drjolo

Owl refractor is with me since February this year, so I decided to share some images that I captured using that glass and APS-C format cameras. I use 0.8x adjustable flattener from TS https://www.teleskop-express.de/shop/product_info.php/info/p12209_TS-Optics-REFRACTOR-0-8x-corrector-for-refractors-up-to-102-mm-aperture---ADJUSTABLE.html and CEM26 mount. All data was captured under my suburban sky with sky brightness level usually around 19-19.5 mag/arcsec2. First light went to M45 - it is 150x1 minute captured with QHY247C color camera. Also with the same color camera another frame around Tadpoles nebula. 7 hours of total exposures And Christmas Tree cluster area - 5 hours of total exposure Then I switched to mono QHY268M and the first target was two globular clusters: M53 and NGC5053 - 240 minutes of LRGB frames with 2 minutes subs: Pinwheel galaxy - 340 minutes with QHY268M, LRGB filters and 2 minutes subs IC1805 nebula - Ha only, and RGBHO composite. 10h Ha, 6h Oiii, 2h RGB. Comparison of Melotte 15 fragment captured with 90mm refractor and 254mm SCT (the same location - my backyard): Distant objects around M82 - enlarged and 1:1 cropped fragment - 310 minutes of luminance with Owl and QHY268M camera: IC405 and 410 area - RGBHO composite with QHY268M camera. About 10 hours of total exposure with RGB and HO filters. And Sun captured with QHY268M camera, 2x barlow and Baader SC filter (plus mylar filter of course). I forgot about IR cut filter It improves SC images, because SC passes some IR light as well. I am quite happy with the images that refractor creates. The plan was to have a setup with APS-C format that operates around 450mm FL, because I have never had that combination. I imaged so far with either 135mm lens, or 800-1700mm telescopes. I expect now many 3x2 degrees frames to land into my disk

All the things vlaiv described plus monitor the histogram, so the image is not saturated in highlights - there is no way to recover details in saturated areas. What scope do you plan to use?

First solar light of my new glass - Tecnosky 90/540 Owl. I put it on the AZ4 mount, attached barlow x2 and Sony A7II and captured 15 frames. 10 of them were processed with PIPP and AutoStakkert. Seeing was far from good.

What is that grey plate made of? Steel? I am thinking about two additional metal rings on both focuser sides. Or another option is to made a 15-20cm wide collar with carbon mate and resin around the tube.

I decided to upgrade focuser in my GSO200/1000, because there was significant tilt of focuser tube under the load. When I put laser into the focuser and simulated mono camera with filter wheel weight attached to the focuser drawtube, it turned out that laser dot at the main mirror moves about 3mm around. I assume it is too much to keep collimation even for f/5 mirror. I ordered Baader Diamond Steeltrack, but I will also need to stiffen the steel tube around the focuser, because it is a bit floppy.

It actually depends heavily on the target type you capture. Since you are doing mosaic I assume that may be emission or dark nebulae, no galaxy or planetary nebulae. Then if you do only RGB frames with mono camera and filters, there is not much upgrade in terms of amount of data captured compared to OSC camera. There may be some resolution benefit. But if you go for LRGB, then there will be more amount of data captured, and the ratio of L exposures to RGB exposures will determine this gain. Mono camera with L filter only collects about 2-3 times more data than its OSC version (depends on actual sensor model and the spectrum of the target). But you need also color data, so for real life example it will be less of course. And then processing is more time consuming. That is the price of OSC comfort And if you go to narrowband or narrowband + LRGB, then it becomes more complicated, both to process and also to calculate the benefit

Hi Chris, Just a bit from my past - I started to image with 6" newton and modded Canon 20D, and then realized that I was very much interested in galaxies. I switched to CCD mono camera with small sensor (Atik314) and used just L filter at the beginning, and I was extremely happy with these monochromatic frames. After some time I invested in filters and manual wheel, and was able to pick color images as well. The sensitivity boost you get with mono sensor compared to OSC version is quite significant, so if you can live with BW images for a while, you may consider this approach.

The last images I have captured with my 10 inches Meade ACF 10" telescope. Now it is gone to another happy amateur that has already big plans for it M56 cluster in Lyra - together with M71 it is my favorite globular cluster, because of the dense starfield in the background. Image below is 140x1 minute stack of LRGB frames made with QHY163M on EQ6 mount. And the M76 planetary nebula. I always wanted to image it, and waited for the better conditions, but I failed Here is about 4 hours of total subframes time made with RGB, Ha and Oiii filters. QHY163M and EQ6 as telescope company.

It's bad news I knew that MPCC for example shows the same behavior - not quite corrected corners and soft center, especially for telescopes faster than f/5. But I hoped to spare some money with that 0.95x coma corrector.

I may not agree, unless you define "considerably". I just checked a 180s luminance frame captured with f/10 telescope and QHY163M camera. Background noise is 167ADU, while bias noise at the same gain is 20ADU. Background noise with 25ADU read noise would be about 167.7ADU, and with 15ADU read noise would be around 166.5ADU. I would not call it a significant difference. It is based on assumption, that smaller pixel has the same readout noise as larger (and other noise sources are insignificant). But that is rarely true. If the read noise of the smaller pixel is smaller proportionally to the pixel area difference, then there is no loss in SNR.

Yes, you are right, my mistake. The information at the page https://www.altairastro.com/altair-hypercam-269c-colour-camera---tec-cooled-1097-p.asp is misleading "5280x3956 active 3.3 micron pixels in a 20.49 mm × 17.83 mm array. Physical sensor size, 4/3rds" 21.77mm diagonal."

Why do you? The only problem with oversampling is adding the read noise to the signal. And for CMOS cameras that is not a big problem, unless you want to do narrow bands with OSC camera.

I would not worry with modern CMOSes oversampling at all. 294 is larger than 269 and also larger than 533 - and that is the quality that is often ignored, but for astrophotography that is quite fundamental. Together with sensitivity (quantum efficiency). There were quite many nights that I missed larger sensor. Harder calibration or dithering requirement was never a pain for me

I have been imaging with 6 f/5 and 8 f/4 inches newtonians - one steel and one carbon tube. Both were quite heavily modded though. In my opinion the mirror quality even in low budget newtonians are good enough to capture the quality images. The real pain is mechanics in entry level telescopes. The stock focusers are pretty useless for anything heavier than light DSLR camera. The drawtube tilts inside the focuser tube, but also the telescope steel tube (or even thin carbon tube) bends under the load of 1-2kg already. It is clearly visible when you put laser into the focuser, press the drawtube and watch the laser spot on the main mirror. 2 mm movement is enough to degrade f/5 telescope collimation. For f/4 the sweet spot is much less of course. Main mirror cell is also usually poor in entry level newtonians. It sometimes moves aside just under the mirror load at different telescope positions. Mirror holders are either too loose or too tight. Another examples are counter screws in GSO cells - all 6 screws are positioned symmetrically around the cell, and counter screw bends the mirror cell (and mirror as well) when tighten too much. Currently I just got back to imaging with newtonian. I collected second hand steel tube GSO 200/1000 in very good condition and now I am in the process of upgrading it - focuser replacement, external stiffening rings on focuser both sides, main mirror 195mm mask to get rid of three mirror holder shadows, changing the position of the counter screws in the main mirror cell, and probably flocking the tube interior. Then selection of coma corrector (probably TS 0.95x Maxvision) and that tube should work well with APS-C format sensor. I will write about the results for sure. I may recommend the book "Star Testing Astronomical Telescopes" by Harold Richard Suiter - quite complete source of knowledge and testing routines for amateurs.

Mine just arrived - serial number 7, and Strehl 0.973. It looks gorgeous, quite heavy, focuser works smooth and is quite stiff. Collimation checked with Cheshire is perfect. But the weather forecast is not promising at all, unfortunately

I think that may bend at the point I marked red here (all three around of course): so what you can do is to put some a few mm diameter steel cables (blue lines) with a device to stretch it (sorry, do not know the correct name - see below). Once you stretch all three legs it should be much stiffer. Then you may put this modified tripod on three concrete blocks and that should work much better.

I am currently looking for upgrade of my travel astroimaging setup, and searching for a 90-100mm triplet that will fit my 0.8x FF/FR https://www.teleskop-express.de/shop/product_info.php/info/p12209_TS-Optics-REFRACTOR-0-8x-corrector-for-refractors-up-to-102-mm-aperture---ADJUSTABLE.html and will cover APS-C format camera (QHY247C, but mono IMX571 in the future). My attention is on two triplets: Sharpstar 94EDPH f/5.5 like this https://www.teleskop-express.de/shop/product_info.php/info/p12607_TS-Optics-94-mm-f-5-5-Triplet-Apo-Refractor-Telescope.html Tecnosky 90/560 Owl like this https://www.teleskop-express.de/shop/product_info.php/info/p13566_Tecnosky-FPL55-90-560-mm-Apochromat--OWL-Series.html First one contains two ED elements, but is a bit larger and a bit faster, and with reducer it will give f/4.4 - I am afraid that may be a little bit more demanding with regards to collimation, and also more susceptible for tilt. So I am now a bit towards the Owl refractor - "regular" f/6 FPL-55 based triplet, that is also supplied with Strehl protocol. Do you know maybe any pros or cons for these two models? Or maybe there is somewhere a better alternative around 1500EUR price? Many thanks in advance!

I think ISO800 is a good starting point, however as far as I remember this Canon 50/1.8 lens requires to be stopped down. Just make several images of some star field with the same EV to compare, so f/2 at 30s, f/2.8 at 60s, f/4 at 120s and then inspect the images on the monitor to find out the optimal f stop, when stars look good.

Sh2-188 is quite interesting planetary nebula in Cassiopeia. Its shape is very asymmetric due to the interaction with interstellar medium. It is considered to be one of the most extreme examples of planetary nebula and interstellar medium interaction. Supernovae remnants are often much more distorted, but they also live longer than planetary nebulae. Data captured at my backyard setup with Meade ACF 10" f/10, CCDT67 reductor, EQ6 mount and QHY163M camera. It is HaO3RGB composition, about 400 minutes of total exposure time under suburban sky with medium seeing.

Another light - first in this year. I think this is the first setup I had that was capable to capture whole M31 (not counting Samyang 135). Conditions were as usual at my location during the winter - little smog, light pollution. This setup field of view is 3x2 degrees, so to catch full width of M31 (3 degrees) I need to put it horizontally or diagonally. I will do it next time, under really dark sky WO Zenithstar II ED80 f/6.8, 0.8x FF/FR, iOptron CEM26, QHY247C, 80x2 minutes. Suburban sky, transparency medium. And starless version. This little something at the lower right corner is UGC394. Starnet++ was able to recognize it as non-stellar object

You may also consider FOV for your imaging targets. 533 is significantly smaller chip, it has 128mm2, while 294 has 248mm2. It may look like a few mm larger in the specs, but that is actually two times larger imaging area.

The same for me. I have been storing all data some time ago, but eventually gave up on it. Mono cameras are quite alright, but OSC ones are pain. One 24Mpx frame after debayer takes 280MB 100 frames project made with PixInsight batch processing with calibration frames takes 83GB ... I keep all the frames for photometry and spectroscopy projects now, but for pretty imaging I keep only stacks and processed images. I know that disk space is not expensive now, but I did not need any source frames ever for the last 10 years I do imaging.

I had similar problem and longer dovetail with rings at the end and in the middle solved it: Dovetail (yellow) is mounted in the saddle at the rear part, and rings (green arrows) in the front part of the dovetail.

Observing faint objects is a little bit complex process that is performed by eyes and brain in the same time. Ability to spot low surface brightness objects depends also on its angular size. The larger the object is with the same surface brightness, the easier to observe. In your case, enlarging the exit pupil does not make galaxies easier to observe, because they have now lower angular size. Plus 72mm APO has significantly smaller aperture than 127mm MAK, and basically you collect less light. Telescope aperture is the most important thing for observing faint targets. Once you enlarge aperture, you may play with eyepieces, powers and exit pupils. You may check this book for more details: Human Vision and The Night Sky: How to Improve Your Observing Skills, Michael P. Borgia

You need to remember that RA increases to the east, and Dec increases to up. So when your solved coordinates RA is smaller than target and Dec is larger than target, then you need to move east and bottom. The amount of movement you need to determine experimentally If you use PlateSolve 2 and enter target as Starting parameters, then you will see both starting and solved values and you can compare easily: