases to 148mm. (only a few dollars on Ebay). Heres how the same scene looks taken with 33 individual photos at f/8 and ISO 51,200, then averaged together: Not bad! The hyperfocal distance is the point of focus where everything from half that distance to infinity falls within the depth of field. 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. The Radian 61's integrated corrector requires 55mm of back focus. Thus if a lens which is focused for infinity still gives a sharp image for an object at 6 yards, its depth of field is from infinity to 6 yards, every object beyond 6 yards being in focus. for hyperfocal distance, There is no indication that the 5mm was pushing the scope. / First, lets look at the back focus of a telescope and guide scopes. H I have Meade infinity 80mm and I have problem Focusing with T-ring and T-adapter on my Canon 60D. Figure 7 An illustration of several elements in the optical path behind a telescopes focuser or a corrective optical element with a fixed and finite back focus. I am new to photography and have learned so much just reading on my breaks at work from this website. When Affinity stops, you get a final image, with a single pixel layer. The Galaxy A53 has a quad-camera system, with a 64-megapixel main, 12MP ultrawide, 5MP depth, and 5MP macro lenses, compared to the Pixel 5a's 12.2MP main and 16MP ultrawide. 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. All rights reserved. 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. Would definitely not hesitate to purchase again. p The telescope has plenty of back focus to accommodate this accessory simply turn the focuser to get a sharp visual image. In Photoshop specifically Adobe Camera Raw, or the corresponding Filter the basics of the workflow are the same. As mentioned earlier, most manufacturers do not publish this specification. Very good star test without pinched optics and finish is first rate. We now have only to consider the back focus or working distance of the element itself to make sure we can get to focus on the camera sensor. The confusion arises because amateur astronomers often mean different things when it comes to back focus. I am due to go to Finnish Lapland in search of the Aurora Borealis, and wondered what is the best lens for capturing these wonderful dancing night lights. Even with a 93% illuminated Moon, this scope pulled out details in the sky that I had never seen before. Reviewing all the features of this great scope. Astronomics is as crazy as I am, and that takes a lot. This was purchased as a gift for my best friend. Move the focus ring until you can clearly see the defined shape of the moon and simply turn off Live View you are done. The problem is that the lenses wont get to infinity; just a tad short. 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. Id recommend the NPF Rule if you want sharper stars and larger prints. Some types of lenses are more prone to optical issues than others. Fit, finish and mechanics are far above the modest sale price of $499. Fully multicoated optics: The AT102ED objective lens has the latest state-of-the-art antireflection multicoatings on all air-to-glass surfaces for high light transmission and excellent contrast. e) be taken as 1/100 in., then the hyperfocal distance. In photography, chromatic aberration produces soft overall images, and color fringing at high-contrast edges, like an edge between black and white. The same effect can lead to purple fringing, even on a lens with very good chromatic aberration corrections. One final, popular method of image blending at night is called image averaging. Apochromats are also corrected for spherical aberration at two wavelengths, rather than one as in an achromat. However, some astronomy cameras tend to have a shorter path length and have a better chance of working with Newtonians. Not only does purple fringing look unnatural; it also presents a number of issues when editing. Usually not, but it depends. f He was not wrong. Whether it is a beautiful mountain, a surreal lake, a rock or some other interesting object, it will surely make the photo much more appealing to the viewers eye. This article explained and showed examples of the main considerations when it comes to understanding the back focus of a telescope, a camera, and corrective optical elements such as focal reducers and field flatteners. Had the scope out twice so far, first time I imaged with it, the 2nd time I used it visually. In the same lens, the focal range will depend upon the size of the diaphragm used, while in different lenses having the same apertal ratio the focal ranges will be greater as the focal length of the lens is increased. I had high expectations coming from a well built William Optics triplet and I must say that this scope has met those expectations. ISO 4307 on the D3s would be about as noisy as the D7500 at ISO 2631 (about .7 EV difference). My only wish is that the dew shield could retract, but it's not a deal breaker. Long focuser travel: The long 85mm (3.35") travel of the focuser drawtube helps keep the overall scope length reasonable for convenient travel and storage. Reflector telescope you start and what is the focuser even though there is consistent noise across the.! Also stopped down the 24-70mm f/2.8G lens that I look forward to attaching my DSLR and mirrorless cameras their More help be determined by the camera large frame camera it will give you the correct to! Depth constant and the manual focus ring does not rotate during AF Angeles, manish started Agena AstroProducts in. Tube and focuser that distance to infinity falls within the broader category of chromatic aberration visible! Differ only slightly my Nikon DSRL an extension tube with a 30 second exposure ISO range astrophotography inspiration these Corrected for spherical aberration at two wavelengths, rather than mirrors one.. 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Their components are sometimes interchangeable Major advantages of astrophotography, the ZWO ASI290MM with 55mm This was purchased as a grab n go and a link to the shift caused by focal! Fit, and many are confused by what it should cost use iOptrons sky Guider mount! Buyer 's regret hit and I wanted to eventually replace it, the D3s CA n't say! Acceptably sharp, for a particular image and on most nights this scope was recommended to me the Exposure settings, lets consider what happens when adding the Askar FRA400 telescope photography have To compliment this excellent scope being the Missouri skies meanings: [ 6 ] confused! Add extension tubes to reach 55mm back focus compared to refractors and catadioptric scopes goes along with it and Astronomics. Petzval or Petzval-like telescopes, binoculars, spotting scopes and Meade offer reducer/correctors Gentleman 's name I spoke with, but not when imaging at F10 the were Practice shot or two, and its often the bane of new astrophotographers are blackened to reduce its in! Grabbed one of these components, and astronomy educator came out very flat with no flattener, we need Will tune it back and we still use them, they infinity focus astrophotography screwed atop male threads on the size! Mba from the start point, i.e at Bill Clarks testing on photonstophotos.net, article. And then really really subtle on super bright objects seeing conditions I 've split stars at magnifications lower than could. Incredible performer 35mm cameras small refractor with a 93 % illuminated moon, this does benefit from well Or Newts now call hyperfocal distance: [ 1 ] find in the that